01762nas a2200169 4500008004100000022001400041245007700055210006900132260007900201300001100280490000700291520111900298100002101417700002101438700002201459856011101481 2010 eng d a1539-375500aStrain-rate frequency superposition in large-amplitude oscillatory shear0 aStrainrate frequency superposition in largeamplitude oscillatory aONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USAbAMER PHYSICAL SOCcMAR a0314010 v813 a

In a recent work, Wyss et al. [Phys. Rev. Lett. 98, 238303 (2007)] have noted a property of ``soft solids'' under oscillatory shear, the so-called strain-rate frequency superposition. We extend this study to the case of soft solids under large-amplitude oscillatory shear (LAOS). We show results from LAOS studies in a mono-disperse hydrogel suspension, an aqueous gel, and a biopolymer suspension and show that constant strain-rate frequency sweep measurements with soft solids can be superimposed onto master curves for higher harmonic moduli with the same shift factors as for the linear viscoelastic moduli. We show that the behavior of higher harmonic moduli at low frequencies in constant strain- rate frequency sweep measurements is similar to that at large strain amplitude in strain- amplitude sweep tests. We show surface plots of the harmonic moduli and the energy dissipation rate per unit volume in LAOS for soft solids and show experimentally that the energy dissipated per unit volume depends on the first harmonic loss modulus alone, in both the linear and the nonlinear viscoelastic regime.

1 aKalelkar, Chirag1 aLele, Ashish, K.1 aKamble, Samruddhi uhttps://library.ncl.res.in/content/strain-rate-frequency-superposition-large-amplitude-oscillatory-shear-002591nas a2200229 4500008004100000022001400041245007700055210006900132260007100201300001400272490000700286520177200293100001702065700002502082700001802107700002202125700002402147700003202171700002502203700002702228856010602255 2010 eng d a0024-929700aVolume transition of PNIPAM in a nonionic surfactant hexagonal mesophase0 aVolume transition of PNIPAM in a nonionic surfactant hexagonal m a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAY a4782-47900 v433 a

We investigate the volume transition of a thermoresponsive polymer, poly(N-isopropylacrylamide), PNIPAM, in the presence of an aqueous solution of nonionic surfactant, C(12)E(9). We combine turbidimetry with optical microscopy, NMR, and SAXS to follow the volume transition of the PNIPAM and the H(1)-isotropic transition of the surfactant/water system. Nonionic surfactants such as C(12)E(9) are known to interact weakly with PNIPAM. Accordingly, we show that there is only a small change in the volume transition temperature for the PNIPAM in isotropic micellar solutions of C(12)E(9), even for relatively high concentrations of C(12)E(9). Interestingly, once the surfactant forms an H(1) phase, there is a dramatic decrease in the coil globule transition onset temperature. We believe that this behavior results from a competition between C(12)E(9) in the H(1) phase, and PNIPAM to associate with water. When PNIPAM in the H(1) phase is cooled to low enough temperatures so as to be in the coil state, it locally disturbs the hexagonal phase ordering. Thus, we show that for PNIPAM in a weakly interacting surfactant matrix, it is the phase behavior of the matrix rather than the matrix chemistry that governs the coil globule transition. Finally, we show that in a PNIPAM copolymer with a higher LCST we observe an interesting sequence of transitions in the surfactant phase: on cooling from a high temperature free-blowing turbid globular state (similar to 75 degrees C), we enter a free-flowing translucent coil phase (similar to 47 degrees C), then a turbid gel (similar to 25 degrees C) where the copolymer is collapsed in the HI phase, and finally a low-temperature clear gel (similar to 5 degrees C) where the copolymer is in the expanded coil state.

1 aJijo, V., J.1 aSharma, Kamendra, P.1 aMathew, Renny1 aKamble, Samruddhi1 aRajamohanan, P., R.1 aAjithkumar, Thalasseril, G.1 aBadiger, Manohar, V.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/volume-transition-pnipam-nonionic-surfactant-hexagonal-mesophase-002046nas a2200265 4500008004100000022001400041245006600055210006600121260005700187300001200244490000700256520123100263653002601494653002001520653000901540653001201549653001401561653001301575653001301588100002201601700001901623700002001642700002101662856009701683 2013 eng d a0035-451100aAscertaining universal features of yielding of soft materials0 aAscertaining universal features of yielding of soft materials a233 SPRING ST, NEW YORK, NY 10013 USAbSPRINGERcNOV a859-8650 v523 a

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.

10aColloidal suspensions10aEntangled melts10aGels10aGlasses10aMicrogels10aRheology10aYielding1 aKamble, Samruddhi1 aPandey, Anurag1 aRastogi, Sanjay1 aLele, Ashish, K. uhttps://library.ncl.res.in/content/ascertaining-universal-features-yielding-soft-materials-0