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Showing papers by "Anand Yethiraj published in 2017"


Journal ArticleDOI
TL;DR: The polymer size is very weakly affected by the presence of crowders, consistent with recent computer simulations, and the radius of gyration changes linearly with an increase in polymer concentration.
Abstract: The effect of particles on the behavior of polymers in solution is important in a number of important phenomena such as the effect of ``crowding'' proteins in cells, colloid-polymer mixtures, and nanoparticle ``fillers'' in polymer solutions and melts. In this Letter, we study the effect of spherical inert nanoparticles (which we refer to as ``crowders'') on the diffusion coefficient and radius of gyration of polymers in solution using pulsed-field-gradient NMR and small-angle neutron scattering (SANS), respectively. The diffusion coefficients exhibit a plateau below a characteristic polymer concentration, which we identify as the overlap threshold concentration ${c}^{\ensuremath{\star}}$. Above ${c}^{\ensuremath{\star}}$, in a crossover region between the dilute and semidilute regimes, the (long-time) self-diffusion coefficients are found, universally, to decrease exponentially with polymer concentration at all crowder packing fractions, consistent with a structural basis for the long-time dynamics. The radius of gyration obtained from SANS in the crossover regime changes linearly with an increase in polymer concentration, and must be extrapolated to ${c}^{\ensuremath{\star}}$ in order to obtain the radius of gyration of an individual polymer chain. When the polymer radius of gyration and crowder size are comparable, the polymer size is very weakly affected by the presence of crowders, consistent with recent computer simulations. There is significant chain compression, however, when the crowder size is much smaller than the polymer radius gyration.

24 citations


Journal ArticleDOI
TL;DR: In this article, the role of elastic and non-elastic deformations in the examination of real-space experiments of solid-solid Martensitic transitions has been discussed in a model system of micron-scale ionic microgel colloids, and it has been shown that BCO crystallites formed through shear may coexist with those resulting from local rearrangements within the same sample.
Abstract: We present a framework to segregate the roles of elastic and non-elastic deformations in the examination of real-space experiments of solid-solid Martensitic transitions. The Martensitic transformation of a body-centred-tetragonal (BCT) to a body-centred-orthorhombic (BCO) crystal structure has been studied in a model system of micron-scale ionic microgel colloids (P. S. Mohanty, P. Bagheri, S. Nojd, A. Yethiraj and P. Schurtenberger, Phys. Rev. X, 2015, 5, 011030). Non-affine fluctuations, i.e., displacement fluctuations that do not arise from purely elastic (affine) deformations, are detected in particle configurations acquired from the experiment. Tracking these fluctuations serves as a highly sensitive tool in signaling the onset of the Martensitic transition and precisely locating particle rearrangements occurring at length scales of a few particle diameters. Particle rearrangements associated with non-affine displacement modes become increasingly favorable during the transformation process. The nature of the displacement fluctuation modes that govern the transformation are shown to be different from those predominant in an equilibrium crystal. We show that BCO crystallites formed through shear may, remarkably, co-exist with those resulting from local rearrangements within the same sample.

14 citations


Journal ArticleDOI
TL;DR: In this article, the authors apply pulsed-field-gradient NMR (PFG NMR) technique to measure the translational diffusion for both uncharged and charged polysaccharide (Ficoll70) in water.
Abstract: We apply pulsed-field-gradient NMR (PFG NMR) technique to measure the translational diffusion for both uncharged and charged polysaccharide (Ficoll70) in water. Analysis of the data indicate that NMR signal attenuation above a certain packing fraction can be adequately fitted with a bi-exponential function. The self-diffusion measurements show also that the Ficoll70, an often-used compact, spherical polysucrose molecule, is itself non-ideal, exhibiting signs of both softness and attractive interactions in the form of a stable suspension consisting of monomers and clusters. Further, we can quantify the fraction of monomer and cluster. This work strengthens the picture of the existence of a bound water layer within and around a porous Ficoll70 particle.

12 citations


Journal ArticleDOI
TL;DR: Analysis of the data indicates that the NMR signal attenuation above a certain packing fraction can be adequately fitted with a bi-exponential function, and strengthens the picture of the existence of a bound water layer within and around a porous Ficoll70 particle.
Abstract: We apply pulsed-field-gradient NMR (PFG NMR) technique to measure the translational diffusion for both uncharged and charged polysaccharide (Ficoll70) in water. Analysis of the data indicates that the NMR signal attenuation above a certain packing fraction can be adequately fitted with a bi-exponential function. The self-diffusion measurements also show that the Ficoll70, an often-used compact, spherical polysucrose molecule, is itself nonideal, exhibiting signs of both softness and attractive interactions in the form of a stable suspension consisting of monomers and clusters. Further, we can quantify the fraction of monomers and clusters. This work strengthens the picture of the existence of a bound water layer within and around a porous Ficoll70 particle.

12 citations


Journal ArticleDOI
TL;DR: It is found, via different measures of macromolecular mobility, that the mobility of the flexible polymer in the crowding limit is 10-100 times larger than that of the compact, spherical crowder in spite of their similar size, implying that the flexiblepolymer chain is able to squeeze through crowder interstices.
Abstract: We have examined the effect of crowder particle charge on macromolecular structure, studied via small-angle neutron scattering, and translational dynamics, studied via pulsed-field gradient NMR, in...

11 citations


Posted Content
TL;DR: It is shown that BCO crystallites formed through shear may, remarkably, co-exist with those resulting from local rearrangements within the same sample, and be different from those predominant in an equilibrium crystal.
Abstract: We present a framework to segregate the roles of elastic and non-elastic deformations in the examination of real-space experiments of solid-solid Martensitic transitions. The Martensitic transformation of a body-centred-tetragonal(BCT) to a body-centred-orthorhombic(BCO) crystal structure has been studied in a model system of micron-scale ionic microgel colloids. Non-affine fluctuations, i.e., displacement fluctuations that do not arise from purely elastic(affine) deformations, are detected in particle configurations acquired from the experiment. Tracking these fluctuations serves as a highly sensitive tool in signaling the onset of the Martensitic transition and precisely locating particle rearrangements occurring at length scales of a few particle diameters. Particle rearrangements associated with non-affine displacement modes become increasingly favorable during the transformation process. The nature of the displacement fluctuation modes that govern the transformation are shown to be different from those predominant in an equilibrium crystal. We show that BCO crystallites formed through shear may, remarkably, co-exist with those resulting from local rearrangements within the same sample.

7 citations


Journal ArticleDOI
TL;DR: It is found that all the information in the bond-orientational order parameters is well captured by persistent homology analysis methods that only use the centers of the particles as input data, and it is expected that these methods will prove useful in characterizing other disordered structures.
Abstract: Polycrystals of thin colloidal deposits, with thickness controlled by spin-coating speed, exhibit axial symmetry with local 4-fold and 6-fold symmetric structures, termed orientationally correlated polycrystals (OCPs). While spin-coating is a very facile technique for producing large-area colloidal deposits, the axial symmetry prevents us from achieving true long-range order. To obtain true long-range order, we break this axial symmetry by introducing a patterned surface topography and thus eliminate the OCP character. We then examine symmetry-independent methods to quantify order in these disordered colloidal deposits. We find that all the information in the bond-orientational order parameters is well captured by persistent homology analysis methods that only use the centers of the particles as input data. It is expected that these methods will prove useful in characterizing other disordered structures.

7 citations


Journal ArticleDOI
TL;DR: Two kinds of disorder, shape- and translational disorder, that occur in frequency-amplitude space are found and regimes where drop breakup is dominant, and where order/disorder of large drops can be probed without significant drop breakup are found.
Abstract: Correction for 'Tunable hydrodynamics: a field-frequency phase diagram of a non-equilibrium order-to-disorder transition' by Somayeh Khajehpour Tadavani et al., Soft Matter, 2017, 13, 7412-7424.

2 citations


Journal ArticleDOI
02 May 2017-Langmuir
TL;DR: The dimensionless electrophoretic mobility is constant, consistent with expectations for frequencies below the ion-diffusion frequency, and has a value E = 1.6 ± 0.4.
Abstract: We carry out frequency-dependent solvent impedance measurements and alternating current (ac) colloid microelectrophoresis experiments in partially polar solvents in the low-frequency regime (0.25 Hz ≤ f ≤ 10 Hz). Solvent electrode polarization effects are quantified first in partially polar solvent mixtures containing bromocyclohexane (CHB). We find that the polarization capacitance from electrode polarization exhibits a clear power law behavior Cp = Cp0 f–m with power law exponent m = 0.25 ± 0.04. Once we account for electrode polarization effects, we are able to obtain quantitative mobilities in the low-frequency regime from our ac microelectrophoresis measurements; for these measurements, we use poly(methyl methacrylate colloids that are gravitationally confined to a plane while suspended in a low-polar solvent mixture of cis–trans decahydronapthalene and CHB. We find that the dimensionless electrophoretic mobility is constant, consistent with expectations for frequencies below the ion-diffusion freque...

2 citations


01 Jan 2017
TL;DR: In this paper, the first results of an experimental setup to make AC electro-rheology measurements on aqueous dispersions of ionic PNIPAM microgel colloids over a range of particle volume fractions were presented.
Abstract: In the presence of an external electric field, dispersions of ionic microgels in water show microstructural changes with a complex phase behaviour as a function of volume fraction and electric field amplitude. [3] In this work, we present our first results of an experimental setup to make AC electro-rheology measurements on aqueous dispersions of ionic PNIPAM microgel colloids over a range of particle volume fractions. We will compare the ER response of these soft colloids to more standard dipolar silica colloids.