液滴蒸發的咖啡環現象不只在日常生活中出現，對於噴墨列印、塗層技術等應用中，咖啡環現象的出現會降低產品品質或是性能等因素。因此，本研究在不同溫度的基板上，以及在懸浮溶液中添加不同濃度的表面活性劑(sodium dodecyl sulfate, SDS)兩種抑制咖啡環效應的方法，以達到獲得均勻沉積圖案的目的。在液滴蒸發的過程中，主要受到毛細流、表面張力梯度、溫度梯度引發的馬倫哥尼流以及液滴界面下降四種因素的影響，這些因素都會對液滴沉積的結果產生影響。
本文實驗在三種基板的溫度(30˚C、50˚C和70˚C)以及四種SDS濃度(0 wt %、0.05 wt %、0.50 wt %和1.00 wt %)下進行實驗。實驗結果顯示，只有在基板溫度為30˚C且SDS濃度為低濃度(0 wt %和0.05 wt %)時，沉積圖案為咖啡環。而提高SDS濃度(0.50 wt %和1.00 wt %)或是提高基板溫度(50˚C、70˚C)，實驗結果皆顯示大多數的粒子沉積於液滴內部或是中心區域，呈現了抑制咖啡環現象。

關鍵詞：咖啡環現象、噴墨列印、表面活性劑

The coffee ring phenomenon observed during the evaporation of droplets occurs not only in everyday life but also in applications such as ink-jet printing and coating technologies. The coffee ring effect in these applications can negatively affect product quality and performance, among other factors. In this study, we employed two methods to suppress the coffee ring: varying the substrate temperature and adding different concentrations of surfactant (sodium dodecyl sulfate, SDS). The aim is to achieve a uniform deposition pattern. During the droplet evaporation process, four major factors influenced the droplet: capillary flow, surface tension gradients, Marangoni flow induced by temperature gradients, and the descent of the droplet interface. All of these factors can affect the final droplet deposition.
This study conducted experiments at three different temperatures (30˚C, 50˚C, and 70˚C) and with four different SDS concentrations (0 wt %, 0.05 wt %, 0.50 wt %, and 1.00 wt %). The experimental results reveal that coffee ring deposition pattern only occurs when the substrate temperature is at 30˚C and the SDS concentration is low (0 wt % and 0.05 wt %). Increasing the SDS concentration or raising the substrate temperature leads to most particles being depositing within the droplet or in its central region, demonstrating the suppression of the coffee ring phenomenon.

Keywords: coffee-ring phenomenon, inkjet printing, surfactant

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