Polymeric membranes hydrophilicity/hydrophobicity

Hydration of polymeric membranes may be influenced by the chemical identity of the polymers. A hydrophilic polymer has a higher potential to hydrate than a hydrophobic one. Sefton and Nishimura [56] studied the diffusive permeability of insulin in polyhydroxyethyl methacrylate (37.1% water), polyhydroxy-ethyl acrylate (51.8% water), polymethacrylic acid (67.5% water), and cupro-phane PT-150 membranes. They found that insulin diffusivity through polyacrylate membrane was directly related to the weight fraction of water in the membrane system under investigation (Fig. 17). 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

The nature of the supporting membrane also plays an important role in the performance of supporting ionic liquid membranes. In this context, de los Rios et al. [3] nsed two polymeric membranes, nylon and mitex, as supporting membranes. Nylon membrane was a hydrophilic polyamide membrane with a pore size of 0.45 pm and a thickness of 170 pm. Mitex membrane was a hydrophobic polytetrafluoroethylene membrane with a pore size of 10 pm and a thickness of 130 pm. It was observed that less ionic liquid was absorbed into the mitex membranes, which was explained by the different textural properties and the high hydrophobic character of these membranes, which probably restrict interaction with the hydrophilic ionic liquids used [27]. 

An important class of polymeric nanocarriers is based on nanocapsules with a polymeric membrane. As outlined earlier, in aqueous solutions, for example, of specific amphiphilic block copolymers above the CMC, self-assembly to spherical micelles takes place in the simplest case. However, depending on the polymer structure and architecture, block length, and hydrophilic/hydrophobic balance, the formation of more complex vesicular structures can also take place (see Section 5.1 Figs. 5.5a and 5.9). 

We expect that the proposed approach for the surface modification of polymeric membranes and the generation of the multilayered membrane assembUes can be straightforwardly employed as an efficient platform to fabricate breathable protective materials. The platform is highly tunable and upgradeable, since various parameters can be varied at will. First of all, membranes of different natures with different pore sizes can be employed. Second of all, various pre-modified (re)active/hydrophilic/hydrophobic membranes can be assembled together in a number of sequences. An additional advantage is the possibility of loading intermembrane space with functional micro- and nanoparticles, such as catalysts and/or adsorbents. Finally, in the assembly, protective elements are prefabricated and located at different levels and, thus, the compatibility issue can be resolved and multi-functionality can be achieved. 

A variety of membrane materials have been tested for SILM preparation, including, among others, polymeric Nylon (hydrophilic polyamide) [57] and PTFE (hydrophobic polytetrafluoroethylene) [58], PES (hydrophiHc polyethersuUbne) [59,... 

These arious techniques allow to prepare microfiltration membranes from Trtually all kinds of materials of which polymers and ceramics are the most important. Synthetic polymeric membranes can be divided in two classes, i.e. hydrophobic and hydrophilic. Various polymers which yield hydrophobic and hydrophilic membranes are listed below. Ceramic membranes are based mainly on two materials, alumina (A1203) and ziiconia (Zr02). However, other materials such as titania (TiOj) can also be used in principle. A number of organic and inorganic materials are listed below ... 

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