Interfacial rheology and conformations of triblock copolymers adsorbed onto the water-oil interface

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• 作者：Pablo Ramí ; rez^a ; ^{pramirez@us.es} ; Antonio Stocco^b ; ^{Antonio.Stocco@univ-montp2.fr} ; José ; Muñ ; oz^a ; Reinhard Miller^c
• 关键词：Pluronics ; Non-ionic triblock copolymer ; Interfacial rheology ; Ellipsometry ; Oil&ndash ; water interface ; Conformational transitions ; Adsorbed layer
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 期刊代码：125_00219797
• 类别：ch
• 出版时间：15 July, 2012
• 卷：378
• 期：1
• 页码：135-143
• 文件大小：953 K

摘要

The conformation and the dilatational properties of three non-ionic triblock PEO-PPO-PEO (where PEO is polyethyleneoxide and PPO is polypropyleneoxide) copolymers of different hydrophobicity and molecular weight were investigated at the water-hexane interface.

The interfacial behavior of the copolymers was studied by combining dilatational rheology using the oscillating drop method and ellipsometry.

From the dilatational rheology measurements the limiting elasticity values, E₀, of the Pluronics as function of surface pressure, 螤, and adsorption time were obtained, i.e. E₀(t) and E₀(螤). Here, it is shown that E₀(t) depends on the number of PEO units and on the bulk concentration, showing maximum and minimum surface elasticity values which indicate conformational changes in the interfacial layer.

Furthermore, in the framework of the polymer scaling law theory, conformational transitions were discussed in E₀ vs. 螤 plots. In a dilute regime (螤 < 14 mN m^鈭?) at the water-hexane interface, E₀ = 2螤 fits well all the data, which indicates a two-dimensional 鈥渟tretched chain鈥?conformation. Increasing 螤, two other interfacial transitions could take place. The different behavior of Pluronic copolymers could be also described by the local minima of E₀, which depends on the hydrophobicity of the copolymers.

Conformational transitions observed by interfacial rheology were compared to ellipsometric data. Experimental results were discussed and explained on the basis of two- and three-dimensional copolymer structure taking into account that PPO chains could be partially immersed in hexane and water.