On one hand, centrifugal separation could remove the graphite particles which do not dissolve in water. On the other hand, it has accelerated the settlement process of graphite emulsion so as to click here evaluate the dispersion stability. After centrifugation, the supernatants are separated to analyze the absorbance on a UV–vis spectrophotometer. Figure 3 shows the changing curves between absorbance and wavelength at different temperatures. The curves in Figure 3 exhibit a similar change tendency.
There is nearly no absorption when the wavelength is beyond 550 nm. The absorbance increases with the decrease of wavelength in the range of 550 to approximately 250 nm, and the increasing rate MK0683 becomes larger and larger. There exhibits a one-to-one correspondence between absorbance and wavelength within the range 550 to approximately 250 nm.
Any wavelength in this range could be used as the characteristic absorption wavelength to evaluate the dispersion stability of graphite emulsion. In this study, 350 nm is selected as the fixed detection wavelength. Figure 4 displays the absorbance under different polymerization conditions at 350 nm. According to the Lambert-Beer law A = εLc (A absorbance; ε absorptivity; L width of colorimetric ware; c concentration), the absorbance is proportional to the concentration of graphite emulsion, and the concentration could then reflect the dispersion stability of graphite particles in the emulsion. From Figure 4, the maximum absorbance is corresponding to the condition of 70°C (polymerization temperature) and 5 h (polymerization selleck kinase inhibitor time). Therefore, 70°C and 5 h is considered as the optimal polymerization condition. The water-soluble nanographite obtained under this condition is chosen to be the lubrication additive of water-based cutting fluid. Figure 3 Change of absorbance with wavelength under different polymerization conditions. Temperatures at (A) 60°C, (B) 70°C,
and (C) 80°C. Figure 4 Absorbance under different see more polymerization conditions at the wavelength of 350 nm. Dispersion state Figure 5 shows the microdispersion state of graphite particles in aqueous environment. Figure 5a,b shows SEM images with different magnifications. It can be indicated from Figure 5a that the graphite particles are uniformly dispersed in the emulsion. The agglomeration between graphite particles is avoided effectively. From Figure 5a, it could be recognized that there is a membrane-like substance coating around the graphite particles. This demonstrates that the nanographite/polymethyl acrylate composite is synthesized successfully. Figure 5b is the partial amplification image of Figure 5a. It displays the morphology of a single graphite flake which is coated by the polymethyl acrylate membrane. The surface of the graphite particle is modified by emulsion polymerization, and the original laminated structure of the nanographite is not destroyed.
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