Papers by Rustem Valiullin
Mass transfer processes in which specific interactions with environments lead to complex diffusio... more Mass transfer processes in which specific interactions with environments lead to complex diffusion patterns, such as the occurrence of transient sub-diffusive behaviors or of heterogeneous diffusion, were studied by means of two different experimental techniques, namely single-particle tracking operating with single molecules and nuclear magnetic resonance operating with large molecular ensembles. As an important point, the combined application of these techniques allowed for a deeper insight into the microscopic diffusion mechanism in such complex systems, including those with broken ergodicity. Particle tracking concentrated on the "Influence of substrate surface properties on heterogeneous diffusion of probe molecules in ultrathin liquid films". The mobility of liquids at solid-liquid interfaces is influenced by substrate heterogeneities. Here we study the distribution of surface silanols on differently treated silicon wafers with thermal oxide by confocal florescence microscopy of adsorbed Rhodamine G molecules. We further investigate the influence of the substrate properties on probe molecule diffusion in ultrathin liquid TEHOS films by single molecule tracking. The results are compared to simulations of two-layer diffusion employing heterogeneous substrates. Nuclear magnetic resonance has been applied to study translational diffusion of small organic molecules in nanopores and of polymer globules in the presence of larger polymer species. In both cases, the experiments revealed the occurrence of normal diffusion on the time scale of NMR experiments from ten to hundreds of milliseconds. While single particle tracking revealed the identical diffusivities for the former case, thus experimentally confirming the validity of the ergodicity theorem for diffusion, the discrepancies were noted for the latter case. More complex behavior revealing non-ergodic © 2015, T. Albers et al. 2 diffusion-fundamentals.org 23 (2015) 3, pp 1-25 behavior for propagation of solid-liquid interfaces in disordered nanopores has further been studied using nuclear magnetic resonance cryoporometry. A common basis for comparing and analyzing the experimental observables accessed by the two methods is the distribution of diffusivities, which provides the probability of observing a given diffusivity fluctuation along a trajectory or in an ensemble. An overview of its properties is given and the advantages in analyzing heterogeneous, anisotropic, or anomalous diffusion processes are elaborated.
Soft Matter, 2011
Diffusion in a series of ionic liquids is investigated by a combination of Broadband Dielectric S... more Diffusion in a series of ionic liquids is investigated by a combination of Broadband Dielectric Spectroscopy (BDS) and Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). It is demonstrated that the mean jump lengths increase with the molecular volumes determined from quantum-chemical calculations. This provides a direct means-via Einstein-Smoluchowski relation-to determine the diffusion coefficient by BDS over more than 8 decades unambiguously and in quantitative agreement with PFG NMR measurements. New possibilities in the study of charge transport and dynamic glass transition in ionic liquids are thus opened.
Adsorption-journal of The International Adsorption Society, Nov 6, 2010
The formation of adsorption hysteresis in mesoporous material with random pore structure may be i... more The formation of adsorption hysteresis in mesoporous material with random pore structure may be interrelated with different distributions of the fluid density attained along different paths of the system preparation. To access microscopic details of these distributions, in addition to the main sorptive liquid, distribution of which along the pore space of Vycor porous glass was of interest, a small
Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Sep 30, 2008
Adsorption-journal of The International Adsorption Society, Apr 15, 2016
The rate of mass transfer is among the key numbers determining the efficiency of nanoporous mater... more The rate of mass transfer is among the key numbers determining the efficiency of nanoporous materials in their use for matter upgrading by heterogeneous catalysis or mass separation. Transport enhancement by pore space optimization is, correspondingly, among the main strategies of efficiency promotion. Any such activity involves probing and testing of the appropriate routes of material synthesis and post-synthesis modification just as the exploration of the transport characteristics of the generated material. Modelling and molecular simulation is known to serve as a most helpful tool for correlating these two types of activities and their results. The present paper reports about a concerted research activity comprising these three types of activities. Recent progress in producing pore space replicas enabled focusing, in these studies, on ''complementary'' pore spaces, i.e. on pairs of material, where the pore space of one sample did just coincide with the solid space of the other. We report about the correlations in mass transfer as observable, in this type of material, by pulsed field gradient NMR diffusion studies, with reference to the prediction as resulting from a quite general, theoretical treatment of mass transfer in complementary pore spaces.
Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Jul 24, 2015
Journal of Physical Chemistry C, Oct 18, 2017
A silicious material containing massive array of spherical nanocages connected to each other by s... more A silicious material containing massive array of spherical nanocages connected to each other by small micropores was used to study ice nucleation in conned water under conditions of welldened pore geometry. By purposefully selecting small size of the interconnecting pores below 2 nm, ice nucleation and growth were limited to occur only within the nanocages. By exploiting nuclear magnetic resonance ice nucleation rates at dierent temperatures were accurately measured. These rates were obtained to be substantially higher than those obtained for micrometer-sized water droplets in air. In addition, the occurrence of correlations between ice nucleation in one nanocage with the phase state in the adjacent cages were observed. These results have important implication for a deeper understanding of ice nucleation, especially in conned geometries. 1
Scientific Reports, Jan 20, 2017
Nanoporous silicon produced by electrochemical etching of highly B-doped p-type silicon wafers ca... more Nanoporous silicon produced by electrochemical etching of highly B-doped p-type silicon wafers can be prepared with tubular pores imbedded in a silicon matrix. Such materials have found many technological applications and provide a useful model system for studying phase transitions under confinement. This paper reports a joint experimental and simulation study of diffusion in such materials, covering displacements from molecular dimensions up to tens of micrometers with carefully selected probe molecules. In addition to mass transfer through the channels, diffusion (at much smaller rates) is also found to occur in directions perpendicular to the channels, thus providing clear evidence of connectivity. With increasing displacements, propagation in both axial and transversal directions is progressively retarded, suggesting a scale-dependent, hierarchical distribution of transport resistances ("constrictions" in the channels) and of shortcuts (connecting "bridges") between adjacent channels. The experimental evidence from these studies is confirmed by molecular dynamics (MD) simulation in the range of atomistic displacements and rationalized with a simple model of statistically distributed "constrictions" and "bridges" for displacements in the micrometer range via dynamic Monte Carlo (DMC) simulation. Both ranges are demonstrated to be mutually transferrable by DMC simulations based on the pore space topology determined by electron tomography.
Chemical Society Reviews, 2016
Adding mesopore networks in microporous materials using the principles of hierarchical structure ... more Adding mesopore networks in microporous materials using the principles of hierarchical structure design is recognized as a promising route for eliminating their transport limitations and, therefore, for improving their value in technological applications. Depending on the routes of physico-chemical procedures or post-synthesis treatments used, very different geometries of the intentionally-added transport mesopores can be obtained. Understanding the structure-dynamics relationships in these complex materials with multiple porosities under different thermodynamical conditions remains a challenging task. In this review, we summarize the results obtained so far on experimental and theoretical studies of diffusion in micromesoporous materials. By considering four common classes of bi-porous materials, which are differing by the inter-connectivities of their sup-spaces as one of the most important parameter determining the transport rates, we discuss their generic transport properties and correlate the results delivered by the equilibrium and non-equilibrium techniques of diffusion measurements.
Chemical Society Reviews, 2013
Angewandte Chemie, Mar 25, 2018
Nuclear magnetic resonance (NMR) cryoporometry is an experimental technique for the structural ch... more Nuclear magnetic resonance (NMR) cryoporometry is an experimental technique for the structural characterization of mesoporous materials. In this updated review, different aspects of its application to study details of the pore structure in mesoporous silicon are presented. In particular, the information obtained with the help of NMR cryoporometry is compared to that assessed using more conventional gas sorption techniques. The potentials of NMR cryoporometry to reveal fine details of the pore structure in intentionally nanostructured mesoporous silicon are demonstrated. The technique’s ability to monitor structural evolution in liquids is also starting to find uses in biomedical applications such as drug delivery.
Magnetic Resonance in Solids. Electronic Journal, 2014
The process of self-diffusion of particles confined to porous solids is studied for time interval... more The process of self-diffusion of particles confined to porous solids is studied for time intervals corresponding to particle displacements shorter than the characteristic pore size. The solid matrix is modeled as a (random) potential field with an infinitely large potential within the solid which decays to zero at distances of the order of a few particle sizes from the pore walls. Diffusion of particles in the thus created potential field is described by the Smoluchowski diffusion equation. It is shown that, for short diffusion times, the resulting equation for the time-depended diffusivity reproduces that earlier obtained in the literature [Mitra et al., Phys. Rev. Lett. 68, 3555 (1992)], but with the numerical constant differing by factor 2. The conditions under which this discrepancy arises are highlighted and discussed.
Ensembles of molecules confined to mesopore spaces reveal features which may notably deviate from... more Ensembles of molecules confined to mesopore spaces reveal features which may notably deviate from their behavior both in the bulk phase and under dominating host-guest interaction. A previous detailed investigation of molecular dynamics in Vycor porous glass with a pore diameter of 6 nm using pulsed field gradient nuclear magnetic resonance (PFG NMR) indicated that under identical external conditions (temperature, pressure), different "histories" of sample preparation may give rise to dramatic differences in their microdynamics [1-3]. One approach to rationalize the occurrence of historydependent states in mesoporous host-guest systems is the occurrence of a geometric disorder-induced rugged landscape in the free energy. To get deeper insight into this phenomenon, novel options provided by the development of IR micro-imaging [4] have been used in the present work.
Magnetic Resonance Imaging, May 1, 2007
Angewandte Chemie, Dec 16, 2011
ABSTRACT Coincidence between the mean squared displacements determined for the same molecule over... more ABSTRACT Coincidence between the mean squared displacements determined for the same molecule over sequential time intervals and for all molecules over the same time interval follows as a consequence of the ergodic theorem. In their Communication (DOI: 10.1002/anie.201105388), C. Bräuchle et al. confirm experimentally this fundamental principle of thermodynamics by diffusion studies using fluorescence microscopy and NMR ensemble measurements with pulsed field gradients.
Angewandte Chemie, Dec 19, 2011
Übereinstimmung … … zwischen den mittleren quadratischen Verschiebungen, die für dasselbe Molekül... more Übereinstimmung … … zwischen den mittleren quadratischen Verschiebungen, die für dasselbe Molekül während aufeinanderfolgender Zeitintervalle sowie für alle Moleküle im selben Zeitintervall bestimmt wurden, ergibt sich aus dem Ergodentheorem. In der Zuschrift auf S. 1178 ff. bestätigen C. Bräuchle et al. dieses Prinzip der Thermodynamik mithilfe von Diffusionsuntersuchungen unter Verwendung von Fluoreszenzmikroskopie und NMR-Spektroskopie mit gepulsten Feldgradienten.
Nucleation and Atmospheric Aerosols, 2011
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Papers by Rustem Valiullin