Surface rheology: macro- and microrheology of poly(tert-butyl acrylate) monolayers
Surface rheology: macro- and microrheology of poly(tert-butyl acrylate) monolayers
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DOI：
10.1039/c1sm05225j
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Ortega, Francisco
中科院分区：
文献类型：
--
作者：
Maestro, Armando;Bonales, Laura J.;Ortega, Francisco
通过跟踪不同粒径和表面化学性质的示踪粒子在空气/水界面上的布朗运动，研究了聚（丙烯酸叔丁酯）Langmuir单分子膜在空气/水界面上的表面剪切粘弹性。表面剪切模量已被提取的颗粒均方位移（MSD），使用不同的方法：流体动力学计算的阻力系数和直接反演的MSD通过广义斯托克斯-爱因斯坦方程。已经发现，这些不同的理论方法导致剪切界面粘度的可比值独立的聚合物浓度和分子量。此外，未检测到探针的大小或化学性质的影响。结果已经证明了所使用的微流变技术的一致性，并且证实了PtBA单层中缠结的存在，如最近从扩张弹性和粘度测量中推断的，[ Maestro等人，Soft Matter，2010，6，4407]。一个意想不到的结果是，从微观流变学获得的界面粘度值已被发现是几个数量级低于与宏观界面剪切流变仪获得的。目前还没有明确的解释这种分歧，虽然它是无关的探针大小或其化学性质。此外，这种差异与所使用的分析方法无关，包括当探针尺寸范围内存在不均匀性时，3D微观流变学中使用的两点相关函数的计算。
We have studied the surface shear viscoelasticity of poly(tert-butyl-acrylate) Langmuir monolayers spread at the air/water interface, by tracking the Brownian motion of tracer particles with different sizes and surface chemical nature, trapped at the same interface. Surface shear moduli have been extracted from the particles mean square displacements (MSD), using different approaches: hydrodynamic calculations of drag coefficients and direct inversion of the MSD by means of the generalized Stokes-Einstein equation. It has been found that these different theoretical approaches lead to comparable values of the shear interfacial viscosity independent of the polymer concentration and molecular weight. In addition, no effect of the size or chemical nature of the probe has been detected. The results have demonstrated the consistency of the microrheological techniques used, and confirm the existence of entanglements in PtBA monolayers, as recently deduced from dilational elasticity and viscosity measurements, [ Maestro et al., Soft Matter, 2010, 6, 4407]. An unexpected result was that the interfacial viscosity values obtained from microrheology have been found to be several orders of magnitude lower than the ones obtained with macroscopic interfacial shear rheometers. At the moment there is no clear explanation for this disagreement, although it is not related to the probe size or their chemical nature. Furthermore, this discrepancy is not related to the analysis methodology used, including the calculation of the two-point correlation function used in 3D microrheology when there are heterogeneities present within the range of the probe size.