Direct osmotic pressure measurements on partially neutralized poly(acrylic acid) gels

Abstract
We present a new experimental device to measure the osmotic pressure in gels. The system has been tested on partially neutralized poly(acrylic acid) gels. The variation of the osmotic pressure with polymer concentration, Φ, and ionization degree, α, is linear, provided that α is not too high (I.e. the counterions do not condense on the chains). These results are in good agreement with theoretical models and with compressibility measurements obtained by light scattering experiments. The very charged gels are also studied, and the results are discussed in the frame of existing theories and experiments.