Academic literature on the topic 'Solvent-induced swelling behaviour'

Thermo-responsive shape-memory polymer (SMP) has been experimentally demonstrated that shape recovery can be induced by plasticizing solvent. Subject to being immersed into solvent, deformed SMP recover from the temporary shape to original shape, leading to shape recovery induced by the molecular interaction. The actuation of styrene-based SMP has been carried out by electrostatic dipole-dipole interaction and physical swelling effect, respectively. The model can be used to predict the effect of prestress, strain, volume change and chemical potential on SMP actuation in the solvent. Finally, it is found that the simulation agrees well with experimental results. The authors show that the chemo-mechanical instability occurs when the Hessian of the free-energy function ceases to the positive definite. Their calculations show that the shape recovery behavior of SMP is driven by the entropy change markedly, agreeing with existing experimental observations.

A fundamental understanding of the effect of a crosslinker on gel properties is important for the design of novel soft materials because a crosslinking is a key component of polymer gels. We focused on post-polymerization crosslinking (PPC) system utilizing activated ester chemistry, which is a powerful tool due to structural diversity of diamine crosslinkers and less susceptibility to solvent effect compared to conventional divinyl crosslinking system, to systematically evaluate the crosslinker effect on the gel properties. A variety of alkyldiamine crosslinkers was employed for the synthesis of poly(N-isopropylacrylamide) (PNIPAAm) gels and it was clarified that the length of alkyl chains of diamine crosslinkers strongly affected the gelation reaction and the swelling behavior. The longer crosslinker induced faster gelation and decreased the swelling degree and the response temperature in water, while the crosslinking density did not significantly change. In addition, we were able to modify the polymer chains in parallel with crosslinking by using a monoamine modifier along with a diamine crosslinker. This simultaneous chain modification during crosslinking (SMC) was demonstrated to be useful for the regulation of the crosslinking density and the swelling behavior of PNIPAAm gels.

Abstract The concept of double networks, which impart chain orientation to elastomers, is a rather new idea. Double networks were induced in natural rubber vulcanizates cured with different accelerator systems. Double networked natural rubber with different extensions cured with N-cyclohexyl benzothiazyl sulphenamide (CBS) and 1-phenyl 5-ortho -tolyl 2,4 dithiobiuret was studied and the effect of extension on the mechanical properties and swelling was analyzed. The extent of chain orientation was analyzed through anisotropic swelling studies. The modulus, tensile strength and tear strength showed an increase with increased residual extension ratio. The effect was more predominant in the longitudinal direction than in the transverse direction. The ultimate tensile elongation showed a slight deterioration. It was revealed that the formation of double networks with higher residual extension ratios restricted the entry of the solvent. Based on the studies it was concluded that residual extension has a profound effect in determining the final properties of vulcanizates.

In the present study, a different approach for the preparation of poly(ethylene glycol) diacrylate-gelatin (PEGDA-gelatin) hydrogels was investigated. Gelatin type A from porcine skin was used as the co-initiator of a radical photo-initiating system instead of the traditional aliphatic or aromatic amines. This became possible because, upon visible-light irradiation, the amine sequences within gelatin generate initiating free-radicals through the intermolecular proton transfer in a Norrish type II reaction with camphorquinone (CQ). PEGDA-gelatin hydrogels were prepared by visible-light-induced photopolymerization. The gelatin content in the precursor formulations was varied. The influence of gelatin on the kinetics of the photocuring reaction was investigated, and it was found that gelatin fastened the rate of polymerization at all concentrations. The covalent attachment of gelatin segments within the cross-linked hydrogels was evaluated by means of attenuated total reflectance-infrared spectroscopy (ATR-FTIR) spectroscopy after solvent extraction. The thermo-mechanical properties, as well as the swelling behavior and gel content, were also investigated.

Abstract Vildagliptin (VID) is a dipeptidyl peptidase-4 (DPP-4) inhibitor used in controlling blood glucose level in type 2 diabetes. Vildagliptin improves beta cells function and is also suggested to effectively control the inflammation. The possible ocular anti-inflammatory property of vildagliptin has been explored using topically applied plasticized ocular film formulation. Film formulation was prepared by solvent cast and evaporation method using triethanolamine (TEA), dimethyl sulphoxide (DMSO), and polyethylene glycol 400 (PEG 400) as the plasticizer in HPMC hydrogel matrix base. Anti-inflammatory study was carried out in the carrageenan induced ocular rabbit model. Analytical methods confirmed that the drug was present almost in completely amorphized form in the film formulation. Level of hydration, swelling and erosion rate of the film played the controlling factor in the process of drug release, ocular residence and permeation. Maximum swelling rate of 363 h−1 has been shown by VHT compared to other formulation of VHD and VHP (174 and 242 h−1 respectively). Film containing DMSO exhibited highest in vitro release as well as ex vivo ocular permeation. Film formulation has shown a fast recovery of ocular inflammation in contrast to the untreated eye after inducing inflammation. Plasticized vildagliptin hydrogel film formulation could be utilized in the management and control of ocular inflammation particularly with diabetic retinopathy after proper clinical studies in higher animal and human individuals.

AbstractAmine-functionalized thin films were prepared by plasma induced deposition of allylamine. Radio frequency (rf) plasma polymerization was carried out under both continuous wave (CW) and pulsed plasma conditions to control the film chemistry, all other process variables being held constant. Using plasma polymerized films for subsequent grafting reactions or for direct biomedical applications usually involves exposure of the films to a solvent environment. It was the major focus of this work to investigate both the chemical and physical effects of solvents on plasma polymerized allylamine films. Film properties were determined using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Waveguide Mode Spectroscopy (WaMS) and Surface Plasmon Spectroscopy (SPS). WaMS provided an ideal opportunity to study the complex swelling and drying behaviour of these films by allowing a simultaneous study of the changes in film thickness and refractive index. Although the amine groups of the monomer were increasingly retained in the films as the RF duty cycle was lowered, a larger amount of oxygen was also found to be incorporated upon exposure to air. Extraction in ethanol led to a decrease in film thickness, especially for the films produced at low duty cycles, but appeared to have little effect on the film composition, as measured by XPS and FTIR.

The solvent-induced swelling behaviour of Victorian brown coals was examined in detail to probe the bonding mechanisms in very low rank coals (in this case Victorian brown coal). Correlation of solvent properties with differences in observed swelling behaviour were interpreted in terms of the coal structure, and means of predicting the observed behaviour were considered. Modification of the coal structure via physical compression (briquetting), chemical digestion, thermal modification, and functional group alkylation was used to further elucidate those structural features which govern the swelling behaviour of Victorian brown coals. Briquette weathering (i.e. swelling and disintegration of briquettes when exposed to variations in humidity and temperature) was examined by making alterations to briquette feed material and observing the effects on swelling in water. The application of solubility parameter alone to prediction of coal swelling was rejected due to the many exceptions to any proposed trend. Brown coal swelling showed a minimum when the solvent electron-donor number (DN) minus its electron-acceptor number (AN) was closest to zero, i.e. when DN and AN were of similar magnitude. The degree of swelling increased either side of this point, as predicted by theory. In contrast to the solubility parameter approach (which suffers from the uncertainty caused by specific interaction between coal and solvent), the electron donor/acceptor approach is about specific interactions. It was concluded that a combination of total and three-dimensional solubility parameters and solvent electron donor/acceptor numbers may be used to predict solvent swelling of unextracted brown coals with some success. Solvent access to chemically densified coal was found to be insensitive to a reduction in pore volume, and chemical effects were dominant. Thermal modification of the digested coal resulted in reduced swelling for all solvents, indicating that the structure had adopted a minimum energy configuration due to decarboxylation and replacement of hydrogen bonds with additional covalent bonds. Swelling of oxygen-alkylated coals demonstrated that the more polar solvents are able to break relatively weak hydrogen bonded crosslinks. The large difference between the rate and extent of swelling in water (and hence weathering) of Yallourn and Morwell briquettes was shown to be almost entirely attributable to exchanged magnesium. Magnesium exchange significantly increases the rate and extent of swelling of Yallourn coal. It was also shown that the swelling of briquettes due to uptake of water by magnesium-exchanged coals is reduced significantly with controlled ageing of the briquettes. The solvent swelling behaviour of Victorian brown coals is consistent with the notion that coal is a both covalently and non-covalently crosslinked and entangled macromolecular network comprising extractable species, which are held within the network by a wide range of non-covalent, polar, electron donor/acceptor interactions. Solvents capable of significant extraction of whole brown coals are also capable of significant swelling, but not dissolution, of the macromolecular coal network, which supports the view that the network is comprised of both covalent and ionic bonding. Victorian brown coals have also been shown to exhibit polyelectrolytic behaviour due to a high concentration of ionisable surface functionalities.

Shape memory polymers (SMPs) are a widely studied class of materials due to their numerous applications in various fields of engineering. They find applications in deployable structures, biomedical devices, adaptive optical devices, sensors and actuators, in textiles etc. Recent studies have shown shape memory behavior in many polymers. Sulfonated poly ether ether ketone (SPEEK) is an ionic polymer which is being extensively studied for its application in fuel cells as a Proton Exchange Membrane (PEM) polymer due to its relatively higher thermal and mechanical stability over other PEMs in addition to proton transport. Recent studies on a sulfonated ionomer, Nafion® which has only one broad reversible phase transition, can show tunable, multiple shape memory effects by deforming the polymer at different temperatures without compromising the shape fixity (Rf). This paper reports, for the first time, the swelling (in solvents) induced shape memory behavior observed in SPEEK. The study was motivated by the preliminary observations of the response of SPEEK to solvent stimulus. SPEEK samples of varying degrees of sulfonation (DS) were prepared by the sulfonation of poly ether ether ketone (PEEK). The shape fixation and recovery rates (Rr) of the polymer under different temperatures and solvent conditions are reported. A comparative study of the shape memory response of the material with varying DS was also carried out. We also report for the first time the potential use of the parallel plate geometry of a rheometer for estimating the force during the shape recovery process. Visual demonstration of the shape memory effect is carried out using solvents at different temperatures.