1,584 research outputs found
Letter from Phyllis Zaccone, December 3, 1967
No full textLetter from Phyllis Zaccone to Fayez Sayegh, December 3, 1967, regarding his appearance on the David Susskind show and the Arab-Israeli conflict
Analytical solution for the polydisperse random close packing problem in 2D
No full textAn analytical theory for the random close packing density, φRCP, of polydisperse hard disks is provided using an equilibrium model of crowding (Zaccone, 2022) which has been justified on the basis of extensive numerical analysis of the maximally random jammed (MRJ) line in the phase diagram of hard spheres (Anzivino et al., 2023). The solution relies on the equations of state for the hard disk fluid and provides predictions for φRCP as a function of the ratio, s, of the standard deviation of the distribution of disk diameters to its mean. For a power-law size distribution with s=0.246, the theory yields φRCP=0.892, which compares well with the most recent numerical estimate φRCP=0.905 based on the Monte-Carlo swap algorithms (Ghimenti et al., 2024)
Pair correlation function of charge-stabilized colloidal systems under sheared conditions
No full textThe pair correlation function of charge stabilized colloidal particles under strongly sheared conditions is studied using the analytical intermediate asymptotics method recently developed in Banetta and Zaccone (Phys. Rev. E 99, 052606 (2019) to solve the steady-state Smoluchowski equation for medium to high values of the Péclet number; the analytical theory works for dilute conditions. A rich physical behaviour is unveiled for the pair correlation function of colloids interacting via the repulsive Yukawa (or Debye-Hückel) potential, in both the extensional and compressional sectors of the solid angle. In the compression sector, a peak near contact is due to the advecting action of the flow and decreases upon increasing the coupling strength parameter Γ of the Yukawa potential. Upon increasing the screening (Debye) length κ− 1, a secondary peak shows up, at a larger separation distance, slightly less than the Debye length. While this secondary peak grows, the primary peak near contact decreases. The secondary peak is attributed to the competition between the advecting (attractive-like) action of the flow in the compressions sector, and the repulsion due to the electrostatics. In the extensional sectors, a depletion layer (where the pair-correlation function is identically zero) near contact is predicted, the width of which increases upon increasing either Γ or κ− 1
Reply to Comment on ‘Disentangling interatomic repulsion and anharmonicity in the viscosity and fragility of glasses’
No full textIn this Reply, we discuss the differences between physical parameters used in the derivation of the Krausser-Samwer-Zaccone model of viscosity and those used in the justification of the empirical power-density scaling for repulsive power-law fluids. These fundamental differences preclude a direct combination of the two approaches
"Effect of Temperature on High Shear-Induced Gelation of Charge-Stabilized Colloids without Adding Electrolytes"
No full textWe demonstrated previously (Wu, H.; Zaccone, A.; Tsoutsoura, A.; Lattuada, M.; Morbidelli, M. Langmuir 2009,25, 4715) that, for a colloid stabilized by charges from both polymer chain-end groups and adsorbed sulfonate surfactants, when the surfactant surface density reaches a certain critical value, the shear-induced gelation becomes unachievable at room temperature, even at an extremely large Peclet number, Pe = 4.6 x 10(4). This is due to the presence of the short-range, repulsive hydration force generated by the adsorbed surfactant. In this work, we investigate how such hydration force affects the shear-induced gelation at higher temperatures, in the range between 303 and 338 K. It is found that a colloidal system, which does not gel at room temperature in a microchannel at a fixed Pe = 3.7 x 10(4), does gel when temperature increases to a certain value. The critical initial particle volume fraction for the gelation to occur decreases as temperature increases. These results indicate that the effect of the hydration force oil the gelation decreases as temperature increases. Moreover, we have observed that at the criticality only part of the primary particles is converted to the gel network and the effective particle volume fraction forming the gel network does not change significantly with temperature. The effective particle volume fraction is also independent of the surfactant surface coverage. Since the effective particle volume fraction corresponds to space filling requirement of a standing gel network, which is mainly related to the clusters structure, this result indicates that at a given shear rate the Cluster structure does not change significantly with the surfactant Surface coverage. Oil the other hand, since the cluster morphology is a strong function of the shear rate, we have observed that when the Peclet number is lowered from Pe = 3.7 x 10(4) to 1.7 x 10(4), the effective particle Volume fraction reduces from 0.19 to 0.12 at 3 13 K
Reply to Comment on Temperature dependence of nuclear fission time in heavy-ion fusion-fission reactions
No full textIn this Reply, we address the issues raised by Gontchar andChushnyakova in the precedingComment [Gontchar and Chushnyakova, Phys. Rev. C 98, 029801 (2018)] with respect to the relation between the Eccles-Roy-Gray-Zaccone (ERGZ) analytical model of nuclear fission lifetime and previous models based on the mean-first passage time approach. We clarify that the originality of the ERGZ approach lies in the ability to provide closed-form expressions for the lifetime valid across the entire range of nuclear temperature
Patchy Colloidal Particles Via Surfactant Adsorption: Interactions and Gels of Tunable Structure
No full textThe presence of charged molecules attached on the surface of Brownian particles can dramatically affect their mutual interaction as well as their interactions with foreign surfaces. With respect to aggregation, the coexistence of domains of charged adsorbed molecules and hydrophobic domains on polymer colloids opens up the possibility of tuning the interactions in a wide range from homogeneously hydrophobic surfaces to completely hydrophilic repulsive surfaces with strong hydration forces. In a well characterized system made of styrene-acrylate copolymer particles and two different ionic surfactants, aliphatic C-18 carboxylate and aliphatic C-15 sulfonate, we have shown experimentally by means of laser light scattering that an initial, gas-like state of noninteracting adsorbed molecules laying down to the particle surface is followed, with increasing surfactant concentration, by the formation of condensed domains prior to reaching full coverage of the particle surface. In the low salt limit, by shearing the dispersion at very high shear-rate in a microchannel, it is shown that the surfactant domains on two particles can fuse/adhere leading to aggregation as long as an even small-sized uncovered polymer patch is present and aggregation is always possible on the free hydrophobic polymer patches. In the case of fully developed films, by analyzing the mechanism of shear aggregation in the low-salt limit theoretically, we show that short-range hydration repulsive forces dominate over DLVO forces and adhesion/aggregation can never be achieved even upon application of extremely high collision energies. We can also provide evidence that gels obtained by shearing the dispersion at high-shear rate at low-salt exhibit a structure that is strongly affected by the degree of coverage of surfactant, i.e. by the relative extension of charged-hydrophilic to hydrophobic patches. The fractal dimension of the gel can indeed vary from 2.1 at high surfactant coverage where only a few small patches are available for aggregation (valence-limited case) to 2.8 at low surfactant coverage where the gel is made of very compact clusters. This finding unfolds new possibilities for making engineered mesoscopic disordered materials by tuning the surface properties at microscopic level.
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, 112, 1976 (2008)
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, in pres
Translation-invariant relativistic Langevin equation derived from first principles
No full textThe relativistic Langevin equation poses a number of technical and conceptual problems related to its derivation and underlying physical assumptions. Recently, a method has been proposed in Petrosyan and Zaccone [J. Phys. A 55, 015001 (2022)JPAMB51751-811310.1088/1751-8121/ac3a33] to derive the relativistic Langevin equation from a first-principles particle-bath Lagrangian. As a result of the particle-bath coupling, a new "restoring force"term appeared, which breaks translation symmetry. Here we revisit this problem aiming at deriving a fully translation-invariant relativistic Langevin equation. We successfully do this by adopting the renormalization potential protocol originally suggested by Caldeira and Leggett. The relativistic renormalization potential is derived here and shown to reduce to Caldeira and Leggett's form in the nonrelativistic limit. The introduction of this renormalization potential successfully removes the restoring force and a fully translation-invariant relativistic Langevin equation is derived for the first time. The physically necessary character of the renormalization potential is discussed in analogy with nonrelativistic systems, where it emerges due to the renormalization of the tagged particle dynamics due to its interaction with the bath oscillators (a phenomenon akin to level repulsion or avoided crossing in condensed matter). We discuss the properties that the corresponding non-Markovian friction kernel has to satisfy, with implications ranging from transport models of the quark-gluon plasma to relativistic viscous hydrodynamic simulations and to electrons in graphene.
The Elasticity and Breakage of Colloidal Aggregates In Shear and Turbulent Flows
No full textRecently, we proposed a free energy expansion-based model for the shear modulus of random colloidal aggregates as they are formed in shear and turbulent flows, resorting to the Cauchy-Born theory of solids. Considering only harmonic terms, application of the fundamental relations of linear elasticity yields an expression for the shear modulus of the aggregates which is proportional to the packing fraction, to the bond rigidity and the coordination number n. The latter term is modelled based on statistical mechanical theories of the liquid state. The main assumption of the model is that interparticle bonds are rigid and the particles are multiply connected. n accounts for the short-range liquid-like order which is a good approximation for dense aggregates that have a high fractal dimension (>=2.5) and introduces a further dependence on the packing fraction. However, also empirical scattering data for the structure can be employed. The model has already been validated against data for cohesive packings of beads. We will show how this approach, combined with the most detailed description of breakage rate in turbulent flows and accounting for turbulence intermittency via a multifractal description, is able to predict the experimentally observed asymptotic scaling between size and shear rate in turbulent breakage of aggregates, without any free parameters.
Zaccone et al., Journal of Chemical Physics, 200
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