Polymerization-induced self-assembly (PISA) and in situ crosslinking of the formed nanoparticles are successfully realized by activators regenerated by electron-transfer atom transfer radical polymerization (ARGET ATRP) of glycidyl methacrylate (GMA) or a mixture of GMA/benzyl methacrylate (BnMA) monomers in ethanol. Poly(oligo(ethylene oxide) methyl ether methacrylate) was employed as macroinitiator/stabilizer, and a cupric bromide/tris(pyridin-2-ylmethyl)amine complex as catalyst. Tin (2-ethylhexanoate) was used as reducing agent for ARGET ATRP, and simultaneously acted as a catalyst for ring-opening polymerization of oxirane ring in GMA. The kinetics shows that the double bond in GMA was completely polymerized in 4.0 h, while only a 33% conversion of oxirane ring in GMA was reached at 117.0 h. Such a large difference would guarantee a smooth PISA and a subsequent in situ crosslinking of formed nanoparticles. The transmission electron microscopy and dynamic light scattering show spherical nanoparticles formed. With a feed molar ratio [BnMA] /[GMA] = 150/50, 100/100, and 50/150, the nanoparticles formed in ethanol can dissociate or swell in toluene. When pure GMA was used, the solid nanoparticles were observed in toluene or ethanol. The ARGET ATRP provides an efficient strategy to stabilize the nanoparticles formed in the PISA of GMA-containing system.
The twinned structure of nanoscale metal particles is considered to be an important factor in the formation of novel morphologies. Nevertheless, most studies are focused on the growth of nanoparticles with stable twinned structures and little is known about the intrinsic relationship between the morphological evolution and the strain relaxation induced by twin boundary migration. In this study, we elucidated the mechanisms of symmetry breaking induced by strain relaxation in Ag nanoparticles by employing transmission electron microscopy, electron tomography, and strain analysis. The experimental results reveal that decahedral nanoparticles larger than ∼50 nm evolve into asymmetrical rhomboid pyramids to relax the lattice strain energy in the 5fold twin through twin pole migration. This migration is achieved by coordinating slip and dissociation of partial and perfect dislocations. In addition, we found that the rhomboid pyramid further evolves into a rhomboid bar during growth in a specific way to avoid increasing the strain energy in the crystal.
Nanoparticle (NP) superlattices have attracted increasing attention due to their unique physicochemical properties. However, key questions persist regarding the correlation between short‐ and long‐range driving forces for nanoparticle assembly and resultant capability to predict the transient and final superlattice structure. Here the self‐assembly of Ag NPs in aqueous solutions is investigated by employing in situ liquid cell transmission electron microscopy, combined with atomic force microscopy‐based force measurements, and theoretical calculations. Despite the NPs exhibiting instantaneous Brownian motion, it is found that the dynamic behavior of NPs is correlated with the van der Waals force, sometimes unexpectedly over relatively large particle separations. After the NPs assemble into clusters, a delicate balance between the hydration and van der Waals forces results in a distinct distribution of particle separation, which is ascribed to layers of hydrated ions adsorbed on the NP surface. The study demonstrates pivotal roles of the complicated correlation between interparticle forces; potentially enabling the control of particle separation, which is critical for tailoring the properties of NP superlattices.
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