A particularly promising outcome of this work is the potential to control the formation of specific structures or polymorphs by creating charged patterns on the substrate. 9 Low-density (ρ = 1.05 g/cm 3 ) polystyrene (PS) and low-refractive-index (n = 1.39) pentafluoropropyl methacrylate (PFPMA) colloids were synthesized via surfactant-free emulsion polymerization for bright-field microscopy and laser scanning confocal microscopy experiments, respectively. For the synthesis of 200 nm diameter positively charged PS particles, a mixture of 550 mL deionized water and 3 mL styrene monomer (≥ 99% from MilliporeSigma) was stirred at 330 rpm in a 1 L three-neck round-bottom flask. After purging with nitrogen for 1 hour, 0.5 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA) (97% from MilliporeSigma), dissolved in 10 mL deionized water, was injected into the mixture. The components were then heated to 60 • C and stirred at 330 rpm under nitrogen overnight. The particles were stabilized by adding 5 mL of 5 wt% Pluronic F108 solution and washed via repeated sedimentation and resuspension cycles. Finally, the particle suspensions were dialyzed against deionized water for one week using 50 kD Spectra/Por dialysis tubing, with daily water changes to ensure complete removal of salt. Negatively charged PS particles were synthesized similarly, replacing AIBA with an equivalent weight of potassium persulfate (KPS) (≥ 99% from MilliporeSigma).