Langmuir-Blodgett films of novel mesophase polysiloxanes

Some novel linear and cyclolinear (CLPOS) polyorganosiloxanes without classical mesogenes in their macromolecules can form thermotropic mesophases that can be classified as columnar mesophases. In the study, the pi/A-isotherms for a series of CLPOS were investigated to clarify their phase and mesophase behavior. Similarly to polydimethylsiloxane (PDMS), which is known to be able to spread and form thermodynamically stable monolayers, all CLPOS studied were capable of spreading and building LB films in the vicinity of 20 Angstrom(2) per [Si(R(2))O] repeat unit, which seems to correspond to LB-film formation, where oxygens are fixed on the water surface and the side groups are directed to the air. Unlike PDMS, CLPOS form stable multilayers whose thickness depends on the surface pressure pi. The transition from the monolayer to bi- and tri- (up to seven) layers is partly reversible and characterized by sharp steps in pi/A-isotherms. In the temperature range 2 - 60 degrees C, the position of steps is independent of temperature. The steps in pi are closely related to the molecular structure. A model is suggested, in which the steps are treated as a result of a sliding mechanism and crystalline and mesophase behavior.