Modeling of the Salt and pH Effects on the Permeability of Grafted Porous Membranes

Abstract

A simple theoretical model describing the effects of pH and salt concentration on the permeability and counterion transport number of variable permeability membranes has been presented and validated experimentally for the case of poly(vinylidene fluoride) membranes graft modified with poly(acrylic acid) chains by radiation-induced grafting. The model incorporates explicitly the statistical conformations of a polyacid chain grafted onto the pore surface. The electrostatic interactions between the bound charges in the chains are screened according to the Debye−Hückel theory. The charged capillary model for porous membranes is then used to evaluate the permeability and counterion transport number of the membrane. This theoretical approach is able to describe the experimental trends observed for a range of KCl concentrations and pH values when the grafting ratios are low. In particular, the fact that the membrane permeability changes by several orders of magnitude when the properties of the external solution are varied can be rationalized in terms of very simple physical principles.

Novel pH-sensitive polymers containing sulfonamide groups

“…Following report by Eisenberg et al on the phase transition of pHsensitive polymers in 1950 12) , Michaeli and Katchalsky investigated carboxylic acid-based pH-sensitive hydrogels in mid 1950s 13) . Since then, numerous pH-sensitive polymeric systems, including linear polymers 14) , grafted polymers 15) , hydrogels 16) , and interpenetrating polymer networks 17) , have been investigated for applications in pharmaceutical areas, such as enteric coating materials 18) , site-specific targeting 19) , and tumor-specific delivery 20) , self-regulating insulin delivery systems 21) , and sensors 7,22) . The pK a of carboxylic acid in polymers varies depending on the surrounding molecular environment (monomer structure and copolymer composition) and ranges typically from 4 to 6, leading to the phase or swelling transition in the similar pH range.…”

Environmentally responsive polymeric "intelligent" materials: the ideal components of non-mechanical valves that control flow in microfluidic systems

“…These movable membranes are further coupled to magnetic, piezoelectric or pressure actuated methods which allow external switching. Some examples of mechanical actuators include permeable membranes (Hautojarvi et al, 1996;Kontturi et al, 1996;Ulbricht, 1996;Peng and Cheng, 1998;Peng and Cheng, 1999;Peng and Cheng, 2001;Chu et al, 2003;Gatimu et al, 2006), and nanofabricated reservoirs that act as constant sources of reagents (Groisman et al, 2005;Frevert et al, 2006;Keenan et al, 2006).…”

Passive Transport of Ionic Drugs through Membranes with pH-Dependent Fixed Charges

“…For the amphoteric membrane, both charged groups are present in the grafted chains. In all cases, the ionization state of the weak polyelectrolyte fixed groups changes with the local pH within the membrane (7)(8)(9)(10)(11), which is what makes the membranes ideally suited to those experimental situations where the membrane permeability to the ionic drug must be controlled by the external pH (drug delivery systems, separation processes in biotechnology, and biochemical sensors) (1)(2)(3)(4)(5).…”