Functional Materials Group

Research into the Physics of Liquids and Solids on the Nano- to Meso-Scale Dr. J.B.W. Webber.

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Nano-science :

We have now been studying the structure, dynamics and phases of nano-structured to micro-structured liquids and their solids for more than 15 years, and are actively unraveling the behaviour of liquids in confined geometry, and at and near surfaces. Even so there is much that we still need to understand about even such basic systems as water in a silica pore.

Much of this basic research has been carried out at the University of Kent, some of the recent work in conjunction with Heriot Watt University, and Lab-Tools are intending to continue these investigations in conjunction with both universities, and in the Lab-Tools NMR laboratory, both as research of great interest in its own right, but also as needed to support the metrology development. Dr. Beau Webber has also been awarded a total of 88 days of neutron scattering time to aid these studies (23 days as main proposer), at the central facilities at the Institute Laue Langevin in Grenoble (ILL); Laboratoire Leon Brillouin (LLB), Saclay, Paris; at the Jülich Centre for Neutron Science (JCNS), Germany, and ISIS at the Rutherford Lab. , to investigate this nano-science and nano-metrology.

Our main experimental techniques are based on: NMR relaxation, NMR cryoporometry (figure 2), NMR diffusion in a magnetic gradient, Neutron Diffraction (NS), Small Angle Neutron Scattering (SANS) (figure 3), Quasi-Elastic Neutron Scattering (QENS) X-ray Scattering, N2 Gas Adsorption, Differential Scanning Calorimetry (DSC) and Thermoporosimetry. Our analytic and simulation techniques include: Direct analytic/numerical calulation of small angle neutron scattering from model porous systems, and their alignment to measured scattering results. ab-initio Quantum Mechanical - Molecular Dynamic simulation of liquids at and near surfaces, in model porous systems - Figure 1.

Figure 1: 3D model of laminar silicon porous system, with surface films of liquid nitrogen - one timestep from a CASTEP ab-initio QM MD simulation.

Nano-scale to micro-scale metrology :

We have completed a number of academic research projects and industrial and commercial analysis projects using the techniques that we have developed.

Following the above basic research into the behaviour of liquids and their solids in confined geometry, in well characterised porous materials, we then apply this by imbibing these liquids into as yet uncharacterised porous systems, and use the knowledge that we have gained about the changes in their physical properties, when nano-structured, to deduce information about the host porous structure and metrology.

The basic techniques that use these changes in the thermodynamic properties in nano-structured systems are : Gas adsorption, Thermoporosimetry, NMR Cryoporometry. Of these techniques, NMR Cryoporometry is now often our preferred technique, although the others may provide invaluable comparative information. We have used NMR Cryoporometry in a number of academic research projects and industrial contracts, to measure pore volumes and pore size distributions in materials such as porous carbons, fired and un-fired clays, marine sediments, oil-bearing rocks, meteorite fragments .... More detailed information about NMR Cryoporometry is available by following the link below to our NMR Cryoporometry pages.

Figure 2: Normalised pore size distributions for selected porous silicas, as measured by NMR Cryoporometry. The intrinsic resolution of the technique is better than the red curve, for SBA-15, which is fully resolved.

Lab-Tools performs contract analyses of Pore Size Distributions using NMR Cryoporometry : Lab-Tools has measured pore sizes in a wide range of materials, and the technique can be applied to oil and/or water wet materials, and also to materials that can not be dried out without losing their structure. The Lab-Tools pore-size distribution measurement range extends from about 1nm up to over 2µm. Please contact us to discuss pore size measurements on your samples. Prices are competitive, but depend on the pore-size range to be covered, and precision needed. We frequently find these techniques may be preferable to more established methods such as BET gas adsorption or DSC thermal porisimetry.

X-ray and neutron scattering based metrology calibration program :

With all these thermodynamic techniques, however there is increasingly a supposition that as atomic dimensions are approached, the calibration from the thermodynamics may change. Thus we have mounted a separate metrology program using neutron and X-ray scattering. These have the advantage that they are inverse techniques, by which is meant that the smaller the structure being observed, the larger is the scattering angle. Further, there is no existing reason to suppose that these scattering techniques are length-scale dependent. i.e. if one has a good calibration at one length-scale, it should also be good at all other length-scales. To transform a measured scattering to a metric of the structures in the sample, we create extended models of pore systems, and calculate the scattering using numerical integration. These show very good agreement with measured scattering, figure 3. Our existing measurements using sol-gel silicas have shown that while the thermodynamic techniques are in close agreement with the scattering measurements for dimensions above 10nm, below this dimension there appears to be an increasing divergence between the scales of the thermodynamic and scattering metrologies. Dr. Beau Webber has been awarded measurement time at the Institute Laue Langevin (ILL), on the D4 and D22 instruments, and this has enabled him to develop and verify his models. Dr. Beau Webber was recently awarded measurement time (as first user) on the excellent new wide-scattering range ISIS Target Station 2 instrument NIMROD, and 17 porous samples were measured on this most successful run, with very pleasing preliminary results. Simulation models are being run to match the results, and the models, results and conclusions will be presented in a paper.

Figure 3: Fully density corrected radial distribution function measured for 7 sol-gel silicas (red lines), compared with that calculated for extended arrays of pores with Gaussian variance (green dots).

Cryoporometry pages

Porous Media pages

Publications

• Combined publications list
• Prof. John Dore
• Prof. John Strange
• Dr. Beau Webber