SPs were synthesized using a modified Stöber process (50 ). SMPs were prepared by oxidation and polymerization of dopamine (Sigma-Aldrich) in a mixture of water, ethanol, and ammonia hydroxide at room temperature following our previous reported protocol (33 (link)). Particle sizes were controlled by changing the amount of ammonium hydroxide (28 to 30% wt %; Sigma-Aldrich). We followed our previous reverse emulsion assembly protocol to make binary supraballs (11 (link)). Typically, we added 30 μl of aqueous solution of SPs/SMPs (filling volume fraction 3%) into 1 ml of anhydrous 1-octanol (Sigma-Aldrich). We used a vortex to shake the mixture to form reverse emulsion at a speed of 1600 rpm for 2 min and then 1000 rpm for 3 min. After supraball particles precipitated, we removed the supernatant and dried the samples under 60°C.
We used an evaporative assembly method to make films from mixtures of SP and SMP solutions (6 ). Typically, we prepared a solution of mixed SPs and SMPs at a filling volume fraction of 0.5%. A clean silicon wafer was vertically immersed into a suspension bath, and particles were deposited onto the clean silicon wafer to form films when the water evaporated at 60°C overnight. The water evaporating rate was recorded to be 0.5 mm/hour by tracking the decrease of water height in the container.
We used an evaporative assembly method to make films from mixtures of SP and SMP solutions (6 ). Typically, we prepared a solution of mixed SPs and SMPs at a filling volume fraction of 0.5%. A clean silicon wafer was vertically immersed into a suspension bath, and particles were deposited onto the clean silicon wafer to form films when the water evaporated at 60°C overnight. The water evaporating rate was recorded to be 0.5 mm/hour by tracking the decrease of water height in the container.
