Enthalpies of Micellization of Double Chain and Gemini Cationic Surfactants

Microcalorimetric measurements have been made on double chain cationic surfactants with the formula [C(N)H(2N+1)C(M)H(2M+1)N(CH(3))(2)]Br, referred to as C(N)C(M)DAB, and a cationic gemini surfactant with the formula [C(12)H(25)(CH(3))(2)N(CH(2))(12)N(CH(3))(2)C(12)H(25)]Br(2), referred to as C(12)C(12)C(12)Br(2). The CMCs and enthalpies of micellization for the compounds C(12)C(6)DAB, C(14)C(4)DAB, C(16)C(2)DAB, and C(12)C(12)C(12)Br(2) are obtained from experiments. The effect of the ratio (N/M) of the two alkyl chain lengths for the C(N)C(M)DABs on the micellization process has been investigated. The contribution of DeltaH(mic) to DeltaG(mic) is about 3.4% at N/M=2, about 11% at N/M=3.5 and about 39% at N/M=8, suggesting that when the total carbon atoms (N+M) remain constant, the micellization process will be driven by entropy or entropy and enthalpy jointly with increasing ratio (N/M). In addition, the comparison between C(12)C(12)C(12)Br(2) and its corresponding monomer (C(12)C(6)DAB) is interesting. The micellization process for C(12)C(12)C(12)Br(2) is driven jointly by enthalpy and entropy, whereas the micellization process for C(12)C(6)DAB is driven mainly by entropy. Copyright 2001 Academic Press.