CN112284979B - Method for measuring dynamic contact angle of droplet boundary - Google Patents
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Abstract
The invention discloses a method for measuring a dynamic contact angle of a microdroplet boundary, belonging to the technical field of interface chemical test. The invention discloses a micro-liter and nano-liter double liquid inlet device, which is characterized in that volume marginal increment is formed by increasing the volume of liquid, the dynamic change of a contact angle value is caused by testing the volume marginal increment, finally, a contact angle below 60 degrees is taken as a maximum value and is taken as a real contact angle, and a contact angle above 60 degrees is taken as a minimum value and is taken as a real contact angle.
Description
Technical Field
The invention relates to a method for measuring a dynamic contact angle of a microdroplet boundary, belongs to the technical field of interfacial chemical test, and is used for testing the influence of a real contact angle and a surface structure of a solid material on an apparent contact angle.
Background
The contact angle value is one of the important indexes for characterizing the physicochemical properties of solid materials, particularly the interfacial adhesion. With the development of industries such as nano materials, bionic science, semiconductor wafers and the like, the measurement of the contact angle and the precision and reliability thereof directly influence the final effect representation and value evaluation. Especially, the influence degree of the real contact angle value and the apparent contact angle by the surface structure is crucial to the success of the bionic material design and the quality evaluation of the wafer manufacturing process.
The contact angle measurement technology is mainly two technologies of static contact angle measurement and dynamic contact angle measurement at present.
The static contact angle measurement is generally used for measuring and characterizing the obtained liquid drop profile, and the contact angle values under the conditions of different viewing angles of left, right, front and back 360 degrees are evaluated and obtained by adopting an ADSA-RealDrop algorithm and applying a Young-Laplace equation. Patent No. 201510225605.5, a 3D contact angle testing device and method. At present, the measurement method of the static contact angle in the world basically stays at the stage of a digital protractor, and the static contact angle value is analyzed by adopting a simple circular, elliptical or polynomial equation with geometric significance. The digital protractor methods are susceptible to gravity, the fluctuation amount of the measured value is very large, the sensitivity of the measured value data is low, and the measured value precision and the data reliability can not meet the requirements of high precision, reliability and scientificity in the nanometer material and semiconductor industries.
Methods of dynamic contact angle measurement generally include three methods:
1 increase, decrease liquid method. By adding liquid drops, the profile of the liquid drops is changed constantly, when the Contact point position of the liquid drops moves on the surface of a solid, a Contact Angle value of a moving critical state is obtained and recorded as an Advanced Contact Angle value; by reducing the liquid drops, the profile of the formed liquid drops is changed continuously, and when the Contact point position of the liquid drops is hydraulically driven on the surface of a solid, the Contact Angle value of the moving critical state is obtained and recorded as a Receded Contact Angle. And obtaining a contact angle lagging image value by comparing the difference value of the advancing angle and the receding angle.
The liquid drop profile of the liquid method is increased and reduced and is easily influenced by the surface energy of the needle head, and the exchange process of a gas-solid interface and a liquid-solid interface is easily influenced by the extra energy of spitting and absorbing the liquid, so the accuracy and the repeatability of the measured value are poor. Moreover, this method does not allow to obtain true contact angle values, only a simple hysteretic angular deviation of the gas-solid to liquid-solid interface interchange. Therefore, the method cannot be used for evaluating the true contact angle and the apparent contact angle of the bionic material, the influence degree of the surface structure on the contact angle and the like.
2 tilting the sample method. After the sample is inclined by a certain angle, the angle value of the contact point position on one side of the liquid drop is increased and the angle value of the contact point position on one side is decreased due to the influence of gravity, and when the liquid drop rolls on the surface of the solid, a large-angle-value advancing angle and a small-angle-value retreating angle in a critical state are analyzed, so that the hysteresis contact angle value of the solid material is evaluated.
3 increasing and decreasing liquid after punching on the surface of the sample. The method is proposed by professor group a.w.neumann, toronto university, canada. Similar to the first increasing and decreasing liquid method in the operation flow, the analysis results are also similar.
None of the above methods can achieve the design objectives described in this patent. As can be seen from the results of practical experiments, as shown in fig. 1, the measured value of the nearly true contact angle value of the smooth solid surface was 80 °. As shown in fig. 2, when the increase and decrease liquid method is used, the advance angle value is 114 °, the recede angle value is 14 °, and the lagging contact angle value is 100 °, it is clear that this angle value has no relation to the true contact angle value as mentioned above. As shown in fig. 3, when the method of tilting the sample was used, the advancing angle value was 141 °, the receding angle value was 106 °, and the hysteresis contact angle was 35 °. The same method of tilting the sample does not yield a true contact angle value that is reliable and scientifically based. Obviously, the existing dynamic contact angle testing technology only obtains the maximum stagnation force of a liquid drop at a certain position on the solid surface due to the surface free energy, and is not a real contact angle measuring technology based on surface nano-structure or micro-structure analysis in a true scientific sense.
Zhao national seal and Zhu from action principle of surfactant
Yao works, china light industry Press page 503 has used scientific description of the definition and application of advancing and receding angles in principle, and contact angle hysteresis is reflected in the phenomenon that contact angles are different in the process of mutual substitution of liquid-solid and gas-solid interfaces. Further, it is further theoretically demonstrated that the difference between the true contact angle and the apparent contact angle based on the nanostructure condition as described above cannot be obtained by advancing and retreating the angle. From the scientific theory analysis, pages 505 to 507, it is further suggested that the contact angle value is influenced by the chemical diversity of the surface unevenness and the surface roughness.
In 1936, robert N.WENZEL geometrically confirmed the effect OF surface structure in the article "RESISTANCE OF SOLID SURFACTOS WETTING BY WATER" INDUSTRIAL AND ENGINEERING CHEMISTRY VOL.28, no.8, pages 988-994. And a simplified Wenzel formula COS theta W = rCOS theta is further provided and is used for calculating the real contact angle value after the influence of the surface roughness is corrected when the contact angle value is smaller than 90 degrees. In 1944, A.B.D.CASSITE and S.BAXTER in article WETTABILITY OF POROUS SURFACES, trans.Faraday Soc.40 (1944) 546-551, further based on geometry, we obtained the Cassie-Baxter formula COS θ E = r φ sCOS θ 1+ (1- φ s) COS θ 2 for evaluating the true contact angle value after surface roughness correction when the contact angle value is greater than 90 degrees. In 2009, wojae Choi et al, in article A modified case-Baxter correlation to extract contact angle hysteresis and alkali on non-wet treated surfaces W.Choi et al/Journal of Colloid and Interface Science 339 (2009) 208-216, further obtained an improved Cassie-Baxter formula based on geometric analysis, and analyzed the forward and backward angles in a manner of combining surface roughness to obtain the true contact angle value. However, as mentioned above, these science and theory are based on simple geometric derivation and have a great difference from the actual measured value. Meanwhile, the influence of the nano structure on the real contact angle is simply attributed to the factor of the surface roughness, and a simple factor substitution mode is adopted, so that the real contact angle is far related to the actual real contact angle measured value result.
The pseudo-super-hydrophobic contact angle value is easily formed by designing a micron-scale structure (100-200 um) of the material with the true contact angle value of more than 60 degrees. As shown in fig. 4, the true contact angle value of the aluminum alloy is around 80 degrees, while the contact angle value of the 0.1mm micron structure is close to 150 degrees. In principle, the formation mechanism of the super-hydrophobic Contact Angle value profile is that when the volume of a liquid drop is far larger than the Contact area of the nano structure and the liquid, the liquid profile naturally forms a Young-Laplace pressure arc, and the mechanism is the same as that of a Lamella Contact Angle Meniscus Contact Angle (LMCA) always formed when the thin plate is inserted into the liquid. As shown in fig. 5.
Thus, the measurement of true contact angle or contact angle value is more influenced by the surface structure than simply the surface roughness. Typically, the nano-or low micron structures 10um are not distinguishable by a microscope of a conventional contact angle measuring instrument. Meanwhile, the structure of the material surface is very complex, and the material surface is divided into three types, namely a 1-side groove type nano structure chart 6, a 2-protrusion type nano structure chart 7 and a 3-pit type nano structure chart 8 in the patent, however, the structure of the actual material surface is more complex, and the situation of combining the size structure and the structure is very common. Nanostructures of the side channel type can be easily identified when the value is measured. However, the latter two structures are extremely difficult to be easily distinguished due to the optical path of the image.
The surface structure of the bionic material such as lotus effect and the like is disclosed, and the design of the super-hydrophobic property and the super-hydrophilic property of the material is very critical. The criterion for assessing the plausibility of the structural design has hitherto generally been limited to a simple static contact angle value. The uniqueness of such an assessment tool is most easily misled by the false superhydrophobic angles, which are mostly influenced by surface structures, due to the low values of the true contact angles caused by the surface structures. Similarly, in the semiconductor manufacturing process, there is also a situation that the angle variation caused by the nanostructure cannot obtain a true and accurate representation of the true angle value in the representation tool of the static contact angle value. Therefore, both the research of the nano bionic material and the industries of semiconductor design, manufacturing process and the like have urgent needs for measuring the real contact angle value or accurately representing the stable and real contact angle value of the material.
The invention discloses a measurement method of a micro drop dynamic contact angle based on a marginal droplet method, which is used for testing a real contact angle and evaluating the influence degree of an apparent contact angle on a surface structure. This patent has adopted microliter and the two inlet means of nanoliter level, forms volume marginal increment through increasing the liquid volume, and test volume marginal increment leads to the dynamic change of contact angle value, finally adopts the contact angle value in the marginal dynamic change scope below 60 degrees to get the maximum value as true contact angle, and the contact angle value in the marginal dynamic change scope more than 60 degrees gets the minimum value as true contact angle. The method has an extremely important role in the physical and chemical measurement in the industries of materials, bionic science, nano science, chemistry, semiconductors, wafers and the like, and has extremely high popularization value.
SUMMERY OF THE UTILITY MODEL
The present invention is implemented by the following technical solutions in view of the technical problems mentioned in the background art:
a method for measuring the dynamic contact angle of the boundary of a droplet, comprising the following steps:
s1, forming initial droplet volume:
forming a nano-liter initial liquid drop volume through a piezoelectric ceramic valve injection liquid inlet system, wherein the initial liquid volume is generally 100 picoliters;
s2, testing an initial contact angle value:
capturing a liquid drop image through an imaging system of a lens and a camera, and respectively calculating a 3D contact angle value of the liquid drop by adopting an ADSA-RealDrop algorithm;
s3, forming different volumes at the same position by using the equal volume or variable volume marginal increment liquid volume, and respectively calculating 3D contact angle values under different volume conditions by adopting an ADSA-Realdrop algorithm after real-time image capture of a lens and a camera;
and S4, analyzing data.
As a preferred example, in S4, the following occurs:
a1, when the initial contact angle value is larger than 60 degrees, the dynamic change curve of the liquid drop profile in the dynamic contact angle and the real contact angle value larger than 60 degrees have a nano-structured tested solid surface, the contact angle value caused by the surface free energy of the material is larger, an extra Young-Laplaced pressure arc is easily formed, liquid is not easily absorbed into a nano or micro structure, air exists at the bottom of the liquid drop, the lower edge of the liquid drop profile and the air, liquid and solid three-phase contact interface profile of the solid nano structure, and the apparent contact angle value is larger than the real contact angle value.
And A2, when the initial contact angle is less than 60 degrees, the profile of the liquid drop in the dynamic contact angle is dynamically changed, the true contact angle value of the liquid drop in the dynamic contact angle is less than 60 degrees, the relation of the surface of the tested solid with the nano structure is completely changed with the previous condition, and the apparent contact angle value is less than the true contact angle value.
As a preferred example, in A1, the following occurs:
1.1, when the marginal increment of the volume of the liquid drop does not reach two end surfaces of the nano structure and is influenced by the retention force of the surface free energy of the structure, the contact angle value keeps a section of stable small contact angle value, the marginal increment of the volume of the liquid drop with the angle value ensures that a contour contact line of the liquid drop is just tangent to the inner side of the nano structure, the marginal increment of the volume of the liquid drop ensures that the contour contact line of the liquid drop is positioned on the end surface of the nano structure, and the marginal increment of the volume of the liquid drop ensures that the contour contact line of the liquid drop is positioned on the outer side of the nano structure and is tangent;
1.2, when the volume marginal increment of the liquid drop reaches the two end surfaces of the outer side of the nano structure, the volume marginal increment of the liquid drop can cause the contact angle value to be continuously increased, the contact angle value is continuously increased due to the fact that the volume marginal increment of the liquid drop is influenced by surface free energy on the outer side of the nano structure, and the maximum increment of the outline of the marginal liquid drop forms a maximum contact angle;
1.3, analyzing the change of the contact angle value caused by the increment change of the marginal droplet liquid volume through 1.1 and 1.2, and taking a small contact angle value in a range with a smaller fluctuation range as a real contact angle value; taking the maximum contact angle value as an apparent contact angle value; the influence of the contact angle caused by the surface structure was evaluated by analyzing the deviation of the apparent contact angle from the true contact angle.
As a preferred example, in A2, the following occurs:
2.1, liquid is absorbed due to the fact that the surface of the solid structure in the nano structure is high in freedom, the increment of the volume margin of liquid drops is too small, and the liquid drops are completely absorbed into the nano structure; increasing the volume of the liquid, wherein the marginal increment of the volume of the liquid drop is increased, so that the liquid drop climbs in the nano structure but does not climb to the apparent surface of the solid;
2.2, by changing the increment of the marginal droplet, the contact angle value of the droplet is continuously increased to form the increment of the marginal droplet volume, so that the upper surface of the droplet protrudes to the highest position of the nanostructure, the increment of the marginal droplet volume ensures that the contour of the droplet reaches the maximum contact angle value due to the surface free energy limitation of a solid material, the increment of the marginal droplet volume ensures that the droplet moves at the top end of the nanostructure, the increment of the marginal droplet volume ensures that the contact angle of the droplet at the top end of the nanostructure is in a critical state when the contact angle is tangent to two sides of the nanostructure, and the contact angle value at the stage keeps a high contact angle value for a period of time;
2.3, when the liquid drop volume marginal increment is reached, the liquid drop is in a critical state when a contact angle of the liquid drop on the top end of the nano structure is tangent to two sides of the nano structure, the liquid can be absorbed into the nano structures on the two sides, and the angle value is reduced;
and 2.4, analyzing the change condition of the dynamic contact angle of the marginal droplet method through 2.1, 2.2 and 2.3, taking the maximum contact angle value as a real contact angle value and taking a small angle value as an apparent contact angle value.
As a preferred example, the following steps should also be included:
and S5, changing the marginal micro-drop amount of the liquid drop, and evaluating the real contact angle and the apparent contact angle under different measuring ranges.
As a preferred example, in S5, the resulting change in contact angle is evaluated by forming a marginal increment of a marginal droplet escalation by a microliter-grade fluid system of the microsyringe system, and the apparent contact angle value is evaluated by evaluating the contact angle value at which the true contact angle is maximized by taking a small contact angle value within a range of relatively small fluctuation range as described in 1.3.
As a preferred example, in S5, the marginal increment of the marginal droplet microliter scale is formed by the microliter scale liquid system of the microsyringe system, the resulting contact angle change is evaluated, the true contact angle is evaluated using the largest contact angle value of 2.4, and the apparent contact angle value is evaluated using small angle values.
The invention has the beneficial effects that: the invention is used for testing the influence of a real contact angle and a surface structure of a solid material on an apparent contact angle, the invention discloses a microliter-level and nanoliter-level double liquid inlet device, volume marginal increment is formed by increasing the volume of liquid, the dynamic change of a contact angle value is caused by testing the volume marginal increment, finally, the maximum value of the contact angle below 60 degrees is taken as the real contact angle, the minimum value of the contact angle above 60 degrees is taken as the real contact angle, and the invention has an extremely important role in the physical and chemical measurement of the industries such as materials, bionic science, nano science, chemistry, semiconductors, wafers and the like, and has extremely high popularization value.
Drawings
FIG. 1 is a graph showing the results of measurements of near true contact angles for aluminum alloys;
FIG. 2 is a graph showing the results of measurements of the advance angle and the retreat angle of an aluminum alloy microstructure by increasing and decreasing liquid processes;
FIG. 3 is a graph of forward and backward angular measurements of tilted samples for aluminum alloy nanostructures;
FIG. 4 is a graph of the apparent contact angle measurement results for aluminum alloy microstructures;
FIG. 5 illustrates a Young-Laplace pressure arc of the nanostructure droplet profile and structure edge;
FIG. 6 is a schematic view of a side-grooved nanostructure;
FIG. 7 is a schematic view of a raised nanostructure;
FIG. 8 is a schematic diagram of a cratered nanostructure;
FIG. 9 is a schematic structural view of the present invention;
FIG. 10 is a schematic diagram of the right side of the structure of the liquid inlet system according to the present invention;
FIG. 11 is a schematic front view of the structure of the liquid inlet system of the present invention;
FIG. 12 is a schematic view of the left side of the structure of the liquid inlet system according to the present invention;
FIG. 13 is a schematic representation of the dynamic contact angle change resulting from dynamic changes in drop volume margin for true contact angle values greater than 60 degrees in accordance with the present invention;
FIG. 14 is a graph illustrating dynamic contact angle changes due to dynamic changes in drop volume margin at true contact angle values of less than 60 degrees in accordance with the present invention.
In the figure: a background light source 1, a liquid inlet system 2, a microscope lens 3, a camera 4, a liquid storage sample tube 5, a Ruhr conversion head 6, a fixed bracket 7, a nozzle 8, a piezoelectric ceramic valve 9, a micro liquid inlet device thimble fixed clamp 10, a motor 11, a motor fixed seat 12, a motor base 13, a piezoelectric ceramic valve fixed connecting block 14, a micro liquid inlet device 15, a micro liquid inlet device main body fixed clamp 16 and a needle 17,
the dynamic change in drop profile in dynamic contact angle curve 18,
the lower edge of the liquid drop profile is in contact with the three-phase contact interface profile 18-1 of the air, liquid and solid of the solid nanostructure,
the marginal increase in drop volume is such that the drop profile contact line is at the state just tangent to the inside of the nanostructure 18-2,
the marginal increase in drop volume is such that the drop profile contact line is at state 18-3 on the end face of the nanostructure,
the marginal increase in liquid volume is such that the contact line of the droplet profile is at state 18-4 where the outer phase tangent to the nanostructure,
the droplet profile state 18-5 when the contact angle value is increased due to the increase of the volume increment of the marginal droplet influenced by the surface free energy on the outer side of the nano structure,
the maximum increment of the marginal drop profile forms the drop profile state at the maximum contact angle 18-6,
a solid surface 19 under test having nanostructures with true contact angle values greater than 60 degrees,
the dynamic change in the drop profile in the dynamic contact angle curve 20,
the marginal increase in droplet volume is too small such that the droplet is fully imbibed into the droplet-outline state 20-1 in the nanostructure,
the incremental increase in the droplet volume margin causes a droplet profile state 20-2 as the droplet climbs in the nanostructure,
the incremental increase in the volume margin of the droplet is such that the upper surface of the droplet protrudes to the highest position of the nanostructure in the droplet state 20-3,
the marginal increase in drop volume is such that the drop profile reaches a maximum contact angle value of 20-4 due to surface free energy limitations of the solid material,
the marginal increase in drop volume is such that the drop profile states 20-5 and 20-6 for the drop as it moves over the tips of the nanostructures,
the marginal increase in drop volume is such that the drop is at a critical state 20-7 when the contact angle at the top of the nanostructure is tangent to both sides of the nanostructure,
a tested solid surface 21 with nanostructures having true contact angle values of less than 60 degrees.
Detailed Description
In order to make the technical means, the original characteristics, the achieved purposes and the effects of the invention easy to understand, the invention is further explained by combining the specific drawings and the embodiments.
Example one
As shown in fig. 9, a dynamic contact angle testing device using a marginal droplet method includes a testing device body, where the testing device body includes a background light source 1, a liquid inlet system 2, a microscope lens 3 and a camera 4, the microscope lens 3 and the camera 4 are connected through a standard interface at an opening C to form an imaging functional assembly, and the imaging functional assembly and the background light source 1 are respectively located at two sides of the liquid inlet system;
as shown in the right side view of the liquid inlet system 2 in fig. 10, the liquid inlet system 2 includes a liquid storage sample tube 5, a luer adapter 6, a fixing bracket 7, a nozzle 8, a piezoelectric ceramic valve 9, a micro liquid inlet device thimble fixing clip 10, a motor 11, a motor fixing seat 12, a motor base 13, and a piezoelectric ceramic valve fixing connection block 14, as shown in the front schematic view of the structural relationship of the liquid inlet system 2 in fig. 11, the liquid inlet system 2 further includes a micro liquid inlet device 15, a micro liquid inlet device main body fixing clip 16, and a needle 17;
the top end of the micro liquid feeder 15 is connected with a needle head 17 through a luer quick connector; the thimble part of the trace liquid feeder 15 is connected by a trace liquid feeder thimble fixing clamp 10, the main part of the trace liquid feeder 15 is connected with a trace liquid feeder main part fixing clamp 16, and the motor 11, the motor fixing seat 12 and the motor base 13 are combined into a moving mechanism; the thimble fixing clamp 10 and the fixing clamp 16 are respectively connected with the moving end and the fixed end of the moving mechanism, so as to form a micro-upgrading liquid inlet system;
after the liquid storage sample tube 5 and the luer conversion head 6 are connected through the luer quick connector, the liquid storage sample tube is fixed on a fixing support 7, the fixing support 7 is connected with a piezoelectric ceramic valve 9 through a screw structure, a nozzle 8 is connected with the piezoelectric ceramic valve 9 through a thread structure, a nano-upgrading liquid inlet system is formed through the connection relation, and a piezoelectric ceramic valve fixing connecting block 14 is fixedly connected with a motor fixing base 12 through a fixing screw, so that the double liquid inlet system 2 with different liquid inlet volume ranges is formed.
The testing method of the device; as described in the background section, how to solve the problems of measuring the true contact angle value under the influence of the surface structure and evaluating the degree of influence of the apparent contact angle by the surface structure, the measurement method of the dynamic contact angle adopts the MicroDrop method including:
s1, forming initial droplet volume
And (4) injecting the liquid inlet system through a piezoelectric ceramic valve to form nano-liter initial liquid drop amount. Typically the initial liquid volume is 100 picoliters or 0.05mm, where 0.05mm is the diameter of the contact surface of the droplet at 100 picoliters of the droplet volume, which can be considered as 100 picoliters (contact diameter is about 0.05 mm);
s2, testing the initial contact angle value
Capturing a liquid drop image through an imaging system of a lens and a camera, and respectively calculating a 3D contact angle value of the liquid drop by adopting an ADSA-RealDrop algorithm;
s3, forming different volumes at the same position by using the equal volume or variable volume marginal increment liquid volume, and respectively calculating 3D contact angle values under different volume conditions by adopting an ADSA-Realdrop algorithm after real-time image capture of a lens and a camera;
s4, data analysis
A1, when an initial contact angle value is larger than 60 degrees, as shown in fig. 13, a dynamic change curve 18 of a liquid drop profile in a dynamic contact angle and a tested solid surface 19 with a nano structure larger than a real contact angle value of 60 degrees have a larger contact angle value due to the surface free energy of a material, an extra Young-Laplaced pressure arc is easily formed, liquid is not easy to absorb into a nano or micro structure, air exists at the bottom of the liquid drop, the profile arc is shown as 18-1 in fig. 13, the lower edge of the liquid drop profile and an air, liquid and solid three-phase contact interface profile of the solid nano structure, and the apparent contact angle value is larger than the real contact angle value;
1.1, when the marginal increment of the volume of the liquid drop does not reach two end surfaces of the nano structure and is influenced by the retention force of the surface free energy of the structure, the contact angle value keeps a section of stable small contact angle value, as shown in 18-2, 18-3 and 18-4 of fig. 13, the marginal increment of the volume of the liquid drop at the moment enables the profile contact line of the liquid drop to be in a state 18-2 when the profile contact line of the liquid drop is just tangent to the inner side of the nano structure, the marginal increment of the volume of the liquid drop enables the profile contact line of the liquid drop to be in a state 18-3 when the profile contact line of the liquid drop is positioned on the end surface of the nano structure, and the marginal increment of the volume of the liquid drop enables the profile contact line of the liquid drop to be in a state 18-4 when the profile contact line of the liquid drop is positioned on the outer side tangent line of the nano structure;
1.2, when the volume marginal increment of the liquid drop reaches the two outer end faces of the nano structure, as shown in 18-4, 18-5 and 18-6 of FIG. 13, the volume marginal increment of the liquid drop can cause the contact angle value to be continuously increased; the outline state of the liquid drop is 18-5 when the contact angle value is continuously increased due to the increase of the volume increment of ten million marginal liquid drops under the influence of surface free energy on the outer side of the nano structure, and the outline state of the liquid drop is 18-6 when the maximum increment of the outline of the marginal liquid drop forms the maximum contact angle;
1.3, analyzing the change of the contact angle value caused by the increment change of the marginal droplet liquid volume through 1.1 and 1.2, and taking a small contact angle value in a range with a smaller fluctuation range as a real contact angle value; taking the maximum contact angle value as an apparent contact angle value; the influence degree of the contact angle caused by the surface structure is evaluated by analyzing the deviation value of the apparent contact angle and the real contact angle.
When the initial contact angle is less than 60 degrees, as shown in fig. 14, the relation between the dynamic change curve 20 of the liquid drop profile in the dynamic contact angle and the tested solid surface 21 with the nano structure with the real contact angle value less than 60 degrees is completely changed with the aforementioned conditions, and the apparent contact angle value is less than the real contact angle value;
2.1, the liquid is absorbed due to the higher surface freedom of the solid structure in the nano structure, so that the marginal increment of the volume of the liquid drop is too small, and the liquid drop is completely absorbed into a liquid drop profile state 20-1 in the nano structure; increasing the volume of the liquid, the marginal incremental increase in the volume of the liquid droplet being such that the liquid droplet climbs in the nanostructure in a droplet profile state 20-2, but not to the apparent surface of the solid;
2.2, through the change of the marginal droplet increment, the contact angle value of the droplet can be continuously increased, a droplet state 20-3 when the droplet volume marginal increment is increased to enable the upper surface of the droplet to protrude to the highest position of the nanostructure is formed, the droplet profile state 20-4 when the droplet profile reaches the maximum contact angle value due to the surface free energy limitation of the solid material is formed by the droplet volume marginal increment, the droplet profile states 20-5 and 20-6 when the droplet moves at the top end of the nanostructure are formed by the droplet volume marginal increment, the critical state 20-7 when the contact angle of the droplet at the top end of the nanostructure is tangent to the two sides of the nanostructure is formed by the droplet volume marginal increment, and the contact angle value at the stage keeps a high contact angle value for a period of time;
2.3, after the critical state 20-7 that the liquid drop is tangent from the contact angle of the top end of the nano structure to the two sides of the nano structure is achieved when the liquid drop volume marginal increment is reached, the liquid can be absorbed into the nano structures on the two sides, and the angle value is reduced;
2.4, analyzing the change condition of the dynamic contact angle of the marginal droplet method through 2.1, 2.2 and 2.3, taking the maximum contact angle value as a real contact angle value, and taking a small angle value as an apparent contact angle value;
s5, changing the marginal micro-drop amount of the liquid drop, and evaluating the real contact angle and the apparent contact angle under different measuring ranges;
forming marginal increment of marginal microdroplet micro-upgrading through a micro-liter level liquid feeding system of the microsyringe system, evaluating the change condition of a contact angle caused by the marginal microdroplet micro-upgrading, and evaluating a real contact angle value by taking a small contact angle value within a smaller fluctuation range from 1.3; the largest contact angle value was taken to evaluate the apparent contact angle value.
Example two
In the present embodiment and the marginal micro-drop method dynamic contact angle testing apparatus and the testing method of the embodiment, S1, S2, S3, and S4 are the same, only S5 is different, and S5 is as follows:
s5, changing the marginal micro-drop amount of the liquid drop, and evaluating the real contact angle and the apparent contact angle under different measuring ranges;
and (3) forming a marginal increment of the marginal droplet micro-upgrade through a micro-upgrading liquid feeding system of the microsyringe system, evaluating the change condition of the contact angle caused by the marginal droplet micro-upgrade, evaluating a real contact angle value by adopting a maximum contact angle value in 2.4, and evaluating an apparent contact angle value by adopting a small angle value.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (3)
1. A method for measuring the dynamic contact angle of the boundary of a droplet, comprising the following steps:
s1, forming initial droplet volume:
forming a nano-liter initial liquid drop volume through a piezoelectric ceramic valve injection liquid inlet system, wherein the initial liquid volume is generally 100 picoliters;
s2, testing an initial contact angle value:
capturing a liquid drop image through an imaging system of a lens and a camera, and respectively calculating a 3D contact angle value of the liquid drop by adopting an Asha algorithm;
s3, forming different volumes at the same position by using the equal volume or variable volume marginal increment liquid volume, and respectively calculating 3D contact angle values under different volume conditions by adopting an Asha algorithm after real-time image capture of a lens and a camera;
s4, data analysis, wherein the following conditions occur in the S4 data analysis:
a1, when an initial contact angle value is larger than 60 degrees, a dynamic change curve of a liquid drop profile in a dynamic contact angle and a tested solid surface with a nano structure larger than a real contact angle value of 60 degrees are provided, the contact angle value caused by the surface free energy of the material is larger, an extra Young-Laplaced pressure arc is easily formed, liquid is not easy to be absorbed into a nano or micro structure, air exists at the bottom of the liquid drop, the lower edge of the liquid drop profile and the air, liquid and solid three-phase contact interface profile of the solid nano structure, and the apparent contact angle value is larger than the real contact angle value;
a2, when the initial contact angle is less than 60 degrees, the profile of the liquid drop in the dynamic contact angle is dynamically changed, the actual contact angle value of the liquid drop in the dynamic contact angle is less than 60 degrees, the relation of the surface of the tested solid with the nano structure is completely changed with the above conditions, and the apparent contact angle value is less than the actual contact angle value;
respectively analyzing the two conditions A1 and A2, and judging the apparent contact angle value and the real contact angle value by analyzing the change condition of the dynamic contact angle of the marginal droplet method;
when the situation in A1 occurs, the following steps are performed:
1.1, when the marginal increment of the volume of the liquid drop does not reach two end surfaces of the nano structure and is influenced by the retention force of the surface free energy of the structure, the contact angle value keeps a section of stable small contact angle value, the marginal increment of the volume of the liquid drop with the angle value ensures that a contour contact line of the liquid drop is just tangent to the inner side of the nano structure, the marginal increment of the volume of the liquid drop ensures that the contour contact line of the liquid drop is positioned on the end surface of the nano structure, and the marginal increment of the volume of the liquid drop ensures that the contour contact line of the liquid drop is positioned on the outer side of the nano structure and is tangent;
1.2, when the volume marginal increment of the liquid drop reaches the two end surfaces of the outer side of the nano structure, the volume marginal increment of the liquid drop can cause the contact angle value to be continuously increased, the contact angle value is continuously increased due to the fact that the volume marginal increment of the liquid drop is influenced by surface free energy on the outer side of the nano structure, and the maximum increment of the outline of the marginal liquid drop forms a maximum contact angle;
1.3, analyzing the change of the contact angle value caused by the increment change of the marginal droplet liquid volume through 1.1 and 1.2, and taking a small contact angle value in a range with a smaller fluctuation range as a real contact angle value; taking the maximum contact angle value as an apparent contact angle value; evaluating the influence degree of the contact angle caused by the surface structure by analyzing the deviation value of the apparent contact angle and the real contact angle;
when the situation in A2 occurs, the following steps are performed:
2.1, liquid is absorbed due to the fact that the surface free energy of the solid structure in the nanometer structure is high, the increment of the volume margin of liquid drops is too small, and the liquid drops are completely absorbed into the nanometer structure; increasing the volume of the liquid, wherein the marginal increment of the volume of the liquid drop is increased, so that the liquid drop climbs in the nano structure but does not climb to the apparent surface of the solid;
2.2, through the change of the marginal droplet increment, the contact angle value of the droplet is continuously increased to form the increase of the marginal increment of the volume of the droplet, so that the upper surface of the droplet protrudes to the highest position of the nanostructure, the marginal increment of the volume of the droplet enables the maximum contact angle value reached by the contour of the droplet due to the surface free energy limitation of the solid material, the marginal increment of the volume of the droplet enables the droplet to move at the top end of the nanostructure, the marginal increment of the volume of the droplet enables the contact angle of the droplet at the top end of the nanostructure to reach the critical state when the two sides of the nanostructure are tangent, and the contact angle value at the stage keeps the high contact angle value for a period of time;
2.3, when the liquid drop volume marginal increment is reached, the liquid drop is in a critical state when a contact angle of the liquid drop on the top end of the nano structure is tangent to two sides of the nano structure, the liquid can be absorbed into the nano structures on the two sides, and the angle value is reduced;
2.4, analyzing the change condition of the dynamic contact angle of the marginal droplet method through 2.1, 2.2 and 2.3, taking the maximum contact angle value as a real contact angle value and taking a small angle value as an apparent contact angle value;
and S5, changing the marginal micro-drop amount of the liquid drop, and evaluating the real contact angle and the apparent contact angle under different measuring ranges.
2. The method of claim 1, wherein the method comprises the steps of: in S5, the resulting change in contact angle is evaluated by forming a marginal increment of a marginal droplet escalation by the microliter-grade fluid system of the microsyringe system, and the apparent contact angle value is evaluated by taking a small contact angle value within a range of relatively small fluctuation range as described in step 1.3 to evaluate the true contact angle value with the largest contact angle value.
3. The method for measuring the dynamic contact angle of the droplet boundary according to claim 1, wherein: in S5, the marginal increment of the marginal droplet upgrade is formed by the microliter scale liquid system of the microsyringe system, the resulting change in contact angle is evaluated, the true contact angle is evaluated by taking the maximum contact angle value and the apparent contact angle value is evaluated by taking the small angle value as described in step 2.4.
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