Colloidal Chains Assembled from Nanoscale Micelles of Diblock Copolymers and Their Orientation for Linear Alignment of Fluorophores and Nanoparticles

Colloidal particles in nano- or micro-scale can assemble into a variety of superstructures, which can deliver cooperative properties not observed in individual particles. Patches created on the particle exterior, which are chemically or physically different from the particle surface, are useful for effective bindings between colloidal particles. Thus, the patchy particles can be combined into structures like colloidal molecules and chains by utilizing directional bonding between the patches. In particular, colloidal chains exhibit anisotropic properties that can be intensified at the macroscopic scale by orientating the chains. In this presentation, we confirmed the step-growth mechanism in the self-assembly of patchy micelles of diblock copolymers and also functionalized the colloidal chains with fluorophores and nanoparticles. To elucidate the mechanism of assembling the micelles, we investigated well-separated colloidal chains with sufficient numbers using electron microscopy and evaluated the dimensional evolution of the chains. As the assembling process progressed, the chains appeared to become longer, confirmed by an increase in the number of longer chains in the size distribution, which follows the most probable distribution, a feature of the step-growth polymerization. Based on the mechanism, we were able to accelerate colloidal polymerization by increasing the initial concentration of patchy micelles and form cyclic chains by diluting the solution. In addition, the colloidal chains were coated differently by drop-casting and spin-coating. Then, the orientation and stretching of the chains were analyzed quantitatively by directly observing individual chains with an electron microscope. For drop-cast chains without external force, no specific orientation was observed. In contrast, the spin-coated chains subjected to centrifugal force were oriented in the radial direction. The spin-coated chains also exhibited stretched conformations compared to the drop-cast chains. We utilized these oriented and stretched chains as a template to align fluorophores and nanoparticles. By incorporating red-emitting fluorophores into the cores of patchy micelles forming colloidal chains, we observed the oriented chains showing red fluorescence. We also synthesized Au and Pt nanoparticles at the location of the oriented chains by loading the precursors into the micellar cores of the chains, followed by plasma treatment, which resulted in their linear alignment.