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Luminescence enhancement of the rare-earth ion Eu(iii) in supramolecular hydrogels formed by self-assembly of the hydrogelator N,N-dibenzoyl-l-cystine (DBC) was observed by fluorescent optical microscopy and steady-state luminescence. The spectra of varying temperature luminescence showed that luminescence intensities of Eu(iii) in DBC gels decreased with an increase of temperature and a dramatic decrease observed in the range 60–70 °C, which can be ascribed to the dissociation of DBC aggregates. This implied that the luminescence enhancement of Eu(iii) in supramolecular hydrogels is related to the self-assembled DBC. The morphology of DBC aggregates in the presence of Eu(iii) shows highly entangled and thin fibrillar aggregates compared with less entangled and thick aggregates in the absence of Eu(iii). The phase transition temperature (TSG) of DBC gels increased with an increase of Eu(iii) concentration. This suggests that interaction occurs between Eu(iii) and DBC aggregates. The UV and FT-IR spectra of the DBC gels in the presence of Eu(iii) indicated the formation of complexation between Eu(iii) and oxygen atoms of DBC aggregates. The results reveal the mechanism of the luminescence enhancement of Eu(iii) in supramolecular hydrogels, which most likely involve the interaction between Eu(iii) and DBC aggregates. [ABSTRACT FROM AUTHOR]

A new hydrogelator based on Lphenylalanine with a long hydrophobic chain and positively charged terminus was synthesized, and its gelation behavior in H2O was investigated. Polarized optical microscopy POM, field emission scanning electron microscopy FESEM, and Xray diffraction XRD results indicate that the hydrogelator selfassembles into fibreslike aggregates which then lead to the formation of a hydrogel. 1HNMR and CD spectra of hydrogels and aqueous solution revealed that intermolecular Hbonding between the amide groups was the driving force for gelation. A luminescence study, in which ANS 8anilinonaphthalene1sulfonic acid was used as a probe, indicated that the hydrophobic interactions between long chains were the driving force for gelation. Consequently, it was proved that the hydrogelator selfassembles into fibrelike aggregates and then forms supramolecular hydrogels through the Hbonding and hydrophobic interactions. [ABSTRACT FROM AUTHOR]

The article discusses polymer engineering research wherein thermosensitive nanogels with varied monomer compositions were prepared via precipitation polymerization. The aqueous dispersions of these nanogels showed in situ gelable characteristics. Steady-state and dynamic rheological analyses demonstrated that their dispersions were typical pseudoplastic liquids at room temperature. As the acrylamide content increased, so did the viscosity of the dispersions at a constant shear rate. A sol-gel phase transition occurred during temperature raises.

The self-assembly of low molecular weight gelators confined within the nano-scale interlayer space of organo-montmorillonite is likely to be different from that under normal conditions (bulk space). Four kinds of gelators, 1-methyl-2,4-bis(N′-n-octadecylureido) benzene (MBB18), 1-methyl-2,4-bis(N′-n-dodecylureido)benzene (MBB12), bis(4′-stearamido phenyl) methane (BSM18) and bis(4′-octanamido phenyl)methane (BOM8), were used to investigate gelation of organic solvents confined within the nano-scale interlayer space of organo-montmorillonite. The possible morphologies of these gelators aggregates confined within the nano-scale space of organo-montmorillonite will be discussed in comparison with that in bulk space by employing differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Herein, two types of organogels were prepared under the same conditions. One of them was formed within the interlayer space of organo-montmorillonite and another was formed in bulk space. The XRD patterns confirm that self-assembly of gelators takes place viaan unusual pathway within the confined interlayer space of organo-montmorillonite, indicating that the alkyl chains of gelators adopt a parallel arrangement and do not insert into each other. This unusual arrangement of gelators confined within the interlayer space of organo-montmorillonite does lead to the different thermal effect observed by the DSC measurements. These features ultimately strengthen the thermodynamic stability of gelator aggregates, for example MBB18, and raise the gel-to-sol transition temperature, which jumps from 60 to 123 °C. [ABSTRACT FROM AUTHOR]

Abstract  Ionically cross-linked polyampholytic hydrogels were synthesized by redox copolymerization of acrylamide and an ionic complex of (N,N-diethylamino)ethyl methacrylate and acrylic acid (designated as PADA hydrogel). The swelling behavior of the hydrogels in water indicated that a minimal equilibrium swelling ratio is found when the molar ratio of anionic/cationic monomers was 1.55. In NaCl solution, the hydrogels exhibited the typical swelling behavior of conventional polyampholytic gels. Their equilibrium swelling ratios increased with an increase in the NaCl concentration. In solutions of multivalent ions (CaCl2 and trisodium citrate solutions), the equilibrium swelling ratios of the hydrogels increased first and were then followed by a decrease with an increase in salt concentration. Interestingly, an unexpected abrupt swelling phenomenon was observed when the fully swollen hydrogels in salt solution were transmitted to pure water. The unique swelling behavior of PADA hydrogels depends not only on the molar ratio of the anionic/cationic monomers but also on the valency of the ions. [ABSTRACT FROM AUTHOR]

The enzymatic degradation mechanism of semi‐interpenetrating network (semi‐IPN) hydrogel of poly (acrylic acid‐acrylamide‐methacrylate) crosslinked by azocompound and amylose in vitro was investigated in the presence of Fungamyl 800L (α‐amylase) and rat cecum content (cecum bacteria). The degradation mechanism involves degradable competition, i.e., reduction of azo crosslinkage is dominant in the earlier period of degradation. Subsequently, the degradation of gels is continued by combination of reduction of azo crosslinkage and hydrolysis of amylose. The cumulative release ratios of Bovine serum albumin (BSA, as a model drug) loaded semi‐IPN gels are 25% in pH 2.2 buffer solutions and 74% in pH 7.4 buffer solutions within 48 h. Moreover, the release behavior of BSA from the semi‐IPN gels indicates that it follows Fickian diffusion mechanism in pH 2.2 media and non‐Fickian diffusion and polymer chains relaxation mechanism in pH 7.4 media. The results indicate that the release of BSA from the semi‐IPN gels was controlled via a combined mechanism of pH dependent swelling and specificity to enzymatic degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [ABSTRACT FROM AUTHOR]

Abstract??In situ gelable poly(N-isopropylacrylamide-co-acrylamide) microgels were prepared by precipitation polymerization in the presence of various amounts ofN,N?-methlenebisacrylamide as a crosslinker. The diameters of microgels were in the range of 200?300?nm with narrow distributions as determined by photo correlation spectroscopy. The equilibrium swelling ratio and thermosensitive properties of the microgels increased with decreasing crosslinker content. The volume phase transition of microgels dispersions at high concentrations were investigated by phase diagrams. The microgels dispersions experienced four phases when the temperature was increased: semitranslucent swollen gel, clear flowable suspension, cloud flowable suspension, and white shrunken gel. The related phase transition temperatures were influenced by crosslinker content and the concentration of the microgel dispersions. Herein, the gelation temperature was changed by more than 20??C, shrinking temperatures were slightly changed by about 3??C, and cloud point temperatures showed almost no change. The three phase transition temperatures of microgels dispersed in phosphate-buffered saline solutions were lower than that in water. As drug carriers, the release rates of bleomycin from bleomycin-loaded microgel dispersions exhibited diffusion control at human body temperature. [ABSTRACT FROM AUTHOR]