Physics at Lancaster University

Room: A56 Physics Building
Tel: +44 (0)1524 593219
Fax: +44 (0)1524 844037
EMail: h Dot M hyphen Pollock At Lancaster Dot AC Dot Uk

Research Interests

Micro-thermal Analysis:

This new technique, developed in collaboration with Loughborough University, TA Instruments, and the TopoMetrix Corporation, provides microscope images at sub-micron resolution, whose contrast is determined by the variation of thermal properties across the specimen. It is being used to study phase changes, glass transitions, etc. and may well partly replace electron microscopy for such purposes. L-CA (localised calorimetric analysis) and L-TMA (localised thermomechanical analysis) both build upon this "scanning thermal microscopy" technique, in order to add spatial resolution to two well-established methods of chemical fingerprinting: these (respectively) are modulated-temperature differential scanning calorimetry (M-T DSC) and dynamic mechanical analysis (DMA). In both cases, a temperature ramp is used to subject the sample to "events" such as a glass transition or melting. In MT-DSC, a cyclic heat flow signal `sees' only the reversible heat capacity associated with molecular vibrations, whereas the underlying measurement also sees endotherms and exotherms associated with kinetically-controlled events. In DMA, the thermal events are revealed through changes in the real and imaginary parts of the elastic modulus. L-FTIR (localised Fourier transform infrared spectroscopy) allows the microscopic identification of areas that are selectively heated by absorption of infrared radiation: the aim is to develop a version of FTIR having sub-micron spatial resolution. For more detail, please see http://www.lancs.ac.uk/users/spc/Research/CondMatt/Micro/Micro.html

Other work involves studying the micro-mechanical properties of surfaces, where data are obtained from nanoindentation, adhesion, force spectroscopy and creep experiments. This work relates to the broader topics of adhesion, wear and powder compaction.

Nanoindentation:

We developed the most sensitive hardness tester ever made. It has been used for:

• explaining the mechanism of the POLISHING WEAR of ion-implanted titanium/aluminium alloys (with NRL Washington),
• indenting individual grains of pharmaceutical powders (with ICI Pharmaceuticals),
• measuring the room-temperature creep rate of salt, and correlating the results with its resistance to ATTRITION in chemical engineering processes (with Surrey University and with Brunner Mond and Company), measuring the near-surface properties of nylon, P.E.T., and other polymers (depths as small as 150 nanometres), with ICI Technology.

Measuring Surface Forces:

As well as for imageing, we use an atomic force microscope in non-scanning mode ("ATOMIC FORCE SPECTROSCOPY) to plot curves of surface force against separation. This technique offers a simple and extremely sensitive indication of surface condition (e.g. it will detect a fluorinated monolayer on diamond). We argue that the existence of PATCH CHARGES can be important here. They arise whenever there are variations in work function over a surface.

Little is known about the forces that act between individual powder particles. This new technique of AFS allows these forces to be quantified. Useful predictions of the effects of surface treatments on powder flow and compaction will be possible.