Effects of Functional Groups and Ionization on the Structure of Alkanethiol-Coated Gold Nanoparticles

We report classical atomistic molecular dynamics simulations of alkanethiol-coated gold nanoparticles solvated in water and decane, as well as at water/vapor interfaces. The structure of the coatings is analyzed as a function of various functional end groups, including amine and carboxyl groups in various ionization states. We study both neutral and charged end groups for two different chain lengths (9 and 17 carbons). For the charged end groups, we simulated both mono- and divalent counterions. For the longer alkanes, we find significant local bundling of chains on the nanoparticle surface, which results in highly asymmetric coatings. In general, the charged end groups attenuate this effect by enhancing the water solubility of the nanoparticles. On the basis of the coating structures and density profiles, we can qualitatively infer the overall solubility of the nanoparticles. This asymmetry in the alkanethiol coatings is likely to have a significant effect on aggregation behavior. Our simulations elucidate the mechanism by which modulating the end group charge state can be used to control coating structure and therefore nanoparticle solubility and aggregation behavior

Atomistic Simulations Predict a Surprising Variety of Morphologies in Precise Ionomers

The nature of ionic aggregates in ionomers remains an important open question, particularly considering its significance to their unique electrical and mechanical properties. We have carried out fully atomistic molecular dynamics simulations of melts of lithium-neutralized precise ionomers that reveal the structural features of ionic aggregates in unprecedented detail. In particular, we observe a rich variety of aggregate morphologies depending on neutralization level and ionic content, including string-like and percolated aggregates. The traditional assumption of spherical ionic aggregates with liquid-like ordering that is typically used to interpret experimental scattering data is too simplistic; a more rich and complex set of structures exist that also fit the scattering data

Influence of Cation Type on Ionic Aggregates in Precise Ionomers

We report atomistic molecular dynamics (MD) simulations of model ionomers with precise spacing between charged groups (polyethylene-<i>co</i>-acrylic acid). We explore different counterion types, neutralization levels, and spacer lengths between acid groups and provide a thorough analysis of the resulting ionic aggregate morphologies. Structure factors computed from the simulations are in good agreement with previous experimental X-ray scattering data, which provides strong validation of the simulation methods. Aggregate morphologies range from small spherical aggregates to string-like shapes and large percolated networks. The unexpected morphologies of the ionic aggregates suggest the need for a novel interpretation of scattering data for these materials. We quantify cation–anion and oxygen–hydrogen association, the two interactions primarily responsible for aggregate formation, and report detailed information pertaining to local structures around cations. This information is difficult to obtain experimentally and may have important consequences for ion transport

Mechanically Encoded Cellular Shapes for Synthesis of Anisotropic Mesoporous Particles

The asymmetry that pervades molecular mechanisms of living systems increasingly informs the aims of synthetic chemistry, particularly in the development of catalysts, particles, nanomaterials, and their assemblies. For particle synthesis, overcoming viscous forces to produce complex, nonspherical shapes is particularly challenging; a problem that is continuously solved in nature when observing dynamic biological entities such as cells. Here we bridge these dynamics to synthetic chemistry and show that the intrinsic asymmetric shapes of erythrocytes can be directed, captured, and translated into composites and inorganic particles using a process of nanoscale silica-bioreplication. We show that crucial aspects in particle design such as particle–particle interactions, pore size, and macromolecular accessibility can be tuned using cellular responses. The durability of resultant particles provides opportunities for shape-preserving transformations into metallic, semiconductive, and ferromagnetic particles and assemblies. The ability to use cellular responses as “structure directing agents” offers an unprecedented toolset to design colloidal-scale materials