CN110873700A

CN110873700A - Simple method for measuring refractive indexes of colloid, solid and liquid

Info

Publication number: CN110873700A
Application number: CN201811028592.2A
Authority: CN
Inventors: 张怡宁
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-08-30
Filing date: 2018-08-30
Publication date: 2020-03-10

Abstract

The invention relates to a simple method for measuring refractive index. The laser beam is used to glancing a smooth, non-deformable and well-scattered artificial scattering surface to display the incident laser beam at the interface between the material to be measured and the air. Displaying a refracted laser beam in the colloid by using the tyndall effect of the colloid; in the tested transparent solid and transparent liquid, the refracted laser beam is displayed by glancing the ground observation surface with the refracted laser beam. The reflected laser beam on the interface also sweeps the artificial scattering surface and is displayed simultaneously with the incident beam. By utilizing the principle that the incident angle is equal to the reflection angle, the angular line of the included angle between the incident light and the reflection light is the normal of the measured material and the air interface. The incident angle and the refraction angle of the gel, the transparent solid and the transparent liquid are measured, and the refraction indexes are calculated by the law of the refraction angle.

Description

Simple method for measuring refractive indexes of colloid, solid and liquid

Technical Field

The invention relates to a physical parameter measuring technology of a material, in particular to a method for measuring refractive indexes of colloid, solid and liquid.

Background

Refractive index is an important physical parameter describing the properties of a material. The method for measuring the refractive index comprises a pin method, a minimum deviation angle method, an interference method, an Abbe refractometer and the like, wherein the pin method requires that a measurement sample is a thick flat plate with two parallel surfaces; the minimum deflection angle method is to process a measured material into a triangular prism, and then measure the minimum deflection angle by using a spectrometer, obviously, the measured object of the minimum deflection angle method only can be a transparent solid; in an interference method, such as a Michelson interferometer, measurement objects are a thin film and a transparent sheet, and the operation of the interferometer has certain difficulty, so that higher requirements are also put forward for experimenters; the Abbe refractometer is the most classical refractive index measuring method, is improved and improved for many years, has high measuring precision, can measure the refractive index of liquid and the refractive index of solid, has certain limitation (between about 1.3 and 1.7) on the range of the refractive index, processes a sample into an optical plane with a certain area when measuring the solid, is a precise instrument, and has higher price. The above-mentioned measurement methods are for liquids and solids. Methods and apparatus for measuring the refractive index of colloids, particularly gels, have not been reported. The colloid is often encountered in industrial production, such as mineral separation, sewage treatment, dehydration of petroleum crude oil, preparation of nano materials, preparation of partial Chinese and western medicine injection and preparation of plastics and rubber in the metallurgical industry. While donkey-hide gelatin, antler gelatin, pectin, gelatin, agar, jelly, etc. are common gels in the food industry. The refractive index of the colloid is a function of the concentration of the dispersoid, and the refractive index also changes during the gelation of the colloidal solution. Therefore, a simple and widely available method for measuring the refractive index of the colloid is provided, which is not only beneficial to the research of the colloid, but also beneficial to the monitoring of the colloid components in industrial production. The invention is not only suitable for measuring the refractive index of colloid, but also suitable for measuring the refractive index of transparent solid and transparent liquid.

The laser beam is used for displaying the light propagation path in the invention, because the divergence angle of the laser is small, the directivity is good, the total optical path in the experiment is only dozens of centimeters, and because the laser beam is close to the exit of the laser, the light beam can not be diverged greatly. The beam diameter and spot are on the order of millimeters. It is convenient to use it to show traces of both incident and refracted rays. The laser that the laboratory was used is equipped with special power, and the price is higher. Laser beams generated by Laser pointers (commonly called Laser pens) which are easily purchased in the market are adopted, and the Laser pens can be driven by batteries, are flexible to use, are convenient to carry and are low in price. The method has the advantages that the method has low manufacturing requirements on the tested sample, and the tested sample only needs to have a flat interface with a few square millimeters for laser incidence. It is therefore appropriate to use it in combination with a scattering source to achieve the display and measurement of the angle of incidence and angle of refraction.

We have experience that when the PPT reports to the user that the laser pointer is being used, we can only see the spot of the laser beam that falls on the screen, and not the laser beam that it emits. This is because its intensity is too low and there are not enough scattering sources in the air to scatter the laser light to the eyes of the listener. If a blast of dust is raised or smoke or steam is added on the way of laser propagation, the laser beam is invisible. However, such scattering sources are unstable and a burst of air blows away dust and smoke, leaving the laser beam behind. In the same way, when the light beam emitted by the laser pen passes through pure liquid (such as pure water) and transparent solid (such as glass, crystal and the like), the light beam cannot be seen. We must incorporate an artificially stable source of scattering to make the path of the laser beam clearly visible. How the scattering source is made will be described in the summary of the invention.

Disclosure of Invention

Firstly, measuring the refractive index of colloid: this is meant to include both lyosols and gels, as well as solids, and for the time being aerosols. Kraft paper is flatly stuck on a 3 mm-thick organic glass plate by using adhesive sticker to be used as an artificial scattering plate. The sample is suspended and fixed, and a sample to be measured is placed below the sample. The samples to be tested may be colloidal solutions or gels thereof, which are contained in 1 sample box having a width of 65mm, a height of 100mm and a thickness of 25 mm. The box top is opened so that the laser beam is incident on the interface of the colloid to be measured and air; if the sample to be measured is a solid gel, such as a colored glass plate, a few square millimeters of flat surface must be ground and polished on top of it for the laser beam to be incident. When one side edge of the laser beam passes through the artificial scattering plate and is incident on the top of the hydrosol or the solid sol, the incident light beam can be displayed. Most of laser beams left after glancing are irradiated on the interface of air and the colloid to be detected, refraction is generated due to the Tyndall effect of the colloid, and the refracted light beams of the laser beams in the colloid are clearly visible. The reflected light beams of the interface are also observed on the diffuser plate. In order to avoid measurement errors caused by deviation of the measured interface from the horizontal, by utilizing the principle that the incident angle is equal to the reflection angle in the reflection law, the experiment specifically operates as follows when the incident angle is measured on the front surface by using a circular protractor with the diameter of 150 mm: firstly, the origin of the protractor is aligned to the center of the laser beam at the falling point of the interface, and the protractor is slightly rotated to enable the incident light beam and the reflected light beam to have bilaterally symmetrical readings, for example, the incident light beam is in the first quadrant, the incident line is read to be 50 degrees, the reflected light beam is in the third quadrant, the reading is also 50 degrees, and then the 90-degree line of the protractor is the normal of the measured interface. At this time, the included angle between the refracted light beam and the 90-degree line is the refraction angle gamma, the included angle between the incident light beam and the 90-degree line is the incident angle i, and the refractive index of the measured colloid is calculated by the refraction theorem to be n sini/sin gamma. In this measurement, the suspended artificial diffusion plate and the measured interface of the colloidal solution or gel are not in contact and are separated by about millimeter magnitude, so that the artificial diffusion plate is a nondestructive test to prevent the contact of the artificial diffusion plate and the colloidal solution or gel from damaging the surface of the colloidal solution, thereby ensuring that the directions of the reflected light beam and the refracted light beam are not interfered. Measurement of refractive index of transparent solid: such as a transparent glass plate. Its refractive index measurement is similar to that of an organic glass plate containing impurities in a solid gel, and also a plane of several square millimeters is ground and polished at its top end for laser incidence, which is different from the solid gel in that it does not have the tyndall effect, and the refracted beam of the laser beam is not visible, so that its front surface (viewing surface) must be ground to show the refracted beam. The specific operation method is that the laser beam passes through the suspended artificial scattering surface to display the incident beam. The remaining laser beam is directed onto the transparent solid to be measured placed below. The viewing surface of the transparent solid frosted surface is raised (on the order of millimeters) from the scattering surface of the suspended artificial scattering plate. The measured transparent solid is moved back and forth, namely the amount of the protrusion is adjusted, so that the refracted ray of the laser beam in the transparent solid is the clearest. This means that observation of its refracted beam through the transparent solid frosting produces scattering to reveal the refracted beam. Then we can use the origin of the circular protractor to align the falling point of the laser beam on the transparent solid, and rotate the protractor to make the incident ray and the reflected ray have the same reading, so as to find the normal of the measured interface. Then, the incident angle and the refraction angle are measured to calculate the refractive index of the measured transparent solid. It is a piece of transparent cullet with an irregular shape. The requirements on the shape and the processing of the sample are low, and the measuring tool is only a laser pen and a scattering plate. This is an advantage of this measurement method. It makes the method especially suitable for the measurement of field ore and the like.

Secondly, measuring the refractive index of the transparent liquid: because pure liquids (such as purified water) and true solutions do not have the tyndall effect, its refracted ray is not visible. Its measuring device is somewhat changed. The device is a transparent box similar to a goldfish bowl and used for containing liquid to be measured, and can be made of glass or organic glass. The box in this experiment is box width 150mm, thick 40mm, high 120mm, and box wall thickness 5mm, top opening, the fluting of two side walls in the box to perpendicular to liquid level insert the frosted, middle trompil (diameter 30mm) organic glass board (thick 3mm, the size is 150mm) as the scattering face. The reason for the openings in the diffuser is that the meniscus, which is produced by capillary action of the frosted plexiglass and liquid in the liquid being measured, tends to strike a curved surface when the laser beam grazes along the diffuser, thus causing the reflected and refracted light to deviate from the plane of incidence. Holes are made in the diffuser plate to ensure that the liquid level of the incident laser beam remains level around the liquid level drop point. For the same reason, the inserted diffuser plate is also a few millimeters inside the front panel of the box to avoid the effect of the meniscus on the laser beam reflected and refracted rays by the inner wall of the box. The box is filled with transparent liquid to be measured, the liquid level of the transparent liquid approximately submerges half of the hole, and the laser beam is adjusted to enable the falling point to be in the center of the round hole. In order to further determine the position of the falling point of the laser beam on the liquid level, a magnet is arranged above the round hole of the scattering plate, a sharp needle with adjustable verticality, left and right positions and height is arranged above the round hole of the scattering plate, and the needle point is just above the liquid level but is not contacted with the liquid level. After the falling point of the laser beam on the liquid surface is determined with the help of the sharp needle, the origin of the circular protractor is aligned with the center of the laser beam on the falling point of the liquid surface, the protractor is rotated to enable the incident light and the reflected light to have the same reading, so that the normal line of the liquid surface is found out, then the incident angle and the refraction angle are measured, and the refractive index is calculated.

In the refractive index measurement of colloid, transparent solid and transparent liquid, the diameter of a circular protractor is increased (for example to the meter order), and the size of a measured sample is increased, so that the arc length corresponding to each degree of the protractor is increased, and the thickness of a laser beam has small change along with the distance, because the reading precision of an incident angle and a refraction angle can be improved, and the refractive index measurement precision is improved, and the method has potential in industrial application.

The requirement for manufacturing the artificial scattering surface is that the flatness is good and the artificial scattering surface is not deformed; has stronger scattering to the glancing laser beam. The incident light beam is displayed in the measurement of the refractive indexes of colloid and transparent solid, a flat plate with certain thickness and difficult deformation is used, a scattering film or paper is flatly pasted for manufacturing, an organic glass plate with the thickness of 3mm is used in the experiment, and adhesive paper is flatly pasted for manufacturing the scattering plate. The observation surface of the transparent solid was made to be a fine ground surface to scatter the refracted light beam. For transparent liquids, artificial scattering surfaces

The upper half is used for displaying incident light beams, and the lower half is inserted into the measured liquid to scatter refracted light, so that the material plate which does not interact with the measured liquid is selected to be finely ground. For pure water, a fine frosted organic glass plate is used for the convenience of processing. For the organic solution, a finely ground glass plate was selected.

The refractive index measurement is in the specific embodiment.

Drawings

FIG. 1 is a refractive index measurement of gelatin aqueous solution gel. (agar gel refractive index measurement is similar)

FIG. 2 is a refractive index measurement of a colloidal solution detergent.

FIG. 3 is a refractive index measurement of a solid gel (plexiglass containing impurities).

FIG. 4 is a refractive index measurement of transparent solid glass.

Fig. 5 is a refractive index measurement of transparent liquid purified water.

Detailed Description

The laser wavelength in the following measurements was 650 nm.

The measurements for each sample were repeated five times, and their refractive index averages and average errors were obtained.

1. Refractive index measurement of gelatin gels

According to the proportion that the weight percentage concentration of the gelatin aqueous solution is 11 percent, the gelatin powder is put into purified water to be soaked for more than 2 hours, so that the gelatin powder fully absorbs water to swell. Heating the mixture over water to make the sol temperature be 75 ℃. Pouring into a mold for measurement, and freezing in a refrigerator. Taking out after gelling and placing at room temperature. The measured refractive index average and error are: n is 1.415 ± 0.003, and the measurement temperature is 24 ℃.

2. Refractive index measurement of agar gel

Weighing agar water solution with 2% of weight percentage concentration, soaking agar powder in a small amount of purified water for more than 2 hours to make the agar powder fully absorb water and expand, boiling the purified water added according to the proportion requirement, and pouring the agar into the boiled water until the agar is completely dissolved. Quickly pouring into a mold for measurement, and placing in a refrigerator for freezing and gelling. The sample was taken out to room temperature before measurement. The average value and the error of the refractive index are measured as follows: n-1.369 +/-0.004 (measuring temperature 25℃)

3. Measurement of refractive index of detergent

The detergent is an aqueous solution of a surfactant, a solubilizer, essence and the like, is a viscous liquid, has an obvious Tyndall effect as can be seen from a picture 2, is a colloidal solution, and has the following refractive index average values and errors: n-1.338 +/-0.004 (measuring temperature 25℃)

4. Measurement of refractive index of organic glass containing impurities

The measurement sample was a plexiglass plate containing impurities and having a thickness of 8mm, which was seen from photograph 3 to have a pronounced Tyndall effect and was therefore a solid gel. The upper end surface of the device is ground and polished for laser beam incidence, and the measured average value and error of the refractive index are as follows: n-1.502 +/-0.004 (measuring temperature 26℃)

5. Refractive index measurement of transparent glass (transparent solid)

The sample was a piece of clear cullet plate 3.9mm thick and irregular in shape. The top end is ground flat and polished for laser incidence. The front surface is sanded for observation of glancing of the refracted laser beam. Reference is made to photograph 4. The measured refractive index average and error are: n-1.522. + -. 0.004 (measuring temperature 24 ℃ C.)

6. Pure water refractive index measurement

The measured refractive index average and error are: n is 1.327 ± 0.004 (measurement temperature 26 ℃).

Claims

1. A simple method for measuring the refractive index of a material by displaying the propagation path of light by glancing laser beams on an artificial scattering surface and scattering in the material to be measured so as to realize the measurement of the incident angle and the refraction angle of the interface between the material and air, and the specific measurable materials and methods are as follows:

(1) based on the method as set forth in claim 1, for colloidal solution, gel of colloidal solution, and solid gel, using laser beam to graze the artificial scattering surface to display the incident beam of colloid-air interface; and displaying the laser beams which are remained after glancing and enter the colloid for refraction by utilizing the Tyndall effect of the colloid so as to realize the measurement of an incident angle and a refraction angle, and calculating the refraction index of the colloid to be measured by using a refraction theorem.

(2) Based on the method as set forth in claim 1, for the transparent solid to be measured, a polishing plane of several square millimeters is ground for the laser beam to enter, the front surface perpendicular to the small plane is sanded to be used as the observation surface, the laser beam enters the transparent solid to be measured, after refraction, glancing is performed on the ground observation surface, the refracted laser beam is displayed, so as to realize the measurement of the incident angle and the refraction angle, thereby measuring the refraction index of the transparent solid.

(3) The method as claimed in claim 1, wherein for transparent liquid, a frosted artificial scattering plate is inserted into a transparent liquid-containing box for the liquid to be measured, the laser beam is projected to the plate to expose the upper half of the liquid surface, the incident laser beam is displayed, the rest laser beam enters the liquid to be measured after being projected, refraction is generated, the refracted light beam is displayed by the part of the artificial scattering plate immersed in the liquid, so that the measurement of the incident angle and the refraction angle is realized, and the refraction index of the transparent liquid is measured.

2. Based on the method of claim 1, the normal of the interface between the measured material and the air is determined during the measurement of the incident angle and the refraction angle, i.e. both the incident light and the reflected light are glancing off by the artificial scattering surface, i.e. the incident light and the reflected light are displayed simultaneously, and by using the principle that the incident angle and the reflection angle are equal, the partial angle line of the included angle between the incident light and the reflected light is the actual normal of the interface of the measured material, and the normal determination ensures the correct measurement of the incident angle and the refraction angle.

3. Based on the manufacturing requirements and method of the artificial diffusion plate used in claim 1, the diffusion plate is made of a material which has good planarity, is not easy to deform and has good laser diffusion. In the measurement of the refractive index of colloid and transparent solid, the scattering surface of incident light beam is formed by flatly pasting scattering film or paper on the plate material meeting the requirement; the scattering surface for displaying the refracted light beam of the transparent solid is made of an observation surface of fine grinding sand; for the transparent liquid to be measured, the smooth plate fine frosted surface which does not interact with the liquid to be measured is used for making an artificial scattering surface to display the refracted light beam.

4. The method according to claim 1 or 3, wherein the refractive index of the transparent liquid is measured by opening a hole in the scattering plate so that the laser beam is irradiated around the drop point of the liquid surface to be measured without being disturbed by the scattering plate, and maintaining the liquid level around the drop point of the laser beam.

5. The simple measurement method of refractive index according to claim 1 is extended to industrial applications and to the idea of improved accuracy. The diameter of the circular protractor is enlarged, and the scales of a measured sample pool and an artificial scattering surface are enlarged simultaneously, so that the arc length corresponding to the minute value of the protractor is enlarged, the thickness of a laser beam is slightly changed along with the propagation distance, and the measurement accuracy of the incident angle and the refraction angle is improved.