Linear growth of colloidal dumbbells into three-lobed polymer nanoparticles mediated by a gradient in surface wettability

Abstract

Anisotropy is a deciding factor in determining the hydrodynamics and self-assembly of colloidal particles. Linking particle morphology to said behaviors promoted the development of strategies to obtain anisotropic particles exhibiting defined shapes and symmetries. Dumbbell-shaped polymer particles made by phase separation during seeded polymerization are prominent examples. Phase separation among monomer and seed particle yields a liquid protrusion of monomer on the seed. This protrusion is then polymerized, becoming solid and yielding a solid spherical lobe. When this process is performed with spherical seeds, two-lobed particles, known as colloidal dumbbells, are obtained. Repeating this process of lobe formation one or more times could pave the way to tailored particle morphologies. Given the higher degree of anisotropy, multi-lobed particles can expand the rich phase behavior already found for dumbbells. We propose a new route in making anisotropic polymer particles by directing phase separation in a linear direction, thus permitting linear growth. Colloidal particles composed of three individual polymer lobes with the potential for site-specific modifications are obtained. Triggering of the phase separation is done complementary to prior efforts in fabricating three-lobed polymer particles based on cross-linked precursor particles. We will show that tailored surface properties of anisotropic seed particles can prove as an effective tool not only to promote the monomer-polymer phase separation, but also to guide it in a linear direction. Such gradients in surface functionalization open perspectives for making polymer colloids on a large scale in whose custom-tailored shapes their phase behavior and superstructure formation are already established.