Gelation mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) chains in dispersion solutions containing multiwall carbon nanotubes (MWNTs) analyzed in terms of liquid-liquid phase separation

Abstract

Gelation mechanisms of ultra-high-molecular-weight polyethylene (UHMWPE) in dispersion solutions containing multiwall carbon nanotubes (MWNTs) were investigated in terms of liquid-liquid phase separation mechanisms. When an incident beam of He-Ne gas laser was directed to the dispersion solution quenched to a desired temperature, the logarithm of scattered intensity increased linearly with elapsing time and tended to deviate from this linear relationship. The two different increasing behaviors of the scattered intensity were termed as initial and latter stages, respectively, of the phase separation. The linear increase in logarithmic light-scattered intensity was analyzed within the framework of the linear theory of spinodal decomposition in terms of the viewpoint that the quenched solution becomes thermodynamically unstable and tends to incur phase separation to resolve the unstable state. The growth rate of the concentration fluctuation of neat UHMWPE solution (without MWNTs) calculated from the slope of linear increase was faster than that of the dispersion solution. In spite of the rapid growth rate, however, the gelation time of the dispersion solution was much shorter than that of the neat UHMWPE solution and the gelation and quasispinodal temperatures were slightly higher. These phenomena were in contradiction with the result of the concentration fluctuation. This contradiction was thought to be due to the fact that diffused UHMWPE chains in the dispersion solution were gelled easily on the MWNT surface rather than the gelation by self-coagulation.