The First Moment of Azimuthal Anisotropy in Nuclear Collisions from AGS to LHC Energies

We review topics related to the first moment of azimuthal anisotropy ($v_1$), commonly known as directed flow, focusing on both charged particles and identified particles from heavy-ion collisions. Beam energies from the highest available, at the CERN LHC, down to projectile kinetic energies per nucleon of a few GeV per nucleon, as studied in experiments at the Brookhaven AGS, fall within our scope. We focus on experimental measurements and on theoretical work where direct comparisons with experiment have been emphasized. The physics addressed or potentially addressed by this review topic includes the study of Quark Gluon Plasma, and more generally, investigation of the Quantum Chromodynamics phase diagram and the equation of state describing the accessible phases.Comment: Accepted for publication in Advances in High Energy Physic

Thiol–Ene Chemistry: A Greener Approach to Making Chemically and Thermally Stable Fibers

Fibers of micrometer and submicrometer diameters have been of significant interest in recent years owing to their advanced applications in diverse fields such as optoelectronics, regenerative medicine, piezoelectrics, ceramic materials, etc. There are a number of processes to make thin fibers including electrospinning, melt blowing, and recently developed Forcespinning. However, use of solvents or heat to lower viscosity for processing is common to all existing polymer fiber manufacturing methods, and a greener approach to making fibers remains a challenge. Interestingly, nature has engineered spiders and silkworms with a benign way of making mechanically strong and tough fibers through an intricate self-assembly of protein constituents during the fiber formation process. Comprehending the biosynthetic process and precisely replicating it has been a challenging task. However, we find that extruding small functional segments into solid fibrillar structures, through mediation of chemical interactions between the subunits, is a design approach that can be broadly adapted from nature to realize a greener fiber manufacturing process. Using the robust chemistry of thiol–ene photopolymerization, we demonstrate here that a photocurable mixture of a multifunctional acrylate, a tetrafunctional thiol, and a photoinitiator can be processed into continuous fibers by <i>in situ</i> photopolymerization during electrospinning under ambient conditions. The fibers are mechanically robust and have excellent chemical and thermal stability. While electrospinning has been used to demonstrate this concept, the chemistry could be broadly adapted into other fiber manufacturing methods to produce fibers without using solvents or heat

Thermooxidative Stabilization of Polymers Using Natural and Synthetic Melanins

Melanin is a biopolymer well-known for its intriguing chemical structure and physiological functions including photoprotection, radical scavenging, and metal-ion chelation. Although it has a suite of properties not common to many known organic materials, efforts to exploit those properties in technologically relevant materials have been few compared to other biopolymers such as cellulose, chitin, or collagen. Besides its natural presence in many animals including humans, melanin is also commonly consumed by humans in soups, sauces, and pastas and is widely available in large quantities from a variety of natural sources, suggesting it could serve as a nontoxic additive for enhancing the properties of common polymers. To this end, we report for the first time the potential of natural and synthetic melanins as thermal stabilizers for common polymers by evaluating the addition of melanin to several model polymers with well-known degradation pathways. When added to poly(methyl methacrylate) (PMMA) in very low amounts (0.5–5 wt %), synthetic melanin-like polymers significantly altered the radical initiated chain scission behavior of PMMA and caused a dramatic increase (by about 50–90 °C) in its onset decomposition temperature in both inert and air atmospheres. Moreover, PMMA samples with up to 1 wt % melanin achieved nearly the maximum enhancement level yet retained more than 80% light transmission from 350 to 800 nm in 100 μm thick films. Natural melanin extracted from the ink sac of Sepia officinalis (commonly known as cuttlefish) also displayed significant thermal stabilization effects on PMMA and polypropylene at similar loadings. From molecular weight characterization studies, the associated delay in the molecular weight decrease of PMMA and other polymers at elevated temperature could be potentially beneficial for high-temperature processing or increasing their upper use temperature in demanding applications. It is likely that the thermal stabilization benefits of melanin could be realized in many polymers due to the diversity of its known radical scavenging capabilities in both living systems and the polymers presented in this article. Since natural and synthetic melanin additives are macromolecules, they are also less likely to leach from the base polymer in the same way that small molecule additives often do