Flow of nonfreezing water interlayers and frost damage in porous solids

On the basis of the thermodynamics of irreversible processes, a solution has been obtained for the problem of mass transfer between nonfreezing interlayers in a slit model of a pore filled with ice, and also between the thawed and frozen zones of a porous solid. The disjoining pressure plays a role in determining the equilibrium thickneses of the interlayers and in the phenomena of frost damage and heaving of soils. The theory that is developed in this work is supported by experimental findings, and guidelines are formulated for future research in the field of the theory of moisture movement in porous solids during the freezing process.     

Mass transfer in frozen porous bodies

The theory of moisture transport in frozen porous bodies under the action of temperature gradient along unfreezing communications represented by water in thin pores and in interlayers between the pore surface and the ice was elaborated. It was shown that most of the flow in the pores filled with water is directed toward a cold side and can be calculated using the disjoining pressure isotherms of unfreezing interlayers. To obtain isotherms, we used the data of previous measurements of the thickness of unfreezing interlayers in micron-sized quartz capillaries as a function of pressure and temperature. The viscosity of unfreezing interlayers in quartz capillaries was estimated based on the measurements of the displacement velocity of ice columns in the quartz capillaries. Calculated flow rates of unfreezing moisture were consistent with the experimental data for the model porous bodies and frozen grounds.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 835–839.Original Russian Text Copyright © 2004 by Churaev.     

Modern state of the investigation of long-range surface forces

Development of the concept of surface long-range forces and, in particular, the equilibrium disjoining pressure of liquid and gaseous interlayers has been set forth. Considered are the molecular, adsorption, electrical, structural, and electronic components of disjoining pressure. The contribution of the disjoining pressure to the hydrodynamics of thin layers is considered. The first theory of the frost heaving of soils has been formulated. Stated are the investigations of surface forces, in particular, in the processes of the formation of new interfaces and arising phenomena of the emission of electrons, ions, photons, and neutrons.     

Porous Organic Polymer Films with Tunable Work Functions and Selective Hole and Electron Flows for Energy Conversions

Organic optoelectronics are promising technologies for energy conversion. However, the electrode interlayer, a key material between active layers and conducting electrodes that controls the transport of charge carriers in and out of devices, is still a chemical challenge. Herein, we report a class of porous organic polymers with tunable work function as hole‐ and electron‐selective electrode interlayers. The network with organoborane and carbazole units exhibits extremely low work‐function‐selective electron flow; while upon ionic ligation and electro‐oxidation, the network significantly increases the work function and turns into hole conduction. We demonstrate their outstanding functions as anode and cathode interlayers in energy‐converting solar cells and light‐emitting diodes.     

Disjoining pressure of thin nonfreezing interlayers

At subzero temperatures, it has been found that nonfreezing water interlayers form between the inner smooth surface of a thin quartz capillary and the ice in the capillary core. The dilatometry method has been used to measure the thicknesses of these nonfreezing interlayers over a range of temperatures between -1 and -0.14 degrees C and for applied pressures up to 8 MPa. The measured data are used to calculate the disjoining pressure isotherms of nonfreezing water interlayers. It is shown that structural forces caused by structural changes of nonfreezing water are the main contribution to the disjoining pressure. The structural changes are also responsible for the phenomenon of the nonfreezing interlayers.     

Soy protein isolate/MXene decorated acidified carbon paper interlayer for long-cycling Li–S batteries

The terrible shuttling of lithium polysulfides (LiPSs) is a major obstacle for commercializing lithium–sulfur (Li–S) batteries as high-performance energy storage systems. In this study, a carbon-based interlayer with effective suppression capability on the shuttle effect is developed by simply coating a well-dispersed mixture of soybean protein isolate/MXene onto the acidified carbon paper (ACP). The resultant composite interlayer (SM@ACP) is able to synergistically diminish the shuttle effect through chemical adsorption and physical blocking. Meanwhile, this interlayer displays excellent conductivity and facilitates the diffusion of Li ions due to the composite coating to promote both electron/ion conduction as well as the porous structure of ACP. Benefiting from the unique properties of the composite interlayer, the as-assembled Li–S batteries with SM@ACP interlayers show a great improvement in the cycling stability and rate performance, delivering a very low-capacity decay rate of 0.071% per cycle at 0.5 C even after 800 cycles. This work provides a feasible route to realize rational design and commercial mass production of desirable interlayers for promoting the commercialization of Li–S batteries.     

Main factors affecting the stability of colloids

A general survey is given on the role that interparticular attraction forces play in the aggregative stability of colloidally dispersed systems. Special attention is paid to the disjoining pressure acting between interlayers. The importance of recent results obtained by the author using the so-called flow ultramicroscope method is emphasized as these data allow the interpretation of the kinetics of slow coagulation, not only in the initial stage as does Fuchs' theory, but also in the whole of the process.     

TiO2-carbon porous nanostructures for immobilization and conversion of polysulfides

Lithium-sulfur batteries (LSBs) are among the most promising series of next-generation high density energy storage systems. However, the problem of “shuttle effect” caused by dissolution and migration of polysulfide intermediates has severely inhibited their practical applications. Herein, TiO₂-carbon nanocomposites embedded hierarchical porous carbon (T-hPC) interlayers are fabricated via Ti₃C₂ MXene assisted phase separation and annealing method. The T-hPC processes micro- to macro-scale multi-pores along with highly adsorptive and catalytic carbon supported TiO₂ nanoparticles, which significantly enhances the polysulfides immobilization and improves the redox reaction kinetics when applied as lithium-sulfur battery interlayers. An initial discharge specific capacity of 1551.1 mAh/g and a stable capacity of 893.8 mAh/g after 200 cycles at 0.5 C are obtained, corresponding to a capacity decay rate of only 0.04% per cycle. The investigations in this paper can provide a simple and effective strategy to enhance the electrochemical properties for lithium-sulfur batteries.     

Disjoining pressure of thin layers of binary solutions

Theory of dispersion forces and thermodynamics was used for the calculation of the adsorption and disjoining pressure of a binary solution interlayer between two identical and two dissimilar plates. Disjoining pressure isotherms were obtained for liquid interlayers between solids, for wetting and free films of solutions. The conditions were determined under which the overlapping of the diffuse adsorption layers of the solute can provide the main contribution to the interaction and make the disjoining pressure positive. It has been shown by numerical methods that the disjoining pressure isotherms of thin interlayers of solutions may intersect the thickness axis, and that the repulsion forces appear at small distances. Thus, disperse systems may be stabilized in the presence of binary, nonionic solutions.     

Isothermal Flows of Micropolar Liquids: Formulation of Problems and Analytical Solutions

Models for flows of a non-Newtonian liquid have been considered within the framework of the micropolar theory. Different forms of constitutive equations and boundary conditions have been compared. Available analytical solutions and possible applications of the micropolar theory have been reviewed. A mechanically substantiated formulation of the problem relevant to the flow of a micropolar liquid in a Brinkman porous medium has been considered. Formulations of the boundary problem have been proposed for a micropolar liquid flowing in a porous cell.     

Spectroscopic Mimicry for the Protonated Retinal Schiff Base in vivo with Modified Amphiphilic Clay Interlayers as a Possible Model of Opsin Environment

Abstract— We have found that clay acts as a novel model matrix for the amphiphilic protein-opsin to mimic the visible absorption spectrum of a protonated retinal Schiff base (RSB) in vivo. Without strong acids at ambient temperature, a visible broad absorption spectrum with a LDmax at 530 nm covering the range from 400 to 680 nm was achieved for the protonated RSB with cationic surfactant-modified montmorillonite clay. The interlayers of the dimethyloctadecylamine (DOA) modified clay were found to provide amphiphilic space allowing the amphiphilic RSB to be intercalated easily and sequentially and protonated by the DOA. It is proposed that the visible absorption spectrum at LD, 530 nm was attributable to electrostatic effects, permitting the appropriate distance between the nitrogen of the protonated RSB and the negatively charged clay interlayers and also to the anisotropic orientation of the RSB molecules in the interlayers.     

Encapsulation of Functional Organic Compounds in Nanoglass for Optically Anisotropic Coatings

A novel approach is presented for the encapsulation of organic functional molecules between two sheets of 1 nm thin silicate layers, which like glass are transparent and chemically stable. An ordered heterostructure with organic interlayers strictly alternating with osmotically swelling sodium interlayers can be spontaneously delaminated into double stacks with the organic interlayers sandwiched between two silicate layers. The double stacks show high aspect ratios of >1000 (typical lateral extension 5000 nm, thickness 4.5 nm). This newly developed technique can be used to mask hydrophobic functional molecules and render them completely dispersible in water. The combination of the structural anisotropy of the silicate layers and a preferred orientation of molecules confined in the interlayer space allows polymer nanocomposite films to be cast with a well‐defined orientation of the encapsulated molecules, thus rendering the optical properties of the nanocoatings anisotropic.     

微孔中简单流体粘度的分子动力学模拟及关联模型

用分子动力学模拟计算了微孔介质中流体氩在不同温度、不同密度和不同孔径下的剪切粘度.并根据Chapman-Enskog关于硬球流体传递性质的理论以及Heyes的关于Lennard-Jones流体粘度的表达式,提出了两个描述微孔介质中流体粘度的模型,该模型可以计算微孔中流体氩在不同状态下的粘度值.通过与计算机模拟值的比较,证明这两个微孔流体粘度模型是可用的.     

Experimental and actual values of self-diffusion coefficients of liquids in porous media

Self-diffusion coefficients D* of liquids in porous media, as measured by the pulsed-field gradient NMR method, have been investigated as functions of the interval t ₁ between the first and the second radio-frequency pulses (the time of spin dephasing) in the “stimulated echo” pulsed procedure. Experimental D*(t ₁) dependences have been shown to be adequately described by the relations of the Fatkullin theory for moderate and short correlation times of spin motion in an internal random Gaussian magnetic field. Actual self-diffusion coefficients and some parameters of the porous media have been estimated.     

Calorimetric Study of Frost Attack During Cement Hardening

This report deals with practical and experimental studies of the effects of frost attack on hardening cement stone and concrete. The basic component of concrete, cement stone, is a typical capillary-porous material formed from solid, liquid and gaseous phases. The level of knowledge on the effects of frost attack on cement stone and concrete hardening is insufficient, due to the complexity of the mechanisms of the accompanying effects. The values of internal pressures are determined among others by ice formation parameters, by the characteristics of the porous structure and the solid phase of the cement stone, and also by technological factors. The quantitative estimation of certain parameters is important for an approach to the understanding of the mechanism of frost attack and the choice of methods of its regulation for technological purposes. These are the temperature of pore liquid crystallization T _f, the degree of freezing F _d and the mass of ice I _m formed during freezing. Examples of changes in ice formation parameters on variation of some of the technological factors are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fundamentals of lead-acid cells: Part XI. Phase formation at solid and porous lead electrodes

The development of lead sulphate on lead (charged) electrodes (massive and porous) has been examined by the potential-step technique. The behaviour of the solid electrode conforms to control by nucleation and growth processes. The exact form of the process is potential-dependent and becomes two-dimensional at more positive potentials. The behaviour of the porous electrode can be interpreted in terms of well-established theory for porous materials assuming that the same crystallisation processes are observed as for the case of solid electrodes.     

Preparation of poly (L‐lactic acid) with aligned structures by unidirectional freezing

Honeycomb monolith structured porous poly (L‐lactic acid, PLA) was simply fabricated by employing a unidirectional freeze‐casting technique. Dimethyl sulfoxide (DMSO) was used as a solvent for PLA, and the solution was unidirectionally frozen. The DMSO was nucleated in the solution and was grown in the freezing direction. The PLA was solidified and structured with the DMSO crystal as a template. Then DMSO was leached by water, ethanol, or the mixture of them, and subsequently the porous PLA was dried by oven. It was found that the freeze‐casting protocol can significantly influence the morphological features such as the tube diameter and wall thickness of tube can be tuned by varying of PLA concentration, freezing temperature, and the nature of leaching solvent. Because DMSO has a special solubility of a number of polymers, this method may be a general way for designing and preparing aligned porous materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetic adhesion of bacterial cells to sand: cell surface properties and adhesion rate

Correlation between microbial surface thermodynamics using the extended DLVO (XDLVO) theory and kinetic adhesion of various bacterial cells to sand was investigated. Two experimental setups were utilized. Adhesion tests were conducted in batch reactors with slow agitation. Also, bacteria were circulated through small sand columns in a closed loop and the results were analyzed with a simple model which accounted for the rate of the adhesion phenomena (omega in h(-1)) and adhesion percentage. Cells surface properties were derived from contact angle measurements. The wicking method was utilized to characterize the sand. Zeta potentials were measured for the sand and the cells. Kinetic of bacterial retention by the porous media was largely influenced by the electrostatic interactions which are correlated with omega from the model (R(2)=0.71). Negative zeta potentials resulted in electrostatic repulsions occurring between the sand and the bacterial cells which in result delayed bacterial adhesion. While no correlation was found between the adhesion percentage and the total interaction energy calculated with the XDLVO theory the respective behavior of hydrophobic and hydrophilic bacteria as well as the importance of electrostatic interactions was evidenced. All the bacterial strains studied adhered more in the column experiments than in the adhesion tests, presumably due to enhanced collision efficiency and wedging in porous media, while filtration could be ignored except for the larger Bacillus strains. Approximate XDLVO calculations due to solid surface nanoscale roughness, retention in a secondary minimum and population heterogeneity are discussed. Our results obtained with a large variety of different physicochemical bacterial strains highlights the influence of both surface thermodynamics and porous media related effects as well as the limits of using the XDLVO theory for evaluating bacterial retention through porous media.     

Shear viscosity of simple fluids in porous media: molecular dynamic simulations and correlation models

Equilibrium molecular dynamic simulations have been used to calculate the shear viscosity of liquid argon in macrovolume system and in porous media at different temperatures, densities and pore widths. On the other hand, based on the Chapman–Enskog theory and Heyes relationships, two correlation models which can describe the viscosity of simple liquids in porous media are proposed as a function of the reduced temperature, density and pore width. The validity of the models is evaluated by comparing the calculated viscosity to simulation data.     

可控阵列微纳结构超疏水铜表面冰霜传质特性

金属表面粗糙结构及其润湿性对其露、霜、冰的相变及传质现象有重要影响. 通过电火花微加工和化学氧化法,本文首先实现了铜片表面微米、纳米阵列结构的可控制备. 针对条纹,方柱和四棱锥三种典型微米结构特征,对比研究了单级粗糙结构和二级复合结构超疏水表面的润湿性、结露、结霜、结冰及其融化过程. 微纳复合结构可有效增强超疏水性,减少霜晶形核和生长速度,同时还能大幅度延缓结冰的时间,多次冷热循环处理后,表面仍能保持较好的防霜抗冰性能. 通过经典形核理论,Brown 凝并,一维传热及传质理论,综合分析了冰霜在这种表面的传质特性.