The molecular scale of switchable wetting

可转换投注的分子规模

• 批准号: 422852727
• 负责人: Professorin Dr. Ellen Backus
• 金额: --
• 依托单位: Max-Planck-Institut für Polymerforschung
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/422852727?language=en
• 关键词: molecular; scale; switchable; wetting

Intermolecular interfacial interactions co-determine macroscopic wetting properties, yet insights into wetting at the molecular level have been lacking. Here, we propose to use photoswitchable surfaces based on spiropyran/merocyanine isomerization to instantaneously switch the surface’s wetting properties, and follow the molecular response of water in real-time. In the closed spiropyran form, the molecule is nonpolar, while it is zwitterionic in the open merocyanine form. Under UV light irradiation the merocyanine form is obtained; visible light switches the molecule back to the closed form. It is well-known that surfaces functionalized with the spiropyran/merocyanine pair behave hydrophobic for the spiropyran case, but hydrophilic for the merocyanine form. The ability to switch the hydrophobicity of these surfaces using ultrashort laser pulses – shorter than the timescales on which molecules reorient –provides a unique way to follow the response of water to a step change in the hydrophobic surface properties. In this manner, we aim to obtain molecular-level information about the (de)wetting dynamics at switchable substrates and to correlate molecular-level details on the water organization with macroscopic wetting properties. The structure of water and the organic coating at the interface will be investigated before, during, and after photoswitching using sum frequency generation (SFG) spectroscopy. In SFG, an infrared laser pulse and a visible laser pulse are overlapped at the interface. If the infrared laser pulse is in resonance with a molecular vibration, the signal is strongly enhanced. Due to its selection rules, SFG probes specifically the interfacial layers and does not see the bulk water. The vibrational frequency provides information about the strength of the hydrogen bond network, while the intensity of the signal is a measure for the amount of water alignment. Furthermore, we can obtain information about the ordering of the polymer from its CH vibrations. By combining the SFG probe method with an optical pulse to initiate the transition between hydrophobic and hydrophilic surface, we can obtain dynamical information on sub-picosecond timescales, to probe the molecular timescales on which the water molecules adapt to the new surface structure. Typical questions we aim to address are: - What are differences in the hydrogen bond network of water and the water orientation for the hydrophobic and hydrophilic structure? - How fast does the photoswitch switch and how fast does the rest of the polymer change ordering and orientation? - How fast does the water adapt to the new situation?- What is the dynamics of the contact line spreading? This study will provide unprecedented insights into wetting phenomena at a molecular level, expected to open avenues not only for a better fundamental understanding, but also for designing superior active surfaces.

分子间的界面相互作用共同决定宏观润湿性能，但在分子水平上润湿的见解一直缺乏。在这里，我们建议使用基于spiropyran/mercury异构化的光开关表面来瞬时切换表面的润湿特性，并实时跟踪水的分子响应。在封闭的螺吡喃形式中，分子是非极性的，而在开放的Mercury形式中它是两性离子的。在紫外光照射下，获得汞的形式;可见光将分子切换回闭合形式。众所周知，用螺吡喃/mercury对官能化的表面对于螺吡喃情况表现为疏水性，但对于mercury形式表现为亲水性。使用超短激光脉冲（比分子重新定向的时间尺度更短）切换这些表面疏水性的能力提供了一种独特的方式来跟踪水对疏水表面特性阶跃变化的响应。以这种方式，我们的目标是获得分子水平的信息（去）润湿动力学在可切换基板和相关的水组织与宏观润湿性能的分子水平的细节。水和有机涂层在界面处的结构将被调查之前，期间和之后使用和频发生（SFG）光谱的光开关。在SFG中，红外激光脉冲和可见激光脉冲在界面处重叠。如果红外激光脉冲与分子振动共振，则信号被强烈增强。由于其选择规则，SFG专门探测界面层，看不到大量的水。振动频率提供了关于氢键网络强度的信息，而信号强度是水排列量的量度。此外，我们还可以从聚合物的CH振动中获得有关聚合物有序性的信息。通过结合SFG探针方法和光脉冲引发疏水和亲水表面之间的转变，我们可以获得亚皮秒时间尺度上的动力学信息，以探测水分子适应新表面结构的分子时间尺度。典型的问题，我们的目标是解决：-什么是水的氢键网络和水的疏水和亲水结构的取向的差异？- 光开关的开关速度有多快，聚合物的其余部分改变顺序和方向的速度有多快？- 水适应新形势的速度有多快？什么是接触线传播的动力学？这项研究将提供前所未有的见解润湿现象在分子水平上，预计开辟道路，不仅为更好的基本理解，而且为设计上级活性表面。