Our previous study [R. Bhardwaj and A. Agrawal, “Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface,” Phys. Fluids 32, 061704 (2020)] showed that the drying time of typical respiratory droplets is on the order of seconds, while the survival time of the coronavirus on different surfaces was reported to be on the order of hours in recent experiments. We attribute the long survival time of the coronavirus on a surface to the slow evaporation of a thin nanometer liquid film remaining after the evaporation of the bulk droplet. Accordingly, we employ a computational model for a thin film in which the evaporating mass rate is a function of disjoining and Laplace pressures inside the film. The model shows a strong dependence on the initial thickness of the film and suggests that the drying time of this nanometric film is on the order of hours, consistent with the survival time of the coronavirus on a surface, seen in published experiments. We briefly examine the change in the drying time as a function of the contact angle and type of surface. The computed time-varying film thickness or volume qualitatively agrees with the measured decay of the coronavirus titer on different surfaces. The present work provides insights on why coronavirus survival is on the order of hours or days on a solid surface under ambient conditions.

中文翻译：

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冠状病毒如何在表面存活数天


我们之前的研究[R. Bhardwaj 和 A. Agrawal，“冠状病毒在固体表面沉积的呼吸道飞沫中存活的可能性”，Phys。 Fluids 32, 061704 (2020)]表明，典型呼吸道飞沫的干燥时间为秒量级，而最近的实验报道冠状病毒在不同表面上的存活时间为小时量级。我们将冠状病毒在表面上的较长存活时间归因于大液滴蒸发后残留的纳米薄液膜的缓慢蒸发。因此，我们采用了薄膜的计算模型，其中蒸发质量速率是薄膜内部分离压力和拉普拉斯压力的函数。该模型显示出对薄膜初始厚度的强烈依赖性，并表明这种纳米薄膜的干燥时间约为数小时，与已发表的实验中看到的冠状病毒在表面上的存活时间一致。我们简要研究了干燥时间随接触角和表面类型的变化。计算出的随时间变化的薄膜厚度或体积与不同表面上冠状病毒滴度的测量衰减定性一致。目前的工作提供了关于为什么冠状病毒在环境条件下在固体表面上的存活时间为数小时或数天的见解。