Surface Modification of Membranes

Fig. 1 shows the increase of nitrite band near 780 cm- for various alcohol contents in ethylene-vinyl alcohol copolymers. The analysis of the hydroxyl region of the IR spectra (not shown) indicated that the reaction was not quantitative (residual OH band). The precise analysis of this band ( 34(X) 70 I / mol. cm) as w ell as the nitrite band (e780 639 I / mol. cm) allows to evaluate the reaction yield considering the total film thickness (Transmission 1R). The values decrease when the OH content increases (0.75 0.62 0.59 ans 0.59 for vinyl alcohol contents 2.6,4.9, 7.7 and 10.1% respectively). Complementary analysis by reflexion IR (HATR) showed that the first 5-8 pm (Germanium crystal) were fully transformed while the analysis of the first 20-25 pm (Zinc Selenide crystal) revealed a decrease of the yield from 1 to 0.5 when the alcohol content was increasing. Then, this treatment can be helpfull for surface modification of membranes. 

Other research groups also performed surface modification of membranes for MD. The following is a brief summary of their efforts. 

Fig. 9 Surface modification of cells with ssDNA-PEG-lipid. (a) Real-time monitoring of PEG-lipid incorporation into a supported lipid membrane by SPR. (r) A suspension of small unilamellar vesicles (SUV) of egg yolk lecithin (70 pg/mL) was applied to a CH3-SAM surface. A PEG-lipid solution (100 pg/mL) was then applied, (ii) Three types of PEG-lipids were compared PEG-DMPE (C14), PEG-DPPE (C16), and PEG-DSPE (C18) with acyl chains of 14, 16, and 18 carbons, respectively, (b) Confocal laser scanning microscopic image of an CCRF-CEM cell displays immobilized FITC-oligo(dA)2o hybridized to membrane-incorporated oligo(dT)20-PEG-lipid. (c) SPR sensorigrams of interaction between oligo(dA)2o-urokinase and the oligo (dT)2o-PEG-lipid incorporated into the cell surface, (i) BSA solution was applied to block nonspecific sites on the oligo(dT)20-incorporated substrate, (ii) Oligo(dA)20-urokinase (solid line) or oligo(dT)20-urokinase (dotted line) was applied...

Another approach to enhance separation performance of membrane for dehydration of isopropanol is the modification of PVA membranes in gaseous plasma [30], The modification of membrane properties in nitrogen plasma environment lead to increase in selectivity by about 1477 at 25 °C such increase in the selectivity is justified by an increase of cross-linking on membrane surface provoked by plasma treatment. 

Shimizu, Y., T. Yazawa, H. Yanagisawa and K. Eguchi. 1987. Surface modification of alumina membranes for membrane bioreactor. Yogyo Kyokaishi 95 1067-72. 

This work concerns mainly the modification of commercial polymers bearing hydroxy fonctions as alcohol, hydroperoxide or carboxylic acid, by reactive gases or liquid volatil compounds capable to penetrate in the polymer matrix. The modifications of membranes properties as gas permeability or surface tension will also be reported. Few examples will also concern the reaction of double bond with 12 and HBr vapor as well as the oxidation of piperidine group by peracetic acid. 

Grebenyuk, V.D., Chebotareva, R.D., Peters, S., andLinkov, V. 1998. Surface modification of anion-exchange electrodialysis membranes to enhance anti-fouling characteristics. Desalination 115,... 

M. Langsam, M. Anand and E.J. Karwacki, Substituted Propyne Polymers I. Chemical Surface Modification of Poly [ 1 -(trimethylsilyl)propyne] for Gas Separation Membranes, Gas Sep. Purif. 2, 162 (1988). 

In a similar way, a well-adhered surface modification of BC fibers can be achieved with Ti(>2 nanoparticles (with a diameter of about 10 nm) by the hydrolysis of titanium tetraisopropanolate adsorbed onto the fibers. It was observed that the titania-coated surface appears to be dense and have low porosity and to consist of near-spherical grains. By washing with sodium carbonate solution, the TiC>2 films were not removed during neutralization. It seems that the particles have formed strong interactions with BC. The coated membranes showed substantial bactericidal properties under UV radiation and white light (containing a small fraction of UV) conditions, too. This effect is caused by the photocatalytic destruction of the bacterial cells. 

In addition to fluid dynamics, surface modification of the membrane can reduce the attractive forces or even create repulsive ones between potential fouling solutes and the membrane (Belfort, Davis, and Zydney, 1994). 

Graft copolymers combine the properties of their polymeric constituents and as such are polymer alloys, which open a vast field of new polymeric species. This is why active research along these lines is performed in many academic and industrial research laboratories all over the world. However, only few applications have reached a commercial level today. They involve the production of specific polymeric adhesives, perm-selective membranes, bio-medical devices and the surface modification of certain products. 

Luminous chemical vapor deposition (LCVD) and luminous gas treatment (LGT), which does not yield the primary deposition, could be used in the preparation and modification of membrane and barrier [1]. The term primary deposition refers to the direct deposition of material from the luminous gas (LCVD) in contrast to secondary deposition that results from the deposition of ablated material in LGT. It should be emphasized, however, that both methods are nanofilm technologies and require the substrate membrane on which LCVD nanofilm is deposited or the surface is modified. Accordingly, their use should be limited to special cases where such a nanofilm could be incorporated into membrane or the LGT of surface is warranted. 

Hirotsugu Yasuda is Professor Emeritus of Chemical Engineering and Director of the Center for Surface Science and Plasma Technology, University of Missouri-Columbia. He has over. 300 publications in refereed journals and books and was a pioneer in the exploration of low-pressure plasma for surface modification of materials and deposition of nanofilms as barrier and permselective membranes in the late 1960s. He received the Ph.D. degree in physical and polymer chemistry from the State University of New York, College of Environmental Science and Forestry, Syracuse. 

Beeskow TC, Kusharyoto W, Anspach FB, and Kroner KH. Surface modification of microporous polyamide membranes with hydroxyethyl cellulose and their application as affinity membranes. J. Chromatogr. A 1995 715 49-65. 

Kusakahe K, Shihao F, Zhao G, Sotowa K-I, Watanabe K, and Saito T. Surface modification of silica membranes in a tubular type module. J. Membr. Sci. 2003 215 321-326. 

Peters S. Surface modification of electro-dialysis membranes to enhance anti-fouling characteristics. PhD dissertation. University of the Western Cape, Cape Town, South Africa, 2000. 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

Belfort, G. and Ulbricht, M., Surface modification of ultrafiltration membranes by low temperature plasma. I. Treatment of polyacrylonitrile, J. Appl. Polym. Sci., 56, 325, 1995. 

Belfer, S. et al., Surface modification of commercial composite polyamide reverse osmosis membranes, J. Membr. Sci., 139, 175, 1998. 

Belfer, S., Purinson, Y., and Kedem, O., Surface modification of commercial polyamide reverse osmosis membranes by radical grafting An ATR-FT-IR study, Acta Polym., 49, 574, 1998. 

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