Through polymers

Vieth W R 1991 Diffusion In and Through Polymers (Munich Flanser) p 1... 

The more permeable component is called the. st ga.s, so it is the one enriched in the permeate stream. Permeability through polymers is the product of solubihty and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 22-23 after Breck, Zeolite Molecular Sieves, Wiley, NY, 1974, p. 636). 

The diffusion of oxygen through polymer films has been examined by a number of workers. Guruviah measured the permeability to oxygen of films cast from five paints (Tabic 14.4) and compared the results with the... 

Fig. 20a-c. Equatorial sections through polymer dispersed Gay-Berne liquid crystal droplets of various radii at high T = 3.0) (left) and low T = 0.6) (right) scaled temperatures for droplets with scaled radii of a 7.1 b 10.0 c 20.0... 

The ability of nanoclay incorporation to reduce solvent transmission through polymers such as polyamides has been demonstrated. Data provided by de Bievre and Nakamura [203] of UBE Industries reveal significant reductions in fuel transmission through poIyamide-6/66 polymers by incorporation of a nanoclay hller. As a result, considerable interest is now being shown in these materials as both fuel tank and fuel line components for cars. Of further interest, the reduced fuel transmission characteristics are accompanied by significant material cost reductions. 

Campion, R.P., Permeation through Polymers for Process Industry Applications, MTI Publication No. 53, Materials Technology Institute of the Chemical Process Industries, St Louis, MO distributed by Elsevier Science, Amsterdam, The Netherlands, 2000. 

P Meares. Transient permeation of organic vapors through polymer membranes. J Appl Polym Sci 9 917-932, 1965. 

AT DiBenedetto, DR Paul. Interpretation of gaseous diffusion through polymers by using fluctuation theory. J Polym Sci Part A 2 1001-1015, 1964. 

GM Zentner, JR Cardinal, J Feijen, S-Z Song. Progestin permeation through polymer membranes. IV. Mechanism of steroid permeation and functional group contributions to diffusion through hydrogel films. J Pharm Sci 68 970-975, 1979. 

K Burczak, T Fujisato, M Hatada, Y Ikada. Protein permeation through polymer membranes for hybrid-type artificial pancreas. Proc Jpn Acad B 67 83-88, 1991. 

Numerous models have been proposed to interpret pore diffusion through polymer networks. The most successful and most widely used model has been that of Yasuda and coworkers [191,192], This theory has its roots in the free volume theory of Cohen and Turnbull [193] for the diffusion of hard spheres in a liquid. According to Yasuda and coworkers, the diffusion coefficient is proportional to exp(-Vj/Vf), where Vs is the characteristic volume of the solute and Vf is the free volume within the gel. Since Vf is assumed to be linearly related to the volume fraction of solvent inside the gel, the following expression is derived ... 

Figure 14 The reversibilities of insulin permeation through polymer membranes in a two-compartment diffusion cell AH20 ( ), AS 15 (A), AS20 ( ), H ( ). Numbers indicate the content of styrene or HEMA in feed compositions in moles. H represents a cross-linked poly(2-hydroxyethyl methacrylate) (HEMA). (From Ref. 34.)... 

S Sato, SW Kim. Macromolecular diffusion through polymer membranes. Int J Pharm 22 229-255, 1984. 

Permeation of small molecules through polymers takes place in four steps. In the first stage, the permeating molecules, know as the diffusants, wet or adsorb onto the polymer s surface. Secondly, the diffusant molecules dissolve in the polymer. In the third step, the molecules diffuse down a concentration gradient towards the opposing surface. Finally, the diffusant molecules desorb or evaporate from the surface, or are absorbed into another material. 

Regarding the question of the rate of electron transport through polymer films, it is not yet clear what ultimate rate can be achieved. In solar energy applications the important issue is whether the rate can be high enough so that the net electron transfer rate is light intensity limited. 

Direct fluorination of polymer or polymer membrane surfaces creates a thin layer of partially fluorinated material on the polymer surface. This procedure dramatically changes the permeation rate of gas molecules through polymers. Several publications in collaboration with Professor D. R. Paul62-66 have investigated the gas permeabilities of surface fluorination of low-density polyethylene, polysulfone, poly(4-methyl-1 -pentene), and poly(phenylene oxide) membranes. 

These traps, (Fig. 6) and similar effects in the motion of holes and other charges through polymers, would eventually be correlated also with such structural probes as positron lifetimes in macromolecular solids. Extensive recent studies of positron lifetime are based on positronium decay. In this, the lifetime of o-positronium (bound positron-electron pair with total spin one) is reduced from about 140 nanoseconds to a few nanoseconds by "pick-off annihilation" in which some unpaired electron spins in the medium cause conversion quenching of orthopositronium to para-positronium. The speed of the t2 effect is supposed, among other things, to represent by pick-off annihilation the presence of defects in the crystalline lattice. In any case, what amounts to empty space between molecules can then be occupied by orthopositronium.(14,15,16) It is now found in linear polyethylene, by T. T. Wang and his co-workers of Bell Laboratories(17) that there is marked shift in positron lifetimes over the temperature range of 80°K to 300°K. For... 

It may be seen that a very high separation factor of organic liquid isomers through polymer membranes has been obtained for PrOH isomers [84],... 

I I heology is an integral part of life, from decorative paint and movement of volcanic lava to the flow of blood in our veins. This book describes, without the use of complex mathematics, how atoms and molecules interact to control the handling properties of materials ranging from simple ionic crystals through polymers to colloidal dispersions. 

Polymers dynamics of polymer chains microviscosity free volume orientation of chains in stretched samples miscibility phase separation diffusion of species through polymer networks end-to-end macrocyclization dynamics monitoring of polymerization degradation... 

W. R. Veith, Dijfusion In and Through Polymers, Hanser Verlag, Munich, 1991, p. 19. 

Ding, J., Chuy, C. and Holdcroft, S. 2001. A self-organized network of nanochannels enhances ion conductivity through polymer films. Chemistry of Materials 13 2231-2233. 

We have already discussed ion association in Section 6.2. In that section we referred to evidence for the existence of ion clusters from static techniques such as IR, Raman, EXAFS and X-ray diffraction. In this section we examine ion association from the point of view of dynamics, concentrating in particular on electrochemical measurements which reveal the presence of ion clusters. Because ion association is so intimately connected to the transport of matter and charge through polymer electrolytes, it seems appropriate to consider these two topics in the same section. 

For example, spheres of narrow size distribution of polyl/Mm-butylstyrene) were obtained by exposing the corresponding monomer droplets to the trifluorometh-anesulfonic acid initiator vapor (Fig. 1.5.8). The polymer particles ranged in diameter from I to 3 p,m, and their uniformity was sensitive to the monomer-to-initiator mass ratio. Under certain conditions the normally smooth spheres appeared connected through polymer whiskers (Fig. 1.5.9) (67). Using styrene monomer and adjusting the boiler temperature, uniform polystyrene particles up 10 xm in diameter and spheres of 20 p,m of broader size distribution could be prepared (67). 

---