Distribution of alkane probes in heterogeneous PDMS resins

Silicone elastomers are well known to have a network structure, but it is also apparent from AFM studies that there is a larger scale network of densely and sparsely cross-linked regions on a nm scale. We wish to better understand this distribution and its implications for the permeation and distribution of small molecules in such networks. Our first experiment with a surfactant additive in PDMS revealed this heterogeneous structure, but we could not resolve the scattering contributions arising from the PDMS structure, and the long or short-range organisation of the surfactant. Using a series of homologous alkane additives, which have systematically varying entropy and enthalpy of mixing, we will isolate the PDMS structure in terms of densely and sparsely cross-linked regions. This will be invaluable in (i) interpreting data for complex additives and (ii) computational modelling.