以密度汎函理論探討兩成分混合物系統之相行為以及濕透行為

Abstract

用密度汎涵理論（density functional theory）分別結合SAFT（statistical associating fluid theory）與ISM（interaction-site model），以研究對兩成分水+兩性化合物混合物系統，探討分子間作用力（包含氫鍵作用力）與分子大小對於相行為以及濕透行為的影響。我們以具溫度效應之特殊方向性能量作用力參數來模擬水和兩性化合物之間的氫鍵作用力。當改變氫鍵作用力強度或是其他能量參數時，我們可以得到這些兩成分混合物系統之van Konynenburg 與Scott 相行為分類會落在type I、type II、type III、type V、type VI。考慮一個三液相（α，β，γ）平衡的系統，其中間β相的濕透行為可以輕易的藉由微量中間相之接觸角θ（α-β與β-γ界面的夾角）認識，包含非濕透、部分濕透以及完全濕透。而部分濕透與 完全濕透（或非濕透）之間的轉變，我們稱之為濕透轉變，反之亦然。本研究也會針對界面間的濕透行為以及濕透轉變做仔細的檢查。我們會藉由掃描能量參數空間對四種不同鏈長之兩成分水＋兩性化合物混合物系統有系統地探討並描繪出不同相行為及濕透行為轉變的區域。研究結果顯示，在部分參數條件下具有完全濕透區域，可以被利用在第三級原油採集時兩性化合物之選擇參考。本研究中亦發現在這些兩成分混合物系統中部分接近下臨界溫度的低溫區有lamellar phase 的存在，但在較短鏈的系統中並不存在lamellar phase。

A density functional theory is incorporated with the statistical associating fluid theory and interaction-site model to investigate the effect of hydrophobic chain length of amphiphile and interaction energy including hydrogen bonding strength on phase and interfacial wetting behaviors of binary water + amphiphile mixtures. The hydrogen bonding interaction between water and amphiphile is imitated by temperature-dependent energy parameter according to specific orientation. The phase behavior of this binary mixture would fall into type I, II, III, V, and VI of the classification scheme of van Konynenburg and Scott by varying the hydrogen bonding strength and the energy parameters. Consider a system of three fluid phases, α, β, and γ in equilibrium, the wetting behavior of the middle β phase can be easily realized by the contact angle θ spanned by the α-β and the β-γ interfaces for the droplet of the middle β phase, such as nonwetting, partial wetting, and complete wetting. The transition from a partial wetting to a complete wetting (or nonwetting), or vice versa, is called a wetting transition. The interfacial wetting behavior and wetting transition in the three-phase-coexisting regions of these binary mixtures are carefully examined. The global phase diagram and wetting behavior are carefully delineated and systematically discussed by scanning the energy parameter space for the binary water + amphiphile mixtures with four different hydrophobic chain lengths of amphiphile. Lamellar phase can be observed at low temperatures close to its lower critical end point in these binary systems with certain chain length of amphiphile. There exists no lamellar phase in the water + amphiphile system when the hydrophobic chain length of amphiphile is too short.