Water permeation studies

H. Vromans and J. A. Van Laarhoven. Study on water permeation through rubber closures of injection vials. Int. J. Pharm., 79, 301 (1992). 

The study of the dynamical behavior of water molecules and protons as a function of the state of hydration is of great importance for understanding the mechanisms of proton and water transport and their coupling. Such studies can rationalize the influence of the random self-organized polymer morphology and water uptake on effective physicochemical properties (i.e., proton conductivity, water permeation rates, and electro-osmotic drag coefficients). 

Two-compartment glass permeation cells were used for solute permeation study as a function of temperature. Hydrocortisone was used as a model solute. The volume of each compartment was 6 cm and the area for the diffusion was 1.77 cm. Stirring was maintained at 600 rpm for all experiments via internal bar magnet. The donor compartment was filled with 2 wt% hydrocortisone aqueous solution (the hydrocortisone water solubility at 25°C is 280 pig/cm ) and the receptor compartment was filled with water. 

As stated, the capability of plasma deposits to reduce the access of water to corrosion-sensitive surfaces may be an important motivation for their application in corrosion protection. In order to study this property, Kapton polyimide film was selected as the substrate because of its high inherent permeability to water and its ability to resist elevated temperatures. The response of Kapton film overcoated by PPHMDSO to the permeation of water vapor is shown in Fig. 1. Clearly, the presence of the organo-silicone plasma film greatly reduces water permeation. The magnitude of the effect is much enhanced when plasma polymers are produced at high T and p. 

A zero time base for the halogenated ethane permeation studies was established as follows The aqueous side of the cell was filled with 100 mL of water and allowed to reach thermal equilibrium with the water bath. Likewise, the particular organic compound being tested... 

Polypeptides obtained by the anionic polymerization of optically active N-carboxy-a-amino acid anhydrides are apt to have such an ordered structures as a-helices, which is useful for investigation on the relationship between the physical structure and the permeability of the membrane. Takizawa et al.44 46) studied the water permeation and solute separation through poly(n-alkyl L-glutamate) membranes 3. It was concluded that water molecules permeate through relatively large free spaces... 

From a formulative point of view, it is important to take into consideration that the base in which liposomes are incorporated could also affect the drug delivery profile as well as the interactions between the liposomes and skin structures. The effect of formulation bases on dyphylline skin permeation from liposomes was examined by Touitou et al. [9]. In this work the effect of four bases for dyphylline liposomes (polyethylene glycol (PEG), carbopol gel, a PEG-enhancer base, and water) was studied. With these bases, the lowest skin permeation flux and a superior skin partitioning of liposomal dyphylline were reported for the PEG base, suggesting that this base favored dyphylline accumulation within the skin. A number of liposomes are currently marketed by cosmetic raw material companies for incorporation in different bases to obtain final products. It is important to keep in mind that the delivery properties of the final formulation could be altered by the vehicle used and should be tested to confirm any performance characteristics claimed. 

Ion channel studies motivated Allen et al. [47] who have developed an elegant variational formalism to compute polarization charges induced on dielectric interfaces. They solved the variational problem with a steepest descent method and applied their formulation in molecular dynamics (MD) simulations of water permeation through nanopores in a polarizable membrane [48-50], Note that the functional chosen by Allen et al. [47] is not the only formalism that can be used. Polarization free energy functionals [51-53] are more appropriate for dynamical problems, such as macromolecule conformational changes and solvation [54-57],... 

Permeation Studies. Matsuura and co-workers have made use of liquid chromatography to estimate the extent of partitioning between free solution and the membrane phase (48>87-89)> the magnitude of A-M and B-M interactions due to electrostatic repulsion and van der Waals attraction (48,49,89-91), the thickness of bound or interfacial water associated with the membrane (87-89), as well as the average size and size distribution of the transport corridor on the membrane surface (92-94). 

Two questions have been studied using the thin film samples does EvOH offer any resistance to water permeation in a LEP structure and can an irreversible change in EvOH oxygen permeability during retort be caused in controlled experiments We consider these questions in separately. 

A similar situation does not presently exist for multilayer retortable food packages. In our initial study of LEP and PEP food packages we found that there are very few experimental studies on water permeation in polymers. The studies which we did find were usually limited to low temperature, far removed from retort conditions. The effect of water activity on transport and sorption behavior has not received much attention especially for water-sensitive polymers such as EvOH. In EvOH-type systems the problem is especially acute because EvOH exhibits case II sorption at moderate humidities and its effective glass transition is depressed below storage temperatures at high humidities. Thus, modelling the transport in this type of material is very complex and does not lend itself to analysis with existing models. 

During initial studies, blends of several types of ethylene vinyl alcohol copolymers were made with all three types of platelet fillers, aluminum flake, mica and talc. Blend loadings were from 9 to 33 wt % filler. Thin films, 1 to 2 mils in thickness, were melt pressed from these composites and used to measure oxygen and water permeation rates. 

Pervaporation can also be used as a micropump. Isopropanol was placed inside the polyimide membrane microchannels described above, and water was deposited on top of the permeation area. The large selectivity for water transport over alcohol resulted in water permeation at a rate of 70 pm s [263]. In a similar study, a micropump was developed using pervaporation to transport a volume of 300 pL of Ringer s solution out of a membrane over a 6-day period. Capillary forces then induced additional flow into the membrane device to produce a very constant flow of 35 nL min [265]. Although this device did not utilize microchannel architectures, the low fabrication costs and high reliability of such a system make pervaporation an attractive approach to pumping small flow rates for microfluidic devices. 

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