Tuning Phase Assembly of Block Copolymer Films for Large Strain Deformation and High-throughput Membranes
The peculiar morphologies of block copolymers (BCPs) offer an expansive platform to design and adjust specific properties, desirable for the improved functionality of their films or coatings. Due to this, they attracted substantial attention in industry and academia and found applications as thermoplastic elastomers, adhesives, filtration membranes, stretchable electronics, storage media, sensors, 3D printing filaments etc. In the first study, the tensile deformation of styrenic thermoplastic elastomer (TPE) films with glassy amorphous end blocks and ethylene-propylene elastomeric mid-block was examined. Polystyrene cylinders with lateral and vertical orientations were obtained by varying the thickness of the films and the choice of solvents. The mechanical properties of the triblock copolymer TPE films were dependent on the domain orientation and ordering which were then compared using deformation studies. Thermal based approaches were used in another study to understand the morphology of ~ 100 nm thin films of styrenic TPEs under various conditions. Low glass transition temperature (Tg) of the rubbery block of the TPE contributes significantly to its fast ordering and enables to realize highly aligned dynamic cold-zone annealed (CZA) films even when a gradient maximum (Tmax) of 130-140 0C was applied. Shearing with soft layer on thin films brings about phase separated meandering blocks with horizontally and vertically oriented domains. In a separate study, permeability of liquids through the nanopores of membranes prepared from diblock copolymeric films was measured as a function of cylinder alignment. Here also, the solution casting conditions were carefully controlled to promote the formation of vertical domain structure. In order to maximize water fluxes, plasticizing additives with up to 60 wt% concentrations were added to the polymer solution before the preparation of thin films. As the non-volatile additives migrate selectively towards the domains, increasing the plasticizer concentrations increases the pore dimensions. To withstand high transmembrane pressures in the process, 0.2-8.0 μm microporous membranes were tested as sandwich supports. Etching conditions were also varied to improve the performance of the membranes. Through various solution and thermal based approaches, the structure-property studies performed in this work investigates the interrelation between BCP morphology, mechanical properties and their membrane applications in thin and thick films.