Surface potential and temperature effect studies of homo- and copolysiloxanes through Langmuir Blodgett technique

Faridah Lisa Supian

Abstract

Hydrophilic backbone chains with substituted hydrophobic organic groups give rise to amphiphilic polysiloxane. This property is of great interest as it can form a Langmuir monolayer, an orderly arranged layer that can be utilised in any potential nanoscale application. Hence, a study was conducted on the surface pressure, surface potential and effective dipole moment of various homopolysiloxane and copolysiloxane Langmuir films to clarify some of their monolayer properties. A NIMA Langmuir 611D trough accompanied with a NIMA surface potential (S-POT) probe was employed in this work. The space filling model, generally known as the Corey, Pauling and Koltun (CPK) precision molecular model, was used to construct the siloxanes unit of each set of polysiloxanes to estimate the siloxane unit size. From the surface pressure isotherm, it was observed that copolysiloxanes are more condensed than homopolysiloxanes. By comparing the results extrapolated from the graph with CPK modelling, the structure was further explored. The correlation of surface potential (?V) and effective dipole moment (µ?) at room temperature were investigated, and from the results and Helmholtz equation, it seemed to be dependent on each other. A study on the effects of temperature on maximum effective dipole moment (µ? max) of each polysiloxane was also carried out. It was found that as the temperature increases, the µ? max decreases. These results can be utilised for the potential application studies of polysiloxanes in the future

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