@article { ISI:000299291900033, title = {Nanocomposite silica surfactant microcapsules by evaporation induced self assembly: tuning the morphological buckling by modifying viscosity and surface charge}, journal = {Soft Matter}, volume = {8}, number = {6}, year = {2012}, month = {DEC}, pages = {1955-1963}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Nanocomposite microcapsules of silica and surfactants have been synthesized using evaporation induced self-assembly through spray drying. It was established using electron microscopy and small-angle neutron/X-ray scattering experiments that the viscosity of the virgin dispersion and surface charge of colloidal components play a significant role in the buckling of spray droplets during drying. Hollow spherical grains are realized at relatively low viscosity and higher surface charge while mushroom like grains manifest at higher viscosity and lower surface charge. In the intermediate conditions, deformed doughnut shaped microcapsules are obtained. Scattering experiments establish the presence of the organization of micelle like aggregates of surfactants in the dried grains and also corroborate with the observations from electron microscopy. A plausible mechanism regarding the chronological pathways of morphological transformation is illustrated. Computer simulation, based on buckling of an elastic shell using a surface evolver, has been attempted in order to corroborate the experimental results.

}, issn = {1744-683X}, doi = {10.1039/c1sm06964k}, author = {Sen, D. and Bahadur, Jitendra and Mazumder, S. and Verma, G. and Hassan, P. A. and Bhattacharya, S. and Vijai, K. and Doshi, Pankaj} } @article { ISI:000314748100011, title = {Necking in extrusion film casting: the role of macromolecular architecture}, journal = {Journal of Rheology}, volume = {57}, number = {2}, year = {2013}, month = {MAR}, pages = {559-583}, publisher = {JOURNAL RHEOLOGY AMER INST PHYSICS}, address = {STE 1 NO 1, 2 HUNTINGTON QUADRANGLE, MELVILLE, NY 11747-4502 USA}, abstract = {

Extrusion film casting (EFC) is used on an industrial scale to produce several thousand tons of polymer films and coatings. While significant research has been carried out on necking of films of viscoelastic melts in EFC, the influence of macromolecular chain architecture on the necking behavior is not yet fully understood. In the present research, we have explored experimentally and theoretically the effects of long chain branching and molecular weight distribution on the extent of necking during EFC. Polyethylenes of essentially linear architecture but having narrow and broad molecular weight distributions, and polyethylenes having long chain branching were used for experimental studies. The EFC process was analyzed using the one-dimensional flow model of Silagy et al. [Polym. Eng. Sci. 36(21), 2614-2625 (1996)] in which multimode molecular constitutive equations namely the {\textquoteleft}{\textquoteleft}extended pom-pom{\textquoteright}{\textquoteright} equation (for long chain branched polymer melts) and the {\textquoteleft}{\textquoteleft}Rolie-Poly (Rouse linear entangled polymers){\textquoteright}{\textquoteright} equation (for linear polymer melts) were incorporated. We show that the model qualitatively captures the salient features of the experimental data thereby elucidating the role of chain architecture on the extent of necking. (C) 2013 The Society of Rheology. [http://dx.doi.org/10.1122/1.4788911]

}, issn = {0148-6055}, doi = {10.1122/1.4788911}, author = {Pol, Harshawardhan V. and Thete, Sumeet Suresh and Doshi, Pankaj and Lele, Ashish K.} } @article { ISI:000329101700009, title = {Nonisothermal analysis of extrusion film casting process using molecular constitutive equations}, journal = {Rheologica Acta}, volume = {53}, number = {1}, year = {2014}, month = {JAN}, pages = {85-101}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Extrusion film casting (EFC) is a commercially important process that is used to produce several thousand tons of polymer films and coatings. In a recent work, we demonstrated the influence of polymer chain architecture on the extent of necking in an isothermal film casting operation (Pol et al., J Rheol 57:559-583, 2013). In the present research, we have explored experimentally and theoretically the effects of long-chain branching on the extent of necking during nonisothermal film casting conditions. Polyethylenes of linear and long-chain branched architectures were used for experimental studies. The EFC process was analyzed using the 1-D flow model of Silagy et al. (Polym Eng Sci 36:2614-2625, 1996) in which the energy equation was introduced to model nonisothermal effects, and two multimode constitutive equations, namely the {\textquoteleft}{\textquoteleft}extended pom-pom{\textquoteright}{\textquoteright} (XPP, for long-chain branched polymer melts) equation and the {\textquoteleft}{\textquoteleft}Rolie-Poly stretch version{\textquoteright}{\textquoteright} (RP-S, for linear polymer melts) equation, were incorporated to account for the effects of polymer chain architecture. We show that the model does a better job of capturing the qualitative features of the experimental data, thereby elucidating the role of chain architecture and nonisothermal conditions on the extent of necking.

}, keywords = {Branched, Extrusion, Film, Linear, Necking, Nonisothermal, Polyethylene}, issn = {0035-4511}, doi = {10.1007/s00397-013-0739-x}, author = {Pol, Harshawardhan and Banik, Sourya and Azad, Lal Busher and Thete, Sumeet Suresh and Doshi, Pankaj and Lele, Ashish K.} } @article {43397, title = {New insights into the use of multi-mode phenomenological constitutive equations to model extrusion film casting process}, journal = {Journal of Plastic Film \& Sheeting}, volume = {33}, year = {2017}, month = {JAN}, pages = {35-71}, abstract = {This article is concerned with the effect of the individual viscoelastic relaxation modes of a polymer melt on its behavior in polymer melt extrusion film casting process. We compare the predicted versus experimentally obtained film necking or neck-in profile as a function of draw ratio. The predicted necking profile was obtained using well-established one-dimensional isothermal flow kinematics and consisted of using two different phenomenological constitutive equations, upper convected Maxwell and Phan-Thien-Tanner, with a discrete spectrum of relaxation times. The numerical simulations, containing the two different phenomenological constitutive equations, provided an insight into the effect of the slow and the fast relaxing modes on the stresses, strains, and strain/extensional rates that develop in the molten polymer film as it is stretched from the die exit to the chill-roll. The slow relaxing modes follow trends that are directly proportional to strain (similar to Hookean solids), whereas the fast relaxing modes follow trends that are directly proportional to the stretch rate (in accordance with Newton{\textquoteright}s law of viscosity). Comparing the numerical predictions with the experiments showed that predictions using the upper convected Maxwell constitutive equation best described the long-chain branched polymers (like low-density polyethylene, which shows extensional strain hardening) in the extrusion film casting process. On the other hand, predictions using the Phan-Thien-Tanner constitutive equation best described the linear polymers (like linear low-density polyethylene, which does not show noticeable extensional strain hardening) in the extrusion film casting process.}, doi = {10.1177/8756087915627843}, author = {Thete, Sumeet S. and Doshi, Pankaj and Pol, Harshawardhan V.} }