Webinar

Lipids, which are generally charged or zwitterionic, serve as the fundamental structural scaffold for model cell membranes. The structural and dynamical characteristics of the biological membranes are affected by inter- and intra-electrostatic interactions, which change as a function of electrolyte concentration in the surrounding aqueous media. Model lipid membranes have also been exploited for investigating nanoparticle-membranes for biomedical applications. In this study, using Langmuir-Blodgett technique, we performed insitu experiments at the air-water interface to investigate the interaction between nanoclays and a mixture of zwitterionic/cationic lipids and its influence on the structural and viscoelastic properties of the composite layer. The surface pressure-mean molecular area isotherm curve reveals an increase in the lift-off area for lipid-nanoclay hybrid layer compared to neat lipid layer suggesting nanoparticle adsorption at the lipid layer via electrostatic interaction between nanoclay-lipid molecules. The stress response of the interfacial layer decays exponentially and the stress-response changes drastically as a function of interfacial charge concentration. The ex-situ structure of the composite films was characterized using an atomic force microscope measurement which reveals nanoclays bind to cationic head groups of lipids and increase the average mean molecular area and the thickness of the mixed composite layer.

Using barrier oscillation measurements, we measured frequency-independent response for the elastic and loss modulus for the neat lipid layer. All the systems, the neat lipid, and hybrid (lipid-nanoclay) layer form a solid film at the interface. The power-law analysis of frequencydependent dynamic viscoelastic responses of the interfacial films points out to a transition from glass-like to gel-like behavior for the interfacial layer in the presence of nanoclay particles in the sub-phase relative to the neat lipid layer. The formation of the extended gel network at the interface is confirmed from the change in power exponent of the viscoelastic moduli relative and also complemented from ex-situ GISAXS analysis.