Ring assembly of silica nanospheres mediated by amphiphilic block copolymers with oxyethylene moieties

Abstract

Silica nanospheres (SNSs) of ca. 15 nm in diameter assemble into nanoring structures with the aid of amphiphilic block copolymers containing the oxyethylene side chains poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] [poly(EOVEb-MOVE)]. Cryo-transmission electron microscope observation confirms that the ring assembly of SNSs occurs in the liquid phase. The SNSs favorably assemble into ring-like nanostructures in the presence of 1-2 wt% EOVE 100 -b-MOVE 310 at pH~7.8 and 45°C. Irregular aggregates of SNSs form at 60°C, most likely because of the hydrophobic collapse of the thermoresponsive block copolymer. A series of poly(EOVE-b-MOVE) with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that the polymer's molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) assemble one-dimensionally into chain-like nanostructures in the presence of EOVE 100 -b-MOVE 310 .

Ring-Like Assembly of Silica Nanospheres in the Presence of Amphiphilic Block Copolymer: Effects of Particle Size

“…We previously reported synergistic self-assembly between silica nanospheres (SNSs) and amphiphilic block copolymers containing oxyethylene moieties in an aqueous phase in relatively dilute conditions (∼2 wt % silica and ∼2 wt % polymers). − SNSs have no ligands but instead interact with the copolymers through hydrogen bonding between the silanol groups of silica and the ether oxygens of the copolymers . SNSs were assembled into one-dimensional (1D) nanochains, − 2D nanorings, and 3D vesicles depending on the polymer structure, pH, and temperature. In particular, pH critically influences the formation of ordered structures.…”

“…Ring-like nanostructures have attracted attention because of their unique electric, magnetic, and optical properties. − In general, NP rings as 2D nanostructures have been fabricated using templates, such as lithographic patterns, solid spheres, droplets, , or bubbles, , which are prepared on solid substrates. Liquid-phase assembly of NPs into rings is an alternative approach that can yield free-standing nanorings. ,− One such example uses magnetic NPs that could be assembled into rings without templates due to the flux-closure mechanism. , Alternatively, ring-like structures consisting of gold and silver NPs were formed on viral protein templates in an aqueous phase. , And while its mechanism is still under investigation, nanodroplet-mediated ring-like assembly of platinum NPs has also recently been reported . In our approach, nanorings of SNSs are obtained in the presence of a synthetic polymer, poly­[(2-ethoxyethyl vinyl ether)– block –(2-methoxyethyl vinyl ether)] (EOVE–MOVE) at 45 °C in the proper pH range .…”

A well-defined block copolymer synthesis via living cationic polymerization and nitroxide-mediated polymerization using carboxylic acid-based alkoxyamines as a dual initiator

“…5 Following the discovery of a hydrogen iodide/iodine initiating system by Higashimura and Sawamoto, 6 a variety of binary initiating systems consisting of protonic acid/Lewis acid were developed to polymerize vinyl ether monomers in a living/controlled manner. [7][8][9][10][11][12][13] Hence, various functional block copolymers composed of vinyl ether monomer units were synthesized acting as polymer surfactants, 14,15 antibacterial agents, [16][17][18][19][20][21] glycopolymer stimuli-responsive micelles and gels, 16,[18][19][20][21] thermoplastic elastomers, 22,23 or optical plastics. 24 By combination those binary initiating systems with living/ controlled radical polymerization techniques such as reversible addition-fragmentation transfer polymerization (RAFT) or atom transfer radical polymerization (ATRP), block-, statisticaland graft copolymers of vinyl ether monomers with radically polymerizable monomers have been subsequently achieved using the chain-end chemical transformation strategy or the use of a dual initiator.…”

Early Formation Pathways of Surfactant Micelle Directed Ultrasmall Silica Ring and Cage Structures

“…Ultrasmall inorganic particles with sizes in the single-nanometer regime have recently attracted significant research attention due to their unique size-dependent properties, e.g., in optics, catalysis, and medicine. − Recent advances in electron microscopy have provided new mechanistic insights into their formation enabling unprecedented synthesis control. − Ultrasmall inorganic particles have therefore become one of the most promising building blocks for bottom-up fabrication of novel nanomaterials − and superlattices. − For crystalline nanomaterials, geometrical anisotropy is an important driver of structure control in self-assembly. , Amorphous inorganic particles are lacking this control parameter and organic templates or scaffolds are typically employed to direct structures. , Examples include surfactant self-assembly directed silica formation, which since first discoveries were reported , has seen steady progress in morphological control. , …”

“…13,14 Amorphous inorganic particles are lacking this control parameter and organic templates or scaffolds are typically employed to direct structures. 15,16 Examples include surfactant self-assembly directed silica formation, which since first discoveries were reported 17,18 has seen steady progress in morphological control. 19,20 Despite growing appreciation that clusters about 2 nm in size are the primary building blocks of various templated silica nano-and mesostructures, 21 elucidation of early formation and structural transformation pathways and their complexity has remained limited.…”