Stress Isotherms of Porous Thin Materials: Theoretical Predictitions From a Nonlocal Density Functional Theory

Recent beam bending (BB) experiments of microporous t31rns with very small pores have shown that the fluid confined in these pores exhibits monotonic compressive stresses as the relative pressure is varied from vacuum to saturation (relative vapor pressure, p/p. = 1). The variation of the stress near saturation is found to be linear in hz(p) and given by the saturated liquid density to within 20%. Capillary condensed fluids are traditionally described by the Laplace-Kelvin (LK) theory. LK theory correctly predicts the slope of the stress near saturation to be pl, but also predicts that the stress should be zero at saturation and tensile between saturation aud the capillary transition pressure. Hence LK theory does not capture the monotonic compressive stress observed in BB experiments. This report describes the results of density functional theory calculations for a simple fluid continued to a slit pore network. We show how the presence of even a small amount of polydispersity in pore size leads to both a monotonic compressive stress as well as the observed LK slope

Supercritical fluid thermodynamics for coal processing. Topical report

Because of their unusual solvating and mass transfer properties, supercritical fluids show potential for a variety of coal processing applications. We have established a database of coal model compound equilibria; to add to this database, we have developed and are testing methods of rapidly measuring cosolvent effects on solubility. In addition, we have used fluorescence spectroscopy to study the nature of cosolvent effects on molecular level. The solubility and spectroscopic measurements are being used to guide the development of an equation of state that includes both physical and chemical interactions. The equation of state will be used to predict solubility behavior to systems can be designed for the processing of coal with supercritical fluids. 8 figs

A Model of Hysteresis in Narrow Pores

PACS. 68.10 -Fluid surfaces and interfaces with fluids (inc. surface tension, capillarity, PACS. 68.15 -Liquid thin films. PACS. 64.70F -Liquid-vapour transitions. wetting and related phenomena). Abstract. -We introduce a new model of adsorption ..ysteresis that takes the formation of a meniscus explicitly into account by allowing the density to vary in the direction parallel to the walls. We apply the new geometry to a lattice gas model and solve the self-consistent equations for the density profile in the mean-field approximation. Adsorption is similar to that in single, infinitely long pores. Desorption is qualitatively different: a meniscus forms at the pore ends and subsequently recedes. Our results justify recent assumptions made about the nature of hysteresis. Significant progress has recently been made in understanding fluid phase behaviour in mesoporous solids from a molecular point of view. In particular, the physics underlying the phase transitions in an idealized infinitely long pore has been elucidated by employing meanfield density functional theory (DFT) methods [l]. The theory quite accurately predicts capillary condensation. That is, it locates the undersaturated bulk pressure (or chemical potential) at which a gaslike state coexists with a liquidlike state. Moreover, by using the most refined version of DFT, namely, the smoothed density approximation (SDA) introduced by Tarazona [2], an accurate description of fluid structure is obtained that is in excellent agreement with recent simulations [3, In spite of these successes the theory of single, infinitely long pores does not seem to give a complete account of the experimental adsorption isotherms. Experimentally one generally observes a hysteresis loop [51. The adsorption branch rises steeply at a pressure which is higher than that of the desorption branch. The interpretation is that the states along the adsorption branch are not represented by stable states but instead are thought to be metastable corresponding to a local minimum in the grand potential, since they are beyond the thermodynamic transition point. This idea goes back to Cassell[61 and was subsequently explored in more detail by Hi11 [7]. Similarly, for pressures less than the condensation pressure the states along the desorption branch are only metastable. Metastable states naturally arise in the mean-field theory and the theory appears to give a proper account of the adsorption process. However, it fails to give a realistic account of desorption. Namely, i

The European Federation of Organisations for Medical Physics Policy Statement No. 10.1: Recommended Guidelines on National Schemes for Continuing Professional Development of Medical Physicists

Continuing Professional Development (CPD) is vital to the medical physics profession if it is to embrace the pace of change occurring in medical practice. As CPD is the planned acquisition of knowledge, experience and skills required for professional practice throughout one's working life it promotes excellence and protects the profession and public against incompetence. Furthermore, CPD is a recommended prerequisite of registration schemes (Caruana et al. 2014 [1]; [2]) and is implied in the Council Directive 2013/59/EURATOM (EU BSS) [3] and the International Basic Safety Standards (BSS) [4]. It is to be noted that currently not all national registration schemes require CPD to maintain the registration status necessary to practise medical physics. Such schemes should consider adopting CPD as a prerequisite for renewing registration after a set period of time. This EFOMP Policy Statement, which is an amalgamation and an update of the EFOMP Policy Statements No. 8 and No. 10, presents guidelines for the establishment of national schemes for CPD and activities that should be considered for CPD

Bulk inhomogeneous phases of anisotropic particles: A fundamental measure functional study of the restricted orientations model

The phase diagram of prolate and oblate particles in the restricted orientations approximation (Zwanzig model) is calculated. Transitions to different inhomogeneous phases (smectic, columnar, oriented, or plastic solid) are studied through minimization of the fundamental measure functional (FMF) of hard parallelepipeds. The study of parallel hard cubes (PHC's) as a particular case is also included motivated by recent simulations of this system. As a result a rich phase behavior is obtained which include, apart from the usual liquid crystal phases, a very peculiar phase (called here discotic smectic) which was already found in the only existing simulation of the model, and which turns out to be stable because of the restrictions imposed on the orientations. The phase diagram is compared at a qualitative level with simulation results of other anisotropic particle systems.Comment: 11 pages, 10 figure

Fluids of platelike particles near a hard wall

Fluids consisting of hard platelike particles near a hard wall are investigated using density functional theory. The density and orientational profiles as well as the surface tension and the excess coverage are determined and compared with those of a fluid of rodlike particles. Even for low densities slight orientational packing effects are found for the platelet fluid due to larger intermolecular interactions between platelets as compared with those between rods. A net depletion of platelets near the wall is exhibited by the excess coverage, whereas a change of sign of the excess coverage of hard-rod fluids is found upon increasing the bulk density.Comment: 6 pages, 9 figure

Preparation of microporous films with sub nanometer pores and their characterization using stress and FTIR measurements

The authors have used a novel technique, measurement of stress isotherms in microporous thin films, as a means of characterizing porosity. The stress measurement was carried out by applying sol-gel thin films on a thin silicon substrate and monitoring the curvature of the substrate under a controlled atmosphere of various vapors. The magnitude of macroscopic bending stress developed in microporous films depends on the relative pressure and molar volume of the adsorbate and reaches a value of 180 MPa for a relative vapor pressure, P/Po = 0.001, of methanol. By using a series of molecules, and observing both the magnitude and the kinetics of stress development while changing the relative pressure, they have determined the pore size of microporous thin films. FTIR measurements were used to acquire adsorption isotherms and to compare pore emptying to stress development, about 80% of the change in stress takes place with no measurable change in the amount adsorbed. The authors show that for sol-gel films, pore diameters can be controlled in the range of 5--8 {angstrom} by ``solvent templating``

Capillary stress in microporous thin films

Development of capillary stress in porous xerogels, although ubiquitous, has not been systematically studied. The authors have used the beam bending technique to measure stress isotherms of microporous thin films prepared by a sol-gel route. The thin films were prepared on deformable silicon substrates which were then placed in a vacuum system. The automated measurement was carried out by monitoring the deflection of a laser reflected off the substrate while changing the overlying relative pressure of various solvents. The magnitude of the macroscopic bending stress was found to reach a value of 180 MPa at a relative pressure of methanol, P/Po = 0.001. The observed stress is determined by the pore size distribution and is an order of magnitude smaller in mesoporous thin films. Density Functional Theory (DFT) indicates that for the microporous materials, the stress at saturation is compressive and drops as the relative pressure is reduced

Generalized Interpolation Material Point Approach to High Melting Explosive with Cavities Under Shock

Criterion for contacting is critically important for the Generalized Interpolation Material Point(GIMP) method. We present an improved criterion by adding a switching function. With the method dynamical response of high melting explosive(HMX) with cavities under shock is investigated. The physical model used in the present work is an elastic-to-plastic and thermal-dynamical model with Mie-Gr\"uneissen equation of state. We mainly concern the influence of various parameters, including the impacting velocity $v$, cavity size $R$, etc, to the dynamical and thermodynamical behaviors of the material. For the colliding of two bodies with a cavity in each, a secondary impacting is observed. Correspondingly, the separation distance $D$ of the two bodies has a maximum value $D_{\max}$ in between the initial and second impacts. When the initial impacting velocity $v$ is not large enough, the cavity collapses in a nearly symmetric fashion, the maximum separation distance $D_{\max}$ increases with $v$. When the initial shock wave is strong enough to collapse the cavity asymmetrically along the shock direction, the variation of $D_{\max}$ with $v$ does not show monotonic behavior. Our numerical results show clear indication that the existence of cavities in explosive helps the creation of ``hot spots''.Comment: Figs.2,4,7,11 in JPG format; Accepted for publication in J. Phys. D: Applied Physic