Peters Gerrit W M, Zdravkov Alexander N, Meijer Han E H
Dutch Polymer Institute, Materials Technology, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
J Chem Phys. 2005 Mar 8;122(10):104901. doi: 10.1063/1.1856454.
We demonstrate the influence of molecular weight and molecular weight asymmetry across an interface on the transient behavior of the interfacial tension. The interfacial tension was measured as a function of time for a range of polymer combinations with a broad range of interfacial properties using a pendant/sessile drop apparatus. The results show that neglecting mutual solubility, assumed to be a reasonable approximation in many cases, very often does not sustain. Instead, a diffuse interface layer develops in time with a corresponding transient interfacial tension. Depending on the specific combination of polymers, the transient interfacial tension is found to increase or decrease with time. The results are interpreted in terms of a recently proposed model [Shi et al., Macromolecules 37, 1591 (2004)], giving relative characteristic diffusion time scales in terms of molecular weight, molecular weight distribution, and viscosities. However, the time scales obtained from this theoretical approach do not give a conclusive trend. Using oscillatory dilatational interfacial experiments the viscoelastic behavior of these diffusive interfaces is demonstrated. The time evolution of the interfacial tension and the dilatational elasticity show the same trend as predicted by the theory of diffuse interfaces, supporting the idea that the polymer combinations under consideration indeed form diffuse interfaces. The dilatational elasticity and the dilatational viscosity show a frequency dependency that is described qualitatively by a simple Fickian diffusion model and quantitatively by a Maxwell model. The characteristic diffusion times provided by the latter show that the systems with thick interfaces (tens of microseconds and more) can be considered as slower diffusive systems compared to the systems with thinner interfaces (a few micrometers in thickness and less) can be considered as fast diffusive systems.
我们展示了界面两侧分子量和分子量不对称性对界面张力瞬态行为的影响。使用悬滴/座滴装置，针对一系列具有广泛界面性质的聚合物组合，测量了界面张力随时间的变化。结果表明，在许多情况下被认为是合理近似的忽略互溶性这一假设，往往并不成立。相反，随着时间的推移会形成一个扩散界面层，同时伴随着相应的瞬态界面张力。根据聚合物的具体组合，发现瞬态界面张力会随时间增加或减小。依据最近提出的一个模型[Shi等人，《大分子》37, 1591 (2004)]对结果进行了解释，该模型给出了与分子量、分子量分布和粘度相关的相对特征扩散时间尺度。然而，从这种理论方法获得的时间尺度并没有给出一个确凿的趋势。通过振荡拉伸界面实验，证明了这些扩散界面的粘弹性行为。界面张力和拉伸弹性的时间演化显示出与扩散界面理论预测相同的趋势，这支持了所考虑的聚合物组合确实形成扩散界面的观点。拉伸弹性和拉伸粘度表现出频率依赖性，这可以用一个简单的菲克扩散模型进行定性描述，并用一个麦克斯韦模型进行定量描述。后者提供的特征扩散时间表明，与具有较薄界面（厚度为几微米及以下）的系统可被视为快速扩散系统相比，具有厚界面（几十微秒及更长时间）的系统可被视为较慢的扩散系统。
