Temperature-sensitive Membranes Research Articles

Development of oxygen and temperature sensitive membranes using molecular probes as ratiometric sensor

In this work we show that, the combination of (i) high mechanical stability (provided by a PS matrix), (ii) high sensitivity and selectivity (provided by a two-dye system of Tris (1,10-phenanthroline)ruthenium(II) chloride hydrate (Ru(phen)3) and 7-​Methoxy-​4-​methylcoumarin) and (iii) high reproducibility in the output signal/response, results in a membrane able for monitoring O2 and temperature in membrane processes at laboratory and industrial scales.Due to the matched sensitivity of the developed ratiometric probe to oxygen and temperature a simple correction algorithm was implemented, which allows at overcoming the vulnerability of the ratiometric signal to the temperature, leading to a robust evaluation of the oxygen concentration.The impact of introducing this photochemical activity in membranes opens a new perspective for non-invasive monitoring of membrane processes (e.g. measurement of temperature in membrane distillation processes, oxygen measurement for monitoring of biofilm onset and development in reverse osmosis).

Temperature-sensitive membranes prepared from blends of poly(vinylidene fluoride) and poly(N-isopropylacrylamides) microgels

In this study, temperature-sensitive membranes were prepared by phase transition of the mixture of the temperature-sensitive poly(N-isopropylacrylamides) (PNIPAAM) microgels and poly(vinylidene fluoride). The results of Fourier transformed infrared spectrometer, X-ray photoelectron spectroscopy, elemental analysis, and scanning electron microscope photographs indicate that the PNIPAAM microgels are distributed more in the inner membrane than on the surface. The scanning electron microscope photographs reveal the blend membranes having porous surfaces with nanometer sizes and porous cross-sections with micrometer sizes. The addition of the PNIPAAM microgels is found to improve the porosity, the pore size, water flux, as well as to enhance the hydrophilicity and anti-fouling property of the blend membranes. The blend membrane shows temperature-sensitive permeability and protein rejection with the most dramatic change at around 32 °C which is the lower critical solution temperature of PNIPAAM, when water or bovine serum albumin solution flow through. Specifically, below 32 °C, the blend membrane shows a high protein rejection ratio which decreases with increasing temperature and a low water flux which increases with increasing temperature; above 32 °C, the blend membrane shows a low protein rejection ratio which decreases with increasing temperature and a high water flux which increases with increasing temperature.

Characterization of temperature-sensitive membranes prepared from poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) copolymers obtained by atom transfer radical polymerization

In this paper, poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAm) copolymers were synthesized directly via grafting temperature-sensitive material NIPAAm on PVDF by atom transfer radical polymerization (ATRP). The chemical structure of the graft copolymers was characterized by Fourier transform infrared (FTIR) and 1H-NMR spectroscopy. The temperature-sensitive membranes were prepared from the PVDF-g-PNIPAAm copolymers by the immersion precipitation process of the phase inversion method. The chemical composition and pore structure of the PVDF-g-PNIPAAm membranes were studied by X-ray photoelectron spectroscopy (XPS) and an automatic mercury porosimeter, respectively. The effects of temperature on pure water flux and bovine serum albumen (BSA) rejection ratio of the membranes were also investigated. The results showed that the grafted PNIPAAm chains tended to enrich on the surfaces of the membranes or the membrane pores during the membrane-forming process. Pore diameter and porosity of the copolymer membranes were larger than those of the pristine PVDF membranes. Also, the PVDF-g-PNIPAAm membranes could exhibit temperature-sensitive performance in water flux and BSA rejection measurements.

Temperature-sensitive Composite Membranes with "Double Switch" on Water Vapor Permeability

Temperature-sensitive Composite Membranes with "Double Switch" on Water Vapor Permeability

Thermo-Responsive Porous Membranes of Controllable Porous Morphology from Triblock Copolymers of Polycaprolactone and Poly(N-isopropylacrylamide) Prepared by Atom Transfer Radical Polymerization

Stimuli-responsive polymers are of crucial importance in the design of smart biomaterials. The thermo-responsive triblock copolymers of polycaprolactone (PCL) and poly( N-isopropylacrylamide) (P(NIPAAm)), or P(NIPAAm)- b-PCL- b- P(NIPAAm) copolymers, were synthesized in this work via atom transfer radical polymerization (ATRP). The P(NIPAAm)- b-PCL- b-P(NIPAAm) copolymers were cast by phase inversion in water into porous membranes with well-defined and uniformly distributed pores. The P(NIPAAm) content in the P(NIPAAm)- b-PCL- b- P(NIPAAm) copolymers and the temperature of the aqueous medium for phase inversion could be used to control the pore size and porosity of the membranes. The thermo-responsive characteristics of the membranes were illustrated in the controlled water uptake and temperature-dependent glucose transport through the membranes. These temperature-sensitive membranes with controllable morphology have potential applications in biomedical engineering, drug delivery, and tissue engineering.

Drug permeation through temperature-sensitive membranes prepared from poly(vinylidene fluoride) with grafted poly( N-isopropylacrylamide) chains

Temperature-responsive copolymers, poly(vinylidene fluoride)- graft-poly( N-isopropylacrylamide) (PVDF- g-PNIPAAM), were synthesized by thermally-induced graft copolymerization of N-isopropylacrylamide (NIPAAM) with the ozone-pretreated PVDF. Temperature-sensitive microfiltration membranes were then prepared from the PVDF- g-PNIPAAM copolymers by phase inversion. The chemical structure and composition of the PVDF- g-PNIPAAM copolymers were characterized by FT-IR spectroscopy and elemental analysis. X-ray photoelectron spectroscopy (XPS) analyses of the membranes revealed a substantial surface enrichment in grafted NIPAAM polymer. The pore sizes of the PVDF- g-PNIPAAM membranes were measured using a Coulter ® Porometer. The temperature-dependent swelling behavior of the membranes in aqueous solution was studied by atomic force microscope (AFM) and water retention behavior. Increasing the surface graft concentration of the membrane resulted in a higher degree of temperature-sensitive swelling. The copolymer membranes also exhibited reversible temperature-dependent permeability to calcein and fluorescein isothiocyanate (FITC)–dextran in phosphate buffer solutions (pH 7.4), with the most drastic change in permeability being observed in the temperature range between 27 and 32 °C.

Nano-, micro- and macroscopic hydrogels synthesized by radiation technique

Radiation techniques, due to the additive-free initiation and easy process control, are very suitable tools for synthesis of biomaterials, especially hydrogels. In our group, a number of techniques have been elaborated allowing for targeted synthesis of gels of various size ranges, from internally crosslinked individual macromolecules, via microgels to macroscopic hydrogels. An example of a mature technology of this kind are hydrogel wound dressings, being now produced on large scale in Poland and other countries. Current research projects include: hydrogel-based system for anticancer therapy due to local drug delivery, systems for encapsulation of living cells, new approach to the synthesis of polymeric material for intervertebral discs implant, temperature-sensitive membranes, hydrogel phantoms of 3D radiation dosimeter for radiotherapy, degradation-resistant nanogels and microgels for biomedical purposes (e.g. synovial fluid substitute), hydrogel-based dietary products and adjustment of the molecular weight of biopolymers.

Temperature-sensitive membranes prepared by UV photopolymerization of N-isopropylacrylamide on a surface of porous hydrophilic polypropylene membranes

Novel multifunctional membranes were prepared by ultraviolet photopolymerization of N-isopropylacrylamide (NIPAAm) on the surface of porous hydrophilic polypropylene microfiltration membranes. The poly N-isopropylacrylamide PNIPAAm gels were generated on the surface of the membrane through a covalent bond in the presence of a crosslinking agent, N, N′-methylenebisacrylamide. The crosslinked PNIPAAm gels are temperature-responsive hydrogels that can swell and deswell reversibly in aqueous solution around the vicinity of the lower critical solution temperature (LCST) of PNIPAAm. With a change of temperature, the effective pore size of the membrane surface can be enlarged or shrunk as the PNIPAAm gels swell or deswell. Above the LCST of PNIPAAm, the fluxes of water and solution containing 500 ppm of dextran (molecular weight: 1.67×10 5 g/mol) through the temperature-sensitive membranes are about 6 and 85 times higher than those below the LCST of PNIPAAm, respectively. The changeable flux makes it possible to employ the temperature-sensitive membranes as a sensor or valve that regulates filtration properties by responding to temperature. Solutions of dextran with a molecular weight from 6300 to 2,000,000 were used to evaluate the separation performance of the temperature-sensitive membranes as the ultrafiltration membrane. The ranges of rejection of dextran and the flux of solution are from 0 to 90 and 8 to 32 l/m 2 h, respectively, depending on the temperature, pressure, and molecular weight of dextran. It is clear that the temperature-sensitive membrane exhibits multifunctional characteristics; that is, the microfiltration membrane is above the LCST of PNIPAAm, and the ultrafiltration membrane is below the LCST of PNIPAAm.

Electron-beam Graft-modified Membranes with Externally Controlled Flux

Pre-irradiation grafting as a means to modify commerical poly(vinylidene fluoride) (PVDF) membranes has been studied. The membranes prepared were weak cation-exchange membranes (acrylic acid functionality), anion-exchange membranes (trimethyl ammonium functionality) and temperature-sensitive membranes (N-isopropyl amide functionality). Different graft loads were obtained by varying reaction time, radiation dose and in the case of acrylic acid the graft solution composition. The trimethyl ammonium chloride functionality was obtained by grafting vinyl benzyl chloride onto a PVDF membrane and aminating the benzyl chloride groups in a 45% trimethyl amine–water solution. For a membrane grafted with 9 wt% acrylic acid the flux increased approximately 70 times when the pH was decreased from 6 to 2. For a membrane with 5 wt% trimethyl ammonium functionality the flux increased both when pH was decreased below 3 and increased above 11. For a membrane grafted with 18 wt% N-isopropyl acrylamide a sharp increase of flux was observed when the temperature was raised above 32°C.

Electron‐beam Graft‐modified Membranes with Externally Controlled Flux

Pre-irradiation grafting as a means to modify commerical poly(vinylidene fluoride) (PVDF) membranes has been studied. The membranes prepared were weak cation-exchange membranes (acrylic acid functionality), anion-exchange membranes (trimethyl ammonium functionality) and temperature-sensitive membranes (N-isopropyl amide functionality). Different graft loads were obtained by varying reaction time, radiation dose and in the case of acrylic acid the graft solution composition. The trimethyl ammonium chloride functionality was obtained by grafting vinyl benzyl chloride onto a PVDF membrane and aminating the benzyl chloride groups in a 45% trimethyl amine–water solution. For a membrane grafted with 9 wt% acrylic acid the flux increased approximately 70 times when the pH was decreased from 6 to 2. For a membrane with 5 wt% trimethyl ammonium functionality the flux increased both when pH was decreased below 3 and increased above 11. For a membrane grafted with 18 wt% N-isopropyl acrylamide a sharp increase of flux was observed when the temperature was raised above 32°C.

Pervaporation of ethanol-water mixtures through temperature-sensitive poly(vinyl alcohol- g- N-isopropyacrylamide) membranes

Novel temperature-sensitive membranes have been synthesized by grafting poly( N-isopropyacrylamide) (poly(NIPAAm)) onto a poly(vinyl alcohol) (PVA) backbone using hydrogen peroxide-ferrous ion as initiator. Due to the grafting of poly(NIPAAm), the hydrophilic/hydrophobic balance and the polarity of the pendent groups within the membranes are modified. Significant temperature sensitivity of the grafted membranes is observed close to the LCST of linear poly(NIPAAm) in the pervaporation processes for ethanol-water separation. Both the pervaporation and sorption selectivities for water show a maximum value in the vicinity of 30–32°C for an ethanol content of 75 and 80%. The temperature sensitivity of the grafted membranes also depends on the ethanol concentration. The maxima of pervaporation and sorption selectivities disappear when the ethanol content is lower than 75% because the much larger degree of swelling reduces the size screening effect of the membranes.

Composition- and temperature-sensitive membranes composed of phosphatidylcholine and triton X-100 for the remarkably enhanced stereoselective-hydrolysis

The optimum composition (32 mol% DPPC/68 mol% Triton X-100) hybrid-assemblies presented the highest enantioselectivity and the markedly enhanced enantioselectivity was observed at the phase transition of liposomes composed of 65 mol% DPPC and 35 mol% Triton X-100.

Preparation of temperature-sensitive membranes by graft polymerization onto a porous membrane

Temperature-sensitive membranes were prepared by grafting of poly ( N-isopropylacrylamide) (polyIPAAm) and its copolymers onto a porous poly(vinylidene fluoride) membrane. PolyIPAAm is soluble in water but has a lower critical solution temperature (LCST) around 31-33°C. The water filtration rate of the polyIPAAm grafted membrane varied more than 10-fold between temperatures above and below the LCST, reflecting the drastic configuration change of polyIPAAm. The temperature sensitivity was reversible and reproducible. It is likely that the grafted chains acted as a sensor of temperature and as a valve to regulate filtration characteristics. The temperature region where the filtration rate sharply changed could be shifted to higher or lower temperature by copolymerizing IPAAm with a hydrophilic monomer, such as acrylamide, or a hydrophobic monomer, such as n-butyl methacrylate, respectively. All of the temperature-sensitive membranes remained constant in size and could respond quickly to temperature changes.