David B. Grandy

Micro‐thermal analysis of polymers: current capabilities and future prospects

The current state of development of micro-thermal analysis (micro-TA) and related techniques are briefly reviewed. Results for a PET/epoxy resin composite and a bilayer polymer film are given as illustrations. Details are given of a new interface that enables the micro-TA unit to be placed inside a conventional FTIR spectrometer to carry out photothermal IR microscopy. New results are presented for a micro-pyrolysis-mass spectroscopy technique. The limitations of the current instrumentation are discussed in terms of the overriding problem being one of spatial resolution. Images obtained using pulsed force mode AFM with a high-resolution heated tip indicate the scope for future development of this technique. The possibility of even higher spatial resolution with other forms of probe are discussed along with the potential for imaging micro-pyrolysis time of flight mass spectroscopy and even tomography. It is concluded that these methods offer excellent prospects for characterising a wide range of polymer systems.

Thermally assisted nanosampling and analysis using micro-IR spectroscopy and other analytical methods

Micro-thermal analysis is a technique in which the probe in a scanning probe microscope is equipped with an ultra-miniature electrical resistor that serves both as a source of heat and a means of measuring temperature. Thermal properties can be imaged and local thermal analysis can be performed by placing the tip on a selected point and linearly ramping its temperature. When a material is softened in this way, the tip often becomes contaminated with the sample. The tip can easily be cleaned by heating it to a temperature high enough to cause the contaminant to decompose. However, prior to this, the contaminant can be analysed by, amongst other techniques, photothermal IR spectroscopy.

The use of micro-thermal analysis as a means of in situ characterisation of a pharmaceutical tablet coat

The technique of micro-thermal analysis (MTA) has been applied to a commercial sugar coated ibuprofen tablet in order to identify the ability of the method to differentiate between the coat and the tablet core and to characterise the thermal properties of both components using localised thermal analysis. Thermal conductivity measurements in conjunction with intensity histogram analysis indicated that differentiation across the coat/core interface was possible, with a bimodal distribution of pixel intensities corresponding to thermal conductivity noted. Localised thermal analysis studies indicated that the bulk response was dominated by the incorporated ibuprofen, with a discontinuity seen at ca. 70–80°C, corresponding to the published melting point of the drug. The coat showed a discontinuity at ca. 220°C that may be reasonably ascribed to the melting process. It was also noted that the coat showed a small discontinuity at a temperature corresponding to the melting of ibuprofen. In summary, the technique was shown to be capable of identifying the core/coat interface using thermal conductivity measurements, while localised thermal analysis experiments enable the operator to perform thermal analysis experiments on the individual components in situ.

Chemical Imaging by Dissolution Analysis: Localized Kinetics of Dissolution Behavior to Provide Two-Dimensional Chemical Mapping and Tomographic Imaging on a Nanoscale

A new approach to achieving chemical mapping on a nanoscale is described that can provide 2D and tomographic images of surface and near-surface structure. The method comprises dissolving material from the surface of the sample by applying a series of aliquots of solvent, then analyzing their contents after removing them; in between exposures, the surface is imaged with atomic force microscopy. This technique relies on being able to compensate for any drift between images by use of software. It was applied to a blend of two polymers, PMMA and PS. The analytical data identified the material that was dissolved, and the topography images enabled the location of the various materials to be determined by analyzing local dissolution kinetics. The prospects for generalizing the approach are discussed.

A High Resolution Multiple Analysis Approach Using Near‐Field Thermal Probes

We have been developing new analytical techniques using resistive type thermal probes, as employed in scanning thermal microscopy (SThM), to implement different measurement mechanisms. The same active sensor is used to probe chemical, morphological and physical properties of the surface of materials with high spatial resolution. As well as providing passive (temperature) and active (thermal properties) mapping of the surface of a sample, the probe is used to perform localised thermo‐mechanical measurement similar to that achieved by bulk techniques such as differential scanning calorimetry (DSC) and thermo‐mechanical analysis (TMA). Photothermal infrared micro‐spectroscopy and spatially resolved pyrolysis mass spectrometry are also implemented by interfacing a scanning probe microscope to a FTIR spectrometer and a mass spectrometer respectively. An approach to multiple analysis, based on proximal probe methodology and using the same sensor to obtain different information from precisely the same area is thus established. Effective data correlation and identifications of species is hence possible with high spatial resolution. The techniques, their implementation and continuous development are described and typical results obtained from measurements on polymeric materials are presented.We have been developing new analytical techniques using resistive type thermal probes, as employed in scanning thermal microscopy (SThM), to implement different measurement mechanisms. The same active sensor is used to probe chemical, morphological and physical properties of the surface of materials with high spatial resolution. As well as providing passive (temperature) and active (thermal properties) mapping of the surface of a sample, the probe is used to perform localised thermo‐mechanical measurement similar to that achieved by bulk techniques such as differential scanning calorimetry (DSC) and thermo‐mechanical analysis (TMA). Photothermal infrared micro‐spectroscopy and spatially resolved pyrolysis mass spectrometry are also implemented by interfacing a scanning probe microscope to a FTIR spectrometer and a mass spectrometer respectively. An approach to multiple analysis, based on proximal probe methodology and using the same sensor to obtain different information from precisely the same area is th...