Influence of cationic polyelectrolytes on structure formation in lamellar liquid crystalline systems

The influence of cationic polyelectrolytes, poly[(diallyldimethylammonium chloride)-co-(N-methyl-N-vinylacetamide)] (poly(DADMAC-co-NMVA)) of different charge density in contract to that of a noncharged polymer, poly(N-methyl-N-vinylacetamide) (polyNMVA), on the lamellar liquid crystalline system sodium dodecyl sulfate (SDS)/decanol/water was investigated by means of microscopy observation between crossed polarizers, by small angle X-ray diffraction, and by theology. The lamellar liquid crystal remained stable in all investigated formulations. The results depended on the charge density as well as the concentration of the incorporated polymer. For the polymer with the highest charge two lamellar structures existed concurrently. In excess of a certain concentration the highest charged polymer adsorbed flat onto the SDS-decanol bilayer as shown by its changed interlayer spacing, whereas at lower concentration the polymer did not have a discernible effect on the X-ray diffraction pattern. The results obtained for mixtures of the lowest charged polymer are in accordance with a loop adsorption of the polymer onto the SDS-decanol bilayer. Incorporation of the noncharged polymer did not lead to such adsorption structures and a conclusion of the importance of electrostatic interactions depending on the charge density of the polymer is reasonable. The results obtained by SAXS measurements were supported by the results of rheological measurements.