A flexibly hierarchical porous polydimethylsiloxane film for Passive

daytime radiative cooling

Xiongbo Yanga,b , ShuminYaoa, XinyuTana,c,* , Yiteng Tu a , Jialin Geng a , Guiguang Qi a ,Yulong Qiao

a ,RuizhenXub,* ,YanliZhangd

a Hubei Provincial Engineering Technology Research Center for Microgrid, College of Electrical Engineering & New Energy, China Three Gorges University, Yichang, Hubei 443002, P. R. China

b College of Science, China Three Gorges University, Yichang, Hubei 443002, P. R. China

c Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, College of Materials and Chemical Engineering, China Three Gorges University,Yichang, Hubei 443002, P. R. China

d The MOE Key Laboratory of Special Machine and High Voltage Apparatus, Shenyang University of Technology, Shenyang 110870, P.R. China

ABSTRACT

Passive daytime radiative cooling (PDRC) is a technology without requiring additional energy that cools objects by reflecting sunlight and radiating heat into outer space. However, the design process of PDRC films is relatively complicated or costly, which is not conducive to large-scale fabrication. For this, we fabricated a flexibly hier archical porous polydimethylsiloxane (PDMS) radiative cooling film, which is simple and fast to fabricate and can be used for efficient large-scale production. It can reach the average emissivity of 0.95 in the transparent atmospheric window (8–13 μm). The average reflectance is above 0.7 in the solar wavelength band (0.3–2.5 μm),which is nearly 9 times of the non-porous tructure. Thus, the porous PDMS films realize excellent sub-ambienttemperature drop of 14.9 ◦C at the solar intensity of 910 W/m2 .

Keywords: Polymers;Porous materials;Phase-separation;Radiative cooling

1. Introduction

Global warming and energy shortage are two major problems facing the world. Passive daytime radiative cooling (PDRC) has a significant advantage that it requires no additional energy to drive the cooling process, so it has received a lot of attention [1–4]. With PDRC devel opment, many new structures and materials with excellent cooling effects were fabricated and designed [5], such as nanoparticle-doped materials [6,7], multilayer structures [8,9], photonic structures [10,11],and metamaterials [12]. Although these designs have achieved excellentradiative cooling performance, their development is severely limiteddue to their high cost and complex preparation process, resulting in poor large-scale scalability.

In this work, PDMS was chosen as the material for its excellent chemical stability and high emissivity in atmospheric transparent window. We propose a simple and inexpensive method to fabricate hierarchical porous PDMS films, which is conducive to large-scale application(Table S1, Supporting Information). Experiments showed that the temperature of the film is on average 14.9 ◦C lower than sub-ambient temperature at an average solar intensity of 910 W/m2 . In addition,the porous PDMS film has a modulus of elasticity of 1.12 MPa, which indicates that it exhibits great flexibility (Fig. S1, Supporting Information). It can be believed that this porous PDMS film with a novel fabrication method has the potential for commercialization.

2. Experimental section

2.1. Material

The PDMS elastomer based and the hardener (PDMS, Sylgard 184)was purchased from Shanghai DejiShangmao Co., ltd., China. N-hexane(AR, ≥97.0 %) was purchased from Tianjin Fuyu Fine Chemical Co., ltd.,China. Deionized (DI) water is prepared in the laboratory.

2.2. Fabrication of the porous PDMS films

The typical procedure is shown in Fig. 1. The PDMS elastomer based(part A) and n-hexane were evenly mixed at mass ratio of 1:3 (Fig. S2,Supporting Information). After magnetic stirring for 30 min, the DIwater and PDMS hardener (part B) were added to mixture. The mixture......

论文下载链接：A Flexibly Hierarchical Porous Polydimethylsiloxane film  materials letters 20230115.pdf