Gelation Of Aqueous Solutions Research Articles

Synthesis and Self-Assembling Properties of Diacetylene-Containing Glycolipids

Diacetylene-containing glycolipids are interesting molecules that have many potential applications. The polydiacetylenes formed by the cross-linking of the diacetylene lipids are new stimuli-responsive materials. In particular, diacetylene lipids that can form gels in aqueous solution are of great interest in designing functional biocompatible materials. We have synthesized a series of diacetylene-containing sugar lipids with different chain lengths, substituents, and positions of diyne and studied their self-assembling properties in several solvents including hexane, ethanol, and ethanol/water mixture. Among the 24 diacetylene-containing glycolipids synthesized, many of them exhibited excellent gelation properties in ethanol or ethanol/water mixture. Typically very long chain diacetylene lipids formed gels in ethanol and hexane. Shorter chain diacetylene lipids and compounds with one free hydroxyl group can form gels in aqueous solution. The position of the diyne and chain length affect the self-assembling properties significantly. The systematic study of the gelation properties for diacetylene lipids with different lipid chains can help us to understand the structure requirement for the desired physical properties. Optical microscopy studies showed that the molecules form interesting architectures such as tubules, rods, sheets, and belts. The resulting organogels can also be cross-linked and give different colored polymerized gels depending on their structures.

Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane

A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m 2 g −1 with a pore size of 3.5 nm, a pore volume of 0.564 cm 3 g −1, and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5–67.5 kJ mol −1 depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.

Elastic properties of swollen polyelectrolyte gels in aqueous salt solutions

The elastic relaxation responding to a uniaxially stretched poly(acrylic acid) rodlike gel in the aqueous NaCl solution was investigated. The relaxation elucidated the shear (mu) and bulk (K) moduli and the frictional coefficients (sigma) of the fully ionized gel at pH above 9 as functions of the degree of swelling, which was controlled by the NaCl concentration (C(S)) of the solution. Two gels, cross-linked chains of which consist of 500 (GelA500) and 50 (GelA50) monomeric units, were examined to investigate the effect of the chain length on the elastic behavior. The moduli of GelA500 increased with swelling at C(S) below 100 mM and decreased at C(S) above it. The mu values of both gels can be characterized by the power function of gel diameter, d as mu proportional, variantd(beta). The beta values being -1 at C(S) above 100 mM transitionally changed to 1.2 at C(S) about 100 mM. That is, the dimensionality of space for the chains to distribute, n(dim) [= (beta+5)/(beta+2) according to the conventional theory [Sasaki et al., J. Chem. Phys. 102, 5694 (1995)]], changed from 4 (n(dim) of ideal chain) to 1.9 at C(S) = 100 mM. This indicates that the electrostatic repulsion between gel chains reduces the n(dim) at C(S) below 100 mM but not at C(S) above it. It was found that the K values of GelA500 were well described by the conventional theory but those of GelA50 not. The sigma(zr)/sigma(rr) (sigma(zr) is an off-diagonal element of the friction coefficient tensor and sigma(rr) is a diagonal element of the friction coefficient tensor) was found to be 2.7 x 10(-2), which was the same as the previously reported value for the swollen poly(acrylamide) gel [Sasaki, J. Chem. Phys. 120, 5789 (2004)]. The sigma(rr) of unit volume of the GelA500 is well explained by the free draining model while the sigma(rr) of GelA50 is less than that of the free draining model, suggesting the slip between water and ionized chain.

Design and Application of Self‐Assembled Low Molecular Weight Hydrogels

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design and Application of Self‐Assembled Low Molecular Weight Hydrogels

AbstractOver the past years, the gelation of aqueous solutions by low molecular weight (LMW) compounds has become an area of increasing interest, owing to developments in the field of LMW organogelators. Until recently, LMW hydrogelators were found only by serendipity, nowadays rational design as well as application of LMW hydrogelators has become feasible. As a consequence, an increasing number of responsive and functional LMW hydrogels are reported, offering great prospects for diverse applications including drug delivery and smart materials. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Specific Interactions of Poly(4-vinyl phenol) Gel with Cationic and Anionic Surfactants

Binding behaviors of ionic surfactants (decyl- and dodecyltrimethylammonium bromide (C(10)TAB, C(12)TAB), sodium decane sulfonate (SDeSo), and sodium dodecyl sulfate (SDS)) to poly(4-vinyl phenol) (P4VPh) gel were investigated to elucidate a specific swelling behavior that has been found for P4VPh gel in aqueous solutions of tetraalkylammonium salts. With increasing cationic surfactant concentration, P4VPh gel significantly deswelled and then remarkably reswelled at a concentration somewhat below the respective cmc values. On the other hand, in the case of the anionic surfactants, the gel only showed a marked swelling at a concentration just below the respective cmc values. A similar charge-specific behavior of the surfactants was also found for the P4VPh dispersion system studied with a UV-vis spectroscopy; namely, in the cationic surfactant-P4VPh systems, the turbidity of the dispersion first increased with increasing the surfactant concentration and then decreased. This result suggests that aggregation of P4VPh particles first occurred and finally the particles were solubilized. A red shift followed by a blue shift observed for a pi-pi absorption of phenol at around 278 nm was also consistent with the aggregation-solubilization behavior. In the anionic surfactant-P4VPh system, however, only solubilization of the polymer particle was observed, and the UV peak only showed a blue shift. All these results in the gel and the dispersion systems strongly suggest that the cation-pi interaction is involved in the binding of the cationic surfactants to P4VPh.

Rheological and Morphological Characterization of Triblock Copolymer (PEO-PPO-PEO)-Clay Gel in Aqueous Solution

AbstractThermal gelation and structure properties of high concentration triblock copolymer poly (ethylene oxide)99-poly(propylene oxide)69-poly(ethylene oxide)99 (Pluronic F127)-clay aqueous solutions were characterized by rheological measurements and scanning electron microscopy (SEM). The sol-gel transition temperature, as well as the viscosity of the F127 solution was found to depend both on the concentration of polymer and clay filler. In all cases, Pluronic F127 gels are pseudoplastic, showing the shear-thinning behavior. Above the gel transition, the viscosity of the solutions increased with increasing the clay concentration. The corresponding macrostructure of the gels was studied by lyophilizing thick samples and scanning them with a scanning electron microscope (SEM). A well-ordered network of porosity was observed as a function of polymer concentration and orientation.

Novel Method of Producing Polymer Gels in Aqueous Solution Using UV Irradiation

AbstractSummary: We developed a novel method of producing polymer gels in aqueous solution using UV irradiation. Persulfates were effective photosensitive initiators of polymerization and/or gelation of acryloyl‐type monomers/polymers. The gelation was confirmed by an abrupt increase in light scattering intensity, 〈I(q)〉T, at the gelation point. The gelation method entails significant advantages: it does not need any cross‐linkers, temperature control (heating), and additives except the persulfate.The UV irradiation time dependence of light scattering intensity, 〈I(q)〉T, for pre‐gel solutions containing N‐isopropylacrylamide (NIPAm) and/or ammonium persulfate (APS).imageThe UV irradiation time dependence of light scattering intensity, 〈I(q)〉T, for pre‐gel solutions containing N‐isopropylacrylamide (NIPAm) and/or ammonium persulfate (APS).

Electromechanical properties of hydrogels based on chitosan and poly(hydroxyethylmethacrylate) in NaCl solution

A semi-interpenetrating polymer network (semi-IPN) hydrogel, composed of chitosan andpoly(hydroxyethyl methacrylate) (PHEMA), exhibited electrically sensitive behavior. Theswelling behavior of the chitosan/PHEMA semi-IPN hydrogel was studied by immersion ofthe gel in aqueous NaCl solutions at various concentrations. The stimulus response of thechitosan/PHEMA semi-IPN hydrogel in electric fields was also investigated. When swollen,the semi-IPN was placed between a pair of electrodes, and showed bending behavior uponthe application of an electric field. The electro-responsive behavior of the present semi-IPNwas also affected by the electrolyte concentration of the external solution, and alsoshowed various degrees of increased bending behavior depending on the electricalstimulus.

SANS Studies on Spatial Inhomogeneities of Slide-Ring Gels

Slide-ring gels (SR gel) [previously termed as topological or polyrotaxane gels: Okumura, Y.; Ito, K. Adv. Mater. 2001, 13, 485] have remarkable physical properties, such as large extensibility and mechanical strength. The SR gels are cross-linked polyrotaxane (PR) consisting of poly(ethylene glycol) (PEG) chains and α-cyclodextrin (CD), in which the cross-linkers are made of CD dimers and capable of sliding along the PEG chains. To elucidate the physical picture and properties, the scattering functions, I(q)s, of SR gel in NaOD aqueous solutions (NaODaq) and in deuterated dimethyl sulfoxide (d-DMSO) were investigated by small-angle neutron scattering (SANS) and were compared with those of pregel solutions, where q is the magnitude of the scattering vector. The following facts were disclosed: (1) The polyrotaxane chains take a rodlike conformation in d-DMSO, whereas a Gaussian chain in NaODaq. (2) The degree of inhomogeneities of SR gel in NaODaq has a minimum around the sol−gel transition, whereas that in d-DMSO increases monotonically with increasing cross-linker concentration. (3) I(q) of SR gel in NaODaq can be described by a Lorentz function, while that in d-DMSO is given by the sum of a squared Lorentz function and a scattering function for a rod. These differences in I(q) are ascribed to the difference in the stacking behavior of CD molecules on PEG chains in PR.

NMR investigations of the 4-ethyl guaicol self-diffusion in iota (ι)-carrageenan gels

Self-diffusion coefficient of an aroma molecule (4-ethyl guaicol) was measured using the pulsed field gradient spin echo NMR (PGSE-NMR) method in order to investigate the influence of a macromolecular matrix on its diffusion and release processes. Iota (ι)-carrageenan was used for its ability to form thermoreversible gels in aqueous salt solutions. Variations of the ι-carrageenan and the salt concentrations permitted various gels with different thermal and rheological properties to be obtained. These latter were modified by an isotope effect obtained by preparing gels in D 2O. The NMR self-diffusion measurements realised for water and the aroma molecules indicated neither chemical interactions with ι-carrageenan, nor obstruction effects from the polysaccharide chains. In ι-carrageenan gels, the diffusional phenomenon was highly dependent on the heterogeneous gel structure and controlled by hydrodynamic interactions due to frictional drag between each molecule of the system and water microviscosity changes.

Electrical sensitivity behavior of a hydrogel composed of polymethacrylic acid/poly(vinyl alcohol)

AbstractAn interpenetrating polymer network (IPN) composed of polymethacrylic acid (PMAA) and poly(vinyl alcohol) (PVA) was prepared and exhibited electrical sensitivity behavior. The swelling behavior of the PMAA/PVA IPN hydrogel was studied by immersion of the gel in aqueous NaCl solutions at various concentrations and pH values. The stimuli response of the PMAA/PVA IPN hydrogel in electric fields was also investigated. When swollen IPN hydrogel was placed between a pair of electrodes, the PMAA/PVA IPN hydrogel exhibited bending behavior upon the application of an electric field. The PMAA/PVA IPN hydrogel also showed stepwise bending behavior depending on the electric stimulus. Also, for biomedical applications, the bending behavior of PMAA/PVA IPN hydrogel in Hank's solution at pH 7.4 was studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3613–3617, 2004

Study of Gelation in Aqueous Solutions of Cysteine and Silver Nitrate

A gel based on aqueous solutions of cysteine and silver nitrate is obtained for the first time. The possibility of gelation in the presence of competing ions and ligands is studied. Structural transformations occurring at an early stage of the gelation are studied by the dynamic light scattering, IR Fourier spectroscopy, and viscometry. The process of the self-organization in the system under consideration is assumed to be accompanied by the formation of fractal structures.

Interaction of non‐ionic hydrogels with small aromatic molecules

AbstractMeasurements are reported on the swelling behaviour at 20°C of poly (N‐isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l, the uptake of these solutions is similar. Phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds are significantly different (870 and 9080 mmol/l, respectively), and are far above this critical concentration. In the collapsed condition, the expelled liquid spreads on the surface of the phenol‐treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case, an acute contact angle was observed. Copyright © 2003 John Wiley & Sons, Ltd.

Electrical sensitive behavior of a polyelectrolyte complex composed of chitosan/hyaluronic acid

A polyelectrolyte complex (PEC), composed of chitosan (CS) and hyaluronic acid (HA), was prepared, which exhibited electrical sensitive behavior. The swelling behavior of the CS/HA PEC was studied by immersion of the gel in aqueous NaCl solutions at various concentrations and pHs. The stimuli response of the CS/HA PEC was also investigated in electric fields. When swollen, the PEC was placed between a pair of electrodes, and exhibited bending behavior on the application of an electric field. It also showed a stepwise bending behavior in relation to the magnitude of the electric stimulus.

Interaction of non‐ionic hydrogels with weak aromatic acids

AbstractMeasurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid‐base titration that the PNIPA/water system may exhibit a slight ion exchanging character.

Characteristics of electrical responsive alginate/poly(diallyldimethylammonium chloride) IPN hydrogel in HCl solutions

Interpenetrating polymer network (IPN) hydrogel composed of sodium alginate (SA) and poly(diallyldimethylammonium chloride) (PDADMAC) exhibited electrical-sensitive behavior. The SA/PDADMAC IPN hydrogel was synthesized using the sequential IPN method. The swelling behavior of the IPN hydrogel was studied by immersion of the gel in aqueous HCl solutions at various concentrations and pHs. The stimuli response of the IPN hydrogel in electric fields was also investigated. When swollen IPN hydrogel was placed between a pair of electrodes, the IPN exhibited bending behavior upon the application of an electric field. The IPN also showed stepwise bending behavior depending on the electric stimulus.

Inter/Intramolecular Interaction and Chiral Recognition of Water-Soluble Copolymers and Their Hydrogels Containing an Optically Active Group

Aqueous solutions of copolymers, consisting of N-isopropylacrylamide (NIPA) and optically active N-acryloyl-l-alanine (NALA) (poly(NIPA-co-NALA)), exhibited phase-separation temperatures (cloud point, Tc), and they were soluble at the lower temperatures and phase-separated at the higher temperatures. The Tc decreased with increasing NALA composition and increased with increasing pH of the solutions. The results of Tc measurements in the presence of NaCl and a urea derivative and Fourier transform infrared measurements with a curve-fitting method indicated that an increase in the composition of NALA in the copolymers induced hydrogen bonding in and between the copolymer chains. The partition coefficient (K) and diffusion coefficient (D) of R- and S-[1-(dimethylamino)ethyl]ferrocene (DMAEFc) in poly(NIPA-co-NALA) gels in aqueous solutions were estimated by a membrane permeation method. Negligible difference was observed for K between R- and S-DMAEFc; however, D of R-DMAEFc became smaller than that of S-DMAEFc when the gels started to collapse.

Electrical response characterization of chitosan/polyacrylonitrile hydrogel in NaCl solutions

A semi-interpenetrating polymer network (semi-IPN) hydrogel composed of chitosan and polyacrylonitrile (PAN) exhibited electrical-sensitive behavior. The swelling behavior of the semi-IPN was studied by immersion of the gels in aqueous NaCl solutions at various concentrations. The swelling ratio decreased with an increase in the concentration of the electrolyte solution. The stimulus response of the semi-IPN hydrogel in electric fields was also investigated. When swollen, the semi-IPN was placed between a pair of electrodes, and it exhibited bending behavior upon application of an electric field. The electro responsive behavior of the semi-IPN was also affected by the electrolyte concentration of the external solution. The semi-IPN also showed various degrees of increase in bending behavior depending on the electrical stimulus. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 91–96, 2003

Particle formation and gelling behaviour of anionic oligoesters in aqueous solution

Abstract Certain oligomeric, phthalate-based polyester molecules, prepared by a melt condensation polymerisation reaction and having a controlled degree of sulfonation, have been shown to form gels in aqueous solution. The inclusion of the sulfonate moieties into the oligoester molecules increases their aqueous dissolution from the melt. Light scattering and rheology studies suggest that the mechanism controlling the gelation is thought to depend on the formation and aggregation of small colloidal particles which themselves result from the association of individual oligoester molecules. Studies of the phase behaviour of these anionic oligoesters in aqueous solution have shown that gels only form for certain levels of sulfonation of the oligoesters and then at higher oligoester concentrations. At lower concentrations liquid/liquid type phase separation may be observed. Increasing NaCl concentration significantly influences the rate of phase separation or gel formation. Optical microscopy studies confirm that the gel-forming systems contain chain-like particulate aggregates.