Swollen hydrogel

Interfacial polymerization membranes are less appHcable to gas separation because of the water swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is highly water swollen and offers Httle resistance to water flow, but when the membrane is dried and used in gas separations the gel becomes a rigid glass with very low gas permeabiUty. This glassy polymer fills the membrane pores and, as a result, defect-free interfacial composite membranes usually have low gas fluxes, although their selectivities can be good. 

The GGM-rich hemicelluloses, isolated from water-impregnated spruce chips by heat-fractionation [218], has been used as pre-polymers after modification with methacrylic functions [439]. Radical polymerization of the modified hemicelullose with 2-hydroxyethyl methacrylate in water yielded elastic, soft, transparent, and easily swollen hydrogels. 

AP Sassi, HW Blanch, JM Prausnitz. Characterization of size-exclusion effects in highly swollen hydrogels Correlation and prediction. J Appl Polym Sci 59 1337-1346, 1996. 

Here, a is the elongation ratio of the polymer chains in any direction and (r/j1/2 is the root-mean-square, unperturbed, end-to-end distance of the polymer chains between two neighboring crosslinks (Canal and Peppas, 1989). For isotropically swollen hydrogel, the elongation ratio, a, can be related to the swollen polymer volume fraction, u2,j> using Eq. (11). 

In Eq. (13) Mr is the molecular weight of the repeating units from which the polymer chain is composed. Finally, when one combines Eqs. (10) through (13), the correlation distance between two adjacent crosslinks in a swollen hydrogel can be obtained ... 

Due to the chemical interactions between PVA and boric acid that lead to directly proportionally of the swollen hydrogel shrinking and the boric acid concentration, a sensor for this acid, difficult to determine by classical titration because of its weakness, has been proposed [162],... 

Kost, J. and Langer, R. Equilibrium swollen hydrogels in controlled release applications, in N. A. Peppas, ed. Hydrogels in Medicine and Pharmacy, pp. 95-107. CRC Press, Boca Raton, FL, 1986. 

Substituting equation 4 into the water flux equation(equation 1) yields a correlation between the water flux(F ) and pressure, which is identical with the empirical relationship suggested earlier by Paul ( ), for solvent permeation through swollen hydrogels ... 

A unique 3D porous structure is observed in the swollen hydrogel (Fig. 21), which is not determined in the unswollen state. Different pore sizes and morphologies between the surface and the interior of swollen hydrogels are visible [175]. 

When a slab of the PE0/PU hydrogel 2.8mm thick was swollen to equilibrium in an aqueous solution of morphine hydrochloride at 37°C, briefly rinsed, then transferred to water at 37°C, the rate of release of morphine was, as predicted by theory, proportional to time t O and 50° 0f the morphine content was released in the first 45 minutes. The release/time plot is shown in Figure 1. Results from experiments like this one can be used to calculate diffusion coefficients (8) in fully swollen hydrogels and help interpret the complex mechanism of diffusion in swelling hydrogels. 

Corpart and Candau [68, 69] described the formulation of polyampholytes containing both positive and negative charges in inverse microemulsions. The copolymers can show very different behaviors in the aqueous solution, ranging from insoluble, water-swollen hydrogels to water-soluble compounds, depending on the monomer composition. For polyampholytes with balanced stoichiometry, the polymer behavior is controlled by attractive electrostatic forces. The compound is usually insoluble in water, but becomes soluble upon the addition of salt. 

Pathak [3] prepared polyalkoxyether hydrogels, (VII) and (VII), that absorbed a substantial portion of water present in whole blood so that when the swollen hydrogel phase was removed a fibrinogen-rich phase was isolated. 

Colombo I, Grassi M, Lapasin R, and Pricl S. Determination of the drug diffusion coefficient in swollen hydrogel polymeric matrices by means of the inverse sectioning method. J. Control. Rel. 1997 47 305-314. 

Drug (D) in swollen hydrogel Drug = pilocarpine, progesterone... 

In some applications, the interaction of the polymer with a specific "solvent" and/or with certain molecules carried by that solvent is not a detrimental event, but an essential aspect of the operation of the polymer. Reverse osmosis membranes and swollen hydrogels used in applications such as the desalination of water, kidney dialysis, soft contact lenses and surgical implants [17] are among such polymers. 

Water is dominant in the IR spectrum of swollen hydrogels. Figure 19a shows the ATR spectrum of water-containing PVP. The three strongest absorption bands are due to vibrational modes of water. The weak bands that are indicated by a star in Fig. 19a arise from PVP. The Raman spectrum of the same sample is represented in... 

Diffusion of Small Molecules into a Swollen Hydrogel... 

As shown in Fig. 3b a normally open (NO) valve can be designed to keep the conic valve seat open by the swollen hydrogel. The valve seat is closed after shrinking of the gel. 

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