Kinetic aspects, rheological properties and mechanoelectrical effects of hydrogels composed of polyacrylamide and polystyrene nanoparticles

Snake-cage gels were prepared using monodisperse polystyrene (PS) nano-sized particles (R = 200 nm) in place of the more commonly used linear polymer. The kinetics of the formation of the complementary polyacrylamide (PAM) hydrogel was studied alone or in the presence of the PS nanoparticles by H-1-NMR. Without PS, the reactivity ratios of the acrylamide (Am) and the cross-linking agent N,N'-methylene-bisacrylamide (BisAm) were computed using the initial kinetics of PAM gel at high cross-linker concentration (r(A) = 0.52 and r(B) = 5.2 for Am and BisAm, respectively). In the presence of PS, during the formation of nanoparticle composite (NPC) gels, there was a decrease in the conversion rate with an increasing fraction of PS nanoparticles. This could be explained by steric effects, which induce an increase of the elastic modulus of the matrix with the increasing fraction of PS nanoparticles. There was a considerable increase in the rheological properties of the NPC gels (i.e. tensile modulus), which was more pronounced at higher fractions of nanoparticles. We used particular mechanical properties to develop a stimulus-responsive ("smart'') material, i.e. a mechanoelectrical effect, which may be used in the development of soft and wet tactile-sensing devices.