An aqueous radiation curable dispersant formulation includes water and styrene acrylic resin stabilized thioxanthone derivative photoinitiator particles dispersed in the water. The styrene acrylic resin stabilized thioxanthone derivative photo initiator particles have a volume-weighted mean diameter of less than 40 nm. The styrene acrylic resin stabilized thioxanthone derivative photo initiator particles include a water-insoluble, thioxanthone derivative photoinitiator core having one, two, or three units. When the water-insoluble, thioxanthone derivative photoinitiator core includes two units or three units, the units are covalently bonded together.