Enthalpies of micellization of double chain and gemini cationic surfactants

Microcalorimetric measurements have been made on double chain cationic surfactants with the formula [CNH2N+1CM H2M+1N(CH3)(2)]Br, referred to as C(N)C(M)DAB, and a cationic gemini surfactant with the formula [C12H25(CH3)(2)N(CH2)(12)N (CH3)(2)C12H25]Br-2, referred to as C12C12C12Br2. 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 C12C12C12Br2 are obtained from experiments. The effect of the ratio (NIM) 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 NIM = 2, about 11% at NIM = 3.5 and about 39% at NIM = 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 (NIM). In addition, the comparison between C12C12C12Br2 and its corresponding monomer (C12C6DAB) is interesting. The micellization process for C12C12C12Br2 is driven jointly by enthalpy and entropy, whereas the micellization process for C(12)C(6)DAB is driven mainly by entropy. (C) 2001 Academic Press.