Kodger Thomas E, Guerra Rodrigo E, Sprakel Joris
School of Engineering and Applies Sciences, Harvard University, Cambridge, 02138, USA.
Department of Physics, Harvard University, Cambridge, MA, 02138, USA.
Sci Rep. 2015 Sep 30;5:14635. doi: 10.1038/srep14635.
Model colloidal systems studied with confocal microscopy have led to numerous insights into the physics of condensed matter. Though confocal microscopy is an extremely powerful tool, it requires a careful choice and preparation of the colloid. Uncontrolled or unknown variations in the size, density, and composition of the individual particles and interactions between particles, often influenced by the synthetic route taken to form them, lead to difficulties in interpreting the behavior of the dispersion. Here we describe the straightforward synthesis of copolymer particles which can be refractive index- and density-matched simultaneously to a non-plasticizing mixture of high dielectric solvents. The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction. We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation. The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.
利用共聚焦显微镜研究的模型胶体系统，已为凝聚态物质的物理学带来了诸多见解。尽管共聚焦显微镜是一种极其强大的工具，但它需要精心选择和制备胶体。单个颗粒的大小、密度和组成以及颗粒间相互作用的不受控制或未知变化，通常受形成它们所采用的合成路线影响，这给解释分散体的行为带来了困难。在此，我们描述了共聚物颗粒的直接合成方法，这些颗粒可以同时与高介电常数非增塑溶剂混合物实现折射率和密度匹配。通过使用原子转移自由基聚合（ATRP）进行聚合物刷的表面接枝，可精确调节颗粒间的相互作用，从类似硬球的相互作用到长程静电排斥或混合电荷吸引。我们还通过改变共聚物比例来调节颗粒的浮力密度，同时保持其与悬浮溶液的折射率匹配，从而实现对沉降的良好控制。颗粒间相互作用的可调性、溶剂的低挥发性以及使颗粒的折射率和密度同时与流体匹配的能力，为探索胶体系统的物理学开辟了新的可能性。
