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Sol-gel Transition (sol-gel + transition)
Selected AbstractsElectroaddressing of Cell Populations by Co-Deposition with Calcium Alginate HydrogelsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Xiao-Wen Shi Abstract Electroaddressing of biological components at specific device addresses is attractive because it enlists the capabilities of electronics to provide spatiotemporally controlled electrical signals. Here, the electrodeposition of calcium alginate hydrogels at specific electrode addresses is reported. The method employs the low pH generated at the anode to locally solubilize calcium ions from insoluble calcium carbonate. The solubilized Ca2+ can then bind alginate to induce this polysaccharide to undergo a localized sol-gel transition. Calcium alginate gel formation is shown to be spatially controlled in the normal and lateral dimensions. The deposition method is sufficiently benign that it can be used to entrap the bacteria E. coli. The entrapped cells are able to grow and respond to chemical inducers in their environment. Also, the entrapped cells can be liberated from the gel network by adding sodium citrate that can compete with alginate for Ca2+ binding. The capabilities of calcium alginate electrodeposition is illustrated by entrapping reporter cells that can recognize the quorum sensing autoinducer 2 (AI-2) signaling molecule. These reporter cells were observed to recognize and respond to AI-2 generated from an external bacterial population. Thus, calcium alginate electrodeposition provides a programmable method for the spatiotemporally controllable assembly of cell populations for cell-based biosensing and for studying cell-cell signaling. [source] Small-angle X-ray scattering study of the smart thermo-optical behavior of zirconyl aqueous colloidsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000L.A. Chiavacci The smart thermo-optical systems studied here are based on the unusual thermoreversible sol-gel transition of zirconyl chloride aqueous solution modified by sulfuric acid in the molar ratio Zr/SO4:3/1. The transparency to the visible light changes during heating due to light scattering. This feature is related to the aggregates growth that occurs during gelation. These reversible changes can be controlled by the amount of chloride ions in solution. The thermoreversible sol-gel transition temperature increases from 323 to 343 K by decreasing the molar ratio Cl/Zr from 7.0 to 1.3. In this work the effect of the concentration of chloride ions on the structural characteristics of the system has been analyzed by in situ SAXS measurements during the sol-gel transition carried out at 323 and 333 K. The experimental SAXS curves of sols exhibit three regions at small, medium and high scattering vectors characteristics of Guinier, fractal and Porod regimes, respectively. The radius of primary particles, obtained from the crossover between the fractal and Porod regimes, remains almost invariable with the chloride concentration, and the value (4 Å) is consistent with the size of the molecular precursor. During the sol-gel transition the aggregates grow with a fractal structure and the fractal dimensionality decreases from 2.4 to 1.8. This last value is characteristic of a cluster-cluster aggregation controlled by a diffusion process. Furthermore, the time exponent of aggregate growth presents values of 0.33 and 1, typical of diffusional and hydrodynamic motions. A crossover between these two regimes is observed. [source] Kinetic Study of Thermally Induced Inulin GelJOURNAL OF FOOD SCIENCE, Issue 7 2001Y. Kim ABSTRACT: Heated inulin solution undergoes a sol-gel transition during cooling and forms a white smooth gel under optimized conditions. The degree of gel formation is negatively related to hydrolysis of inulin during heating. Heating makes inulin soluble; overheating causes hydrolysis of dissolved inulin into smaller molecules. Using a 2-step model including a solubilization step and a hydrolysis of inulin step, we found that both steps follow pseudo first-order kinetics. Separate studies on initial rates of the solubilization and hydrolysis of inulin steps at constant temperatures show that the solubilization rate of inulin is much faster than that of the hydrolysis of inulin. Gel formation of inulin may be related to the average chain length of inulin after heating. [source] N -Isopropylacrylamide/2-Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive BehaviorMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006Zhiqiang Cao Abstract Summary: Tri-arm star diblock copolymers, poly(2-hydroxyethyl methacrylate)- block -poly(N -isopropylacrylamide) [P(HEMA- b -NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a two-step ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well-controlled polymerization of trifunctional macro-initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature-variable 1H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I-(HEMA40 -NIPAAm320)3 solutions developed into core-shell micelles with diameters of approximately 100 nm. I-(HEMA40 -NIPAAm320)3 was used as a representative example to elucidate the mechanism underlying temperature-induced phase transition of copolymer solution. In this study we proposed a three-stage transition process: (1) separately dispersed micelles state at ,17,22,°C; (2) aggregation and fusion of micelles at ,22,29,°C; (3) sol-gel transition of PNIPAAm segments at ,29,35,°C, and serious syneresis of shell layers. Molecular architecture of Poly(HEMA- b -NIPAAm). [source] Hydrogels assembled by inclusion complexation of poly(ethylene glycol) with alpha-cyclodextrinASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Jie Wang Abstract Polymeric hydrogels were prepared based on the inclusive complexation between ,-cyclodextrin (,-CD) and poly(ethylene glycol) (PEG). Because the rheological property of a thermodynamic stable hydrogel should be gap-independent, it is found in this work that the uniformed hydrogel can be distinguished from gel-like aggregation by changing the plate gap during the rheological measurement. By this rheological method it is determined that suitable storage duration is necessary for the preparation of uniform hydrogels. However, the sonication technique after mixing CD and PEG solutions or increasing PEG concentration can shorten the time to form stable hydrogels. Moreover, the molecular weight of PEG should be high enough (,8000 g/mol) for sol-gel transition. The higher the molecular weight of PEG is, the longer storage time is needed to obtain a uniform hydrogel. From the observation by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) of prepared hydrogels, we concluded that the driving force of networks should be attributed to the crystallization of complexed ,-CDs in the ,-CD/PEG pseudo-polyrotaxanes. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||