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本文通过单光束梯度力光学镊子-拉曼光谱系统,对硫酸镁单液滴随着相对湿度变化的反应进行了探究。当硫酸镁单液滴被光镊捕获之后,通过相对湿度的梯度变化探究了捕获液滴的蒸发动力学变化。发生在与耳语回音模相称波长的受激拉曼散射可以用来准确地确定液滴半径,因此,可以通过腔增强拉曼散射得到在不同湿度下处于平衡的液滴半径信息。本研究通过光镊对硫酸镁单液滴的实时监测,阐述了在某个相对湿度范围内该液滴的粒径变化的过程和结果,在此之前的硫酸镁吸湿性研究中没有先例。研究结果表明在相对湿度逐渐降低至40%的过程中硫酸镁液滴半径的变化速率逐渐变小。而当相对湿度低于40%时,液滴半径的减小会被严重抑制。这种现象表示在高浓度条件下硫酸镁液滴中水的蒸发扩散速率会降低。另一方面,在蒸发过程后的相对湿度上升过程中,硫酸镁液滴尺寸的增加明显缓慢于湿度增长速度。这一现象显示液滴的尺寸变化是不可逆的。说明胶态的形成导致了传质受阻,从而阻碍了液滴中水分子的交换。
In this paper, single-beam gradient force optical tweezers - Raman spectroscopy system, a single drop of magnesium sulfate with changes in relative humidity was explored. After a single drop of magnesium sulfate was captured by optical tweezers, the change in evaporation kinetics of the captured droplets was explored by a gradient change in relative humidity. Stimulated Raman scattering, which occurs at a wavelength that is commensurate with the whispering pattern, can be used to accurately determine the droplet radius so that Raman scattering can be enhanced through the cavity to obtain information about the drop radius at equilibrium at different humidities. In this study, the real-time monitoring of single droplet of magnesium sulfate by optical tweezers was used to describe the process and result of the particle size change of the droplet within a certain relative humidity range. There is no precedent in this study on the hygroscopicity of magnesium sulfate. The results show that the rate of change of magnesium sulfate droplet radius gradually decreases when the relative humidity is gradually reduced to 40%. When the relative humidity is less than 40%, the drop of the droplet radius is seriously suppressed. This phenomenon indicates that the evaporation diffusion rate of water in magnesium sulfate droplets will decrease under high concentration conditions. On the other hand, the increase in droplet size of magnesium sulfate was noticeably slower than the rate of humidity increase during the relative humidity increase after the evaporation process. This phenomenon shows that the droplet size change is irreversible. It shows that the formation of colloids leads to the impediment of mass transfer, which hinders the exchange of water molecules in the droplets.