Interfacial water from molecular to mesoscopic scale and its relation to tunable hydrophobicity

弗吉尼亚联邦大学的Alenka Luzar获得了化学学部化学理论、模型和计算方法项目的资助，开展了具有拓扑和化学非均质表面的可逆润湿转变和纳米润湿研究。方法包括统计力学理论和模拟技术的结合，以及计算算法的发展，以处理纳米密闭空间中水的界面特性。研究了三个具体问题：(1)在超疏水表面上的电场或压力诱导跃迁，实现Cassie态和Wenzel态之间的可逆切换；(2)纳米液滴在电极上的驱动，在连续介质物理学最多只能提供非常粗略的预测的情况下，提供施加电压下液滴和电极动态响应的详细和自一致的微观图像；(3)探索化学非均质基底上表面力可加性的程度，以解决它们如何很好地预测混合表面与纯表面之间的力。该研究对材料科学、工程、生物学等多个学科具有广泛的影响。在分子水平上理解外部刺激对表面疏水性的智能控制可以在纳米流体和电光学中找到实际应用。第一个主题阐明了在电和/或压力控制下，材料的耐湿和亲水行为之间的可逆切换是否可以在纳米尺度上实现，以及所涉及的时间尺度是什么。第二个主题是电子控制下的纳米光学元件的设计。他们想了解可调谐光学器件是否可以小型化到纳米级，以及与宏观光学器件相比，其本质优势或挑战是什么。第三个主题影响纳米技术和生物物理学中自组装材料的研究。

Alenka Luzar of Virginia Commonwealth University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to carry out research on reversible wetting transitions and nanowetting of surfaces with topological and chemical heterogeneities. The methodologies include a combination of theory and simulation techniques in statistical mechanics and development of computational algorithms to deal with interfacial properties of water in nanoconfined spaces. Three specific problems are being investigated: (1) electric field or pressure-induced transitions on superyhdrophobic surfaces to achieve reversible switching between contrasting Cassie and Wenzel states; (2) nanodroplet actuation on an electrode to provide a detailed and self-consistent microscopic picture of drop and electrode dynamic responses under applied voltage, at conditions where continuum physics offers at best very crude predictions; and (3) probing the extent of surface force additivity on chemically heterogeneous substrates to address how well they can predict forces between mixed surfaces from those between pure ones.The research has broad impact on many disciplines including materials science, engineering, and biology. Molecular level understanding of intelligent control of surface hydrophobicity by external stimuli can find real-world applications in nano-fluidics and electro-optics. The first topic elucidates if reversible switching between wetting-resistant and hydrophilic behavior of a material is achievable at the nanoscale under electric and/or pressure control, and what are the time scales involved. The second topic concerns the design of nano-sized optical elements under electric control. They want to learn if tunable optical devices can be miniaturized to the nanoscale level, and what could be the essential advantages or challenges in comparison to macroscopic ones. The third topic impacts research into self-assembling materials studied in nanotechnology, as well as biophysics.