CN101539502A - Method for measuring liquid-drop contact angle on solid surface and device thereof - Google Patents

Abstract

The invention relates to a method for measuring a liquid-drop contact angle on a solid surface and a device thereof, which are used for measuring the contact angles of the liquid drops with different mediums and different sizes on the solid surface. The method comprises the following steps of: according to one-to-one correspondence between a liquid drop volume and a liquid drop contact angle, obtaining a plurality of liquid drop profiles which correspond to different contact angles, thus establishing a database used for storing different liquid drop profiles; when in measuring, fixing a sample on an earthquake isolation platform, and dropping the liquid with known volumes on the surface of the sample by utilizing a micro-injector; after the liquid drops achieve balance, acquiring a liquid drop image on the surface of the sample by utilizing an optical imaging system, a CCD camera and a computer; utilizing an image matching method to carry out processing and analyzing to the shapes of the liquid drops by computer software, and then carrying out calculation to obtain contact angles of the liquid drops; and matching the liquid drop profiles obtained by experimental measurements with the liquid drop profiles in the database so as to determine the corresponding contact angles. Compared with the existing method, the method takes the influence of volume and weight of the liquid drop in to consideration, thus improving the measuring precision.

Description

A kind of measuring method of liquid-drop contact angle on solid surface and device

Technical field

The present invention relates to a kind of measuring method of liquid-drop contact angle, be used for accurately measuring the contact angle of drop on solid surface of different medium and size, belong to field of measuring technique.

Background technology

Various materials comprise organism, inorganics, and the moistening character in interface that liquid metal etc. characterizes out is the emphasis of research in the modern physics chemical field, and contact angle then is the important parameter that characterizes the moistening character in interface.At present, even state-of-the-art in the world contact angle measurement is bigger or when contact angle is bigger (such as super hydrophobic material) at drop, all can not well provide the value of contact angle, very big error appears in these measurement results and test findings sometimes.A main cause that causes error is not consider the influence of gravity when measuring contact angle, does not consider the influence that the variation of volume brings the drop profile, and therefore, measuring accuracy is not fine, and the scope of measuring error is at 5～10 °.But the drop when actual measurement often is subjected to the influence of gravity, and for liquid metal, even volume is very little, the influence of gravity is also very important.Therefore in contact angle was measured, droplet size should be treated as an important parameter.Therefore, be necessary to develop a kind of method that can under the situation of considering drop gravity, accurately measure contact angle.

Summary of the invention

The objective of the invention is in order to overcome the deficiencies in the prior art and shortcoming, aim to provide a kind of measuring method, in the hope of obtaining accurate measurement result based on liquid-drop contact angle on the solid surface of images match.

The technical scheme of invention is as follows:

A kind of measuring method of liquid-drop contact angle is characterized in that this method carries out as follows:

1) under action of gravity, be positioned at and all satisfy arbitrarily some the following formula equation on the sessile drops on the sample surfaces:

$\mathrm{\&rho;gw}+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A20091013610100081.png"\; state="\{\{state\}\}">P</figure-callout>}}_0=[\frac{w^{\&prime;\&prime;}}{{(1+w^{\&prime;2})}^{3/2}}+\frac{w^{\&prime;}}{\sqrt{1+w^{\&prime;2}}}\frac{1}{r}]{\mathrm{\&gamma;}}_{\mathrm{LV}}---\left(1\right)$

ρ represents the density of tested drop in the equation (1); G represents acceleration of gravity; W represent axis of ordinates value, r represents the value of horizontal ordinate, w '=dw/dr, w "=d ²W/dr ², Δ P ₀Represent the inside and outside pressure difference of drop, γ _LVRepresent the surface tension coefficient of drop;

2) according to the one-to-one relationship of droplet size and contact angle, for different drop surface tension coefficient, drop density and volumes, utilize numerical method solving equation (1), obtain a plurality of drop profiles, thereby set up a database that is used for storing different drop profiles corresponding to different contact angles;

3) utilize micro syringe with fluid drips on sample surfaces, obtain the tested drop of known volume, after tested drop reaches balance, utilize CCD camera and computing machine to obtain the aspect graph picture of the tested drop on the sample plane;

4) utilize the method for graphical analysis that tested drop aspect graph is looked like to discern automatically, obtain the coordinate figure of each point on this tested drop profile;

5) surface tension coefficient, density, volume and the contact angle measurement range of the tested drop of input;

6), from the drop profile that database obtains, obtain a series of coordinate figure (X according to input parameter _i, Y _i), horizontal ordinate X wherein _iAbscissa value x with tested drop real profile _iEquate, i.e. X _i=x _i

7) definition error function $F=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{(Y_i-y_i)}^2,$ Y _iAnd y _iThe drop profile that obtains of representation database and the ordinate value of actual drop profile respectively, for given different contact angle, different by the profile that calculates with the matching degree of measured value, so the value of error function F is also different, wherein the representative of error minimum is mated the most with the profile of true drop, and its pairing contact angle is exactly the true contact angle that drop contacts with sample surfaces.

In the technique scheme, described numerical method adopts shooting method.

The device of realization said method provided by the invention is as follows: a kind of measurement mechanism of liquid-drop contact angle on solid surface is characterized in that: this device comprises shock insulation platform, support, article carrying platform, lifting table, light source, CCD camera, micro syringe and computing machine; Described support and lifting table are fixed on the shock insulation platform, and described article carrying platform, micro syringe and light source are arranged on the support; Described CCD camera is arranged on the lifting table, and corresponding with described light source, utilizes the CCD camera to take the drop image by light hole, and the image of collection is sent to computing machine in real time by cable and handles.

The present invention's basic high-lighting effect that has the following advantages: the present invention compared with the prior art: 1. considered the influence of droplet size and weight, improved the measuring accuracy of contact angle liquid-drop contact angle.2. adopt the image processing method of drop outline, enlarged measurement range.

Description of drawings

Fig. 1 is a sessile drops profile synoptic diagram.

Fig. 2 is a contact angle measurement mechanism synoptic diagram.

Fig. 3 ... program flow diagram.

Among the figure: 1-shock insulation platform; The 2-support; The 3-light source; 4.-article carrying platform; The 5-material sample; The 6-micro syringe; The 7-drop; The 8-light hole; The 9-lifting table; The 10-CCD camera; The 11-cable; The 12-computing machine.

Embodiment

Fig. 2 is a contact angle measurement mechanism synoptic diagram, and this device comprises shock insulation platform 1, support 2, light source 3, article carrying platform 4, micro syringe 6, lifting table 9, CCD camera 10 and computing machine 12.Described support 2 and lifting table 9 are fixed on the shock insulation platform 1, and described article carrying platform, micro syringe and light source are arranged on the support; Described CCD camera 10 is arranged on the lifting table 9, and corresponding with described light source 3, utilizes the CCD camera to take the drop images by light hole 8, and the image of collection is sent to computing machine in real time by cable and handles.

Utilize above-mentioned measurement mechanism, at first material sample 5 is placed on the article carrying platform 4, utilize micro syringe 6 with the fluid drips of known volume on sample surfaces, after drop reaches balance, utilize optical imaging system, CCD camera and computing machine to obtain droplet morphology image on the sample plane, and utilize the method for images match that droplet profile is handled and analyzed by software for calculation, calculate the contact angle of drop.If the surface tension coefficient of given drop, density and volume, for specific substrate, the shape of drop and contact angle are one to one; According to the correspondence one by one of droplet size and contact angle, set up a database again, drop profile that experiment measuring is obtained and the drop profile in the database are done coupling, determine corresponding contact angle, thereby the measurement of contact angle is reached very high precision.

Concrete measuring process is as follows:

1) under action of gravity, be positioned at and all satisfy arbitrarily some the following formula equation on the sessile drops on the sample surfaces:

$\mathrm{\&rho;gw}+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A20091013610100081.png"\; state="\{\{state\}\}">P</figure-callout>}}_0=[\frac{w^{\&prime;\&prime;}}{{(1+w^{\&prime;2})}^{3/2}}+\frac{w^{\&prime;}}{\sqrt{1+w^{\&prime;2}}}\frac{1}{r}]{\mathrm{\&gamma;}}_{\mathrm{LV}}---\left(1\right)$

ρ represents the density of tested drop in the equation (1); G represents acceleration of gravity; W represent axis of ordinates value, r represents the value of horizontal ordinate, w '=dw/dr, w "=d ²W/dr ², Δ P ₀Represent the inside and outside pressure difference of drop, γ _LVRepresent the surface tension coefficient of drop;

2) according to the one-to-one relationship of droplet size and contact angle, for different drop surface tension coefficient, drop density and volumes, utilize numerical method solving equation (1), obtain a plurality of drop profiles, thereby set up a database that is used for storing different drop profiles corresponding to different contact angles;

3) utilize micro syringe with fluid drips on sample surfaces, obtain the tested drop of known volume, after tested drop reaches balance, utilize CCD camera and computing machine to obtain the aspect graph picture of the tested drop on the sample plane;

4) utilize the method for graphical analysis that tested drop aspect graph is looked like to discern automatically, obtain the coordinate figure of each point on this tested drop profile;

5) surface tension coefficient, density, volume and the contact angle measurement range of the tested drop of input;

6), from the drop profile that database obtains, obtain a series of coordinate figure (X according to input parameter _i, Y _i), horizontal ordinate X wherein _iAbscissa value x with tested drop real profile _iEquate, i.e. X _i=x _i

7) definition error function $F=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{(Y_i-y_i)}^2,$ Y _iAnd y _iThe drop profile that obtains of representation database and the ordinate value of actual drop profile respectively, use for given different contact, different by the profile that calculates with the matching degree of measured value, so the value of error function F is also different, wherein the representative of error minimum is mated the most with the profile of true drop, and its pairing contact angle is exactly the true contact angle that drop contacts with sample surfaces.

Embodiment:

As shown in Figure 3, concrete enforcement is divided into two major parts: 1) set up database; 2) calculate contact angle in real time.The concrete operations of wherein setting up database are:

1) the initial physical constant of given tested drop: surface tension coefficient, density, volume.Given initial boundary condition in the numerical solution process (given contact angle θ, w in concrete computation process ₀=0, the width r of any given attachment zone ₀| _W=0The external and internal pressure difference Δ P that goes out in substrate with drop ₀| _W=0).

2) find the solution by shooting method that (formula of shooting method is r _i| _W=0=r ₀+ Δ r, Δ P _i| _W=0=Δ P ₀+ Δ P);

3) judge that whether final boundary condition satisfies (is the condition V=V that program stops ₀, ${\frac{\mathrm{dw}}{\mathrm{dr}}|}_{{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20091013610100072.png,A20091013610100081.png"\; state="\{\{state\}\}">r</figure-callout>}}_1=0}=0$ Whether satisfy).If, then store the data represented drop profile of this group, if not, get back to step 2), continue to find the solution with shooting method;

4) by changing droplet size and contact angle continuously, set up database, the x of the profile of the different contact angles of storage certain volume scope correspondence, y coordinate figure.

The concrete operations of calculating contact angle in real time are:

1) starts contact angle measurement and contact angle Survey Software;

2) initial parameter of input drop: fluid density, surface tension coefficient, droplet size;

3) inject the drop of respective volume size with micro syringe;

4) Survey Software is obtained the profile of drop automatically;

5) from database, seek outline line, mate;

6) judge accuracy requirement (by error function control), if satisfy desired precision, coupling stops, if do not satisfy, then proceeds search matched;

7) provide by 6) value of the contact angle that obtains;

8) finish

Claims (3)

1, a kind of measuring method of liquid-drop contact angle on solid surface is characterized in that this method carries out as follows:

1) under action of gravity, be positioned at and all satisfy arbitrarily some the following formula equation on the sessile drops on the sample surfaces:

$\mathrm{\&rho;gw}+\mathrm{\&Delta;}{P}_0=[\frac{w^{\&prime;\&prime;}}{{(1+w^{\&prime;2})}^{3/2}}+\frac{w^{\&prime;}}{\sqrt{1+w^{\&prime;2}}}\frac{1}{r}]{\mathrm{\&gamma;}}_{\mathrm{LV}}---\left(1\right)$

ρ represents the density of tested drop in the equation (1); G represents acceleration of gravity; W represent axis of ordinates value, r represents the value of horizontal ordinate, w '=dw/dr, w "=d ²W/dr ², Δ P ₀Represent the inside and outside pressure difference of drop, γ _LVRepresent the surface tension coefficient of drop;

2) according to the one-to-one relationship of droplet size and contact angle, for different drop surface tension coefficient, drop density and volumes, utilize numerical method solving equation (1), obtain a plurality of drop profiles, thereby set up a database that is used for storing different drop profiles corresponding to different contact angles;

3) utilize micro syringe with fluid drips on sample surfaces, obtain the tested drop of known volume, after tested drop reaches balance, utilize CCD camera and computing machine to obtain the aspect graph picture of the tested drop on the sample plane;

4) utilize the method for graphical analysis that tested drop aspect graph is looked like to discern automatically, obtain the coordinate figure of each point on this tested drop profile;

5) surface tension coefficient, density, volume and the contact angle measurement range of the tested drop of input;

6), from the drop profile that database obtains, obtain a series of coordinate figure (X according to input parameter _i, Y _i), horizontal ordinate X wherein _iAbscissa value x with tested drop real profile _iEquate, i.e. X _i=x _i

7) definition error function $F=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{(Y_i-y_i)}^2,$ Y _iAnd y _iThe drop profile that obtains of representation database and the ordinate value of actual drop profile respectively, for given different contact angle, different by the profile that calculates with the matching degree of measured value, so the value of error function F is also different, wherein the representative of error minimum is mated the most with the profile of true drop, and its pairing contact angle is exactly the true contact angle that drop contacts with sample surfaces.

2. according to the measuring method of the described liquid-drop contact angle on solid surface of claim 1, it is characterized in that: step 2) described in numerical method adopt shooting method.

3. one kind is adopted the measurement mechanism of the liquid-drop contact angle on solid surface of method according to claim 1, it is characterized in that: this device comprises shock insulation platform (1), support (2), article carrying platform (4), lifting table (9), light source (3), CCD camera (10), micro syringe (6) and computing machine (12); Described support (2) and lifting table (9) are fixed on the shock insulation platform (1), and described article carrying platform, micro syringe and light source are arranged on the support; Described CCD camera (10) is arranged on the lifting table (9), and corresponding with described light source (3), utilizes the CCD camera to take the drop image by light hole (8), and the image of collection is sent to computing machine in real time by cable and handles.

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