| 摘要: | 液滴蒸發在生活當中無所不在，而其中主要的現象「咖啡環效應」更是影響廣泛。
對於噴墨技術、表面塗層技術等領域，咖啡環效應會降低成品品質。因此本研究想要探
討溫度以及表面活性劑SDS(sodium dodecyl sulfate, SDS)兩種抑制咖啡環的因素，從而
獲得更加均勻的沉積圖案。在液滴蒸發的過程中，主要受到毛細流、表面張力梯度和溫
度梯度所引發的馬蘭戈尼流以及液滴擴展行為等因素的影響，從而改變液滴蒸發特性和
沉積圖案的結果。
本文實驗探討低於臨界膠束濃度(Critical micelle concentration，簡稱 CMC)下四種
SDS 濃度(0、0.025、0.05、0.15 wt%)以及四種基板溫度(25、35、40、50 °C)下進行實驗。
實驗結果顯示，在低SDS濃度(0、0.025 wt%)以及未加熱基板(25°C)條件下，沉積圖案
為咖啡環。而基板溫度上升後(35、40、50 °C)，則形成咖啡眼的沉積圖案。在高SDS濃
度(0.05、0.15 wt%)以及未加熱條件(25°C)下，液滴蒸發初期會產生擴展行為，沉積圖案
面積增加。而基板溫度上升後(35、40、50 °C)，液滴的擴展行為會減小。;Droplet evaporation is ubiquitous in daily life, and the main deposition phenomenon
"coffee ring " usually appears. However, coffee ring effect will lower the quality of the products
in some application like inject printing, surface coating, etc. Therefore, the effect of temperature
and surfactant SDS (sodium dodecyl sulfate, SDS) for suppressing coffee ring effect is
considered in this study. During the droplet evaporation process, droplet is mainly affected by
capillary flow, and Marangoni flow which is induced by the gradient of surface tension, etc.
These mechanisms change the results of droplet evaporation characteristic and deposition
pattern.
In this experiment, four kinds of SDS concentration (0, 0.025, 0.05, 0.15 wt%) below the
critical micelle concentration (CMC) and four kinds of substrate temperature (25, 35, 40, 50 °C)
is considered. Experiment results show in lower SDS concentration (0, 0.025 wt%) and non
heated substrate temperature (25°C) cases, deposition pattern reveals coffee ring. For heated
substrate cases (35, 40, 50 °C), deposition pattern reveals coffee eye. In higher SDS
concentration (0.05, 0.15 wt%) and non-heated substrate temperature cases (25°C), contact line
spreading behavior is observed at the early stage of the droplet evaporation, lead to a larger area
pattern. For the heated substrate cases (35, 40, 50 °C), the spreading behavior is weakened. |
