Polymers zeolite/polymer interface

To improve the adhesion and interaction in the zeolite/polymer interface, the surface of the zeolites can also be sized (or primed ) by coating the zeolite with an ultrathin layer of the matrix polymer or a different polymer. Sizing of the zeolite particles prior to dispersion in the polymer matrix reduced the stress at the... 

Organosilane coupling agents have been widely used to improve the adhesion at the zeolite/polymer interface of the mixed-matrix membranes ]62, 63, 65, 70]. 

Most reported zeolite/polymer mixed-matrix membranes, however, have issues of aggregation of the zeolite particles in the polymer matrix and poor adhesion at the interface of zeolite particles and the polymer matrix. These issues resulted in mixed-matrix membranes with poor mechanical and processing properties and poor separation performance. Poor compatibility and poor adhesion between the polymer matrix and the zeolite particles in the mixed-matrix membranes resulted in voids and defects around the zeolite particles that are larger than the micropores of the zeolites. Mixed-matrix membranes with these voids and defects exhibited selectivity similar to or even lower than that of the continuous polymer matrix and could not match that predicted by Maxwell model [59, 60]. 

Most recently, significant research efforts have been focused on materials compatibility and adhesion at the zeoHte/polymer interface of the mixed-matrix membranes in order to achieve enhanced separation property relative to their corresponding polymer membranes. Modification of the surface of the zeolite particles or modification of the polymer chains to improve the interfacial adhesion provide new opportunity for making successful zeolite/polymer mixed-matrix membranes with significantly improved separation performance. 

Jiang, L.Y., Chung, T.S., and Kulprathipanja, S. (2006) A novel approach to fabricate mixed matrix hollow fibers with superior intimate polymer/zeolite interface for gas separation. AIChE/., 52, 2898-2908. 

The size-exclusion and ion-exchange properties of zeolites have been exploited to cause electroactive species to align at a zeolite—water interface (233—235). The zeolite thus acts as a template for the self-organization of electron transfer (ET) chains that may find function as biomimetic photosynthetic systems, current rectifiers, and photodiodes. An example is the three subunit ET chain comprising Fe(CN )g anion (which is charge-excluded from the anionic zeolite pore structure), Os( bipyridine (which is an interfacial cation due to size exclusion of the bipyridine ligand), and an intrazeolite cation (trimethylamino)methylferrocene+ (F+ ). A cationic polymer bound to the (CN)6 anion holds the self-assembled structure at an... 

The first known article concerning mixed-matrix membranes was published in 1960 by Barter and James. It examined several different zeolites dispersed in an inert polymer resin to create ion exchange membranes." " Voids were noted at the interface of the two media (i.e., where polymer and sieve meet). These voids resulted in a degradation of mixed-matrix performance. Today, researchers still struggle with material compatibility issues that exist at the solid-polymer interface, as well as other nonideal morphologies introduced by the solid-polymer mixed-matrix technology. ... 

A number of polymers have been embedded with zeolites to form mixed-matrix membranes however, like Barrer, many researchers note poor adhesion at the solid-polymer interface. The use of silane coupling agents to chemically link polymer to the zeolite particles, membrane formation under high-temperature conditions, and membrane annealing are common tools used to heal a poorly adhered, sieve-in-a-cage, interface. ... 

Polyvinyl acetate (PVAc) is another rubbery polymer used in mixed-matrix research. Its flexible nature helps to prevent void formation at the solid-polymer interface. Although it may not have practical industrial applications, PVAc aids in developing proof-of-concept associated with mixed-matrix membranes. Zeolite 4A-PVAc membranes have been proven to enhance membrane selectivity in mixed-matrix membranes with only 15 vol% zeolite " however, the permeability is lower than predicted presumably due to matrix rigidification. The rubbery nature of PVAc allows for more polymer relaxation at the solid-polymer interface as compared to the case with traditional, glassy polymers." ... 

Poly (vinyl alcohol) (PVA) has also been applied to alcohol-water pervaporation. ZSM-5 was again utilized, and mixed-matrix enhancements resulted. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water-isopropyl alcohol separation. Membrane swelling and fluxes increase as the water concentration in the feed increases. " Sorption studies of ZSM-5/PVA systems indicate that this hybrid material is a good candidate for the extraction of water from alcohol. Modified poly (vinyl chloride) embedded with NaA zeolite has demonstrated both flux and selectivity enhancements for the ethanol-water separation at high zeolite loadings. Voids at the solid-polymer interface prevented seleetivity enhaneement at low zeolite loadings. ... 

One of the first zeolite based membranes were composite membranes, obtained by dispersion of zeolite crystals in dense polymeric films in order to make zeolite filled polymeric membranes [59,60,61], These membranes have been developed at the end of the 80 s for both gas separation and pervaporation. The clogging of zeolite pores by the matrix and the quality of the interface between the zeolite crystals and the polymer matrix (non-selective diffusion pathways) were key points. 

For structuring, the IL has to be immobilised. This can be done using i.e. zeolitic structures or molecular sieves. It is obvious that with increasing surface area of the solid phase, the motion of the liquid and the proton transport will be hindered. From polymerisation experiments it is known that the stiffening of polymers by cross-linking can be compared with the polymer-surface interaction. Electrode surfaces and solids such as silica, carbon black or cathode powder also stiffen the polymer [52]. This can be explained by different transport properties at the interfaces. As a consequence it must be expected that at the surface of the added particles the ionic liquid will behave in a different way than in the immobilised liquid phase. 

Co-catalysis by Zeolite Water. The initial catalytic effect of water (F. 5) declines at about ca., 5% by weight (g/g of dry zeolite). This behaviour implies that polymerization on the water free catalyst occurs both at the polymer-catalyst interface and at sites within the crystal. Intracrystalhne sites are 1 acce ble and consequently less effective than those at the surface. With increase in the amount of... 

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