Porous membranes, polymeric

Through these processes dissolved substances and/or finely dispersed particles can be separated from liquids. All five technologies rely on membrane transport, the passage of solutes or solvents through thin, porous polymeric membranes. 

In this system, the pathway of drug transport is no longer straight, but tortuous. The porosity e of the membrane and the tortuosity r of the pathway must therefore also be considered. Thus for a porous polymeric membrane, Equation 4.4 is modified as follows ... 

Kamide, K., Manabe, S. Material Science of Synthetic Membranes Role of Microphase Separation Phenomena in the Formation of Porous Polymeric Membrane , Loyed, D. R. ed., ACS Symposium Series 269, ACS, Washington D.C., 1985, Chp. 9, pl97... 

Disadvantages of the known porous polymeric membrane preparation processes are that they involve additional process steps after the formation of the fiber to come to a final product. It is therefore desirable to have a more efficient preparation process. A new method to prepare structures of any geometry (Figure 3.11c through 3.1 If) and large variety of functionality... 

Enantioseparations of Amino Acids Using Apoenzymes Immobilized in a Porous Polymeric Membrane [3]... 

Lakshmi, B.B. and Martin, C.R. Enantioseparation using apoenzymes immobilized in a porous polymeric membrane. Nature 388, 758-760, 1997. 

The first three methods involve the measurement of structural-related parameters while the last one is a typical permeation-related teclmique. Both electron microscopy and AFM can provide qualitative measurement of membrane materials. Figure 7 shows the top surface of porous polymeric membrane observed by scaiming electron microscopy (SEM). The bubble point method and permeation measurement, on the other hand, provide quantitative information of membrane materials. 

Fig. 7. Visualization of top surface of a porous polymeric membrane by scanning electron microscopy (10,000x).

Role of Microphase Separation Phenomena in the Formation of Porous Polymeric Membranes... 

A theoretical approach to the formation of porous polymeric membranes is demonstrated through the phase separation phenomena of polymer solutions. 

The theory presented here for the formation of porous polymeric membranes will also be applicable to the formation of dense membranes. In the latter membrane formation, the solution at stage (b) In Figure 2 (or at most between stages (b) and (c)) Is dipped Into a nonsolvent bath and rapid coagulation and gelation occur. If this is true, the theory predicts the existence of heteogenelty on order of some tens of nanometres, even In the dense polymer membrane. 

We can conclude the following from an Inspection of Figures 20, 21 and 22. Equation 32 gives an accurate pore size distribution function for the porous polymeric membrane prepared by the microphase separation method. The mean radius Increases and the pore size distribution broadens with S. and Pr. The reduced pore distribution N(r)S vs. r/S curve is Independent of S. but dependent on Pr. The effect of Pr on N(r) Is more remarkable than that of S. The reduced pore size distribution curves widen with an Increase In Pr. 

In an SLM, the effective diffusion coefficient has to be corrected according to the morphological characteristic of the porous polymeric membrane in which the Hquid is immobilized. Therefore, the apparent diffusion coefficient is related to the coefficient in bulk membrane phase D, ... 

Membrane separation of gaseous small molecules through dense (non-porous) polymeric membranes occurs because of differences in solubility and diffusivity, while membrane performance is characterized by permeability and selectivity. The permeability of component i. Pi, is defined as the product of the diffusion and solubility coefficients (A and Si, respectively) (Eq. (9-13)). 

Disadvantages of the known porous polymeric membrane preparation processes are that they involve additional process steps after the formation of the fiber to come to a final product. It is therefore desirable to have a more efficient preparation process. A new method to prepare structures of any geometry (Figure 6.13c through f) and large variety of functionality was recently proposed [61]. The authors proposed to incorporate the functionality by dispersion of particles in a polymeric porous structure formed by phase inversion. A slurry of dissolved polymer and particulate material can be cast as a flat film or spun into a fiber and then solidified by a phase inversion process. This concept is nowadays commercialized by Mosaic Systems. The adsorber membranes prepared via this route contain particles tightly held together within a polymeric matrix of different shapes, which can be operated either in stack of microporous flat membranes or as a bundle of solid or hollow-fiber membranes. 

F.F. Stengaard (Dow) Permeable, porous, polymeric membrane with hydrophilic character, methods for preparing said membranes, and their use. EP 0257635 Bl, March 1993. 

Kamide K, Manabe S (1985) Role of microphase separation phenomena in the formation of porous polymeric membranes. In Lloyd DR (ed) Materials science of synthetic membranes. ACS Symposium Series 269. American Chemical Society, Washington, DC, p 197 Raman LP, Cheryan M, Rajagopalan N (1994) Chem Eng Prog 90 68... 

Vidaurre, E.F.C., Achete, C.A., Simao, R.A. and Habert, A.C. 2001. Surface modification of porous polymeric membranes by RF-plasma treatment. 

Gas permeation through non-porous polymeric membranes is generally described by the solution-diffusion mechanism [2], This is based on the solubility of specific gases within the membrane and their diffusion through the dense membrane matrix. In turn, the solubility of a specific gas component within a membrane is a function of its critical temperature, as this is a measure of the gas condensability. Critical temperatures for a range of gas components are provided in Table 11.2. Conversely, the diffusivity depends upon the molecular size, as generally indicated by the kinetic diameter. Indeed, Robeson et al. [9] have recently postulated that the relationship between the ideal permeability of one species P, and that of another Pj are related by a simple function ... 

Haemodialysers Replacement of deficient kidneys for blood purification Flowing blood anticoagulated with heparin Flexible polymers for tubing porous polymeric membranes modified cellulose, PAN copolymers, polysulfone... 

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