Network structure of poly(methyl methacrylate) based gels

The large scale structure of polymer gels and polymer gel electrolytes have been investigated using small angle neutron scattering. The gels consist of poly(methyl methacrylate) (PMMA) and propylene carbonate (PC) and the gel electrolytes are based on LiClO4 dissolved in propylene carbonate/ethylene carbonate which is stabilized with PMMA. The systems were investigated over large polymer concentration ranges. The data reveal at least two different length-scales of the gels. The shorter one, 4-25 angstroms, is the polymer inter-chain distance, which is highly concentration dependent. It exhibits a power-law dependence of the volume concentration with an exponent of -1.1, in agreement with previous investigations of polymer gels. The larger scale structure is in the range 150-300 angstroms and also concentration dependent. It appears to be due to, at least for high polymer concentrations, a combination of cross-links and static polymer concentration fluctuations. The investigated gel electrolytes have a similar structure as the gels and thus the dissolved salt has little influence in the large scale structures.