Gel Sol Research Articles

Thermal decomposition approach for the synthesis of CdS–TiO2 nanocomposites and their catalytic activity towards degradation of rhodamine B and reduction of Cr(VI)

CdS–TiO2 nanocomposites were prepared by a simple thermal decomposition approach. The effect of using four different types of TiO2 (as-prepared sol–gel TiO2 nanoparticles, sol–gel TiO2 after calcination at 500°C, sol–gel TiO2 after calcination at 700°C and macro-crystalline TiO2 ) on the structure, optical properties and photocatalytic activity of the nanocomposites was investigated. The nanocomposites were characterized by powder X-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy, diffuse reflectance spectroscopy and photoluminescence spectroscopy. The CdS–TiO2 nanocomposites consist of cubic CdS and anatase TiO2 nanocrystallites when as-prepared sol–gel TiO2 nanoparticles, sol–gel TiO2 calcined at 500°C and macro-crystalline TiO2 were used. On the other hand, when sol–gel TiO2 after calcination at 700°C was used, the nanocomposites were found to consist of rutile TiO2. TEM results indicate uniform distribution of CdS nanoparticles (10.5±1.6nm) on the TiO2 matrix in the nanocomposites prepared using as-prepared sol–gel TiO2 nanoparticles and sol–gel TiO2 after calcination at 500°C. In the nanocomposites, a blue shift of the band gap of CdS compared to bulk CdS is observed. The CdS–TiO2 nanocomposites act as good catalyst for the photodegradation of rhodamine B (RhB) and reduction of Cr(VI) in the presence of sunlight.

Phase transitions in cellulose microfibril dispersions by high-energy mechanical deagglomeration.

It is shown that dispersions of cellulose microfibrils display gel-sol and direct gel-colloidal liquid crystalline structure transitions. This is achieved by applying high-energy mechanical deagglomeration to bacterial cellulose (BC) networks in the presence of sodium carboxymethyl cellulose (CMC). At high CMC content adsorption of the polymer leads to a significant increase in the ζ potential. The resulting apparent phase diagram shows transitions from aggregates to single microfibril dispersions with increasing the CMC/BC weight ratio at low microfibril concentrations. At higher concentrations, liquid crystalline ordering was observed and the microstructure becomes more homogeneous with increasing the CMC content. The observed liquid crystalline ordering was found to be reminiscent of nematic gels. Applying deagglomeration in the presence of CMC, thus, transitions the system from aggregates and gels to dispersions of single microfibrils and nematic gel-type structures.

Gel–sol–gel transition of kappa-carrageenan and methylcellulose binary systems studied by differential scanning calorimetry

Kappa-carrageenan (κC) was mixed with methylcellulose (MC) with various mixing ratios. Phase transition behaviour of the above mixed solutions with 1 and 2% concentration was investigated by visual observation and differential scanning calorimetry (DSC). Three regimes showing unique transition behaviour were observed: Regime I which is an MC rich region where only sol–gel transition is found, Regime II an intermediate mixing range of κC and MC where sinusoidal change of gel–sol–gel transition was observed, and Regime III a κC rich region where only gel–sol transition was detected. A phase diagram of κC/MC binary systems was established based on transition temperatures obtained by visual observation and DSC.

Spatiotemporal control of synergistic gel disintegration consisting of boroxole- and glyco-based polymers via photoinduced proton transfer.

We demonstrate here a local- and remote-control of gel disintegration by using photoinduced proton transfer chemistry of photoacid generator (PAG). The gels were prepared by simply mixing two polymers, poly(N-isopropylacrylamide-co-5-methacrylamido-1,2-benzoxaborole) (P(NIPAAm-co-MAAmBO)) and poly(3-gluconamidopropyl methacrylamide) (PGAPMA) via the synergistic interaction of benzoxaborole and diol groups. The o-nitrobenzaldehyde (o-NBA) was then loaded into the gel as a PAG. The benzoxaborole-diol interaction was successfully disintegrated upon UV irradiation due to the local pH decrease inside the gel. When the gel was irradiated to a specific gel region, the synergistic interactions were disintegrated only at the exposed region. Of special interest is that the whole material eventually transitioned from gel to sol state, as the generated protons diffused gradually toward the nonilluminated region. The ability of the proposed gel-sol transition system via photoinduced proton diffusion may be beneficial for not only prompt pH changes within the gel but also the design of predictive and programmable devices for drug delivery.

An electric field responsive drug delivery system based on chitosan–gold nanocomposites for site specific and controlled delivery of 5-fluorouracil

A novel drug delivery system based on an electric field and pH dual-stimuli responsive chitosan–gold nanocomposite (CGNC) is reported in the present study for site specific controlled delivery of the anticancer drug 5-fluorouracil (5-FU). At a higher pH of the solution CGNC encapsulates the drug molecules in its 3D-network and releases the drug at a relatively lower pH due to its reversible gel–sol transition properties. A sulphorhodamine B cytotoxicity assay showed that the chitosan–gold nanocomposite–fluorouracil conjugate (CGNC–FU) has higher cytotoxicity than 5-FU to the cervical cancer cells, SiHa. Drug release from CGNC has been controlled by applying a weak, external DC electric field. The drug delivery system is illustrated to be effective for the loading and delivery of 5-FU. The encapsulation efficiency of CGNC was found to be 36% and about 63% of the drug was released by applying the electric field. The biocompatibility of CGNC was demonstrated by growing SiHa cells successfully on a CGNC film electrodeposited on an indium tin oxide (ITO) coated glass plate. SiHa cells grown on a CGNC–FU conjugate modified ITO plate showed less viability and further application of an electric field of 1.5 V for the release of 5-FU led to the complete death of the cells. A highlight of the present drug delivery system is that the drug release can be controlled externally.

Plugging behavior of gellan in porous saline media

ABSTRACTIn this article, the hydrodynamic behavior of dilute aqueous solutions of a natural polysaccharide—gellan in the porous media under the modeled oilfield conditions is described. The hydrodynamic properties of gellan and poly(acrylamide) solutions in saline porous media are compared. The influence of inorganic salts NaCl, KCl, CaCl2, MgCl2, and BaСl2 on sol–gel and gel–sol transitions of dilute gellan solutions was evaluated. The mechanism of sol–gel transition in the presence of individual alkaline and alkaline‐earth metal salts is described on the basis of literature data. The viscometric measurements revealed that the effectiveness of salts to enhance gelation of gellan changes in the following order: BaСl2 > CaCl2 ≈ MgCl2 > KCl > NaCl. The sol–gel and gel–sol phase transitions of gellan solution were also observed upon addition of oil field water containing 73 g L−1 of alkaline and alkaline earth metal ions. During the injection of gellan solutions into the porous media saturated by saline water an oscillation of the injection pressure was observed. Such behavior of gellan is explained by either the sol‐to‐gel and the gel‐to‐sol transitions of the polymer taking place in saline water or the step‐by‐step plugging of high permeable channels until all high permeable channels of sand packs are plugged due to gellan invasion. The application of brine‐initiated gelation of gellan for water shutoff operations (WSO) in field conditions was demonstrated. Higher technological effectiveness of gellan injection in comparison with existing gelation systems was shown. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41256.

Correlation between site preference and magnetic properties of Co–Zr doped BaCoxZrxFe(12−2x)O19 prepared under sol–gel and citrate precursor sol–gel conditions

Herein, we report the synthesis of Co–Zr doped BaCoxZrxFe(12−2x)O19 (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) M-type hexagonal ferrites under sol–gel (series 1) and citrate precursor sol–gel (series 2) conditions. These compounds were characterized by TG-DTA, FT-IR, XRD, EDS and BET techniques. XRD patterns and parameters reflect that series 2 yield more symmetrical structures with lower average particle size. Results reveal that magnetization and magnetocrystalline anisotropy are closely related to the distribution of Co–Zr on the five sub lattices. The compounds of series 1 register a steep fall in coercivity [5428Oe (x=0) to 630.2Oe (x=1.0) than series 2 [2790Oe (x=0) to 1210Oe (x=1.0)]. MS varies from 63.63 to 56.94emu/g and 62.79–53.78emu/g in series 1 and 2, respectively. Mössbauer analysis suggests that site preferences strongly depend upon the nature of dopant, fuel and the preparatory conditions.

Thermosensitive porphyrin-incorporated hydrogel with four-arm PEG–PCL copolymer: Preparation, characterization and fluorescence imaging in vivo

A biodegradable thermosensitive hydrogel based on four-arm PEG–PCL copolymer was prepared with porphyrin as a fluorescence tag. Its structure and composition were characterized by FTIR, 1H NMR and GPC. Sol–gel–sol transition was evaluated by the test tube-inverting method and rheological analysis. The optical properties of hydrogel were investigated by UV–vis and fluorescence spectroscopy in vitro and by fluorescence imaging system in vivo. The results show that the thermosensitive hydrogel possesses dual function of fluorescence and injectability in vivo with good biocompatibility. Consequently it can be potentially applied in biomedical field as a visible implant for in situ monitoring.

Fabrication of organogels achieved by prodrug-based organogelators of ketoprofen

The treatment strategy of curing diseases using prodrugs of an anti-inflammatory drug is widespread. In the present study, we report on the synthesis of prodrugs of ketoprofen, consisting of a derivatization of ketoprofen and long hydrocarbon chain of fatty acids with diacylhydrazine linkage. The presence of an acidic moiety in ketoprofen may lead to ulceration in the gastrointestinal tract that reduces the efficacy of the drug with an increased adverse effect. The synthesis of prodrugs of ketoprofen involves the use of fatty acids as a carrier and hydrazine as a spacer. Synthesized prodrugs were characterized by infrared, 1H-NMR and mass spectroscopy. The resulting prodrugs were found to be insoluble in water and precipitated out in acetonitrile, hexane, benzene, and so on. The synthesized prodrugs are slightly soluble in chloroform, methanol and ethanol and only form a gel like structure in carbon tetrachloride. The resulting gels are referred as organogels and prodrugs are referred to as organogelators. The surface morphology of the prepared organogels were studied by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), and other spectral characteristics were also investigated. FE-SEM and TEM images revealed that there were continuous elongated fiber-like structures present that were in the nanometer size range. Gel–sol temperature profiles of the prepared organogels were also studied using differential scanning calorimetry. The results from all these techniques are presented and discussed from point of view of the use of the derivatives as prodrug formulations. It is demonstrated that the prodrug containing the diacylhydrazine moiety has the ability to form a gel.

Copillar[5]arene-based supramolecular polymer gels

Copillar[5]arene-based supramolecular polymer gels were obtained in acetonitrile. These supramolecular polymer gels were driven by C–H⋯π interactions, presented two phases as time goes on, and finally formed a supramolecular organic framework. Notably, the supramolecular polymer gels showed reversible gel–sol phase transitions upon heating and cooling. Moreover, the gels exhibit excellent self-healing properties.

Redox-Switchable Copper(I) Metallogel: A Metal–Organic Material for Selective and Naked-Eye Sensing of Picric Acid

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

Sonication induced morphological transformation between 3D gel network and globular structure in a two-component gelation system

A two-component gelator (B1⋯C12⋯B1) based on interaction between dendritic branch (Branch1 (COOH)) and diaminododecane is designed and synthesized, and its self-assembly behavior in methyl methacrylate (MMA) is firstly investigated. It is interesting to find that the gel formation depends on the concentration and sonication during cooling of the B1⋯C12⋯B1/MMA solution. Sonication plays as a switch simulator for exchanging morphology between a 3D gel network and globular structure in a certain concentration range. Thermal stability, rheological properties, morphology and self-assembly mechanism of the gels were investigated with tube inversion methodology, Dynamic oscillatory measurement, SEM and FTIR, respectively. The results indicated that Sonication-induced-gel (S-gel) exhibits much higher gel–sol temperature, storage modulus and lower critical gelator concentration compared with Temperature-induced-gel (T-gel), while sonication could partially destroy the hydrogen bond network and benefit the formation of the organogels.

Gel–sol–gel′ evolution triggered by formic acid

Supramolecular “gel A” based on β-cyclodextrin as the gelator and K2CO3 as the salt bridge can be activated by the addition of HCOOH to evolve into another “gel B”. In the process, the release of CO2 dissociated the network of the “gel A” bridged by K2CO3 and the new network of the “gel B” can be reorganized with the help of the newborn HCOOK. The two gels, “A and B”, were investigated by optical microcopy, scanning electron microscopy, small- and wide-angle X-ray scattering, Fourier transform-infrared spectroscopy and X-ray diffraction. The “gel B” with greater elastic modulus (G′, 1×105Pa) could endure higher applied stress (the yield point 300Pa) than the “gel A” (G′, 3×104Pa; the yield point 180Pa). The “gel B” also exhibited the higher phase transition temperature (161.75°C) than that (34.4°C) of the “gel A” in differential scanning calorimetry. The influence of analogous salts on the macroscopic aspect of the samples was also reported. The reason behind the gel–sol–gel′ phase transition was the salt bridge evolution. This work is the first report on gel evolution with phase reorganization triggered by chemical additive (HCOOH), which may be of great significance to develop drug controlled release materials, and other more complex stimuli-responsive materials.

Restless cell syndrome

Restless cell syndrome

Responsive Supramolecular Polymer Metallogel Constructed by Orthogonal Coordination-Driven Self-Assembly and Host/Guest Interactions

An emerging strategy for the fabrication of advanced supramolecular materials is the use of hierarchical self-assembly techniques wherein multiple orthogonal interactions between molecular precursors can produce new species with attractive properties. Herein, we unify the spontaneous formation of metal-ligand bonds with the host/guest chemistry of crown ethers to deliver a 3D supramolecular polymer network (SPN). Specifically, we have prepared a highly directional dipyridyl donor decorated with a benzo-21-crown-7 moiety that undergoes coordination-driven self-assembly with a complementary organoplatinum acceptor to furnish hexagonal metallacycles. These hexagons subsequently polymerize into a supramolecular network upon the addition of a bisammonium salt due to the formation of [2]pseudorotaxane linkages between the crown ether and ammonium moieties. At high concentrations, the resulting 3D SPN becomes a gel comprising many cross-linked metallohexagons. Notably, thermo- and cation-induced gel-sol transitions are found to be completely reversible, reflecting the dynamic and tunable nature of such supramolecular materials. As such, these results demonstrate the structural complexity that can be obtained when carefully controlling multiple interactions in a hierarchical fashion, in this case coordination and host/guest chemistry, and the interesting dynamic properties associated with the materials thus obtained.

Stimuli-induced gel-sol transition of supramolecular hydrogels based on β-cyclodextrin polymer/ferrocene-containing triblock copolymer inclusion complexes

A novel kind of host-guest hydrogel possessing gel–sol phase transformation in response to temperature, oxidizing agent and glucose was prepared by ferrocene (Fc)-containing pluronic F127 and β-cyclodextrin (β-CD) linear polymer, which was synthesized in aqueous alkali by using native β-CD and epichlorohydrin in the presence of toluene. Because of the reversible association–dissociation of Fc-β-CD inclusions and F127 micelles, the gel-sol transition was easily observed. Two-dimension nuclear overhauser effect spectroscopy (2D NOESY), nuclear magnetic resonance (NMR), TEM (transmission electron microscopy) and TGA (thermogravimetric analysis) measurements were used to clarify the inclusion complexes of Fc-β-CD. The results showed that the formation of inclusion complexes affected the micelle size and stabilized the hydrogels. The rheological properties of solution and hydrogels were measured. The viscosity of hydrogel was enhanced markedly, to about 90 times higher than that of Fc-F127-Fc solution at the same concentration. Due to the coactions of PPO aggregation and Fc-β-CD inclusion, the gelation temperature of hydrogel was lower than that of Fc-F127-Fc solution. The reversible gel-sol transition and multi-sensitive supramolecular hydrogels may potentially be used in injectable hydrogel for drug delivery.

Thermal and photo reversible gel–sol transition of azobenzene based liquid crystalline organogel

Abstract Azobenzene based photoresponsive gelator, 1,2-bis[4-(4-(10-decyloxy)phenylazo)]-benzoylhydrazine showing selective gelation in alcoholic solvent is described. Whilst their thermodynamic behaviors are investigated by polarized optical microscopy and differential scanning calorimetry, the related layer arrangement is measured by X-ray diffraction techniques in which the organogel shows monotropic liquid crystalline phase. Present work shows that the non-liquid crystalline gelator can be converted into liquid crystalline organogel in the presence of alcoholic solvent in which the trans-cis isomerization of the azobenzene moiety disrupts the entanglement of gel fibers of self-assembly resulting in gel–sol transition. The present result also shows that the organogel is capable of the thermal and photo induced transition from gel–sol and vice versa.

Direct evidence of gel–sol transition in cyclodextrin-based hydrogels as revealed by FTIR-ATR spectroscopy

The phase transition from gel to liquid suspension in cyclodextrin (CD)-based hydrogels is in depth monitored by using Fourier transform infrared spectroscopy in attenuated total reflectance geometry. Cyclodextrin nanosponges (CDNS) synthesized by polymerization of CD with the cross-linking agent ethylenediaminetetraacetic dianhydride at different cross-linking agent/CD molar ratios have been left to evolve from gel phase into liquid suspension upon gradual increase of the hydration level. Measurements of the changes occurring in the vibrational dynamics of the system during this transition provide direct evidence of the gel-sol progress of the CNDS hydrogel, by accounting for the connectivity pattern of water molecules concurring to the gelation process. The experimental results clearly indicate that the increase of the hydration level is accompanied by the corresponding increase of the population of H2O molecules engaged in high-connectivity hydrogen-bond networks. The water tetrahedral arrangement is thus dominant above a characteristic cross-over hydration level, experimentally determined for all the investigated samples. The observation of this characteristic cross-over point for the CDNS hydrogel and its correlation with other parameters of the system (e.g. the absorption ability of CDNS and elasticity of the polymer matrix) is, once again, modulated by the cross-linking agent/CD molar ratio. The latter seems indeed to play a key role in defining the nano- and microscopic properties of nanosponge hydrogels.

A supramolecular polymer gel with dual-responsiveness constructed by crown ether based molecular recognition

A supramolecular polymer gel was prepared from self-assembly of a heteroditopic A–B monomer based on benzo[18]crown-6. Such a gel shows interesting gel–sol transitions in response to dual-stimuli owing to the dynamically reversible complexation between benzo[18]crown-6 and primary alkylammonium salt moieties.

Characterization and phase transition study of a versatile molecular gel from a glucose-triazole-hydrogenated cardanol conjugate

The synthesis and gelation properties of a structurally simple, renewable-resource-based glucose-triazole-hydrogenated cardanol conjugate (GTHCC) are reported. The conjugation of hydrogenated cardanol and glucose was done using a triazole linker employing copper(I) mediated acetylene azide cycloaddition ‘click’ chemistry in the key step. The GTHCC was found to form four different classes of gels; namely, (i) hydrogel from aqueous-protic solvents, (ii) organogel from non-polar solvents, (iii) gel from vegetable oil and (iv) gel from petroleum oil. In a water–methanol (1 : 1) mixture, the conjugate acted as a stable thermoreversible supergelator, even at a very low gelator concentration of 0.03% w/v. Unlike glycoside-based gels derived from hydrogenated cardanol and glucose, the GTHCC is stable under acidic as well as basic conditions, owing to the covalent linkages in the tether. The intrinsic fluorescence of the hydrogel was found to be sensitive towards a gel–sol transition.