Surface-modifying macromolecules SMMs

It is known that, in a polymer blend, thermodynamic incompatibility between polymers usually causes demixing of polymers. If the polymer is equilibrated in air, the polymer with the lowest surface energy (hydrophobic polymer) will concentrate at the air interface and reduce the system s interfacial tension as a consequence. The preferential adsorption of a polymer of lower surface tension at the surface was confirmed by a number of researchers for a miscible blend of two different polymers. Based on this concept, surface modifying macromolecules (SMMs) as surface-active additives were synthesized and blended into polymer solutions of polyethersulfone (PES). Depending on the hydro-phobic or hydrophilic nature of the SMM, the membrane surface becomes either more hydrophobic or more hydrophilic than the base polymeric material. ... 

Khayet, M., Suk, D.E., Narbaitz, R.M., Santerre, J.P. and Matsuura, T. 2003. Study on surface modification by surface-modifying macromolecule (SMMs) and its applications in membrane-separation processes. 9 2902-2916. 

The objectives of this chapter are to describe the fabrication of novel composite hydrophobic/hydrophilic membranes for DCMD using different surface-modifying macromolecules (SMMs) and a hydrophilic polymer polyetherimide (PEI). The membrane characteristics are related to the DCMD performance. 

Mahmud et al. (2001) studied the PV performance of PES membranes prepared by incorporating surface-modifying macromolecules (SMMs). The experimental data showed that the PES-SMMs membrane appeared to be water-selective as a significant depletion of chloroform was achieved in the permeate. 

Even though there have been various methods of SPEEK modification, there is no reported study on the surface-modifying macromolecule (SMM) approach. The next section looks at surface modification in a simpler way that is, by the addition of SMMs so that the monbrane surfaces can be modified via a single casting step. 

Khayet and Matsuura (2003a) found that the FEP values of both the modihed hydrophilic polyetherimide (PEI) membranes by surface modifying macromolecules (SMMs) and the unmodihed ones increased with the increase of the PEI concentration in... 

Other strategies for producing hydrophobic membranes for MD are the modification of hydrophilic polymers or ceramic materials. Qtaishat et al. [144] produced two different types of hydrophobic surface-modifying macromolecules (SMMs) and prepared hydrophobic/hydrophilic polyetherimide composite membranes. The SMMs blended PEI membranes achieved better DCMD fluxes than those of a commercial PTFE membrane tested under the same conditions. Similarly fluorinated SMMs were used to modify hydrophilic poly(sulfone) [145]. Krajewski et al. [146] used lH,lH,2H,2H-perfluorodecyltriethoxysilane to create a hydrophobic active layer on commercial tubular zirconia membranes supported on alumina. The produced membranes were tested in air-gap MD (AGMD). Hendren et al. [147] used 1H,1H,2H,2H-perfluorodecyltriethoxysilane, trichloromethylsilane, and trimethylchlorosilane to modify, by surface grafting, two types of alumina Anodise ceramic membranes. The authors demonstrated that this surface treatment was effective and tested the produced membranes in DCMD. 

Pluronic FI 27 = poly (ethylene oxide)-h-poly(propylene oxide)-h-poly(ethylene oxide) (PEO-PPO-PEO). SMM, surface modifying macromolecule. Type of SMM used = L2MM. 

To make the modified surface properties (hydrophilic/hydrophobic) more permanent, siuface-modifying macromolecules (SMMs) were developed. SMM has an amphi-phatic structure consisting theoretically of a main polyurethane chain terminated with two low polarity polymer chains (i.e., fluorine segments) [65]. 

Rahbari-Sisakht et al. [54] investigated the effect of novel surface modifying macromolecules (nSMMs) on the morphology and performance of PSf hollow-fiber membrane for CO2 absorption. The performance of surface-modifled membrane in contactor application for CO2 absorption through distilled water as absorbent was studied. The results show that surface-modified membrane had higher performance compared to plain polysulfone membranes. With the membrane prepared from SMM in the spinning dope, a maximum CO2 flux of 5.8 X 10 mol/m s was achieved at 300 ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% after 50 h of operation of the surface-modified membrane. 

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