@article { ISI:000227321900006, title = {Hydrophobically modified poly(acrylic acid) using 3-pentadecylcyclohexylamine: synthesis and rheology}, journal = {Macromolecular Chemistry and Physics}, volume = {206}, number = {4}, year = {2005}, month = {FEB}, pages = {464-472}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

Hydrophobically modified poly(acrylic acid) was synthesized using 3-pentadecylcyclohexylamine (3-PDCA), which was in turn synthesized from 3-pentadecylphenol, one of the components of cashew-nut shell liquid (CNSL), a renewable resource material. H-1 NMR spectra confirmed the incorporation of 3-PDCA onto PAA and a series of HMPs with three different molar concentrations, viz. congruent to 3, 5 and 7 mol-\% of 3-PDCA, were synthesized. An increase in viscosity with increasing hydrophobic content was observed by rheological measurements. The critical association concentrations were determined using an Ubbelohde viscometer and a controlled stress rheometer. The stability of HMPs towards temperature and shear was studied. Rheological measurements showed that there was a steady increase in viscosity with increase in hydrophobe content due to the formation of reversible networks. These polymers exhibited gel-like behavior at low concentrations (greater than or equal to2 wt.-\%) with an apparent yield stress (ca. 10 Pa) and showed shear thinning properties (non-Newtonian). However, below a critical concentration, c [eta], they showed Newtonian behavior.

}, keywords = {3-pentadecylcyclohexylamine (3-PDCA), hydrophobically modified polymers (HMPs), poly(acrylic acid), reversible associations, Rheology}, issn = {1022-1352}, doi = {10.1002/macp.200400392}, author = {Shedge, A. S. and Lele, Ashish K. and Wadgaonkar, P. P. and Hourdet, Dominique and Pcrrin, P. and Chassenieux, Christophe and Badiger, Manohar V.} } @article { ISI:000234528800001, title = {Studies on shrikhand rheology}, journal = {Journal of Food Engineering}, volume = {74}, number = {2}, year = {2006}, month = {MAY}, pages = {169-177}, publisher = {ELSEVIER SCI LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

Shrikhand, a popular Indian dessert made from yogurt, is manufactured on an industrial scale using several chemical engineering unit operations such as mixing, filtration and heat transfer. Understanding the rheology of shrikhand is not only relevant for designing large scale mixers but can also provide quantitative means for linking the microstructure of shrikhand to its perception of texture, consistency and taste. We show here that shrikhand exhibits a combination of several rheological properties such as weak gel-like viscoelasticity, an apparent yield stress, thixotropy and long structural recovery time scales. For instance, the elastic modulus is always higher than the loss modulus over the measurable frequency range and that both moduli show only weak frequency dependence that is a characteristic of gel-like consistency. Forward and reverse rate sweep tests show a distinct hysteresis loop, which is a signature of thixotropic character. In an attempt to trace the origins of these rheological properties in shrikhand we characterized its microstructure and showed that there exist two different microstructures: one composed of crystallites of milk fats having a length scale of similar to 50-100 mu m, and the other composed of aggregates of colloidal cascin micelles of similar to 0.5-10 mu m size. Our studies show that while the temperature sensitivity of the viscoelastic parameters is dominated by the semicrystalline milk fat microstructure, the shear sensitivity is largely dictated by the protein network. (c) 2005 Elsevier Ltd. All rights reserved.

}, keywords = {Microstructure, Rheology, shrikhand}, issn = {0260-8774}, doi = {10.1016/j.jfoodeng.2005.02.029}, author = {Kulkarni, C. and Belsare, N. and Lele, Ashish K.} } @conference { ISI:000257623000188, title = {Gelation of regenerated fibroin solution}, booktitle = {15th International Congress on Rheology/80th Annual Meeting of the Society-of-Rheology}, series = {AIP CONFERENCE PROCEEDINGS}, volume = {1027}, year = {2008}, note = {15th International Congress on Rheology/80th Annual Meeting of the Society-of-Rheology, Monterey, CA, AUG 03-08, 2008}, month = {AUG}, pages = {573-575}, publisher = {Amer Inst Physics, 2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USA}, organization = {Amer Inst Physics, 2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USA}, address = {Monterey, CA.}, abstract = {

Silk fibroin is a high molecular weight multiblock ampiphillic protein known for its ability to form high strength fibers. It is also biocompatible; silk sutures have been traditionally used for many centuries. Recently, there has been much interest in making silk hydrogels for applications ranging from tissue engineering to controlled delivery. Fibroin gels can be formed from aqueous solutions by changing one or more state variables such as pH, temperature and ionic strength. In this work we present our investigations on the gelation of aqueous fibroin solutions derived from Bombyx Mori silk using light scattering, confocal microscopy and rheological techniques.

}, keywords = {dynamic light scattering, Rheology, silk fibroin gel}, isbn = {978-0-7354-0549-3}, issn = {0094-243X}, author = {Nagarkara, Shailesh and Lele, Ashish K. and Chassenieux, Christophe and Nicolai, Taco and Durand, Dominique}, editor = {Co, A. and Leal, L. G. and Colby, R. H. and Giacomin, A. J.} } @article { ISI:000264247300034, title = {Reactive extrusion of poly(L-Lactic Acid) with glycidol}, journal = {Journal of Applied Polymer Science}, volume = {112}, number = {3}, year = {2009}, month = {MAY}, pages = {1391-1398}, publisher = {JOHN WILEY \& SONS INC}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

Glycidol modified polylactic acid (PLLA) polymers have been prepared by reactive extrusion. Influences of residence time and the concentration of glycidol on the extent of reaction with different weight average molecular weight (45,000, 65,000, and 100,000) PLLA{\textquoteright}s were studied. Structure-property relationship has been established by measuring molecular, mesoscopic, and macroscopic properties. Under reactive extrusion conditions glycidol reacted with the end groups of PLLA to initiate chain extension. Low-molecular weight PLLA reacted with glycidol faster than the medium molecular weight PLLA, whereas high-molecular weight PLLA did not show significant reactions. The glass transition temperature, melting temperature, crystallization temperature, and heat of fusion were measured for unmodified and modified PLLA{\textquoteright}s. Chain extended PLLA had higher T(g) and T(m) than the unmodified samples. Time sweep rheological experiments were performed to test the melt stability of PLLA. Chain extended PLLA{\textquoteright}s were found to retain viscoelastic properties for much longer time than the unreacted samples. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1391-1398, 2009

}, keywords = {biodegradable, reactive extrusion, Rheology, structure-property relations, Thermal properties}, issn = {0021-8995}, doi = {10.1002/app.29581}, author = {Deenadayalan, E. and Lele, Ashish K. and Balasubramanian, M.} } @article { ISI:000277423200006, title = {Hydrophobically modified poly(vinyl alcohol) using alkoxy-substituted methyl gallate: synthesis and rheology}, journal = {Journal of Polymer Science Part B-Polymer Physics}, volume = {48}, number = {10}, year = {2010}, month = {MAY}, pages = {1054-1063}, publisher = {JOHN WILEY \& SONS INC}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

Hydrophobically modified poly(vinyl alcohol) (HMPVA) polymers were synthesized by potassium t-butoxide-catalyzed reaction of PVA with methyl 3,4,5-tris(n-octyloxy) benzoate (MGC(8))/3,4,5-tris(n-dodecyloxy) benzoate (MGC(12)) and 1,3-propane sultone. The concentration of 1,3-propane sultone was kept constant at 10 mol \%. and that of MGC(8) (2, 3, and 4 mol \%)/MGC(12) (2 and 3 mol \%) was varied to obtain HMPVAs with different hydrophobic contents. The incorporation of MGC(8)/MGC(12) and 1,3-propane sultone onto HMPVA was confirmed by NMR spectroscopy. Rheological properties of aqueous solutions also confirmed the presence of hydrophobic and charged functional groups on HMPVAs. In the semidilute regime, the specific viscosity of HMPVAs followed concentration scaling that is typical of polyelectrolytes. At higher concentrations, the HMPVA solutions with 3 and 4 mol \% of MGC(8) exhibited large increase in specific viscosity. Oscillatory experiments on these solutions exhibited gel-like behavior at polymer concentrations of 40-50 g/L. Confocal microscopy images of HMPVA with 4 mol \% of MGC(8) clearly indicated the existence of microgels. The tendency of formation of microgels further increased with increasing chain length of the hydrophobe, that is, with MGC(12). These samples exhibited rheological behavior that is typical of soft solids and was therefore probed by the strain-rate frequency superposition technique reported recently in the literature. HMPVAs with improved rheological properties show potential applications as thickeners in cosmetic creams, lotions and as drug carriers in pharmaceutical formulations. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1054-1063, 2010

}, keywords = {gallic acid, hydrophobically modified poly(vinyl alcohol), Rheology, water-soluble polymers}, issn = {0887-6266}, doi = {10.1002/polb.21995}, author = {Shedge, Aarti S. and Wadgaonkar, Prakash P. and Lele, Ashish K. and Badiger, Manohar V.} } @article { ISI:000326049600005, title = {Ascertaining universal features of yielding of soft materials}, journal = {Rheologica Acta}, volume = {52}, number = {10-12}, year = {2013}, month = {NOV}, pages = {859-865}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Many metastable complex fluids, when subjected to oscillatory shear flow of increasing strain amplitude at constant frequency, are known to show a characteristic nonlinear rheological response which consists of a monotonic decrease in the elastic modulus and a nonmonotonic change in the loss modulus. In particular, the loss modulus increases from its low strain value, crosses the elastic modulus, and then decreases with further increase in the strain amplitude. Miyazaki et al. (Europhys Lett 75:915-921, 2006) proposed a qualitative argument to explain the origin of the nonmonotonic nature of the loss modulus and suggested that in fact this response could be universal to all complex fluids if they are probed in a certain frequency window in which the fluid is dominantly elastic in the small strain limit. In this letter, we confirm their hypothesis by showing that a wide variety of complex fluids, irrespective of their thermodynamic state under quiescent conditions, indeed show the aforementioned characteristic nonlinear response. We also show that the maximum relative dissipation during yielding occurs when the imposed frequency resonates with the characteristic beta relaxation frequency of the fluid.

}, keywords = {Colloidal suspensions, Entangled melts, Gels, Glasses, Microgels, Rheology, Yielding}, issn = {0035-4511}, doi = {10.1007/s00397-013-0724-4}, author = {Kamble, Samruddhi and Pandey, Anurag and Rastogi, Sanjay and Lele, Ashish K.} } @article { ISI:000326049600003, title = {Rheology and microstructural studies of regenerated silk fibroin solutions}, journal = {Rheologica Acta}, volume = {52}, number = {10-12}, year = {2013}, month = {NOV}, pages = {833-840}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Regenerated silk fibroin solutions (RSF) are produced by dissolving degummed silk fibers in water. We have observed that RSF solutions at a concentration less than 15 \% by weight exhibit an unusual gel-like response in conventional shear rheology measurements. At higher concentrations, the response is predominantly viscous (or liquid-like). We have probed this counterintuitive behavior of silk fibroin solutions by using microrheology, and interfacial rheometry. Scattering techniques were also used to understand the microstructure of RSF solutions as a function of the concentration. Our studies suggest that the gel-like response of the RSF solution may result from the formation of an interfacial film at the air-solution interface, which dominates the bulk rheological response.

}, keywords = {Interfacial rheology, Microrheology, Rheology, Silk}, issn = {0035-4511}, doi = {10.1007/s00397-013-0723-5}, author = {Nisal, Anuya and Kalelkar, Chirag and Bellare, Jayesh R. and Lele, Ashish K.} } @article {46918, title = {Microstructure and yielding of capillary force induced gel}, journal = {Rheologica Acta}, volume = {59}, year = {2020}, month = {MAY}, pages = {291-306}, type = {Article}, abstract = {

We have investigated the rheology and structure of a gel formed from a mixture of non-Brownian particles and two immiscible liquids. The suspension of particles in a liquid undergoes gelation upon the addition of a small content of second, wetting liquid which forms liquid bridges between particles leading to a sample spanning network. The rheology of this gel primarily exhibits a yield stress at low shear rates followed by a linear variation of shear stress at high shear rates. The apparent yield stress extracted from the flow curves increases rapidly with volume fraction of the second liquid before saturation, while it exhibits a monotonic increase with increasing particle concentration. Rescaling of the yield stress curves using suitable shift factors results in an empirical expression for the yield stress showing squared dependence on liquid fraction and a rapid increase with particle fraction above a certain value, both combined in a highly non-linear manner. The microstructural variations with changing secondary liquid content and particle fractions are captured using three-dimensional X-ray tomography technique. The microstructure is observed to show increased local compactness with increased liquid content and increased spatial homogeneity with increased particle fractions. The images from X-ray tomography are analysed to obtain the distributions of particle-particle bonds (coordination number) in the system which serve to explain the observed yield stress behaviour in a qualitative manner.

}, keywords = {Capillary force, Flow curve, gel, Microstructure, Rheology, Yield stress}, issn = {0035-4511}, doi = {10.1007/s00397-020-01189-6, Early Access Date = MAR 2020}, author = {Huprikar, Sameer and Usgaonkar, Saurabh and Lele, Ashish K. and Orpe, Ashish V.} }