Nanoporous phase separation

Bilayer films of poly(ethyleneimme) (positively charged) and poly(ethylene-co-maleic acid) have been used for chemical sensing [49]. The technique of surface plasmon resonance was used to monitor, in-situ, the deposition of these films. Subsequent exposure to aqueous solutions of metal acetate (metal = copper, nickel) resulted in a shift in position of the SPR curve. Phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition have also been exploited for erasable nanoporous antireflection coatings, opening up applications for biore-sponsive materials and membrane applications [50]. 

In the phase separation approach, a polymer is solubilized and then undergoes the gelation process. Due to the physical incompatibility of the gel and the solvent, solvent is removed and the remaining structure, after freezing, is obtained in nanofibrilar form. Template synthesis implies the use of a template or mold to obtain a desired structure. Commonly metal oxide membranes with nanopores are used, where a polymer solution is forced to pass through to a nonsolvent bath, originating nanofibers, depending on the pores diameter. 

The templating strategy by BCPs has been used since the late 1980s and is extensively described by Hillmyer and collaborators [39,49]. The resulting porous materials exhibit the pore morphology of their parent structures, mainly in the range of nanopores, because of the nanophase separation morphology of the BCPs. Because the blocks are chemically linked, they can only phase separate at a nanolevel. 

Microdialysis, Figure 4 (a) Microdialysis membrane sandwiched between two etched sets of silicon microchannels with Interdigitated sensing electrodes. Image taken from [10]. (b) Schematic of optical setup for phase separation polymerization to define the microdialysis membrane. Image taken from [ ]. (o) Schematic of crossed microfluidic channels separated by a nanoporous microdialysis membrane. Image taken from [12]... 

Many experiments and molecular simulations of the freezing of fluids confined in nanoporous solids have been reported [1]. This effort is devoted to the understanding of the effect of confinement, surface forces, and reduced dimensionality on the thermodynamics of fluids. These works are also of practical interest for applications involving confined systems (lubrication in nanotechnologies, synthesis of nano-structured materials, phase separation, etc). Beside the abundant literature for pure fluids in nanopores, few studies [2-7] have focused on the freezing of confined mixtures. As in the case of pure substances, the pore width H and the ratio of the wall/fluid to the fluid/fluid interaetions (parameter a [8]), play an important role in the phase behavior of the mixture. The ratio of the wall/fluid interaction for the two species is also a key parameter in describing freezing of these systems. 

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