| 摘要: | 液滴的蒸發現象在日常生活中十分常見，其蒸發後所形成的沉積圖案受多種因素影響。其中最典型的例子為「咖啡環效應」，此效應在多項應用領域中扮演著關鍵角色，既可能帶來負面影響，也能創造有利條件。以噴墨列印為例，咖啡環效應會導致顏料不均勻沉積，影響列印品質；然而在醫學檢測中，該效應可促進檢測目標集中，有助於提升觀察方便性與準確性。
此外，液滴於蒸發前的擴展行為對最終沉積圖案的範圍具有決定性影響。這是由於在蒸發過程中，液滴與基板之間的接觸面積會隨時間改變，進而影響內部溶質的輸運與沉積位置。因此，釐清液滴擴展機制對於理解沉積行為與控制最終沉積圖具有重要意義。
本研究系統性地探討了不同基板溫度（27、40、50、60 °C）與甘油濃度（30、40、50 wt%）對液滴在親水性基板上擴展與蒸發行為的影響。實驗結果顯示，在低甘油濃度（30 wt%）下，液滴可達到較大的最大擴展直徑；而在較高甘油濃度（40、50 wt%）條件下，擴展受到抑制，推測與甘油提升液滴黏度、限制其流動性有關。此外，基板升溫亦會抑制液滴的擴展行為，此抑制效果在低濃度甘油液滴中尤為顯著，而在高濃度條件下則相對較弱。;The evaporation of droplets is a common phenomenon in daily life, and the resulting deposition patterns after evaporation are influenced by various factors. One of the most typical examples is the "coffee-ring effect," which plays a critical role in many application fields—bringing both benefits and drawbacks. For instance, in inkjet printing, the coffee-ring effect leads to uneven pigment deposition, resulting in poor print quality. In contrast, in
medical diagnostics, this effect can help concentrate the target analyte at the droplet edge, enhancing both the ease and accuracy of detection.
Furthermore, the spreading behavior of a droplet before evaporation has a decisive impact on the final deposition pattern. This is because, during evaporation, the contact area between the droplet and the substrate changes over time, influencing the transport and deposition of solutes within the droplet. Therefore, understanding the mechanism of droplet spreading is essential for controlling the final deposition pattern.
This study systematically investigates the effects of substrate temperature (27, 40, 50, and 60 °C) and glycerol concentration (30, 40, and 50 wt%) on the spreading and evaporation behavior of droplets on hydrophilic substrates. Experimental results show that droplets with a
lower glycerol concentration (30 wt%) exhibit a larger maximum spreading diameter. In contrast, higher glycerol concentrations (40 and 50 wt%) suppress spreading, presumably due to increased viscosity limiting droplet mobility. In addition, elevated substrate temperatures
also reduce the extent of droplet spreading, with this suppression being more pronounced at lower glycerol concentrations and relatively less evident at higher concentrations. |
