Quantitative evaluation of a smart material: PVA-borate gelation and the gel`s response to diols

Smart materials that respond to chemical stimuli are important building blocks for the next generation of intelligent systems. The authors are developing a quantitative understanding to describe polymer solution behavior for polymers that can undergo noncovalent crosslinking (in solution). The polymer system known to school children as {open_quotes}Slime{close_quotes} is such a system, thus, the authors have chosen to study this system in some detail. Slime consists of a solution of borax that span a range of concentrations have been prepared. The viscosity of the solutions has been measured at 30C. At high (0.25 M in diol) polymer cocentration and high borate concentration (around 2 mM) the solution forms a homogenous gel. At low polymer concentration (0.15 M) and high borate concentration there is a phase separation. The authors have modeled the formation of the gel using a combination of chemical equilibria, to define how many borate crosslinks that are, and entanglement theory, to determine the viscosity of the crosslinked polymer. The theory correctly predicts the compositions that yield gels, but the predicted viscosity is too low.