Monomeric, dimeric, and polymeric cationic surfactants.

Abstract

Another subject of this work in chapter 4 is the binding of chromate anions by polymeric surfactants, namely polyethyleneimine (PEI), hexyl PEI and lauryl PEI. PEI, one of the most widely studied polyelectrolytes, is known to be a highly branched water-soluble polyamine of variable molecular weight. It is believed to contain primary, secondary, and tertiary amine groups in the ratio of approximately 1:2:1. Owing to its cationic character, in aqueous solution PEI exhibits a strong affinity to anionic materials, including organic and inorganic anions and polyanions. Hexyl PEI and lauryl PEI were synthesized in this work from PEI and alkyl bromide. A series of ultrafiltration experiments were then performed in which chromate ions were bound by PEI, hexyl PEI and lauryl PEI at various pH values and chromate to EI ratios.

This dissertation deals with three types of cationic surfactants, i.e., monomeric, dimeric and polymeric surfactants.

Dimeric surfactants, which are also referred to as gemini or bipolar surfactants, are made up of two identical amphiphilic moieties connected by a spacer near the head group. Most of the studies published so far are concerned with dimethylalkylammonium halide type which are referred to as m-s-m, 2X- surfactants, where s and m are the carbon numbers of the alkanediyl spacer and of the alkyl chain of the hydrocarbon chain, respectively, and X- is the halide counterion. One of the interesting properties of the dimeric surfactants is their co-micellization with conventional surfactants. Synergism was reported for the mixed dimeric and conventional surfactant systems. In chapter 2 and 3 of this dissertation, the study of binary mixed monomeric and dimeric surfactant systems is described. Five bis(quaternary ammonium bromide) surfactants (m-s-m 2Br$\sp-), $ namely 12-2-12, 14-2-14, 16-2-16, 16-4-16 and 16-6-16 were synthesized, and a series of conductivity measurements were performed to obtain the Krafft temperatures and cmc's of all five pure dimeric surfactants and their mixtures with cetyltrimethylammonium bromide (CTAB).