LANGMUIR-BLODGETT-FILMS OF NOVEL MESOPHAS E POLYSILOXANES

Some novel linear and cyclolinear (CLPOS) polyorganosiloxanes without classical mesogenes in their macromolecules can form thermotropic meso phases that can be classified as columnar mesophases. In the study, th e pi/A-isotherms for a series of CLPOS were investigated to clarify th eir phase and mesophase behavior. Similarly to polydimethylsiloxane (P DMS), which is known to be able to spread and form thermodynamically s table monolayers, all CLPOS studied were capable of spreading and buil ding 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 a re fixed on the water surface and the side groups are directed to the air. Unlike PDMS, CLPOS form stable multilayers whose thickness depend s 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 degr ees C, the position of steps is independent of temperature. The steps in pi are closely related to the molecular structure. A model is sugge sted, in which the steps are treated as a result of a sliding mechanis m and crystalline and mesophase behavior.