Effects of the Density of Chemical Cross-links and Physical Entanglements of Ultraviolet-Irradiated Polystyrene Chains on Domain Orientation and Spatial Order of Polystyrene-block-Poly(methyl methacrylate) Nano-Domains.

Ultraviolet irradiation (UVI) of varied duration caused cross-linking and neutralization of polystyrene (PS) homopolymers of molar mass (Mn) from 6 to 290 kg mol-1 on a silicon-oxide surface. An optimal neutral skin layer on the surface of the PS was obtained via brief UVI in air (UVIA), by which the PS had no preferential interaction with either block in the copolymer. UVI in an inert environment (gaseous dinitrogen) (UVIN) stabilized the PS layers via cross-linking and enabled the PS networks to have an effective adhesive contact with the underlying substrate. Thorough examination of domain orientations and spatial orders of a series of block copolymer, polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), thin films deposited on these UVI-treated PS support layers yielded clear evidence that a dense layer of neutralized PS chains was required for the perpendicular orientation of PS-b-PMMA nanodomains. In particular, in addition to neutralization, two factors-the densities of physical entanglements and of chemical crosslinks-both in UVI-treated PS should be considered for the perpendicular orientation of nanolamellae and nanocylinders in symmetric and asymmetric PS-b-PMMA thin films. The density of physical entanglement in PS depends intrinsically on Mn of the PS, whereas the density of chemical cross-links was controlled with a varied duration of UVIN. Sufficiently large densities of physical entanglements and chemical cross-links can prevent PS-b-PMMA chains from penetrating through the neutral skin layer. The total density of physical entanglements and chemical cross-links required for the perpendicular orientation is correlated with the dimensions of the PS-b-PMMA chains.

High-Performance SERS Substrate Based on Hierarchical 3D Cu Nanocrystals with Efficient Morphology Control.

Cu nanocrystals of various shapes are synthesized via a universal, eco-friendly, and facile colloidal method on Al substrates using hexadecylamine (HDA) as a capping agent and glucose as a reductant. By tuning the concentration of the capping agent, hierarchical 3D Cu nanocrystals show pronounced surface-enhanced Raman scattering (SERS) through the concentrated hot spots at the sharp tips and gaps due to the unique 3D structure and the resulting plasmonic couplings. Intriguingly, 3D sword-shaped Cu crystals have the highest enhancement factor (EF) because of their relatively uniform size distribution and alignment. This work opens new pathways for efficiently realizing morphology control for Cu nanocrystals as highly efficient SERS platforms.

A Single-Step Hydrothermal Route to 3D Hierarchical Cu2 O/CuO/rGO Nanosheets as High-Performance Anode of Lithium-Ion Batteries.

As anodes of Li-ion batteries, copper oxides (CuO) have a high theoretical specific capacity (674 mA h g-1 ) but own poor cyclic stability owing to the large volume expansion and low conductivity in charges/discharges. Incorporating reduced graphene oxide (rGO) into CuO anodes with conventional methods fails to build robust interaction between rGO and CuO to efficiently improve the overall anode performance. Here, Cu2 O/CuO/reduced graphene oxides (Cu2 O/CuO/rGO) with a 3D hierarchical nanostructure are synthesized with a facile, single-step hydrothermal method. The Cu2 O/CuO/rGO anode exhibits remarkable cyclic and high-rate performances, and particularly the anode with 25 wt% rGO owns the best performance among all samples, delivering a record capacity of 550 mA h g-1 at 0.5 C after 100 cycles. The pronounced performances are attributed to the highly efficient charge transfer in CuO nanosheets encapsulated in rGO network and the mitigated volume expansion of the anode owing to its robust 3D hierarchical nanostructure.