Estimation of the minimum pore size sufficient for capillary hysteresis

A procedure for determination of the minimum pore sizes suitable for the formation of an adsorption-desorption hysteresis loop was developed. Conditions for the formation of hysteresis in infinite rectangular channels and in the cavities restricted along three directions (spheres, rectangular parallelepipeds) and in channels with different cross-sections and limited lengths are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 18–28, January, 2008.     

Highly Selective Zeolite Topologies for Flue Gas Separation

The separation of carbon dioxide from flue gas is essential for the reduction of greenhouse gas emissions. In adsorptive methods, the challenge lies in the choice of suitable porous materials. Among all zeolite topologies, a number of adsorbents with pore dimensions in the range of the guest molecules were identified to allow an excellent separation by diffusion, and MRE and AFO zeolite topologies appear to be the best candidates based on equilibrium adsorption. Also, it was found that the behavior of this gas mixture in DFT and APD zeolites differed from the normal behavior.     

Adsorption and selectivity of carbon dioxide with methane and nitrogen in slit-shaped carbonaceous micropores: Simulation and experiment

We have used the grand canonical Monte Carlo method to study the adsorption and selectivity of mixtures of carbon dioxide with methane and nitrogen at high (i.e., ambient) temperatures in model slit pores with graphitic surfaces. Experimental data, including new high pressure measurements for carbon dioxide and methane on a non-porous graphitic standard, were used to test the potential models. The mixture simulations predict that carbon dioxide is preferentially adsorbed in both systems. The results are discussed in terms of competing energetic and entropic effects and the underlying molecular mechanisms.     

Solubility of aminotriethylene glycol functionalized single wall carbon nanotubes: A density functional based tight binding molecular dynamics study

Pristine CNTs are exemplary hydrophobic solutes; properly functionalized CNTs can be seen as hydrophilic ones. The solubility of aminotriethylene glycol (ATG) functionalized single walled carbon nanotubes (fSWCNTs) were examined using density functional based tight binding method. According to the dynamics study, the ATG-fSWCNTs interaction energies (IE) and diffusion coefficients (D) are diameter dependent. As the diameter of the (n,0) tube is incrementally increased, a distinguishable pattern is observed, specifically the IE of the ATG-fSWCNT in water is quite higher for n that is an integral multiple of three (n = 9,12,15) while the D is lower due to its π bonding structures. In general, the metallic ATG functionalized nanotube possess a higher IE and a much lower D in aqueous media. © 2019 Wiley Periodicals, Inc.     

Monte Carlo Computer Simulation of a Single Semi-Flexible Macromolecule at a Plane Surface

Summary: The properties of a single semiflexible mushroom chain at a plane surface with a long-ranged attracting potential are studied by means of lattice Monte Carlo computer simulation using the bond fluctuation model, configurational bias algorithm for chain re-growing and the Wang-Landau sampling technique. We present the diagram of states in variables temperature T vs. strength of the adsorption potential, ε_w, for a quite short semiflexible chain consisting of N = 64 monomer units. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil and cylinder-like liquid-crystalline globule. At low values of the adsorption strength ε_w the coil–globule and the subsequent liquid–solid globule transitions are observed upon decreasing temperature below the adsorption transition point. At high values of ε_w these two transitions change into a single transition from an adsorbed coil to a cylinder-like liquid-crystalline solid globule. We conclude that for a semiflexible chain the presence of a plane attracting surface favors the formation of a globule with internal liquid-crystalline ordering of bonds.     

Characteristic features of phase diagrams describing condensation of adsorbate in narrow pores

The phase diagrams describing condensation of adsorbate in micro- and mesoporous adsorbents having slit-shaped and cylindrical pores whose size varied from 1 to 20 monolayers were constructed. The study was performed using the lattice-gas model in the quasichemical approximation to take into account the intermolecular interactions. The phase diagrams for various values of the potential arising from different types of adsorbate--adsorbent interaction were analyzed for adsorption of helium, neon, methane, and carbon tetrachloride in graphite pores. Other adsorption systems are considered and the relationship between the pressure and temperature of adsorbate condensation is discussed. A nonmonotonic variation of the critical densities for pore widths from 3 to 10 molecular diameters was found. The pattern of this variation depends on the ratio of the energy of lateral interactions of the adsorbate molecules to the energy of interaction of the adsorbate molecules with pore walls. The critical temperature decreases monotonically with a decrease in the pore width. The stronger the adsorbate interaction with the pore walls, the greater the decrease in the critical temperature.     

用实验吸附等温线和计算机分子模拟表征中孔分子筛MCM-41

首先比较了表征MCM-41的两个势模型对吸附等温线的影响。发现在一维势模型 中,低压部分的吸附应与选用的势模型的势阱深度有关,而毛细凝聚发生的位置与 孔壁在离壁面较远处与流体分子的相互作用的强弱有关。然后作者使用了一个“混 合”的势模型,即采用作者提出的势函数表征孔壁中氧原子对MCM-41中流体分子的 作用,而采用Tjatjopoulos等提出的势函数近似地表征MCM-41表面硅醇基团以及一 些未知因子对流体分子的作用。虽然这种势模型仍然是一维的,但这种势模型将孔 壁内氧原子的作用和表面上非均匀性分开考虑,具有较明确的物理意义。通过计算 机模拟与实验数据的比较发现,这种势模型可以较好地拟合氮气在MCM-41中的吸附 等温线。     

Controlling the role of nanopore morphology in capillary condensation

The effect of pore morphology on capillary condensation and evaporation in nanoporous silicon is studied experimentally. A variety of cooperative and local effects are observed in tailored nanopores with well-defined regions by directly probing gas adsorption in each region using optical interferometry. All observations are ascribed to the ability of the nanopore region to access the gas reservoir directly and the nucleation of liquid bridges at local heterogeneities within the nanopore region. These assumptions, consistent with recent simulations, can be extended to any real nanoporous system.     

Effect of capillary condensation on friction force and adhesion

Friction force measurements have been conducted with a colloid probe on mica and silica (both hydrophilic and hydrophobized) after long (24 h) exposure to high-humidity air. Adhesion and friction measurements have also been performed on cellulose substrates. The long exposure to high humidity led to a large hysteresis between loading and unloading in the friction measurements with separation occurring at large negative applied loads. The large hysteresis in the friction-load relationship is attributed to a contact area hysteresis of the capillary condensate which built up during loading and did not evaporate during the unloading regime. The magnitude of the friction force varied dramatically between substrates and was lowest on the mica substrate and highest on the hydrophilic silica substrate, with the hydrophobized silica and cellulose being intermediate. The adhesion due to capillary forces on cellulose was small compared to that on the other substrates, due to the greater roughness of these surfaces.     

Critical temperature of capillary condensation in narrow cylindrical pores

The dependence of the critical temperature of capillary condensation of an adsorbate in cylindrical pores on the diameter of pores is investigated. The calculation is carried out in the quasi-chemical approximation with a calibration function providing the agreement of results for small pores with exact values obtained by the fragment method. The contribution of the size effect to the calibration function as a function of the diameter of pores is considered in terms of the concept of quasi-one-dimensional behavior of the adsorbate in narrow pores. Various adsorbate-adsorbate potentials are considered.     

超临界状态下炭基材料的储氢

评介了目前各种储氢方法，指出了炭基材料作为储氢材料的优势，综述了近年来纳米炭材料在储氢方面的进展，详细探讨了超临界状态下氢气在纳米孔隙中的吸附机理，并在此基础上提出了研究中的问题及进一步的研究方向。     

The behavior of capillary suspensions at diverse length scales: From single capillary bridges to bulk

Liquid-liquid-solid systems are becoming increasingly common in everyday life with many possible applications. Here, we focus on a special case of such liquid-liquid-solid systems, namely, capillary suspensions. These capillary suspensions originate from particles that form a network based on capillary forces and are typically composed of solids in a bulk liquid with an added secondary liquid. The structure of particle networks based on capillary bridges possesses unique properties compared with networks formed via other attractive interactions where these differences are inherently related to the properties of the capillary bridges, such as bridge breaking and coalescence between adjacent bridges. Thus, to tailor the mechanical properties of capillary suspensions to specific requirements, it is important to understand the influences on different length scales ranging from the dynamics of the bridges with varying external stimuli to the often heterogeneous network structure.     

煤的润湿性及吸附性对煤成浆性的影响

本文讨论大同煤的润湿性、吸附性与煤成浆性的关系。不同类型的添加剂改善煤润湿性的能力不同,只有适当增加煤的润湿性才能配制成性能良好的煤浆。添加剂的合理用量可根据煤表面对添加剂的平衡吸附量来确定,此平衡吸附量用紫外分光光度计测定。实验表明,可用煤的润湿性、吸附性数值初步筛选煤浆的有效添加剂并确定其用量。     

A macrothermodynamic approach to the limit of reversible capillary condensation

The threshold of reversible capillary condensation is a well-defined thermodynamic property, as evidenced by corresponding states treatment of literature and experimental data on the lowest closure point of the hysteresis loop in capillary condensation-evaporation cycles for several adsorbates. The nonhysteretical filling of small mesopores presents the properties of a first-order phase transition, confirming that the limit of condensation reversibility does not coincide with the pore critical point. The enthalpy of reversible capillary condensation can be calculated by a Clausius-Clapeyron approach and is consistently larger than the condensation heat in unconfined conditions. Calorimetric data on the capillary condensation of tert-butyl alcohol in MCM-41 silica confirm a 20% increase of condensation heat in small mesopores. This enthalpic advantage makes easier the overcoming of the adhesion forces by the capillary forces and justifies the disappearing of the hysteresis loop.     

Stability considerations of the capillary condensation within a cylindrical pore

A proof of the stability of the unduloid configuration within a cylindrical pore is given. The proof involves calculus of variation techniques and in particular the theory of the problem of Bolza is used. It is shown that the unduloid configuration is stable to small disturbances provided dV/dκ < 0, where V represents the volume of the configuration and κ is the curvature of the configuration. If this condition is not satisfied the unduloid configuration is unstable.