SURFACE-POTENTIAL STUDIES OF LANGMUIR MONOLAYERS AND LANGMUIR-BLODGETT DEPOSITED FILMS OF P-MEC6H4S(O)(CH2)11S(CH2)10COOH

The behavior of the bipolar molecule p-MeC6H4S(O)(CH2)11S(CH2)10CO2H (pTSA) at the air/water interface has been investigated by using surface pressure and surface potential isotherms. It is shown that in the condensed phase, the molecules pack vertically with the carboxyl moiety in the water surface. Strong hysteresis in the pressure isotherm is related to interactions between the horizontally directed SO dipoles in the distal function. The surface potential measurements were extended to Langmuir-Blodgett (LB) deposited monolayers of pTSA from which it was deduced that, upon deposition, molecules undergo a slight tilting. It is also shown that surface potential measurements can be utilized for determining macroscopic film homogeneity and for studying aging effects in deposited films and provide a noncontacting method for measuring the pyroelectric coefficient of LB films. Finally, it is demonstrated that surface potential is a sensitive indicator of chemical reactions and interactions at the surface of thin films.