Beyond the electrical double layer model: ion-dependent effects in nanoscale solvent organization.

The nanoscale organization of electrolyte solutions at interfaces is often described well by the electrical double-layer model. However, a recent study has shown that this model breaks down in solutions of LiClO in acetonitrile at a silica interface, because the interface imposes a strong structuring in the solvent that in turn determines the preferred locations of cations and anions. As a surprising consequence of this organisation, the effective surface potential changes from negative at low electrolyte concentration to positive at high electrolyte concentration.

The Projectile Perforation Resistance of Materials: Scaling the Impact Resistance of Thin Films to Macroscale Materials.

From drug delivery to ballistic impact, the ability to control or mitigate the puncture of a fast-moving projectile through a material is critical. While puncture is a common occurrence, which can span many orders of magnitude in the size, speed, and energy of the projectile, there remains a need to connect our understanding of the perforation resistance of materials at the nano- and microscale to the actual behavior at the macroscale that is relevant for engineering applications. In this article, we address this challenge by combining a new dimensional analysis scheme with experimental data from micro- and macroscale impact tests to develop a relationship that connects the size-scale effects and materials properties during high-speed puncture events.

Unsupervised Pharmaceutical Polymorph Identification and Multicomponent Particle Mapping of ToF-SIMS Data by Non-Negative Matrix Factorization.

Crystal polymorphism of pharmaceutical compounds directly impacts resulting physicochemical characteristics, a critical aspect in active pharmaceutical ingredient (API) production. Tools to characterize and chemically map these polymorphs at the single particle scale remain important to advancing directed manufacture of targeted polymorphs. Here, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed for chemically imaging inkjet printed acetaminophen samples.

Controlling toughness of polymer-grafted nanoparticle composites for impact mitigation.

Toughness in an entangled polymer network is typically controlled by the number of load-bearing topological constraints per unit volume. In this work, we demonstrate a new paradigm for controlling toughness at high deformation rates in a polymer-grafted nanoparticle composite system where the entanglement density increases with the molecular mass of the graft. An unexpected peak in the toughness is observed right before the system reaches full entanglement that cannot be described through the entanglement concept alone.

Using microprojectiles to study the ballistic limit of polymer thin films.

The dynamic impact between a particle and a planar material is important in many high impact events, and there is a growing need to characterize the mechanical properties of light-weight polymeric materials at dynamic loading conditions. Here, a laser-induced projectile impact test (LIPIT) is employed to investigate the ballistic limit (V0) and materials properties at impact velocities ranging from 40 m s-1 to 70 m s-1. An analytical expression describing the various energy dissipation mechanisms is established to estimate the yield stress and elasticity for polycarbonate thin films.

How clean is the solvent you use to clean your optics? A vibrational sum-frequency-generation study.

Solvents for cleaning optics often come into contact with plastic and/or rubber during storage and transfer. To explore the effects that exposure to these materials can have on solvents, we used vibrational sum-frequency-generation spectroscopy to study a silica optic following cleaning with solvents that had come into contact with either low-density polyethylene, high-density polyethylene, or rubber. Our studies show that even brief contact of acetone, methanol, or isopropanol with plastic or rubber can cause otherwise pure solvents to leave a persistent residue.

Reorientation-induced spectral diffusion in vibrational sum-frequency-generation spectroscopy.

There is a growing appreciation that dynamic processes play an important role in determining the line shape in surface-selective, nonlinear spectroscopies such as vibrational sum-frequency-generation (VSFG). Here we analyze the influence that reorientation can have on VSFG spectra when the vibrational transition frequency is a function of orientation. Under these circumstances, reorientation-induced spectral diffusion (RISD) causes the underlying spectral line shape to become time dependent.