Polymer Engineering and Colloid Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai-600 036, India.
Soft Matter. 2016 Jul 6;12(27):5950-8. doi: 10.1039/c6sm00809g.
Non-spherical patchy particles are potential candidates as building blocks for the design of target colloidal structures via spontaneous self-organization. We report a facile scheme to synthesize non-spherical particles with patchy electrostatic interactions. In this method, charged spherical latex particles such as polystyrene (PS) are deformed unequally at an oil-water interface due to heating and partial swelling. The spherical particles then evolve into non-spherical shapes such as 'acorn-like' and 'idly-like'. We explain the mechanism of differential deformation by comparing the heat of viscous dissipation and the interfacial energies. Furthermore, if oppositely charged additives such as the cetyltrimethylammonium bromide (CTAB) surfactant or silica nanoparticles are present in water (subphase), electrostatic attraction leads to adsorption of these species on the PS surface exposed to water. As a result, one side of the particles is selectively functionalized, while the other side remains unaltered. As the latex particles are negatively charged initially, this method yields particles that are non-spherical in shape and with negative charges on one side and positive charges on the other side. The degree of shape deformation and patch coverage can be varied by choosing different surface active additives. We extend this approach to curved interfaces and demonstrate a high throughput emulsion based approach for the synthesis of such particles. Self-assembly of these particles shows interesting structures such as linear, branched polymeric or worm-like chains and micelle-like spherical aggregates. These shape anisotropic particles with orientation specific interactions that mimic bio-macromolecular systems can be further explored for self-assembly into hierarchical mesoscale structures.
非球片状的微粒是通过自组装设计目标胶体结构的潜在候选物。我们报告了一种通过静电相互作用制备非球片状微粒的简易方法。在该方法中，由于加热和部分溶胀，带电荷的球形乳胶微粒（如聚苯乙烯 PS）在油水界面上会发生不均匀变形。这些球形颗粒随后会演变成非球形状，如“橡果状”和“陀螺状”。我们通过比较粘性耗散热和界面能来解释这种差异变形的机制。此外，如果在水中（底相）存在相反电荷的添加剂，如十六烷基三甲基溴化铵（CTAB）表面活性剂或硅纳米粒子，静电吸引会导致这些物质吸附在暴露于水的 PS 表面上。结果，颗粒的一侧被选择性功能化，而另一侧保持不变。由于乳胶颗粒最初带负电荷，因此这种方法得到的颗粒形状为非球型，一侧带负电荷，另一侧带正电荷。通过选择不同的表面活性添加剂，可以改变形状变形和补丁覆盖率的程度。我们将这种方法扩展到弯曲界面，并展示了一种基于乳液的高通量方法来合成这种颗粒。这些颗粒的自组装显示出有趣的结构，如线性、分支聚合物或蠕虫状链和胶束状球形聚集体。这些具有特定取向相互作用的形状各向异性颗粒可以进一步探索用于自组装成分级介观结构。
