Porous polymer membranes

Whereas the liquid-solid filtration processes described so far can separate particles down to a size of around 10 xm, for smaller particles that need to be separated, a porous polymer membrane can be used. This process, known as microfiltration, retains particles down to a size of around 0.05. im. A pressure difference across the membrane of 0.5 to 4 bar is used. The two most common practical arrangements are spiral wound and hollow fiber. In the spiral wound arrangement, flat membrane sheets separated by spacers for the flow of feed and filtrate are wound into a spiral and inserted in a pressure vessel. Hollow... 

The main emphasis in this chapter is on the use of membranes for separations in liquid systems. As discussed by Koros and Chern(30) and Kesting and Fritzsche(31), gas mixtures may also be separated by membranes and both porous and non-porous membranes may be used. In the former case, Knudsen flow can result in separation, though the effect is relatively small. Much better separation is achieved with non-porous polymer membranes where the transport mechanism is based on sorption and diffusion. As for reverse osmosis and pervaporation, the transport equations for gas permeation through dense polymer membranes are based on Fick s Law, material transport being a function of the partial pressure difference across the membrane. 

Figure 5.9 A supported liquid membrane (SLM) a porous polymer membrane whose pores are filled with the organic liquid and a carrier, set in between the aqueous source phase and the aqueous receiving phase, which are being gently stirred.

Figure 2.2 SEM micrograph of a microtome cross-section of a porous polymer membrane with an anisotropic structure on a nonwoven as mechanical support (reprinted from [9], with permission from Wiley-VCH, 2006).

The penetration of a solvent, usually water, into a polymeric implant initiates dmg release via a diffusion process. Diffusion of dmg molecules through non-porous polymer membranes depends on the size of the dmg molecules and the spaces available between the polymeric chains. Even through the space between the polymer chains may be smaller than the size of the dmg molecules, dmg can still diffuse through the polymer chains due to the continuous movement of polymer chains by Brownian motion. 

Microfil- tration Symmetric micro-porous polymer membrane. Pore size 0.05-10 ym Hydrostatic pressure 1-5 bar Sieving mechanism, pore si2e and particle diameter determine separation characteristics Sterile filtration, clarification, cell harvesting bacteria, viruses separation. 

Table 9-16. Plasma Modification of Porous Polymer Membranes...

Ionic liquids supported on porous polymer membranes can enhance the gas separation performance as this design improves both permeability and selectivity for a series of industrially relevant gas mixtures [27]. 

The diffusion of solutes through a porous polymer membrane under the temperature gradient is named thermal diffusion or Soret effect. Few studies deal with this phenomenon. Its importance in the transfer through membranes is often neglected compared to the other coupled mechanisms of transfer. 

Esch, M.B., Sung, J.H., Yang, J., Yu, C., Yu, J., March, J.C., and Shuler, M.L. 2012. On chip porous polymer membranes for integration of gastrointestinal tract epithehum with microfluidic body-on-a-chip devices. Biomed Microdevices, 14 895-906. 

Gas-diffusion membranes Hydrophobic porous polymer membranes with air filling the membrane pores have been used successfully in the online separation of volatile and semivolatile analytes between two miscible liquid streams in flow injection analysis (FIA) systems. The corresponding technique is frequently referred to as gas-diffusion EIA. The mass transfer of an analyte across a gas-diffusion membrane is controlled by the membrane pore size and the solubility of the analyte in the feed and receiver solutions. The latter can be manipulated by appropriately modifying the chemical composition of the two solutions. In this way it is possible to enhance both the evaporation of the analyte from the feed solution into the membrane pores and its subsequent absorption into the receiver solution. 

Membranes for dialysis and membrane-assisted liquid-liquid extraction Depending on the hydrop-hobicity of a porous polymer membrane and the solutions in contact with it, the membrane pores can be filled with the feed solution, the receiver solution, or a mixture of both solutions. If both solutions are miscible (e.g., aqueous) the separation of the analyte is based on dialysis, while if they are immiscible the separation process is often referred to as MALLE. 

ESEM provides opportunities for the detailed study of dynamic phenomena in real-time (crystallisation, corrosion, etc.). For example, ESEM allows visualisation of acrylic latex particles dispersed in water or the observation of a single water droplet condensing on a cellulose fibre. Images such as these may help to reveal local contact angles and also the heterogeneity of any surface treatment. The wetting properties of micro porous polymer membranes... 

Ito Y, Ochiai Y, Park YS et al. pH-Sensitive gating by conformational change of a polypeptide brush grafted onto a porous polymer membrane. J Am Chem Soc 1997 119 1619-1623. 

Supported liquid membrane extraction techniques employ either two or three phases, with simultaneous forward- and back-extraction in the latter configuration. The aqueous sample phase is separated from the bulk organic or an aqueous receiver phase by a porous polymer membrane, in the form of either a flat sheet or a hollow fiber that has been impregnated with the organic solvent phase. The sample phase is continuously pumped, the receiver phase may be stagnant or pumped, and the organic phase in the membrane pores is stagnant and reusable [8-10]. 

Example In template synthesis, metal ions are plated electrochemically on porous polymer membranes, which are then dissolved to leave metal nanotubes. 

The most widely used separators in LIBs were the porous polymer membranes. Such membranes were very good electronic insulators and had the capability of conducting ions either by intrinsic ionic transmission or by ion migration through the soaked electrolyte. They were able to minimize any processes that adversely affect the electrochemical energy efficiency of the batteries. Different... 

Besides phase inversion and traditional casting with solvent, electrospinning can also be used to prepare porous polymer membranes. The prepared... 

The matrices of polymers such as poly(vinyl pyrrolidone) (PVP), polysul-fone, poly(trimethylene carbonate) (PTMC), triethylene glycol diacetate-butyl propenoate copolymer [28], and cellulose [29] are different from the mentioned polymers in Sections from 11.1 to 11.5. For example, when porous polysulfone is used as the polymer carrier, the ionic conductivity (3.93 x 10 S/cm at room temperature) and mechanical performance are greatly improved after adding plasticizers. When organic electrolyte is added to PTMC, the uptake ability is greatly improved because its structure is similar to that of the organic electrolyte. Methylcellulose (MC) is prepared easily as a porous polymer membrane, as illustrated in Figure 11.34. It can absorb liquid electrolyte to become a gel polymer electrolyte whose ionic conductivity is 0.2 mS/cm and lithium-ion transference number is 0.29. These results can compare with the commercial separator [29]. 

---