Schönhoff M, Söderman O
Chemical Center, University of Lund, Sweden.
Magn Reson Imaging. 1998 Jun-Jul;16(5-6):683-5. doi: 10.1016/s0730-725x(98)00023-x.
Surfactant adsorption layers on polystyrene latex particles are investigated concerning their equilibrium exchange dynamics with surfactant molecules in solution. Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) self-diffusion measurements of the nonionic surfactant C12(EO)5 are performed, making use of the difference of the diffusion coefficients of adsorbed and free surfactant in solution. On variation of the gradient pulse spacing the echo decay data show a transition from fast to slow exchange, giving the possibility of a quantitative evaluation. A two-site model is applied to fit the data and obtain average residence times of the surfactant in both sites. The results are consistent with diffusion-controlled adsorption of surfactant monomers and additional micellar contributions to the exchange, whereas no evidence for kinetic barriers is found for these nonionic surfactants on the relevant timescale (10 ms).
研究了聚苯乙烯胶乳颗粒上的表面活性剂吸附层与溶液中表面活性剂分子的平衡交换动力学。利用溶液中吸附态和游离态表面活性剂扩散系数的差异，对非离子表面活性剂C12(EO)5进行了脉冲场梯度(PFG)核磁共振(NMR)自扩散测量。随着梯度脉冲间隔的变化，回波衰减数据显示出从快速交换到慢速交换的转变，从而提供了定量评估的可能性。应用双位点模型对数据进行拟合，得到表面活性剂在两个位点的平均停留时间。结果与表面活性剂单体的扩散控制吸附以及交换过程中胶束的额外贡献一致，而在相关时间尺度(10 ms)上未发现这些非离子表面活性剂存在动力学障碍的证据。
