No abstract

Liquid metal (LM) micro/nano droplets have promising applications in various fields such as flexible electronics, catalysis, and soft composites as well as biomedicines. However, the preparation of highly stable LM nanodroplets suspension based on eutectic gallium/indium (EGaIn) alloys is still challenging. Herein, we report a general and robust strategy to fabricate EGaIn nanodroplets stabilized by polymer brushes (polymer brushes/EGaIn nanodroplets) via in situ attachment of well-defined diblock copolymers with short poly(acrylic acid) (PAA) anchoring segments. Under ultrasonication, the anchoring PAA block is in situ attached onto the gallium oxide "skin" layer of EGaIn nanodroplets to form polymer brushes. The attachable diblock copolymer surfactants allow for highly efficient formation of EGaIn nanodroplets in high yield and with narrow size distribution. The polymer brushes/EGaIn nanodroplets contain very low fractions of attached polymer (<1 wt %) and exhibit high colloidal stability (>30 days) and good redispersibility. Precise control of polymer architecture by atom-transfer radical polymerization was employed to prepare various block copolymers for suspensions in a variety of solvents.

An aqueous-based approach for the scalable synthesis of nitrogen-doped porous carbons with high specific surface area (SSA) and high nitrogen content is presented. Low molecular weight polyacrylonitrile (PAN) is solubilized in water in the presence of ZnCl that also acts as a volatile porogen during PAN pyrolysis to form mesoporous structures with significantly increased SSA. By templating with commercial SiO nanoparticles, nanocellulose fillers or filter paper, nanocarbons with SSA = 1776, 1366, and 1501 m/g, respectively and 10 wt % N content were prepared. The materials formed by this benign process showed excellent catalytic activity in oxygen reduction reaction via the four-electron mechanism.

Structurally tailored and engineered macromolecular (STEM) gels constitute part of an emerging field of smart materials. STEM gels are polymer networks containing latent initiator sites available for postsynthesis modification. STEM gels synthesized by controlled radical polymerization (CRP) are presented. First, reversible addition–fragmentation chain transfer (RAFT) polymerization was used to copolymerize (meth)­acrylate monomer, di­(meth)­acrylate cross-linker, and inimer for the subsequent atom transfer radical polymerization (ATRP) grafting-from process. The resulting STEM gels were infiltrated with a second monomer, which formed side chains grafted from the inimer sites by photoactivated ATRP. This approach permits significant spatial and temporal control over the structure of the resulting material. Here, the technique was used to transform primary STEM gels into single-piece amphiphilic and hard/soft materials.

A series of polyacrylonitrile-block-poly(butyl acrylate) (PAN-b-PBA) copolymers were prepared by supplemental activator reducing agent atom transfer radical polymerization (SARA ATRP). These copolymers were then used as precursors to pyrolytic nanostructured carbons with the PAN block serving as a nitrogen-rich carbon precursors and the PBA block acting as a sacrificial porogen. The study revealed that while the size of mesopores can be controlled by the size of the porogenic block, the connectivity of pores diminishes with the decrease of the overall molecular weight of the precursor. This partial loss of mesopore connectivity was attributed to the weaker phase segregation between the blocks of shorter lengths inferred from the shape of small-angle X-ray scattering profiles and from the crystallinity of polyacrylonitrile phase.