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Responsive Hydrogels (responsive + hydrogel)
Selected AbstractsPreparation and characteristic of electric stimuli responsive hydrogel composed of polyvinyl alcohol/poly (sodium maleate- co -sodium acrylate)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yi Gao Abstract Maleic anhydride was used to preparare polyvinyl alcohol/poly (sodium maleate- co -sodium acrylate) hydrogels (PVA/poly(SMA-SAA)) by a repeated frost-defrost process because of its higher charge density and potential electric stimuli sensitivity. The bending angle was measured in a noncontact electric field using carbon as plate electrodes. It was found that the bending angle was dependent on various factors, including composition of hydrogel, concentration of NaCl solution, types of electrolyte solution, and electric voltage. It exhibited that the bending angle increased when the concentration of NaCl solutions and the electric voltages increased. An abnormal bending direction was observed, and it was affected not only by the kinds of hydrogels, but also by the exterior variations. The hydrogel showed good reversibility in on-off electric field and could be a candidate for practical application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Multiphysics Modelling of Volume Phase Transition of Ionic Hydrogels Responsive to Thermal StimulusMACROMOLECULAR BIOSCIENCE, Issue 9 2005Hua Li Abstract Summary: This paper presents the analysis of the volume phase transition of ionic thermo-sensitive hydrogels to thermal stimulus through mathematical modelling. The model is termed the multi-effect-coupling thermal-stimulus (MECtherm) model and it considers the effects of multi-phases and multi-physics. Its application to steady-state analysis of the hydrogels in swelling equilibrium is validated against available experimental data for the relation between volume swelling ratio and temperature, in which very good agreement is achieved. The phenomenon of volume phase transition is studied for the thermal-stimulus responsive hydrogel. The numerical studies predict well the influences of initially fixed charge density and initial volume fraction of polymeric network on the swelling equilibrium of the hydrogels. Comparison of numerical simulations with the experimental swelling data for the thermo-sensitive PNIPA hydrogels in pure water. [source] Electrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2007E. Segal Abstract A thermoresponsive hydrogel, poly(N -isopropylacrylamide) (poly(NIPAM)), is synthesized in,situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry,Pérot fringes characteristic of thin film interference, enabling direct, real-time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature-dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite. [source] Dual responsive poly(N -isopropylacrylamide) hydrogels having spironaphthoxazines as pendant groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2009Erandimala U. Kulawardana Abstract Stimuli responsive hydrogels (PNIPAAm-MSp) with a thermoresponsive backbone and photochromic pendant groups were synthesized via free radical polymerization using N -isopropylacrylamide, modified spironaphthoxazines with a polymerizable double bond (MSp) as photochromic monomer, the crosslinker N,N,-methylenebis(acrylamide) and the initiator 2,2,-azobis(isobutyronitrile) in dimethylsulfoxide. The polymers are dual responsive, in that poly(N -isopropylacrylamide) (PNIPAAm) responds to temperature changes whereas the pendant spironaphthoxazines respond to light. Irradiation enhanced the water absorption of the polymers while increases in temperature decreased it. The irradiated PNIPAAm-MSp showed best water absorption at 0 °C (Q = 3.25) while water desorbed at higher temperatures (35 °C; Q = 0.30); where Q is the amount of water absorbed by a gram of dry polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3318,3325, 2009 [source] Chemical actuation in responsive hydrogels,POLYMER INTERNATIONAL, Issue 3 2009Joshua MG Swann Abstract Chemically actuated hydrogels share a unique feature with living systems: they are both driven by their ability to convert chemical energy into a mechanical response. However, macroscopic applications of hydrogels are limited due to the slow response rate of these materials. This problem has been overcome by developing materials at micrometre length scales, as the diffusion kinetics are related to the square of the size of the smallest dimension of the gel. Herein, the progress in the field of chemical actuation in hydrogel systems is reviewed, with an emphasis on the ways in which new devices have been designed. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||