Conductivity enhancement by aggregate formation of sodium deoxycholate in poly(N-vinyl-2-pyrrolidinone) gel

The polymer gels [cross-linked poly(N-vinyl-2-pyrrolidinone), c-PVP] containing sodium deoxycholate (NaDC) and N-methyl-2-pyrrolidinone (NMP) were prepared, and their conductivity was measured as a function of temperature and NaDC concentration. The NaDC molecules in the c-PVP film formed aggregates above a concentration of ca. 2 x 10(-2) mol kg(-1) (per kg of gel). The conductivity of the gel increased from 1 x 10(-7)to 4 x 10(-6) S cm(-1) with the formation of the NaDC aggregates in the gel. The conductivity jump is induced by an increase in the number of charge carriers produced by the increased dissociation of NaDC molecules. Interaction between the polymer matrix and NaDC plays an important role in the conductivity enhancement.