Sonochemistry of surfactants in aqueous solutions: An EPR spin-trapping study
Sonochemistry of surfactants in aqueous solutions: An EPR spin-trapping study
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DOI：
10.1021/ja010857b
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发表时间：
2001-11-07
影响因子：
15
通讯作者：
Riesz, P
中科院分区：
文献类型：
--
作者：
Sostaric, JZ;Riesz, P
溶质的表面活性剂性质在水溶液的声化学和声致发光中起着重要的作用。最近，它已被证明，对于相对低分子量的表面活性剂，这些效果可以与吉布斯表面过剩的溶质。在本研究中，我们调查是否这种相关性是有效的相对高分子量的表面活性剂和表面活性剂的分解过程中的超声波分解的机制。用EPR和3，5-二溴-4-亚硝基苯磺酸盐自旋捕获技术研究了非挥发性表面活性剂[正烷基磺酸盐、正烷基硫酸盐、正烷基铵基丙磺酸盐（APS）和聚氧乙烯（POE）]在氩气饱和水溶液中的声分解反应。仲碳基（-（CH）-C-.-），通过提取反应形成，对于所有超声处理的表面活性剂都观察到。伯碳（-（CH 2）-C-.）和甲基（（CH 3）-C-.）通过热解形成的自由基对于两性离子是最大的（即，APS）和非离子表面活性剂（即，POE）。（-（CH）-C-.-）在n-烷基阴离子表面活性剂[戊磺酸钠（SPSo）、辛烷磺酸钠（SOSo）、辛基硫酸钠（SOS）和十二烷基硫酸钠（SDS）]的超声分解之后测量自由基。在0- 0.3mM的浓度范围内，-（CH）-C-.自由基产率的增加顺序为SDS接近SOS接近SOSo > SPSo。在较高浓度下，最大（-（CH）-C-.-）对于每种表面活性剂达到自由基产率，其遵循近似于SOSo > SDS的顺序SPSo > SOS;即，自由基清除效率随着N-烷基链长度的减小而增加。对于（CH 3）-C-观察到类似的趋势。在n-烷基APS表面活性剂的同源系列的超声分解之后的产率。结果表明，某些非挥发性表面活性剂的吉布斯表面过量与水溶液中超声分解后的分解程度无关。相反，表面活性剂的分解取决于它们的化学结构和它们在本体溶液和空化气泡的气体/溶液界面之间平衡的能力。
The surfactant properties of solutes play an important role in the sonochemistry and sonoluminescence of aqueous solutions. Recently, it has been shown, for relatively low molecular weight surfactants, that these effects can be correlated with the Gibbs surface excess of the solute. In the present study we investigate whether this correlation is valid for relatively high molecular weight surfactants and the mechanisms of surfactant decomposition during sonolysis. Sonolysis of argon-saturated aqueous solutions of nonvolatile surfactants [n-alkanesulfonates, n-alkyl sulfates, n-alkylammoniopropanesulfonates (APS), and poly(oxyethylenes) (POE)] was investigated by EPR and spin-trapping with 3,5-dibromo-4-nitrosobenzenesulfonate. Secondary carbon radicals (-(CH)-C-.-), formed by abstraction reactions, were observed for all surfactants that were sonicated. The yield of primary carbon (-(CH2)-C-.) and methyl ((CH3)-C-.) radicals that are formed by pyrolysis is greatest for the zwitterionic (i.e., APS) and nonionic surfactants (i.e., POE). The yield of (-(CH)-C-.-) radicals was measured following sonolysis of n-alkyl anionic surfactants [sodium pentanesulfonate (SPSo), sodium octanesulfonate (SOSo), sodium octyl sulfate (SOS), and sodium dodecyl sulfate (SDS)]. In the concentration range of 0-0.3 mM, the -(CH)-C-.- radical yield increases in the order SDS approximate to SOS approximate to SOSo > SPSo. At higher concentrations, a plateau in the maximum (-(CH)-C-.-) radical yield is reached for each surfactant, which follows the order SPSo > SOS approximate to SOSo > SDS; i.e., the radical scavenging efficiency increases with decreasing n-alkyl chain length. A similar trend was observed for the (CH3)-C-. yield following sonolysis of a homologous series of n-alkyl APS surfactants. The results show that the Gibbs surface excess of certain nonvolatile surfactants does not correlate with the extent of decomposition following sonolysis in aqueous solutions. Instead, the decomposition of surfactants depends on their chemical structure and their ability to equilibrate between the bulk solution and the gas/solution interface of cavitation bubbles.