Microthermal analysis

Microthermal analysis has been used in surface and depth profiling studies of PP [51,52], multi-block copolymers [53], polytetrafluoroethylene/silicone blends [14],PEG/polylactic acid blends [55], and PS/polyvinyl methyl ether blends [56]. See also Section 3.12. 

Murray in Proceedings of a Rapra Conference on Polymer Rheology 2001  

A Practical Approach to Quality Control for the Rubbers and Plastics Industries, Shawbury, UK, 2001, Paper No.9. 

Mirabella in Infrared Microspectroscopy Theory and Applications, Eds., G. Messerschmidt and M.A. Harthcock, Practical Spectroscopy 6, Marcel Dekker Inc., New York, NY, USA, 1988. 

Applications of FT-IR Microscopy to Polymer Analysis, Spectratech Application Note Volume No.lO, Spectratech Lord, 1988. 

TA Instruments were one of the first companies to produce a commercial microthermal analysis instrument [105, 106]. This device is useful for the analysis of polymers in certain applications because it can obtain DSC and TMA data on very small (i.e. micrometre-sized) areas. Examples of these are presented below  

Determination of the homogeneity of polymer blends. The surface of a product can be mapped and occurrence of the events which are characteristic of individual polymers can be obtained. The relative intensity of these will indicate whether some areas of the sample are richer in one polymer than the others. For example in a gasket, which is a blend of polyisobutylene rubber (PIB) and LDPE, the Tg of the PIB (TMA trace) and the TJn (DSC trace) of the LDPE will be focused on. 

Studying surface modification processes. A number of rubber and plastic products are modified after production by such processes as corona discharge and sterilisation by radiation. These processes will change the physical properties (e.g. modulus) of the surface layer of the polymer due to cross-linking and/or oxidation reactions. The microthermal analyser can be used to determine how uniform across the surface this modification is. 

Characterisation of localised thermal history. During the processing of plastics, stresses can become frozen into products due to their being cooled too quickly. This is undesirable as when these stresses relax in service the product can become distorted. In certain manufacturing processes, such as the extrusion of thin walled and small bore tubing. 

A thorough review of the techniques and applications of microthermal analysis has been published by Pollock and Hammiche [107]. 

---

Microsyringe injection, gas chromatography, 4 611 Microtex polyester fibers, 13 393 Microthermal analysis, recent developments in, 79 577 Micro total analysis system (pTAS),... 

Microthermal analysis is a recently introduced thermoanalytical technique that combines the principles of scanning probe microscopy with thermal analysis via replacement of the probe tip with a thermistor. This allows samples to be spatially scanned in terms of both topography and thermal conductivity, whereby placing the probe on a specific region of a sample and heating, it is possible to perform localized thermal analysis experiments on those regions. 

FIGURE 31-16 A microthermal analysis probe. (Reprinted from P. G. Royall, D. Q. M. Craig, and D. B. Grandy. Thermochim. Acta. 2001. 380 (2). 165-173 with permission from Elsevier.)... 

Although microthermal analysis is a very new technique. commercial instruments are available. Applications to pharmaceuticals, polymers, and foods have been reported. The technique also has applications in the ceramics industry and in imaging biomedical. samples. 

Gtiesser, U.J., Auer, M.E. Burger, A. (2000) Microthermal analysis, FTIR- and Raman-microscopy of (R,5)-proxyphylline crystal forms, Microchem. J. 65, 283-292. 

Figure 14 Topographic top left) and thermal conductivity (bottom left) images of the surface of a paracetamol tablet. The right-hand plot shows the results of localised microthermal analysis on the two phases revealed in the conductivity image...

Figure 9.9 Thermal signal and cantilever deflection vs. tip/surface during the approaching cycle for a polyethylene sample. The approaching velocity is 5pm s and the initial probe temperature is 50 °C. (Reprinted with permission from thermochimica Acta, Microthermal analysis of polymeric materials by V. V. Tsukruk, K K Gorbunov and N. Fuchigami, 395, 1-2, 151-158. Copyright (2002) Elsevier Ltd)...

Reprinted with permission from Thermochimica Acta, Microthermal analysis of rubber-polyaniline core-shell microparticles using frequency-dependent thermal responses by Changshu Kuo, Chien-Chung Chen and William Bannister. 403, 1, 115-127. Copyright... 

V.V. Tsukruk, V.V Gorhunov, and N. Fuchigami, Microthermal analysis of polymeric materials, Thermochim. Acta, 395, 151-158 (2003). 

Recent developments have been in the area of microthermal analysis using thermal conductivity with thermal diffiisivity signals or AFM to visualize specific areas or domains in the material and perform localized thermal analysis studies (183,184). Relaxational behavior over time and temperature is related to changes in free volume of the material. Positron annihilation lifetime spectroscopy (PALS) measurements of positron lifetimes and intensities are used to estimate both hole sizes and free volume within primarily amorphous phases of polymers. These data are used in measurement of thermal transitions (185,186) structural relaxation including molecular motions (187-189), and effects of additives (190), molecular weight variation (191), and degree of crystallinity (192). It has been used in combination with DSC to analyze the range of miscibility of polymethyl methacrylate poly(ethylene oxide) blends (193). 

Impurity inclusions and surface defects are a cause of many difficulties to the polymer producer and user. Equipment used for studying these phenomena discussed in Chapter 4 include electron microprobe x-ray emission/spectroscopy, NMR micro-imaging, various forms of surface infrared spectroscopy, e.g., diffusion reflection FTIR, ATR, also photoacoustic spectroscopy and x-ray diffraction - infrared microscopy of individual polymer fibres. Newer techniques such as scanning electron microscopy (SECM), transmission electron microscopy, time of flight secondary ion mass spectrometry (TOFSIMS), laser induced photoelectron ionisation with laser desorption, atomic force microscopy and microthermal analysis are discussed. 

Microthermal analysis combines the visualisation power of AFM with the characterisation ability of thermal analysis [333]. The AFM head is fitted with an ultra-miniature thermal probe, which provides not only topographic and thermal contrast information, but also information similar to traditional thermal analysis on a sub-micrometre scale. 

Microthermal analysis is being developed as a tool for carrying out studies in a nnmber of areas including morphology, topography, glass transitions, depth probing, and phase separation studies. 

Depth profiling studies Grossette and co-workers [347] used microthermal analysis and FT-IR spectroscopy to study the physical heterogeneity induced by the photooxidation of PP at a sub-micrometric level. 

Phase separation studies Song and co-workers [348] used microthermal analysis to study the phase separation process in a 50 50 (by weight) PS/polyvinylmethylether blend and nitrile rubber. Microthermal analysis will image the composition in the near-surface region or surface region of multi-component materials if the resolution is high enough. 

Microthermal analysis combines thermal analysis with atomic force microscopy. It is actually a family of scanning thermal microscopy techniques in which thermal properties of a surface are measured as a function of temperature and used to produce a thermal image. In microthermal analysis the tip of an atomic force microscope is replaced by a thermally sensitive probe such as a thermistor or thermocouple. The surface temperature can be changed externally or by the probe acting both as a heater and as a temperature-measuring device. 

A microthermal analysis apparatus, pictured in Figure 31-17, can be operated in either a constant-temperature mode or a constant-current mode. The constant-temperature mode is simplest and most often... 

---