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Gelation Process (gelation + process)
Selected AbstractsRobust Organic/Inorganic Hybrid Porous Thin Films via Breath-Figure Method and Gelation ProcessMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2007Ke Zhang Abstract A novel organic/inorganic hybrid honeycomb patterned porous thin film was prepared using the breath-figure method combined with a sol-gel process. An in situ formed gelable block copolymer, formed by mixing poly(styrene- alt -maleic anhydride)- block -polystyrene (P(St- a -MAn)- b -PS) and 3-aminopropyltrimethoxysilane (APS), was used as the structure directing agent. The porous film produced was dipped into an acid aqueous solution to induce a sol-gel process in the wall of film. As a result of gelation, the structure of this film transformed into a crosslinked silica oxide hybridized with PS, and this film resisted those organic solvents which were once good solvents for the copolymer precursor. [source] Effect of milk source on the rheological properties of yogurt during the gelation processINTERNATIONAL JOURNAL OF DAIRY TECHNOLOGY, Issue 3 2001R Y Jumah This paper presents research on the effect of milk source on the rheological properties of curd during the gelation process of yogurt. The highest value for viscosity was exhibited by ovine milk, followed by caprine, bovine and camel milks. For bovine, ovine and caprine milk, three different transient viscosity stages were identified and described by mathematical expressions, whereas camel milk showed no significant variation in viscosity during gelation. The chemical composition of milk, namely total solids and protein content, has a major effect on the rheological properties of curd. A power law model allows the determination of the flow behaviour index and the consistency coefficient of curd made from different milk sources. [source] RHEOLOGICAL PROPERTIES OF SET YOGURT AS INFLUENCED BY INCUBATION TEMPERATURE AND HOMOGENIZATIONJOURNAL OF FOOD QUALITY, Issue 5 2002R.R. SHAKER The effect of incubation temperature and homogenization on the rheological nature of yogurt curd during gelation was investigated in this study. Our results indicated that the optimum incubation temperature for acid development was 45C. The minimum viscosity was observed at 40C while the maximum viscosity was at 48C. Our results also indicated that incubation temperature affected yogurt viscosity during the gelation process while homogenization had no significant effect. Increasing the incubation temperature decreased the flow behavior index and increased the consistency coefficient; homogenization increased the flow behavior index and decreased the consistency coefficient as described by a power law model. [source] Modeling the mass transfers during the elaboration of chitosan-activated carbon composites for medical applicationsAICHE JOURNAL, Issue 6 2010A. Venault Abstract Hydrogels composites composed of chitosan and activated carbon were prepared for medical applications using the vapor-induced phase separation process. Since the gelation process involves mass exchanges between the polymer solution and the air, the kinetics of mass transfer were investigated through experimental and modeling approaches. Among the formulation and process parameters, gravimetric measurements exhibited that mass transfers were mostly controlled by the initial ammonia partial pressure. A nonisotherm mass-transfer model was developed to predict the nonsolvent and solvent exchange rates, therefore, the water and ammonia concentration profiles within the sample during the process. The numerical results were successively validated with gravimetrical kinetic curves obtained in a chamber where the process parameters were controlled. The model aimed also at predicting the pH moving front along the film thickness. The gelation time could also be predicted for different operating conditions (formulation and process parameters). © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Using Differential Scanning Calorimetry to Follow How Gelcasting ProceedsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007BoonSing Ng Differential scanning calorimetry studies on aqueous low-toxicity monomer,crosslinker gelcasting systems loaded with zirconia powder provided information on the onset and kinetics of the polymerization reaction. A simple procedure was developed to determine the relative importance of the individual components on the gelation process. It was found that the thermal stability and dissociation of the initiator control the gelation rate and that the zirconia particles accelerate the gelation. [source] Gelling of Alumina Suspensions Using Alginic Acid Salt and Hydroxyaluminum DiacetateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2002Andre R. Studart This paper proposes a novel direct casting method of alumina suspensions using alginic acid salt and the coagulation agent hydroxyaluminum diacetate (HADA). These two compounds allowed the consolidation of alumina suspensions through a simultaneous time-delayed physical and chemical gelation process. The physical gel was formed by the gradual release of aluminum and acetate ions from the HADA in water, while the chemical gel originated from the cross-linking of alginate molecules by the polyvalent aluminum ions. Wet alumina green bodies displayed enhanced mechanical properties with the addition of minimal contents of organic material (<0.1 wt%). [source] U-PVC gelation level assessment, part 1: Comparison of different techniquesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2006Louise-Anne Fillot Several different gelation assessment methods such as differential scanning calorimetry, capillary rheometry, solvent absorption, wide angle x-ray scattering, transmission electron microscopy, and atomic force microscopy were applied to a typical PVC window profile formulation subjected to various thermomechanical histories. Shear applied during the process could be decomposed into two components: (i) a thermal component corresponding to the self-heating that was generated and (ii) a "mechanical" component associated with a "pure" shearing action deprived of any thermal aspect. Shear sensitivity of the above-mentioned gelation assessment techniques was evaluated by considering both aspects. Gelation levels established by differential scanning calorimetry and capillary rheometry were especially compared, thus allowing a comparison of the two physical aspects evidenced by each technique, i.e., crystallite melting and macromolecular network development. It appeared that as soon as the PVC particulate structure had been fragmented into micronic entities (primary particles) the gelation process was governed mainly by the thermal aspect, i.e., crystallite melting. J. VINYL. ADDIT. TECHNOL. 12:98,107, 2006. © 2006 Society of Plastics Engineers. [source] Temperature Dependence of Sol-Gel Conversion Kinetics in Gelatin-Water SystemMACROMOLECULAR BIOSCIENCE, Issue 4 2009Kai Chen Abstract The conversion kinetics of an aqueous gelatin solution to gel was studied by temperature modulated and regular DSC under isothermal and continuous cooling conditions. Isothermal runs revealed a decrease in the quasi-static heat capacity primarily associated with syneresis (phase separation) of the gel. Above 19,°C the isothermal process demonstrated negative effective activation energy that turned positive below 14,°C. Continuous cooling runs detected a reversing heat flow apparently related to the continuing formation and melting of new gel structures. Isoconversional kinetic analysis of continuous cooling measurements yielded negative activation energy for the whole range of conversions and temperatures suggesting that nucleation remained a rate controlling step throughout the whole gelation process. [source] Blending Chitosan with Polycaprolactone: Porous Scaffolds and ToxicityMACROMOLECULAR BIOSCIENCE, Issue 9-10 2007Aparna R. Sarasam Abstract The preparation and characterization of porous scaffolds from chitosan-PCL blends by freeze extraction, freeze gelation and freeze drying is reported. Using freeze extraction, stable structures were obtained only from PCL, but these were not porous. No stable scaffolds were obtained using the freeze gelation process. Stable scaffolds of chitosan/PCL mixtures could not be obtained using 77% acetic acid by any of these techniques. With 25% aqueous acetic acid, stable scaffolds of chitosan/PCL mixtures were obtained by the freeze drying technique. The stability and pore morphology of freeze dried scaffolds were dependent on the relative mass ratio of chitosan and PCL. A chorioallantoic membrane assay showed that formed 3D chitosan/PCL mixtures were not toxic to vasculature. [source] Agarose Sols and Gels RevisitedMACROMOLECULAR SYMPOSIA, Issue 1 2006Jean-Michel Guenet Abstract Agarose sols have been seen for long as solutions of flexible chains that, on cooling, produce thermoreversible gels through double-helix formation. Investigations of the chain conformation in the sol state by small-angle neutron scattering reveals instead a rigid chain with a very large persistence length (lp,>,9 nm). The chain cross-section radius and mass per unit length correspond to characteristics of helices as those described by Foord and Atkins. These results lead one to a reappraisal of the occurrence of double helices in the gelation process, as they rather suggest a transition of the type loose-single helix,tight single helix. Studies of gels from agarose/water/cosolvent where the cosolvent is Dimethyl Sulfoxide (DMSO), Dimethyl Formamide (DMF), and Methyl Formamide (MF) have led one to conclude on the formation of agarose/water/ cosolvent ternary complexes. The contrast variation method by neutron scattering gives further support to this assumption. Finally, determination of the gel nanostructure allows one to account for the two regimes observed for the variation of the elastic modulus vs concentration. 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