@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:000301712600016, title = {Rapid self-healing hydrogels}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {12}, year = {2012}, month = {MAR}, pages = {4383-4388}, publisher = {NATL ACAD SCIENCES}, address = {2101 CONSTITUTION AVE NW, WASHINGTON, DC 20418 USA}, abstract = {

Synthetic materials that are capable of autonomous healing upon damage are being developed at a rapid pace because of their many potential applications. Despite these advancements, achieving self-healing in permanently cross-linked hydrogels has remained elusive because of the presence of water and irreversible cross-links. Here, we demonstrate that permanently cross-linked hydrogels can be engineered to exhibit self-healing in an aqueous environment. We achieve this feature by arming the hydrogel network with flexible-pendant side chains carrying an optimal balance of hydrophilic and hydrophobic moieties that allows the side chains to mediate hydrogen bonds across the hydrogel interfaces with minimal steric hindrance and hydrophobic collapse. The self-healing reported here is rapid, occurring within seconds of the insertion of a crack into the hydrogel or juxtaposition of two separate hydrogel pieces. The healing is reversible and can be switched on and off via changes in pH, allowing external control over the healing process. Moreover, the hydrogels can sustain multiple cycles of healing and separation without compromising their mechanical properties and healing kinetics. Beyond revealing how secondary interactions could be harnessed to introduce new functions to chemically crosslinked polymeric systems, we also demonstrate various potential applications of such easy-to-synthesize, smart, self-healing hydrogels.

}, keywords = {adhesives, biomimetic materials, Hydrophobicity, molecular dynamics, smart materials}, issn = {0027-8424}, doi = {10.1073/pnas.1201122109}, author = {Phadke, Ameya and Zhang, Chao and Arman, Bedri and Hsu, Cheng-Chih and Mashelkar, Raghunath Anant and Lele, Ashish K. and Tauber, Michael J. and Arya, Gaurav and Varghese, Shyni} } @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 {47020, title = {Rheological quantification of the extent of dissolution of ultrahigh molecular weight polyethylene in melt-compounded blends with high density polyethylene}, journal = {Journal of Rheology}, volume = {64}, year = {2020}, month = {JAN}, pages = {1-12}, type = {Article}, abstract = {

Melt compounding of ultrahigh molecular weight polyethylene (UHMWPE) with high density polyethylene (HDPE) promises to be an alternative route to prepare bimodal polyethylene grades. However, complete dissolution of UHMWPE in HDPE cannot be guaranteed during melt compounding. Indeed, in an earlier work [K. Chaudhuri et al., Polym. Eng. Sci. 59, 821-829 (2019)], it was shown that a fully entangled UHMWPE did not mix well with commercial HDPE. However, a disentangled UHMWPE (dPE) could be melt-mixed in the same HDPE as evidenced qualitatively by rheological measurements. The present work is focused on quantifying the extent of dissolution of dPE in HDPE. The proposed method involves fitting rheological models for linear viscoelasticity of entangled bimodal blends of polydisperse polymers to dynamic oscillatory shear data and extracting information on the extent of dissolved species. The time-dependent diffusion model of des Cloizeaux is used along with the theory of double reptation (DR) to describe the dynamics of polydisperse homopolymers and also to extract the molecular weight distribution of the UHMWPE sample. A quadratic mixing rule, consistent with the DR model, is used to describe the dynamics of bimodal blends. Melt-mixed dPE/HDPE blends were prepared and characterized for their linear viscoelastic response by frequency sweep tests. The blends showed complex behavior with multiple crossover points, especially for the higher content of dPE. The bimodal model was then fit to the experimental frequency sweep data to determine the only unknown parameter, namely, the extent of dissolved dPE. It was found that a considerable fraction of dPE is dissolved in HDPE during melt compounding.

}, keywords = {blends, Disentangled UHMWPE, double reptation, HDPE, Mathematical modeling}, issn = {0148-6055}, doi = {10.1122/1.5113705}, author = {Chaudhuri, Krishnaroop and Lele, Ashish K.} }