COMPARISON OF THE AGGREGATION BEHAVIOR OF DIBLOCK AND TRIBLOCK NONIONIC AMPHIPHILES WITH LINEAR AND CYCLIC HYDROPHOBIC TAILS

The micellization characteristics of nonionic surfactants of the type C7E26 and symmetric C7E26C7 where C-7 = the heptanoic acid (C7H14O2) O r the cyclohexanecarboxylic acid (C7H12O2) group is investigated. Stru ctural formulas being nearly the same, the linear and cyclic analogues possess roughly the same molecular weights and hydrophilic-lipophilic balance (HLB) values. Surface tension and fluorescence experiments pr ovide information on the thermodynamics of micellization, interfacial adsorption, mean aggregation number, etc. Comparisons are made between linear and cyclic analogues and between diblocks and triblocks. The r esults indicate that, compared to their Linear counterparts, amphiphil es with cyclic hydrophobes possess higher CMC values and the micelles formed are less compact with lower aggregation number. A qualitatively similar trend is seen between diblock and triblock surfactants. The r esults for triblocks are consistent with a micellar structure in which the PEG chain folds to insert both the terminal hydrophobic segments into the micellar core.