CN103575621A - Method for measuring apparent contact angle of liquid on surfaces of particles - Google Patents

Abstract

The invention relates to a method for measuring the apparent contact angle of liquid on the surfaces of particles. The method comprises the following steps: (1) placing particles in a container, and adding liquid; (2) measuring apparent heat conduction coefficient for multiple times, and calculating an average value and the relative error of the measurement value each time and the average value; (3) changing the amount of the added liquid, and repeating the step (2) until the liquid added cannot enter pores among the particles and is accumulated to the top of the stacked particles; (4) analyzing the rule that the measurement relative error of the apparent heat conduction coefficient changes along with the volume rate of the liquid in the pores, and determining the critical liquid content; and (5) calculating according to a mathematical model to acquire the apparent contact angle. According to the invention, the requirement that the solid surface needs to be an ideal surface in contact angle measurement can be lowered, so that the contact angle of the liquid on the surface of the particulate solid can be measured.

Description

A kind of liquid of measuring is in the method for particle surface apparent contact angle

Technical field

The present invention relates to a kind of liquid of measuring in the method for particle surface apparent contact angle.

Background technology

Contact angle is at solid, liquid, gas three-phase intersection, from solid-liquid interface, passes through liquid internal to angle folded gas-liquid interface.Contact angle not only plays an important role in surface infiltration phenomenon, is also the performance of relevant solid-liquid interface upper surface tension force simultaneously.

The existing method of testing of contact angle has two kinds conventionally: one is profile image analysis method; It two is weight method.The latter is commonly referred to wetting balance or osmosis contact angle instrument.But at present most widely used general, measured value is the most directly with accurately or profile image analysis method.

The principle of profile image analytical method is: drop is dripped in solid sample surface, by microlens and camera, obtain the outside drawing picture of drop, then use Digital Image Processing and some algorithms that the contact angle of drop in image is calculated.

The method of calculating contact angle can be regarded as the part of ball or cone based on specific mathematical model as drop conventionally, then by measuring specific parameter as wide/high or calculate contact angle value by direct matching.Young-Laplace equation has been described inside and outside pressure differential and the curvature at interface and the relation of interfacial tension at sealing interface, can be used to describe exactly the appearance profile of axisymmetric drop, thereby calculates its contact angle.

Existing contact angle measuring method is drop is dropped on surface and measured; but there are some solid materials cannot be processed into plane; or can change its surface physics attribute after being processed into plane; as soil particle, cereal-granules etc.; but during physical mechanisms such as migration in the medium forming at this type of material at Study of Liquid, conventionally can relate to liquid at the contact angle on solid skeletal surface, and this to be prior art means be difficult to measure.

Summary of the invention

The object of the invention is the problem of liquid being measured at the lip-deep apparent contact angle of the granular solids that cannot be processed into plane for there is no at present effective technology means, provide a kind of method simple, easy to operate contact angle method of testing.

For achieving the above object, the present invention adopts following technical scheme:

Measure liquid in a method for particle surface apparent contact angle, comprise the following steps:

1) get particle and be contained in container, add liquid and fully mix, obtain potpourri;

2) with thermal conductivity measurement instrument, the apparent coefficient of heat conductivity of potpourri is carried out to several times measurement, the relative error of calculating mean value and each measured value and mean value, obtains apparent thermal conductivity measurement relative error;

3) change the amount of liquid adding, then repeating step 2), until the liquid adding again can not enter inter-granular porosity and accumulate in packed particle top;

4) analyze apparent thermal conductivity measurement relative error and account for liquid the rule that pore volume fraction changes, determine while accounting for pore volume fraction increase with liquid relative error critical liquid content from large to small;

5) according to the critical liquid content of setting up and the contact angle mathematical model of liquid at particle surface, calculate acquisition contact angle.

Described step 2) in, the apparent coefficient of heat conductivity of potpourri is carried out to 3 above measurements.

Described in step 3), change the testing liquid amount add, each amount of liquid changes and is no more than 5% of void content between packed particle.

Void content can be measured by multiple way, and after void content is determined, amount of liquid change amount is easy to determine by methods such as weight methods.

Described in step 4), critical liquid content is, within relative error is decreased to the reproducibility error scope that thermal conductivity measurement instrument is given;

Mathematical model described in step 5) is:

$\begin{array}{c}0.20711\mathrm{\π}+0.18198\mathrm{\π}[\tan (0.25\mathrm{\π}+\mathrm{\θ})-\frac{0.25-\mathrm{\θ}}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]\\ \mathrm{\ϵ}=\frac{+0.07538\mathrm{\π}[\frac{1}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}-(0.25\mathrm{\π}-\mathrm{\θ})\frac{\tan (0.25\mathrm{\π}+\mathrm{\θ})}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]}{4-2\mathrm{\π}/3}\end{array}$

Wherein:

ε: critical liquid content accounts for packed particle pore volume fraction;

θ: liquid is at the apparent contact angle of particle surface.

The invention has the beneficial effects as follows: while reducing contact angle test, solid surface must be the requirement of ideal surfaced, and liquid can be measured at the contact angle on granular solids surface.

Accompanying drawing explanation

Fig. 1 accounts for the variation of pore volume fraction containing the wet apparent thermal conductivity measurement relative error of beaded glass of piling up with liquid;

Fig. 2 accounts for the variation of pore volume fraction containing the wet apparent thermal conductivity measurement relative error of the grains of sand of piling up with liquid.

Embodiment

Below in conjunction with embodiment, the present invention will be further described

Embodiment 1: measure distilled water at the apparent contact angle on beaded glass surface

1) the clean beaded glass of about 200ml is piled up and is contained in beaker, then in sample, add the distilled water that accounts for void content 5%, and by means such as vibration, stirrings, water is uniformly distributed as far as possible in sample, obtain potpourri;

2) utilize Hot Disk thermal constant analyser (TPS2500) to measure the apparent coefficient of heat conductivity of potpourri, carry out 3 times and measure, the relative error of calculating mean value and each measured value and mean value, obtains apparent thermal conductivity measurement relative error;

3) change the amount of the distilled water adding, amount of water respectively is 10%, 15%, 20% of void content ... the distilled water that 75%(adds to 75% time again can not enter inter-granular porosity and accumulate in packed particle top, cause distilled water evenly to add), repeating step 2), coefficient of heat conductivity during to each pore volume fraction all carries out 3 times and measures, and calculate the relative error of each measured value and mean value, and obtain relative error and change with liquid content, see Fig. 1;

4) Hot Disk thermal constant analyser measuring repeatability error is no more than 2%, as seen from Figure 1, when liquid content is less than 35%, coefficient of heat conductivity relative error is larger, and water cut is while being greater than 35%, coefficient of heat conductivity relative error is less, is no more than 2%, when obviously water cut accounts for void content 35%, is critical liquid content;

5) the contact angle mathematical model at particle surface according to the critical liquid content of setting up and liquid is as follows:

$\begin{array}{c}0.20711\mathrm{\π}+0.18198\mathrm{\π}[\tan (0.25\mathrm{\π}+\mathrm{\θ})-\frac{0.25-\mathrm{\θ}}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]\\ \mathrm{\ϵ}=\frac{+0.07538\mathrm{\π}[\frac{1}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}-(0.25\mathrm{\π}-\mathrm{\θ})\frac{\tan (0.25\mathrm{\π}+\mathrm{\θ})}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]}{4-2\mathrm{\π}/3}\end{array}$

Wherein:

ε: critical liquid content accounts for packed particle pore volume fraction;

θ: liquid is at the apparent contact angle of particle surface.

By this calculated with mathematical model, can obtain apparent contact angle is 35.4 °.

Embodiment 2: measure distilled water at the apparent contact angle on grains of sand surface

1) first the clean grains of sand of about 200ml are piled up and are contained in beaker, then in sample, add the distilled water that accounts for void content 5%, and by means such as vibration, stirrings, water is uniformly distributed as far as possible in sample, obtain potpourri;

2) utilize Hot Disk thermal constant analyser (TPS2500) to measure the apparent coefficient of heat conductivity of potpourri, carry out 3 times and measure, the relative error of calculating mean value and each measured value and mean value, obtains apparent thermal conductivity measurement relative error;

3) change the amount of the distilled water adding, amount of water respectively is 10%, 15%, 20% of void content ... the distilled water that 60%(adds to 60% time again can not enter inter-granular porosity and accumulate in packed particle top, cause distilled water evenly to add), repeating step 2), coefficient of heat conductivity during to each pore volume fraction all carries out 3 times and measures, and calculate the relative error of each measured value and mean value, and obtain relative error and change with liquid content, see Fig. 2;

4) Hot Disk thermal constant analyser measuring repeatability error is no more than 2%, as seen from Figure 2, when liquid content is less than 25%, coefficient of heat conductivity relative error is larger, and liquid content is while being greater than 25%, coefficient of heat conductivity relative error is less, is no more than 2%, when obviously water cut accounts for void content 25%, is critical liquid content;

5) the contact angle mathematical model at particle surface according to the critical liquid content of setting up and liquid is as follows:

$\begin{array}{c}0.20711\mathrm{\π}+0.18198\mathrm{\π}[\tan (0.25\mathrm{\π}+\mathrm{\θ})-\frac{0.25-\mathrm{\θ}}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]\\ \mathrm{\ϵ}=\frac{+0.07538\mathrm{\π}[\frac{1}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}-(0.25\mathrm{\π}-\mathrm{\θ})\frac{\tan (0.25\mathrm{\π}+\mathrm{\θ})}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]}{4-2\mathrm{\π}/3}\end{array}$

Wherein:

ε: critical liquid content accounts for packed particle pore volume fraction;

θ: liquid is at the apparent contact angle of particle surface.

By this calculated with mathematical model, can obtain apparent contact angle is 18.7 °.

Experimental example: the apparent contact angle that the apparent contact angle that above-described embodiment 1～embodiment 2 is recorded and profile image analytical method record compares.

Embodiment 1 illustrated the apparent contact angle recording by method of the present invention and the result of measuring on glass plate by classic method more consistent, classic method can not be measured the lip-deep contact angle of non-tablet, so the present invention is feasible.The contact angle of the immeasurable material surface of embodiment 2 explanation classic method, the present invention can measure.

Claims (5)

1. measure liquid in a method for particle surface apparent contact angle, it is characterized in that there are following steps:

1) get particle and be contained in container, add liquid and fully mix, obtain potpourri;

2) with thermal conductivity measurement instrument, the apparent coefficient of heat conductivity of potpourri is carried out to several times measurement, the relative error of calculating mean value and each measured value and mean value, obtains apparent thermal conductivity measurement relative error;

3) change the amount of liquid adding, then repeating step 2), until the liquid adding again can not enter inter-granular porosity and accumulate in packed particle top;

4) analyze apparent thermal conductivity measurement relative error and account for liquid the rule that pore volume fraction changes, determine while accounting for pore volume fraction increase with liquid relative error critical liquid content from large to small;

5) according to the critical liquid content of setting up and the contact angle mathematical model of liquid at particle surface, calculate acquisition apparent contact angle.

2. a kind of liquid of measuring according to claim 1, in the method for particle surface apparent contact angle, is characterized in that: described step 2), the apparent coefficient of heat conductivity of potpourri is carried out to 3 above measurements.

3. a kind of liquid of measuring according to claim 1, in the method for particle surface apparent contact angle, is characterized in that: described in step 3), change the testing liquid amount add, each amount of liquid changes and is no more than 5% of void content between packed particle.

4. a kind of liquid of measuring according to claim 1, in the method for particle surface apparent contact angle, is characterized in that: described in step 4), critical liquid content is, within relative error is decreased to the reproducibility error scope that thermal conductivity measurement instrument is given.

5. a kind of liquid of measuring according to claim 1, in the method for particle surface apparent contact angle, is characterized in that: the mathematical model described in step 5) is:

$\begin{array}{c}0.20711\mathrm{\π}+0.18198\mathrm{\π}[\tan (0.25\mathrm{\π}+\mathrm{\θ})-\frac{0.25-\mathrm{\θ}}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]\\ \mathrm{\ϵ}=\frac{+0.07538\mathrm{\π}[\frac{1}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}-(0.25\mathrm{\π}-\mathrm{\θ})\frac{\tan (0.25\mathrm{\π}+\mathrm{\θ})}{{\cos }^2(0.25\mathrm{\π}+\mathrm{\θ})}]}{4-2\mathrm{\π}/3}\end{array}$

Wherein:

ε: critical liquid content accounts for packed particle pore volume fraction;

θ: liquid is at the apparent contact angle of particle surface.

Images