Compression/expansion rheology of oil/water interfaces with adsorbed proteins. Comparison with the air/water surface
Compression/expansion rheology of oil/water interfaces with adsorbed proteins. Comparison with the air/water surface
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DOI：
10.1021/la060441h
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发表时间：
2006-07-04
期刊：
影响因子：
3.9
通讯作者：
Lucassen-Reynders, E. H.
中科院分区：
文献类型：
--
作者：
Benjamins, J.;Lyklema, J.;Lucassen-Reynders, E. H.
测量了四种蛋白质在三个流体界面上的动态界面张力和表面膨胀模量，作为时间和浓度的函数。这些蛋白- -酪蛋白、- -乳球蛋白、牛血清白蛋白和卵清蛋白被空气、正十四烷和三酰基甘油油从水溶液中吸附。在适用于稠油相的动态液滴张力计中，在0.005 ~ 0.5 Hz的频率范围内实现了正弦界面压缩/膨胀。通常，当界面压力高达15 mN/m时，膨胀模量在0.1 Hz的频率范围内是纯弹性的。在此弹性范围内，表面内松弛要么基本完成，要么在10秒左右的时间内尚未开始。在这段时间内，与散装溶液的蛋白质交换可以忽略不计。在表面内弛豫在规定时间内完成的情况下，模量仅取决于平衡Pi（Gamma）关系。我们用一个简单的二维溶液模型来解释这些结果，该模型基于吉布斯分曲面，考虑到熵和焓的一阶非理想混合。界面混合焓对弹性有主要影响，两者的量按三酰甘油<十四烷<空气的顺序递增。我们还认为，焓和清洁界面张力之间有很强的相关性，它们以相同的顺序增加。在每个界面上，焓随分子刚度的增加而增加：β -酪蛋白< β -乳球蛋白<牛血清白蛋白<卵清蛋白。与实验数据最一致的是最近扩展的模型，该模型考虑了蛋白质随着表面压力的增加而采用更小的分子面积。当界面压力大于15mn /m时，模量通常不再是纯弹性模量，粘性损失角可达36度。在这个高压范围内，模量取决于松弛机制，因此必须建立特定的动力学模型。
Dynamic interfacial tensions and surface dilational moduli were measured for four proteins at three fluid interfaces, as a function of time and concentration. The proteins-beta-casein, beta-lactoglobulin, bovine serum albumin, and ovalbumins were adsorbed from aqueous solution against air, n-tetradecane, and a triacylglycerol oil. The sinusoidal interfacial compression/expansion, at frequencies ranging from 0.005 to 0.5 Hz, was effected in a dynamic drop tensiometer suited to viscous oil phases. Generally, at interfacial pressures up to 15 mN/m, dilational moduli were purely elastic at frequencies from 0.1 Hz. In this elastic range, in-surface relaxation either was essentially completed or had not yet started within a time on the order of 10 s. Within this time span, protein exchange with the bulk solution was negligible. In cases where in-surface relaxation was completed in the imposed time, the moduli depended only on the equilibrium Pi(Gamma) relationship. We interpret these results in terms of a simple two-dimensional solution model, based on a Gibbs dividing surface, accounting for nonideal mixing to the first order with respect to both entropy and enthalpy. Interfacial mixing enthalpy is shown to have a major effect on the elasticity, with both quantities increasing in the sequence triacylglycerol < tetradecane < air. We also suggest a strong correlation between enthalpy and clean-interface tension that increases in the same order. At each interface, the enthalpy increases with increasing molecular rigidity: beta-casein < beta-lactoglobulin < bovine serum albumin < ovalbumin. Best agreement with the experimental data was obtained with a recently extended version of the model accounting for proteins adopting smaller molecular areas with increasing surface pressure. For interfacial pressures above 15 mN/m, the moduli were generally no longer purely elastic, with viscous loss angles ranging up to 36 degrees. In this range of high pressures, the moduli depended on relaxation mechanisms for which specific kinetic models must be developed.