Polymer swelling profile

Ion selective membranes are the active, chemically selective component of many potentiometric ion sensors (7). They have been most successfully used with solution contacts on both sides of the membrane, and have been found to perform less satisfactorily when a solid state contact is made to one face. One approach that has been used to improve the lifetime of solid state devices coated with membranes has been to improve the adhesion of the film on the solid substrate (2-5). However, our results with this approach for plasticized polyvinylchloride (PVC) based membranes suggested it is important to understand the basic phenomena occurring inside these membranes in terms of solvent uptake, ion transport and membrane stress (4,6). We have previously reported on the design of an optical instrument that allows the concentration profiles inside PVC based ion sensitive membranes to be determined (7). In that study it was shown that water uptake occurs in two steps. A more detailed study of water transport has been undertaken since water is believed to play an important role in such membranes, but its exact function is poorly understood, and the quantitative data available on water in PVC membranes is not in good agreement (8-10). One key problem is to develop an understanding of the role of water uptake in polymer swelling and internal stress, since these factors appear to be related to the rapid failure of membranes on solid substrates. 

Baumgartner S, Lahajnar G, Sepe A, et al. (Quantitative evaluation of polymer concentration profile during swelling of hydrophilic matrix tablets using H NMR and MRI methods. Eur J Pharm Biopharm 2005 59(2) 299-306. 

FIGURE 11.9 (a) Water uptake ( , a) and residual dry polymer ( , A) profiles and (b) swelling (a, a) and erosion ( , A) front profiles of HPC matrices manufactured by direct compression (dotted lines) and HME (solid lines). (Reprinted with permission from Loreti, G. et al., Eur. J. Pharm. Sci., 52, 77, 2014.)... 

In their study of branched PSA, Maniar et al. (1990) found that the molecular architecture of branched polymers affects the release kinetics in a variety of ways. They found that the branched polymers degraded faster than linear PSA of comparable molecular weight (Maniar et al., 1990). They also noted that drug (morphine) release profiles were more characteristic of bulk erosion than surface erosion An initial lag time during which very little drug was released was associated with the time required for water to swell the polymer. This was followed by a period of relatively fast release, which tapered off as the device disintegrated. The polymer matrix lost its mechanical integrity before the release experiment was complete (Maniar et al., 1990). Despite the increase... 

Table 13.2 Die-swell ratio as a function of mean residence time in the capillary0 for the three polymers shown in Table 13.1 [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning , Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

Fig. 13. Profile (r/re) of swelling and drawn from capillary extrudate versus ratio of the distance from the end of the capillary (z) and the average velocity of polymer leaving the capillary (V). The lines correspond to data for homogeneous extension calculated by (13) and points correspond to experimental data obtained photographically...

Nonerodible systems. In the second matrix system, the matrix does not change during dissolution (insoluble, no disintegration, and no swelling). Polymers that are hydrophobic or cross-linked polymers often are used for the matrix. The drug solid is dissolved inside the matrix and is released by diffusing out of the matrix. Both dissolution and diffusion contribute to the release profile of this type of matrix systems. The mathematical expression for this system can be derived from the following equation ... 

Whipple s careful experimental study of the velocity profile in the region before and after the capillary exit is an initial step in answering some of these needs. He found that polymer melts anticipate the swelling phenomenon, in that, just before the exit, axial decelerations and radial velocity components are observed. Thus the exit velocity profile is not the same as in the fully developed region and the flow there is not viscometric.4... 

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