Monte Carlo Simulations of Atom Transfer Radical (Homo)polymerization of Divinyl Monomers: Applicability of Flory–Stockmayer Theory

It is well known that free radical (co)­polymerization of multivinyl monomers (MVMs) leads to insoluble gels even at a low monomer conversion, and the gelation point can be predicted by Flory–Stockmayer theory (F–S theory) based on two assumptions: (1) equal reactivity of all vinyl groups and (2) the absence of intramolecular cyclization. This theory has been experimentally studied and verified with conventional free radical (co)­polymerization (FRP) of several MVMs (e.g., divinylbenzene, DVB). However, it is still debatable whether this theory is applicable for the polymerization of MVMs using reversible deactivation radical polymerization (RDRP) approaches, such as atom transfer radical polymerization (ATRP). Herein, Monte Carlo simulations using two statistical modelswith cyclization (<b>w.c.</b>) and without cyclization (<b>wo.c.</b>, corresponding to F–S theory)and dynamic lattice liquid (DLL) models were conducted to study ATRP of divinyl monomers. The simulated gel points using <b>w.c.</b> and <b>wo.c.</b> models were compared with those obtained from ATRP experiments, from calculation using F–S theory, and from simulations using DLL models. The molecular weights, dispersity, and extent of intermolecular/intramolecular cross-linking were calculated as a function of double bond and cross-linker conversion. The results demonstrated that the gel points obtained from both <b>w.c.</b> and <b>wo.c.</b> models were lower than the values from DLL models and experiments. This indicates that F–S theory cannot be used to accurately predict the polymerization of divinyl monomers via ATRP. Our study shows that the limitation of F–S theory in predicting ATRP reaction of divinyl monomers is not only due to neglecting intramolecular cyclization but also due to spatial restrictions which can cause the reactivity and accessibility of vinyl groups becoming nonequivalent in ATRP of divinyl monomers

Using Legacy Data to Explore the Onset and Development of the Southern Hemisphere Supergyre

The Southern Hemisphere Supergyre refers to the strong connections and intertwining of the southern subtropical gyres. Tasman Leakage is a fundamental part of the supergyre, as well as of the  global thermohaline circulation, as it provides a return flow from the Pacific and Indian Oceans to the North Atlantic at intermediate depths.   However, both are only relatively recently documented, and the timing and conditions of onset are not well understood.This study characterizes the newly identified onset of Tasman Leakage in sedimentary records in and around the Indian Ocean using core descriptions and data derived from sediments.  Since much of this is legacy core material, core photographs were used to develop complementary and more continuous records to help refine the timing of onset.  These newly constructed time series based on core photographs are compared with X-ray Fluorescence time series based on core scanning provide both insight into onset of Tasman Leakage and a first test of the utility of time series based on core photos.This effort will focus on the intermediate water pathway associated with Tasman Leakage and identify conditions at critical around the basin from at least 8 Ma at Broken Ridge and Mascarene Plateau to understand the role of Indian Ocean intermediate waters in the Southern Hemisphere Supergyre in major climate events of the late Miocene. This proposed work provides the first synoptic view of SHS onset using intermediate depth cores, which in turn will provide an important framework for basin-wide synthesis of Indian Ocean drilling, much of which is outside of the main pathway of the SHS.  It will also serve as a test of the utility of legacy material as primary data

Kirigami Nanocomposites as Wide-Angle Diffraction Gratings

Beam steering devices represent an essential part of an advanced optics toolbox and are needed in a spectrum of technologies ranging from astronomy and agriculture to biosensing and networked vehicles. Diffraction gratings with strain-tunable periodicity simplify beam steering and can serve as a foundation for light/laser radar (LIDAR/LADAR) components of robotic systems. However, the mechanical properties of traditional materials severely limit the beam steering angle and cycle life. The large strain applied to gratings can severely impair the device performance both in respect of longevity and diffraction pattern fidelity. Here, we show that this problem can be resolved using micromanufactured kirigami patterns from thin film nanocomposites based on high-performance stiff plastics, metals, and carbon nanotubes, <i>etc</i>. The kirigami pattern of microscale slits reduces the stochastic concentration of strain in stiff nanocomposites including those made by layer-by-layer assembly (LBL). The slit patterning affords reduction of strain by 2 orders of magnitude for stretching deformation and consequently enables reconfigurable optical gratings with over a 100% range of period tunability. Elasticity of the stiff nanocomposites and plastics makes possible cyclic reconfigurability of the grating with variable time constant that can also be referred to as 4D kirigami. High-contrast, sophisticated diffraction patterns with as high as fifth diffraction order can be obtained. The angular range of beam steering can be as large as 6.5° for a 635 nm laser beam compared to ∼1° in surface-grooved elastomer gratings and ∼0.02° in MEMS gratings. The versatility of the kirigami patterns, the diversity of the available nanocomposite materials, and their advantageous mechanical properties of the foundational materials open the path for engineering of reconfigurable optical elements in LIDARs essential for autonomous vehicles and other optical devices with spectral range determined by the kirigami periodicity

Fig 2 -

Soil profile of (A) biochar carbon (BC) recovery, and (B) native soil organic carbon (non-BC) measured after 4.5 y field emplacement with biochar applied in the 0–7 cm depth interval. Bars represent depth averages with standard error across three replicate samples. Asterisks indicate values that are significantly different from that of the reference plot (no biochar added). Yellow, green, and blue colors indicate coarse (1–5 mm), intermediate (0.5–1 mm) and fine (< 0.5 mm) particle sizes, respectively and striping pattern differentiates low (1.5–2%) and high (3–4%) biochar dosages for each particle size class.</p

Fig 3 -

Recovery of maize cob biochar carbon (BC) from soil profiles with treatments fine (< 0.5 mm, left panel) and intermediate (0.5–1 mm, right panel) particle size biochar 1 y (dashed line) and 4.5 year (solid line) after application. One year data is from Obia et al. (2017a) where BC application depth was 0–5 cm instead of 0–7 cm in the current study.</p

Soil and biochar properties.

Although biochar application to soils has been found to increase soil quality and crop yield, the biochar dispersion extent and its impacts on native soil organic carbon (SOC) has received relatively little attention. Here, the vertical and lateral migration of fine, intermediate and coarse-sized biochar (</div

S1 File -

Contains S1 Fig. Photos of biochar field application at different stages at Mkushi, Zambia. Photos taken by J. Mulder in April 2013. From A. Obia 2015 Doctorate Thesis; S2 Fig. Soil profiles of a) δ13C isotope signatures and b) total carbon contents after 4.5 y field emplacement with biochar applied in the 0–7 cm depth interval. Bars represent depth average values with standard error across three replicate samples. Asterisks indicate mean values that are significantly different from that of the reference plot (no biochar added). The vertical dashed line in the left panel indicates the δ13C of the original soil (-19.5‰). Yellow, green, and blue colors indicate coarse (1–5 mm), intermediate (0.5–1 mm) and fine (S1 Table. Mean total organic carbon stock (g) in the soil profile 4.5 years after biochar addition; S2 Table. Mean quantities and recovery rates of maize cob biochar carbon (BC) recovered by depth interval in the soil profile, 4.5 years after application; S3 Table. Mean native soil organic carbon (non-biochar C, g) 4.5 years after biochar addition; S4 Table. Comparison of mean biochar carbon (BC) recovery from soil profiles, 1 and 4.5 years after biochar application; and S5 Table. Compilation of data used in this study. (PDF)</p

Schematic of experimental design.

(A) Layout of 50 x 50 cm plots. Numbers in boxes indicate biochar dose by weight percent and yellow, green, and blue colors represent fine, medium and coarse sized biochar, respectively. (B) 1 x 50 cm (length x width) samples collected from each plot over depth intervals indicated.</p

Materials Engineering of High-Performance Anodes as Layered Composites with Self-Assembled Conductive Networks

The practical implementation of nanomaterials in high capacity batteries has been hindered by the large mechanical stresses during ion insertion/extraction processes that lead to the loss of physical integrity of the active layers. The challenge of combining the high ion storage capacity with resilience to deformations and efficient charge transport is common for nearly all battery technologies. Layer-by-layer (LBL/LbL) engineered nanocomposites are able to mitigate structural design challenges for materials requiring the combination of contrarian properties. Herein, we show that materials engineering capabilities of LBL augmented by self-organization of nanoparticles (NPs) can be exploited for constructing multiscale composites for high capacity lithium ion anodes that mitigate the contrarian nature of three central parameters most relevant for advanced batteries: large intercalation capacity, high conductance, and robust mechanics. The LBL multilayers were made from three function-determining components, namely polyurethane (PU), copper nanoscale particles, and silicon mesoscale particles responsible for the high nanoscale toughness, efficient electron transport, and high lithium storage capacity, respectively. The nanocomposite anodes optimized in respect to the layer sequence and composition exhibited capacities as high as 1284 and 687 mAh/g at the first and 300th cycle, respectively, with a fading rate of 0.15% per cycle. Average Coulombic efficiencies were as high as 99.099.4% for 300 cycles at 1.0 C rate (4000 mA/g). Self-organization of copper NPs into three-dimensional (3D) networks with lattice-to-lattice connectivity taking place during LBL assembly enabled high electron transport efficiency responsible for high battery performance of these Si-based anodes. This study paves the way to finding a method for resolution of the general property conflict for materials utilized in for energy technologies

On-Chip Ultralow-Threshold Tunable CdSSe Nanobelt Lasers Excited by the Emission of Linked ZnO Nanowire

The integration of optical waveguide and on-chip nanolasers source has been one of the trends in photonic devices. For on-chip nanolasers, the integration of nanowires and high antidamage ability are imperative. Herein, we realized the on-chip ultralow-threshold and wavelength-tunable lasing from alloyed CdSSe nanobelt chip that is excited by the emission from linked ZnO nanowires. ZnO nanowire arrays are integrated into CdSSe nanobelt chips by the dry transfer method. A one-dimensional (1D) ZnO nanowire forms high-quality optical resonators and serves as an indirect pumping light to stimulate CdSSe nanobelt chips, and then wavelength-tunable lasing is generated with the ultralow threshold of 3.88 μW. The lasing mechanism is quite different than direct excitation by nanosecond laser pulse and indirect pumping by ZnO emission. The ZnO-CdSSe blocks provide a new solution to realize nanowire lasing from linked nanowires rather than direct laser pumping and thus avoid the light direct damage under general nanosecond laser excitation