Solvent-free extrusion emulsification (SFEE) is new technique for a twin-screw extruder to prepare submicron-sized particles (100-500 nm) without using hazardous solvents. The particle size is reliant upon the thickness of striated lamellae, which can be monitored rheologically based on the viscosity change occurring at the SFEE process. The lamellae coarsening rate is predominantly affected by the interfacial energy of the system when a surfactant is added but shows stronger dependency on viscosity change when interfacial growth between the polymer and water phases is solely determined by the end-groups conversion into carboxylate species. For this latter case, the dissolution of the sodium hydroxide species and the kinetics of end-groups conversion prove to be rate-limiting phenomena to generating thinner striated lamellae. Additionally, the ionic strength of the system is notably important to the viscosity response and particle size produced, particularly when surfactant is not added. (c) 2018 American Institute of Chemical Engineers AIChE J, 64: 2113-2123, 2018