An Investigation of CO2 Laser Pattern-Creation on Polydimethylsiloxane Thin Film Surface
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Authors
Li, Yunjie
Date
2025-05-05
Type
thesis
Language
eng
Keyword
CO2 Laser , Curing , Polymer pattern-creation , PDMS , Daytime passive cooling
Alternative Title
Abstract
Passive daytime radiative cooling (PDRC) has been drawing people’s attention in recent years. It aims to let objects radiate energy under direct sunlight to the cooler outer space and cool down without any energy input. It takes advantage of certain materials that reflect in the UV-visible spectrum region and emit in the infrared region. Thermal radiation is selectively emitted through the atmospheric transparent window, where the atmosphere has minimal absorption of the wavelengths emitted at 8-13 μm. With these kinds of materials covering a building, the building can cool down during the daytime. Polydimethylsiloxane (PDMS) is a commonly used organo-silicon polymer with great flexibility, transparency, and non-toxicity. It also has a strong emission at the atmospheric transparency window. The average emissivity of PDMS in 8-13 μm is about 0.92, and to obtain an even higher emissivity, creating micrometre-scale patterns on the PDMS surface can enhance the emissivity to 0.99. However, the creation of the patterns makes use of non-green solvents and molds, and a large amount of waste can be produced if a massive production of patterned PDMS films is required. Here, we propose a mold-free and solvent-free pattern creation method, by sending a CO2 laser at an appropriate intensity to an uncured PDMS surface, and the surface responds with a self-forming pattern. Two types of patterns are observed on the surface: one grows around the CO2 beam contact area and the other grows inside it. Emissivity and cooling performance of the patterned PDMS were investigated, showing potential in radiative cooling. In addition to that, CO2 laser can selectively cure PDMS thin films by manipulating the laser intensity and distance between the laser and the film, and a detailed study of the topography and curing conditions is discussed.