Schelling M P M, Verouden T W J, Stevens T C M, Meijer J-M
Department of Applied Physics and Science Education, Eindhoven University of Technology, Groene Loper 19, 5612 AP Eindhoven, The Netherlands.
Institute for Complex Molecular Systems, Eindhoven University of Technology, Groene Loper 19, 5612 AP Eindhoven, The Netherlands.
Soft Matter. 2024 Aug 14;20(32):6343-6352. doi: 10.1039/d4sm00517a.
Controlled crystallization, melting and vitrification are important fundamental processes in nature and technology. However, the microscopic details of these fundamental phenomena still lack understanding, in particular how the cooling rate and presence of a wall influence the crystal nucleation and glass formation. Thermoresponsive microgels provide the possibility to study phase transitions at the single-particle level, owing to the ability to tune the particle size with temperature. In this study, we employ composite microgels consisting of a hard core and a crosslinked poly(-isopropyl acrylamide--methacrylic acid) shell to study the crystallization of dense suspensions of soft colloids near a wall using confocal microscopy. We investigate the effect of the cooling rate on the fluid-to-solid transition close to the sample wall. The structures formed during cooling range from glassy in the case of a rapid temperature quench to crystalline when a slow cooling rate is used. Detailed analysis of the final structure reveals that the cooling rate also sets the degree of alignment of the crystal domains with the wall as a result of a balance between homogeneous and heterogeneous crystal nucleation. The results presented here yield valuable insight into the microscopic details of temperature-controlled crystallization near a wall. This understanding will help pave the way towards optimal crystallization conditions for microgel applications.
可控结晶、熔化和玻璃化是自然界和技术领域中重要的基础过程。然而，这些基础现象的微观细节仍未得到充分理解，尤其是冷却速率和壁的存在如何影响晶体成核和玻璃形成。热响应性微凝胶由于能够随温度调节粒径，为在单粒子水平研究相变提供了可能性。在本研究中，我们使用由硬核和交联聚（N-异丙基丙烯酰胺-N-甲基丙烯酸）壳组成的复合微凝胶，通过共聚焦显微镜研究靠近壁的软胶体浓悬浮液的结晶过程。我们研究了冷却速率对靠近样品壁的流体-固体转变的影响。冷却过程中形成的结构范围从快速温度猝灭时的玻璃态到缓慢冷却速率时的晶态。对最终结构的详细分析表明，由于均匀和非均匀晶体成核之间的平衡，冷却速率还决定了晶畴与壁的排列程度。本文给出的结果为靠近壁的温度控制结晶的微观细节提供了有价值的见解。这种理解将有助于为微凝胶应用的最佳结晶条件铺平道路。
