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British scientists combined differential scanning calorimetry with thermal microscopy to analyze the energy changes and optical characteristics of materials

Dr. Gareth Parkes of the University of Huddersfield in the UK and Duncan Stacey of Linkam scientific instruments in the UK combined differential scanning calorimetry with thermal microscopy to analyze the energy changes and optical characteristics of materials.

Tagged photos of the equipment used in this study. A) Optical dsc450,b) Linkam imaging station (stereo microscope), c) high-resolution digital camera, d) PC running link, e) controller unit, f) liquid nitrogen pump unit, g) touch screen control and H) liquid nitrogen storage tank

© Ashton, G.P., Charsley E.L., Harding, L.P., and Parkes, G.M.B. Applications of a simultaneous differential scanning calorimetry — thermomicroscopy system. Journal of Thermal Analysis and Calorimetry, 2022; 147:1345-1353

Understanding the behavior of materials under different conditions is crucial to optimize their use in almost all applications, from industrial polymers to drug development. Thermal analysis methods such as thermal microscope enable researchers to observe the optical and physical changes of materials in the reaction process. Energy changes (enthalpy) can also be measured by integrating other technologies, such as differential scanning calorimetry (DSC).

DSC is one of the most widely used thermal analysis techniques, which is used to measure the temperature and heat flow related to the thermal transformation of materials. Although it can be used to measure almost any reaction with energy change, DSC is non-specific. Therefore, it must be combined with other methods (such as thermal microscope) to directly observe phase transitions, such as solid-solid transition, fusion reaction and decomposition.

Although the combination of DSC and thermal microscope has obvious advantages, and a system integrating these two methods can be used, surprisingly, there are few studies using synchronous DSC thermal microscope to analyze various materials. The improvement of the quality of the digital microscope and the improvement of the available computing power in the laboratory may arouse greater interest in this technology in the next few years.

Researchers from the thermal methods research center (tmru) of the University of Huddersfield, UK, led by Dr. Gareth Parkes, studied the use of combining heat flux DSC plates into a hot table to allow DSC thermal microscope measurements of the same sample, and at the same time. In this paper, we discuss the advantages of this technology in obtaining information about the optical and enthalpy properties of various materials – these materials are selected based on the fact that they show optical transitions and/or energy changes and cover a wide range of systems.

New thermal system


In this study, the recently introduced DSC thermomicroscopy system was used to study the phase transition of rubidium nitrate and the oxidation of polyethylene. This is the first time that DSC and thermal microscope are used to analyze these materials on the same instrument.

The optical dsc450 system includes a heat flux DSC board integrated into the heat table, a t96-s temperature controller unit and link software (as shown in the above figure). The system operates in the temperature range of -150 to 450 ° C. Thermal microscopic imaging is obtained by a high-resolution digital camera coupled with a stereo microscope.

Thermal stability of polymers

polyethylene

为了更好地了解聚合物材料的氧化降解及其对高温稳定性的影响,TMRU小组对超高分子量polyethylene (UHMWPE)进行了氧化诱导时间(OIT)实验。采用光学DSC450系统将样品温度控制在30-205°C之间,并在惰性氮气气氛下分析OIT效应,然后在等温期间切换到干燥空气。

The melting of UHMWPE was observed at the initial temperature of tonset 109.9 ° C (as shown on the left of the figure below), and the DSC curve showed the beginning of exothermic oxidation. At the same time, using thermal microscope, optical micrograph can observe these processes optically and correlate with DSC curve. With the beginning of oxidative degradation, researchers can see the change of surface texture after the melting of liquid polymer.

OIT tests showed the expected DSC curve, but other information about the subtle changes in surface morphology that occurred at the beginning of oxidation was revealed optically.

正在对超高分子量polyethylene(UHMWPE)样品进行氧化诱导试验。DSC曲线(蓝色实线)和温度程序(红色虚线)已绘制为时间的函数。垂直线表示气体何时从N2切换到空气。选定的显微照片(标记为t0和 a-c)链接到 DSC配置文件

© Ashton, G.P., Charsley E.L., Harding, L.P., and Parkes, G.M.B. Applications of a simultaneous differential scanning calorimetry — thermomicroscopy system. Journal of Thermal Analysis and Calorimetry, 2022; 147:1345-1353

Rubidium nitrate was analyzed with dsc450 (Linkam scientific). Differential scanning calorimetry (DSC) (lower) and region of interest (ROI) intensity (upper) curves are plotted as a function of temperature. Selected photomicrographs (marked a, b) are linked to DSC and ROI profiles

© Ashton, G.P., Charsley E.L., Harding, L.P., and Parkes, G.M.B. Applications of a simultaneous differential scanning calorimetry — thermomicroscopy system. Journal of Thermal Analysis and Calorimetry, 2022; 147:1345-1353

Visual phase transition


Rubidium nitrate

显示出多种多晶型转变的材料通常是有用的温度校准标准,因为它们能够覆盖很宽的温度范围。在这项研究中,该小组评估了Rubidium nitrate的多晶型转变,这是一种在150-280°C温度范围内具有三种不同固态转变的材料。 DSC曲线显示三个峰对应于固-固转变,最终峰对应于样品熔化(如上图左所示)。 The contour of the corresponding region of interest (ROI) from the thermal microscope shows the same transformation as a series of steps caused by changes in the reflected light intensity (RLI) of the sample.

These results show the benefits of combining RLI in thermal microscopy with DSC in identifying phase transitions when the sample remains colorless. Tmru’s team also used dsc450 to study the low temperature calibration standard and clarify the influence of temperature cycle on materials.

Future applications

The experiments in this study demonstrate the complementarity of DSC and thermal microscope, and the benefits of simultaneous thermal analysis in revealing the complex thermal processes of some materials. DSC thermal microscopy can provide more information in material research, because optical images help to explain the usually complex and overlapping DSC curves. It is expected that this technology will become more and more popular in the polymer and pharmaceutical fields.

Tmru’s research team is currently exploring whether the unique design of dsc450 can help to study the thermal conductivity of materials through optical means.