ABSTRACT
This chapter deals with the ellipsometric study on surfactants comprising linear alkyl and branched hydrocarbon chains at an air-water interface. An explanation of such anomalous behaviour is proposed on the basis of the effect of methyl substitution on the refractive indices of the surfactants comprising polyisobutylene chains. The surfactants with n-alkyl chains were dissolved in chloroform and the surfactants with polyisobutylene chains were dissolved in hexane for the purpose of spreading. The differences in the molecular area and the collapse pressure observed with the molecules of two different kinds of hydrocarbon chains indicate that branched chains do not pack in a similar way to that of n-alkyl ones. The presence of a large number of methyl substituents on the polyisobutylene chains restricts the rotational degree of freedom around the C-C bond which causes the chains to tilt and prevents them from packing in a close manner.
