Preparation of Nano-organized and Adaptive Polymer Surfaces – ADPOLYSURF

The success on the employment of a certain material for a targeted technical use depends to a large extent on their interfacial behaviour. Control of chemical composition (hydrophilic or hydrophobic regions), crystallinity, microdomains and morphology, roughness and topology can improve the surface properties. Representative examples where surface properties are major parameters to be controlled include friction and lubrication, wetting or cellular adhesion. Typically, untreated surfaces of industrial polymers are hydrophobic. Hydrophobic surfaces present, on the other hand important limitations in their use for instance in adhesion or coating with polar substances or for biomedical purposes where the uncontrolled protein adhesion will cause adverse biological reactions. As a consequence, surface modification techniques in order to adequate the polymer surface interactions is currently a challenge. - - Several methodologies have been reported to modify surface properties in order to adequate them to a demand. Some of them include chemical or physical treatments such as plasma or corona. Major disadvantages of these processes are the loss of functionalities after a certain time due to the surface mobility, damaging of the substrate and the poor control of the surface chemistry giving a variety of functional groups. - - An alternative in which chemists have rarely been involved concerns the use of spontaneous segregation in compatible binary blends. Surface segregation is a phenomenon common to all other materials and concerns the preferential migration of one of the components of a blend to the interface inducing the selective enrichment at the near-surface level. Therefore, surface composition may differ to a large extent from that of the bulk. This process is driven by two main contributions i.e. enthalpic and entropic forces that can operate unconnected or act both simultaneously and depend largely on the environment of exposure (air/solid or water/solid). Appropriate use of segregation phenomena is a challenging issue but, on the other side, may allow the preparation of surfaces with unprecedented behaviours and properties. Other advantages of this methodology of surface preparation include the easy control of the surface chemistry by introducing the appropriated additive quantity and functionalities in the mixture or the stability of the functions at the surface since the system obtained will be closed to the equilibrium state. - - In a first time we will use well known polymerization techniques at the LCPO i.e. controlled radical polymerization (CRP) and more precisely Atom Transfer Radical Polymerization (ATRP) to elaborate the polymer that will be use as additives. Such additives will be based on a central polystyrene structure decorated with other blocks having moieties such as fluoride, ethylene oxide or polypeptide and will be discussed later on. As a matrix, we will employ typical linear polystyrene. - - Two different concepts of surface reversibility will be employed. The first idea is related with the preparation of a polymer surface that may be able to reversibly switch between superhydrophilic to superhydrophobic states. For that target, hydrophilic (polyethylene oxide) and hydrophobic (perfluorinated) segments will be attached to the same molecule using a polystyrene spacer that will assure the compatibility with the matrix. Surface rearrangement induced by environmental changes (either dry air or water vapour) will orient the macromolecule in a different manner. In such way, since the hydrophilic segment will be revealed at the surface under annealing in a humid environment, the hydrophobic segment will be adsorbed at the surface when the treatment is done in dry air as interface. The second approach makes use of a stimuli-responsive polymer, a polypeptide that will be placed at the surface by controlling the migration process. Secondary structure of peptides can be finely-tuned in a variety of manners: solvent, ...