在特定基材上，不同液體呈現不同的潤濕行為，主要區分為部分潤濕和完全潤濕。日常生活中常常遇到由部分潤濕和完全潤濕液體組成的二元混合物，其又稱為拮抗混合物。雖然拮抗混合物的潤濕行為與一般液體有所不同，但針對此現象的研究卻相對稀少。而在奈米尺度上，拮抗混合物組成的奈米液滴的潤濕行為可能與我們現有的理解更加不同。 透過分子動力學模擬，我們研究了石墨烯表面上含有水（部分潤濕）和乙醇或異丙醇（完全潤濕）混合物之奈米液的滴潤濕行為。 通過調整混合物中水的莫耳分率(xw)，可以發現三種不同的潤濕狀態：(I) 在完全潤濕狀態（低xw）下，觀察到自發性的擴散現象；(II) 在平台狀態（中xw）下，表觀的接觸角（CA）保持恆定，但液滴中的醇類化合物會滲漏出來；(III) 在部分潤濕狀態（高xw）下，CA隨xw增加而增加，同時，醇類化合物傾向於聚集在接觸線附近。值得注意的是，擴散係數(S)在xw接近1時才變為負值，其餘情況下為正值。此外，即使在S < 0時，楊氏方程式也被證明不適用。而此篇研究將對這些特殊的潤濕現象進行全面的討論和說明。 ;Hypothesis Binary mixtures, consisting of partially and totally wetting liquids with respect to a specific substrate and known as an antagonistic mixture, are commonly encountered. Although the wetting behavior of antagonistic mixtures deviates from that of conventional liquids, studies exploring this phenomenon are scarce. At the nanoscale, the wetting behavior of nanodroplets containing such mixtures may diverge even further from our established understanding.
Experiments Employing Nanoscale Molecular Dynamics simulations, we explore the wetting behavior of nanodroplets containing mixtures of water (partial wetting) and ethanol or isopropanol (total wetting) on a graphene surface.
Findings By adjusting the water fraction (xw) in the antagonistic mixture, three distinct wetting states have been identified: (I) In total wetting regime (low xw), spontaneous spreading is observed; (II) In plateau regime (medium xw), alcohol leakage from the droplet occurs, with the apparent contact angle (CA) remaining constant; (III) In partial wetting regime (high xw), the CA increases with xw and alcohol molecules tend to accumulate at the contact line. Unexpectedly, the spreading coefficient (S) remains positive and turns negative only as xw near unity. Furthermore, Young’s equation proves to be inapplicable even when S < 0. These peculiar wetting phenomena are comprehensively discussed and elucidated.
