## 1 Introduction
[18] studied high-boiling R113 droplet impingement as a replacement for low-boiling R134a because of the similar physical properties of R113 and R134a. It was found that a rough surface can reduce the splash threshold of a droplet, and surface roughness was considered in the empirical formula of maximum spread diameter. [PERSON] et al. [19] studied droplet impingement of urea water solution on heated porous surfaces. The effects of substrate roughness on the splash, evolution process, and heat transfer were discussed. More recently, the dynamic behaviors of droplet impact on groove-textured surfaces have attracted a lot of interest because of its anisotropy in wettability [20]. [PERSON] et al. [21] proposed that the pinning force exerted by the surface roughness on the three-phase contact line at the periphery did negative work and hindered the droplet spreading due to the energy consumed by the droplet's penetration into the groove-textured structures. They also proposed models of the maximum spreading diameter based on energy conservation. [PERSON] et al. [22] obtained different kinds of disturbances with radioactive strips on the surface during deionized water droplet impingement. [PERSON] et al. [23] analyzed the characteristic of dynamic contact angle on textured surfaces influenced by texture area fraction, Weber number, and surface temperature. [PERSON] et al. [24] designed a low-cost, layered texture surface of heated walls to improve the Leidenfrost Point (LFP) of deionized water on a nanocoated mesh surface. [PERSON] et al. [25] studied droplet dynamics impinging on superhydrophobic surfaces, revealing that the contact time was determined by the Weber number and surface roughness. Further, [PERSON] et al. [26] from the same research group investigated droplet impact dynamics on superhydrophobic surfaces with submillimeter-scale posts, in which an intriguing droplet breakup mechanism of internal rupture was found. This type of breakup greatly shortened the contact time up to 50% compared with the traditional rebound and rim breakup mechanism. In general, scholars have carried out numerous studies on the impact behavior of water, ethanol, and other relatively high boiling-point droplets with low volatility. Though low-boiling refrigerants have been widely used in the field of spray cooling, their high volatility makes it difficult to control and generate a stable droplet at normal atmospheric pressure. There are few reports on the experimental study of the impinging dynamics for single refrigerant droplets, leaving related research and simulation calculations short of reliable data reference. Therefore, establishing a droplet formation system and studying the morphology and dynamic characteristics of low-boiling refrigerant droplet impingement are of vital importance. There are two options to study cryogen droplet impingement. One is to generate a cryogen droplet in a high-pressure environment because high pressure reduces droplet volatility and, thus, could keep the cryogen as a stable droplet before impingement. [PERSON] et al. (2017); [PERSON] et al. (2018); [PERSON] et al. (2019) studied R134a droplet impact on a solid surface in a visual high-pressure vessel and proposed a model to accurately predict the maximum spreading diameter with a large range of surface roughness. However, the high-pressure environment makes it difficult to observe the impact behavior, and the high-pressure vessel has the potential risk of explosion. This study adopted an alternative to cool the cryogen under dew-point temperature at atmospheric pressure before its discharge. This approach can generate a stable cryogen droplet under the atmospheric environment without the high-pressure vessel. Thus, it is far easier and safer to conduct the experiment. Moreover, different from those at high pressure, the liquid properties and air-liquid interaction that affected the impact results conformed with most of the application scenarios at atmospheric pressure.