Lamellar liquid crystals in commercial polyether-modified polydimetilsiloxanes for coating applications: Structure, rheology and cross-linking

Abstract

We have constructed the phase diagrams in water of two commercial additives for coatings consisting of polyether-modified polydimethylsiloxanes. These aqueous systems form a liquid crystal mesophase (LC) at copolymer concentrations higher than 60 wt%. At low copolymer concentrations, this LC coexists with a diluted aqueous phase. Small angle x-ray scattering (SAXS) measurements and polarized optical microscope observations indicate that the structure of the mesophase is lamellar, with an interlayer spacing that increases linearly with the concentration of water in the system. The lamellar liquid crystals display temperature-dependent viscoelastic behavior, with the copolymer with longer spacing showing a much lower elastic modulus. Since one of the copolymer has terminal acryl groups, its lamellar phase can be crosslinked to produce gelled liquid crystals. Other cross-linked self-assembled structures, such as bicontinuous microemulsions, are envisaged.