Hydrophilic membrane

SW Kim, JR Cardinal, S Wisniewski, GM Zenter. Solute permeation through hydrogel membranes, hydrophilic vs. hydrophobic solutes. ACS Symp Ser 127 347-359, 1980. 

In principle, placing a hydrophilic residue in a non-aqueous environment is energetically unfavorable. In integral proteins with multiple a helices that span the membrane, hydrophilic side chains from different helical segments may interact and in some cases form a channel through which ions may diffuse. Portions of the helical segments exposed to the lipid will contain primarily hydrophobic amino acid residues. 

In contrast to small uncharged molecules that can diffuse across cell membranes, hydrophilic molecules and ions do not partition... 

Membrane emulsification is a relatively new technique with specific advantages (simplicity, potentially less energy demands, less surfactant, and narrow droplet-size distributions) compared to conventional emulsification techniques [102]. Depending on the membrane hydrophilicity/hydrophobicity and the composition of the two liquid phases, O/W, W/0, or MW emulsions may be produced. Most often used, O/W membrane emulsification consists of the pressurization of oil (dispersed phase) through membrane pores at high pressure (Figure 6.26). The oil jet flows formed in the circulating continuous phase are... 

In conclusion, 1) Hydrophilic solutes permeate p-HEMA and p-HEMA crosslinked with lower mole % EGDMA via the "pore" mechanism. The diffusion coefficients of the solutes depend on the molecular size and may utilize the "bulk-like" water in the hydrogels. As the water content of hydrogel increases, the solute permeability increases. 2) Hydrophobic solutes permeate p-HEMA and p-HEMA crosslinked with EGDMA via either the "pore" or "partition" mechanisms. Diffusion coefficients are lower than those of hydrophilic solutes however, steroids can permeate even in p-HEMA with 5.25 mole % EGDMA due to the predominant "partition" mechanism for hydrophobic solute permeation in this membrane. Hydrophilic solutes fail to permeate the high crosslinked hydrogels. 

However, there is a main concern with the addition of an amphiphilic copolymer as an additive into the membrane matrix. In certain cases, the poor compatibility between hydrophobic segment and membrane matrix may lead to bad phase separation, producing undesirable membrane properties. In view of this, the use of an amphiphilic copolymer as a membrane-forming material is attempted and has received attention from membrane researchers in recent years [13-15]. Besides enhancing membrane hydrophilicity and water permeability, the use of amphiphilic copolymer in UF m brane fabrication can also offer exceptional advantages such as tuu-able membrane structure and higher degree of compatibility. 

The molecular architecture of PEO-PPO-PEO is more favorable than PPO-PEO-PPO. The larger mass fraction of Pluronic enhanced membrane hydrophilicity. Furthermore, the longer PEO and PPO chain could significantly improve rejection performance and block stability. 

Y-AI2O3 particles were well dispersed in the membrane, and because of this, it enhanced membrane hydrophilicity. The membrane with 2% nanoparticles also has excellent fouling resistance for BS A adsorption. 

The relationship between the type of solvent, polar or nonpolar, and the type of membrane, hydrophilic or hydrophobic, used in separation processes mnst be carefully analyzed. Polar solvents have significantly higher flow (8-10 times) than nonpolar solvents in processes carried out in hydrophilic membranes. In turn, nonpolar solvents have a flow of 2-4 times greater than polar solvents in hydrophobic membranes. As examples can be cited the flnx values obtained for the permeation of methanol (polar) and hexane (non-polar) in a pressure of 13 bar, through a hydrophilic membrane, resulting in flows, respectively, 18 and 2.52 L mr h. On the other hand was observed an opposite tendency in flux for the same compound and same pressure, when the process is conducted in a hydrophobic membrane, the flows obtained were, respectively, 21.6 and 10.8 L m h to methanol and hexane [22]. 

FIGURE 1.9 Ideal gas or vapor membrane La — liquid phase A, Lb microporous membrane (hydrophilic), G — gaseous phase. 

UF of pasteurized and homogenized milk with 3.2% protein and 1.5% fat antifouling properties flux recovery, irreversible flux loss, total flux loss, and fouling resistance of modified membranes were enhanced due to an increase in membrane hydrophilicity (Rahimpour et al. 2009)... 

The interaction of the solutes with the membrane surface is normally characterized by the membrane hydrophilicity/hydrophobicity and a fixed charge using a contact angle measurement and a streaming potential, respectively. In this study, AFM was used to determine the force of adhesion between a HA-coated silica probe (illustrated in Figure 5.27) and the membrane surface. A typical force measurement... 

Wang et al. (2002) demonstrated a composite membrane (subjected to PV) of an asymmetric poly(4-methyl-l-pentene) (TPX) membrane dip-coated with poly(acrylic acid) (PAA). To improve the interface peeling of the PA A/TPX composite membranes, the surfaces of TPX membranes were modified by residual air plasma in a tubular-type reactor. The plasma treatments were effective in rendering the asymmetric TPX membrane hydrophilic. Optimal results were obtained with PAA/TPX composite membrane prepared from the PAA/ethylene glycol (EG)/aluminum nitrate = 1/2/0.05 coating solution at 5 W/30 s plasma treatment condition. Concentration of the water in the permeate was nearly 100%, and a permeate flux of 960 g/m h was obtained with a 3 wt% feed acetic acid concentration. 

A few studies have been made on PV with acidic feeds using zeolite membranes. Hydrophilic zeolites, in general, are not suitable in low pH environments because acid leaches Al from the framework. Zeolite manbranes used for low pH PV, therefore, need to have relatively high Si/Al ratios so that the framework is not destroyed when Al is removed. Stainlesssteel supports are usually used for these applications because AI2O3 supports are susceptible to degradation by acids. A Ge-ZSM-5 membrane removed acetic acid from a 5 wt % acetic acid-water mixture at 363 K with a = 14 and a 16.8 mol/m h flux (Tan et al. 2006). 

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