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Article

Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories

by
Mingyang Yuan
1,2,3,
Ze Zhang
1,2,3,*,
Hang Li
4,
Zhiyuan Wang
1,2,3 and
Doudou Jin
1,2,3
1
College of Civil Engineering and Transportation, Northeast Forestry University, Harbin 150040, China
2
Northeast-China Observatory and Research-Station of Permafrost Geo-Environment of the Ministry of Education, Collaborative Innovation Centre for Permafrost Environment and Road Construction and Maintenance in Northeast China, Northeast Forestry University, Harbin 150040, China
3
China-Russia Joint Laboratory for Cold Regions Engineering & Environment, Northeast Forestry University, Harbin 150040, China
4
Mudanjiang Power Supply Company, State Grid Heilongjiang Electric Power Co., Ltd., Mudanjiang 157001, China
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(4), 375; https://doi.org/10.3390/coatings15040375
Submission received: 21 February 2025 / Revised: 19 March 2025 / Accepted: 20 March 2025 / Published: 23 March 2025
Browse Figures
Versions Notes

Abstract

:
Soil adhesion is one of the basic physical properties of soil. The existence of soil adhesion will cause additional energy consumption of transport vehicles, which is an urgent scientific problem to be solved. In this paper, rubber tires are used as test materials, and the adhesion between rubber tires and different soils is measured by the improved adhesion test device. The rubber surface after the test is processed and analyzed by image analysis software. The results showed that the soil adhesion increased with the increase in soil moisture content and reached the maximum when it was close to the liquid limit. The maximum adhesion increased with the increase in soil clay content. The image processing analysis showed that the watermark area on the rubber surface will gradually increase with the increase in soil moisture content. According to the test results and the characteristics of soil colloid, the electric double-layer theory was introduced to establish the contact, adhesion, and separation model of the rubber–soil interface, and the adhesion mechanism of the rubber–soil interface was expounded. This study will promote the study of soil adhesion and provide a reference for estimating the additional energy consumption caused by adhesion during transportation.

1. Introduction

Adhesion refers to the joining together of surface layers of physical bodies or phases. Adhesion, or “adherence”, means a state in which two surfaces join each other. It is, therefore, a type of force that occurs at the contact surface of two materials that are ultimately to be joined together [1]. When soil and non-soil materials are separated, a force that hinders separation occurs. This tension is called soil adhesion [2]. The smallest and most active part of the soil constitutes the soil colloid, which is the main reason for the complexity of soil properties [3]. Clay in soil is the main parameter of the soil colloid, as well as the main factor affecting soil adhesion. The existence of soil adhesion will cause additional energy consumption of transport vehicles, which will seriously affect the energy supply in the field of transportation [4]. In this paper, rubber tires were used as experimental materials to measure the adhesion force between rubber tires and soil with different clay contents, and the soil adhesion law was analyzed.
For the determination of soil adhesion, scholars have designed a variety of measuring devices. Measurement devices and methods can be roughly divided into three categories: The first type is a device for indirect determination of soil adhesion. Zumsteg and Puzrin put three kinds of clay into a metal shear disc after stirring, with the help of a uniform rotation disc to determine the soil adhesion [5]. The second is to measure the tangential adhesion device. Tokarz measured the tangential adhesion between soil and non-soil materials by improving the ring direct shear test and discussed the influence of soil moisture content and other factors on soil adhesion [6]. Liu used a self-made rotary shear device to measure the tangential adhesion between different soils and metal materials [7]. The third type is a test device for measuring normal adhesion. Most of the normal adhesion force measuring devices are designed in the form of piston drawing or conical drawing [8,9,10]. The test device of piston tensile form is a reliable means to measure soil adhesion [11], and it is also a commonly used measuring device by scholars. The additional energy consumption generated by a vehicle driving on a muddy road is mainly affected by the normal soil adhesion. Therefore, this study will use a piston pull-out test device to measure the normal adhesion force of the soil.
Soil adhesion to foreign objects is a complex multi-phase system. There are many factors affecting adhesion. The influencing factors of soil adhesion can be roughly divided into three categories: the first category is the influence of soil itself, the second category is the influence of non-soil material conditions, and the third category is the influence of other factors, such as environmental conditions. Some scholars have found that soil moisture content has a great influence on soil adhesion, as soil adhesion will increase first and then decrease with the increase of water content [12,13,14]. Soil particle size composition also has a great influence on soil adhesion [15]. Some scholars have found that soil adhesion will increase with the increase of soil permeability [10]. The surface properties of non-soil materials also have a great influence on soil adhesion [16,17]. Materials with high surface free energy and good hydrophilicity have strong adhesion; on the contrary, the materials with low surface free energy and poor hydrophilicity have weak adhesion [18]. Most of the existing soil adhesion tests are carried out with metal materials as experimental materials, and there are few soil adhesion tests with rubber materials as experimental materials [19]. Based on this, this study will use rubber materials as experimental materials to study the adhesion law and mechanism of the rubber–soil interface.
In summary, previous studies on soil adhesion mainly focused on various types of machinery and soil contact parts in the field of agriculture and engineering, most of which were metal materials. There is no uniform standard for the test of soil adhesion. Therefore, this paper will use rubber tires as experimental materials to study the adhesion between the walking parts of the transport machinery and the soil and use an improved adhesion test device to test this. This paper will also combine the existing water film theory and electric double–layer theory to analyze the adhesion mechanism. The research results will promote the study of soil adhesion and help to solve the problem of soil adhesion in the field of transportation.

2. Experimental Design

2.1. Experiment Material

When a vehicle is running on a muddy road, when the walking part is separated from the soil surface, the moisture tension, chemical adsorption force, physical adsorption force, and so on between the two surfaces will hinder the separation of the two surfaces. These forces that hinder the separation form the adhesion force. Because of the existence of this resistance, it affects the normal driving of the vehicle and causes the vehicle to generate additional energy consumption. Therefore, it is necessary to further study the adhesion between the rubber and the soil surface to solve the problem of energy consumption. Because most of the walking parts of the transport vehicles are mainly rubber tires, and the vehicles in agricultural transportation are generally running on muddy roads, the soil adhesion problem is more serious. Therefore, this article is based on the rubber tires of agricultural machinery as the experimental materials for the experiments. The rubber tire was made into a test sample with a diameter of 44 mm and a height of 20 mm. The adhesion force between the rubber and soil was measured, and the adhesion law was analyzed.
In this test, six types of soil samples from different regions were selected. The six types of soil samples were numbered I–VI according to the clay content, from less to more. The morphology of the soil samples is shown in Figure 1.
In this paper, the liquid limit and plastic limit tests of undisturbed soil in 6 different regions were carried out according to the ‘Highway Soil Test Regulations’ [20], and the particle size analysis was carried out using a laser particle size analyzer. The basic parameters of soil are shown in Table 1.
The particle size composition of the soil samples was measured using an automatic laser particle size analyzer, and the grading curve is shown in Figure 2.

2.2. Experimental Equipment

In this experiment, the improved piston pull-out adhesion test device was used to test the soil adhesion, and the adhesion law between rubber material and different soils was explored. This test device overcomes the situation that the lateral measurement of adhesion force may cause the soil sample to flow, uses simple equipment, and allows easy measurement. The test device is shown in Figure 3. This test device is divided into three parts, which are the test loading part, the force transmission part, and the adhesion force measurement part.
The first part presses the pressure weight on the rubber sample to make contact with the soil sample, and the C-shaped weight is placed on the pressure weight to facilitate the adjustment of the pressure size and simulate the load of the transport vehicle. The second part is composed of three fixed pulleys and steel wire rope. The lubricating oil is applied at the contact between the steel wire rope and the pulley to reduce the influence of friction on the test. In the third part, a steel ball with a diameter of 1 mm is used for the adhesive force test. This test method is convenient to control the loading speed, improve the test accuracy, and reduce the test error.

2.3. Experimental Contents

A 500 g weight was used to pressurize the rubber sample to simulate the load of the transport vehicle, and the adhesion between the six kinds of soil and the rubber medium was tested. During the test, the water content of each soil sample should be gradually increased until the adhesion characteristics appear. The specific steps of the test are as follows:
  • The clay and distilled water were mixed into the test soil according to a certain proportion. After stirring evenly, it was placed in an aluminum box, covered with plastic wrap, and allowed to stand for 12 h to ensure uniform water content in all parts of the soil.
  • The test soil was taken out from the aluminum box and put into the test container on the left side of the fixed pulley to compact. The rubber sample was placed lightly on the soil, and the weight of the rubber sample was recorded. After standing for 30 s, the rubber sample was tied to the traction rope. The plastic barrel was tied on the right side of the pulley, and the marbles were added to the barrel at a constant speed until the contact surface of the rubber sample was separated from the test soil. The quality of the barrel and the steel ball was measured and recorded. The soil was taken out and the above operation was repeated three times.
  • The test soil was sampled, weighed, dried in a blast-drying oven, and the temperature was adjusted to 105 °C. After 8 h, it was taken out and weighed, the moisture content of the test soil was measured, and the adhesion of the soil was calculated.
  • According to the corresponding relationship between the water content and adhesion force, the curve in Figure 4 was drawn.

2.4. Experimental Image Data Extraction Method

In order to analyze the adhesion phenomenon of the rubber–soil surface, it was necessary to process and analyze the image of the rubber–soil surface after the test. In this experiment, Image-Pro Plus 6.0 and Adobe Photoshop 2020 software were used to process and analyze the surfaces of rubber and soil, and the characteristic parameters were extracted. The data extraction and calculation methods are shown in Figure 5.
  • The specific steps were as follows:
  • Firstly, Adobe Photoshop was used to denoise the image, and the brightness, contrast, saturation, etc., were adjusted to make the feature points of the image more obvious and facilitate the data extraction of the image.
  • Then, through the Image-Pro Plus software, the polygon feature selection tool was used to automatically identify the feature points, and the feature points that were not easy to identify were supplemented by manual description.
  • Finally, the software was used to automatically calculate the area of the selected feature points and export the data.

3. Analysis of Test Results

The adhesion between six kinds of soil and rubber samples was measured, and the test results are shown in Figure 6. In order to ensure the accuracy of the test results, five adhesion tests were carried out on each soil sample, and the average value was used as the final adhesion test result. The test error of the five tests is shown in Figure 6, and the test error was below 1%. The adhesion of the six kinds of soil increased first and then decreased with the increase of the soil moisture content. When the soil moisture content was lower than the plastic limit, the soil adhesion was very low. After the water content reached the plastic limit, the soil adhesion increased significantly. When the soil moisture content reached the liquid limit, the soil adhesion force reached the peak value. After the water content exceeded the liquid limit, the adhesion force began to decrease. The moisture contents of the six kinds of soil samples were different when the adhesion force reached the peak value.
The peak adhesion force and clay content of the six soils are summarized in Figure 7. It can be seen from the diagram that the clay content of soils I–VI increased in turn. The trend line of clay content of the six soils is shown as the yellow line in the diagram. The trend line of clay content was compared with the peak curve of adhesion force, as shown in the blue line of the peak adhesion force composition diagram of the six soils. The shape of the trend line of the soil clay content was exactly the same as that of the peak curve of adhesion force.
The analysis showed that the peak adhesion force of the six soils from I to VI increased with the increase in clay content. With the increase in clay content from 15.87% to 49.52%, the adhesion also increased from 18.2 kPa to 34.5 kPa. The maximum water content curve corresponding to the peak adhesion force also showed the same law. The maximum water content corresponding to the peak adhesion force increased from 31.84% to 40.69%. This is because the clay in the soil had a large specific surface area and strong activity. The soil with more clay content had stronger water-holding capacity and greater adhesion [15].

4. Discussion

It can be seen from the test results that the adhesion force of the rubber–soil interface was greatly affected by the soil moisture content. During the adhesion test, it was found that after the rubber surface was separated from the soil surface, the rubber surface showed an obvious adhesion phenomenon. This may be the representation of the residual adhesion force after the adhesion experiment. The larger the adhesion force, the larger the response area of the rubber surface. Therefore, the adhesion phenomenon on the rubber surface could be transformed into data to further analyze the soil adhesion law and explore the soil adhesion mechanism. In order to further analyze the relationship between the adhesion force of the rubber–soil interface and the soil moisture content, the adhesion mechanism of the rubber–soil interface was studied. The rubber surface after the test was photographed with a professional camera, and the images were processed and analyzed using Adobe Photoshop, Image-Pro Plus, and other software.

4.1. Rubber Surface Analysis

After the experiment, it was observed that there would be obvious water marks on the rubber surface, and the area of water marks would increase with the increase in soil moisture content. Image-Pro Plus software was used to scan and analyze the pre-processed images, and the image information was converted into data for further analysis. The pretreatment images and scanning analysis images of the six soils are shown in Table 2.
From the pretreatment images, it can be clearly observed that as the soil moisture content increased, the water mark area on the rubber surface gradually increased, and water droplets gradually appeared. When the water content reached a certain value, there was soil adhered to it. In the image of the scanning analysis, the yellow box selected part represents the area of the water mark, and a diameter was selected on each image as a reference to facilitate the conversion of the data extracted by the software into the actual area.

4.2. Relationship Between Water Mark Area and Adhesion Force

The relationship between the soil moisture content and the water mark area on the rubber surface is shown in Figure 8. It was found that the test results of the six kinds of soil showed the same law. With the increase in soil moisture content, the area of the water mark that formed on the rubber surface also increased. By connecting the water mark area with the increase in water content with the connection line, it can be seen that the trend of the water mark area with the increase in water content was consistent with the trend of soil adhesion with the change in water content. The soil adhesion increased with the increase in the water mark area. When the water mark area reached the maximum value, the soil adhesion also reached the maximum value. It can be seen from the figure that the maximum water content when the six soils reached the maximum adhesion increased with the increase in soil clay content. The water content when the water mark area of the six soils reached the maximum also increased with the increase in clay content.
The results showed that the adhesion force between the rubber–soil interface on the rubber surface was mainly controlled by the water mark area generated between the rubber and soil interface. The size of the soil moisture content directly affected the water mark area formed between the rubber and soil interface, thus affecting the size of the soil adhesion force, and the peak adhesion force between different soils was controlled by the clay content of the soil. The clay in the soil had a larger specific surface area, and the peak adhesion force of the soil with more clay content was greater. The clay in the soil also had greater water-holding capacity. The more clay content in the soil, the greater the soil moisture content when the soil adhesion reached the peak.

4.3. Adhesion Theory Analysis

The adhesion of the rubber–soil interface can be divided into three stages: the contact stage, adhesion stage, and separation stage. In this paper, three stages of theoretical models were constructed to better explain the adhesion mechanism of the rubber–soil interface.

4.3.1. Rubber–Soil Interface Contact Model

The contact form between the rubber and soil interface was similar to the five-layer interface model proposed by Qian [21]. The contact form between the rubber and soil interface and the soil moisture content can be divided into two different situations, as shown in Figure 9. When the soil moisture content was far lower than the plastic limit, the contact between the rubber and soil interface was relatively simple, that is, the rubber surface was in direct contact with the soil surface. Because the soil surface and the rubber surface were not absolutely smooth and had a certain roughness, the rubber surface was in contact with the soil surface. The rubber particles were in contact with the soil particles. When the water content was close to the plastic limit, there was water between the rubber and soil interface. The contact model consisted of five layers, which were the soil surface, soil–water interface, water layer, water–rubber interface, and rubber surface.
In order to more thoroughly explain the adhesion law and mechanism between the rubber and soil interface, we introduce the electric double–layer theory for further analysis. The classical theoretical models of the electric double–layer structure include the Helmholtz plate electric double–layer structure model and the Stern diffusion electric double–layer model, as shown in Figure 10 and Figure 11 [22]. The Helmholtz plate electric double–layer structure model is shown in Figure 9. In the figure, φ represents the potential, and the potential at x from the negative charge surface was zero. The Helmholtz model believes that the positive and negative ions are neatly arranged on both sides of the solid–liquid interface layer, and the thickness of the counterion layer is equal to or approximately equal to the diameter of the ions or molecules. However, the model is too simple and only applicable to concentrated solutions and cannot explain the electrokinetic phenomenon [23].
The Stern model considers the actual volume of ions. It is believed that the concentration of counterions in the solution decreases with the increase of the distance from the particle, and the counterion concentration is divided into two layers, including the tight layer and the diffusion layer. The potential change in the tight layer is similar to that of the Helmholtz model, and the diffusion layer is distributed according to the Boltzmann distribution law [24,25].
Based on the Stern electric double–layer model, we can analyze the electric double–layer model on the surface of clay particles, as shown in Figure 12. The electric double layer on the surface of clay particles is formed by the negative charge on the surface of clay and the cation in water [26].
The factors affecting the electric double layer in the soil first depend on the potential on the surface of the soil particles. The potential on the surface of the soil particles is related to the size of the soil particles and the type of mineral composition [27]. The water in the soil can be divided into bound water (strong bound water and weak bound water) and free water (capillary water and gravity water). The water in the electric double layer is bound water, and the water outside the electric double layer is free water. The water most closely connected with soil particles in the electric double layer is strongly bound water, and the water in the electric double layer outside the strongly bound water is weakly bound water. The water outside the electric double layer controlled by capillary action is capillary water, and the water that is not controlled by capillary action and can flow freely under gravity is gravity water [27,28]. Strongly bound water, weakly bound water, and free water in soil can only be removed at 120–230 °C, 75–120 °C, and 25–75 °C, respectively. In this experiment, only free water and some weakly bound water could be removed by the 105 °C drying oven [29].
Therefore, when the water content was very low, the rubber–soil interface contact model was as shown in Figure 13a. There was only bound water in the soil. Therefore, when the two interfaces were in contact, the rubber surface was in contact with the weakly bound water in the soil (diffusion layer), and the rubber surface was negatively charged. After contact with the diffusion layer, an electric double layer was also formed, and the soil particles overlapped with the electric double layer on the rubber surface [30]. When the water content increased, free water appeared in the soil. The contact model is shown in Figure 13b. The rubber surface was in contact with the soil solution, and the soil particles and the rubber surface formed an electric double layer, respectively.

4.3.2. Rubber–Soil Interface Adhesion Model

A variety of theoretical models have been proposed on the adhesion model of soil [2]. However, most scholars believe that the water film theory model is the best model to explain the adhesion theory [31]. The adhesion force of the rubber–soil interface is composed of intermolecular force, water ring attraction, and water film attraction between the rubber and soil interface [32]. However, the theoretical model of water film is based on the assumption that the external contact material is smooth. However, there is no absolutely smooth surface in reality. Therefore, a new adhesion model was proposed based on the analysis of the experimental results. When the water content was lower than the plastic limit, the rubber–soil adhesion model was divided into two models, as shown in Figure 14a,b. An adhesion model is shown in Figure 14a, where the water content in the soil was very low, the soil particles were relatively dry, and the soil was in direct contact with the rubber interface. At this time, the adhesion force of the rubber–soil interface was mainly the intermolecular attraction between the soil particles and the rubber surface, and the soil adhesion force was very low at this time. The other is the model shown in Figure 14b. The soil moisture content increased, most of the soil particles were wet, the soil and the rubber surfaces were still in direct contact, and the soil adhesion was dominated by intermolecular forces. When the soil moisture content was close to the plastic limit, the rubber–soil adhesion model was as shown in Figure 14c. The soil particles were relatively wet, and the contact between the soil and the rubber surfaces was divided into two types. One is that the wet soil particles were in direct contact with the rubber surface, and the other is that the water ring was formed in part of the contact area between the soil and the rubber surface. The contact model in this area is shown in Figure 9b. At this time, the soil adhesion was composed of intermolecular force and water ring attraction. After the soil moisture content reached the plastic limit, the soil adhesion began to increase significantly, which indicated that the soil adhesion began to be dominated by the water ring attraction.
When the soil moisture content was between the liquid limit and the plastic limit, as the soil moisture content gradually increased, the water ring was gradually filled between the soil and the rubber interface and the water film began to appear. In this process, the contact model between the soil and the rubber surfaces was gradually transformed into the contact model shown in Figure 9b. The soil adhesion force was also gradually composed of water ring attraction and water film attraction, and the soil adhesion force was also greatly increased. The adhesion models in this process are shown in Figure 14d and Figure 14e, respectively. When the soil moisture content gradually increased and reached near the liquid limit (the moisture content was WAD), a thin layer of water film formed between the soil and the rubber surfaces, and the soil adhesion reached the peak value. The adhesion model is shown in Figure 14f. When the soil moisture content was greater than the liquid limit, the thickness of the water film between the soil and the rubber surfaces increased, the water film gravity began to decrease, and the soil adhesion also decreased.
The electric double–layer model in Figure 15a–d corresponds to the rubber–soil interface adhesion model in the four stages of Figure 14b–e. When the soil moisture content was very low, there was only bound water in the soil. As shown in Figure 15a, the soil particles were in direct contact with the rubber surface, and an electric double layer was formed between the two surfaces, as shown in Figure 15a. The soil adhesion force was composed of the electrostatic force in the electric double layer, and with the increase in water content, there was a small amount of capillary water in the soil pores. As shown in Figure 15b, there was a water ring between the rubber and soil interface, and the electric double–layer model at the water ring position is shown in Figure 15a. However, the area of the diffusion layer in the electric double layer increased, the total area of the electric double layer formed between the rubber and soil interface was larger, and the soil adhesion force also increased. As the soil moisture content continued to increase, the capillary water in the soil also gradually increased, the soil fluidity began to increase, and the water film between the rubber and soil interface appeared. As shown in Figure 15c, the electric double layer was located at the water film position. As shown in Figure 13b, the soil particles and the rubber surface formed their own electric double layer, respectively, and the area of the diffusion layer of the two electric double layers reached the maximum. The two diffusion layers were filled with free water, and the soil adhesion force also continued to increase due to the increase in the area of the electric double layer. As shown in Figure 15d, when the water content reached the liquid limit, a thin water film formed at the rubber–soil interface. At this time, the total electric double–layer area at the two surfaces reached the maximum, the electrostatic attraction in the electric double layer reached the maximum, and the soil adhesion reached the maximum value. The van der Waals force between the molecules of the soil solution was less than the electrostatic attraction in the diffusion layer and the Stern layer. Therefore, after the soil moisture content exceeded the liquid limit, the water film at the rubber–soil interface became thicker, the soil adhesion force acted via the intermolecular force between the soil solution, and the soil adhesion force began to decrease [26]. The electric double layer formed by soil particles was mainly clay, so when the clay content in the soil increased, the total area of the electric double layer of the soil also increased, and the soil adhesion also increased [33].

4.3.3. Rubber–Soil Interface Separation Model

The adhesion of the rubber–soil interface is a complex problem, and the soil adhesion force still exists in the separation process of the rubber–soil interface. In this paper, the separation model of rubber and soil was established, as shown in Figure 16, to better explain the adhesion mechanism of the rubber–soil interface.
After the soil moisture content reached the plastic limit, there was water between the soil and the rubber surface. When the rubber surface was separated from the soil, the water layer between the two contact surfaces was separated. After the water layer was separated, a part of the water wet the rubber surface. With the increase in soil moisture content, there were water droplets on the rubber surface. When the soil moisture content exceeded the liquid limit, the fluidity of the soil was very large [34]. The cohesive force inside the soil and the adhesive force between the soil and the rubber interface decreased, and the cohesive force inside the soil was less than the adhesive force between the rubber and soil.

5. Conclusions

In this paper, the improved adhesion test device was used to test the adhesion of six different soil soils with rubber tire as the sample material. The soil adhesion force of soils with different clay contents was measured when the soil moisture content changed, and the image of rubber surfaces was processed by Image-Pro Plus and other software to analyze the adhesion characteristics of the rubber–soil interface. The electric double–layer theory of the solid–liquid interface was introduced to further explain the adhesion law and mechanism of the rubber–soil interface, and the following conclusions were drawn:
  • The adhesion of soil increased first and then decreased with the increase in water content. When the soil moisture content increased to the liquid limit, the soil adhesion reached the peak value, and then the soil adhesion began to decrease. With the increase of clay content from 15.87% to 49.52%, the peak adhesion also increased from 18.2 kPa to 34.5 kPa. When the soil adhesion force reached the peak, the corresponding water content also increased from 31.84% to 40.69%.
  • The size of the soil adhesion was related to the area of the infiltrated rubber surface. With the increase in soil moisture content, the soil fluidity increased, the area of water marks formed on the rubber surface gradually increased, and the soil adhesion also increased. Until the soil moisture content reached the liquid limit, the water mark area on the rubber surface reached the maximum, water droplets appeared, and the soil adhesion reached the peak.
  • According to the test results, the contact, adhesion, and separation models of the rubber–soil interface were constructed, and the mechanism of soil adhesion was explained.
  • The electrostatic attraction in the electric double layer was the main component of soil adhesion. The total area of the electric double layer will gradually increase, and the soil adhesion will increase. Near the liquid limit, the total area of the electric double layer reached the maximum, and the soil adhesion also increased to the peak. After the liquid limit, the soil adhesion force mainly acted via the intermolecular force in the soil solution, and the soil adhesion force gradually decreased.

Author Contributions

M.Y., implementation of the experiment, data curation, writing—original draft; Z.Z., project administration, conceptualization, experimental design, writing—review and editing, supervision; H.L., supervision, writing—review and editing; Z.W., software, resources; D.J., investigation, validation. All authors have read and agreed to the published version of the manuscript.

Funding

The authors greatly appreciate the support by the following research grants: (a) the Fundamental Research Funds for the Central Universities for Ze Zhang (2572021DQ04), (b) the Science and Technology Fundamental Resources Investigation Program (Grant No. 2022FY100700), (c) Heilongjiang Transportation Investment Group Co., Ltd. (JT-100000-ZC-FW-2021-0129), and (d) the Natural Science Foundation of China (41771078 and 42011530083).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

Hang Li was employed by Mudanjiang Power Supply Company, The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Coatings 15 00375 g001
Figure 1. Original soil morphology: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
Figure 1. Original soil morphology: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
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Figure 2. Semilogarithmic curve of particle gradation.
Figure 2. Semilogarithmic curve of particle gradation.
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Figure 3. Test device diagram.
Figure 3. Test device diagram.
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Figure 4. Relationship between soil moisture content and adhesion.
Figure 4. Relationship between soil moisture content and adhesion.
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Figure 5. Object marking and parameter calculation.
Figure 5. Object marking and parameter calculation.
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Figure 6. Adhesion characteristic curves: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
Figure 6. Adhesion characteristic curves: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
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Figure 7. Relationship between clay content and peak adhesion force.
Figure 7. Relationship between clay content and peak adhesion force.
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Figure 8. Relationship between water mark area and adhesion force: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
Figure 8. Relationship between water mark area and adhesion force: (a) Type I soil, (b) Type II soil, (c) Type III soil, (d) Type IV soil, (e) Type V soil, and (f) Type VI soil.
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Figure 9. Rubber–soil interface contact model: (a) low water content contact model and (b) high water content contact model.
Figure 9. Rubber–soil interface contact model: (a) low water content contact model and (b) high water content contact model.
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Figure 10. Parallel version of the electric double layer.
Figure 10. Parallel version of the electric double layer.
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Figure 11. Stern electric double layer.
Figure 11. Stern electric double layer.
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Figure 12. Electric double–layer model of soil particles.
Figure 12. Electric double–layer model of soil particles.
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Figure 13. (a) The electric double–layer model of rubber–soil interface contact when the water content was low. (b) The electric double–layer model of rubber–soil interface contact when the water content was high.
Figure 13. (a) The electric double–layer model of rubber–soil interface contact when the water content was low. (b) The electric double–layer model of rubber–soil interface contact when the water content was high.
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Figure 14. Rubber–soil interface adhesion model: (a,b) water ring does not appear, (c) water ring appears, (d) water film appears, (e) a thin water film is formed, and (f) water film becomes thicker. (a) Water content is WA, (b) water content is WB, (c) water content is WC, (d) water content is WD, (e) water content is WAD (WAD is the water content when the adhesion reaches the maximum value), and (f) water content is WF, WA < WB < WC < WD < WAD < WF.
Figure 14. Rubber–soil interface adhesion model: (a,b) water ring does not appear, (c) water ring appears, (d) water film appears, (e) a thin water film is formed, and (f) water film becomes thicker. (a) Water content is WA, (b) water content is WB, (c) water content is WC, (d) water content is WD, (e) water content is WAD (WAD is the water content when the adhesion reaches the maximum value), and (f) water content is WF, WA < WB < WC < WD < WAD < WF.
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Figure 15. (a) Electrical double–layer model of the rubber–soil interface when no water ring formed. (b) Electrical double–layer model of the rubber–soil interface when a water ring formed. (c) Electrical double–layer model of the rubber–soil interface when a water film formed. (d) Electrical double–layer model of the rubber–soil interface when a water film formed.
Figure 15. (a) Electrical double–layer model of the rubber–soil interface when no water ring formed. (b) Electrical double–layer model of the rubber–soil interface when a water ring formed. (c) Electrical double–layer model of the rubber–soil interface when a water film formed. (d) Electrical double–layer model of the rubber–soil interface when a water film formed.
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Figure 16. Rubber–soil interface separation model: (a) in the process of separation and (b) after separation.
Figure 16. Rubber–soil interface separation model: (a) in the process of separation and (b) after separation.
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Table 1. Soil basic parameters.
Table 1. Soil basic parameters.
Serial NumberSoil TypeAreaSoil Clay Content (%)Liquid Limit (%)Plastic Limit (%)Plasticity Index
ISiltLanshan, Lanzhou City15.8729.0419.619.43
IISilty clayHuli Mountain, Greater Khingan Range31.8135.3725.2110.16
IIISilty clayTahe County, Greater Hinggan Mountains35.5635.7918.8716.92
IVSilty clayHarbin36.7936.9524.3312.62
VClayBeilu River in Qinghai Tibet Plateau45.1638.4120.1918.22
VIClayGenhe City49.5241.4822.5818.9
Table 2. Pretreatment pictures and scanning analysis pictures of the six kinds of soil.
Table 2. Pretreatment pictures and scanning analysis pictures of the six kinds of soil.
Type I soil
Water content (%)19.6324.3127.2128.6530.0534.05
Adobe Photoshop pre-processingCoatings 15 00375 i001Coatings 15 00375 i002Coatings 15 00375 i003Coatings 15 00375 i004Coatings 15 00375 i005Coatings 15 00375 i006
Image-Pro Plus scanning analysisCoatings 15 00375 i007Coatings 15 00375 i008Coatings 15 00375 i009Coatings 15 00375 i010Coatings 15 00375 i011Coatings 15 00375 i012
Type II soil
Water content (%)19.0326.9330.2533.1235.2437.61
Adobe Photoshop pre-processingCoatings 15 00375 i013Coatings 15 00375 i014Coatings 15 00375 i015Coatings 15 00375 i016Coatings 15 00375 i017Coatings 15 00375 i018
Image-Pro Plus scanning analysisCoatings 15 00375 i019Coatings 15 00375 i020Coatings 15 00375 i021Coatings 15 00375 i022Coatings 15 00375 i023Coatings 15 00375 i024
Type III soil
Water content (%)19.923.2826.4131.1936.3338.1
Adobe Photoshop pre-processingCoatings 15 00375 i025Coatings 15 00375 i026Coatings 15 00375 i027Coatings 15 00375 i028Coatings 15 00375 i029Coatings 15 00375 i030
Image-Pro Plus scanning analysisCoatings 15 00375 i031Coatings 15 00375 i032Coatings 15 00375 i033Coatings 15 00375 i034Coatings 15 00375 i035Coatings 15 00375 i036
Type IV soil
Water content (%)19.4527.1831.8535.5637.5639.51
Adobe Photoshop pre-processingCoatings 15 00375 i037Coatings 15 00375 i038Coatings 15 00375 i039Coatings 15 00375 i040Coatings 15 00375 i041Coatings 15 00375 i042
Image-Pro Plus scanning analysisCoatings 15 00375 i043Coatings 15 00375 i044Coatings 15 00375 i045Coatings 15 00375 i046Coatings 15 00375 i047Coatings 15 00375 i048
Type V soil
Water content (%)19.3425.4930.2735.1538.2540.12
Adobe Photoshop pre-processingCoatings 15 00375 i049Coatings 15 00375 i050Coatings 15 00375 i051Coatings 15 00375 i052Coatings 15 00375 i053Coatings 15 00375 i054
Image-Pro Plus scanning analysisCoatings 15 00375 i055Coatings 15 00375 i056Coatings 15 00375 i057Coatings 15 00375 i058Coatings 15 00375 i059Coatings 15 00375 i060
Type VI soil
Water content (%)19.4330.2734.1636.1740.6941.78
Adobe Photoshop pre-processingCoatings 15 00375 i061Coatings 15 00375 i062Coatings 15 00375 i063Coatings 15 00375 i064Coatings 15 00375 i065Coatings 15 00375 i066
Image-Pro Plus scanning analysisCoatings 15 00375 i067Coatings 15 00375 i068Coatings 15 00375 i069Coatings 15 00375 i070Coatings 15 00375 i071Coatings 15 00375 i072
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MDPI and ACS Style

Yuan, M.; Zhang, Z.; Li, H.; Wang, Z.; Jin, D. Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories. Coatings 2025, 15, 375. https://doi.org/10.3390/coatings15040375

AMA Style

Yuan M, Zhang Z, Li H, Wang Z, Jin D. Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories. Coatings. 2025; 15(4):375. https://doi.org/10.3390/coatings15040375

Chicago/Turabian Style

Yuan, Mingyang, Ze Zhang, Hang Li, Zhiyuan Wang, and Doudou Jin. 2025. "Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories" Coatings 15, no. 4: 375. https://doi.org/10.3390/coatings15040375

APA Style

Yuan, M., Zhang, Z., Li, H., Wang, Z., & Jin, D. (2025). Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories. Coatings, 15(4), 375. https://doi.org/10.3390/coatings15040375

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