High Polymer Concentrations Research Articles

Ionic Liquids and Deep Eutectic Solvents and Their Use for Dissolving Animal Hair

In recent years, one of the priority areas of research in chemistry has become the processes carried out in an environment of liquid organic salts, the so-called ionic liquids (ILs), which are assessed as environmentally friendly or “green” alternatives to conventional organic solvents. ILs are non-volatile, highly polar solvents that dissolve many organic, inorganic, and organometallic compounds. Since they have no detectable vapor pressure, ILs are considered as potential substitutes for volatile organic compounds traditionally used as solvents. So-called deep eutectic solvents (DES) is a group of ILs that are liquid mixtures of a number of organic and (or) inorganic components taken in a certain ratio (eutectic or close to eutectic). DES deserve a special attention due to their negligible saturated vapor pressure, availability, low cost, as well as ability to dissolve at relatively high concentration of metal salts, metal oxides and various polymers. Particularly DES based on a mixture of choline chloride with urea (DES-1) or a mixture of choline chloride and adduct of urea with hydrogen peroxide (DES-2) give eutectics that are liquid at ambient temperature and have unusual solvent properties, including an ability to dissolve an animal hair in the presence of low concentration of sodium sulfide or ammonium thioglycolate. It was found that depending on the ratio between DES-1 and DES-2 in the mixture of two Deep Eutectic Solvents and the nature of sulfur-containing additive, the solubility of rabbit hair under used conditions, varies from 51% to 79%.

Experimental correlation for pipe flow drag reduction using relaxation time of linear flexible polymers in a dilute solution

AbstractIn this study, we investigate the drag reduction property of a linear flexible polymer, PEO (polyethylene oxide) in a fully turbulent pipe flow. The aim of this study is to develop a correlation to predict the drag reduction using the Weissenberg number, a dimensionless number related to the relaxation time of the polymer and the polymer concentration in dilute solutions. The physical meaning of the relaxation time of polymers and overlap concentration between the dilute and semi‐dilute polymer solution are clarified. A higher polymer concentration, Reynolds number, and Weissenberg number lead to an increasing drag reduction. A semi‐empirical correlation to predict the drag reduction with two dimensionless variables mentioned above is established and can predict the experimental data in this work and other previous works well. Previous correlations that use Reynolds number often require high flow velocity or large pipes in the experimental setup to predict drag reduction in large‐scale industrial applications, which involves extra cost and potential safety issues. The current new correlation method uses relatively low velocities to avoid the problems mentioned above.

Microscopic insights into the phase transition of poly(N-isopropylacrylamide) in aqueous media: Effects of molecular weight and polymer concentration

We study a temperature (T)-induced phase transition of semi-dilute poly(N-isopropylacrylamide) (pNIPAm) in H2O and D2O, focusing on effects of molecular weight and polymer concentration. We use simultaneous small- and wide-angle x-ray scattering (SWAXS) and dielectric relaxation spectroscopy (DRS). The hydration number Zhyd of pNIPAm is determined by DRS. We observe a gradual decrease of Zhyd with increasing T below TS − 6 K, where TS is the spinodal temperature, and its subsequent steep decrease on approaching TS. This eccentric two-mode dehydration behavior implies strong cooperative nature of hydration/dehydration of the pNIPAm chains. Furthermore, the observed dehydration is coupled to the critical fluctuations manifested by a power-law divergence of the correlation length ξ. The emergence of a low-q interference peak provides evidence that high-density microglobules are formed even far below Ts, where a swollen coil state of polymer chains is generally considered to be predominant. The local number density of the microglobules is almost unchanged below Ts, but then exhibits a step-like increase just above Ts, where most pNIPAm chains are already collapsed. This observation suggests that in addition to the ordinary (macroscopic) density order parameter, the local number density of the microglobules should serve as an additional order parameter monitoring the phase transition of aqueous pNIPAm. The correlation length significantly decreases at higher polymer concentration because of the stronger interpenetration effect between different chains. At higher concentration, ξ converges to similar values independent of molecular weight, which indicates an already congested state of the pNIPAm chains. Lowering averaged molecular weight leads to a stronger tendency of inter-chain aggregation and interface formation especially at high T.

The experimental study of silica nanoparticles strengthened polymer gel system

To research the action mechanism of silica nanoparticles in polymer gel, a novel silica nanoparticle strengthened polymer gel (SNSPG) with partially hydrolyzed polyacrylamide (HPAM) and organic zirconium is studied. After adding nanoparticles, when the concentration of HPAM is low (˂0.8 wt%), viscoelasticity of this system has few increases compared with before. The nanoparticles are not strong to bridge the loose three-dimensional network structure. Furthermore, Dynamic Light Scattering (DLS) and zeta potential measurements were tested to explain enhancement of high concentration system (0.8 wt%) by nanoparticles. Differential Scanning Calorimeter (DSC) and Environmental Scanning Electron Microscope (ESEM) measurements results together support the action mechanism of this research. In high polymer concentration, proper amounts of nanoparticles participated in the gelation process to make polymer gel tighter, while too many nanoparticles blocked cross-linking of polymer and cross linker to weaken the system enhancement. This research develops a strengthened polymer gel system which has broad application prospects, and the action mechanism this research proposed provides theoretical support for industrial production.

Cationic starch as the effective flocculant of silica in the presence of different surfactants

The efficiency of cationic starch (CS) as the flocculating agent of silica particles in the presence of different surfactants was studied. Using such techniques as UV–Vis spectroscopy, surface tensiometry and electrophoretic mobility, it was established that cationic starch is an effective flocculant of the silica particles. Furthermore, bridging flocculation was proposed as the main mechanism of flocculation when the concentration of cationic starch is in the range from 1 to 100 ppm. It was also observed that at high polymer concentrations (800 ppm) depletion stabilization of the system occurs. However, the presence of surfactants influences the flocculation process. The conducted measurements show that the interactions between the cationic starch and some anionic surfactants (hydrocarbon as well as fluorinated and silicone ones) lead to the formation of polymer-surfactant complexes. In such case, the efficiency of CS as the flocculating agent is greatly reduced. The paper emphasizes the importance of cationic starch as an effective flocculant but it also points out that in the presence of surfactants, the flocculation conditions have to be adjusted. These results could find many industrial applications for example in the wastewater treatment.

Design and development of artemisinin and dexamethasone loaded topical nanodispersion for the effective treatment of age-related macular degeneration.

Age-related macular degeneration (AMD) is a disease affecting the macula by the new blood vessels formation. AMD is widely treated with a combination of anti-angiogenic and anti-vascular endothelial growth factor (VEGF) agents. The topical administration of nanodispersions showed enhanced ocular residence time with controlled and prolonged drug delivery to the disease site at the back of the eye. In the present study we developed and characterized nanodispersion containing anti-angiogenic (artemisinin) and anti-VEGF agent (dexamethasone) for the topical ocular administration in order to obtain a required drug concentration in the posterior part of the eye. The nanodispersions were prepared with varying concentration of polymer, polyvinyl pyrrolidone K90 and polymeric surfactant, Poloxamer 407. The nanodispersions were found to be smooth and spherical in shape with a size range of 12-26 nm. In-vitro drug release studies showed the 90-101% of artemisinin and 55-103% of dexamethasone release from the nanodispersions. The blank formulation with a high concentration of polymer and polymeric surfactant showed an acceptable level of haemolysis and DNA damage. The chorioallantoic membrane assay suggested that the nanodispersion possess good anti-angiogenic effect. Hence the formulated artemisinin and dexamethasone nanodispersion may have the great potential for the AMD treatment.

Electrospinning of cellulose acetate nanofiber membrane using methyl ethyl ketone and N, N-Dimethylacetamide as solvents

Cellulose acetate (CA) nanofiber membrane was prepared by electrospinning method using solvent mixtures of methyl ethyl ketone (MEK) and N, N, - dimethylacetamide (DMAc) in different ratios (2:1, 1:1, 1:2) and also different concentration of CA (7–19%). MEK was selected in place of acetone due to its high boiling point, thereby, minimises the evaporation loss of the solvent enabling the longer duration of electrospinning. The morphology of electrospun nanofibers was observed by Scanning Electron Microscope (SEM). It was observed that cylindrical fibers formed at higher concentration of polymer with increase of DMAc. Fiber diameters were in the range of 40–500 nm with large diameters formed at higher polymer concentration. Contact angle measurement revealed that membranes have good wetting property. The water flux measurements of membranes were carried out under gravity. A water flux of 10,197 Lm−2h−1 was measured initially and was reduced subsequently to 365-200 Lm−2h−1. The membranes could be reused up to four times without rupture. The above experiments suggest that MEK and DMAc could be an alternate solvent system in addition to other systems.

Efficient dewatering of polymer-rich aerobic granular sludge with cationic polymer containing hydrocarbons

This study compared the dewatering properties of aerobic granular and activated sludge from full-scale wastewater treatment plants, and determined how polymer dose and type affect granular sludge dewatering efficiency. At the same dose, granular sludge filtration cake had about 4% lower humidity than activated sludge cake. Aerobic stabilization improved only activated sludge dewatering. The granular sludge reactor had over 1.5 times more extracellular polymeric substances (1.8 times more alginate) per reactor volume than the activated sludge reactor, but the high polymer content did not decrease granular sludge dewatering. Granular sludge dewatered best with FLOPAM EM 840MEB, due to its composition (n-alkanes, isoalkanes, cyclic/aromatic hydrocarbons). With this polymer, sludge cake moisture was lowest (84.7 ± 0.4%) at 1.6 g polymer/kg MLSS. With all tested polymers, the lowest dose (0.2 g/kg MLSS) ensured low cake humidities; this dose was far lower than typical doses for activated sludge dewatering. Upgrading from activated to granular sludge technology significantly facilitates excess sludge management.

APPLICATION OF NOVEL NATURAL MUCOADHESIVE POLYMER IN THE DEVELOPMENT OF PENTOXIFYLLINE MUCOADHESIVE TABLETS

Objective: The present study was planned to develop a mucoadhesive tablet formulation of the drug pentoxifylline using natural mucoadhesive polymer from the plant Ocimum basilicum Linn.
 Methods: The isolated polymer was used to formulate the mucoadhesive tablets with 3 different concentrations. The tablets were formulated by using direct compression technique and evaluated for various parameters such as thickness, friability, weight variation, hardness, mucoadhesive strength, swelling index by standard methods, and the in vitro drug release studies in USP dissolution test apparatus type-II.
 Results: The swelling index was indirectly proportional to the polymer concentration and the tablets with a high concentration of polymer showed better mucoadhesive strength (28.5532±0.4660). The in vitro drug release showed that the drug release was indirectly proportional to the polymer concentration. The formulation F3 showed the controlled release of drug pentoxifylline (99.84±1.86) for 10 h. The mechanism of drug release was found to be Fickian diffusion and followed the zero-order kinetics, which was proved by its highest linearity (r2) in all the formulations.
 Conclusion: The tablets formulated with the isolated polymer of Ocimum basilicum Linn showed the good mucoadhesive mucoadhesive property and it controlled the release of the pentoxifylline.

Numerical study of Phan-Thien–Tanner viscoelastic fluid flow around a two-dimensional circular cylinder at a low Reynolds number: a new classification for drag variations regimes

This study numerically investigates a low Reynolds two-dimensional flow of a viscoelastic fluid over a circular cylinder using the finite volume method. The Phan-Thien–Tanner model, as one of the most accurate non-linear models, for the first time, describes the viscoelastic behavior of a high concentration polymer solution in the flow over a cylinder in high elastic regime in Re = 10. To avoid divergence and to stabilize the numerical process in high elastic cases, the log-conformation approach proposed by previous researchers is used. The convective terms of the equations are discretized using a high-resolution scheme. The physical instability, as observed by some researchers in the creeping regime of high De flow, is very weak in the cases of this research. The numerical results of this research show both drag reduction (for the elasticity number El 0.025). Compared with the dissipative nature of viscoelastic fluid flows, the drag coefficient, resulted from the polymeric portion of stress, in the high elastic flow regime (El > 10), approached to zero due to an increase in the storing nature of viscoelastic fluid. At these elasticity numbers, the drag coefficient remains constant with El, and the material behaves like a Newtonian fluid. Compared with the shear-thinning behavior and unlike the creeping flow, the elasticity is the main cause of drag variation in most cases. Shear stress affects the drag force directly, while normal stress influences the drag force by changing the pressure distribution over the cylinder. The maximum normal stress occurs at the back of the cylinder due to the wake behind it, while in creeping flow it occurs at its half-front. Finally, the effects of elasticity number, retardation ratio and model parameters on the distribution of stress components, drag coefficient, and vortex dimensions are investigated separately, and a physical discussion is presented.

Study on rheological behavior and salt-thickening mechanism of a synthesized twin-tailed hydrophobically modified polyacrylamide

Hydrophobically modified polyacrylamide (HMPAM) is widely used in petroleum development, whereas it still confronts challenges in high salinity reservoirs. In this work, a twin-tailed modified polyacrylamide was introduced and characterized by FT-IR, 1H NMR and TGA. The rheological properties and thickening mechanism were investigated by viscosimetry, rheology, macroscopic appearance, dynamic light scattering, fluorescence spectroscopy and β-cyclodextrin inclusion. The results revealed that by increasing NaCl from 0 to 50 g/L, the critical association concentration declined and solutions transformed from a transparent fluid of 115 mPa·s to viscoelastic fluid of 2040 mPa·s. Eventually, the viscosity decreased with white precipitation at 200 g/L NaCl. The salinity conduced to the aggregate of hydrophobic groups, while excessive aggregate decreased the hydrodynamic volume, which in turn caused a reduction of macroscopic viscosity. Higher polymer concentrations were conducive to better salt-thickening property. This copolymer showed great salt resistance and prospects for application in high salinity reservoirs.

Isotactic polypropylene–1,2,4,5-tetrachlorobenzene: porous bodies via thermally induced phase separation

Using recently constructed experimental phase diagram isotactic polypropylene–1,2,4,5-tetrachlorobenzene (TeCB), we formulate a physically consistent scenario of the mixture evolution under thermally induced phase separation and predict the morphology of capillary-porous bodies that are formed after cooling down the binary system and removal of the low molecular mass component. This approach allows us to interpret the experimental data obtained by optical microscopy, scanning electron microscopy, and differential scanning calorimetry on the system with two crystallizable components. At any composition, TeCB forms needle-like crystals of nearly square section. Increasing polymer content affects crystal growth by limiting their length and by generating another population of small TeCB crystals of irregular shape and close to log-normal size distribution, located in the amorphous polymer regions. Finite rate of cooling the system leads to a hysteresis, when the values of characteristic temperatures and compositions in the phase diagram appear to be considerably shifted to lower temperatures and higher polymer contents. Combination of structural and calorimetric data provides an opportunity to characterize polymer–solvent systems from both thermodynamic and technological standpoints.

Investigation of electrohydrodynamic atomization (electrospraying) parameters’ effect on formation of poly(lactic acid) nanoparticles

The aim of this study was to develop nanoparticles via electrohydrodynamic atomization (electrospraying) method. These nanoparticles have potential applications such as drug delivery and manipulating surface functionality. Electrosprayed nanoparticles were produced from poly(lactic acid) (PLA). Solution and process parameters were investigated for optimization of the electrospraying process. Different PLA concentrations, solvent types and solvent ratios were investigated as part of the study. The characterization of the electrosprayed solutions was carried out via viscosity, conductivity and surface tension measurements. Also, the effect of process parameters (flow rate, needle to collector distance, electrical field, application time and needle dimension) on particle morphology and dimension was investigated. After the formation of PLA nanoparticles, morphological and dimensional characteristics were analyzed through SEM images and nanosizer measurements. According to some of our findings, particle size increases with higher polymer concentrations and flow rates. Also, increase in electrostatic field and distance result in smaller particle size because of increase in coulombic forces. But a further increase in coulombic forces triggers increase in size of particles and fibril formation with a bimodal distribution. The smallest size and the narrowest distribution were obtained for the smallest inner needle diameter. Deposition time does not have a significant influence on the produced particle sizes and their distributions; it only affects the production amount. As a result of this study, desired monodisperse PLA nanoparticles with comparatively smaller size were successfully achieved. Also, the detailed investigation of electrospraying parameters can be useful for future studies.

Mechanisms and Process Control for Quenching with Aqueous Polymer Solutions∗

Abstract Beginning in the middle of the last century aqueous polymer solutions like polyvinylpyrrolidone (PVP) and polyalkylene glycol (PAG) have been used for immersion quenching because of their unique features and quenching characteristics. Known problems of quenching in polymer solutions are process reproducibility and work safety due to spontaneous reforming of polymer films and almost explosive vapor layers collapse. The boiling and quenching process within polymer solutions and their mechanisms are investigated here. In quasi-steady experiments a newly developed in-line sensor measures the local concentration in the vicinity of a fixed vapor bubble depending on the distance to the phase boundary. These experiments show that the polymer concentration increases with decreasing distance to the vapor bubble surface. Rheological investigations on polymer solutions show that a higher polymer concentration especially increases the solution viscosity considerably. In a typical immersion quenching process with polymer solutions, in the initial phase of the quenching process individual vapor bubbles are formed on the surface of the immersed hot specimen. The high solution viscosity keeps the vapor bubbles on the surface leading to bubble growth and coagulation. Thus, the formation of a vapor layer is promoted. Along with the stabilization of the vapor phase by a concentrated polymer skin a stable vapor layer may emerge. Within the progress of the quenching process, this vapor layer may repeatedly collapse in an explosive like manner. A major influence of this process is the type of polymer (chain length), the polymer concentration and the liquid solution temperature. These effects are also investigated on a larger application-oriented scale setup. Cooling curves and global electric conductance measurements as well as sound and video recordings during specimen quenching in polymer solutions are used to locate vapor layers and their collapses. The experiments show that these effects can be influenced by suitable flow conditions around the specimen.

Core-shell nanostructured organic redox polymer cathodes with superior performance

Core-shell nanoparticles stabilized by a cationic surfactant are prepared from the poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) redox polymer. The nanoparticles are further self-assembled with negatively charged reduced graphene oxide nanosheets and negatively charged multi-walled carbon nanotubes. This results in the formation of a free-standing cathode with a layered nanostructure and a high content of redox polymer that exhibits 100% utilization of the active substance with a measured capacity as high as 105 mAh/g based on the whole weight of the electrode.

Understanding the Role of Polymeric Binders in Water Based Lithium Ion Electrodes

Polymers find application in Lithium ion Batteries (LiB) as binders, providing cohesion in the dry electrode layer as well as adhesion to the current collector. They may also be added as a thickener to control the flow and hence the processing behavior of the paste. Furthermore, polymeric binders can act as dispersing agents for active material or carbon black particles, thus strongly determining the component distribution in dry electrodes. Despite the vast amount of research activities in the field of LiB, the contribution of the binder to the cell performance still remains elusive. Therefore, the adsorption of carboxymethylcellulose (CMC) on LiFePO4 and graphite particles as active material was investigated. The flow behavior of the electrode pastes as well as the electrical conductivity, mechanical properties and microstructure of corresponding dry electrodes were thoroughly characterized. Rheological measurements were carried out to study paste flow behavior as a function of CMC and solid particle concentration. The electrical conductivity of thin electrode layers was measured using the four point resistivity test. The adhesion force between electrode layer and current collector was determined via 90°-peel test. Thick electrode layers were prepared to investigate the cohesion in the electrode employing compression, bending and shear tests. Finally, the microstructure of the dry electrodes was characterize by means of scanning electron microscopy (SEM). Yield stress and viscosity exhibit a pronounced minimum with increasing CMC concentration for both the cathode and anode pastes, indicating that CMC acts as dispersing agent at low concentrations and as a thickener at higher concentration when the equilibrium adsorption concentration is exceeded. Furthermore, the degree of substitution of CMC have no significant influence on the slurry viscosity, whereas higher molecular weights and CMC concentrations lead to significantly higher viscosities. Electrical conductivity of thin electrode layers increases with increasing CMC concentration and yields a pronounced maximum when the equilibrium adsorption concentration is covered, suggesting a critical polymer concentration at which electrode components ideally distribute. In addition, mechanical tests show no clear dependence of the adhesion strength on CMC concentration, irrespective of the degree of substitution or molecular weight, i.e. it does not contribute to the adhesive strength. In contrast, the cohesive strength of the electrode layers increases with higher polymer concentration and molecular weight, but decreases with increasing degree of substitution. Micrographs of the electrode layers show an alignment of the particles for electrodes based on high molecular weight CMC. Preliminary measurements exhibit higher adhesion strength when adding styrene butadiene rubber (SBR), whereas cohesion strength and electrical conductivity significantly decreases. This demonstrates that the optimum CMC concentration has to be chosen according to the required specifications with respect to cohesion and electrical performance.

Electrospinning of uniform nanofibers of Polymers of Intrinsic Microporosity (PIM-1): The influence of solution conductivity and relative humidity

Polymers of Intrinsic Microporosity (PIMs) are ultra-permeable macromolecules, which can be cast as a dense membrane and exploited in a wide spectrum of applications, particularly for gas separation owing to their extremely large inner surface area, free volume and high gas permeability. While they are mostly intended to serve as membranes for gas separation, in recent years, they have been also employed in water treatment applications owing to their solution processability, which enables the production of fibrous membranes by electrospinning. The fibrous form provides an increase in sorption performance, water permeability and flux for their application in water treatment. However, owing to the low conductivity of PIM-1 solutions in 1,1,2,2-tetrachloroethane (TeCA) that is the ideal solvent for the electrospinning of PIM-1 solutions, a higher polymer concentration is required to produce bead-free fibers. Furthermore, the electrospinning of highly concentrated PIM-1 solutions leads to the formation of microfibers. To tackle these problems, we herein incorporated an ammonium salt (i.e., tetraethylammonium bromide, TEAB) to increase the conductivity of PIM-1 solutions and study the impact of solution conductivity on the electrospinning of PIM-1 solutions. In parallel to the conductivity study, the influence of relative humidity on the electrospinning and morphology of PIM-1 fibers was explored. The addition of TEAB significantly increased the solution conductivity and drastically enhanced the electrospinnability of PIM-1. The electrospinning of PIM-1 solutions (10% (w/v)) in the presence 7.5 wt% TEAB (with respect to PIM-1) led to bead-free fibers, while at the same concentration, electrosprayed beads and droplet splashing were observed in the absence of TEAB. On the other hand, increasing humidity did not influence the electrospinnability of PIM-1 and the fiber texture, however, less fibers were formed in a given time at very high humidity conditions (~80%). Overall, the experimental findings revealed that the addition of the salt drastically enhanced the electrospinnability of PIM-1 solutions owing to the enhanced conductivity and could lead to the formation of very thin PIM-1 fibers with 160 nm in diameter while no significant effect of relative humidity on the electrospinnability of PIM-1 solutions was observed.

Alginate-based hydrogels prepared via ionic gelation: An experimental design approach to predict the crosslinking degree

Alginate-based hydrogels can be obtained by the simple addition of bivalent ions to aqueous polysaccharide solutions without the use of toxic chemicals; however, the hydrogels prepared by this way result inhomogeneous and irreproducible due to the extremely fast crosslinking reaction. To overcome such limitations, in the present work a novel preparation approach is proposed and optimized; the method is based on the use of agar moulds rich of bivalent ions as diffusing system to modulate the release of Ca2+, Sr2+, and Ba2+ cations in order to guarantee a better control of the crosslinking process. A full factorial experimental design was applied to assess the effects and the mutual interactions of three selected parameters (sodium alginate concentration, crosslinking agent concentration within the agar moulds, crosslinking time) on the gelation process. The swelling and mechanical properties of the prepared hydrogels were investigated both in deionized water and in a saline environment; furthermore, the hydrogels were characterized by means of thermogravimetric analysis and field-emission scanning electron microscopy. The obtained results demonstrated that both the experimental variables and the environmental conditions have a significant influence on the structure and the performances of the resulting hydrogels. In particular, the use of high polymer concentration and crosslinking agent amount leads to strong hydrogels corresponding to a superior crosslinking degree; more in detail, Ba2+ ions show a great affinity for alginate leading to the hydrogels with the highest mechanical properties. Moreover, the ion-exchange occurring in saline environment seems to strongly reduce the effective crosslinking degree of alginate hydrogels with a consequential loss of mechanical properties and stability. The collected data were finally elaborated through statistical analysis combined with response surface methodology to develop theoretical models successfully able to correlate the crosslinking degree to the experimental conditions, thus opening the way of designing and fabricating alginate-based hydrogels with tailored morphology and mechanical properties.

An electrically light-transmittance-switchable film with a low driving voltage based on liquid crystal/polymer composites

ABSTRACTAs a typical class of electrically light-transmittance-switchable (ELTS) composites materials, polymer dispersed liquid crystal (PDLC) films have been widely used in displays, smart windows, light shutters, etc. However, the commercialised PDLC film still requires a comparatively high voltage to maintain its transparent state, leading to huge power consumption and even a potential safety risk. In this regard, we proposed a ‘heat followed UV’ stepwise polymerisation strategy for preparing a kind of ELTS film with a low driving voltage (~20.7 V) through constructing a coexistent system of polymer dispersed and polymer stabilised liquid crystal (PD&SLC). In this new PD&SLC system, vertically orientated polymer networks were formed within LC domains to induce the vertical alignment of LC, thereby reducing the driving voltage. Also, the as-made PD&SLC film exhibited good flexibility due to the high content of polymer. Moreover, the effects of the liquid crystalline polymerisable monomers content on the polymer morphologies as well as the electro-optical properties of the as-made PD&SLC films were elaborately investigated.

Fabrication and evaluation studies of novel polyvinylpyrrolidone and 2-acrylamido-2-methylpropane sulphonic acid-based crosslinked matrices for controlled release of acyclovir

The aim of the present study was to fabricate chemically crosslinked matrix system of polyvinylpyrrolidone (PVP)-co-poly 2-acrylamido-2-methylpropane sulphonic acid (AMPS) through a free radical copolymerization method for controlled delivery of acyclovir HCl. PVP (polymer) has been chemically crosslinked with AMPS (monomer) by ethylene glycol dimethacrylate as a crosslinker in the presence of ammonium peroxodisulphate/sodium hydrogen sulphite as initiator. PVP-based hydrogel was developed by using different ratios of polymer, monomer and crosslinker, while acyclovir HCl was incorporated as model drug. FTIR, TGA, DSC, SEM, XRD and sol–gel fraction analysis were performed for the characterization and structural analysis of polymeric system. In order to study the pH responsive behaviour of hydrogels, swelling and drug release studies were carried out at both acidic (1.2) and basic pH (6.8). An effect of increasing content of polymer, monomer and crosslinker on swelling and in vitro drug release behaviour of PVP-co-poly (AMPS) was also evaluated. FTIR, TGA, DSC, SEM and XRD revealed the successful grafting of components as well as formation of thermodynamically stable hydrogels. Swelling studies showed high swelling at pH 6.8 as compared to pH 1.2, which confirmed the pH-sensitive behaviour of formulated hydrogels. PVP-based hydrogels exhibited high swelling with increased concentration of monomer, while swelling decreased with a high content of polymer and crosslinker. Drug release studies were found to be swelling controlled. Gel contents increased with an increase in the concentration of polymer, monomer and crosslinker. Drug release kinetics confirmed the controlled release pattern of model drug in developed crosslinked polymeric network. Biocompatibility and cytotoxicity of fabricated hydrogels were evaluated by performing a toxicity study on rabbits. The results revealed that fabricated hydrogels were biocompatible and non-toxic.