INTERPOL

The goals of this project are to study the self-assembly of polymer multi-layers at the oil-water interface and to produce polymeric capsules based on such multi-layers assembled on an oily core using microfluidic techniques. A large part of this project will be devoted to the characterization of the mechanical properties of the polymer layers because these are key parameters for the final properties of the capsules such as their stability and release ability. We will study multi-layers of oppositely charged polyelectrolytes which assembly is driven by electrostatic interactions. The first polymer adsorbing at the oil-water interface has to be amphiphilic: we will use hydrophobically modified polyelectrolytes that will be synthesized in the laboratory. For the subsequent layers, we will first study model systems of oppositely charged polyelectrolytes, such as PDADMAC (polydiallyl dimethyl ammonium chloride) and PSS (polystyrene sulfonate) which have been well studied at solid-liquid interfaces. To study the influence of the polymer hydrophobicity on the properties of the multi-layers, we will also synthesize hydrophobically modified polyelectrolytes of various hydrophobicities. In the first task we will investigate the building of the polymer multi-layers at the oil-water interface by surface tension measurements, ellipsometry and also by PM-IRRAS (Polarization-Modulated Infra-Red Reflection Absorption Spectroscopy). This technique, which is based on infra-red spectroscopy in reflexion, is sensitive to the degree of hydration of adsorbed layers at liquid interfaces. We expect that the hydration of the layers is a key parameter to understand the mechanical properties of the layers and it should depend on the hydrophobicity of the polymer molecules. In the second task, we will characterize the mechanical properties of the adsorbed multi-layers by adapting techniques of interfacial rheology in model geometries. The technical and scientific challenge is to be able to follow the transition from a liquid interface at low number of layers to a very rigid and solid interface, almost an elastic shell. We will adapt the pendant drop method which enables to measure the compression elasticity of the layers by oscillating a pendant drop of oil in water and measuring its shape or internal pressure. Moreover to measure the shear surface elasticity of the layers we will rotate a ring positioned at the oil-water interface and mounted on a classical rheometer to apply and measure the interfacial stress and deformation. We will study the frequency response of the layers as a function of the number of adsorbed layers and physico-chemical nature of the polymers and oils. The goal of the third task is to design microfluidics devices to produce capsules based on the same polymer multi-layers assembled on oil droplets studied in the previous tasks. The oil droplets in water will be produced in a micro-channel and forced to flow through successive zones of the chips containing polymers of alternating charges to build the capsules. We will also characterize the mechanical properties of the capsules by passing through constrictions and measuring the droplets deformation.