Recent Developments in Models and Experimental Methods for Dilational Rheology of Mixed Particle-Surfactant Interfacial Layers

Investigating adsorption and dilational properties at liquid-fluid interfaces is relevant for a vast number of natural processes and technological applications. Among them, most important are systems involving composite interfacial layers containing, for example, mixture of different surface active compounds and/or solid nanoparticles. The study of dilational rheology, especially for composite systems, has been proven to be one of the most effective tool to obtain qualitative and quantitative information about the structural features and the kinetic processes in interfacial layers [1]. To exploit the high potentialities of this kind of investigation it is important, from one side, to rely on experimental methods for an accurate measurement of the interfacial viscoelasticity and, on the other side, the development of theoretical models allowing for the extraction of the maximum of information on the mechanisms at the bases of the dynamic features of the interfacial layers. From the experimental point of view, during last years methodologies based on the analysis of the interfacial tension response to controlled harmonic oscillations of the interfacial area of bubbles and drops have been developed [2] which allows for the characterisation of the rheological properties of the interfacial layer in a quite broad range of characteristic time. These methods have been applied to several surfactant systems containing nanoparticles as well. Classical theoretical models for dilational rheology have been used for the interpretation of the experimental data and some times especially for composite monolayers extension of them were required. Aim of this contribution is to give an overview of recent results in the field of dilational rheology of mixed surfactant - nanoparticle layer obtained by using new interpretative approaches. Some recent results in the field of the theoretical models for dilational rheology will be presented, especially developed to interpret the dilational viscoelasticity of mixed surfactant-nanoparticle interfacial layers. References 1. Miller, R.; Liggieri, L., Interfacial Rheology, Brill, 2009. 2. Ravera F., Loglio G., Kovalchuk V.I, Current Opinion in Colloid & Interface Science 15 (2010) 217-228