KR102475239B1 - Detergent concentration measuring device and measuring method using the instrument having superhydophobic surface - Google Patents

Abstract

The present invention particularly relates to a detergent concentration measuring device and method using a device having a superhydrophobic surface, and a liquid contact device having a superhydrophobic surface in which an angle of contact with pure water droplets is formed at 150 degrees or more, and the above A device and method capable of measuring the detergent concentration of a liquid on the spot with much simpler and more portable equipment than conventional detergent concentration measurement methods by including a measurement module for measuring the contact angle or contact position of a liquid in contact with a superhydrophobic surface want to provide

Description

Detergent concentration measuring device and measuring method using the instrument having superhydrophobic surface {Detergent concentration measuring device and measuring method using the instrument having superhydrophobic surface}

The present invention relates to a detergent concentration measuring device and method, and more particularly to a detergent concentration measuring device and measuring method using a device having a superhydrophobic surface.

In most homes today, a significant amount of detergent is consumed to clean various objects such as tableware, fruit, kitchen utensils and laundry. Detergents contain surfactants and several minor ingredients. Although the use of detergents is unavoidable in daily life, repeated use of detergents can be harmful to health. Excessive exposure of the skin to detergents can cause skin diseases, and some detergents penetrating the skin can cause aplastic anemia. It can also damage the nervous system and cause certain cancers. For this reason, there is a need for a technology capable of instantly and conveniently measuring the amount of detergent remaining after washing.

Several methods have been developed in the prior art for detecting the concentration of detergents in water, including ultraviolet absorption spectroscopy, ion chromatography, gas chromatography, gas chromatography-mass spectrometry and liquid chromatography. These techniques were developed to measure the concentration of surfactants based on the fact that all detergents contain surfactants.

Although the efficacy of the analysis method has been proven, the above techniques have problems such as difficulty in carrying equipment for measurement, so that it cannot be used conveniently on the spot, the sample processing period is too long, and the detection limit is relatively large. Therefore, there is currently no technology for measuring detergent concentration that can be easily applied in daily life, and the development of this is requested.

Registered Patent Publication No. 10-1881639 (Public date: 2018. 08. 27)

Accordingly, the present invention is to provide a device and method capable of instantly measuring the detergent concentration of a liquid with much simpler and portable equipment than conventional detergent concentration measurement methods.

Detergent concentration measuring device using a device having a superhydrophobic surface according to the present invention for achieving this object is a liquid contact device having a superhydrophobic surface formed at an angle of 150 ° or more in contact with pure water droplets, and the and a measurement module for measuring a contact angle or a contact position of a liquid contacting the superhydrophobic surface.

Here, the superhydrophobic surface is preferably formed in a form in which a plurality of nanorods made of zinc oxide (ZnO) protrude from the surface of the liquid contact mechanism, and air is filled between the nanorods.

In this case, the ends of the plurality of nanorods are preferably coated with stearic acid.

In addition, between the plurality of nanorods and the surface of the liquid contact mechanism, preferably, zinc oxide protrusions are formed at positions corresponding to each nanorod.

On the other hand, the liquid contact mechanism may preferably be a plate-shaped member having an area where detergent droplets can form.

At this time, the measurement module is preferably a plurality of cameras installed along the circumference of the liquid contact mechanism, and the contact angle between the detergent droplet and the liquid contact mechanism is received by receiving an image in the form of detergent droplets formed on the surface of the liquid contact mechanism from the measurement module. It further includes an arithmetic module that calculates

Here, the calculation module preferably includes a procedure for calculating an average value of contact angles from contact angles calculated for each image obtained from a plurality of the measurement modules, and a procedure for calculating an average value of contact angles from contact angle data for each detergent concentration that has been measured and stored in advance to obtain the average value An algorithm including a procedure of determining the concentration of the detergent by adopting the detergent concentration data corresponding to the corresponding contact angle may be loaded.

Alternatively, the liquid contact mechanism preferably includes a capillary, and the superhydrophobic surface is formed on the inner circumferential surface of the capillary, so that the final height difference of the liquids having different detergent concentrations rising inside the capillary increases the superhydrophobicity on the inner circumferential surface of the capillary. increased than when there is no surface.

Here, the liquid contact mechanism preferably consists of a capillary tube and a water tank having a volume in which the lower part of the capillary tube can be submerged to a certain height, and a scale capable of measuring the amount of liquid required for measuring the detergent concentration may be formed in the water tank.

At this time, preferably, a grid-shaped support frame having a plurality of holes through which capillaries can be erected may be installed in the water tank.

In addition, the measurement module is preferably a camera disposed to face the top of the liquid raised along the inside of the capillary, a rotation gauge capable of adjusting the direction of the camera so that the camera faces the top of the liquid, and an image of the camera It may be composed of a monitor displaying a target scale at the center so that the center can be accurately aligned with the upper end of the liquid, and a camera lifting unit capable of adjusting the height of the camera.

Alternatively, the measurement module may preferably include a camera having a variable angle while facing the top of the liquid raised along the inside of the capillary, an angle sensor for calculating the angle of the camera in real time, and an image center of the camera accurately measuring the liquid. It consists of a monitor in which a target scale is displayed at the center so as to coincide with the top of the liquid, and the height of the top of the liquid can be calculated through the previously measured horizontal distance between the camera and the capillary and angle information of the camera.

On the other hand, the detergent concentration measurement method according to the present invention includes the step of measuring the contact angle or contact position of the liquid contacting the surface after contacting the liquid to the superhydrophobic surface.

At this time, the measuring step is preferably a step of growing a plurality of nanorods made of zinc oxide (ZnO) on the surface of the liquid contact mechanism in a direction protruding from the surface before measuring the contact angle or contact position of the liquid. includes

Preferably, the measuring step further includes coating stearic acid on the ends of the plurality of nanorods after the growing step.

The measuring step preferably further includes forming a protrusion made of zinc oxide (ZnO) in advance at each position where a plurality of nanorods are to be grown before the growing step.

At this time, the liquid contact mechanism is preferably a plate-shaped member having an area on which detergent droplets can form, and the measuring step is to apply the liquid to be measured for detergent concentration to the surface of the liquid contact mechanism after the step of forming the projections. It is made by measuring the contact angle formed by the droplet of the liquid whose concentration is to be measured on the surface of the liquid contact mechanism with the surface of the liquid contact mechanism.

In this case, the measurement module is preferably a plurality of cameras installed along the circumference of the liquid contact mechanism, and the step of measuring the contact angle includes measuring the contact angle at different points using at least three cameras. The step of obtaining an image, the step of calculating an average value of the contact angle from the obtained measurement image, and the detergent matching the average value of the contact angle measured from the detergent concentration data according to the previously measured contact angle from the average value of the contact angle It consists of calculating the concentration.

Alternatively, the liquid contact mechanism is composed of a capillary tube and a water tank having a volume in which the lower part of the capillary tube can be submerged to a certain height, and the superhydrophobic surface is preferably formed on the inner circumferential surface of the capillary tube, so that different The final height difference of the liquid having the detergent concentration is increased compared to the case where the super-hydrophobic surface is not present on the inner circumferential surface of the capillary, and the measurement module includes a camera arranged to face the top of the liquid raised along the inside of the capillary, and the camera to the top of the liquid. A rotation gauge capable of adjusting the direction of the camera, a monitor displaying a target scale at the center so that the center of the image of the camera can accurately match the top of the liquid, and a camera capable of adjusting the height of the camera A lifting unit and a horizontal chuck installed across the capillary tube and the camera lifting unit while being able to move up and down so as to match the height of the camera to the height of the top of the liquid, the measuring step is to move the liquid, which is the subject of detergent concentration measurement, into a water tank. After filling the inside, immersing the capillary in the water tank for a certain period of time until the liquid rises along the capillary and stops, and until the horizontal gauge coincides with the horizontal direction and the target scale coincides with the upper end of the liquid A step of calculating the height of the top of the liquid by adjusting the height and angle of the camera using the camera elevation unit and the rotation gauge.

In addition, the liquid contact mechanism is composed of a capillary and a water tank having a volume in which the lower part of the capillary can be submerged to a certain height, unlike the previous one, and the superhydrophobic surface is formed on the inner circumferential surface of the capillary, so that different The final height difference of the liquid having the detergent concentration is increased compared to the case where the superhydrophobic surface is not present on the inner circumferential surface of the capillary, and the measurement module includes a camera disposed with a variable angle while facing the top of the liquid raised along the inside of the capillary; By comprising an angle sensor that calculates the angle of in real time and a monitor displaying a target scale at the center so that the center of the image of the camera can accurately match the top of the liquid, the measuring step is performed by changing the angle of the camera to monitor The step of aligning the target scale of the monitor with the top of the liquid, the step of calculating the angle of the camera with the angle sensor while the target scale of the monitor is aligned with the top of the liquid, and the height of the top of the liquid with the angle calculated in the step of calculating the angle and calculating the height of the top of the liquid by adding the height difference between the camera and the height of the top of the liquid to the height of the top of the liquid.

Detergent concentration measuring device and detergent concentration measuring method using a device having a super-hydrophobic surface according to the present invention use a super-hydrophobic surface to measure detergent concentration, so that detergent concentration can be measured accurately and conveniently on the spot, and detergents in everyday life Since concentration measurement can be freely applied, various health problems due to excessive exposure to detergents can be prevented.

1 is a conceptual diagram showing the contact angle of water droplets at each stage of superhydrophobic surface treatment;
2 is a conceptual diagram and graph showing the relationship between a superhydrophobic surface and detergent concentration as a contact angle;
Figure 3 is a conceptual diagram and graph showing the principle that can be applied to the detergent concentration measurement when the inside of the capillary is superhydrophobic,
Figure 4 is a process diagram of modifying the inner surface of the glass plate and capillary to super-hydrophobic;
5 is a SEM image of each step of changing from a glass surface to a superhydrophobic surface;
6 is an XRD pattern before and after stearic acid treatment of the surface on which ZnO nanorods are grown;
7 shows FT-IR spectra before and after stearic acid treatment of the surface on which ZnO nanorods are grown;
8 is a SEM image taken while increasing the magnification step by step of the ZnO nanorods grown on the inner wall of the capillary;

Specific structural or functional descriptions presented in the embodiments of the present invention are merely exemplified for the purpose of explaining embodiments according to the concept of the present invention, and embodiments according to the concept of the present invention may be implemented in various forms. In addition, it should not be construed as being limited to the embodiments described in this specification, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and scope of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The detergent concentration measuring device according to the present invention measures the contact angle or contact position of a liquid contacting device (11, 12) formed with a superhydrophobic surface having a contact angle of 150 ° or more with water, and a liquid contacting the surface. It includes a measurement module (not shown) that

Superhydrophobic refers to a surface that does not get wet to such an extent that when pure water droplets contact the surface of an object, the contact angle with the pure water droplets is formed at 150° or more.

As shown in (a) of FIG. 1, when a pure water droplet is dropped on the glass plate 11, the contact shape between the water droplet and the surface of the glass plate 11 is formed at a contact angle of 13.2 ° as shown in the far left. In FIG. 1 (a), the middle drawing is a water droplet contact angle on the hydrophobic treated surface, which is formed at approximately 89.9 °, and the rightmost drawing in FIG. It can be seen that a contact angle of 156.3° is formed as a shape when pure water droplets fall on the surface. Therefore, it can be seen that when pure water droplets fall on the surface of the glass plate 11 treated with superhydrophobicity, they have a shape close to the original spherical shape of the water droplets.

In view of this point, the present invention started with the idea that the detergent concentration could be measured from the contact shape and angle of the liquid droplet on the superhydrophobic surface. In fact, as shown in (a) of FIG. 2, it was confirmed that the contact angle between the liquid droplet and the superhydrophobic surface gradually decreased as the detergent concentration increased.

Therefore, as a result of measuring the contact angle formed on the superhydrophobic surface through repeated experiments using several types of detergents and detergent solutions prepared with different concentrations for each detergent, the graph shown in FIG. 2 (b) was obtained. The contact angle relationship between the detergent concentration and the superhydrophobic surface has a linear relationship on a semilog plot, as can be seen from the experimental graph shown in FIG. 2 (b). However, although there is a slight difference in the slope or y-axis crossing point depending on the ingredients of the detergent, it can be seen that the difference is not large.

Therefore, if a graph corresponding to (b) of FIG. 2 is obtained for any one detergent solution, the concentration of detergent contained in the liquid can be immediately known by using a superhydrophobic surface. In addition, when trying to obtain a graph corresponding to (b) of FIG. 2 for any one detergent, since the logarithmic detergent concentration and the real contact angle have a linear relationship with each other, the experimental values of any two points are obtained and then connected with a straight line to obtain each concentration. It is concluded that the data on the star contact angle can be obtained as a graph in the form of (b) in FIG.

Therefore, the detergent concentration measuring device according to the present invention includes a liquid contact mechanism (11, 12) formed with a superhydrophobic surface having a contact angle of 150 ° or more, and a contact angle or contact of the liquid contacting the superhydrophobic surface. It can be implemented by using a measurement module that measures the position.

At this time, the superhydrophobic surface is formed by orienting a plurality of ZnO nanorods 17 made of zinc oxide (ZnO) in a protruding form from the surface of the member constituting the liquid contact mechanism, and between each ZnO nanorods 17, air is formed. is filled, the space between each ZnO nanorod 17 is formed in the form of a kind of air pocket 19, so that liquid droplets that fall on top of the ZnO nanorods 17 float without permeating between the ZnO nanorods 17. By landing, a hydrophobic surface can be formed.

In addition, by coating the ends of the plurality of ZnO nanorods 17 with stearic acid 18, the surface energy of the ends of the ZnO nanorods 17 is minimized, so that the air pockets 19 and the ends of the ZnO nanorods 17 are formed. The entire surface becomes superhydrophobic.

At this time, between the plurality of ZnO nanorods 17 and the surfaces of the liquid contact mechanisms 11 and 12, zinc oxide acts as a seed for the growth of the ZnO nanorods 17 at positions corresponding to each ZnO nanorods 17. A protrusion 16 may be formed.

Also, according to a similar principle, in the present invention, when the inner wall of the capillary tube 12 is formed as a super-hydrophobic surface, the final height of the liquid rising along the capillary tube 12 depends on the concentration of the detergent contained in the liquid rising along the capillary tube 12. It was noted that there could be a significant difference. As a result of the experiment, as shown in the graph (d) of FIG. 3, when the inner surface of the capillary tube 12 is treated with a super-hydrophobic surface, the detergent concentration and the final elevation of the capillary tube 12 change in a linear relationship with each other on the counter-number diagram. Could know.

This is because, in the case of a pure glass capillary without superhydrophobic surface treatment on the inner surface, the rising height of the liquid is not very high even when the surface tension is strong like pure water, and as can be seen in (a) of FIG. While all of the final rising heights of the liquid are formed similarly, as shown in FIG. 3 (b), when the inner surface of the capillary 12 is treated with superhydrophobicity, it can be confirmed as an experimental result that a significant height difference occurs depending on the detergent concentration. .

The liquid contact mechanisms 11 and 12 will be largely divided into two embodiments in the present invention.

The first embodiment is an embodiment in which the liquid contact mechanism is formed in the form of a glass plate 11 having a certain area.

In the first embodiment, the concentration of the detergent solution (S) is measured by the contact angle formed between the upper surface of the glass plate 11, which is a liquid contact mechanism, and the droplet of the liquid formed thereon. Here, the measurement module (not shown) may include a camera capable of obtaining an image of a contact angle between a droplet of the detergent solution S and the surface of the glass plate 11 and an arithmetic module that calculates the contact angle from the image.

In the second embodiment, the liquid contact mechanism includes the capillary tube 12, and the inner surface of the capillary tube 12 is super-hydrophobic. In this case, the liquid contact mechanism may include a capillary tube 12 and a water tank 111 in which a certain amount of the detergent solution S to be raised along the inside of the capillary tube is supported.

Therefore, in the second embodiment, the detergent concentration is measured not through the measurement of the contact angle, but through the final height at which the liquid rises along the capillary 12.

Hereinafter, the first embodiment and the second embodiment will be described in detail in order focusing on the contents of the actual experimental process.

<First Embodiment>

In the first embodiment, the liquid contact mechanism is formed of the glass plate 11, and the measurement module (not shown) measures the contact angle of the detergent solution (S) droplet formed on the surface of the glass plate 11 to measure the detergent concentration. is an embodiment of

First, the reagents prepared to make the glass plate 11, which is a liquid contact device, superhydrophobic in the first embodiment are zinc nitrate hexahydrate (ZnO(NO ₃ ) ₂ 6H ₂ O), urea (CO(NH ₂ ) ₂ ) , hexamethylene tetramine (HMTA, C ₆ H ₁₂ N ₄ ), ammonium chloride (NH ₄ Cl), 25% ammonia (NH ₃ ), stearic acid, acetone ((CH ₃ ) ₂ CO) and isopropyl alcohol (isopropyl alcohol, IPA).

Four types of detergents prepared for use in the experiment were prepared, including commercially available rinse dish rinse detergent, one type of detergent, sodium detergent, and potassium detergent. It is known that the types and contents of surfactants and additional components contained in the detergents are different.

The liquid contact device prepared for the experiment is a glass plate 11 with a thickness of 1 mm. At this time, the glass plate 11 having a thickness of 1 mm was subjected to a continuous cleaning process using acetone and IPA, and then completely dried in an oven at 60 °C.

For vertical growth of ZnO nanorod arrays on glass plate 11, a two-step solution process is used, as schematically shown in Fig. 4(a). Here, the two-step process means that in step 1, ZnO protrusions 16 to act as seeds to grow the ZnO nanorod array are first formed on the surface of the glass plate 11, and in step 2, ZnO nanorods 17 are formed from each of the ZnO protrusions. This means a process in which an array of ZnO nanorods 17 is formed by growing.

Although the formation of the ZnO nanorod 17 array may be possible even if only two steps are performed, it can be grown much more uniformly and stably by forming the ZnO protrusions 16 in one step. The effects of step 1 will be described later.

In the first step shown on the left side of FIG. 4 (a), nano-sized ZnO protrusions 16 are formed on the surface of the glass plate 11. For this, 100 mL of an aqueous solution containing 0.01 M ZnO(NO ₃ ) ₂ , 0.02 M NH ₄ Cl, 0.01 M urea and 5 mL of 25% ammonia was prepared. The glass plate (11) was vertically immersed in the solution for ZnO cultivation contained in the beaker (13).

The solution was then heated to 90 °C at a heating rate of 7 °C per minute. After the glass plate 11 was taken out of the solution in the beaker 13 at this temperature, it was rinsed several times with ultrapure water and dried at room temperature.

In the second step, an array of ZnO nanorods 17 is grown vertically from ZnO protrusions 16 (seeds). Aqueous solutions of 50 mM ZnO(NO ₃ ) ₂ and 50 mM HMTA were prepared in advance, and the same amount (50 mL) of the solution was mixed together in a 100 mL beaker (13). A glass plate 11 having ZnO projections 16 was vertically immersed in the mixed solution, and the mixed solution was heated at 90° C. for 2 hours. Finally, the surface-modified glass plate 11 on which the ZnO nanorods 17 array was formed was washed several times and dried at 90 °C.

However, the end surface of each ZnO nanorod 17 is generally hydrophilic due to the hydroxyl group bonded to the surface. To make it hydrophobic, the synthesized ZnO nanorods (17) array was coated with stearic acid (18) as shown in Fig. 4(c). To this end, the glass plate 11 was immersed in an acetone solution containing 2 mM stearic acid for 30 minutes and dried at room temperature for 30 minutes.

The shape of the array of ZnO nanorods 17 on the surface of the glass plate 11, that is, the liquid contact mechanism, was analyzed using a field emission scanning electron microscope (FE-SEM, JEOL JSM-7500F). Another FE-SEM (Hitachi S-4700) obtained cross-sectional images of vertically grown ZnO nanorods (17) arrays. The crystal structure and crystal quality of the ZnO nanorods (17) were analyzed by X-ray diffraction (XRD, PANalytical X'Pert Pro MPD).

The chemical changes on the surface of the ZnO nanorods (17) due to stearic acid treatment were monitored using Fourier Transform Infrared Spectroscopy (FT-IR, PerkinElmer L160000A). The contact angle of water and detergent solution (S) on the superhydrophobic treated glass plate (11) was measured with a fixed amount of droplet (10 μL) using a contact angle goniometer (PHX300 S.E.O.). For this, the sample stage was first flattened.

The glass plate 11 was then loaded onto the stage. After the droplet was deposited on the surface of the glass plate 11, the droplet image was recorded with a CCD camera. The recorded images were analyzed using software (ImageXP 5.9) to determine the contact angle. The contact angle was measured at 5 different locations for each sample, from which an average value was calculated. The surface tension of the detergent solution (S) was measured by the Du-Nouy ring method at 25 °C using a surface tension analyzer (DST60 S.E.O.). A Pt ring was used, and the detergent concentration was controlled in the range of 1–1000 ppm.

5 shows step-by-step SEM images of the surface of the glass plate 11. The images of FIG. 5 (a) and FIG. 5 (b) are images obtained immediately after completing the formation of the ZnO protrusion 16, which is obtained by going through the steps on the left of FIG. 4 (a) and then on the right of FIG. 4 (a). It refers to the state before passing through. FIG. 5 (a) is a planar image, and FIG. 5 (b) is an image of the same object as in FIG. 5 (a) taken from the upper side. As shown in Fig. 5(a), nearly monodisperse dense ZnO asperities 16 with a size of 20-100 nm are evenly distributed on the glass plate 11.

However, when looking at the distribution of the ZnO bumps 16 in detail with reference to FIG. 5 (b), it can be seen that the ZnO bumps 16 have different heights and widths. And, as the width of the ZnO protrusion 16 increases, the height of the protrusion also increases.

As a result of observation, the tall ZnO protrusions 16 appear to promote the growth of the ZnO nanorods 17 array in the subsequent process. The width of the tall ZnO asperities 16 is observed to have a distribution of 107-180 nm. 5(c), it can be seen that a high-density vertical ZnO nanorod array 17 was grown from the glass plate 11 on which the ZnO protrusions 16 were formed. The vertical alignment of the ZnO nanorods 17 array can be seen more clearly in the cross-sectional SEM image in Fig. 5(d). The average inclination angle of the ZnO nanorods 17 array along the cut plane is estimated to be inclined at 11.7° with respect to the vertical line. The cross-sectional SEM image also shows that the diameter and length of the ZnO nanorods 17 are fairly uniform. The average diameter and length of the ZnO nanorods 17 were 210 nm and 1.39 μm, and the average aspect ratio was 6.6. For comparison, when the first step (ZnO protrusion 16 (seed) formation step) was skipped and the glass plate 11 was directly immersed in a solution of zinc nitrate and HMTA at 90 ° C, it had a non-uniform size and density, Inclined ZnO nanorods 17 were observed, demonstrating the necessity of ZnO asperities 16 (seeds) for aligned vertical ZnO nanorods 17 growth (not shown).

5 (e) and (f) show SEM images after treatment with stearic acid (18). The faint top view image in Fig. 5(e) shows that a thin layer of stearic acid (18) covers the top of the ZnO nanorods (17) array. However, since the coating of stearic acid (18) requires dehydration of long alkyl chains, the limited free space between the ZnO nanorods (17) due to the very high density of the ZnO nanorods (17) ) is very likely to be concentrated on the upper surface of In fact, from FIG. 5(f), the stearic acid 18 layer is formed only around the tips of the ZnO nanorods 17, suggesting the possibility that air pockets 19 are formed by trapping air inside the forest of the ZnO nanorods 17. It was confirmed that increasing

FIG. 6 (a) is an XRD pattern when only the ZnO nanorods (17) array is synthesized, and FIG. 6 (b) shows the XRD pattern after stearic acid (18) is additionally treated in FIG. 6 (a). In particular, the synthesized ZnO nanorods 17 array exhibits a sharp and strong peak at 2θ = 34.5°, which corresponds to the (002) plane of wurtzite ZnO crystals, and the ZnO nanorods 17 of the crystals Indicates that it grew preferentially in the c-axis direction.

When stearic acid (18) is coated on the ZnO nanorods (17) array, the overall XRD intensity is significantly reduced due to the X-ray interference effect of the semi-crystalline stearic acid (18).

Nevertheless, the main XRD peaks are clearly observed in the array of stearic acid (18) treated ZnO nanorods (17), as shown in Fig. 6(b). All peaks are assigned to the main crystalline plane of wurtzite ZnO, and the strongest appears on the same (002) plane as the synthesized ZnO nanorods (17). No characteristic peak for stearic acid (18) was found because the main peak of stearic acid (18) is estimated to be below 21°.

In addition, the chemical change of the surface of the ZnO nanorods (17) array accompanying the treatment with stearic acid (18) was analyzed by FT-IR spectroscopy. Stearic acid (18) consists of a long hydrophobic alkyl chain and a carboxylic acid head group. The carboxyl group easily reacts with the hydrophilic hydroxyl group on the surface of the ZnO nanorods (17) to attach stearic acid through a chelation process. When the ZnO nanorods 17 are exposed to stearic acid 18, most of the hydroxyl groups are attached to the top surface of the ZnO nanorods 17, as shown in FIG. A chemical reaction with the carboxyl group results in the formation of a monolayer of zinc stearate.

Meanwhile, the hydrophobic alkyl chain is vertically oriented at the end of the ZnO nanorod 17, that is, at the top of the ZnO nanorod 17, and the surface free energy of the end of the ZnO nanorod 17 is significantly reduced. 7 shows FT-IR spectra of the ZnO nanorod 17 array before treatment with stearic acid 18 and the ZnO nanorod 17 array treated with stearic acid 18 . The peaks at 663 and 888 cm ⁻¹ in the lower graph of FIG. 7 represent in-plane shaking vibration and out-of-plane bending vibration of the —OH functional group, respectively.

These peaks are evident in the array of ZnO nanorods 17 before treatment with stearic acid 17, confirming the presence of hydroxyl groups on the surface. The characteristic peak of ZnO corresponding to the phonon vibration of Zn-O appears in the range of 441 ~ 432 cm ^-1 in both samples, although there is some noise.

The peaks at 1216 and 1366 cm ⁻¹ are due to horizontal plane bending vibrations of the —OH groups in stearic acid. On the other hand, another peak appearing at 1739 cm ^-1 is due to the stretching vibration of C=O. Also, other peaks are observed at 2971 and 2952 cm ⁻¹ , indicating asymmetric and symmetrical stretching of the —CH ₃ (or —CH ₂ ) group present in the long alkyl chain. Since this peak is found only in the array of ZnO nanorods 17 treated with stearic acid 18, it indicates that stearic acid 18 was successfully coated on the surface of the array of ZnO nanorods 17.

Referring to FIG. 1 (a), the water contact angle of the pure glass plate 11 without superhydrophobic surface treatment is only 13.2°. When the array of ZnO nanorods 17 is formed on the surface of the glass plate 11, the contact angle increases to 89.9°, which is the boundary between hydrophobicity and hydrophilicity. This substantial increase in contact angle is due to the relatively low surface energy of ZnO (~40 dyne/cm). Indeed, the contact angle of the ZnO film was measured to be 80.2°, which is in good agreement with previous reports.

An additional increase in the contact angle may occur in the structure of the ZnO nanorod 17 array, and the Wenzel model may be referred to. This model reflects the surface roughness effect on the contact angle, so it needs to be considered. Referring to the drawing on the left of FIG. 1 (b), based on the Wenzel model, a liquid droplet penetrates the groove of the rough surface and the contact angle can be obtained by Equation (1) below.

cos θ ^* = r cos θ ------ (1)

where θ ^* and θ are the contact angles for rough and smooth surfaces, respectively. r is the ratio of the actual surface area to the apparent surface area. Here, the increase in the contact angle is opposite to the expectation of the Wenzel model, indicating that the contact angle of the rough surface should be smaller than that of the smooth surface when θ < 90°.

The apparent discrepancies between observations and predictions indicate limitations of the Wenzel model and suggest the possibility of air trapping in the ZnO nanorod array.

The Cassie-Boxter model can be a useful tool to overcome this discrepancy between observation and prediction. In this model, air can be trapped in the grooves of the rough surface, as shown on the right side of FIG. This is the principle of improving the hydrophobicity of the surface. The Cassie-Boxter model is

cos θ ^* = f(cos θ + 1)-1 ----------- (2)

can be formulated as where f is the area ratio of the liquid-solid interface and thus 1-f represents the ratio of the liquid-air interface. Taking the measured contact angles (θ ^* = 89.9°, θ = 80.2°), f is calculated to be 0.86, indicating that approximately 14% of the droplet surface is in contact with air. When stearic acid 18 is additionally coated on the surface of the ZnO nanorod 17 array on the surface of the glass plate 11, the contact angle greatly increases to 156.3° as shown in FIG. 1 (a), and the surface finally becomes ultra-small. becomes aqueous.

The superhydrophobic surface thus fabricated exhibits perfect roll-off characteristics for water droplets. Although the realization of such superhydrophobicity has a factor of increasing the contact angle due to stearic acid 18, it is analyzed that the factor of the effect of the air pockets 19 of the ZnO nanorods 17 coated with stearic acid 18 is greater. Substituting θ = 80.2° into equation (2) above, f is calculated as only 0.072. This indicates that 93% of the droplet surface is supported by air and thus air pockets 19 exist.

When measuring the contact angle of a detergent solution using a superhydrophobic surface, it was confirmed that the change in contact angle according to the change in detergent concentration was consistent and the range of change increased. In FIG. 2 (a), contact angle images of one type of detergent solution and pure water at various concentrations are shown.

As the detergent concentration increases from 0 to 1000 ppm, the contact angle decreases at a constant rate. The range of change in the contact angle of one type of detergent is 13.7° in the concentration range of 0-1000 ppm. This consistent decrease in contact angle is also observed in other detergent solutions as shown in the graph of Fig. 2 (b). However, since the relationship between the contact angle and the detergent solution concentration is not a linear relationship on the real number diagram, it can be more clearly displayed as a semilog plot as shown in the graph of FIG. 2 (b). In this semilogarithmic diagram, the contact angle (θ _d ) of detergent solutions generally decreases linearly as a function of log concentration (C), and the slopes of the linear relationships are very similar to each other regardless of the type of detergent. For example, in the case of type 1 detergent, the relational expression is as follows.

θd = _-2.358logC + 150 -------------- (3)

This linear relationship and nearly identical linear slope indicate that contact angle measurements on superhydrophobic surfaces can be a simple and useful means of detecting residual detergent concentration in water.

The effectiveness of this method can also be demonstrated by measuring the surface tension of one type of detergent solution (S) according to the detergent concentration by the Du-Nouy ring method. Surface tension consistently decreases with increasing detergent concentration in a manner similar to the change in contact angle. The width of the surface tension change was measured at 7 mN/m, which is almost the same as the width of the contact angle change (7.4°) in the concentration range of 1-1000 ppm.

Meanwhile, in this embodiment, the measurement of the contact angle may be performed by a measurement module including a plurality of cameras installed along the circumference of the liquid contact mechanism in the form of a glass plate 11 (not shown).

At this time, an arithmetic module may be further included that receives an image of a form in which a detergent droplet forms on the surface of the liquid contact mechanism from the measurement module composed of a camera and calculates a contact angle between the detergent droplet and the liquid contact mechanism. (not shown)

And, in the calculation module, a procedure for calculating an average value of contact angles obtained from all contact angles calculated for each image obtained from a plurality of the measurement modules, and corresponding to the average value from contact angle data corresponding to each pre-stored detergent concentration An algorithm including a procedure for calculating the detergent concentration to be used may be loaded.

The calculation module may be a general PC type device or a portable device such as a smart phone. If the calculation module is a smartphone, the algorithm can be produced in the form of an app installed on the smartphone, and the liquid contact mechanism only needs to exist in an area where water droplets can land, and the measurement module is also a micro camera installed on the smartphone. Therefore, the detergent concentration measuring device according to the present invention can be implemented in a very small size and can be carried, so it can be used immediately anywhere.

<Second Embodiment>

Since the second embodiment is in common with the first embodiment in that it uses a superhydrophobic surface, differences between the first embodiment and the second embodiment will be described here.

Unlike measuring the detergent concentration by observing the contact angle by landing a droplet on the superhydrophobic surface in the first embodiment, the second embodiment is characterized by combining the principle of the capillary 12 and the properties of the superhydrophobic surface . Therefore, when the liquid rises along the capillary 12 due to the principle of the capillary, if the inner wall of the capillary 12 is composed of a superhydrophobic surface, the assumption that the height at which the liquid rises will maximize the difference depending on the detergent concentration will be described below. This is an embodiment adopted by being proved by the experimental results to be performed.

In the second embodiment, the ZnO protrusion 16 (seed) and the ZnO nanorod 17 array grown on the inner wall of the capillary 12 are grown on the upper surface of the glass plate 11 in the first embodiment. It is formed using the same reactant solution as

However, in the second embodiment, since the inner surface of the capillary tube 12 needs to be treated, not the surface of the glass plate 11, it cannot be treated in the form of being immersed in the beaker 13 as in the first embodiment.

Therefore, ZnO protrusions 16 (seeds) are formed in the form shown on the left side of FIG. 4 (b), and an array of ZnO nanorods 17 is formed in the form shown on the right side of FIG. 4 (b). Specifically, as shown in FIG. 4 (b), the reactant solution for forming the array of ZnO protrusions 16 (seeds) or ZnO nanorods 17 consists of a perfluoroalkoxy (PFA) tube and a perfluoroalkoxy tube. A syringe 122 inserted into the end is used and delivered to the capillary tube 12 . For ZnO asperity 16 (seed) formation, a mechanical pump pumps the solution at a rate of 10 μL/min until the capillary tube 12 is filled with the solution. When the capillary tube 12 is full, the operation of the pump is stopped and the capillary tube 12 is stored overnight in an oven at 60 °C. In the next step, the growth of the ZnO nanorods 17, a mixed solution of 50mM ZnO(NO ₃ ) ₂ and 50mM HMTA was first introduced at a rate of 5 μL/min using the perfluoroalkoxy tube, the syringe 122, and a mechanical pump. and supplied to the capillary tube 12. Subsequently, the ZnO nanorods 17 are grown by maintaining them at 90° C. for 2 hours. After all reactions are complete, the capillary tube 12 is rinsed with ultrapure water and dried at 90 DEG C to complete the surface treatment process on the inner surface of the capillary tube 12 as a liquid contact mechanism.

For reference, the stearic acid (18) coating performed on the surface of the ZnO nanorods (17) array was performed by injecting an acetone solution with 2 mM stearic acid into the capillary at a pumping rate of 1 μL/min for 30 min and drying at room temperature for 1 h. done by doing

8 shows SEM images taken at different magnifications of the array of ZnO nanorods 17 grown on the inner wall of the capillary 12 through the above-described process. The pictures were taken at different positions on the same capillary 12. The average diameter of the ZnO nanorods 17 is estimated to be 81.7 nm in FIG. 8(c), which is much smaller than the ZnO nanorods 17 on the surface of the glass plate 11 in the first embodiment.

This reduction in ZnO nanorod 17 size could be due to the reduced ZnO asperity 16 (seed) size and limited amount of precursor solution, or it could be due to the low incubation temperature (60 °C) and limited internal volume of the capillary.

8(d) is a SEM image of ZnO nanorods 17 after treatment with stearic acid 18. The overall shape, arrangement and size of the ZnO nanorods 17 are very similar to those before treatment with stearic acid 18. The average diameter of the ZnO nanorods 17 after treatment with stearic acid 18 is 81.5 nm. The fact that the surface of the ZnO nanorods 17 appears brighter while having almost the same diameter indicates that stearic acid 18 is uniformly coated on the surface of the ZnO nanorods 17 . The central white particle is presumed to be a mass of stearic acid (18).

Using this inner wall modified capillary 12, the rise height of the pure water capillary 12 and the rise height of the detergent solution S were compared experimentally. Figures 3 (a) and (b) show a clear contrast between the height of the solution rise according to the detergent concentration of the capillary 12 whose surface is not treated and the capillary 12 whose surface is modified to be superhydrophobic. 3 (a) and (b), the detergent solution (S) is prepared using one type of detergent, and after 1 minute of vertically immersing the capillary tube 12 in the water tank 111 in which each detergent solution (S) is supported image was taken. In the case of the capillary 12 whose inner surface is not treated, there is no significant difference in the height of the inside of the capillary 12 corresponding to each detergent concentration, as shown in FIG. 3 (a). On the other hand, in contrast, in the capillary tube 12 whose inner surface is modified to be superhydrophobic, as shown in FIG. 3 (b), a clear and constant difference is observed in the rising height of the capillary tube 12 according to the detergent concentration.

As shown in FIG. 3 (c), the final height h of the liquid rising along the capillary 12 in the vertically erected capillary 12 is expressed as Equation (4) below.

h = (2γcosθ)/(ρgr) ---------------- (4)

Referring to FIG. 3 (c) together, γ and ρ are the surface tension and density of the liquid, g is the gravitational acceleration, θ is the contact angle of the liquid on the wall, and r is the radius of the capillary 12. The liquid inside the capillary 12 spontaneously rises to an equilibrium level to balance the capillary 12 phenomenon with gravity.

Based on Equation 4, assuming that the density of the liquid remains constant, it is logical that the rising height inside the capillary 12 decreases as the liquid surface tension decreases. This is because both γ and cos θ become small in the case of a liquid with low surface tension. Thus, the detergent concentration dependent decrease in the height of the capillary 12 in FIG. 3(b) clearly indicates that the surface tension of the detergent solution steadily decreases as the detergent concentration increases.

In other solutions using different types of detergents, the capillary 12 height change appears in a similar form (not shown). As shown in FIG. Looking at it, the solution rising height seems to be independent of the detergent concentration, rather, it can be attributed to the phenomenon of physical adsorption of water molecules on the inner wall of the capillary 12 and the hydrogen interaction between the inner wall of the capillary 12 and the detergent solution. On the other hand, it can be inferred that hydrogen interaction between the detergent solution and the inner surface of the capillary 12 does not occur in the capillary tube 12 whose inner surface is treated with superhydrophobicity.

Similar to the relationship between the contact angle (θd) and the concentration in the first embodiment, the relationship between the height of the capillary 12 and the concentration is non-linear in real terms, and a linear relationship appears when the concentration is logarithmically treated, so FIG. 3 In the graph of (d), the relationship between h and log C is displayed linearly.

On the other hand, in the second embodiment, the liquid contact mechanism is composed of a capillary tube 12 and a water tank 111 having a volume in which the lower portion of the capillary tube 12 can be submerged to a certain height, and the water tank 111 is used for measuring the detergent concentration. A scale capable of measuring the required amount of liquid may be formed. Because, when the same solution is raised from the bottom of the capillary under the same conditions, the conditions must be the same to obtain the same result. because it has to be displayed.

In addition, a lattice-shaped support frame having a plurality of holes through which the capillaries 12 can be erected may be installed in the water tank 111 (not shown). It can help you maintain an upright posture.

The measurement module may have two embodiments. In the first embodiment, the measurement module includes a camera arranged to face the top of the liquid raised along the inside of the capillary tube 12, a rotation gauge capable of adjusting the direction of the camera so that the camera faces the top of the liquid, It can be composed of a monitor displaying a target scale at the center so that the center of the image of the camera can be accurately aligned with the top of the liquid, and a camera lifting unit that can adjust the height of the camera (not shown). That is, while watching the monitor By adjusting the angle of the camera by turning the rotation gauge, the height of the top of the solution rising through the capillary can be calculated with the angle value of the rotation gauge when the target scale displayed on the monitor and the top of the liquid coincide. (not shown)

In the second embodiment, the measurement module includes a camera disposed with a variable angle while facing the top of the liquid raised along the inside of the capillary tube 12, an angle sensor that calculates the angle of the camera in real time, and an image center of the camera. It consists of a monitor in which a target scale is displayed at the center so that it can be accurately matched to the top of the liquid, and the height of the top of the liquid is calculated through the horizontal distance between the camera and the capillary measured in advance and the angle information of the camera. Yes (not shown)

Meanwhile, since the detergent concentration measuring method according to the present invention is the same as the description in the detergent concentration measuring device described above, the description will be omitted to avoid redundancy.

The present invention described above is not limited by the foregoing embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within a range that does not deviate from the technical spirit of the present invention. will be clear to those who have knowledge of

D: liquid droplet S: detergent solution
11: glass plate 12: capillary
13: beaker 16: ZnO projection
17: ZnO nanorod 18: stearic acid
19: air pocket 111: water tank
122: syringe

Claims (10)

A liquid contact mechanism having a superhydrophobic surface formed at an angle of contact with pure water droplets of 150° or more;
A measurement module for measuring a contact angle or contact position of a liquid contacting the superhydrophobic surface;
The superhydrophobic surface is formed in a form in which a plurality of nanorods made of zinc oxide (ZnO) protrude from the surface of the liquid contact mechanism, and air is filled between the nanorods,
Ends of the plurality of nanorods are coated with stearic acid,
Between the plurality of nanorods and the surface of the liquid contact mechanism, zinc oxide protrusions serving as seeds for growing nanorods are formed at positions corresponding to each nanorod,
The zinc oxide projection is prepared using an aqueous solution containing ZnO(NO ₃ ) ₂ , NH ₄ Cl, urea and ammonia,
The liquid contact mechanism
It is composed of a plate-shaped member having an area on which detergent droplets can form, and the contact angle relationship between the detergent concentration and the superhydrophobic surface at a detergent concentration of 1 to 1000 ppm is linear on a semilog plot, or
Alternatively, a capillary whose inner circumferential surface is formed as the superhydrophobic surface, a water tank having a volume in which the lower part of the capillary can be submerged to a certain height, and a lattice-shaped support frame having a plurality of holes so that the capillary can stand upright inside the tank and the final height difference of the liquids having different detergent concentrations rising inside the capillary is increased than the height difference when there is no superhydrophobic surface on the inner circumferential surface of the capillary, and the detergent concentration and capillary rise at detergent concentrations of 1 to 1000 ppm The relationship between the heights is linear on the semilog plot,
Detergent concentration measuring device wherein the detergent is a rinse dish rinsing detergent, a type 1 detergent, a sodium detergent, and a potassium detergent. delete delete According to claim 1,
The measurement module is a plurality of cameras installed along the circumference of the liquid contact mechanism,
Detergent concentration measuring device, characterized in that it further comprises a calculation module for receiving the image of the shape of the detergent droplet formed on the surface of the liquid contact mechanism from the measurement module to calculate the contact angle between the detergent droplet and the liquid contact mechanism. According to claim 4,
The calculation module includes a procedure for calculating an average contact angle from the total contact angles calculated for each image obtained from a plurality of measurement modules, and contact angles equal to the average contact angle among previously measured and stored contact angle data for each detergent concentration A detergent concentration measuring device, characterized in that an algorithm including a procedure for determining the detergent concentration by extracting the concentration data at which the angle is formed is mounted. According to claim 1,
The measurement module includes a camera disposed with a variable angle while facing the top of the liquid raised along the inside of the capillary, an angle sensor that calculates the angle of the camera in real time, and the center of the image of the camera exactly coincides with the top of the liquid. Detergent concentration measuring device, characterized in that the height of the top of the liquid is calculated through a pre-measured horizontal distance between the camera and the capillary and angle information of the camera. A detergent concentration measuring method using the detergent concentration measuring device of claim 1,
Measuring a contact angle or a contact position of a liquid contacting the surface after contacting the superhydrophobic surface with a liquid;
The measuring step includes growing a plurality of nanorods made of zinc oxide (ZnO) on the surface of the liquid contact mechanism in a direction protruding from the surface before measuring the contact angle or contact position of the liquid,
The measuring step includes forming a protrusion made of zinc oxide (ZnO) in advance at each position where a plurality of nanorods are to be grown before the step of growing the nanorods,
The measuring step further includes coating stearic acid on the ends of the plurality of nanorods after the step of growing the nanorods,
Detergent concentration measurement method, characterized in that the protrusion is prepared using an aqueous solution containing ZnO (NO ₃ ) ₂ , NH ₄ Cl, urea and ammonia. delete According to claim 7,
The liquid contact mechanism is a plate-shaped member having an area where detergent droplets can form,
In the measuring step, after the step of forming the nanorods, a liquid whose concentration is to be measured is dropped on the surface of the liquid contact device in the form of droplets, and the droplet of the liquid whose concentration is to be measured is contacted with the liquid on the surface of the liquid contact device. It is made by measuring the contact angle with the surface of the instrument,
The measurement module is a plurality of cameras installed along the circumference of the liquid contact mechanism,
The step of measuring the contact angle includes obtaining measurement images of the contact angle at different points with at least three cameras;
Calculating an average value of contact angles from the obtained measurement image;
Detergent concentration measuring method comprising the step of calculating a detergent concentration matching the average value of the contact angle measured from the detergent concentration data according to the previously measured contact angle from the average value of the contact angle. According to claim 7,
The liquid contact mechanism is composed of a capillary tube and a water tank having a volume in which the lower portion of the capillary tube can be submerged to a certain height, and the superhydrophobic surface is formed on the inner circumferential surface of the capillary tube to have different detergent concentrations rising along the inside of the capillary tube. The final height difference of the liquid is increased compared to the case where there is no superhydrophobic surface on the inner circumferential surface of the capillary,
The measurement module includes a camera disposed with a variable angle while facing the top of the liquid raised along the inside of the capillary, an angle sensor that calculates the angle of the camera in real time, and the center of the image of the camera exactly coincides with the top of the liquid. By being made up of a monitor on which the target scale is displayed in the center,
The measuring step may include adjusting the target scale of the monitor to the top of the liquid by changing the angle of the camera;
Calculating the angle of the camera with an angle sensor while the target scale of the monitor is aligned with the top of the liquid;
Detergent concentration measuring method comprising the step of calculating the height of the top of the liquid by adding the difference between the height of the top of the liquid and the height of the camera to the height of the top of the liquid at the angle calculated in the step of calculating the angle.

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