Search

The lifetime and application of electrochemical storage devices are always threatened by thermal runaway. Intelligent self-protecting gel electrolytes can be designed using temperature-responsive polymers. However, the mechanisms and factors affecting protective behavior are unclear. Here, we fabricated supercapacitors using temperature-responsive polyacrylamide-2-hydroxyethyl acrylate (PNIPAM-co-HEA) hydrogel polyelectrolytes. It was found that the polymer changed from hydrophilic to hydrophobic with increasing temperature, and the physical cross-linking of the polymer molecular strands in the electrolyte was enhanced, thus restricting conductive ion migration and closing the ion transportation pathway. The hydrophilic–hydrophobic transition on the gel surface also contributed to the suppression of the specific capacitance of the supercapacitor. This self-protection feature is repeatable. In addition, we investigated the effect of methyl groups in the main chain structure on the electrochemical properties using poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNIPAM-co-HEMA). Methylene enhanced the hydrophobicity of the polymer at room temperature and reduced the thermo-protective effect. The methyl group in the main chain also reduced the thermal response temperature of the polymer. This study explores the mechanism by which temperature-responsive polymers inhibit thermal runaway in supercapacitors and provides support for the design of more rational and efficient temperature-sensitive electrolytes. [ABSTRACT FROM AUTHOR]

The objective of this study is to enhance the comprehension of the mechanism of enzymatic gelation in milk by investigating statistically significant changes in milk viscosity and carrying out corresponding electron microscopic studies of the process of structure formation at the enzymatic stage of coagulation using various enzyme preparations. Employing a non-destructive method (Hot-Wire) to monitor viscosity, we were able to confirm a decrease in viscosity during the middle of this stage and identify a previously undescribed peak in viscosity change at the end of the enzymatic stage. By conducting parallel studies utilizing transmission electron microscopy and various methods of specimen preparation, it was possible to discover that a hierarchical transformation process in the protein component of milk started at the end of the enzymatic stage of gelation in milk. This process is triggered by a cooperative conformational transition in casein micelle clusters, which leads to a series of increasingly energy-intensive reactions resulting in the transformation of loosely bound micelle clusters into denser aggregates. The final structure of the milk gel primarily consists of the previously formed individual micelle aggregates. It was noted that no changes in the microstructure of the milk gel were observed during the enzymatic stage of gelation when milk-clotting enzymes (MCEs) of animal, plant, and microbial (GMO) origins were used. Furthermore, investigations into the molecular weight distribution of soluble protein substances in samples generated with different types of MCEs revealed that the enzyme derived from the fungi of Rhizomucor miehei had a greater proteolytic effect on milk proteins compared to other variants of MCEs. [ABSTRACT FROM AUTHOR]

The work studied the effect of structuring of gelatin solution with a different content of acetic acid on the stability of electrospinning process and obtained nanofibers morphology. Using the method of dynamic light scattering and analysis using the Arrhenius equation, it was found that the process of formation of gelatin sol is thermally activated, and the activation energy of the process increases from 70.2 to 102.2 kJ/mol with the introduction of 10 vol.% acetic acid. Using dynamic mechanical analysis of viscoelastic properties, it was found that when the solution concentration is more than 15 wt.% in the presence of 10 vol.% acid, a structure of the solution close to a gel is formed. It has also been shown that as the fraction of acid increases to 25 vol.% and higher solutions are characterized by a sol state with an increase in the elastic component after 24 h of solution settling. It was found that the structuring of the solution during settling affects the stability of electrospinning. Statistical analysis of the morphology of gelatin nanofibers showed that with an acid content of 25 vol.% the average diameter of nanofibers increases by 2 times during settling of 24 h. When using an acetic acid content in a gelatin solution of more than 50 vol.%, a significant increase in the stability of the electrospinning process and in the average diameter of nanofibers were observed, regardless of the settling time. [ABSTRACT FROM AUTHOR]

Nanocomposite hydrogels were elaborated by the addition of citrated magnetic nanoparticles (MNPs) in sodium alginate aqueous solutions ionically crosslinked by in situ release of calcium ions from calcium carbonate (CaCO3) with gradual hydrolysis of d-glucono-δ lactone (GDL). The sol-gel transition was studied by time-resolved mechanical spectroscopy (TRMS) in the linear viscoelastic region. The power law frequency dependence of the storage and loss moduli allowed to determine the gelation time (tg), the power law relaxation exponent (Δ), and the gel stiffness (S) at the critical gel (gel at tg) for different calcium and MNP concentrations. The effect of an applied magnetic field on these parameters was also studied for the first time. The obtained results show an effect of the concentration of both calcium and MNPs on the kinetics (tg) and properties at the critical gel (S and Δ) obtaining faster kinetics and harder critical gels for higher calcium and lower MNP concentrations. Moreover, the application of the magnetic field allows to modulate the viscoelastic properties before the gel point, but no effect was observed on the structural properties of the critical gel. Finally, this work highlights how the shear viscoelastic, compressive, and swelling properties of totally gelled nanocomposite hydrogels can be successfully modulated when MNPs are introduced in the calcium alginate matrices with a good agreement between all these properties and with the properties of the critical gels. [ABSTRACT FROM AUTHOR]

In this study, diclofenac sodium (DS) is post-loaded directly into thermo-sensitive hydrogels fabricated from chitosan and β-glycerophosphate (GP) for temperature-controlled-release application at the inflammatory sites. Experiments analyzing the effect of GP concentration and simulated physiological temperature show that the hydrogels have a compatible heat-sensitive response through sol-gel and swelling behaviors. The hydrogels are soluble at 25 °C and rapidly gel above 37 °C with a decrease in the gelation time from 4 to 1 min when the temperature rises to 41 °C. Specific surface area, pore size, and pore volume of developed chitosan hydrogels are respectively 16.91–34.62 m2/g, 4.16–4.61 nm, and 0.08–0.28 cm3/g. Moreover, all hydrogels exhibit adaptive swelling to temperature changes as evidenced by the increase in equilibrium swelling ratio from 18.4–66.0% (25 °C) to 34.8–88.5% (37 °C) and 56.0–108.4% (39 °C). In terms of DS delivery, the highest loading capacity of the developed hydrogel is achieved at 8.81 mg/g with the GP content of 25 w/v%, the initial drug concentration of 2000 µg/ml, and the drug dissolution solvent being water, indicating the 23.8 times higher DS loading capacity compared with co-crosslinked chitosan/GP/genipin hydrogels in the previous work. About 87 and 95% of the loaded DS amount is released from the prepared chitosan hydrogels after 5 h at 37 and 39 °C correspondingly. The findings demonstrate that the ability to carry and release the anti-inflammatory DS of the thermo-sensitive chitosan hydrogels is significantly influenced by many subjective (composition) and objective (media temperature, initial drug concentration, and drug dissolution solvent) factors which can be adjusted to monitor the DS delivery at the right time and the right dose as required. Highlights: Diclofenac sodium is directly post-loaded into thermo-sensitive chitosan hydrogel. The hydrogel is soluble at 25 °C and rapidly becomes gel at 39 °C in 4 min. The highest swelling ratio of the hydrogel is 108.4% at 39 °C. The maximum drug loading of the hydrogel is 8.81 mg/g. 87% and 95% of drug-loaded is released after 5 h at 37 °C and 39 °C, respectively. [ABSTRACT FROM AUTHOR]

The influence of chitosan on orientation–micellar association of Pluronic F-127 in an aqueous medium in the temperature range of 4–37°C has been studied by polarization microscopy and rotational viscometry. It is established that, with an increase in temperature, this amphiphilic copolymer undergoes a phase transition to a shape-stable hydrogel, characterized by optical dichroism and rheograms of viscosity with the yield stress. Chitosan additive suppresses the effect of optical anisotropy and influences the gel-formation time and viscoelastic characteristics of the binary mixture with implementation of flow curves of dilatant fluids or structured compositions with different degrees of micellar ordering. The optical texture of the macroscopic gel phase of Pluronic F-127 and its mixtures with chitosan is found to correlate with the viscoelastic properties of the polymer system. [ABSTRACT FROM AUTHOR]

Alginate-based hydrogels are being produced worldwide for a broad spectrum of biotechnological applications, from biomedicine to agriculture. In particular, nanosized alginate-based particles have emerged as promising platforms mainly for drug delivery applications. In view of their size they can be delivered in a minimally invasive manner, and being structurally similar to the extracellular matrix of many tissues they freely diffuse to the target cells. The mild conditions of the sol-gel process are intrinsically adapted for the development of applications that require the inclusion of bio-entities during synthesis. However, one of the limitations of these systems is the fast gelling rate that hinders an adequate inclusion of bioactive molecules in nano-size hydrogel systems. In this work, we present a literature review and explore the classical theoretical work on sol-gel chemistry of alginates to discuss the range of conditions in which alginate sol-gel processes can be controlled, aiming at nanogel preparation. Highlights: The design and characterization of alginate nanosized gels for biomedical applications is revised. We review the classical theoretical work on sol-gel chemistry of alginates. The range of conditions in which alginate cross-linking can lead to a stable nanogel are discussed. [ABSTRACT FROM AUTHOR]

As an example of polycondensation of trifunctional monomers (PC-3), PC-3 of methyltrimethoxysilane to high conversions at pH 2.9 and 22°C has been studied by 29Si NMR. The relative concentrations of nonbonded Si atoms (T0) and those bonded by one (T1), two (T2), and three (T3) Si–O–Si bonds have been determined from the intensities of multiplets assigned to linear and branched oligomers and tri- and tetraatomic rings that are similar to the crystaline lattice facets. A chain growth model is proposed that takes into account the interconversions of these elements, in which cyclization increases the critical conversion at the gel point from the value of 0.5 expected for acyclic chains to ~0.80–0.85. [ABSTRACT FROM AUTHOR]

Precise a priori prediction of time required to achieve colloidal sol-gel transition is a challenging task. This is because not much system-specific theoretical work has been carried out on kinetics of colloidal gelation, where the physical bond formation is strongly affected by the surface characteristics of the colloidal particles. Under such situation, drawing analogies from apparently dissimilar phenomena that share the same physical foundation can prove helpful. Interestingly the physical processes such as the fracture dynamics in a material leading to failure, as represented by the Bailey criterion of durability, and sol-gel transition are known to satisfy the Markovian criterion, suggesting equivalent mathematical formalism. Such equivalence leads to a simple mathematical formalism given by the modified Bailey criterion which is identical in construction to the criterion in fracture dynamics. In this work, we assess the modified Bailey criterion of durability to predict the time required to attain the sol-gel transition in a colloidal dispersion under non-isothermal conditions. The model parameters are derived from the gelation experiments on colloidal clay dispersion conducted under the isothermal conditions. Interestingly, the prediction of the time to attain the sol-gel transition under non-isothermal condition from the modified Bailey criterion matches the experimental observation with remarkable accuracy, thereby validating an independent methodology to obtain vital knowledge on colloidal sol-gel transition. This work, therefore, validates the mathematical formalism of one Markovian process (fracture dynamics) by carrying out experiments on another Markovian process (sol-gel transition), which are otherwise distinctly different from each other. Such correspondence highlights the profound similarity in the microstructural changes occurring in the two distinct systems. [ABSTRACT FROM AUTHOR]

Tetrabutylammonium acetate (TBAA) solution in dimethyl sulfoxide (DMSO) can dissolve cellulose efficient at a mild condition and it seems to have favorable properties for cellulose molding applications, e.g. fiber spinning. However, if water or other hydrogen bond donors are present, the solvent's ability to dissolve cellulose is greatly reduced. A non-solvent (water) post-added to the cellulose/TBAA/DMSO solutions caused significant changes in flow properties. Specifically, the rheological behaviours of distinct phases formed in 6–8%(w/w) cellulose/TBAA/DMSO solutions due to the addition of water was investigated. With the water concentrations increased, a sol–gel transition had been detected. The Cox–Merz rule and Cross model have been used to fit the rheological data. We explain the sol–gel transformation in cellulose/TBAA/DMSO/water solutions by percolation theory. Meanwhile, a mechanism of cellulose aggregation and the sol–gel transitions have been proposed: water can effectively break the cellulose–Ac− H-bonds and lead to the formation of cellulose–cellulose H-bonds, which grow the aggregation of cellulose, form a network structure in the whole sample and then result in gelation. Sol-gel transition of cellulose/tetrabutylammonium acetate/dimethyl sulfoxide solutions with different water concentrations. [ABSTRACT FROM AUTHOR]

Investigating and understanding in detail the sol-to-gel transition in inorganic and hybrid systems is a very challenging task. The transition is a critical phenomenon that can only be described with statistical but not thermodynamic models. Graphic schemes, therefore, cannot easily represent such a complicated process. The sol-to-gel transition has been illustrated with the support of several drawings. Representing complex media, such as the sol and the gel, by a scheme, is however quite tricky. Using oversimplified pictures can mislead the comprehension of the process, which is difficult to describe in general terms, as it depends so much on the synthesis and processing conditions. In this short tutorial, a fault-finding discussion based on the most common pictures drawn to illustrate the sol-to-gel transition has been used for a critical description of the process. Highlights: Sol–gel transition is a critical phenomenon described by statistical models. Description of sol–gel transition through pictures should be done with care, to avoid a misinterpretation of the process. [ABSTRACT FROM AUTHOR]

Naturally derived hydrogels are the most common bioink material for droplet-based bioprinting. The mechanical stability of the printed construct and the cell viability are closely related to the gelation process of natural hydrogels, which is initiated by the coil-to-helix transition in a single polymer chain and followed by association of helices. In this study, a phase-field-based modelling approach is employed to simulate the gelation process of microdroplets. A thermo-viscoelastic model incorporating a phase-field variable is used to describe the deformation behaviour of hydrogels in the thermal-induced gelation process. In connection with the gelation kinetics, a new form of the bulk free energy density is proposed to include the free energies related to the mixture of macromolecules in the solution and the coil-to-helix transition. Using the proposed phase-field model, numerical simulations are performed to study the effects of the droplet size and the printing medium on the gelation process of microdroplets. [ABSTRACT FROM AUTHOR]

When irradiation generates two radicals capable of initiating chain growth with different rate constants for chain transfer, two polymerization routes with different average chain length emerge. These pathways are not mixed in the initial part of the ballistic growth. Their mixing in chain transfer events is accompanied by transition from ballistic to diffusion growth. In the sol–gel transition region, the routes are spatially separated if the chain transfer depends on the rotational mobility of the reactants and decreases with increasing viscosity as the resulting oligomers accumulate. As an example, the polymerization of tetrafluoroethylene in solutions of silanes and oxysilanes is considered. [ABSTRACT FROM AUTHOR]

This work investigates the effect of relative humidity (RH) and temperature on drying phenomenon of a siloxane coating during the sol-gel process. An experimental approach was taken, due to a lack of available data in existing literature. Dynamic Vapor Sorption, Fourier Transform Infra-Red spectroscopy and X-ray Photoelectron Spectroscopy analyses were performed during sol drying, while controlling RH and temperature. The drying time increased exponentially when RH was increased. This was linked to water uptake and evaporation rate decrease, forming a more condensed coating. The thermally activated process was fitted by the Arrhenius law with an activation energy of 41.7 kJ mol−1. A double exponential law was proposed to describe the time needed for drying the sol as a function of temperature and RH. Finally, differences in the gel formed were clearly demonstrated. Between a RH of 30 and 50%, the gel formation turned from a dry-before-gel to a gel-before-dry phenomenon, stressing the importance of temperature and RH control during the drying process of the sol. Temperature and relative humidity have an exponential influence on drying time. The sol-gel kinetics is also modified, which leads to a chemical evolution of the formed gel. This change is related to the relationship between drying and chemical reaction rates. Highlights: Sol drying on steel was monitored by DVS and FTIR diffuse reflection. XPS analyses on films revealed differences with temperature and RH conditions. The drying time increased exponentially when RH was increased, due to water uptake. The process was fitted by the Arrhenius law with activation energy of 41.7 kJ mol−1. A general law was proposed to describe sol drying time according to temperature & RH. [ABSTRACT FROM AUTHOR]

Abstract: Thermal runaway is posing big threat towards common electrochemical devices, such as lithium ion batteries and supercapacitors. It is caused by heat accumulated within electrochemical device and can cause devices to lose functionality, shorten service-life, or even cause hazardous fires and explosions. One effective approach to tackle thermal runaway is to break the electrochemical reaction Arrhenius thermal loop by introducing reaction inhibiting components into the system. Herein, through facile wet casting method, a temperature responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) was cast into thin film and sandwiched in between polypropylene (PP) to make into a temperature responsive separator. It was found that once the temperature rose to 70 °C, instead of increasing in capacitance like in the control, PNIPAM-included batches decreased in capacitance. This capacitance reduction was mainly contributed by increased charge transfer resistance, which was caused by the sol-gel transition and precipitating PNIPAM chains residing upon PP membrane. A similar capacitance reduction was also observed for the ferricyanide redox system. Further investigation also revealed thicker PNIPAM films exhibited enhanced capacitance reduction and scan rate dependency. Temperature responsive polymer separators may prove to be an effective method to suppress high temperature electrochemical reactions and thus offer promise to reversible, thermally stabilized electrochemical devices.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: In this article, we studied the multiwave rheology properties of a two-step tetraethoxysilane (TEOS) hydrolysis, as well as condensation processes and optimized particle synthesis conditions by focusing on the colloidal particle aggregation and growth behavior. Combining with the dynamic light scattering (DLS) technique, we systematically investigated the gelation process, network structure, overall apparent activation energy, DLS size growth trend and complex viscosity. Our results revealed that the overall apparent activation energy of the two-step-catalyzed process was lower than that of the single step and the gelation time was decreased with an increase in water-TEOS molar ratio. During our studies, we successfully simplified the rheological measurement for the two-step process by setting the base addition moment as the zero time. This method can also be applied for structure and density tuning, providing a new path to successfully synthesize customized materials in a sol-gel process.The five-stage scheme of the sol-gel transition. The viscosity and DLS size curves were divided into five parts. Based on this route and combined with rheological measurements, the control of our sol-gel process can be realized and eventually obtained desired features. Investigate the gelation time and the gel structure of a two-step sol-gel process by combining MWDT with DLS method.The rheological measurement for the two-step process was simplified by setting the base addition moment as the zero time.The synthetic strategy can be applied to other sol-gel systems for structure and density tuning. [ABSTRACT FROM AUTHOR]

The sol-gel transition entropy is estimated by using a modified Clapeyron-type equation for κ-carrageenan hydrogel systems under load. The effect of alkali metal salts on the sol-gel transition behavior is also investigated. The transition temperature decreases with increasing compressional stress, while the transition entropy remains unchanged. Both the transition entropy and the transition temperature at the zero stress limit vary almost in accordance with the Hofmeister series, but the inversion occurs for RbCl and CsCl. For the gels examined, a positive correlation exists between the transition entropy and the transition temperature at the zero stress limit. [ABSTRACT FROM AUTHOR]

The viscoelastic properties of poly(methyl methacrylate) (PMMA)/grafted poly(butyl acrylate) (PBA) nanoparticle systems were investigated. The rubber particles consist of PBA core (60 nm in diameter) and grafted PMMA shell. The grafting degree, defined as the weight ratio of grafted PMMA to PBA particles, ranges from 0.8 to 1.5. Two series of samples, A series with 7.5 wt.% of PBA content and B series with 12 wt.% of PBA content, were used. The systems exhibited fast and slow relaxation process, the former reflecting the relaxation of the matrix PMMA chains and the latter being attributed to grafted PBA particles. For A series samples, time-temperature superposition (TTS) was held well over the frequency (ω) and temperature ( T) ranges measured. However, for B series samples, TTS was not satisfied at low ω due to the particle-particle interaction of grafted PBA particles, although the samples obeyed TTS at high ω associated with the relaxation with entanglement of matrix PMMA. At high T and low ω region, the B series samples showed a sol-gel transition at elevating T and the critical gel behavior characterized with a power-law relationship, G′ = G″/tan( nπ/2) ∝ ω, was observed. This behavior suggested formation of a self-similar, fractal structure of grafted PBA particles. The critical gel temperature ( T ) and the critical exponent ( n) were determined for the B series samples. TEM observations revealed that as-prepared A and B samples had well-dispersed particles but the B samples after viscoelastic measurements had fragmented networks of the PBA particles, confirming that the sol-gel transition occurred for the PMMA/grafted PBA systems at elevating T. [ABSTRACT FROM AUTHOR]

In this study, NbO alcogels and mesoporous ambigels were formed via a new acid-catalyzed polymeric synthesis pathway using NbCl as a precursor. The effect of hydrolysis, catalyst, and propylene oxide molar ratios on sol-gel transition, rheological properties, and physical properties of NbO ambigels were investigated. A common behavior for the sol-gel transition of NbO on the viscosity vs. time curves was identified. The molar ratios of HO:Nb and HNO:HO significantly influenced the gelation time, the rheological properties of alcogels, as well as the physical properties of the respective ambigels. The gels presented yield stress and shear-thinning behavior with different degrees of thixotropy. Microstructure analysis of the ambigels revealed a mesopore network formed by interconnected NbO nanoparticles. An increase in the molar ratios of HNO:HO (lower pH) increased the surface area and pore volume of NbO, and yielded a finer nanostructure of NbO mesoporous ambigels. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Sol-gel transition properties play a key role in various applications of thermosensitive hydrogels, but conventional methods for studying the sol-gel transition have some limitations. For extensive characterization of the water-polymer interaction and microstructure change during sol-gel transition, we propose a rapid and nondestructive method based on monitoring water mobility through low field NMR (LF-NMR), and this was applied to chitosan/β-glycerophosphate (CS/GP) hydrogels. The spin-spin relaxation time ( T ) that depicted water mobility was measured by LF-NMR within 90 s. The T component corresponding to water protons trapped in polymer networks ( T ) was very sensitive to sol-gel transition. A remarkable decrease of T value indicated obvious variations of water mobility when CS/GP was heated, and a turning point was observed on the T -time curve. The gel point associated with this turning point could be easily determined by fitting the T -time curves to a bilinear regression model, and the results showed good accuracy and repeatability owing to the nondestructive nature of LF-NMR. Variations in water components and microstructure of CS/GP caused by water migration after solidification were also analyzed by monitoring dynamic changes of T . This rapid, nondestructive method provides a powerful tool for studying the sol-gel transition of hydrogels. [ABSTRACT FROM AUTHOR]

The gel-like comb micro block hydrophobic associating polymer (CBHAP) was synthesized by mixed micellar polymerization. The chemical structure of the copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR). The rheological properties of CBHAP in fresh water and saline water at semi-dilute region were investigated. The experimental results show that, because of the intermolecular forces, shear thickening phenomenon can be observed obviously in brine solution and the Newtonian viscosity plateau could be observed clearly before 40 s. When the concentration reaches 3,000 mg/L, the G' and G' becomes stable, indicating that CBHAP experiences the sol-gel transition after 3,000 mg/L. However, the curl structure is formed by adding salt, resulting in a higher concentration of the sol-gel transition than that in fresh water. Once the curl structure is destroyed by shearing or stretching, the intermolecular forces will take into effect and complete the sol-gel transition at semi-dilute region. [ABSTRACT FROM AUTHOR]

Well-defined 'smart' injectable hydrogel based on hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(lactic acid-co-glycolic acid) (PLA/PGA) copolymer (PLGA-PEG-PLGA) gelling at the body temperature was modified by bioactive hydroxyapatite (HAp) in the form of micro-, nano-, and core-shell particles (μ-HAp, n-HAp, and CS-x, respectively) to be applicable as calcium delivery system in bone regeneration. Viscoelastic moduli increased with HAp content as expected. Whereas systems containing μ-HAp or CS-x particles maintained two sol-gel and gel-sol phase transitions, the n-HAp containing system showed only one sol-gel phase transition due to the strong interactions between polymer chain and the n-HAp surface. In vitro, studies proved the controlled uniform release of calcium cations from both CS-x and n-HAp over the 9-day period without any initial burst release. [ABSTRACT FROM AUTHOR]

The effect of the seaweed drying temperatures (35, 45, 55 and 85 °C), prior to the biopolymer extraction, on the rheological properties of kappa/iota-hybrid carrageenan (KI) gels in NaCl extracted from Mastocarpus stellatus seaweed is reported, together with the thermal stability of obtained gels. The average molecular mass (ranged between 2.25 × 10 and 1.02 × 10 kg kmol) of extracted KI, determined by gel permeation chromatography, and estimated intrinsic viscosities (ranged between 0.935 and 0.258 m kg), conducted in a capillary viscometer, decreased with increase of the seaweed drying temperatures. The parameters ( K and a) of the Mark-Houwink-Sakurada (MHS) equation for KI are also reported. Thermo-rheological oscillatory measurements were conducted in a stress-controlled rheometer in order to clarify the kinetics of gel formation and to characterize the structure of the matured gels. Rheological results indicated a weakening of the KI gelling properties at smaller average molecular masses (i.e. larger seaweed drying temperatures, above 45 °C). Even so, KI samples exhibited stable and weak gel properties (i.e. elastic modulus <200 Pa). KI gels reached stability after 20 min of maturation. Cooling and heating profiles showed a strong temperature dependency. Gel setting temperatures significantly depended on the biopolymer content, whereas gel melting temperatures (68.0 ± 0.3 °C) were unvaried. No complete thermal stability was observed for gels formed with tested biopolymers, the most thermal stable being those prepared with KI with larger molecular masses (i.e. lower seaweed drying temperatures, below 45 °C). [ABSTRACT FROM AUTHOR]

A double thermoresponsive ABC-type triblock copolymer (poly(ethyleneglycol)-block-poly(2-(2-methoxyethoxy) ethyl methacrylate)-block-poly(2-(2-methoxy ethoxy) ethyl methacrylate- co-oligo(ethylene glycol) methyl ether methacrylate, PEG- b-PMEOMA- b-P(MEOMA- co-OEGMA)) was designed and synthesized by reversible additionfragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer endowed a thermal-induced two-step phase transition at 29 and 39 °C, corresponding to the thermosensitive properties of PMEOMA and P(MEOMA- co-OEGMA) segments, respectively. The two-step self-assembly of copolymer solutions was studied by UV transmittance measurement, dynamic light scattering (DLS), transmission electron microscopy (TEM) and so on. The triblock copolymers showed the distinct thermosensitive behavior with respect to transition temperatures, aggregate type and size, which was correlated to the degree of polymerization of thermosensitive blocks and the molar fraction of OEGMA in the P(MEOMA- co-OEGMA) segments. In addition, micelles could further aggregate to form the hydrogel by the self-associate of PEG chains under the abduction of the concentration and temperature. The transition from sol to gel was investigated by a test tube inverting method and dynamic rheological measurement. [ABSTRACT FROM AUTHOR]

A novel multiple responsive polymer-peptide bioconjugate, which exhibits responses to calcium ion, pH, and temperature, was presented. In our study, a peptide with calcium ion response was conjugated with a thermo-responsive polymer at the N terminus to generate a polymer-peptide bioconjugate. Several experiments were conducted to characterize the environmental response of the bioconjugate. Results suggest that electrostatic interaction and hydrogen bonding are the driving forces for peptide self-assembly. Additionally, the incorporation of polymer endows new property to the peptide, though it may disrupt the inner-molecular interactions between peptides in some extent. This study will highlight the fundamental understanding of polymer-peptides that are of potential utility as stimuli-responsive biomaterials. [ABSTRACT FROM AUTHOR]

The performances of a conducting paste and the thick film fabricated from it depend critically on the dispersion state of the functional powders. Detailed mechanisms dictating the interactions between functional powder, surfactant, and, in particular, polymer binder that lead to optimum particle dispersion remain elusive in general. For a series of practical micrometer-sized silver pastes (with a powder content of ~47 wt% or 7 vol%, in a commonly used solvent α-terpineol), we reported rheological fingerprints (i.e., significantly promoted sample elasticity) suggesting that while the surfactant (stearic acid, SA) aids the initial, local (~1 nm) particle dispersion, the polymer binder (ethyl cellulose, EC) then becomes effective to help achieve larger-scale (~30 nm) particle dispersion, permitting the development of colloidal fractals and time-evolving microphase transition closely mimicking typical sol-gel transition. The enhanced particle dispersion is evidenced also by the scanning electronic microscope morphologies of dried printing thick films. Overall, similar phase transition had rarely been reported for metal pastes, yet the underlying particle dispersion seems crucial to achieve as (environmentally required) decreasing powder content makes a paste and the fabricated thick film increasingly unlikely to fulfill the percolated state desirable for efficient electron conduction. [ABSTRACT FROM AUTHOR]

As one of the most widely used thermosensitive polymers, commercially available Pluronic F127 copolymer has been used as an attractive candidate for injectable hydrogel system. To tune its characteristics for better biomedical applications, the effects of collagen incorporation on its thermogelation in aqueous system and resultant hydrogel properties were investigated by dynamic rheological tests, scanning electron microscopic observation, in vitro drug release, and cytocompatibility assays. For its aqueous solution, the collagen incorporation was found to improve appropriately the sol-gel transition temperature for good injectability at room temperature and enhance obviously the temperature sensitivity for fast thermogelation. When compared to single Pluronic F127 copolymer thermogel, the composite thermogel with collagen showed a prolonged release for encapsulated drug and better cell compatibility. In addition, the effects on the morphology and viscoelastic behavior of resultant thermogel were also studied with respect to the concentration of incorporated collagen. [ABSTRACT FROM AUTHOR]

A well-defined temperature responsive ABA triblock copolymer, poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b- poly(ethylene glycol)-b-poly (2-(2-methoxyethoxy) ethyl methacrylate-co-N- hydroxymethyl acrylamide) [P(MEO2MA-co-HMAM)-b-PEG-b-P(MEO2MA-co- HMAM)], was synthesized by atom transfer radical polymerization (ATRP). The synthesized triblock copolymer was characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). The aqueous solution phase behaviors of the triblock copolymers were investigated by UV transmittance measurements, surface tension measurement, laser particle size and viscosity analysis. The micellization of temperature responsive triblock copolymer was investigated by fluorescence probe technique, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the molecular weight of the poly(ethylene glycol) (PEG), the N-hydroxymethylacrylamide (HMAM) content, and the degree of polymerization (DP) of the P(MEO2MA-co- HMAM) block for the synthesized triblock copolymers could all affect the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The higher the molecular weight of the PEG and the HMAM content for a given triblock copolymer are, the higher the LCST of its aqueous solution. The higher the DP of the P(MEO2MA-co-HMAM) block is, the lower the LCST of the copolymer aqueous solution. Sol–gel transition temperature (Tsol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the molecular weights of the PEG, the DP of the P(MEO2MA-co-HMAM) blocks and the concentration of the copolymer aqueous solution. Copolymer hydrogels loaded with bovine serum albumin (BSA) were used for the release study. The results revealed that 1) the hydrogels had sustained release for the BSA, 2) the release rate for the BSA is dependent of the length of the PEG chain, and 3) the longer the PEG chain is, the faster the release rate of the hydrogel for the BSA. [ABSTRACT FROM AUTHOR]

Novel hydrophilic, temperature responsive, and biodegradable ABA tribl°Ck-graft copolymers, [poly( ɛ-caprolactone)- g-poly(2-(2-methoxyethoxy) ethyl methacrylate- co-oligo(ethylene glycol) methacrylate)]- b-poly(ethylene glycol)- b-[poly(-caprolactone)- g-poly(2-(2-methoxyethoxy) ethyl methacrylate- co-oligo(ethylene glycol) methacrylate)] ([PCL- g-P(MEOMA- co-OEGMA)]- b-PEG- b-[PCL- g-P(MEOMA- co-OEGMA)]) (tBGs), were synthesized via a combination of ring-opening polymerization (ROP) of ɛ-caprolactone ( ɛCL) and α-chloro- ɛ-caprolactone ( αCl ɛCL) in the presence of PEG and atom transfer radical polymerization (ATRP) of MEOMA and OEGMA. Temperature responsive P(MEOMA- co-OEGMA) graft chains on the hydrophobic PCL block of PCL- b-PEG- b-PCL not only improved the solubility of PCL- b-PEG- b-PCL in water, but also endowed it with temperature sensitivity. The synthesized temperature responsive triblock-graft copolymers formed well-defined core-shell micelles as the temperature was above their LCST ( ca. 35 °C), with hydrophilic PEG block as shell, P(MEOMA- co-OEGMA) graft chains on the PCL block and hydrophobic PCL block aggregates as core. The micellization induced by temperature for the tBGs in aqueous solutions had been investigated by transmittance measurement, laser particle size measurement, HNMR in DO, DLS and TEM. For a given tBG5 aqueous solution (30 wt%), a weak hydrogel was available at 35 °C, and its sol-gel transition temperature gradually decreased with increasing concentration. In addition, the tBG5 hydrogels loaded with anethole were used for hydrophobic drug release, and in vitro the sustained release of anethole from the tBG5 hydrogels was examined, which is a significant for anethole for their biomedical applications. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Hydrocarbons are easily extracted by organic solvents such as n-decane from wet samples of Botryococcus braunii by thermal pretreatment at 90 °C even after being cooled to room temperature. However, hydrocarbon recoveries are not as readily achieved at room temperature from samples pretreated at temperatures lower than 80 °C. This suggests that there is the point of no return for pretreatment temperature that enables effective solvent extraction of hydrocarbons at room temperature from wet algal samples of B. braunii. To elucidate the mechanism of hydrocarbon recovery from B. braunii following thermal pretreatments, we investigated the thermophysical properties of the water phase separated from heated algal slurry. Differential scanning calorimetry (DSC) measurements revealed sol-gel transitions in the water phase of algal slurry after protein denaturation at 64 °C in samples that was pretreated at 70 or 80 °C but not in those pretreated at 90 °C. Furthermore, the pretreated >70 °C water-soluble polymers revealed polysaccharides composed of galactose, arabinose, and uronic acid. These results suggest that the transition from sol state to gel state of water-soluble polysaccharides in algal slurry prevented hydrocarbon recovery with organic solvents since hydrocarbons were easily recovered from sol state samples pretreated at 70 or 80 °C when the extraction temperature was kept the same as the pretreatment temperature. These results reveal that the presence of water-soluble polymers with gelation ability in the water phase and removal of these polymers in sol state enable effective recovery of hydrocarbons at room temperature after thermal pretreatments. [ABSTRACT FROM AUTHOR]

The colloidal sol-gel transition based on zirconyl nitrate solution systems is investigated in this work. The different steps occurring in the transition have been identified by coupling small angle X-ray scattering with Raman spectroscopy and rheology measurements. The effect of the experimental conditions, such as the zirconium precursor concentration and pH, on the transition is studied. The precise mechanisms involved during the transition are based on a detailed understanding of the nanostructure of these systems. In particular, the dissolution of the zirconium salt leads to the formation of cyclic tetramers that self-organize into a cylindrical shape. We clearly demonstrate that increasing the pH induces a strong attractive interaction between the cylinders, giving rise to a mass fractal dimension. For each system, two characteristic pH values have been determined via rheological measurements analysis, where gelation is notably slow below the first pH value and precipitation occurs above the second one. The complete description of the quaternary system (zirconyl nitrate + acetylacetone + ammonia + water) is an efficient formulation guide for the further combination with a templating route leading to structured Zr-based materials. [ABSTRACT FROM AUTHOR]

In this study, various surfactants were added to control the gelation time of silk fibroin (SF) aqueous solution. The gelation behaviors of SF aqueous solution in the presence of surfactant were investigated with attenuated total reflectance infrared, SEM, and a viscometer. When surfactants other than chitooligosaccharide were added into an SF aqueous solution, the gelation time of the solution was decreased under the fixed conditions. Particularly, anionic surfactant was found to be more effective than non-ionic and cationic surfactants in accelerating the gelation of SF. In addition, the conformational changes of SF hydrogel with or without surfactant were investigated in a time-resolved manner using infrared spectroscopy. Conformational transitions of SF nanofibers from random coil to β-sheet forms were strongly dependent on the inherent properties of surfactant, and on the different interactions between surfactant and SF molecules in aqueous solution. This approach to controlling the gelation of SF aqueous solution by the surfactant, and to monitoring their conformational changes on a real-time scale, may be critical in the design and tailoring of SF hydrogels useful for biomedical applications. [ABSTRACT FROM AUTHOR]

Methylcellulose (MC), a hydrophobically modified cellulose derivative, in an aqueous solution undergoes sol-to-gel and gel-to-sol transitions on heating and cooling, respectively. Using differential scanning calorimetry, MC in light (HO) and heavy (DO) water solutions has been investigated to elucidate the solvent isotope effect on the transitions. As a result, their transition temperatures are higher in HO by about 4 °C than DO. This phenomenon is rationalized in terms of the strength of the hydrophobic attractive interaction; the strength is enhanced by DO. We discuss the reason for the enhancement and the difference in the isotope effect between MC and a poly( N-isopropylacrylamide) polymer which shows an opposite trend to MC. [ABSTRACT FROM AUTHOR]

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca, Mg, and K ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg or Ca ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation. [ABSTRACT FROM AUTHOR]

Because of both its complexing ability toward Ti cations and reactivity in highly acidic medium, N, N-dimethylformamide (DMF) can be used to control the hydrolysis and condensation of Titanium oxide frameworks, starting from Ti oxychloride as precursor. The addition of water allows promotion of hydrolysis of the aldehyde while controlling the size of the nanoparticles formed in the solution. The as-prepared colloidal solutions are very stable, up to 3 months, depending on the initial titanium concentration, the DMF/Water ratio, and the thermal treatment. The sol to gel transformation was monitored by viscosimetry measurements as a function of ageing time and heat treatment temperature. Optimization of pre-treatment at moderate temperature leads to fine control over the gelation process. [ABSTRACT FROM AUTHOR]

The sol-gel transition of methylcellulose (MC) solutions in the presence of ortho-methoxycinnamic acid (OMCA) or cetyltrimethylammonium bromide (CTAB) and in the coexistence of OMCA and CTAB was determined by the rheological measurement. It has been found that the sol-gel transition temperature of MC solutions increases linearly with the concentration of either OMCA or CTAB in solution, respectively. However, in the coexistence of OMCA and CTAB, the sol-gel transition temperature of MC solutions remains invariable, independent of the concentration of CTAB in solution. The experimental results show that OMCA has priority to adsorb on the methyl group of MC chains to form polymer-bound aggregates. In particular, these aggregates inhibit the hydrophobic interaction between CTAB and the methyl group of MC chains completely. Taking into account the fact that OMCA is almost insoluble in MC-free solutions but dissolves very well in aqueous MC solutions, we propose the formation of the core-shell architecture prompted by OMCA and the methyl group of MC chains, with the methyl group of MC chains serving as the core and the self-assembly of OMCA molecules serving as the shell. Obviously, the formation of the core-shell structure increases the solubility of OMCA, improves the stability of methyl groups of MC chains at high temperatures and inhibits the hydrophobic interaction between CTAB and the methyl group of MC chains in solution. The abnormal behavior relating to the sol-gel transition of MC solutions in the presence of OMCA or in the coexistence of OMCA and CTAB is therefore explained. Upon UV irradiation, the sol-gel transition temperature of MC solutions in the presence of OMCA, or in the coexistence of OMCA and CTAB, decreases notably. However, the dependence of the sol-gel transition temperature of MC solutions as a function of OMCA concentration, or CTAB concentration in the presence of OMCA, does not change after UV irradiation. [ABSTRACT FROM AUTHOR]

The effects of NaCl and osmotic dehydration on the linear viscoelastic behavior of duck egg yolk were evaluated. An increase in NaCl concentrations from 0% to 3.0% ( w/ w) resulted in a remarkable change in the linear viscoelastic behavior by inducing a sol-gel transition, specifically. The transition was more pronounced when 1.5% ( w/ w) NaCl was incorporated. The effect of dehydration on aggregation and network formation was predominant than that of the NaCl addition. Nevertheless, at a lower degree of dehydration, the addition of NaCl could modulate the viscoelastic behavior of duck egg yolk, resulting in a well-developed gel network. Addition of NaCl into duck egg yolk could stabilize the protein molecules as evidenced by an increase in denaturation temperature as well as a delay in gel network formation. As visualized by a scanning electron microscope, the denser network with smaller voids was observed in duck egg yolk gel with increasing NaCl concentration and degree of dehydration. [ABSTRACT FROM AUTHOR]

In this paper, it was discovered that during the heating process from 35 to 63 °C, hydroxypropyl cellulose (HPC) concentrated aqueous solution (20 wt%) would first go through coil-to-globule transition and then sol-gel transition with temperature elevation. The microdynamic mechanisms of the two phase transitions were thoroughly illustrated using mid and near infrared spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique. Mid infrared spectroscopy is an effective way to study the hydrophobic interactions in HPC molecules. And near infrared spectroscopy is a potent method to study hydrogen bonds between HPC molecules and water molecules. Boltzmann fitting and PCMW could help determine the exact transition temperatures of each involving functional groups in the two processes. Moreover, 2Dcos was used to discern the sequential moving orders of the functional groups during the two phase transitions. Depending on the structure of HPC and the thermodynamic conditions, the dominating associative elements in either process might vary. During the coil-to-globule transition, HPC molecules precipitated to form an opaque system with mobility.It was discovered that the driving force of the coil-to-globule transition process in microdynamics could only be the dehydration and hydrophobic interactions of C-H groups. However, in the sol-gel transition, the system crosslinked to form a physical network with no mobility. The driving force of this process in microdynamics was primarily the self-assembly behavior of O-H groups in HPC 'active molecules'. [ABSTRACT FROM AUTHOR]

Thermogelling block copolymers composed of polyester and polyether are faced with a dilemma of achieving powder form in order to easily handle the samples in the bulk state and avoid unexpected ahead-of-time gelling of the corresponding polymer aqueous solution below the thermogelling temperature due to the spontaneous crystallization of some polymer segments in water. In order to resolve this dilemma, we synthesized amphiphilic poly(ɛ-caprolactone- co-glycolide)-poly(ethylene glycol)-poly(ɛ-caprolactone- co-glycolide) (PCGA-PEG-PCGA) triblock copolymers with a series of ratios regarding caprolactone (CL) and glycolide (GA). The different polymer morphologies from powder to sticky paste were obatined by altering the ratios to adjust the ability of crytallization for the PCGA blocks. All of the copolymers reported in this paper were able to dissolve in water, and their aqueous solutions underwent a sol-gel transition upon heating. The polymer with an appropriate CL/GA ratio not only exhibited the powder form in the bulk state, but also achieved the sol stability in water. The triblock copolymers formed micelles in water and the micellar aggregation occurred with increasing temperature, resulting in physical gelation upon the percolation of micelles. The injectability and gellability of the copolymer-water systems were confirmed both in vitro and in vivo. Consequently, this study provides a promising injectable biomaterial, and also affords a new successful case of the molecular design of functional polymers, based upon common monomers. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Functionalised triblock copolymers based on poly((lactic acid)- co-(glycolic acid)) and poly(ethylene glycol) (PLGA-PEG-PLGA) further modified with 3-methylenetetrahydrofuran-2,5-dione (itaconic anhydride; ITA) exhibited sol-gel transition induced by increasing temperature. Rheological properties of a series of ITA/PLGA-PEG-PLGA/ITA copolymer concentrations (6-24 mass %) in deionised Milli-Q water were studied by both the test tube inverting method (TTIM) and rheometer. The gel stiffness increased with the polymer concentration shifting the gel point of the copolymer to the lower temperature. The present study demonstrates that each method describes a sol-gel transition, but the combined method gives comprehensive information about changes in colour, viscosity, elastic and loss moduli. Characterisation of such a gel is necessary for its further use, in order to determine whether the material is appropriate as an injectable biomedical hydrogel. [ABSTRACT FROM AUTHOR]

Water-soluble cyanoethyl cellulose (CEC) samples were synthesized by homogeneous reaction of cellulose with acrylonitrile in LiOH/urea aqueous solutions. The dynamic viscoelastic property of CEC with different degree of substitution (DS) in water at different temperatures and concentrations were investigated. At low concentrations, the CEC solutions displayed liquid-like behavior with G′ smaller than G′′ at low frequencies; while the curves of G′ and G′′ intersected at the middle of the frequency range at higher concentration, indicating an existence of chain aggregation and entanglement network. The gelation temperature ( T) was determined from the point of intersection in tan δ versus temperature ( T) at different frequencies, indicating the validity of Winter-Chambon criteria. It was found that T increased with increasing DS, and that the exponent ( n) values at the gel point decreased with increasing DS. The heating-cooling process proved that the sol-gel transition for CECs in water was thermally irreversible. The AFM images revealed that the particles packed loosely together to form gel aggregates. Moreover, the Maxwell model with four elements was used to describe the frequency dependencies of G′ and G′′ for CEC in aqueous solution. [ABSTRACT FROM AUTHOR]

Poly( D,L-lactide- co-glycolide)- b-poly(ethylene glycol)- b-poly( D,L-lactide- co-glycolide) (PLGA-PEGPLGA) triblock copolymers were synthesized at 130 and 160 °C. The concentrated aqueous solutions of both specimens underwent reversible sol-to-(transparent gel)-to-(opaque gel) transitions upon heating but exhibited different critical gelation concentrations and transition temperatures, possibly due to the minor sequence differences between D,L-lactide (LA) and glycolide (GA) in the PLGA blocks. Aqueous solutions (20 wt%) of the copolymers synthesized at 130 and 160 °C spontaneously formed an opaque gel and a transparent gel at body temperature, respectively. The resulting hydrogels displayed similar in vitro degradation profiles in phosphate buffer saline solutions at 37 °C. Nevertheless, the late-stage releases of bovine serum albumin from the physical hydrogels differed. The present study reveals for the first time that transparent vs. opaque thermogel state influences some of their biomaterial-related properties via the 'overheat degree' of the thermogelling systems at a given working temperature, usually 37 °C. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This article is concerned about the sol-gel transition of asphalt by dynamic mechanical analysis. By sol-gel transition of asphalt, we mean here the transition from viscoelastic fluid to viscoelastic solid as the temperature is varied. In this investigation two types of asphalt of the same specification grade but manufactured by different process (blending and air blowing) were tested at unaged, short-term aged and long-term aged conditions. Sol-gel transition from G′- G″ cross-over, torque and normal force were captured. The transition point measured was frequency dependent when determined using G′- G″ cross-over and torque and this frequency dependency vanished above 40 Hz. The measurement of normal force during these experimental investigation revealed interesting details. As the normal force recorded was only due to the contraction of the material during temperature sweep, the transition point measured was frequency independent. It was also found that the transition point calculated with normal force was close to the transition point calculated with G′- G″ cross-over and torque at higher frequencies. Also, the transition temperature increased as the material aged. [ABSTRACT FROM AUTHOR]

Linear viscoelastic properties of carbon black (CB) suspensions in a mixture of a rosin-modified phenol resin-type varnish (Varnish-1)/an alkyd resin-type varnish (Varnish-2), which exhibited a sol-gel transition on an increase in CB concentration, were investigated from 30°C to 80°C. The viscoelastic properties were reversible from 30°C to 60°C. In contrast, at temperatures above 60°C, the storage ( G′) and loss ( G″) moduli were irreversible and increased significantly with increasing temperature. This increase in the moduli is due to a change of the dispersion state to agglomerated state by heating. The agglomerated state was held, when the suspensions were lowered at 30°C. However, the G′ and G″ recovered to the original values upon shearing. This heat-induced gelation should be a universal feature for suspensions of weakly attractive particles. The temperature and shearing histories of the suspensions were discussed in relation to adsorption of polymeric component in the varnish on the CB particles. [ABSTRACT FROM AUTHOR]

Linear viscoelastic properties of carbon black (CB) suspensions with various CB concentrations (c) in two suspending media, mixtures of a rosin-modified phenol resin-type varnish (Varnish-1)/an alkyd resin-type varnish (Varnish-2) and Varnish-1/petroleum solvent (AF) were investigated. The former medium has higher affinity and the latter has poorer affinity toward CB particles than Varnishi-1, although these two media have almost the same viscoelastic properties. Both CB/(Varnish-1/Varnish-2 = 60/40) and CB/(Varnish-1/AF = 80/20) suspensions exhibited a sol-gel transition on an increase in c, as similar to the behavior of CB/Varnish-1 suspensions. But, for the CB/(Varnish-1/Varnish-2 = 60/40) suspensions the critical gel concentration (c) was lower and the critical relaxation exponent ( n) was higher than that of CB/Varnish-1 suspensions. In contrast, for the CB/(Varnish-1/AF = 80/20) suspensions c and n, respectively, were almost the same value as those of CB/Varnish-1 suspensions. These results strongly suggest that c and n are attributable to the medium affinity, but not to the medium viscosity, and the CB fractal structure changes from plane-like to straight-line structure with increasing medium affinity. [ABSTRACT FROM AUTHOR]

The objective of this work was to delineate the effect of hydrophilic and hydrophobic polymeric additives on sol-gel transition and release profile of timolol maleate (TM) from poly (ethylene glycol)-poly (ε-caprolactone)-poly (ethylene glycol) (PEG-PCL-PEG)-based thermosensitive hydrogel. Polycaprolactone (hydrophobic additive) and polyvinyl alcohol (PVA) (hydrophilic additive) reduced critical gel concentration of PEG-PCL-PEG triblock polymer. The effect of PCL on sol-gel transition was more pronounced than PVA. However, with PCL no statistically significant difference in release profile was observed. The effect of PVA on release profile was more pronounced, which reduced the cumulative percentage release of TM from 86.4 ± 0.8% to 73.7 ± 1.8% over 316 h. Moreover, cytotoxicity of the hydrogel was also investigated utilizing rabbit primary corneal epithelial culture cells. No significant cytotoxicity of hydrogel alone or in presence of additives was observed. So, polymeric additive strategy serves as a valuable tool for optimizing TM release kinetics from PEG-PCL-PEG hydrogel matrix. [ABSTRACT FROM AUTHOR]

Uniaxial elongational viscosity of SiO/(acrylic polymer/epoxy (AP/EP)) suspensions with various SiO volume fractions ( ϕ) in a blend of acrylic polymer and epoxy was investigated at various temperatures ( T). The matrix polymer ((AP/EP) blend) contained 70 vol.% of EP. At ϕ ≤ 35 vol.% at T ≤ 80°C, where the suspensions were in sol state, strain-hardening behavior was observed. This strain hardening of the suspensions is attributable to the elongational flow properties of (AP/EP) medium. At critical gel state ( ϕ = 35 vol.% and T = 100°C) and in gel state ( ϕ ≥ 40 vol.%), the elongational viscosity exhibited the strain-softening behavior. These results strongly suggest that the strain softening results from the strain-induced disruption of the network structure of the SiO particles therein. [ABSTRACT FROM AUTHOR]

Large deformation, nonlinear stress relaxation modulus G( t, γ) was examined for the SiO suspensions in a blend of acrylic polymer (AP) and epoxy (EP) with various SiO volume fractions ( ϕ) at various temperatures ( T). The AP/EP contained 70 vol.% of EP. At ϕ ≤ 30 vol.%, the SiO/(AP/EP) suspensions behaved as a viscoelastic liquid, and the time-strain separability, G( t, γ) = G( t) h( γ), was applicable at long time. The h( γ) of the suspensions was more strongly dependent on γ than that of the matrix (AP/EP). At ϕ = 35 vol.% and T = 100°C, and ϕ ≥ 40 vol.%, the time-strain separability was not applicable. The suspensions exhibited a critical gel behavior at ϕ = 35 vol.% and T = 100°C characterized with a power law relationship between G( t) and t; G( t) ∝ t. The relaxation exponent n was estimated to be about 0.45, which was in good agreement with the result of linear dynamic viscoelasticity reported previously. G( t, γ) also could be approximately expressed by the relation $G(t,\gamma) \propto t^{-n^{\prime}}$ at ϕ = 40 vol.%. The exponent n increased with increasing γ. This nonlinear stress relaxation behavior is attributable to strain-induced disruption of the network structure formed by the SiO particles therein. [ABSTRACT FROM AUTHOR]

This paper reports the effects of precipitate agents used in the collection of block copolymers composed of poly(lactic acid- co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) on their thermogelling aqueous behaviors. We synthesized PLGA–PEG–PLGA triblock copolymers with a relatively wide distribution of molecular weight (MW) and then separated the crude polymers via three different precipitate agents (diethyl ether, hexane, or methanol). The obtained products exhibited, however, significantly different macroscopic states in water: some were sols, some were precipitates, and some underwent sol–gel transition upon heating. We found that by using different precipitate agents, ingredients of different MW were collected from the synthesized polymers, which accounted for the different states of the separated products in water. Our study strengthens the importance of an appropriate precipitate agent and reveals the subtle balance of hydrophobicity and hydrophilicity in this sort of amphiphilic block copolymers. [ABSTRACT FROM AUTHOR]