Search results for "Shear modulus"
showing 10 items of 45 documents
Thermodynamic formalism for transport coefficients with an application to the shear modulus and shear viscosity.
2016
We discuss Onsager's thermodynamic formalism for transport coefficients and apply it to the calculation of the shear modulus and shear viscosity of a monodisperse system of repulsive particles. We focus on the concept of extensive "distance" and intensive "field" conjugated via a Fenchel-Legendre transform involving a thermodynamic(-like) potential, which allows to switch ensembles. Employing Brownian dynamics, we calculate both the shear modulus and the shear viscosity from strain fluctuations and show that they agree with direct calculations from strained and non-equilibrium simulations, respectively. We find a dependence of the fluctuations on the coupling strength to the strain reservoi…
The boson peak
2013
The vibrational properties of glasses in the THz range differ very much from what is expected from Debye's elasticity theory: the density of states (DOS) deviates from Debye's ω2 law [the “boson peak” (BP)], the sound velocity shows a negative dispersion in the BP frequency regime and there is a strong increase in the sound attenuation near the BP frequency. These anomalies are related to an anomalous temperature dependence of the specific heat and thermal conductivity in the 10 K regime. An overview of the heterogeneous-elasticity theory is given, by means of which all these anomalies can be explained and shown to arise from the structural disorder, leading to spatial fluctuations of the s…
Do we understand the solid-like elastic properties of confined liquids?
2021
Recently, in polymeric liquids, unexpected solid-like shear elasticity has been discovered, which gave rise to a controversial discussion about its origin (1⇓–3). The observed solid-like shear modulus G depends strongly on the distance L between the plates of the rheometer according to a power law G ∝ L − p with a nonuniversal exponent ranging between p = 2 and p = 3 . Zaccone and Trachenko (4) have published an article in which they claim to explain these findings by a nonaffine contribution to the liquid shear modulus. The latter is represented as Δ G ∝ − ∑ λ = L , T 1 V … [↵][1]1To whom correspondence may be addressed. Email: giancarlo.ruocco{at}roma1.infn.it. [1]: #xref-corresp-1-1
Confined Crystals on Substrates: Order and Fluctuations in Between One and Two Dimensions
2010
The effect of lateral confinement on a crystal of point particles in d = 2 dimensions in a strip geometry is studied by Monte Carlo simulations and using phe- nomenological theoretical concepts. Physically, such systems confined in long strips of width D can be realized via colloidal particles at the air-water interface, or by adsorbed monolayers at suitably nanopatterned substrates, etc. As a generic model, we choose a repulsive interparticle potential decaying with the twelfth inverse power of distance. This system has been well studied in the bulk as a model for two- dimensional melting. The state of the system is found to depend very sensitively on the boundary conditions providing the …
Effective charges along the melting line of colloidal crystals
2006
The shear modulus G of charged colloidal crystals was measured at several constant particle densities n and varying salt concentrations c up to the melting salt concentration cM using torsional resonance spectroscopy. Far from the phase boundary the samples are polycrystalline and the shear modulus stays roughly constant as a function of c. Upon approaching the melting transition an increasing amount of wall based crystal material is formed surrounding a shrinking polycrystalline core and G drops nearly linearly. When the transition is complete G again stays constant. The morphologic transitions may be scaled upon a single master curve. For the polycrystalline morphology, the elastic data a…
Publisher's Note: "Thermodynamic formalism for transport coefficients with an application to the shear modulus and shear viscosity" [J. Chem. Phys. 1…
2017
Qualitative characterisation of effective interactions of charged spheres on different levels of organisation using Alexander’s renormalised charge a…
2005
Abstract Effective interactions are conveniently determined from experimental or numerical data by fitting a Debye–Huckel potential with an effective charge Z ∗ and an effective electrolyte concentration c ∗ as free parameters. In this contribution we numerically solved the Poisson–Boltzmann equation to obtain the so-called renormalised charge Z PBC ∗ . For sufficiently large bare charge Z one finds a saturation of Z ∗ which scales as Z ∗ = A a / λ B , where a is the particle radius, λ B the Bjerrum length and A a proportionality factor of order (8–10). The saturation value increases with increased total micro-ion concentration and shows a shallow minimum as a function of packing fraction. …
Ordering of two-dimensional crystals confined in strips of finite width.
2007
Monte Carlo simulations are used to study the effect of confinement on a crystal of point particles interacting with an inverse power law potential $\ensuremath{\propto}{r}^{\ensuremath{-}12}$ in $d=2$ dimensions. This system can describe colloidal particles at the air-water interface, a model system for experimental study of two-dimensional melting. It is shown that the state of the system (a strip of width $D$) depends very sensitively on the precise boundary conditions at the two ``walls'' providing the confinement. If one uses a corrugated boundary commensurate with the order of the bulk triangular crystalline structure, both orientational order and positional order is enhanced, and suc…
Flow-induced structures in magnetorheological suspensions
1999
We have measured the yield stress of a magnetic suspension as a function of the external field. To explain the existence of this yield stress, we report a comparison between two models, one based on isolated chains of particles and the other taking into account that the structure is formed by aggregates of particles.
Shear behaviour of undiluted polyisobutylenes
1979
Some new data in shear flow are presented for two commercial polyisobutylene samples, namely Vistanex LMMH and L 100. In particular beyond a few steady state results, the tangential stress build-up after a sudden imposition of a shear rate and the decay after cessation of steady shear flow have been collected. The data are used to further test a constitutive equation already advanced by some of the authors. The comparison seems to confirm the validity of the proposed model, whose single adjustable parameter is shown to be independent of molecular weight.