Which surfactants reduce surface tension faster? A scaling argument for diffusion-controlled adsorption
Which surfactants reduce surface tension faster? A scaling argument for diffusion-controlled adsorption
复制标题
DOI：
10.1016/s0001-8686(99)00027-5
复制
发表时间：
2000-02-01
影响因子：
15.6
通讯作者：
Stebe, KJ
中科院分区：
文献类型：
--
作者：
Ferri, JK;Stebe, KJ
考虑表面活性剂从无限溶液吸附到新形成的平面界面的例子。在这个问题中有一个隐含的长度尺度，即吸附深度h，它是耗尽以提供具有吸附的表面活性剂的界面的深度。根据质量平衡，h可以表示为平衡表面浓度γ（eq）与本体浓度C成比例的比率。扩散到界面的特征时间尺度为τ（D）= h（2）/D，其中D是表面活性剂在溶液中的扩散率。这个时间尺度的意义证明了通过数值积分的扩散控制吸附到一个平面界面的方程。表面张力在1-10倍τ（D）内平衡，与本体浓度无关，即使对于具有强相互作用的表面活性剂也是如此。用悬泡法测得的动态表面张力数据用τ（D）重新标度以标度时间。对于足够高的本体浓度，重新归一化的表面张力演变几乎叠加，表明τ（D）确实是该过程的相关时间尺度。比较了各种表面活性剂的表面张力演变。具有最小tau（D）值的那些平衡最快。由于扩散系数变化很小，表面活性剂的大小相似，不同的表面活性剂溶液的平衡时间的差异可以归因于它们不同的吸附深度。这些深度由平衡吸附等温线确定，允许从平衡表面张力数据先验地计算τ（D），并且表面活性剂溶液根据其将更快速地降低表面张力而被分类。最后，预测的趋势τ（D），以衡量什么样的表面活性剂的性能所需的快速表面张力降低进行了讨论。这些趋势被证明是在协议的指导原则，已建议从以前的结构-性能研究。(C)2000 Elsevier Science B. V.保留所有权利。
Consider the example of surfactant adsorbing from an infinite:solution to a freshly formed planar interface. There is an implicit length scale in this problem, the adsorption depth h, which is the depth depleted to supply the interface with the adsorbed surfactant. From a mass balance, h can be shown to be the ratio of the equilibrium surface concentration Gamma(eq) to the bulk concentration C-proportional to. The characteristic time scale: for diffusion to the interface is tau(D) = h(2)/D, where D is the diffusivity of the surfactant in solution. The significance of this time scale is demonstrated by numerically integrating the equations governing diffusion-controlled adsorption to a planar interface. The surface tension equilibrates within 1-10 times tau(D) regardless of bulk concentration, even for surfactants with strong interactions. Dynamic surface tension data obtained by pendant bubble method are rescaled using tau(D) to scale time. For high enough bulk concentrations, the re-normalized surface tension evolutions nearly superpose, demonstrating that tau(D) is indeed the relevant time scale for this process. Surface tension evolutions for a variety of surfactants are compared. Those with the smallest values for tau(D) equilibrate fastest. Since diffusion coefficients vary only weakly for surfactants of similar size, the differences in the equilibration times for various surfactant solutions can be attributed to their differing adsorption depths. These depths are determined by the equilibrium adsorption isotherms, allowing tau(D), to be calculated a priori from equilibrium surface tension data, and surfactant solutions to be sorted in terms of which will reduce the surface tension more rapidly. Finally, trends predicted by tau(D) to gauge what surfactant properties are required for rapid surface tension reduction are discussed. These trends are shown to be in agreement with guiding principles that have been suggested from prior structure-property studies. (C) 2000 Elsevier Science B.V. All rights reserved.