# Preparation and Lubricating Properties of Polystyrene Composite Microspheres
## 3 Results and Discussion
### Frictional Properties of Composite Microspheres  
#### 3.4.1 Result of Friction and Wear Performance Test  
Figure 6 shows the friction coefficient and wear rate of four kinds of microspheres and pure water under the same experimental conditions. Compared to pure water, the PS reduced the friction coefficient from 0.825 to 0.624. The friction coefficient reduced by about 25%, which indicates that the PS have lubricating properties. The lubricating properties of PS were further improved after adding different composite materials. Among them, the friction coefficient of EGR/PS and OMMT/EGR/PS reduced to 0.592 and 0.433, respectively, revealing a decrease of 28% and 48%. PTFE/PS shows the best antifriction effect, and the friction coefficient was reduced to 0.316. This is about a 62% reduction compared with pure water. Figure 5: (**a**) Metallograph of PTFE/PS before acetone corrosion, (**b**) metallograph of PTFE/PS after acetone corrosion, (**c**) EDS analysis of small particles in PTFE/PS, (**d**) schematic of PTFE/PS. To investigate the anti-wear performance of composite microspheres, a wear analysis test was carried out on ear tracks on the stainless-steel substrate of the friction test. Figure 6b illustrates the wear volumes of the worn substrate under the same test conditions. It can be seen that adding composite microspheres can reduce the wear volumes of stainless substrate to different degrees. The wear volume of samples using PS is 27% lower than that of pure water. The PS compounded with different materials can further reduce the wear volumes. The wear volumes of the worn substrate using EGR/PS, OMMT/EGR/PS and PTFE/PS as lubrication additives are 38%, 58%, and 86% lower than that of pure water, respectively. PTFE/PS has the best anti-wear performance. In order to explore the influence of the particle size of composite microspheres on their lubrication performance, as shown in Table 1, a series of PTFE/PS with different particle sizes were prepared by different polymerization conditions and friction test s carried out. The test results are shown in Table 1.  
From Table 1, it can be seen that the friction coefficient of PTFE/PS gradually decreases and the lubrication performance gradually becomes better as the particle size of microspheres decreases. When the particle size of PTFE/PS containing 0.3 wt% PTFE decreased from 79.35 \(\upmu\)m to 49.00 \(\upmu\)m, the friction coefficient decreased from 0.412 to 0.372. The reduction of friction coefficient is due to the decrease in particle size of composite microspheres, which made it easier for the microspheres to enter between the friction surfaces and played the role of ball bearings, enhancing the effect of lubrication. When the PTFE content was increased from 0.3 wt% to 0.5 wt%, the PTFE/PS particle size changed little, but the friction coefficient decreased significantly. This increase in PTFE concentration enhanced the lubricating performance of PTFE/PS. To further investigate the friction properties of PTFE/PS, Figure 7a shows the friction coefficients of PTFE/PS adding to different amounts of PTFE. As shown in the figure, the 4.0 wt% PTFE/PS sample has the best friction properties, and can reduce the friction coefficient to 0.213, lower by nearly 74% compared to pure water. The result indicates that increasing the PTFE content can improve the lubricating properties of PTFE/PS. Figure 7b shows the substrate's wear volume of worn tracks using PTFE/PS. It can be seen that the wear volume of the PTFE/PS sample is much smaller than other samples, and with the increase in PTFE content in the composite microspheres, the wear volumes will accordingly decrease. The wear volume of PTFE/PS with 4.0 wt% PTFE was 92.4% lower than that of