Yeqiang Tan

Grafting of copolymers onto graphene by miniemulsion polymerization for conductive polymer composites: improved electrical conductivity and compatibility induced by interfacial distribution of graphene

A facile and general method to covalently functionalize graphene oxide (GO) with copolymers, using poly(styrene-co-methylmethacrylate) (P(St-co-MMA)) as an example, via miniemulsion polymerization is described in this study. After in situ reduction, insulating GO is converted to conductive reduced-graphene oxide (RGO). P(St-co-MMA) grafted RGO as conducting filler was incorporated into immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend to prepare conductive polymer composites (CPCs). The lowest percolation threshold (0.02 vol%) among all the reported values for graphene-filled CPCs was achieved due to the controllable preferential distribution of the modified RGO at the interfacial region between PS and PMMA phases, attributed to P(St-co-MMA) grafted on the surface of RGO behaving as compatibilizers to improve interfacial interactions with both the two phases. Moreover, P(St-co-MMA) grafting modified RGO could obviously enhance the compatibility reflected by a significant reduction of the size of dispersed phase, for an example, by nearly one order of magnitude for PS/PMMA (4/1 in volume) blends.

Influence of annealing on linear viscoelasticity of carbon black filled polystyrene and low-density polyethylene

Influence of annealing on linear dynamic rheology of carbon black filled polystyrene and low-density polyethylene before and after annealing was investigated in relation to a recently proposed two phase model. Annealing-induced improvements in dynamic complex modulus of filled polymers in the linearity region are related to increases in amplification factor and characteristic moduli and to retardation in dynamics of the filler phase. It is suggested the characteristic modulus and dynamics of the filler phase are interrelated to each other, and their relationship is independent of thermal history. Moreover, annealing-induced variations in global viscoelasticity of filled polymers are ascribed to the geometric changes of the filler phase consisting of filler clusters with a constant fractal dimension.

Facile regulation of glutaraldehyde-modified graphene oxide for preparing free-standing papers and nanocomposite films

Colloidal suspensions of glutaraldehyde (GA) crosslinked or grafted graphene oxide (GO) sheets were fabricated by simply tailoring the feed sequence. The different structures were confirmed by Fourier transform infrared spectra and X-ray diffraction. As demonstration of the utilities, the different colloidal suspensions were used to prepare free-standing papers by flow-directed filtration and poly(vinyl alcohol) (PVA)-based nanocomposite films by casting. Free-standing papers from GA crosslinked GO sheets exhibited better mechanical properties than unmodified GO paper, while nanocomposite films from GA grafted GO exhibit higher tensile strength and Young’s modulus.

Dispersion stability and rheological behavior of suspensions of polystyrene coated fumed silica particles in polystyrene solutions

Polystyrene coated silica (SiO2@PS) core-shell composite particles with averaged diameter of about 290 nm were prepared by in situ emulsion polymerization of styrene on the surface of γ-methacryloxypropyltrimethoxysilane grafted SiO2 nanoparticles of 20–50 nm in diameter. Rheological behavior and dispersion stability of SiO2@PS suspension in 10 wt% PS solution were compared with suspensions of untreated SiO2 and silane modified SiO2 nanoparticles. Suspensions of the untreated and the silane modified SiO2 exhibited obvious shear thinning. The SiO2@PS suspension exhibits shear viscosity considerably smaller than suspensions of untreated and silane modified SiO2 at low shear rates. Transmission electron microscopy showed that the composite particles can uniformly and stably disperse in PS solution compared to other suspensions, implying that the PS shell can effectively enhance the particle compatibility with PS macromolecules in solution.