Complex permittivity studies on glassy poly(vinyl alcohol)/poly(vinyl pyrrolidone) (1/1) at proper pressuretemperature condition, provide the activation volume and energy values for both dc conductivity and βrelaxation. The temperature dependence of the activation volume, which signatures volume-fluctuations accompanying a dynamic process, maximizes at temperature near the glass transition temperature of neat polyvinyl alcohol. The phenomenon is interpreted by a local softening of polyvinyl alcohol domains, while the blend remains in its glassy state. The scenario is also supported by the dependence of the activation energy upon pressure. Dispersed nano-graphene platelets at volume fractions around the critical conductivity percolation threshold are comparatively studied, so as to determine whether local softening affects the formation of a conductivity percolation network.
The pressure and temperature dependency of the electrical conductivity of poly(vinyl alcohol)/poly(vinyl pyrrolidone) (1/1, w/w) and poly(vinyl alcohol) and composites with dispersed nanographene platelets were studied. Above the critical platelet fraction for electric charge percolation, the composites function as pressure-induced electro-switches. The conductor to insulator transition is optimally intense and stable. The electrical conductivity drops by two orders of magnitude at a critical pressure around 750 bars. The transition is stable over tenths of degrees above room temperature. The reduction of the conductivity upon pressure results from the competition between the pressure dependencies of the polarizability of the polymer matrix and the inter-platelet separation, respectively. Both contributions control the fluctuation induced tunneling of electrons through the polymer barrier separating adjusting conductive platelets. The role of the local electric field at the polymer-platelet interfaces by assisting tunneling is suppressed by the decrease of the polarizability upon pressure.
Water-soluble polyvinyl alcohol (PVA) mixed with piezo-active polyvinylidene fluoride (PVdF) micro-grains constitute hybrid blends for transfusing mechanical energy to electric one. The value of the piezoelectric coefficient is, in principle, a portion of the value that neat PVdF exhibits. In the present work, we investigate the possibility, by dispersing nano-graphene platelets (NGPs), to augment the total electromechanical coupling. Mechanical stress applied on structurally and compositionally heterogeneous solids results in increased values of the internal local stress field: NGPs are likely to amplify the local stress exercised on the surface of individual piezoelectric polymer grains. PVA - PVdF (3:1 w/w), cast from water solution, loaded with various fractions of NGPs boost the value of the overall piezoelectric coefficient by 150 % per weight fraction of NGPs and becomes superior to values reported for neat electro-active PVdF.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.