@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:000234350400019, title = {Synthesis and swelling behaviour of hydrophobically modified responsive polymers in dilute aqueous solutions}, journal = {Polymer}, volume = {46}, number = {26}, year = {2005}, month = {DEC}, pages = {12190-12199}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

New series of associating polymers were synthesised in order to investigate opposite behaviours of hydrophobically modified water-soluble polymers and thermoresponsive water-soluble polymers carrying LCST stickers. On the basis of a poly(acrylic acid) backbone, amino-terminated poly(N-isopropylacrylamide), poly(ethylene oxide-co-propylene oxide) and/or dodecyl chains were grafted following a reaction of condensation activated by carbodiimide. Two homologous series of well-defined single grafted and double grafted copolymers were obtained, with double grafted chains containing both C12 and LCST grafts. The dilute solution properties of these copolymers were carefully studied by capillary viscometry. At low salt concentration and below the LCST of the grafts, the swelling properties of macromolecular chains are controlled either by intramolecular associations between hydrophobes, excluded volume effect exerted by hydrophilic grafts or by a balance between these opposite interactions. The deswelling of macromolecular chains, induced by hydrophobic interactions, is amplified at higher ionic strength and more particularly above the transition temperature of the side chains. (c) 2005 Elsevier Ltd. All rights reserved.

}, keywords = {associating polymers, poly(acrylic acid), viscometry}, issn = {0032-3861}, doi = {10.1016/j.polymer.2005.10.140}, author = {Iyer, N. P. and Hourdet, Dominique and Badiger, Manohar V. and Chassenieux, Christophe and Perrin, P. and Wadgaonkar, P.} } @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:000284967000058, title = {Abrupt shear thickening of aqueous solutions of hydrophobically modified poly(N,N {\textquoteleft}-dimethylacrylamide-co-acrylic acid)}, journal = {Macromolecules}, volume = {43}, number = {23}, year = {2010}, month = {DEC}, pages = {10055-10063}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We report some new and interesting observations on the abrupt and large shear-induced thickening of aqueous solutions of hydrophobically modified poly(N,N{\textquoteright}-dimethylacrylamide-co-acrylic acid). High molecular weight copolymer was prepared by free radical copolymerization of N,N{\textquoteright}-dimethylacrylamide [DMA] and acrylic acid [AA] and was subsequently modified to different extents using a hydrophobic compound, namely, 3-pentadecylcyclohexylamine [3-PDCA], which is derived from a renewable resource material, cashew nutshell liquid [CNSL]. The structural elucidation of the base copolymer and the hydrophobically modified copolymers was performed by (1)H and (13)C NMR spectroscopy. The zero shear viscosities [eta(0)] of the hydrophobically modified polymers were lower than that of the precursor poly(N,N{\textquoteright}-dimethylacrylamide-co-acrylic acid) until some critical polymer concentration, which increased with increase in hydrophobic modification. Above the critical concentrations, the eta(0) of the hydrophobically modified copolymers surpassed that of the precursor at the same concentration. At moderate shear rates some of these hydrophobically modified copolymers exhibited an abrupt shear-induced thickening in which the viscosity of the samples increased severalfold. We show here from creep experiments that thickening occurs only when the shear rate reaches a critical value, (gamma) over dot(crit), and that the thickened samples can be trapped in different metastable states by controlling the applied stress. Interestingly, the shear thickened samples showed further thickening upon decreasing the applied stress. Eventually, the metastable samples revert to their equilibrium states at characteristic time that depends on (small) probe stress.

}, issn = {0024-9297}, doi = {10.1021/ma1017378}, author = {Lele, Ashish K. and Shedge, Aarti and Badiger, Manohar V. and Wadgaonkar, Prakash and Chassenieux, Christophe} } @article { ISI:000276190900021, title = {Structure and gelation mechanism of silk hydrogels}, journal = {Physical Chemistry Chemical Physics}, volume = {12}, number = {15}, year = {2010}, month = {FEB}, pages = {3834-3844}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Silk fibroin was regenerated from cocoons produced by the silkworm Bombyx Mori. Light scattering showed that an aqueous solution of the regenerated silk fibroin (RSF) was made of individual proteins with a weight average molar mass of about 4 x 10(5) g mol(-1) and a hydrodynamic radius of about 10 nm. Gel formation of RSF in acidic solutions was investigated as a function of the pH (2-4), concentration (0.5-10 g L(-1)) and temperature (5-70 degrees C). The structure of the gels was studied using light scattering and confocal laser scanning microscopy. The structure was found to be self-similar from length scales of less than 15 nm up to length scales of about 1 mm, and characterized by a correlation length of a few microns. Gel formation was tracked using turbidity, rheology, light scattering and circular dichroism. Gelation involves the formation of self-similar aggregates with a growth rate that increases exponentially. The protein aggregation is correlated to, and perhaps caused by, the formation of beta-sheets, the fraction of which also increases exponentially with time.

}, issn = {1463-9076}, doi = {10.1039/b916319k}, author = {Nagarkar, Shailesh and Nicolai, Taco and Chassenieux, Christophe and Lele, Ashish K.} }