Monolayers of polyorganosiloxanes on water

Linear organosiloxanes with various substituents differ in their spreading velocities and with respect to the film structure formed on aqueous substrates. The material investigated allows a distinction between siloxanes in which the molecules placed on the subphase in helical form become oriented on the surface of the water to form “spreading chains” and siloxanes in which this is not the case. It is believed that hydrogen bridging is responsible for the orientation effect. Within the first group, a distinction can be made between polymers which on strong compression are lifted off from the water and can be returned to the helical form, and those in which due to great hydrophilicity of the substituents release of “dry” spreading chains from the water can not be achieved. Methyl‐substituted siloxanes, among them especially the dimethyl‐ and methyl‐H‐siloxanes, show quick spreading and good orientability. This may explain why these siloxanes play such an important role since the beginning of silicone technology up to the present day as interfacially active substances. But this behavior is not representative for organosiloxanes in general. The structure of the siloxane skeleton seems to have no decisive influence on the spreading phenomena. Branched or crosslinked methylsiloxanes behave similar to the linear ones and form also, by and large, monomolecular films. Hydrate phases, i.e., mixed phases of the spread substance and the subphase, play an important part in the interpretation of the force/area (F/A) isotherms.