Mesopore-free silica shell with nanometer-scale thickness-controllable on cationic polystyrene core

The formation of mesopore-free silica shell with homogenous shell thickness, smooth surface, and controllable thickness in the nanometer range (from 4 to 12 nm) on core material was studied. Cationic polystyrene particles with various sizes (ranged from 80 to 300 nm) were used as a model of core material, which could be effective to support the electrostatic attraction between the core material and the negatively charged silica without any additives. Different from other reports, mesopore-free shell was produced due to the absence of additive. Basic amino acid (i.e., lysine) was used as a catalyst for forming the silica, which is harmless and able to control the silica growth and produce shell with smooth surface. Homogenous thin shell (thickness <13 nm) with nanometer-scale-controllable was reported, while in the current reports, the modification of the shell in this thickness range was typically difficult and relating to the formation of incomplete/inhomogeneous silica coating and rough surface. The relationships among the reaction parameters were also investigated in detail along with the theoretical consideration and the proposal of the silica coating formation mechanism. The present mesopore-free silica shell was efficiently used for various applications because of their tendency not to adsorb large molecules, as confirmed by the nitrogen sorption and large molecule adsorption analysis.