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2910 Langmuir 1994,10, 2910-2916 Dimeric Surfactants: Spacer Chain Conformation and

Summary: 2910 Langmuir 1994,10, 2910-2916
Dimeric Surfactants: Spacer Chain Conformation and
SpecificArea at the AirNater Interface
Haim Diamant and David Andelman*
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences,
Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel
Received January 3, 1994. In Final Form: May 30, 1994@
We present a theoretical explanation for experimental results obtained recently regarding dimeric
surfactants. The nonmonotonic dependenceof the specificarea at the aidwater interface on the spacer
carbon number is accounted for. In addition, understanding the role of spacer carbon number at the
aidwater interface can elucidatethe shapes of aggregatesformedin the aqueoussolution. The attractive
and repulsiveinteractions of the surfactantmoleculesand the conformationalentropyof the spacer chain
arefoundtobe dominantfactorsindeterminingthis dependence. Ontheotherhand,hydrophobicrepulsion
of the spacerfrom the water surfacedoes not seem to play an important role, if any, contrary to what has
been previously suggested.
1. Introduction
Interestingexperiments have been recently performed
on homologous series of dimeric ~urfactants.l-~These
molecules arecomposedofordinary surfactantmonomers
whose polar headgroups have been chemically linked in


Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University


Collections: Materials Science; Physics