本實驗室利用懸掛氣泡影像數位化測量儀，量測加入100及300 mM NaCl之陰離子型界面活性劑(sodium dodecylsulfate, SDS)水溶液的動態表面張力。並將實驗所得之平衡及動態張力數據與理論質傳模型做最適化比對，以探討SDS界劑水溶液之吸附動力學。由於實驗部分有其困難度，因此量測動態表面張力之實驗由廖育青同學完成，本研究僅使用其實驗數據，以驗證理論質傳模型。
截至目前為止，僅有少數文獻將溶液中之靜電荷作用力或在氣-液界面形成之電雙層對吸/脫附及擴散程序作用之效應，導入動態模型中。究其因為一般離子型界劑之動態表面張力通常在一秒左右即達平衡值，因此極難取得離子型界劑分子在水溶液中之完整的動態表面張力。很幸運地，本研究所探討之SDS界劑水溶液（添加100及300 mM之NaCl），可藉由懸掛氣泡影像測量儀獲得較完整之動態表面張力數據。
除了不易獲得完整之離子型界劑的動態表面張力以外，文獻對於離子型界劑吸附至氣-液界面之動力學的描述亦過於簡單，其僅考慮：已有離子型界劑吸附之界面與溶液中之界劑，因帶有同性之電荷所產生之排斥力，而減緩界劑之吸附速率。在本研究中，不僅考慮上述之排斥力對吸附程序之影響，亦探討此排斥力對脫附程序之影響，且假設此排斥力在脫附程序中，扮演一加速脫附之角色。
本研究使用三種吸附等溫線（ionic-Langmuir、ionic-Frumkin及ionic-generalized Frumkin）來模擬平衡表面張力數據。若假設SDS分子由水溶液中吸附至氣-液界面之質傳機制為擴散控制，並以理論動態張力曲線與動態張力數據做最適化比對，可得其擴散係數約為12×10-6 cm2/s。由於此擴散係數遠低於Wilke-Chang equation所預測之理論擴散係數(5.78×10-6 cm2/s)，故SDS分子由水溶液中吸附至氣-液界面之質傳機制應為混合控制。
在SDS分子由水溶液中吸附至氣-液界面之質傳機制為混合控制之假設下，擴散係數設定為Wilke-Chang equation所預測之5.78×10-6 cm2/s，並以不同吸附等溫線模式進行模擬，其理論動態張力曲線與動態張力數據吻合之情形雖可接受，但仍不如擴散控制，且所得之吸附速率常數也無法隨界劑濃度之變化而呈一定值，因此本研究用以描述離子型界劑分子由水溶液中吸附至氣-液界面之理論質傳模式尚有修正之空間。

The dynamic surface tension for the adsorption of anionic surfactant SDS (sodium dodecylsulfate) in aqueous NaCl solution onto a clean air-water interface was measured by using a video-enhanced pendant bubble tensionmeter. To study the adsorption kinetics of SDS, comparisons were made for the entire relaxation period of the tension data and the ionic model predictions.
So far, only several articles consider the electrostatic effect on the mass transport process because of the difficulty on measuring a complete set of dynamic surface tension of ionic surfactant solution. The time required for reaching the equilibrium surface tension is less than 1 second for most ionic surfactants in pure water. Therefore a solvent with different concentration of mM NaCl was used. This this study we study the adsorption kinetics of SDS aqueous solution with 100 and 300 mM NaCl.
Three adsorption isotherms (ionic-Langmuir, ionic-Frumkin and ionic-generalized Frumkin) were applied on simulating the equilibrium and dynamic surface tensions. The ionic-Frumkin model describes better the surface tension data. When the adsorption transport was assumed to be diffusion-controlled, a diffusivity of SDS molecules was evaluated from the best-fit with the dynamic surface tension profiles and a value of D=12×10-6 cm2/s was resulted. This diffusivity is significantly lower than what the Wilke-Chang equation predicts (5.78×10-6 cm2/s).
The mass transport is therefore considered to be mixed-controlled with D= 5.78×10-6 cm2/s. The theoretical mixed controlled tension curves fitted the dynamic surface tension data nearly as well as the diffusion-control curves.

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