355 research outputs found
The fragile-to-strong dynamical crossover and the system viscoelasticity in attractive glass forming colloids
No full textThis paper is dedicated to Professor Heinz Hoffmann on the occasion of his 80th birthday in celebration of his long-time friendship with both of us (Professors Sow-Hsin Chen and Francesco Mallamace).The dynamical arrest phenomena of an adhesive hard-sphere (AHS) colloid, L64-D 2O system has been studied by using calorimetry and the complex shear modulus. This system is characterized by a rich temperature (T) and volume fraction (ϕ) phase diagram with a percolation line (PT). According to the mode-coupling theory (MCT), a cusp-like singularity and two glassy phases, one attractive (AG) and one repulsive (RG), are supposed to coexist in the phase diagram. The MCT scaling laws used to study the shear viscosity with ϕ and T as control parameters propose the existence of fragile-to-strong dynamic crossover (FSDC) analogous to that observed in molecular supercooled liquid glass formers. The measured critical values of the control parameters, coincident with the PT line, where the clustering process generates the AG phase, define the FSDC locus. This is in agreement with the extended mode-coupling theory that takes into account both cage and inter-cluster hopping effects. In this work, we demonstrate, by considering the frequency dependence of the complex moduli, that there is the onset of a system viscoelasticity as an effect of the clustering accompanying the FSDC. We will show as the measured frequency-dependent complex moduli satisfy the scaling relations predicted by the scalar elasticity percolation theory and well account for the system evolution toward the glass transition process.United States. Dept. of Energy (DOE Grant No. DE-FG02-90ER45429
Logarithmic Decay in Single-Particle Relaxation of Hydrated Lysozyme Powder
No full textWe present the self-dynamics of protein amino acids of hydrated lysozyme powder around the physiological temperature by means of molecular dynamics simulations. The self-intermediate scattering functions of the amino acid residue center of mass display a logarithmic decay over 3 decades of time, from 2 ps to 2 ns, followed by an exponential α relaxation. This kind of slow dynamics resembles the relaxation scenario within the β-relaxation time range predicted by mode coupling theory in the vicinity of higher-order singularities. These results suggest a strong analogy between the single-particle dynamics of the protein and the dynamics of colloidal, polymeric, and molecular glass-forming liquids
Workshop on Colloid and Interface Science on Trends and Applications : Festschrift Sow Hsin Chen on his 60th Birthday
No full textReply to Elmatad: Supercooled viscous liquids display a fragile-to-strong dynamic crossover
No full textTheory predicts a fragile-to-strong (FS) dynamic crossover temperature Tx in supercooled liquids but, contrary to what is reported in ref. 1, Tx must be >Tg (2), where Tg is the glass transition temperature. Ref. 4 of ref. 1 hypothesizes that a parabolic form is valid in a range To > T > Tx, where To is defined as an onset temperature that marks the crossover from normal liquid behavior to supercooled liquid behavior. A second paper by the same authors (ref. 5 of ref. 1) proposes the range of the hypothesized parabolic behavior can be extended to cover T < T
Erratum to: The fragile-to-strong dynamical crossover and the system viscoelasticity in attractive glass forming colloids
No full textErratum to: Colloid Polym Sci http://dx.doi.org/10.1007/s00396-015-3713-6 The original version of this article, unfortunately, contained errors
A mode coupling theory analysis of viscoelasticity near the kinetic glass transition of a copolymer micellar system
No full textWe report a set of viscoelastic measurements in concentrated aqueous solutions of a copolyrner micellar system with short-range inter-micellar attractive interactions, a colloidal system characterized, in different regions of the composition-temperature phase diagram, by the existence of a percolation line (PT) and a kinetic glass transition (KGT). Both these transitions cause dramatic changes in the system viscoelasticity. Whereas the observed variations of the shear moduli at the PT are described in terms of percolation models, for the structural arrest at the KGT we investigate the frequency-dependent shear modulus behaviours by using a mode coupling theory (MCT) approach
The Water Polymorphism and the Liquid–Liquid Transition from Transport Data
No full textNMR spectroscopic literature data are used, in a wide temperature-pressure range (180–350 K and 0.1–400 MPa), to study the water polymorphism and the validity of the liquid–liquid transition (LLT) hypothesis. We have considered the self-diffusion coefficient DS and the reorientational correlation time τθ (obtained from spin-lattice T1 relaxation times), measured, respectively, in bulk and emulsion liquid water from the stable to well inside the metastable supercooled region. As an effect of the hydrogen bond (HB) networking, the isobars of both these transport functions evolve with T by changing by several orders of magnitude, whereas their pressure dependence become more and more pronounced at lower temperatures. Both these transport functions were then studied according to the Adam–Gibbs model, typical of glass forming liquids, obtaining the water configurational entropy and the corresponding specific heat contribution. The comparison of the evaluated CP,conf isobars with the experimentally measured water specific heat reveals the full consistency of this analysis. In particular, the observed CP,conf maxima and its diverging behaviors clearly reveals the presence of the LLT and with a reasonable approximation the liquid–liquid critical point (LLCP) locus in the phase diagram
Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water
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