Tuning the Bulk and Surface Properties of PDMS Networks through Cross-Linker and Surfactant Concentration

[Image: see text] The elastic modulus and hydrophilicity of cross-linked poly(dimethylsiloxane) (PDMS) are tunable via cross-linker concentration and the addition of a simple surfactant, C(12)E(4), before curing. However, the surfactant concentration, [C(12)E(4)], reduces the elastic modulus (73% lower for 6.3% w/w) because it reduces the extent of curing. This is likely because the hygroscopic surfactant results in water poisoning of the catalyst. Three distinct time-dependent hydrophilicity profiles were identified using water contact angle analysis with [C(12)E(4)] determining which profile was observed. This indicates the concentration-dependent phase behavior of C(12)E(4) within PDMS films. Changes in phase behavior were identified using small-angle neutron scattering (SANS) and a compatibility study. No surface excess or surface segregation of surfactant was observed at the PDMS–air interface. However, a surface excess revealed by neutron reflectivity against a D(2)O interface indicates that the increase in hydrophilicity results from the migration of C(12)E(4) to the film interface when exposed to water.