报告人：Prof. Periklis Papadopoulos
题目：Confocal imaging of nanodroplets on hydrophobic surfaces
In the process of solvent exchange, oil droplets nucleate and grow on a solid substrate in response to the oversaturation generated through the displacement of a good oil solvent by a poor one. The mean size of the droplets depends on flow rate, flow geometry and solution conditionsand usually varies from the nanometer to micrometer range [1,2] . They have practical implications for high-throughput chemical and biological analysis, lubrications, laboratory-on-chip devices, and near-field imaging techniques. Here we observe the formation and evolution of oil nanodroplets in a Hele-Shaw cell in situ, by using confocal microscopy  . Unlike AFM that requires low contact angles [1,4] , confocal microscopy can be applied any drop shape, from nearly flat to spherical [5,6] . With proper deconvolution and fitting, drops smaller than the resolution can be analyzed. Thus, 3D videos enable the measurement of contact angle and radius and their dependence on time for isolated nanodroplets. The oils and solvents used represent the typical system for the “ouzo effect“, where anethole is the oil, and ethanol and water are the good and poor solvent, respectively. As anethole drops in water form high contact angles on glass (θadv = 75°, θrec = 45°) compared to previous studies on nanobubbles and nanodroplets on hydrophobic surfaces, we observe qualitatively different effects. The high Laplace pressure gives rise to faster Ostwald ripening that affects the final size and number of nanodroplets, in constrast to systems with low contact angles  . These results show that pinning is essential for the stabilization of nanobubbles and nanodroplets.
1. Zhang, X.; Lu, Z.; Tan, H.; Bao, L.; He, Y.; Sun, C.; Lohse, D. Formation of Surface Nanodroplets under Controlled Flow Conditions. PNAS 2015, 112 (30), 9253–9257.
2. Lohse, D.; Zhang, X. Surface Nanobubbles and Nanodroplets. Rev. Mod. Phys. 2015, 87 (3), 981–1035.
3. P. Papadopoulos, S. Maheshwari, D. Lohse, X. Zhang (in preparation)
4. Tan, H.; Peng, S.; Sun, C.; Zhang, X.; Lohse, D. 3D Spherical-Cap Fitting Procedure for (Truncated) Sessile Nano- and Micro-Droplets & Bubbles. Eur. Phys. J. E 2016, 39 (11), 106.
5. Kajiya, T.; Schellenberger, F.; Papadopoulos, P.; Vollmer, D.; Butt, H.-J. 3D Imaging of Water-Drop Condensation on Hydrophobic and Hydrophilic Lubricant-Impregnated Surfaces. Sci. Rep. 2016, 6, 23687.
6. Schellenberger, F.; Xie, J.; Encinas, N.; Hardy, A.; Klapper, M.; Papadopoulos, P.; Butt, H.-J.; Vollmer, D. Direct Observation of Drops on Slippery Lubricant-Infused Surfaces. Soft Matter 2015, 11 (38), 7617–7626.
7. Xu, C.; Yu, H.; Peng, S.; Lu, Z.; Lei, L.; Lohse, D.; Zhang, X. Collective Interactions in the Nucleation and Growth of Surface Droplets. Soft Matter 2017, 13 (5), 937–944.