MICROSCOPIC AND MACROSCOPIC THERMODYNAMIC OBSERVATIONS IN SWOLLEN POLY(DIMETHYLSILOXANE) NETWORKS

Poly(dimethylsiloxane) (PDMS) networks swollen in toluene are investigated both by small-angle neutron scattering (SANS) and by swelling pressure measurements. The scattering signal from the gels, measured as a function of swelling, is resolved into two components, a solution-like part and a static part. The forward scattering intensity of the solution-like part contains all the thermodynamic information relevant to the gel. The absolute intensity is obtained by calibrating against that of a standard water sample. The Flory-Huggins theory of polymer solutions is adopted to derive the swelling pressure of the gel from the scattering measurements. In addition, the swelling pressure is determined independently at different degrees of dilution of the gels. A comparison is made between these direct macroscopic observations and the results deduced from the scattering intensity.