Single-Step Microfluidic Synthesis of Various Nonspherical Polymer Nanoparticles via in Situ Assembling: Dominating Role of Polyelectrolytes Molecules

In this paper, a microfluidic approach has been used for the synthesis of ellipsoidal, dumbbell, rodlike, and necklacelike polymer nanoparticles. High yields of special types of nonspherical nanoparticles have been achieved by the implementation of an emulsion polymerization into microfluidic arrangement with a micro hole-plate reactor for the formation of monomer droplets. Here, in particular, the formation of nonspherical polymer nanoparticles is dependent on the presence of polyelectrolyte surface active molecules such as poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-PM), poly(sodium-p-styrenesulfonate) (PSSS), and polyanetholesulfonic acid sodium salt (PAES). The shapes and sizes of the interparticle nanoassemblies are precisely controlled by adjusting the concentration of polyelectrolytes in the aqueous phase, and by choosing suitable flow rate ratios (aqueous to monomer phase), respectively. The formation of polymer nanoparticles with different morphologies can be explained by a spontaneous in situ assembling under partial electrostatic repulsive control in the single step synthesis. The effect of particle charge and the competition between thermal motion of particles and electrostatic repulsion on the spontaneous assembling under the condition of a limited polarizability are discussed here as an important factor for the formation process of nonspherical polymer nanoparticles.