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Physical Gels (physical + gel)

Distribution by Scientific Domains

Chemistry	66%
Polymers and Materials Science	33%

Selected Abstracts

A Thermosensitive and Biodegradable Physical Gel with Chemically Crosslinked Nanogels as the Building Block

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2008
Zigang 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]

Spin-Crossover Physical Gels: A Quick Thermoreversible Response Assisted by Dynamic Self-Organization

CHEMISTRY - AN ASIAN JOURNAL, Issue 1 2007
Tsuyohiko Fujigaya
Abstract Iron(II) triazolate coordination polymers with lipophilic sulfonate counterions with alkyl chains of different lengths have been synthesized. In hydrocarbon solvents, these polymers formed a physical gel and showed a thermoreversible spin transition upon the sol,gel phase transition. The formation of a hydrogen-bonding network between the triazolate moieties and sulfonate ions, bridged by water molecules, was found to play an important role in the spin-crossover event. The spin-transition temperature was tuned over a wide range by adding a small amount of 1-octanol, a scavenger for hydrogen-bonding interactions. This additive was essential for the iron(II) species to adopt a low-spin state. Compared with nongelling references in aromatic solvents, the spin-crossover physical gels are characterized by their quick thermal response, which is due to a rapid restoration of the hydrogen-bonding network, possibly because of a dynamic structural ordering through an enhanced lipophilic interaction of the self-assembling components in hydrocarbon solvents. [source]

Biomimetic Self-Assembly of Tetrapeptides into Fibrillar Networks and Organogels

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2008
Sajid Iqbal
Abstract The self-assembly features of a family of tetrapeptides with a silk-inspired structure are presented. An exhaustive study of the influence of the terminal alkyl chain length in this process is undertaken. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), FTIR spectroscopy, and circular dichroism were used for structural analysis. These compounds, as in the natural model, self-assemble into antiparallel ,-sheet structures that further organize to form fibrillar aggregates. Furthermore, some of them arecapable of forming a crowded network that entraps thesolvent leading to physical gels with different microscopic morphologies. A model for the assembly process is proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Rheological Characterization of a Gel Formed During Extensive Enzymatic Hydrolysis

JOURNAL OF FOOD SCIENCE, Issue 5 2001
D. Doucet
ABSTRACT Extensive hydrolysis of whey protein isolate (WPI) by Alcalase 2.4L® caused a dramatic increase in turbidity and viscosity. A gel was formed after the degree of hydrolysis was , 18%, coinciding with < 16%,-lactoglobulin and < 4%,-lactalbumin remaining unhydrolyzed. Heat-induced and enzyme-induced WPI gels were compared. Frequency and strain dependence indicated that both gels could be considered as strong, physical gels. [source]

Atypical polysaccharide physical gels: structure/property relationships

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Alexandra Clayer
Abstract Chitin and chitosan are polysaccharides produced by the biomass. They have the same general chemical structure and constitute the series of linear copolymers of linked ,, (1->4) glucosamine and N-actylglucosamine. We studied the possibility of forming physical gels with all the terms of this series, whatever the proportion of the two kinds of residues included in the polymer chains. We show that physical gelation is still possible through a percolating process when certain important conditions are met. Initially the concentration in polymer must be above C*; a critical value of the balance between hydrophobic and hydrophilic interactions must be achieved and gelation must occur simultaneously everywhere in the medium. These conditions were observed in several situations allowing the formation of different kinds of gels at all values of DA. In view of the rare bio-active properties of chitin and chitosan, these gels were tested for living tissue regeneration and constitute very interesting examples in illustration of our concept of decoys for biological media. [source]

Role of Capping Ligands on the Nanoparticles in the Modulation of Properties of a Hybrid Matrix of Nanoparticles in a 2D Film and in a Supramolecular Organogel

CHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2009
Asish Pal Dr.
Abstract We incorporate various gold nanoparticles (AuNPs) capped with different ligands in two-dimensional films and three-dimensional aggregates derived from N -stearoyl- L -alanine and N -lauroyl- L -alanine, respectively. The assemblies of N -stearoyl- L -alanine afforded stable films at the air,water interface. More compact assemblies were formed upon incorporation of AuNPs in the air,water interface of N -stearoyl- L -alanine. We then examined the effects of incorporation of various AuNPs functionalized with different capping ligands in three-dimensional assemblies of N -lauroyl- L -alanine, a compound that formed a gel in hydrocarbons. The profound influence of nanoparticle incorporation into physical gels was evident from evaluation of various microscopic and bulk properties. The interaction of AuNPs with the gelator assembly was found to depend critically on the capping ligands protecting the Au surface of the gold nanoparticles. Transmission electron microscopy (TEM) showed a long-range directional assembly of certain AuNPs along the gel fibers. Scanning electron microscopy (SEM) images of the freeze-dried gels and nanocomposites indicate that the morphological transformation in the composite microstructures depends significantly on the capping agent of the nanoparticles. Differential scanning calorimetry (DSC) showed that gel formation from sol occurred at a lower temperature upon incorporation of AuNPs having capping ligands that were able to align and noncovalently interact with the gel fibers. Rheological studies indicate that the gel,nanoparticle composites exhibit significantly greater viscoelasticity compared to the native gel alone when the capping ligands are able to interact through interdigitation into the gelator assembly. Thus, it was possible to define a clear relationship between the materials and the molecular-level properties by means of manipulation of the information inscribed on the NP surface. [source]