Mapping amorphous material on a partially crystalline surface: Nanothermal analysis for simultaneous characterisation and imaging of lactose compacts

The use of nanothermal analysis for mapping amorphous and crystalline lactose at a nanoscale is explored. Compressed tablets of amorphous and crystalline lactose (alone and mixed) were prepared and localised thermomechanical analysis (L-TMA) performed using micro- and nanothermal analysis in a addition to single point variable temperature pull-off force measurements. L-TMA was shown to be able to identify the different materials at a nanoscale via measurement of the thermal events associated with the amorphous and crystalline regions, while pull off force measurements showed that the adhesion of the amorphous material increased on approaching the T_g. Imaging was performed isothermally using topographic and pulsed force mode (PFM) measurements; both approaches were capable of discriminating two regions which L-TMA conformed to correspond to the two materials. In addition, force volume imaging (FVI) is suggested as a further approach to mapping the surfaces. We demonstrate that performing heated tip PFM measurements at a temperature close to the T_g allows greater discrimination between the two regions. We therefore suggest that the nanothermal approach allows both characterisation and imaging of partially amorphous surfaces, and also demonstrate that heated tip imaging allows greater discrimination between crystalline and amorphous materials than is possible using ambient studies.