News Flash  

Sep. 2016: Second Workshop on Hierarchical Materials in Erlangen: RV with invited lecture on transport properties of hierarchical porous solids.

Sep. 2015: IUPAC has established the task group "Diffusion in nanoporous solids" involving us as the active members.

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Sep. 2015Our work on diffusion in hollow core-shell nanoparticles just appeared in Langmuir.

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Seminars  

R. Valiullin: Mesoporous materials -- Perspectives revealed by fluids confined in their pore spaces
Mo, 27.06.2016, 17:15–18:00
Universität Hamburg, Fachbereich Chemie, Martin-Luther-King-Platz 6, Hörsaal C

October 21-23, 2015
R. Valiullin: NMR Cryoporometry: From fundamentals to application
Workshop: Methods of Porosimetry and Applications (HZDR Dresden-Rossendorf)

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In the same way as mesoscopic confinements give rise to a rich dynamic behavior of confined fluids, mesoscopic organization of matter and interactions developing on mesoscales may lead to similar phenomena in soft-matter systems. Examples of such situations include the occurrence of sub-diffusion in crowded environments, cage effects in colloids, and complex structure-dynamics relationships in liquid crystals. We use the pulsed field gradient technique of NMR to probe translational dynamics in complex soft-matter. One of our particular goals is developing a unified experimental and theoretical concept for comparing the results of single-particle tracing and ensemble-based techniques. An important example we may refer to in this respect is the first experimental proof of the ergodic theorem by measuring the diffusivity of guest molecules inside a nano-structured porous glass. The data obtained through the direct observation of dye molecule diffusion by single-molecule tracking experiments, i.e. the time-average, was found to be in perfect agreement with the ensemble value obtained in NMR experiments.    

  1. A Shakhov, R Valiullin and J Kärger. Tracing Molecular Propagation in Dextran Solutions by Pulsed Field Gradient NMR. J. Phys. Chem. Lett. 3:1854-1857, 2012. BibTeX

    @article{Shakhov2012,
    	author = "Shakhov, A. and Valiullin, R. and Kärger, J.",
    	title = "Tracing Molecular Propagation in Dextran Solutions by Pulsed Field Gradient NMR",
    	journal = "J. Phys. Chem. Lett.",
    	volume = 3,
    	pages = "1854-1857",
    	year = 2012
    }
    
  2. F Feil, S Naumov, J Michaelis, R Valiullin, D Enke, J Kärger and C Bräuchle. Single-Particle and Ensemble Diffusivities—Test of Ergodicity. Angew. Chem. 124:1178-1181, 2012. BibTeX

    @article{Feil2012,
    	author = "Feil, F. and Naumov, S. and Michaelis, J. and Valiullin, R. and Enke, D. and Kärger, J. and Bräuchle, C.",
    	title = "Single-Particle and Ensemble Diffusivities—Test of Ergodicity",
    	journal = "Angew. Chem.",
    	volume = 124,
    	pages = "1178-1181",
    	year = 2012
    }
    
  3. J R Sangoro, C Iacob, S Naumov, R Valiullin, H Rexhausen, J Hunger, R Buchner, V Strehmel, J Kärger and F Kremer. Diffusion in ionic liquids: the interplay between molecular structure and dynamics. Soft Matter 7:1678-1681, 2011. BibTeX

    @article{Sangoro2011,
    	author = "Sangoro, J. R. and Iacob, C. and Naumov, S. and Valiullin, R. and Rexhausen, H. and Hunger, J. and Buchner, R. and Strehmel, V. and Kärger, J. and Kremer, F.",
    	title = "Diffusion in ionic liquids: the interplay between molecular structure and dynamics",
    	journal = "Soft Matter",
    	volume = 7,
    	pages = "1678-1681",
    	year = 2011
    }
    
  4. M G Mazza, M Greschek, R Valiullin, J Kärger and M Schoen. Entropy-driven enhanced self-diffusion in confined reentrant supernematics. Phys. Rev. Lett. 105:227802, 2010. BibTeX

    @article{Mazza2010,
    	author = "Mazza, M. G. and Greschek, M. and Valiullin, R. and Kärger, J. and Schoen, M.",
    	title = "Entropy-driven enhanced self-diffusion in confined reentrant supernematics",
    	journal = "Phys. Rev. Lett.",
    	volume = 105,
    	pages = 227802,
    	year = 2010
    }
    

 

 

 

 

Among different experimental techniques, NMR cryoporometry provides unique options to probe various details of solid-liquid equilibria in porous solids. In particular, by applying specially designed nuclear magnetic relaxation filters, the phase composition of confined matter and its evolution upon temperature changes can directly be probed. In our work, we use this technique to study freezing and melting transitions of fluids confined to mesoporous host materials. These materials include ones with ordered and disordered pore structures, such as random porous glasses, ordered silicas, or nano-structured mesoporous silicon. With the experimental conditions under which our studies are performed, freezing closely resembles the process of layer-by-layer crystal growth. The kinetics of this process is essentially determined by the pore structure and the thermodynamic conditions with the occurrence of a multitude of metastable configurational states. Melting is controlled by similar mechanisms, but can appear more intricate. Due to their complexity, the analysis of the experimental data obtained on melting in freezing in confined spaces require the application of teoretical models capturing the microscopic details of solid-liquid equilibria. In our work, we base our analysis on the Kosel-Stranski crystal growth model, which we have recently adopted for confined fluids.

  1. D Kondrashova and R Valiullin. Freezing and Melting Transitions under Mesoscalic Confinement: Application of the Kossel–Stranski Crystal-Growth Model. J. Phys. Chem. C 119(8):4312-4323, 2015. BibTeX

    @article{2015,
    	author = "Kondrashova, D. and Valiullin, R.",
    	title = "Freezing and Melting Transitions under Mesoscalic Confinement: Application of the Kossel–Stranski Crystal-Growth Model",
    	journal = "J. Phys. Chem. C",
    	volume = 119,
    	number = 8,
    	pages = "4312-4323",
    	year = 2015
    }
    
  2. D Kondrashova and R Valiullin. Improving structural analysis of disordered mesoporous materials using NMR cryoporometry. Microporous Mesoporous Mat. 178:15-19, 2013. BibTeX

    @article{2013,
    	author = "Kondrashova, D. and Valiullin, R.",
    	title = "Improving structural analysis of disordered mesoporous materials using NMR cryoporometry",
    	journal = "Microporous Mesoporous Mat.",
    	volume = 178,
    	pages = "15-19",
    	year = 2013
    }
    
  3. D Kondrashova, M Dvoyashkin and R Valiullin. Structural characterization of porous solids by simultaneously monitoring the low-temperature phase equilibria and diffusion of intrapore fluids using nuclear magnetic resonance. New J. Phys. 13:015008, 2011. BibTeX

    @article{2011,
    	author = "Kondrashova, D. and Dvoyashkin, M. and Valiullin, R.",
    	title = "Structural characterization of porous solids by simultaneously monitoring the low-temperature phase equilibria and diffusion of intrapore fluids using nuclear magnetic resonance",
    	journal = "New J. Phys.",
    	volume = 13,
    	pages = 015008,
    	year = 2011
    }
    
  4. D Kondrashova, C Reichenbach and R Valiullin. Probing pore connectivity in random porous materials by scanning freezing and melting experiments. Langmuir 26:6380-6385, 2010. BibTeX

    @article{2010,
    	author = "Kondrashova, D. and Reichenbach, C. and Valiullin, R.",
    	title = "Probing pore connectivity in random porous materials by scanning freezing and melting experiments",
    	journal = "Langmuir",
    	volume = 26,
    	pages = "6380-6385",
    	year = 2010
    }
    
  5. M Dvoyashkin, A Khokhlov, R Valiullin and J Kärger. Freezing of fluids in disordered mesopores. J. Chem. Phys. 129:154702-6, 2008. BibTeX

    @article{2008,
    	author = "Dvoyashkin, M. and Khokhlov, A. and Valiullin, R. and Kärger, J.",
    	title = "Freezing of fluids in disordered mesopores",
    	journal = "J. Chem. Phys.",
    	volume = 129,
    	pages = "154702-6",
    	year = 2008
    }
    
  6. A Khokhlov, R Valiullin, J Kärger, F Steinbach and A Feldhoff. Freezing and melting transitions of liquids in mesopores with ink-bottle geometry. New J. Phys. 9:272, 2007. BibTeX

    @article{2007,
    	author = "Khokhlov, A. and Valiullin, R. and Kärger, J. and Steinbach, F. and Feldhoff, A.",
    	title = "Freezing and melting transitions of liquids in mesopores with ink-bottle geometry",
    	journal = "New J. Phys.",
    	volume = 9,
    	pages = 272,
    	year = 2007
    }
    

 

One of the most intriguing phenomena for fluids confined to mesoporous solids is the observation of hysteretic phase transitions. Their development is generally associated with the occurrence of metastable states. In materials with random pore structures, the structural disorder may give rise to very rugged landscapes in the free energy. Depending on the experimental conditions, the system can slowly scramble towards the global equilibrium state. Notably, relaxation dynamics in this regime is barely addressed. By combining different techniques of NMR, we are  able to study macroscopic dynamics accompanying very different phase transitions. In particular, we have shown that, for gas-liquid transitions in disordered mesoporous solids, relaxation dynamics in the hysteresis regime for longer times is dominated by activated barrier crossings between local free energy minima. This is found to be an intrinsically slower process than the relaxation through mass transfer by diffusion which dominates outside the hysteresis regime. Similar observations have been made for liquid-solid transitions occurring in mesoporous solids.

  1. R Valiullin, S Naumov, P Galvosas, J Kärger, H J Woo, F Porcheron and P A Monson. Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials. Nature 443:965-968, 2006. BibTeX

    @article{2006,
    	author = "Valiullin, R. and Naumov, S. and Galvosas, P. and Kärger, J. and Woo, H. J. and Porcheron, F. and Monson, P. A.",
    	title = "Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials",
    	journal = "Nature",
    	volume = 443,
    	pages = "965-968",
    	year = 2006
    }
    
  2. S Naumov, R Valiullin, P A Monson and J Kärger. Probing memory effects in confined fluids via diffusion measurements. Langmuir 24:6429-6432, 2008. BibTeX

    @article{2008,
    	author = "Naumov, S. and Valiullin, R. and Monson, P. A. and Kärger, J.",
    	title = "Probing memory effects in confined fluids via diffusion measurements",
    	journal = "Langmuir",
    	volume = 24,
    	pages = "6429-6432",
    	year = 2008
    }
    
  3. D Kondrashova, C Reichenbach and R Valiullin. Probing pore connectivity in random porous materials by scanning freezing and melting experiments. Langmuir 26:6380-6385, 2010. BibTeX

    @article{2010,
    	author = "Kondrashova, D. and Reichenbach, C. and Valiullin, R.",
    	title = "Probing pore connectivity in random porous materials by scanning freezing and melting experiments",
    	journal = "Langmuir",
    	volume = 26,
    	pages = "6380-6385",
    	year = 2010
    }
    

 

Diffusion is one of the omnipresent phenomena in nature. For fluids confined to mesoporous solids, diffusion, in addition to the complex structure of these materials, is found to be further diversified by their very rich phase behavior. By applying NMR as a non-perturbing experimental technique, we explore the correlations between the phase state and internal dynamics in mesoporous solids in the proximity of the coexistence lines for the entire PT-phase diagram. In turn, we exploit diffusion measurements as a sensitive tool to probe  phase equilibria and material characterization.  In confined systems, different phases may coexist with each other, giving rise to alternations of molecular trajectories between different phases and, in some cases, to severe modifications of the transport mechanisms. In addition, the existence of the interfaces between the domains of different phases, at which quite different boundary conditions (reflecting, adsorbing or partially adsorbing) may apply, makes understanding of the diffusion process a challenging problem. Our current activities in this direction concern the diffusion behavior in the newly emerging class of hierarchical porous solids.

  1. P Zeigermann and R Valiullin. Transport Properties of Gas-Expanded Liquids in Bulk and under Confinement. J. Supercrit. Fluid. 75:43-47, 2013. BibTeX

    @article{Z2013,
    	author = "Zeigermann, P. and Valiullin, R.",
    	title = "Transport Properties of Gas-Expanded Liquids in Bulk and under Confinement",
    	journal = "J. Supercrit. Fluid.",
    	volume = 75,
    	pages = "43-47",
    	year = 2013
    }
    
  2. R Valiullin. Diffusion in Nanoporous Host Systems. Annual Reports on NMR Spectroscopy 79:23-72, 2013. BibTeX

    @article{V2013,
    	author = "Valiullin, R.",
    	title = "Diffusion in Nanoporous Host Systems",
    	journal = "Annual Reports on NMR Spectroscopy",
    	volume = 79,
    	pages = "23-72",
    	year = 2013
    }
    
  3. J Kärger and R Valiullin. Mass Transfer in Mesoporous Materials: The Benefit of Microscopic Diffusion Measurement. Chem. Soc. Rev. 42:4172 - 4197, 2013. BibTeX

    @article{K2013,
    	author = "Kärger, J. and Valiullin, R.",
    	title = "Mass Transfer in Mesoporous Materials: The Benefit of Microscopic Diffusion Measurement",
    	journal = "Chem. Soc. Rev.",
    	volume = 42,
    	pages = "4172 - 4197",
    	year = 2013
    }
    
  4. R Valiullin. Phase State and Dynamics of Fluids in Mesoporous Solids. AIP Conf. Proc. 1330:39-42, 2011. BibTeX

    @article{2011,
    	author = "Valiullin, R.",
    	title = "Phase State and Dynamics of Fluids in Mesoporous Solids",
    	journal = "AIP Conf. Proc.",
    	volume = 1330,
    	pages = "39-42",
    	year = 2011
    }
    
  5. R Valiullin, J Kärger and R Gläser. Correlating phase behaviour and diffusion in mesopores: perspectives revealed by pulsed field gradient NMR. Phys. Chem. Chem. Phys. 11:2833-2853, 2009. BibTeX

    @article{2009,
    	author = "Valiullin, R. and Kärger, J. and Gläser, R.",
    	title = "Correlating phase behaviour and diffusion in mesopores: perspectives revealed by pulsed field gradient NMR",
    	journal = "Phys. Chem. Chem. Phys.",
    	volume = 11,
    	pages = "2833-2853",
    	year = 2009
    }
    
  6. M Dvoyashkin, R Valiullin, J Kärger, W -D Einicke and R Gläser. Direct Assessment of Transport Properties of Supercritical Fluids Confined to Nanopores. J. Am. Chem. Soc. 129:10344-10345, 2007. BibTeX

    @article{2007,
    	author = "Dvoyashkin, M. and Valiullin, R. and Kärger, J. and Einicke, W.-D. and Gläser, R.",
    	title = "Direct Assessment of Transport Properties of Supercritical Fluids Confined to Nanopores",
    	journal = "J. Am. Chem. Soc.",
    	volume = 129,
    	pages = "10344-10345",
    	year = 2007
    }
    

 
 
 
 
   
© Rustem Valiullin, 2006-2013