本研究使用固著液滴接觸角量測儀，在恆溫及恆濕 (飽和濕度)狀態下，於石蠟膜上滴置一含界劑之固著液滴 (SDS、TX100和 C12E6水溶液)，繼而量測固著液滴因蒸發而引起之動態濕潤行為 (潤濕直徑 D、體積 V 和接觸角 CA)。當t = 0 ~70秒時，環境濕度 (Hr)趨近100%，t ＞70秒時，調降Hr至65±5%，使固著液滴緩慢蒸發、體積下降。藉由接觸角隨時間下降的曲線，測量其前進接觸角θa和後退接觸角θr。
SDS水溶液固著液滴生成後，液滴潤濕石蠟膜，其潤濕直徑隨液滴之潤濕擴張而微幅增加 (在Hr~100％時)，此時其液滴之接觸角呈一定值，此為前進接觸角。對於TX-100和C12E6水溶液，在固著液滴生成初期，其接觸角幾乎呈一定值 (設定為θa)，隨後，其潤濕直徑因液滴持續擴張而緩慢上升至一定值，且維持一段時間不變；接觸角因潤濕直徑擴張、體積微幅上升 (在Hr ~ 100％時)而下降。當潤濕直徑於平穩期間時，其接觸角再次呈一定值並維持至環境濕度調降初期；此接觸角為另一個θa。之後，調整環境濕度至65±5%，液滴之潤濕直徑、體積和接觸角皆因液滴之蒸發而下降。實驗結果顯示：TX-100和C12E6水溶液液滴呈現兩個前進接觸角 (θa1和θa2)。
界劑水溶液的濃度 (Cb)明顯影響了動態、前進和後退接觸角，此濃度效歸因於固-液界面和液-氣界面分別的界面張力之變化。對於較低的濃度溶液，θa和θr隨著Cb的增加而降低。SDS水溶液液滴在Cb＜cmc時θa和θr隨濃度的增加而下降，當Cb = cmc時有明顯的轉折，Cb > cmc時θa則為一定值，此現象類似於SDS溶液的平衡表面張力。而TX-100、C12E6水溶液液滴的θa轉折處卻在Cb >> cmc。由於界劑分子的非平衡吸附，相對較慢的吸附速率在液-固和液-氣界面上，導致θa轉折處存在於不同的濃度位置

The evaporation of solution drop of surfactants (SDS, Triton X-100 and C12E6) on parafilm was studied. The relaxations of wetting diameter, contact angle (CA), drop volume, and surface area of the sessile drops of surfactant were monitored using a sessile drop tensiometer during the drop evaporation (relative humidity Hr inside the environmental chamber is ~ 100% at the first 70 s, then Hr ~ 65% at t > 70s). The advancing and receding CA (θa and θr) were then determined from relaxation profile of CA.
For SDS solution droop, the wetting diameter increased slightly right after the sessile drop was formed (at Hr ~ 100%), the CA then remained constant for a specific time period (concentration dependent), at which the θa was determined. For TX-100 and C12E6 solutions, a similar constant CA (set to be the θa) was observed right after the drop being formed. However, the triple line of the sessile drop advanced continuously and then reached a constant wetting diameter. This advance in triple line resulted in a decline in the CA, and another constant CA was observed during as the wetting diameter leveled off. Therefore, two advancing CA (θa1 and θa2) were identified for TX-100 and C12E6 solution drops.
The dynamic, advancing and receding CAs were found to be strongly affected by the concentration (Cb) of the aqueous surfactant solutions. This dependence was attributed to the variations in both the interfacial tension at solid-liquid and liquid-gas interfaces. For diluted solutions, θa and θr were observed to decrease with increasing Cb. The θa of SDS became constant at Cb > cmc; i.e., the relaxation of θa and θr have a clear break at cmc which is similar to that of the equilibrium surface tension of SDS solution. However, the breakpoint of the θa of TX-100, C12E6 were observed at Cb >> cmc. This shift in the breakpoints of θa was attributed to the non-equilibrium adsorption of surfactant molecules at liquid-solid and liquid-gas interfaces that resulted from a relatively slower adsorption rate.

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