A new method: measuring the dance of light and heat

Photothermal conversion is a basic physical process of light-matter interaction, which is widely present in nature and modern industrial systems, and the photothermal conversion efficiency of nanomaterials determines the key parameters of their application characteristics such as photothermal therapy, solar-driven water evaporation and photothermal catalysis. Although there are already some methods to measure the photothermal conversion efficiency of nanocrystalline solutions, their accuracy is still controversial. Therefore, it is of great significance to develop a simple and universal method for measuring the photothermal conversion efficiency of solid nanomaterials.

Recently, Gu Kai et al. of Beijing Institute of Technology developed a method for measuring the photothermal conversion efficiency of solid materials (PEE method) for electro-optical equivalence. It uses the equivalent method of electric heating and photoheating, that is, the temperature rise process of electric heating is used to simulate the temperature rise process of the material under light, and the photothermal conversion efficiency of the material is calculated by the thermal balance formula under simplified conditions. This method breaks through the limitations of previous methods on material systems, is suitable for nanocarbon materials (graphene, carbon nanotubes), semiconductor nanocrystals (lead selenide and gold nanorods) and polymer (polyaniline) systems, and shows good reproducibility, providing a new method for the study of photothermal conversion process and the development of photothermal materials.

The device of the PEE method consists of two modules: electric heating (Module I) and light heating (Module II). In the electric heating module, the sample is heated by a resistor known to have an input power of P0, and a thermal imaging camera is used to monitor the change in its average temperature TE. According to the thermal equilibrium equation, and the linear term considering all heat dissipation pathways, including heat conduction, thermal convection and thermal radiation, it can be obtained that P*-H*ΔTE, max=0 in the heat equilibrium state, where H* is the comprehensive heat dissipation coefficient of the sample under electrical heating, the actual thermal power received by the P* sample, and the relationship between P* and P0 is related to the shape of the resistance. Therefore, by changing the input power P0, the slope H* can be obtained by linear fitting.

In the photoheating module, the sample is heated by a laser with a known power of I0, and the curve of its average temperature TL with time can be used to obtain I0Aη-HΔTL in the thermal equilibrium state, max=0, where A is the absorption rate of the sample, η is the photothermal conversion efficiency, and H is the heat dissipation coefficient under photoheating. In this test system, H under electrical heating is equivalent to H* under photoheating, and the photothermal conversion efficiency of the test material can be derived η=H*ΔTL,max/I0A.

The photothermal conversion efficiency of a variety of materials was measured, and the test error was less than 5%, indicating that the method had good applicability and accuracy. It is important to note that this measurement method is not suitable for material systems that undergo chemical changes under light.

Test principle of PEE method

The article was published in Light: Science & Applications, a top international academic journal, entitled “A general methodology to measure the light-to-heat conversion efficiency of solid materials”, with Kai Gu as the first author of this paper, Haizheng Zhong is the corresponding author of this article. (Source: LightScience Applications WeChat public account)

Related paper information:‍-023-0‍1167-6

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