Preparation of Non-Spherical Janus Particles via an Orthogonal Dissolution Approach.

Post-synthesis modifications are valuable tools to alter functionalities and induce morphology changes in colloidal particles. Non-spherical polymer particles with Janus characteristics are prepared by combining seeded growth polymerization and selective dissolution. First, spherical polystyrene (PS) particles have been swollen with methyl methacrylate (MMA) with an activated swelling method. This is followed by polymerization that led to particles with two well-separated faces: one made of PS and the second of polymethyl methacrylate (PMMA). Subsequently, non-spherical particles are obtained by exposing the Janus colloids to various solvents. Using the two polymers' orthogonal solubility, solvents are identified to selectively dissolve only one face, leading to hemispherical PS or PMMA particles. It is further investigated how changing the composition of the PMMA face - by either co-polymerization with glycidyl methacrylate or by adding a cross-linker - affects the particles' morphology. The poly-methacrylate face can gain total or partial resistance towards the solvents, resulting in intriguing shapes, such as mushroom-like and Janus dimpled particles. The dissolution mechanisms are investigated via optical microscopy, where total or partial dissolutions can be directly observed. Lastly, prematurely quenching the dissolution of the particle's lobes with water can be used to control the Janus mushroom-like particle aspect ratio.