Conformational control of two-dimensional gold nanoparticle arrays in a confined geometry within a vesicular wall

Controlling the Formation of Polyhedral Block Copolymer Nanoparticles: Insights from Process Variables and Dynamic Modeling

This study delves into the formation of nanoscale polyhedral block copolymer particles (PBCPs) exhibiting cubic, octahedral, and variant geometries. These structures represent a pioneering class that has never been fabricated previously. PBCP features distinct variations in curvature on the outer surface, aligning with the edges and corners of polyhedral shapes. This characteristic sharply contrasts with previous block copolymers (BCPs), which displayed a smooth spherical surface. The emergence of these cornered morphologies presents an intriguing and counterintuitive phenomenon and is linked to process parameters, such as evaporation rates and initial concentration, while keeping other variables constant. Using a system of coupled Cahn-Hillard (CCH) equations, we uncover the mechanisms driving polyhedral particle formation, emphasizing the importance of controlling relaxation parameters for shape variable u and microphase separation v. This unconventional approach, differing from traditional steepest descent method, allows for precise control and diverse polyhedral particle generation. Accelerating the shape variable u proves crucial for expediting precipitation and aligns with experimental observations. Employing the above theoretical model, we achieve shape predictions for particles and the microphase separation within them, which overcomes the limitations of ab initio computations. Additionally, a numerical stability analysis discerns the transient nature versus local minimizer characteristics. Overall, our findings contribute to understanding the complex interplay between process variables and the morphology of polyhedral BCP nanoparticles.

Tuning the Packing Density of Gold Nanoparticles in Peptoid Nanosheets Prepared at the Oil-Water Interface

Two-dimensional (2D) arrays of gold nanoparticles that can freely float in water are promising materials for solution-based plasmonic applications like sensing. To be effective sensors, it is critical to control the interparticle gap distance and thus the plasmonic properties of the 2D arrays. Here, we demonstrate excellent control over the interparticle gap distance in a family of freely floating gold nanoparticle-embedded peptoid nanosheets. Nanosheets are made via monolayer assembly and collapse at the oil-water interface, allowing for fine control over the solution nanoparticle concentration during assembly. We used surface pressure measurements to monitor the assembly of the peptoid, nanoparticle, and combined system at the oil-water interface to determine a workable range of nanosheet assembly conditions suitable for controlling the interparticle gap distances within the nanosheets. These measurements revealed that the extent of nanoparticle adsorption to the peptoid monolayer can be tuned by varying the bulk nanoparticle concentration, but the ability for the monolayer to collapse into nanosheets is compromised at high nanoparticle concentrations. Peptoid nanosheets were synthesized with varying bulk nanoparticle concentrations and analyzed using light microscopy and UV-visible spectroscopy. Based on the spectral shift of the localized surface plasmon resonance peaks for the nanoparticles in the nanosheets relative to those well dispersed in toluene, we estimate that we can access interparticle gap distances within the nanosheet interior between 2.9 ± 0.5 and 9 ± 2 nm. Our results suggest that the minimum interparticle distance achievable by this method is limited by the nanoparticle ligand length, and so has the potential to be further tuned by varying the ligand chemical structure. The ability to quantitatively control and monitor the assembly conditions by this method provide an opportunity to readily tune the optoelectronic properties of this new class of 2D nanomaterial, making it a promising platform for plasmonic-based sensing applications.