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The hase behavior of confined fluids adsorbed in nanopores differs significantly from their bulk counterparts and depends on the chemical and structural properties of the confining structures. In general, phase transitions in nanoconfined fluids are reflected in stepwise adsorption isotherms with a pronounced hysteresis. Here, we show experimental evidence and an

Hypothesis Suspensions of nanoporous particles in non-wetting fluids (lyophobic nanoporous suspensions, LPNPS) are explored as energy absorbing materials for shock absorbers, bumpers, and energy storage. Upon application of pressure, the non-wetting fluid invades the pores transforming the impact energy into the interfacial energy that can be stored and released on demand. Experiments Here, we present a comprehensive experimental study of the dynamics of LPNPS compression within a wide range of shock impact energy for three types of mesoporous materials (Libersorb 23, Polysorb-1, and Silochrome-1.5) with water and Wood alloy as non-wetting fluids. Findings Three different regimes of the LPNPS compression-expansion cycle in response to the shock impact are distinguished as the impact energy increases: without fluid penetration into the pores, with partial penetration, and with complete pore filling. In two latter regimes, the suspension compressibility in the process of rapid compression increases by 2–4 decimal decades. This giant effect is associated with the onset of penetration of the non-wetting fluid into the nanopores upon achievement of a certain threshold pressure. The dynamic threshold pressure exceeds the threshold pressure of quasistatic intrusion and does not depends on the impact pressure, temperature, and suspension composition. A dynamic model of suspension compression is suggested that allows to separate the effects of the fluid intrusion into the pores and the elastic deformation of the system.

Pore structure characterization plays a crucial role in the optimization of adsorption properties of nanoporous carbons employed for water purification, gas and liquid phase separations, carbon dioxide reduction, energy storage, and other applications. Here, we present an original methodology for evaluating the pore size distribution in carbons in a wide range of micro- and mesopores from 0.385 to 10 nm from a single isotherm of high-pressure adsorption of CO2 at 273 K. The proposed method is based on the reference theoretical isotherms calculated by Monte Carlo simulations in model pores of slit-shaped and cylindrical geometry. The relationship between the pore size and the pore filling pressure is established. Special attention is given to the predicting of the capillary condensation transitions in mesopores by using the meso-canonical ensemble (gauge cell) Monte Carlo simulations. The proposed technique is demonstrated and verified against the conventional N2 and Ar low temperature adsorption methods drawing on the example of micro-mesoporous carbons of the CMK family. Advantages and limitations of CO2 adsorption characterization of nanoporous materials are discussed and further improvements are proposed.

Phase behavior of confined fluids adsorbed in na-nopores differs significantly from their bulk coun-terparts and depends on the chemical and structural properties of the confining structures. In general, phase transitions in nanoconfined fluids are reflect-ed in stepwise adsorption isotherms with a pro-nounced hysteresis. Here, we show experimental evidence and in silico interpretation of the reversi-ble stepwise adsorption isotherm which is observed when methane is adsorbed in the rigid, crystalline metal-organic framework IRMOF-1 (MOF-5). In a very narrow range of pressures, the adsorbed fluid undergoes a structural and highly cooperative re-construction and transition between low-density and high-density nanophases, as a result of the competition between the fluid-framework and flu-id-fluid interactions. This mechanism evolves with temperature: below 110 K a reversible stepwise iso-therm is observed, which is a result of the bimodal distribution of the coexisting nanophases. This temperature may be considered as a critical temper-ature of methane confined to nanopores of IRMOF-1. Above 110 K, as the entropy contribution in-creases, the isotherm shape transforms to a common continuous S-shaped form that is characteristic to a gradual densification of the adsorbed phase as the pressure increases.

Lipid membranes supported on solid surfaces and nanoparticles find multiple applications in industrial and biomedical technologies. Here, we explore in silico the mechanisms of the interactions of lipid membranes with nanostructured surfaces with deposited nanoparticles and explain the characteristic particle size dependence of the uniformity and stability of lipid coatings observed in vitro. Simulations are performed to demonstrate the specifics of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid membrane adhesion to hydrophilic and hydrophobic nanoparticles ranging in size from 1.5 to 40 nm using an original coarse-grained molecular dynamics model with implicit solvent and large simulation boxes (scales up to 280 × 154 × 69 nm3). We find that one of the major factors that affects the uniformity and stability of lipid coatings is the disjoining pressure in the water hydration layer formed between the lipid membrane and hydrophilic solid surface. This effect is accounted for by introducing a special long-range lipid-solid interaction potential that mimics the effects of the disjoining pressure in thin water layers. Our simulations reveal the physical mechanisms of interactions of lipid bilayers with solid surfaces that are responsible for the experimentally observed nonmonotonic particle size dependence of the uniformity and stability of lipid coatings: particles smaller than the hydration layer thickness (

Adsorption of surfactants at gas-liquid interfaces that causes reduction in the surface tension is a classical problem in colloid and interface science with multiple practical applications in oil and gas recovery, separations, cosmetics, personal care, and biomedicine. Here, we develop an original coarse-grained model of the liquid-gas interface within the conventional dissipative particle dynamics (DPD) framework with the goal of quantitatively predicting the surface tension in the presence of surfactants. As a practical case-study example, we explore the adsorption of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) on the air-water interface. The gas phase is modeled as a DPD fluid composed of fictitious hard-core "gas" beads with exponentially decaying repulsive potentials to prevent penetration of the liquid phase components. A rigorous parametrization scheme is proposed based on matching the bulk and interfacial properties of water and octane taken as the reference compounds. Quantitative agreement between the simulated and experimental surface tension of CTAB solutions is found for a wide range of bulk surfactant concentrations (∼10-3 to ∼1 mmol/L) with the reduction of the surface tension from ∼72 mN/m (pure water) to the limiting value of ∼37.5 mN/m at the critical micelle concentration. The gas phase DPD model with the proposed parametrization scheme can be extended and applied to modeling various gas-liquid interfaces with surfactant and lipid monolayers, such as bubble suspensions, foams, froths, etc.

Customized micro- and mesoporous carbons are in high demand for ecofriendly technologies. Reactivation of the well-characterized pitch-based activated carbon fiber (ACF) can provide a clear understanding of the structural mechanism of steam activation, which would be helpful for designing better micro- and mesoporous carbons. ACFs were reactivated with steam at 973–1173 K. X-ray diffraction and Raman spectroscopy indicated that the stacking number of graphene-like layers of the pore wall decreased with an increase in the reactivation temperature. The average fiber diameter of the ACFs, which was measured via scanning electron microscopy, decreased with the increase in the reactivation temperature. The relationship between the decrease in the fiber diameter and the burn-off suggested that reactivation above 1023 K produced micropores inside the fiber. A deconvolution analysis of the pore-size distribution revealed the variation of the distribution. The peak difference was approximately 0.3 nm, depending on the reactivation temperature. These results indicate that reactivation with steam proceeds via the preferential one-by-one gasification of less-crystalline graphene-like units.

Construction of atomic-scale three-dimensional (3D) molecular models of unoxidized and oxidized activated carbon fiber (ACF) nanoregions is of substantial scientific and technological interest as it allows in-depth analysis of complex interfacial process. The influence of oxygen functionalities on the specific interactions with guest particles is an important factor that controls wettability, competitive adsorption of fluid mixtures, interfacial transport, reactions, or nucleation processes. We combine experimental techniques of wide-angle X-ray scattering and nitrogen adsorption porosimetry with advanced molecular modelling to construct reliable 3D molecular models of unoxidized and oxidized pitch-based ACF-5 nanoregions. ACF-5 is a ultramicroporous carbon molecular sieve with an average pore size of 0.46 ± 0.2 nm. Narrow hydrophobic nanospaces are formed between defective and slightly curved graphene-like sheets. By atomistic-scale modelling of formaldehyde adsorption at room temperature and different values of the relative humidities, we show that oxygen functionalities and water co-adsorption impact the mechanism and uptake of formaldehyde. Our simulation data indicate that hydrophobic nanopores are preferable to adsorb formaldehyde efficiently in the presence of humidity.

The morphology and stability of surfactant-loaded polyelectrolyte gels are of great interest for a variety of personal care, cosmetic, and pharmaceutical products. However, the mechanisms of surfactant interactions with gel-forming polymers are poorly understood and experimentally challenging. The aim of this work is to explore

A better understanding of the specifics of nanoparticle transport through channels with polymer coated walls is of great importance for various biological, technological, and analytical processes. ...

Potential adsorption theory (PAT) suggested by Polanyi back in 1914 is till date one of the most widely used practical methodologies for the treatment of gas adsorption on microporous materials. He...

Flexible single wall carbon nanotube (SWCNT) transparent and conducting films (TCFs) are indispensable to a further development of flexible electronics. Here we describe thermally and mechanically stable near-ultraviolet (near-UV) transparent and conducting films on ultrathin flexible glass produced from Zn/Al complex-SWCNT inks by bar coating. Our SWCNT/glass TCF is flexible and its relative resistance remains almost constant with increasing bending angle up to ∼170°. Sheet resistance decreases from 80 Ω/sq to 68 Ω/sq after heating in vacuum and increases from 80 Ω/sq to 300 Ω/sq after heating in air from 300 to 523 K. Transmittance in the near-UV region is in the range of 80–90% and does not change with increasing temperature up to 523 K. We believe that this SWCNT/glass TCFs should be promising for thermally stable transparent and flexible electronics.

Carbon dioxide adsorption on micro- and mesoporous carbonaceous materials in a wide range of temperatures and pressures is of great importance for the problems of gas separations, greenhouse gas capture and sequestration, enhanced hydrocarbon recovery from shales and coals, as well as for the characterization of nanoporous materials using CO

Consistent adsorption characterization of metal-organic frameworks (MOFs) is imperative for their wider adoption in industry and practical applications. Current approaches are based on the conventional intuitive representation of MOF pore space as a regular network of pore compartments (cages and channels), adsorption in which occurs independently according to their geometric dimensions. Here, we demonstrate that this conventional approach is unable to describe even qualitatively the shape of Ar adsorption isotherms on hydrated and dehydrated Cu-BTC structures, one of the most well-known MOF materials. A combination of geometric characterization of MOF crystallographic structure, molecular simulation, and virtual visualization of the adsorption process reveals that the filling of the adjacent pore compartments proceeds in parallel in a complex cooperative fashion. The proposed synergistic approach helps us to understand the relations between pore structure geometric and chemical features and adsorption behavior, laying down a foundation for improved methods for MOF characterization.

Emerging technologies of production and processing of functionalized nanoparticles (NP) require advanced methods of NP characterization and separation. While various methods are available for NP se...

A facile method for the formation of mesoporosity within nonporous zirconium hydr(oxides) (ZrO2/Zr(OH)4) is presented and their detoxifying capabilities against dimethyl chlorophosphate (DMCP) are ...

Morphological and transport properties of hydrated metal-substituted Nafion membranes doped with metal ions of different valency and coordination strength are explored using coarse-grained dissipative particle dynamics simulations. To incorporate the effects of metal-polymer complexation, we introduce a novel metal ion complexation model, in which the charged central metal ion is surrounded by dummy sites that coordinate with ligands. The model parameters are determined by matching the metal-ligand running coordination numbers and the diffusion coefficients obtained from atomistic simulations and/or experiments. The increase of valency and coordination strength is found to strongly influence both the morphology and transport characteristics of the membrane at all hydration levels. The membrane segregation into hydrophobic and hydrophilic sub-phases is affected by metal-sulphonate coordination induced crosslinking at the hydrophilic/hydrophobic interface. The simulation results indicate that the interfacial crosslinking influences the interfacial tension and thereby affect the growth and coalescence of water clusters upon the increase of hydration. Multivalent complexation hinders water and ion mobility and causes anomalous sub-diffusion and dramatic decrease of the water permeability and ionic conductivity. Our DPD model is found efficient in elucidating the mechanisms of coordination-induced cross-linking and complexation and predicting on a semi-quantitative level the morphological and transport properties of metal-substituted Nafion membranes depending on the ion valency and coordination strength. The proposed model can be further advanced and adopted for other polyelectrolyte systems, such as sulfonated block-copolymers, polysaccharide solutions and composites, and biopolymer assemblies.

Soft porous crystals undergo large structural transformations under a variety of physical stimuli. Breathing-like transformations, occurring with a large volume change, have been associated with an existence of bi-stable or multi-stable crystal structures. Understanding of the mechanism of these transformations is essential for their potential applications in gas adsorption, separation and storage. However, the generic description is still missing. Here, we provide a detailed, multiscale qualitative and quantitative analysis of the adsorption-induced “breathing” transformations in two metal organic frameworks (MOFs): MIL-53(Al) which is a reference case of our approach, and recently synthesized JUK-8, which does not show any bistability without adsorbate. The proposed approach is based on atomistic simulations and does not require any empirical or adjustable parameters. It allows for a prediction of potential structural transformations in MOFs including the adsorption induced deformations derived from adsorption stress model. We also show that the quantitative agreement between calculated and experimental results critically depends on the quality of the dispersion energy correction. Our methodology represents a new, powerful tool for designing and screening of flexible materials, alternative and complimentary to experimental approaches.

Removal of aromatic contaminants, like phenol, from water can be efficiently achieved by preferential adsorption on porous carbons which exhibit molecular sieving properties. Here, we present nanoporous carbon beads exhibiting an outstanding sieving effect in phenol adsorption from aqueous solution at neutral pH, which is evidenced experimentally and theoretically. The molecular sieving with pure phenol adsorbed phase is achieved by tuning the pore size and surface chemistry of the adsorbent. This study elucidates the essential role of hydrophobic interactions in narrow carbon micropores in removal and clean-up of water from organic pollutants. Furthermore, we suggest a new theoretical approach for evaluation of phenol adsorption capacity that is based on the Monte Carlo simulation of phenol adsorption with the relevance to the pore size distribution function determined by the density functional theory method from low temperature nitrogen adsorption.

When a salt is added to a polymer solution, metal cations may coordinate with polymer ligands forming interchain and intrachain links. Metal coordination leads to drastic changes of polymer morphology, formation of clusters, and, ultimately, a sol–gel transition that affect the solution rheology. Although metal coordination is ubiquitous in polymeric systems, the physical mechanisms of coordination-induced morphological and rheological changes are still poorly understood due to the multiscale nature of this phenomenon. Here, we propose a coarse-grained dissipative particle dynamics (DPD) model to study morphological and rheological properties of concentrated solutions of polymers in the presence of multivalent cations that can coordinate the polymer ligands. The coordinating metal is introduced as a 3D complex of planar, tetrahedral, or octahedral geometry with the central DPD bead representing the metal cation surrounded at the vertices by either four or six dummy beads representing coordination sites, s...

Dissipative particle dynamics (DPD) is one of the most efficient mesoscale coarse-grained methodologies for modeling soft matter systems. Here, we comprehensively review the progress in theoretical formulations, parametrization strategies, and applications of DPD over the last two decades. DPD bridges the gap between the microscopic atomistic and macroscopic continuum length and time scales. Numerous efforts have been performed to improve the computational efficiency and to develop advanced versions and modifications of the original DPD framework. The progress in the parametrization techniques that can reproduce the engineering properties of experimental systems attracted a lot of interest from the industrial community longing to use DPD to characterize, help design and optimize the practical products. While there are still areas for improvements, DPD has been efficiently applied to numerous colloidal and interfacial phenomena involving phase separations, self-assembly, and transport in polymeric, surfactant, nanoparticle, and biomolecules systems.

Fabrication of nanographene shows a promising route for production of designed porous carbons, which is indispensable for highly efficient molecular separation and energy storage applications. This process requires a better understanding of the mechanical properties of nanographene in their aggregated structure. We studied the structural and mechanical properties of nanographene monoliths compressed at 43 MPa over different times from 3 to 25 h. While in monoliths compressed over shorter time adsorption isotherms of Ar at 87 K or N2 at 77 K exhibited a prominent hysteresis due to presence of predominant mesopores, compression for long time induces a low pressure hysteresis. On the other hand, compression for 25 h increases the microporosity evaluated by Ar adsorption, not by N2 adsorption, indicating that 25 h compression rearranges the nanographene stacking structure to produce ultramicropores that can be accessible only for Ar. TEM, X-ray diffraction, and Raman spectroscopic studies indicated that the c...

Although recent experimental studies have demonstrated that doping of nanoporous carbons with nitrogen is an effective strategy for highly diluted formaldehyde capture, the impact of carbon surface chemistry and the pore size on formaldehyde capture at ∼ppm concentrations is still poorly understood and controversial. This work presents a combined theoretical and experimental study on dynamic formaldehyde adsorption on pure and oxidized nanocarbons. We find using Monte Carlo simulations and confirm experimentally that cooperative effects of pore size and oxygen surface chemistry have profound impacts on the breakthrough time of formaldehyde. Molecular modeling of formaldehyde adsorption on pure and oxidized model nanoporous carbons at ∼ppm pressures reveals that high adsorption of formaldehyde ppm concentrations in narrow ultramicropores

The heat of adsorption is one of the most important parameters characterizing energetic heterogeneity of the adsorbent surface. Heats of adsorption are either determined directly by calorimetry or calculated from adsorption isotherms measured at different temperatures using the thermodynamic Clausius-Clapeyron equation. Here, we present a method for calculating the isosteric heat of adsorption that requires as input only a single adsorption isotherm measured at one temperature. The proposed method is implemented with either nonlocal (NLDFT) or quenched solid (QSDFT) density functional theory models of adsorption that are currently widely used for calculating pore size distributions in various micro- and mesoporous solids. The pore size distribution determined from the same experimental isotherm is used for predicting the isosteric heat. The QSDFT method has advantages of taking into account two factors contributing to the structural heterogeneity of adsorbents: the molecular level roughness of the surface and the pore size distribution. The method is illustrated with examples of low temperature nitrogen and argon adsorption on selected samples of carbons of different degree of graphitization and MCM-41 mesoporous silicas of different pore size. The isosteric heat predictions from the NLDFT and QSDFT methods are compared against relevant experiments and the results of Monte Carlo (MC) simulations, with good agreement found in the cases where the surface model adequately reflects the pore surface roughness. Analyses with the QSDFT method show that the isosteric heat of adsorption significantly depends of the molecular level roughness of the adsorbent surface, which is ignored in NLDFT and MC models. The proposed QSDFT method with further verification can be used for calculating the isosteric heat as an additional parameter characterizing the adsorbent surface in parallel with routine calculations of the pore size distribution from a single adsorption isotherm.

Understanding the interactions between nanoparticles (NP) and lipid bilayers (LB), which constitute the foundations of cell membranes, is important for emerging biomedical technologies, as well as for assessing health threats related to nanoparticle commercialization. Applying dissipative particle dynamic simulations, we explore adhesion, intake, and release of hydrophobic nanoparticles by DMPC bilayers. To replicate experimental conditions, we develop a novel simulation setup for modeling membranes at isotension conditions. NP-LB interactions are quantified by the free energy landscape calculated by the ghost tweezers method. NPs are studied z of diameter 2 nm (comparable with the LB hydrophobic core), 4 nm (comparable with the LB thickness) and 8 nm (exceeding the LB thickness). NPs are pre-covered by an adsorbed lipid monolayer. It is shown that NP translocation across LB includes (1) NP intake into the hydrophobic core via merging of the monolayer adsorbed on NP with the outer leaflet of bilayer (2) NP release via formation and rupture of a lipid junction connecting NP and LB. Both stages are associated with free energy barriers. The barrier for the intake stage increases with the NP size and becomes prohibitively high for 8 nm NP. The barriers for the release stage are significantly higher which implies that the release stage controls the translocation rate and dynamics. The release energy barrier of 4 nm NP is found smaller than those for 2 and 8 nm NPs which implies the existence of the optimal NP size for unforced trans-membrane transport. Based on the calculated free energy landscape, the dynamics of unforced transport of NP across LB is evaluated using the Fokker-Planck equation, which mimics NP diffusion along the free energy landscape with multiple attempts to reach the barrier. We found that the number of attempts required for successful translocation scales exponentially with the energy barrier.

Polymer adsorption is a ubiquitous phenomenon with numerous technological and healthcare applications. The mechanisms of polymer adsorption on surfaces and in pores are complex owing to a competition between various entropic and enthalpic factors. Due to adsorption of monomers to the surface, the chain gains in enthalpy yet loses in entropy because of confining effects. This competition leads to the existence of critical conditions of adsorption when enthalpy gain and entropy loss are in balance. The critical conditions are controlled by the confining geometry and effective adsorption energy, which depends on the solvent composition and temperature. This phenomenon has important implications in polymer chromatography, since the retention at the critical point of adsorption (CPA) is chain length independent. However, the mechanisms of polymer adsorption in pores are poorly understood and there is an ongoing discussion in the theoretical literature about the very existence of CPA for polymer adsorption on porous substrates. In this work, we examine the mechanisms of chain adsorption on a model porous substrate using Monte Carlo (MC) simulations. We distinguish three adsorption mechanisms depending on the chain location: on external surface, completely confined in pores, and also partially confined in pores in so-called “flower” conformations. The free energies of different conformations of adsorbed chains are calculated by the incremental gauge cell MC method that allows one to determine the partition coefficient as a function of the adsorption potential, pore size, and chain length. We confirm the existence of the CPA for chain length independent separation on porous substrates, which is explained by the dominant contributions of the chain adsorption at the external surface, in particular in flower conformations. Moreover, we show that the critical conditions for porous and nonporous substrates are identical and depend only on the surface chemistry. The theoretical results are confirmed by comparison with experimental data on chromatographic separation of a series of linear polystyrenes.

We demonstrate that in-situ adsorption dilatometry provides a new opportunity for structural characterization of microporous carbons. We present experimental results for CO2 adsorption at 293 K and in-situ deformation obtained by dilatometry on a synthetic monolithic carbon sample. The carbon deformation in the course of adsorption is non-monotonic: the strain isotherm shows the sample contraction at low adsorption followed by progressive expansion. To evaluate structural and mechanical properties of the sample from the experimental adsorption and strain isotherms, a kernel of theoretical adsorption isotherms is obtained with the grand canonical Monte Carlo simulation of CO2 adsorption in a series of carbon micropores ranging from 0.22 to 2.0 nm. The respective kernel of adsorption stress isotherms is constructed using the thermodynamic model of adsorption stress. The pore volume and surface area distributions were calculated independently from a) the experimental excess adsorption isotherm by deconvoluting the generalized adsorption equation and b) the experimental strain isotherm by using the kernel of adsorption stress isotherms. The proposed method of determining the pore size distribution from the strain isotherm validates the thermodynamic model of adsorption stress in micropores and provides additional information about the sample material with respect to mechanical properties of the microporous matrix.

This paper presents a consistent strategy for parametrization of coarse-grained models of chain molecules in dissipative particle dynamics (DPD), where the soft-core DPD interaction parameters are fitted to the activities in solutions of reference compounds that represent different fragments of target molecules. The intercomponent parameters are matched either to the infinite dilution activity coefficients in binary solutions or to the solvent activity in polymer solutions. The respective calibration relationships between activity and intercomponent interaction parameter are constructed from the results of Monte Carlo simulation of the coarse-grained solutions of reference compounds. The chain conformation is controlled by the near neighbor and second neighbor bond potentials, which are parametrized by fitting the intramolecular radial distribution functions of the coarse-grained chains to the respective atomistic molecular dynamics simulations. The consistency, accuracy, and transferability of the proposed parametrization strategy is demonstrated drawing on the example of nonionic surfactants of the poly(ethylene oxide) alkyl ether (CnEm) family. The lengths of tail and head sequences are varied (n = 8-12 and m = 3-9), so that the critical micelle concentration ranges from 10 to 0.1 mM. The surfactants are modeled at different coarse-graining levels using DPD beads of different diameters. We found consistent agreement with experimental data for the critical micelle concentration and aggregation number, especially for surfactants with relatively long hydrophilic segments. Depending on the system, we observed surfactant aggregation into spheroidal, elongated, or core-shell micelles, as well as into irregular agglomerates. Using the models at different coarse-graining levels for the same molecules, we found that the smaller the bead size the better is agreement with experimental data.

In-situ growth of nanometer size metal oxide crystallites within polyelectrolyte block-copolymer membranes is demonstrated with example of ZnO loaded Nexar and SEBS films. The proposed method allows for the controlled synthesis of ZnO nanoparticles ranging from 2 to 8 nm uniformly dispersed within the membranes. The fabricated films are characterized with XRD, TEM and HAADF-STEM techniques. It is shown that particles size and shape can be tuned by varying the solvent composition. Addition of methanol favors the growth of smaller-sized ZnO. The proposed method can be applied to produce other metal oxide – polyelectrolyte nanocomposites, which may find various applications ranging from fuel cells and other electrochemical devices to separation membranes and protective barriers.

Phonons are quantum elastic excitations of crystalline solids. Classically, they correspond to the collective vibrations of atoms in ordered periodic structures. They determine the thermodynamic properties of solids and their stability in the case of structural transformations. Here we review for the first time the existing examples of the phonon analysis of adsorption-induced transformations occurring in microporous crystalline materials. We discuss the role of phonons in determining the mechanism of the deformations. We point out that phonon-based methodology may be used as a predictive tool in characterization of flexible microporous structures; therefore, relevant numerical tools must be developed.

International audience; The use of the osmotic thermodynamic model, combined with a series of methane and carbon dioxide gas adsorption experiments at various temperatures, has allowed shedding some new light on the fascinating phase behavior of flexible MIL-53(Al) metal−organic frameworks. A generic temperature-loading phase diagram has been derived; it is shown that the breathing effect in MIL-53 is a very general phenomenon, which should be observed in a limited temperature range regardless of the guest molecule. In addition, the previously proposed stress model for the structural transitions of MIL-53 is shown to be transferable from xenon to methane adsorption. The stress model also provides a theoretical framework for understanding the existence of lp/np phase mixtures at pressures close to the breathing transition pressure, without having to invoke an inhomogeneous distribution of the adsorbate in the porous sample.

Reliable measurement of permeability of membranes with respect of different chemical compounds is of paramount importance for the design of novel materials for selective separations, protective barriers against chemical warfare agents and toxic industrial chemicals. An original in-situ Raman spectroscopy experimental setup is devised to measure the dynamics of permeation of toxins with example of diffusion of dimethyl methylphosphonate (DMMP), a nerve agent surrogate, across polyelectrolyte composite membranes. Efficiency of the proposed method is demonstrated on two types of commercial membranes, Nafion 117 and Nexar MD9200, modified with metal oxide nanoparticles. It was found that loading membranes with ZnO nanoparticles significantly reduces agent permeation, enhancing its protective capabilities against hazardous substances. The proposed methodology can be adopted and applied for characterization of permeability of other types of CWAs, their simulants, and other chemicals through polymeric membranes of different origin.

Despite extensive research over the last several decades, the microscopic characterization of topological phases of adsorbed phenol from aqueous solutions in carbon micropores (pore size < 2.0 nm), which are believed to exhibit a solid and quasi-solid character, has not been reported. Here, we present a combined experimental and molecular level study of phenol adsorption from neutral water solutions in graphitic carbon micropores. Theoretical and experimental results show high adsorption of phenol and negligible coadsorption of water in hydrophobic graphitic micropores (super-sieving effect). Graphic processing unit-accelerated molecular dynamics simulation of phenol adsorption from water solutions in a realistic model of carbon micropores reveal the formation of two-dimensional phenol crystals with a peculiar pattern of hydrophilic-hydrophobic stripes in 0.8 nm supermicropores. In wider micropores, disordered phenol assemblies with water clusters, linear chains, and cavities of various sizes are found. The highest surface density of phenol is computed in 1.8 nm supermicropores. The percolating water cluster spanning the entire pore space is found in 2.0 nm supermicropores. Our findings open the door for the design of better materials for purification of aqueous solutions from nonelectrolyte micropollution.

Tension-induced rupture of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) lipid membranes with encapsulated hydrophobic nanoparticles is elucidated using dissipative particle dynamics simulations. The dynamics of hole formation is studied, and a nanoparticle size-dependent relationship is established for the probability of membrane rupture within a given time as a function of the membrane tension. Two mechanisms of hole formation are explored: homogeneous nucleation and heterogeneous nucleation at the nanoparticle surface. While the kinetics of homogeneous nucleation in unloaded membranes complies with the predictions of the classical Deryagin-Gutop (DG) theory, the heterogeneous nucleation causes progressively lower lysis tensions as the particle size increases. The thermodynamics of heterogeneous nucleation is treated by introducing an effective contact angle at the three-phase, solvent-membrane-solid boundary into the DG theory. The proposed approach helps quantitatively interpret the simulation results and predict the membrane stability in real experiments with significantly larger (by many orders of magnitude) observation times and spatial scales.

Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the adsorbates and their porous host materials. But, although the interactions of adsorbate molecules with the internal MOF surface and also amongst themselves within individual pores have been extensively studied, adsorbate-adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range adsorbate-adsorbate interactions and the formation of adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption-desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of 'extra adsorption domains'-that is, domains spanning several neighbouring pores, which have a higher adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.

Using dissipative particle dynamics (DPD) simulations, we explore the specifics of micellization in the solutions of anionic and cationic surfactants and their mixtures. Anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) are chosen as characteristic examples. Coarse-grained models of the surfactants are constructed and parameterized using a combination of atomistic molecular simulation and infinite dilution activity coefficient calibration. Electrostatic interactions of charged beads are treated using a smeared charge approximation: the surfactant heads and dissociated counterions are modeled as beads with charges distributed around the bead center in an implicit dielectric medium. The proposed models semiquantitatively describe self-assembly in solutions of SDS and CTAB at various surfactant concentrations and molarities of added electrolyte. In particular, the model predicts a decline in the free surfactant concentration with the increase of the total surfactant loading, as well as characteristic aggregation transitions in single-component surfactant solutions caused by the addition of salt. The calculated values of the critical micelle concentration reasonably agree with experimental observations. Modeling of catanionic SDS-CTAB mixtures show consecutive transitions to worm-like micelles and then to vesicles caused by the addition of CTAB to micellar solution of SDS.

We suggest a coarse-grained model for dissipative particle dynamics (DPD) simulations of solutions with dissociated protons. The model uses standard short-range soft repulsion and smeared charge electrostatic potentials between the beads, representing solution components. The proton is introduced as a separate charged bead that forms dissociable bonds with proton receptor base beads, such as water or deprotonated acid anions. The proton-base bonds are described by Morse potentials. When the proton establishes the Morse bonds with two bases, they form an intermediate complex, and the proton is able to "hop" between the bases artificially mimicking the Grotthuss diffusion mechanism. By adjusting the Morse potential parameters, one can regulate the potential barrier associated with intermediate complex formation and breakup and control the hopping frequency. This makes the proposed model applicable to simulations of proton mobility and reaction equilibria between protonated and deprotonated acid forms in aqueous solutions. The proposed model provides quantitative agreement with experiments for the proton self-diffusion coefficient and hopping frequency, as well as for the degree of dissociation of benzenesulfonic acid.

Lipid bilayers attached to solid surfaces play an important role in bioinspired materials and devices and serve as model systems for studies of interactions of cell membranes with particles and biomolecules. Despite active experimental and theoretical studies, the interactions of lipid membranes with solid substrates are still poorly understood. In this work, we explore, using atomistic molecular dynamics simulations, the equilibrium and stability of a phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine membrane supported on hydroxylated amorphous silica. We reveal two distinct types of thermodynamically stable states, characterized by different widths of the water layer between the membrane and the substrate. In α-states, the membrane is closely attached with the lipid head groups interacting directly with surface hydroxyls; however, because of the molecular level roughness of the amorphous silica surface, there exists an inhomogeneous water layer trapped between the substrate and the membrane. In β-states, the membrane is separated from the silica surface by a water film of ∼2.5 nm in thickness. The thermodynamic equilibrium is quantified in terms of the disjoining pressure isotherm as a function of membrane-substrate separation, which has a double sigmoidal shape with two minima and one maximum, which correspond to the limits of stability of α- and β-states. The thermodynamic properties and bilayer structure are compared with experimental findings and simulation results for relevant systems.