Templated Synthesis and Assembly of Two-, Three- and Six-Patch Silica Nanoparticles with a Controlled Patch-to-Particle Size Ratio

Abstract

We report a fabrication route of silica nanoparticles with two, three or six patches with an easily tunable patch-to-particle size ratio. The synthetic pathway includes two main stages: the synthesis of silica/polystyrene multipod-like templates and the selective growth of their silica core through an iterative approach. Electron microscopy of the dimpled nanoparticles obtained after dissolution of the polystyrene nodules of the multipod-like nanoparticles provides evidence of the conformational growth of the silica core. Thanks to the presence of some polymer chains, which remained grafted at the bottom of the dimples after the dissolution of the PS nodules, the solvent-induced assembly of the patchy nanoparticles is performed. Chains, hexagonal suprastructures and cubic lattices are obtained from the assembly of two-, three- and six-patch silica nanoparticles, respectively. Our study can guide future work in both patchy nanoparticle synthesis and self-assembly. It also opens new routes towards the fabrication of specific classes of one-, two- and three-dimensional colloidal lattices, including complex tilings.

Solvent-induced assembly of mono- and divalent silica nanoparticles

“…First, silica/PS monopods consisting of a central silica core attached to one PS nodule ( Figure 2a ) have been prepared by seeded-growth emulsion polymerization of styrene, as reported elsewhere [ 32 ] (see experimental details). The silica core of the silica/PS monopods was regrown through successive additions of a small amount of tetraethoxysilane (TEOS) interspersed with centrifugation/redispersion cycles in order to avoid the occurrence of secondary nucleation of silica [ 30 ]. Figure 2b –f show the morphology of silica/PS nanoparticles after 1, 2, 4, 9, and 14 iterative silica growth steps, with measured diameter of the silica cap of 130, 165, 195, 250, and 315 nm, respectively.…”

“…It has been previously shown that monofunctional nanoparticles can act as chain stoppers, as their addition into suspensions of soft patchy nanoparticles [ 36 ], gold nanorods [ 27 ], or silver nanoplates [ 37 ] allowed for the control of chain length. We thus studied the capability of 1-PSN to act as chain stoppers when they are mixed with 2-PSN, whose solvent-induced assembly into colloidal polymers was recently reported [ 29 – 30 ]. Indeed, we previously showed that 2-PSN, which exhibit a disk-like morphology with a diameter of 190 nm, formed chains as long as 6 µm ( Figure 6a , bottom row) when 30 vol % of salty water was added into the NP dispersion in THF.…”

“…Following a multistep approach based on the conformational enlargement of the silica core of silica/PS monopods that we recently developed [30][31][32], one-patch silica nanoparticles with a controlled patch-to-particle size ratio ranging from 0.23 to 0.57 were synthesized. The decrease of the solvent quality for the PS patch induced by the addition of salty water made it sticky, which induced the assembly of the patchy silica nanoparticles into mostly dimers when the interactions between the PS chains were not annihilated by steric hindrance between the silica parts.…”

“…According to the procedure reported in [ 30 ], 9.1 mL of absolute ethanol, 0.7 mL of ammonia, and 0.2 mL of the dispersion of monopods (1.8 × 10 16 part/L) or bipods (1.8 × 10 16 part/L) were introduced into a 25 mL flask and the mixture was homogenized using a magnetic bar. A volume of 200 µL of TEOS was added all at once after 5 min.…”

“…By using post-assembly ligand photo-cross-linking [26] or by adding monofunctional nanospheres into a suspension of bifunctional gold nanorods [27], it has been shown that the average degree of polymerization of the resulting chains can be controlled. The reduction of solvent quality may also be employed to induce the assembly of silica/polystyrene (PS) dumbbells [28] and silica nanoparticles with two PS patches (2-PSN) [29][30][31] into multipod-like clusters and colloidal chains, respectively. We have recently reported that the same strategy can be used to assemble one-patch silica nanoparticles (1-PSN) with a well-controlled patch-to-particle size ratio (PPSR) into dimers, trimers, tetramers, and spherical micelles at a low incubation time in mixtures of tetrahydrofuran (THF) and ethanol [32].…”