Measurement Challenges in Dynamic and Nonequilibrium Nanoscale Systems

Abstract

Biological systems exhibit strikingly sophisticated properties, including adaptability, directed motion, regulation, and self-organization. Such systems are often described as being “nonequilibrium” or “out-of-equilibrium”, and it can be instructive to think of them as adopting thermodynamic states that require a constant supply of energy to maintain. Despite their ubiquity, systems that demonstrate these abilities require a remarkably stringent set of chemical requirements to exist. Broadly speaking, they must be (a) capable of consuming some external source of energy that (b) acts as a fuel to do some form of work, (c) all while maintaining highly organized structural features at the nanometer length scale that persist in space and over time. It remains a grand challenge in the field of chemistry to synthesize artificial systems capable of similarly complex nonequilibrium behavior both as a means for greater fundamental understanding and as a way to imbue non-natural structures with dynamic behavior for various applications. Yet an oft-overlooked challenge in this field involves not just the synthesis of nonequilibrium materials but also their characterization. The requirements for measuring nanometer-scale systems of nonequilibrium building blocks with the appropriate temporal and spatial resolution are demanding and have heretofore been largely unavailable to researchers. In this Perspective, we highlight challenges and recent advances in the measurement of dynamic nanoscale systems. We argue that progress in this area is crucial and must occur in parallel to synthetic goals if any meaningful understanding is to occur.

Ring-opening polymerization-induced crystallization-driven self-assembly of poly-L-lactide-block-polyethylene glycol block copolymers (ROPI-CDSA)

“…9). Therefore, we propose that during ring-opening polymerization, it is the release of the lactide ring strain, which drives a non-equilibrium self-assembly evolution (See Supplementary Discussion on non-equilibrium assembly) 55,68 . Although not all of the chemical energy stored in the monomer will be converted into free energy to drive self-assembly (some being lost as heat energy), as the growing polymer chain is unstable, it has a higher free energy than the soluble homopolymer.…”

Anomalous nanoparticle surface diffusion in LCTEM is revealed by deep learning-assisted analysis

“…The advent of in situ liquid cell transmission electron microscopy (LCTEM) has now made it possible to visualize the motion of nanoparticles near a surface with an unprecedented spatial resolution at the nanometer length scale (1)(2)(3). However, the electron beam of a transmission electron microscope (TEM), which is the key acquisition tool to enable nanoscale visualization, can significantly influence both interactions and dynamics of nanoparticles (4)(5)(6). Previous literature has reported that the motion of nanoparticles near the surface of an LC and in the presence of the electron beam is subdiffusive (i.e., non-Brownian, or "anomalous") (7)(8)(9)(10)(11)(12)(13)(14)(15)(16).…”

Understanding Symmetry Breaking at the Single-Particle Level via the Growth of Tetrahedron-Shaped Nanocrystals from Higher-Symmetry Precursors

“…17 Finally, heterogeneity in nanoparticle growth due to random or systematic influences is rarely captured by ensemble measurement techniques, making them particularly ill-suited to address mechanistic questions regarding nanoparticle shape transformations. 18 Recently, the direct imaging of processes in liquids via electron microscopy has emerged as an active field of research that provides time-resolved data regarding nanoscale growth and assembly mechanisms. 18−26 By trapping the sample solution in a sealed cell consisting of electron-transparent windows, the high energy electron beam can penetrate the entire specimen, allowing for the imaging of nanoscale dynamics and structural transformations with high spatial and temporal resolution in an environment that resembles the native ex situ conditions.…”

“…are minimally affected by nanoparticle shape, making the identification of the intermediate stages of growth extremely challenging . Finally, heterogeneity in nanoparticle growth due to random or systematic influences is rarely captured by ensemble measurement techniques, making them particularly ill-suited to address mechanistic questions regarding nanoparticle shape transformations …”

“…Recently, the direct imaging of processes in liquids via electron microscopy has emerged as an active field of research that provides time-resolved data regarding nanoscale growth and assembly mechanisms. − By trapping the sample solution in a sealed cell consisting of electron-transparent windows, the high energy electron beam can penetrate the entire specimen, allowing for the imaging of nanoscale dynamics and structural transformations with high spatial and temporal resolution in an environment that resembles the native ex situ conditions. The past decade has witnessed the powerful ability of liquid cell transmission electron microscopy (TEM) to reveal numerous fundamental processes governing nanocrystal nucleation, growth, etching, and self-assembly all at the single-particle level. − ,,, In particular, the direct observation of single-particle growth pathways allows for the full sequence of intermediate morphologies to be mapped, unequivocally connecting precursor to product.…”