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Large Amplitude Oscillatory Shear (LAOS) rheology is a technique to analyze materials that are viscoelastic in nature. The raw values of stress and strain that were taken out from rheometer during the large amplitude oscillatory shear test are used in the constitutive models. The model parameters from the constitutive model are then analyzed on the materials being tested. Various test protocols and geometries will be used to analyze the materials of interest during LAOS rheological examination. The selection of test protocols and usage of geometry are less studied in testing various kinds of materials using LAOS. Cone and plate and parallel plate geometries are generally used for LAOS. The test protocols would be varying amplitude and varying frequencies. In the present work, quantification of relative performance of test protocols and geometry that have been used during the analysis of cross-linked poly vinyl alcohol hyaluronic acid (PVAHA) gels as material systems are studied using data envelopment analysis (DEA). The methodological approach using output oriented constant return to scale (CRS) and output oriented variable return to scale (VRS) are tested with the decision making units (DMU) as the geometry and test protocols used. These results are then combined with the Shannon's entropy to rank the efficient DMUs. Using Shannon's entropy combined with CRS and VRS, it is suggested that the use of parallel plate geometry with the test protocol of 0.5 rad/s and 50 frequency is best suitable for the cross-linked hyaluronic acid and poly vinyl alcohol gels examined.

Evaluation of transport properties of a drug in a hydrogel matrix is of engineering importance in the assessment of drug delivery systems. Water sorption and solute release are the two important aspects that determine the transport of water/solute in a hydrogel. A novel custom-made diffusion cell is used to examine the transport properties in the hydrogels by chemically cross-linking hyaluronic acid in various alkaline solutions at different cross-linker-to-polymer ratios. The tracer diffusion coefficient in the swollen hydrogel matrix in its rubbery state is estimated using a custom-made diffusional cell. The release kinetics is followed at perfect sink conditions, which transform from a glassy polymer dry membrane state to a swollen rubbery gel state. It is shown that the diffusion of solvent (water) through the hydrogel is case II transport, while the diffusion through the swollen hydrogel is case I (Fickian). The diffusion coefficient is proved to be independent of mesh size and pH of the initial solution. However, the release kinetics is influenced by the diffusion of solute and the relaxation of the polymer in hydrogel. The relaxation coefficient is a function of alkalinity in the solution with which the gel is being made. The contribution of relaxation to the transport during solvent sorption and solute release is found to be similar.

Pluronic F-127 (Pl), a triblock copolymer that exhibits thermoreversible sol-gel transition, is being used with additives such as polysaccharides for enhanced gel stability and mechanical strength for controlled drug delivery applications. This study aims at elucidating the gelation behavior and structure-property relationship (at physiological temperature) of pluronic in the presence of hyaluronic acid (HA) using linear and nonlinear rheology. Small amplitude oscillatory shear of the gels indicated weak frequency dependence of G ′ and G ′ ′. Large amplitude oscillatory shear (LAOS) response indicated flow induced yielding with both the moduli following power law decay beyond the critical strain amplitude. Stress waveform analysis, Fourier analysis, and Chebyshev decomposition indicated similar qualitative features for gels with different HA content. Interestingly, there is a non-monotonic variation in the dynamic light scattering timescales, G ′ (linear regime), and the critical stress values (at corresponding critical strains) with HA content. The physical insights obtained were understood in terms of a cage picture of soft glassy materials. Relaxation times corresponding to yielding transition obtained from strain rate frequency superposition measurements showed similar qualitative variation as those obtained from elastoviscoplastic modeling of the yielding processes occurring during an LAOS cycle. Based on these analyses, we obtain quantitative description of nonlinear rheological response of the Pl-HA gels.Pluronic F-127 (Pl), a triblock copolymer that exhibits thermoreversible sol-gel transition, is being used with additives such as polysaccharides for enhanced gel stability and mechanical strength for controlled drug delivery applications. This study aims at elucidating the gelation behavior and structure-property relationship (at physiological temperature) of pluronic in the presence of hyaluronic acid (HA) using linear and nonlinear rheology. Small amplitude oscillatory shear of the gels indicated weak frequency dependence of G ′ and G ′ ′. Large amplitude oscillatory shear (LAOS) response indicated flow induced yielding with both the moduli following power law decay beyond the critical strain amplitude. Stress waveform analysis, Fourier analysis, and Chebyshev decomposition indicated similar qualitative features for gels with different HA content. Interestingly, there is a non-monotonic variation in the dynamic light scattering timescales, G ′ (linear regime), and the critical stress values...

Numerous methods have been adopted to alter the interfacial tension during the enhanced oil recovery (EOR) system. Much emphasis was given to the conventional methods of EOR because of its ease in operation and understanding. Efforts were made to use surfactants along with Nano particles as they could modify the rheological properties to a great extent with their complexion in the structure and properties. The combination of a cationic polymer (polyacrylamide) (PAM) in the presence of anionic surfactant (sodium dodecyl sulfate) (SDS) with varied concentrations of anionic Nano particle (silicon dioxide) in their complex aqueous solution form is investigated. At a known concentration of polymer and surfactant, the changes in rheological properties of fluid are studied for varied concentrations of silica Nanoparticles. Hydrated and un-hydrated polyacrylamide solutions were subjected to analysis at the well resembling temperature of 90OC, to know the effect of thermal stability of the polymer. It is observed that the fluid viscosity is reduced by two orders of magnitude with the addition of Nano particles, at low shears. However, the fluid showed shear thickening properties due to the complex structure among the polymer, surfactant and particle. The ionic charges interplay leading to the formation of complex structures at the hydrated state of polymer affects the viscosity of the fluid to a great extent.

Over the decades oil spills have been the biggest threat to the aquatic life and to a nation’s economy. Many methods were suggested in the literature to remove the oil that is present on the surface of sea water after the spill. Hydrogel formation is one of the best technique that could be adopted to handle oil spills. Since the oil spill is a oil and water emulsion, formation of hydrogels with these emulsions could lead to the recovery of oil. The formation of hydrogels can be either physically crosslinking the polymer molecules or covalent bonding among the entangled polymer molecules. The methods of making the hydrogels conceivable to acquire surface hydrophobicity and oleophilicity. Hydrogel technology could be more cost effective and efficient in recovering the oil from the spill, eco-friendly and easy to use. It is proposed that the hydrogels could be potential candidates for handling the oil spills. The methods described in this review explains the various hydrogels that could be utilized for oil spill recovery.

After the conventional oil recovery system, it was estimated that huge amount of oil reserves is still remaining un-extracted. Because of tremendous demand for oil and established facilities at the oil exploration sites after conventional recovery got significant attention. Since the oil is entrapped in the porous rock structure and is difficult to evacuate, focus was made on tertiary recovery of oils. Many methods have been suggested by various researchers with different techniques to mobilize the entrapped oil in the well. The classification of the techniques will give different methods of recovery. The rheology, surface tension, mobility ratio are the important parameters that were considered during the enhanced recovery. The review that is presented here gives the overall methods for recovery and various materials and important parameters to be considered for the enhanced oil recovery. A new substitute for the sand pack column is suggested to conduct the bench top experimental set up that would ease the work of flooding with alkaline, surfactant and polymers.

Coal water slurries (CWS) were proposed as a substitute for the fuel oils century ago. As there is a huge demand for energy, it is necessary for us to use such concepts with good understanding of the alternative fuels. As the use of CWS depends on physio-chemical properties of coal and rheological properties of the slurry, coal obtained from Dugda coal washery, Jharkand, India were subjected to examination. These coals are ground and segregated according to the sizes and the samples of CWS were prepared. The prepared samples were tested for their physio-chemical properties first. various samples of coal water slurries were prepared and examined for rheology of the samples by varying their concentration, size and granularity of the particles, shearing time and temperature. A detailed analysis on stress strain relation was analyzed during this study. It is found that the stresses would increase with concentration of CWS when the strain rates are varied. It is found that the size of the particles would play active role in deciding the shear forces when the samples were subjected to varying shear rates with their self assembly. The granularity of the particles in the sample has significant effect in rheological properties of the CWS samples. The temperature has no effect.

Hyaluronic acid (HA)-based materials are being investigated because of their role in biological fluids and tissues. Poly(vinyl alcohol) (PVA) when blended with HA at different compositions leads to superior mechanical properties compared to pure HA. The PVAHA blend hydrogels are potential candidates for pharmaceutical, biomedical, and cosmetic applications. It is essential to understand the structure, gelation time, and morphological properties of these hydrogels. In this work, a blend system of PVA crosslinked with glutaraldehyde in the presence of HA is studied. Semidilute solutions of PVA and HA are blended, followed by gelation due to crosslinking. The crosslinked gels as well as the gel cast membranes were examined. The effect of HA on the gelation process is investigated using rheological characterization. It is shown that kinetics of gelation is influenced by HA content, though storage modulus of the gels is influenced marginally. The structural features of PVAHA gels were also probed with scanning electron microscopy and dynamic light scattering. It is argued that there is a complex interplay between intra- and intermolecular crosslinking of PVA and PVA–HA interactions during the gel formation. Based on the insights obtained from various probing techniques for PVAHA gels with different HA content, three broad structural features were identified. It is shown that the hydrogel is semi-interpenetrating network at lower HA content ( 20% HA). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41081.

There is an increasing demand for designing controlled drug delivery systems with materials which are more biocompatible, economical and materials which can be processed easily. Poly (vinyl alcohol) (PVA) and hyaluronic acid (HA) are promising polymers for applications in drug delivery. PVA forms gel based on the acetal bridges when crosslinked with glutaraldehyde (GA). On the other hand, HA a natural polymer, forms gel with divinyl sulfone (DVS) as a crosslinker. PVA and HA blends upon crosslinking PVA with GA or HA with DVS, in the presence of the other polymer, form gels that are more adaptable to the drug delivery systems. In this work, the mechanical properties and swelling behaviour of PVAHA gels were characterized. The effect of composition on viscoelastic moduli and degree of swelling was determined. The storage modulus (G") of various gels made of PVA, HA and PVAHA blends were measured using rheology and compared with the values available in the literature. Swelling properties were measured and compared among various PVA and HA gels. Collagen is added to PVA solution and the rheological properties were measured in the gel state. Based on the values of storage modulus, gels of various compositions of PVA, HA and collagen might be selected as potential biomaterials for drug delivery system depending on careful understanding the type of application. � 2014, DESIDOC.