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Driving and measuring chemical reactions at the nanoscale is crucial for developing safer, more efficient, and environment-friendly reactors and for surface engineering. Quantitative understanding of surface chemical reactions in real operating environments is challenging due to resolution and environmental limitations of existing techniques. Here we report an atomic force microscope technique that can measure reaction kinetics driven at the nanoscale by multiphysical stimuli in an ambient environment. We demonstrate the technique by measuring local reduction of graphene oxide as a function of both temperature and force at the sliding contact. Kinetic parameters measured with this technique reveal alternative reaction pathways of graphene oxide reduction previously unexplored with bulk processing techniques. This technique can be extended to understand and precisely tailor the nanoscale surface chemistry of any two-dimensional material in response to a wide range of external, multiphysical stimuli. [ABSTRACT FROM AUTHOR]

The expansive use of hydrogels in healthcare relies on carefully tuned properties in dynamic environments with predictable behavior, including time sensitive biological systems and biomedical applications. To meet demands in these settings, nanomaterials are often introduced to a hydrogel matrix which simultaneously elevates potential applications while adding complexity to fundamental characteristics. With respect to drug delivery, gold nanoparticles have modifiable surfaces to carry an array of targeted drug treatments. However, different molecules acting as capping ligands possess different chemical structures that can impact gelation times. To understand the influence of capping ligand chemistry on polyacrylamide (PAM) based nanocomposite hydrogel radical gelation time, gold nanoparticle (Au NP) capping ligands were selected to encompass varying functional groups and molecular weights: citrate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, and poly(acrylic acid). Gelation times were quantified as the storage-loss moduli crossover point in rheological time sweeps at constant strain and frequency. The dominating factor for gelation time was the presence of Au NPs, independent of a diverse range of capping ligand structures. The gelation times were also markedly faster than the same capping ligand structures used as stand-alone molecular additives. The accelerated Au NP gelation times, under 2 min, are attributed to the Au NPs acting as a cross-linker, promoting gelation. These results bolster the potential implementation of Au NP nanocomposite hydrogels in time-sensitive biomedical applications as robust drug carriers., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Graphene has unique mechanical, electronic, and optical properties that make it of interest for an array of applications. These properties can be modulated by controlling the architecture of graphene and its interactions with surfaces. Self-assembled monolayers (SAMs) can tailor graphene-surface interactions; however, spatially controlling these interactions remains a challenge. Here, we blend colloidal lithography with varying SAM chemistries to create patterned architectures that modify the properties of graphene based on its chemical interactions with the substrate and to study how these interactions are spatially arrayed. The patterned systems and their resulting structural, nanomechanical, and optical properties have been characterized using atomic force microscopy, Raman and infrared spectroscopies, scattering-type scanning near-field optical microscopy, and X-ray photoelectron spectroscopy.

Aramid nanofibers (ANFs), or nanoscale Kevlar fibers, are of interest for their high mechanical performance and functional nanostructure. The dispersible nature of ANFs opens up processing opportunities for creating mechanically robust and flexible nanocomposites, particularly for energy and power applications. The challenge is to manipulate ANFs into an electrode structure that balances mechanical and electrochemical performance to yield a robust and flexible electrode. Here, ANFs and graphene oxide (GO) sheets are blended using layer-by-layer (LbL) assembly to achieve mechanically flexible supercapacitor electrodes. After reduction, the resulting electrodes exhibit an ANF-rich structure where ANFs act as a polymer matrix that interfacially interacts with reduced graphene oxide sheets. It is shown that ANF/GO deposition proceeds by hydrogen bonding and π-π interactions, leading to linear growth (1.2 nm/layer pairs) and a composition of 75 wt % ANFs and 25 wt % GO sheets. Chemical reduction leads to a high areal capacitance of 221 μF/cm 2 , corresponding to 78 F/cm 3 . Nanomechanical testing shows that the electrodes have a modulus intermediate between those of the two native materials. No cracks or defects are observed upon flexing ANF/GO films 1000 times at a radius of 5 mm, whereas a GO control shows extensive cracking. These results demonstrate that electrodes containing ANFs and reduced GO sheets are promising for flexible, mechanically robust energy and power.