Tamoto Yushi, Segawa Hiroshi, Shirota Hideaki
Department of Applied Chemistry, Graduate School of Engineering, and Department of General Systems Sciences, Graduate School of Arts & Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Langmuir. 2005 Apr 26;21(9):3757-64. doi: 10.1021/la046953i.
Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (C(n)H(2n+1)N(CH(3))(3)Br; n = 10, 12, 14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10(-10)-10(-8) s is characterized by a biexponential function. The faster solvation time constants are about 110-160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2-2.6 ns and 450-740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H(2)O-C(2)H(5)SO(4)(-) and H(2)O-C(2)H(5)N(CH(3))(3)(+)) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions.
利用皮秒条纹相机系统研究了荧光探针香豆素102在阴离子表面活性剂烷基硫酸钠（C(n)H(2n+1)SO(4)Na；n = 8、10、12和14）和阳离子表面活性剂烷基三甲基溴化铵（C(n)H(2n+1)N(CH(3))(3)Br；n = 10、12、14和16）胶束溶液中的溶剂化动力学。在10(-10)-10(-8) s时间范围内的溶剂化动力学由双指数函数表征。对于阴离子和阳离子胶束溶液，较快的溶剂化时间常数约为110 - 160 ps，烷基硫酸钠和烷基三甲基溴化铵胶束溶液较慢的溶剂化时间常数分别约为1.2 - 2.6 ns和450 - 740 ps。随着烷基链更长的表面活性剂胶束，较快和较慢的溶剂化时间都变慢。烷基硫酸钠和烷基三甲基溴化铵胶束中溶剂化动力学的烷基链长度依赖性可归因于烷基链长度变化导致的极性头基团胶束表面密度的变化。对于相同烷基链长度的表面活性剂，烷基硫酸钠胶束溶液较慢的溶剂化时间常数比烷基三甲基溴化铵胶束溶液慢约3.5倍。通过密度泛函理论计算估计了几何优化模拟簇（H(2)O - C(2)H(5)SO(4)(-)和H(2)O - C(2)H(5)N(CH(3))(3)(+)）的相互作用能，以了解水与烷基硫酸根和烷基三甲基铵头基团之间的相互作用强度。烷基硫酸钠和烷基三甲基溴化铵胶束溶液之间较慢溶剂化时间常数的差异可能源于它们不同的特定相互作用。
