Microphase membranes

Krause S (1987) Partial solubility parameter characterization of interpenetrating microphase membranes. In Lloyd DR (ed), Material science of synthetic membranes, ACS Symposium Series 269, Washington DC, p 351... 

Partial Solubility Parameter Characterization of Interpenetrating Microphase Membranes... 

Schematic representation of microphase separation in Nafion and SPEEKK. (From Kreuer, K. D. 2001. Journal of Membrane Science 185 29-39.)...

Dais membranes are reported to be much less expensive to produce than Nation they are also reported to exhibit a rich array of microphase-separated morphologies because of the ability to tailor the block length and composition of the unsulfonated starting polymer. The main drawback of employing hydrocarbon-based materials is their much... 

We note that earlier research focused on the similarities of defect interaction and their motion in block copolymers and thermotropic nematics or smectics [181, 182], Thermotropic liquid crystals, however, are one-component homogeneous systems and are characterized by a non-conserved orientational order parameter. In contrast, in block copolymers the local concentration difference between two components is essentially conserved. In this respect, the microphase-separated structures in block copolymers are anticipated to have close similarities to lyotropic systems, which are composed of a polar medium (water) and a non-polar medium (surfactant structure). The phases of the lyotropic systems (such as lamella, cylinder, or micellar phases) are determined by the surfactant concentration. Similarly to lyotropic phases, the morphology in block copolymers is ascertained by the volume fraction of the components and their interaction. Therefore, in lyotropic systems and in block copolymers, the dynamics and annihilation of structural defects require a change in the local concentration difference between components as well as a change in the orientational order. Consequently, if single defect transformations could be monitored in real time and space, block copolymers could be considered as suitable model systems for studying transport mechanisms and phase transitions in 2D fluid materials such as membranes [183], lyotropic liquid crystals [184], and microemulsions [185],... 

Needless to say, the best established architecture which can be designed by the macromonomer technique has been that of graft copolymers. With this technique we now have easy access to a variety of multiphased or microphase-separated copolymer systems. This expanded their applications into a wide area including polymer alloys, surface modification, membranes, coatings, etc. [5]. 

Next, an example of CG-KMC from pattern formation on surfaces is presented. Another application to relatively thick membranes was given in Snyder et al. (2004). In the example considered here, atoms adsorb from a fluid reservoir on a flat surface. Subsequently, they may desorb back to the fluid, diffuse on the surface, or be annihilated by a first-order surface reaction, as shown in Fig. 11a. Attractive interactions between atoms trigger a phase transition from a dilute phase (a low coverage) to a dense phase (a high coverage) (Vlachos et al., 1991), analogous to van der Waals loops of fluid vapor coexistence. Surface reactions limit the extent of phase separation the competition between microphase separation and reaction leads to nanoscopic patterns by self-organization under certain conditions (Hildebrand et al., 1998). 

Kamide, K., Manabe, S. Material Science of Synthetic Membranes Role of Microphase Separation Phenomena in the Formation of Porous Polymeric Membrane , Loyed, D. R. ed., ACS Symposium Series 269, ACS, Washington D.C., 1985, Chp. 9, pl97... 

Fig. 22. Chemical structure of Nafion11 and schematic illustration for microphase separation in Nafion " membrane.

As commonly used, the term viscosity refers to isotropic systems of macroscopic dimensions. The term microviscosity is often used to describe the corresponding properties of the microphases in micelles, vesicles and membranes, despite the fact that this property can be highly anisotropic in these environments. Although am-... 

These examples should serve to underscore the difficulty in predicting the effects that interfacial potentials, membrane structure and microphase organization will have on electron-transfer reactions across the membrane interface and within the bilayer itself. The principles involved are common to micelles and vesicles, but the more anisotropic and highly ordered vesicles provide a more complex reaction environment for solubilized or adsorbed reactants. 

Terada T, Hohjoh T, Yoshimasu S, Ikemi IM, and Shinohara T. Separation of benzene/cyclohexane azeotropic mixture through polymeric membranes with microphase separated structures. Polym J 1982 14(5) 347-353. 

Figure 3. Two models describing the microphases of swollen Nation membranes. Top Gierke s [48] suggestion of aqueous inverse spherical micelles connected by water-filled cylindrical channels. Bottom Yeager and Steck s [49] three-region model of a water/ionomer mixture without regular structure. Regions A, B and C are the hydrophobic polymer, the solvent bridges and the hydrophilic regions, respectively.

The effect of polymer morphology on membrane structure and conductance has been shown recently. In Ref. 25 hydrogen-based graft-copolymer membranes were compared in terms of morphology and performance to random copolymer membranes with the same ion content. For the hydrated grafted membranes TEM micrographs revealed a picture of a continuous phase-separated network of water-filled channels with diameters of 5 nm. In contrast to that, the random copolymer membranes exhibit a reduced tendency toward microphase separation water is... 

Role of Microphase Separation Phenomena in the Formation of Porous Polymeric Membranes... 

We can conclude the following from an Inspection of Figures 20, 21 and 22. Equation 32 gives an accurate pore size distribution function for the porous polymeric membrane prepared by the microphase separation method. The mean radius Increases and the pore size distribution broadens with S. and Pr. The reduced pore distribution N(r)S vs. r/S curve is Independent of S. but dependent on Pr. The effect of Pr on N(r) Is more remarkable than that of S. The reduced pore size distribution curves widen with an Increase In Pr. 

These five sets of observations, plus knowledge of the phenomenon of microphase separation in block copolymers leads to a model of reverse osmosis or ion exchange membranes in which the hydrophobic portions of the polymer chains have come together to form one more or less continuous microphase, while the hydrophilic portions of the polymer chains (ionic groups, -OH groups, -NH2 or > NH groups) have "dissolved" in a small amount of water to form another more or less continuous microphase when the meni>rane is swollen in water. The hydrophilic groups, in most cases, probably form clusters but not continuous microphases in the dried membranes. 

It is also useful to consider the interaction of small molecules containing hydrophilic groups as well as hydrophobic groups with the membranes and their transport through the membranes. It is likely that such molecules interact with both types of microphases within the membrane and move through the membrane more or less at the "interface" between microphases. 

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