Constructing helical nanowires via polymerization-induced self-assembly

Colloidal substrate-facilitated synthesis of gold nanohelices

Helical nanostructures have unique optical and mechanical properties, yet their syntheses had always been quite challenging. Various symmetry-breaking mechanisms such as chiral templates, strain-restriction and asymmetric ligand-binding have been developed to induce the helical growth at nanoscale. In this work, with neither chiral ligands nor templates, gold (Au) nanohelices were synthesized via a facile wet-chemical method, through an asymmetric Active Surface Growth facilitated by colloidal silica nanoparticles (NPs). The one-dimensional growth followed the Active Surface Growth, which employs a thiolated ligand to direct continuous deposition of Au at the interface, known as the active surface, between the Au nanostructures and the silica NPs - the colloidal substrates. More importantly, the colloidal substrates are crucial for the helical growth, as the diameter of the obtained nanohelices was found proportional to the size of the colloidal substrates. We propose that the nanoscale size and the curvature of the silica NPs would reduce the size of anchoring point between Au nanowires and the substrates, causing partial blockage of the active surface by the substrate and divergence of the activity on the active surface towards Au deposition. The subsequent inequivalent deposition, and the dynamic shifting of the blockage lead to the asymmetric growth and the formation of nanohelices. Factors that would affect the asymmetric Active Surface Growth were also identified and discussed, including the reduction kinetics, substrate treatment and the type and concentration of the ligand. In particular, variation of the size of the active surfaces would change the degree of the surface inequivalence, and thus affect the yield of the nanohelices.

Fluoropolymer Nanoparticles Synthesized via Reversible-Deactivation Radical Polymerizations and Their Applications

Fluorinated polymeric nanoparticles (FPNPs) combine unique properties of fluorocarbon and polymeric nanoparticles, which has stimulated massive interest for decades. However, fluoropolymers are not readily available from nature, resulting in synthetic developments to obtain FPNPs via free radical polymerizations. Recently, while increasing cutting-edge directions demand tailored FPNPs, such materials have been difficult to access via conventional approaches. Reversible-deactivation radical polymerizations (RDRPs) are powerful methods to afford well-defined polymers. Researchers have applied RDRPs to the fabrication of FPNPs, enabling the construction of particles with improved complexity in terms of structure, composition, morphology, and functionality. Related examples can be classified into three categories. First, well-defined fluoropolymers synthesized via RDRPs have been utilized as precursors to form FPNPs through self-folding and solution self-assembly. Second, thermally and photoinitiated RDRPs have been explored to realize in situ preparations of FPNPs with varied morphologies via polymerization-induced self-assembly and cross-linking copolymerization. Third, grafting from inorganic nanoparticles has been investigated based on RDRPs. Importantly, those advancements have promoted studies toward promising applications, including magnetic resonance imaging, biomedical delivery, energy storage, adsorption of perfluorinated alkyl substances, photosensitizers, and so on. This Review should present useful knowledge to researchers in polymer science and nanomaterials and inspire innovative ideas for the synthesis and applications of FPNPs.