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Gel Transition (gel + transition)
Selected AbstractsIn-Film Bioprocessing and Immunoanalysis with Electroaddressable Stimuli-Responsive PolysaccharidesADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Xiaohua Yang Abstract Advances in thin-film fabrication are integral to enhancing the power of microelectronics while fabrication methods that allow the integration of biological molecules are enabling advances in bioelectronics. A thin-film-fabrication method that further extends the integration of biology with microelectronics by allowing living biological systems to be assembled, cultured, and analyzed on-chip with the aid of localized electrical signals is described. Specifically, the blending of two stimuli-responsive film-forming polysaccharides for electroaddressing is reported. The first, alginate, can electrodeposit by undergoing a localized sol,gel transition in response to electrode-imposed anodic signals. The second, agarose, can be co-deposited with alginate and forms a gel upon a temperature reduction. Electrodeposition of this dual polysaccharide network is observed to be a simple, rapid, and spatially selective means for assembly. The bioprocessing capabilities are examined by co-depositing a yeast clone engineered to display a variable lymphocyte receptor protein on the cell surface. Results demonstrate the in-film expansion and induction of this cell population. Analysis of the cells' surface proteins is achieved by the electrophoretic delivery of immunoreagents into the film. These results demonstrate a simple and benign means to electroaddress hydrogel films for in-film bioprocessing and immunoanalysis. [source] Silica-Based, Organically Modified Host Material for Waveguide Structuring by Two-Photon-Induced PhotopolymerizationADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Stefan Krivec Abstract The three-dimensional fabrication of optical waveguides has gained increasing interest in recent years to establish interconnections between electrical components on a very small scale where copper circuits encounter severe limitations. In this work the application of optically clear, organically modified porous silica monoliths and thin films as a host material for polymeric waveguides to be inscribed into the solid host structure by two-photon-induced photopolymerization is investigated. Porosity is generated using a lyotropic liquid crystalline surfactant/solvent system as a template for the solid silica material obtained by a sol,gel transition of a liquid precursor. In order to reduce the brittleness of the purely inorganic material, organic,inorganic co-precursor molecules that contain poly(ethylene glycol) chains are synthesized and added to the mixture, which successfully suppresses macroscopic cracking and leads to flexible thin films. The structure of the thus-obtained porous organic,inorganic hybrid material is investigated by atomic force microscopy. It is shown that the modified material is suitable for infiltration with photocurable monomers and functional polymeric waveguides can be inscribed by selective two-photon-induced photopolymerization. [source] Light-Triggered Self-Assembly of a Spiropyran-Functionalized Dendron into Nano-/Micrometer-Sized Particles and Photoresponsive Organogel with Switchable FluorescenceADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Qun Chen Abstract The synthesis, self-assembly, and spectroscopic investigations of spiropyran (SP)-functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano-/microparticles occurs due to the transformation of the closed form of SP into the open merocyanine (MC) form. The formation of these nano-/microparticles is confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) experiments in addition to the confocal laser scanning microscopy (CLSM) measurements. These nano-/microparticles exhibit relatively strong red emission. It is interesting to note that the direct cooling of the toluene/benzene solution of 1 to 0,°C leads to gel formation. Multivalent ,,, interactions due to the dendron in 1 may be the driving-force for the gelation. The UV light irradiation cannot destroy the gel phase, and in fact, the gel,gel transition is successfully realized. The purple-blue gel exhibits relatively strong red fluorescence; moreover, the fluorescence can be reversibly switched by alternating UV and visible light irradiation. The results clearly indicate that the MC form after aggregation becomes more stable and fluorescent. [source] Simultaneous light and small-angle neutron scattering on aggregating concentrated colloidal suspensionsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2003Sara Romer A new sample environment has been developed in order to perform light and small-angle neutron scattering (SANS) simultaneously on colloidal systems. The combination of SANS and diffusing wave spectroscopy (DWS) is of particular use in the high-concentration regime. DWS provides information on the local dynamic properties of the individual particles, whereas SANS gives access to the structural properties on similar length scales. The combination of both methods thus allows one to obtain structural and dynamic information over a very large range of length and time scales. Using this new setup, the onset of aggregation and the sol,gel transition in concentrated destabilized polystyrene sphere suspensions have been investigated. At the gel point, a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. However, while the DWS measurements indicate that dramatic changes in the local dynamics occur over a long period, the SANS pattern quickly reaches its final appearance. The SANS experiments thus indicate that a fluid-like structure is arrested in the course of the gel formation. The data are found to be in good qualitative agreement with computer simulations. [source] A Thermosensitive and Biodegradable Physical Gel with Chemically Crosslinked Nanogels as the Building BlockMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2008Zigang Yang Abstract A triblock copolymer, poly(ethylene glycol),poly(propylene glycol),poly(ethylene glycol) was end-capped by acryloyl groups using a biodegradable oligolactide as spacer, and such biodegradable amphiphilic macromers could form micelles in water. A nanogel was prepared via polymerizing macromers in a micelle, and a macroscopic physical gelation was found upon heating a concentrated aqueous nanogel suspension. Such a sol,gel transition with a chemically crosslinked nanogel as the building block was thermoreversible. While the hydrogel affords a promising injectable biomaterial; this research reveals new physics of the thermogelling mechanism of amphiphilic block copolymers. [source] Organic,inorganic hybrid membranes prepared from the sol,gel process of poly(butyleneadipate- co -terephthalate) and TiO2POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2009Chien-Hong Lin Abstract Organic,inorganic hybrids based on poly(butyleneadipate- co -terephthalate)/titanium dioxide (PBAT/TiO2) hybrid membranes were prepared via a sol,gel process. The PBAT/TiO2 hybrid membranes were prepared for various PBAT/TiO2 ratios. The resulting hybrids were characterized with a morphological structure, hydrophilicity, biodegradability, and thermal properties. The results showed that macrovoids underwent a transition into a sponge-like membrane structure with the addition of TiO2. After sol,gel transition, a strong interaction between the inorganic network and polymeric chains led to an increase in glass transition temperature (Tg), thermal degrading temperature, and hydrophilicity, and hence a higher biodegradability. According to X-ray diffraction measurements of the crystal structure of the hybrid, the presence of TiO2 did not change the crystal structure of PBAT. TiO2 networks are uniformly dispersed into the PBAT matrix and no aggregation of TiO2 networks in the hybrid membranes was observed through the small angle X-ray scattering measurements. Thus, the sol,gel process of PBAT and TiO2 can be used to prepare a hybrid with higher application temperature and faster biodegradation rate. Copyright © 2008 John Wiley & Sons, Ltd. [source] A novel route to perovskite lead titanate from lead and titanium glycolates via the sol,gel processAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 12 2006N. Tangboriboon Abstract Pure perovskite lead titanate powder (PbTiO3) is successfully produced via the sol,gel process using lead and titanium glycolates as starting precursors and has been synthesized by the oxide one spot synthesis process. The obtained lead titanate is of the tetragonal form of the perovskite phase, with high purity and nearly zero moisture content. From high-resolution mass spectra, the XRD technique, Raman-FTIR and TGA-DTA analysis, the lead,titanium glycolates undergo sol,gel transition through the formation of PbOTi bonds. From the SEM micrographs, the PbTiO3 particle shape transforms from an agglomerate sphere to a needle and fiber-like shapes as the calcination temperature is varied above Tc. The corresponding molecular structural transformation, from the tetragonal form to the cubic form, occurs at 430 °C. The lead titanate powder calcined at 300 °C for 3 h has the highest dielectric constant and electrical conductivity values, namely 17470 and 1.83 × 10,3, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] Polymeric gels and hydrogels for biomedical and pharmaceutical applicationsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2010Joseph Jagur-Grodzinski Abstract Hydrogels are formed when a three-dimensional polymeric network is loosely crosslinked. They are swollen by water but not dissolved in it. Hydrogels may display reversible sol,gel transitions, induced by changes in the environmental conditions such as temperature, pH, ionic strength, phase separation, wave length of light, crystallinity, etc. Hydrogel is described as smart or intelligent when sharp transition is induced by small change in such conditions. For the shape-memory hydrogels, reversible change in shape may also be induced by such stimuli. The preparation and applications of the molecularly imprinted polymeric hydrogels (MIPs) are illustrated by a few examples. The use of shape sensitive hydrogels in microfluidic is mentioned. Application of hydrogels for chronobiology and chronotherapy is outlined. The conversion of hydrogels into aerogels and their respective properties is discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Reversible Hydrogels from an Ampholytic An(B -b- C)n Heteroarm Star Block TerpolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2008Nikoletta Stavrouli Abstract An asymmetric, amphiphilic, An(B- b -C)n heteroarm star block terpolymer bearing polystyrene and poly(2-vinyl pyridine)- block -poly(acrylic acid) arms, was synthesized by anionic polymerization, using an extending "in-out" method and a post polymerization deprotection reaction. Due to the pH-dependent protonation/deprotonation equilibrium of the P2VP/PAA blocks, a rich phase behavior was observed as a function of pH. At pH,=,2, the star terpolymers form a physical hydrogel through a solvent-induced sol/gel transition in a DMF/water solvent mixture. The gelation mechanism was attributed to a jamming effect mediated by increasing the dielectric permittivity of the medium. 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