Oppositely charged PS particles were separately equilibrated with 0.1 wt% Pluronic F108 and 2-5 mM NaCl for 30 minutes. They were then mixed together while vortexing. The resulting mixture was promptly transferred into hydrophobized borosilicate glass capillaries (VitroCom, model 3520), which were then sealed on both ends with wax (Hampton Research) or epoxy resin (Norland 81). Capillaries were pre-cleaned in a Jelight Model 18 ultraviolet ozone (UVO) cleaner for 20 minutes. Subsequently, they were exposed to methyltrichlorosilane (99%, MilliporeSigma) vapor inside a moisture-free sealed chamber for 1 hour to hydrophobize the surface. After this treatment, the capillaries were washed with water and ethanol for three cycles and finally dried in an oven. This hydrophobization pre-treatment facilitates the formation of a polymer brush on the glass surface when in contact with a Pluronic F108 solution.