Heterogeneity of the surfactant layer in organically modified silicates and polymer/layered silicate composites

摘要

Dynamics and microstructure of the surfactant layer in organically modified silicates and their composites with polystyrene were Studied as a function Of surfactant loading and temperature in the range relevant for melt intercalation. Site selectivity was achieved by using specifically headgroup- and tail-labeled surfactant EPR spin probes and by applying P-31 MAS NMR to phosphonium surfactants. Bimodal dynamics is observed over a broad range of surfactant loadings and temperatures in both the absence and presence of polymers and correlates with a bimodal distribution of surfactant headgroup distances from the silicate surface. Excess surfactant with respect to the cation exchange capacity of the silicate plasticizes the surfactant layer. Electron spin echo envelope modulation on nanocomposites with ammonium surfactant and deuterated polystyrene demonstrates close contact between the polymer and surfactant tail ends. Surfactant dynamics changes strongly during microcomposite formation, i.e., by embedding stacks of organoclay platelets in a polymer matrix, even if no intercalation takes place.