01561nas a2200193   4500008004100000022001400041245005400055210005400109260007100163300001400234490000700248520090200255100002701157700002201184700002601206700002101232700003201253856008201285       2007                        eng d  a0888-588500aGeometrical solution to the sharkskin instability0 aGeometrical solution to the sharkskin instability  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAY  a3048-30560 v463 a<p>We study the effect of die exit divergence on the sharkskin behavior, both experimentally as well as through the use of computational fluid dynamics (CFD) simulations. Sharkskin or surface fracture is known to occur immediately after the die exit, because of the large elongational deformation that a polymer melt experiences as it exits the die. We show that the diverging taper at the die exit postpones or completely removes the occurrence of sharkskin. The corresponding CFD simulations of an equivalent K-BKZ fluid show that the taper at the die exit significantly reduces the severity of the elongational flow, thereby reducing the normal stresses as the polymer melt leaves the die. We believe that, in an extrusion operation, the provision of a diverging taper at the die exit is one of the potential measures by which sharkskin instability can be eliminated on an industrial scale.</p>1 aPol, Harshawardhan, V.1 aJoshi, Yogesh, M.1 aTapadia, Prashant, S.1 aLele, Ashish, K.1 aMashelkar, Raghunath, Anant  uhttps://library.ncl.res.in/content/geometrical-solution-sharkskin-instability02384nas a2200169   4500008004100000245010300041210006900144260000800213300001400221490000700235520175800242100002102000700002102021700002002042700002202062856013002084       2016                        eng d00aPassive microrheology in the effective time domain: analysing time dependent colloidal dispersions0 aPassive microrheology in the effective time domain analysing tim  cAUG  a8167-81760 v123 a<p>We studied the aging dynamics of an aqueous suspension of LAPONITE (R), a model time dependent soft glassy material, using a passive microrheology technique. This system is known to undergo physical aging during which its microstructure evolves progressively to explore lower free energy states. Optical microscopy is used to monitor the motion of micron-sized tracer probes embedded in a sample kept between two glass plates. The mean square displacements (MSD) obtained from the motion of the tracer particles show a systematic change from a purely diffusive behavior at short aging times to a subdiffusive behavior as the material ages. Interestingly, the MSDs at all the aging times as well as different LAPONITE (R) concentrations superpose remarkably to show a time-aging time master curve when the system is transformed from the real time domain to the effective time domain, which is obtained by rescaling the material clock to account for the age dependent relaxation time. The transformation of the master curve from the effective time domain to the real time domain leads to the prediction of the MSD in real time over a span of 5 decades when the measured data at individual aging times are only over 2 decades. Since the MSD obtained from microrheology is proportional to the creep compliance of a material, by using the Boltzmann superposition principle along with the convolution relation in the effective time domain, we predict the stress relaxation behavior of the system in real time. This work shows that the effective time approach applied to microrheology facilitates the prediction of long time creep and relaxation dynamics of a time dependent soft material by carrying out short time experiments at different aging times.</p>1 aVyas, Bhavna, M.1 aOrpe, Ashish, V.1 aKaushal, Manish1 aJoshi, Yogesh, M.  uhttps://library.ncl.res.in/content/passive-microrheology-effective-time-domain-analysing-time-dependent-colloidal-dispersions