Salt-induced polyelectrolyte capsule formation in microfluidics

Microfluidics provides an exceptional platform for the generation of polymer solution droplets and their subsequent manipulation. We describe the formation of carboxymethyl cellulose (CMC) particles and capsules induced by salt diffusion. Generally used as a sodium salt, NaCMC is an anionic, weak, semiflexible polyelectrolyte, and one of the most widely used polyelectrolyte cellulose derivatives, with applications in the food, pharmaceutical, personal care, cosmetic, and paper industries. We employ SANS, light scattering, and rheology to probe the conformation and dynamics of aqueous NaCMC solutions across a wide range of molecular weight (Mw), degree of substitution, salt (mono, di and trivalent) and polymer concentrations. We then investigate the addition of a series of multivalent salts to induce the gelation and/or precipitation of bulk NaCMC solutions, which is spatiotemporally resolved by SANS and microscopy, establishing salt front propagation kinetics and accompanying conformational changes of the polymer. Equipped with this knowledge, we design and fabricate CMC gel capsules and particles with prescribed dimensions and external shape, microstructure and dissolution profile.