Preparation of permeability-controlled track membranes on the basis of ‘smart’ polymers
Introduction
The ability of ‘smart’ polymers to respond to small changes in the environmental conditions can be used in the production of permeability-controlled track membranes. ‘Smart’ or ‘intelligent’ polymers are the nick-names of the water soluble polymers and hydrogels. They are able to change drastically their some properties (volume of macromolecules) in water solution even at small changes in the environment conditions (temperature, pH, magnetic field strength, etc.) [1], [2], [3]. Among ‘smart’ polymers, the greatest number of papers has been devoted to poly-N-isopropylacrylamide (poly-NIPAAM), a thermoresponsive polymer [3], [4], [5]. This polymer has a lower critical solution temperature (LCST) of about 32°C in water. Recently it was proposed to manufacture composite membranes by grafting stimulus-responsive polymers onto porous cast membranes [6], [7] and track membranes [8], [9], [10]. The thermosensitive membranes were used to separate a feed solution containing hydrophobic and hydrophilic solutes [11]. Following this principle, we prepared thermosensitive membranes by the radiation-induced graft polymerization of N-isopropylacrylamide (NIPAAM) onto polyethylene terephalate (PET) and polypropylene (PP) track membranes.
Section snippets
Materials
Biaxially oriented PET films (10 and 20 μm thick) manufactured in Russia and Melinex films (12 μm thick) of ICI (USA) were used. Polypropylene Torayfan films (10 μm thick) of Toray (Japan) were also used. In this work, the monomer to be grafted was NIPAAM obtained from Across Organics. It contained 0.1% of stabilizer and was used as received. Reagent grade acetone and distilled water were used to prepare the monomer solutions. As homopolymerization inhibitors, we used reagent grade CuCl2·2H2O. To
Results and discussion
The grafted polymer can be located both on the membrane external surface and inside the pores, depending on the grafting conditions. On its surface and on the walls of the pores, such a membrane has immobilized polymer molecules which are transformed from one conformation state to another as the environment conditions change even slightly. This transformation leads to an increase or a decrease in the pore size. The electric conductivity of the initial PET membrane is linearly dependent on the
Conclusions
Poly-NIPAAM-grafted polymer track membranes can be prepared by radiation-induced graft polymerization. The polymer is located on both sides of the external surface and inside the pores. Using conductivity method in combination with the scanning electron and atomic force microscopy, the properties of track membranes grafted by responsive hydrogel were analyzed. Poly-NIPAAM inside the pores of track membranes exhibit a change in thickness as the solution temperature changes, and the membrane
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