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Polymer Surfaces and Interfaces

Yvette Tran, Costantino Creton, Guillaume Sudre, David Martina

Interface properties play a valuable role in a wide field of industrial and biological applications as well as in academic research. They dominate bulk considerations in case of great surface-to-volume ratios. The modification of the surface of materials by coatings can improve their properties as it allows control of the interaction of the material and this environment. We study more specifically thin layers of soft polymers, from conventional rubbers to soft swollen polymer in solvent. The layers thickness can range from nanometers to microns.

Among the strategies for the formation of thin organic coatings, the chemical interaction of molecules with the surface (within reason) is mostly preferred to the physical interaction. The advantage is that the monomolecular layer or the surface–attached network is very strongly and irreversibly attached to the surface to ensure the long-term stability of the coating in problematic environments. In our group, we are developing strategies for the functionalization of surfaces with polymers to realize smart surfaces with responsive and adaptative properties. Our research combines the polymer synthesis, as well as the characterization of the structure and the mechanical properties at interface.

Decorated surfaces
Polymer chains can be grafted chemically to surfaces and hence modify the interactions with the environment

As examples of coatings, polymer brushes refer to systems in which polymer chains are attached by one of their two extremities to the surface. The surface-attached chains become crowded and are stretched away from the surface. The polymers are preferentially sensitive to the surrounding environment (solvent or others). Their properties could respond to various stimuli such as pH, temperature, light or electric field.

The chemical components of the thin layers are characterized by spectroscopy such as XPS (X-ray Photolectron Spectroscopy) or ATR-IR (Infrared spectroscopy by Attenuated Total Reflection). The structural aspects are determined by AFM (the topography of the layers) and ellipsometry (the amount of coatings). The neutron reflectivity is a powerful method we often use to study the interfacial structure. For example, owing to the isotopic contrast, we can determine the density profile of a swollen polymer layer in solvent or the interpenetration between two polymer thin layers.