Liquid Metal Nanoparticles as Initiators for Radical Polymerization of Vinyl Monomers

Abstract

Sonication of gallium or gallium-based liquid metals in an aqueous solution of vinyl monomers leads to rapid free radical polymerization (FRP), without the need for conventional molecular initiators. Under ambient conditions, a passivating native oxide separates these metals from solution and renders the metal effectively inert. However, sonication generates liquid metal nanoparticles (LMNPs) of ∼100 nm diameter and thereby increases the surface area of the metal. The exposed metal initiates polymerization, which proceeds via a FRP mechanism and yields high molecular weight polymers that can form physical gels. Spin trapping EPR reveals the generation of free radicals. Time-of-flight secondary ion mass spectrometry measurements confirm direct polymer bonding to gallium, verifying the formation of surface-anchored polymer grafts. The grafted polymers can modify the interfacial properties, that is, the preference of the metal particles to disperse in aqueous versus organic phases. The polymer can also be degrafted and isolated from the particles using strong acid or base. The concept of physically disrupting passivated metal surfaces offers new routes for surface-initiated polymerization and has implications for surface modification, reduction reactions, and fabrication of mechanically responsive materials.

Liquid metal nanocomposites

“…Lastly, there has been increasing interest in utilizing LM nanodroplets for injection in blood for imaging 33 or near-infrared photothermal tumor ablation 34 as well as for nanoparticular mediated polymerization. 35,36 Although not directly related to LM nanocomposites, these applications demonstrate the extraordinary versatility of liquid metal nanoparticles and their potential for wide impact in elds ranging from polymer engineering to nanomedicine.…”

Liquid Metal Initiator of Ring‐Opening Polymerization: Self‐Capsulation into Thermal/Photomoldable Powder for Multifunctional Composites

“…Without the presence of any additional initiator, in situ free radical polymerization was also initiated by sonicating EGaIn in the aqueous solution of vinyl monomers. [ 19 ] The resultant macromolecular shells, when being negatively charged (e.g., alginate [ 3a ] ), could further be reinforced by cross‐linking into the microgels via Ga 3+ produced from EGaIn oxidization. In contrast to the ultrathin shells of oxides and amphiphiles, these flexible macromolecular shells had the thickness tuned from several to dozens of nanometers, [ 3,14,17,20 ] offering both the efficient protection barrier and additional functionalities for multiple applications of EGaIn droplets.…”

“…In contrast to molecular adsorption of small amphiphiles, [ 3b,11a ] in situ polymerization offered a promising opportunity to produce endurable shells of EGaIn capsules from monomers. [ 18 ] Besides the recently reported free radical polymerization of vinyl monomers, [ 19 ] ring‐opening polymerization would enable to synthesize more diverse polymeric shells of EGaIn capsules, for example, biodegradable and biocompatible polylactones, [ 22 ] which could offer not only potential applications in the biomedical field, [ 22a ] but also the compatibility with many different polymers. The polylactone shells were synthesized by following a facile “one‐batch” procedure, for example, sonicating bulk EGaIn in fluidic ε‐CL under N 2 atmosphere and then maintaining at 140 °C for polymerization ( Figure A).…”

“…In comparison with solid electronegative metals (e.g., Al and Sn), [ 24 ] Ga atoms on the surfaces of EGaIn nanodroplets could be at a high energy state under ultrasonication, [ 1,25 ] on account of the dynamic fluidic surfaces, large specific surface area (calculating up to 50 m 2 g −1 ) and high surface energy of EGaIn droplets. [ 19a ] The unpaired electrons of Ga atoms on the surfaces of EGaIn droplets tended to transfer and initiate anionic polymerization of ε‐CL (Figure S2, Supporting Information). [ 19a,26 ] When removing EGaIn or replacing it with Ga 2 O 3 , no trace of polymerization was detected for ε‐ CL at 140 °C for >15 h (Figure S3, Supporting Information).…”

Synthesis of 2D cobalt oxide nanosheets using a room temperature liquid metal

“…12 Recent work has shown that Ga based liquid metals can also be used as a solvent for the synthesis of a wide range of nanomaterials via chemical reactions that occur at the surface of the liquid metal under a variety of conditions including galvanic exchange at the surface of large liquid metal droplets or under sonication conditions which leads to composites containing gold that are catalytically active, 13 metal oxides such as MnO 2 that have photocatalytic properties, 14 Prussian blue nanomaterials, 15 as well as the ability to polymerise materials around the surface of liquid metal droplets. [16][17][18] One aspect that always needs to be considered when using galinstan, EGaIn or Ga in the liquid form is that when these materials are exposed to an oxygen containing atmosphere they spontaneously form a self limiting $0.7 nm layer of Ga 2 O 3 around the outside of the droplet, even when containing additional In or Sn components. 19 This phenomenon can be explained by calculation of the Gibbs free energy of formation (DG f ) of gallium oxide which is much lower than In 2 O 3 or SnO 2 which therefore results in preferential formation of Ga 2 O 3 at the surface.…”