Phase Separation Behavior of Poly(methyl methacrylate)/Poly(vinyl acetate)/Silica Blends

The phase separation of poly(methyl methacrylate)/poly(vinyl acetate)/silica (PMMA/PVAc/SiO2) blends was investigated by optical microscope, rheology, morphological observation and Fourier transform infrared spectroscopy. Strong inter-molecular interaction between PMMA and PVAc was found by the shift of the carbonyl peak position compared to the FTIR of pure polymer and the reduction of chain entanglements inferred from the rheological curves. The addition of nano-silica led to the adsorption of chains of both polymers on the particle surfaces, which changed the inter-molecular interaction between pure PMMA and PVAc. The complex inter-molecular interaction and polymer-particle interaction resulted in the failure of time-temperature superposition over the entire temperature range. So the normalized Cole-Cole plot was proposed to analyze the phase separation process of the blend. Due to the inter-molecular interaction, the normalized Cole-Cole plot of the PMMA/PVAc blend deviates from the polymer, and secondary deviation occurs at the end of the curve during the heating process, which is the contribution of the phase interface. The nanoparticles have different influences on the phase separation behavior of the blend, depending on the blend composition. In the near-critical blends, nano-silica promoted the phase separation and was finally located at the interface of the two phases. In the off-critical blends, nano-silica had little effect on phase separation and was finally located in the island domains. The effect of nanoparticles on phase separation of different blends is related to the mechanism of phase separation: the near-critical blends form discontinuous shapes through the decomposition of the spiral nodal line. The phase separation speed is faster than the Brownian motion speed of nanoparticles, which results in the initial distribution of nano-silica in the two phases, and the subsequent movement towards the interface of two phases. The off-critical blends form island shapes through nucleation growth mechanism. Due to the slow phase separation rate, the nano-slica play the role of nuclei during the phase separation. In other words, the phase separation mechanism, Broenian motion of nanoparticles and dynamic adsorption and desorption of polymer chains on the surface of nanoparticles jointly determine the distribution of nanoparticles. Such selective location of nanoparticles determined by the phase separation mechanism supplied a new approach for the control of aggregation of nanoparticles in polymers. [GRAPHICS] .

Automated summary

The phase separation of PMMA/PVAc/SiO2 blends was investigated, and the effect of nanoparticles on phase separation behavior was analyzed. Strong inter-molecular interaction between PMMA and PVAc was found, and the addition of nano-silica changed the inter-molecular interaction between the two polymers. The distribution of nanoparticles was determined by the phase separation mechanism, Brownian motion of nanoparticles, and dynamic adsorption and desorption of polymer chains on the surface of nanoparticles.