Damage to Polystyrene Polymer Film by Shock Wave Induced Bubble Collapse.

Metallic surfaces that are in contact with solutions are commonly used in numerous applications where these surfaces can be damaged by shock wave induced bubble collapse. Use of polymer films that coat such surfaces to prevent them from damage requires a better understanding of how much harm collapsing bubbles produce in the films. In this study, we report the results from coarse-grained molecular dynamics simulations to study the damage to polystyrene (PS) films coating a hard surface. The damage was caused by a collapsing nanobubble located in the proximity of the film and interacting with an impinging shock wave. This collapse produces a high-speed water jet that impacts the PS film with a greater force than the shock front and creates cavities/pits in the PS film. We observed that polymer molecules located in the jet vicinity undergo conformational extension in the direction perpendicular to the jet motion, while chain molecules in the rest of the film undergo compression. We also observed that damage to the film is sensitive to the strength of the shock wave.

Enhanced Cavitation and Hydration Crossover of Stretched Water in the Presence of C60.

We performed molecular dynamics simulations on systems containing stretched water and a C60 buckyball molecule. Our goals were to understand how the presence of the hydrophobic impurity influences the rate of cavitation in stretched water and how the change in pressure (an increase in the value of negative pressure) affects the nature of hydrophobic hydration. Our simulations show that the presence of a buckyball increases the rate of cavitation in water under negative pressure. When studying the influence of the degree of stretching on hydration, we observed that at pressures above -100 MPa the mechanism of hydrophobic hydration is the one that characterizes hydration of a small particle. At some pressure below -100 MPa, there is a crossover in the mechanism of hydration where dewetting occurs by forming cavities next to the surface of the buckyball, and this is characteristic of hydrophobic hydration of large particles.

Bubbles in water under stretch-induced cavitation.

When a finite sample of water experiences tension, it may develop voids (bubbles). We present here a result for the work (Helmholtz free energy change) that needs to be done for the creation of a bubble in fixed volume of water under tension and show that this result depends on the general form of stress-strain relationship. We observe that it is very important to include the curvature-dependent surface tension into consideration in order to explain bubble stability. The analytical result we obtained for the free energy allows us to make prediction for the values of critical and stable radii of the bubbles. We also performed simulations on the TIP4P/2005 water model and observed creation of bubbles in water under stretch. Combining analytical results obtained from our thermodynamic description with the results from computer simulations allowed us to determine the two parameters that describe the curvature-dependent surface tension and also to find the values of critical and stable bubble radii. We also determined the values of critical bubble radii by using mean first-passage time calculations.

A comparative computational study of coarse-grained and all-atom water models in shock Hugoniot states.

We performed molecular dynamics simulations to study how well some of the water models used in simulations describe shocked states. Water in our simulations was described using three different models. One was an often-used all-atom TIP4P/2005 model, while the other two were coarse-grained models used with the MARTINI force field: non-polarizable and polarizable MARTINI water. The all-atom model provided results in good agreement with Hugoniot curves (for data on pressure versus specific volume or, equivalently, on shock wave velocity versus "piston" velocity) describing shocked states in the whole range of pressures (up to 11 GPa) under study. If simulations of shocked states of water using coarse-grained models were performed for short time periods, we observed that data obtained for shocked states at low pressure were fairly accurate compared to experimental Hugoniot curves. Polarizable MARTINI water still provided a good description of Hugoniot curves for pressures up to 11 GPa, while the results for the non-polarizable MARTINI water substantially deviated from the Hugoniot curves. We also calculated the temperature of the Hugoniot states and observed that for TIP4P/2005 water, they were consistent with those from theoretical calculations, while both coarse-grained models predicted much higher temperatures. These high temperatures for MARTINI water can be explained by the loss of degrees of freedom due to coarse-graining procedure.

Functionalized Nanocellulose-Integrated Heterolayered Nanomats toward Smart Battery Separators.

Alternative materials obtained from natural resources have recently garnered considerable attention as an innovative solution to bring unprecedented advances in various energy storage systems. Here, we present a new class of heterolayered nanomat-based hierarchical/asymmetric porous membrane with synergistically coupled chemical activity as a nanocellulose-mediated green material strategy to develop smart battery separator membranes far beyond their current state-of-the-art counterparts. This membrane consists of a terpyridine (TPY)-functionalized cellulose nanofibril (CNF) nanoporous thin mat as the top layer and an electrospun polyvinylpyrrolidone (PVP)/polyacrylonitrile (PAN) macroporous thick mat as the support layer. The hierarchical/asymmetric porous structure of the heterolayered nanomat is rationally designed with consideration of the trade-off between leakage current and ion transport rate. The TPY (to chelate Mn(2+) ions) and PVP (to capture hydrofluoric acid)-mediated chemical functionalities bring a synergistic coupling in suppressing Mn(2+)-induced adverse effects, eventually enabling a substantial improvement in the high-temperature cycling performance of cells.

Self-Assembled Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)/Graphene Quantum Dot Organogels for Efficient Charge Transport in Photovoltaic Devices.

We report the self-assembly of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) organogel films incorporating graphene quantum dots (GQDs). Because of the electrostatic interaction between the GQDs and the PEDOT chains, GQD@PEDOT core-shell nanostructures are readily formed. We demonstrate that the GQDs affect the reorientation of PEDOT chains and the formation of interconnected structure of PEDOT-rich domains, improving the charge transport pathway. The power conversion efficiency of the organic photovoltaic device containing the self-assembled organogel as the hole extraction layer (HEL) was 26% higher than the device with pristine PEDOT-PSS as the HEL.

Atomistic simulation for coil-to-globule transition of poly(2-dimethylaminoethyl methacrylate).

The coil-to-globule transition of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) in aqueous solution was investigated by all-atomistic molecular dynamics simulations. The polymer consistent force field (PCFF) was applied to the PDMAEMA model with a proper protonation state. The structural analysis indicates a distinct difference in the hydration state of particular functional groups of PDMAEMA as well as in the conformational state of PDMAEMA below and above the lower critical solution temperature (LCST). In particular, by monitoring the motion of water molecules, we observe that water molecules in the vicinity of the carbonyl group are relatively restricted to the motion in the globule state due to the extended relaxation time of hydrogen bonds among water molecules. The degree of protonation was also adjusted to study the effect of protonation on the conformational state of PDMAEMA.

Highly tunable interfacial adhesion of glass fiber by hybrid multilayers of graphene oxide and aramid nanofiber.

The performance of fiber-reinforced composites is governed not only by the nature of each individual component comprising the composite but also by the interfacial properties between the fiber and the matrix. We present a novel layer-by-layer (LbL) assembly for the surface modification of a glass fiber to enhance the interfacial properties between the glass fiber and the epoxy matrix. Solution-processable graphene oxide (GO) and an aramid nanofiber (ANF) were employed as active components for the LbL assembly onto the glass fiber, owing to their abundant functional groups and mechanical properties. We found that the interfacial properties of the glass fibers uniformly coated with GO and ANF multilayers, such as surface free energy and interfacial shear strength, were improved by 23.6% and 39.2%, respectively, compared with those of the bare glass fiber. In addition, the interfacial adhesion interactions between the glass fiber and the epoxy matrix were highly tunable simply by changing the composition and the architecture of layers, taking advantage of the versatility of the LbL assembly.

Interface-controlled synthesis of heterodimeric silver-carbon nanoparticles derived from polysaccharides.

Hybrid nanoparticles composed of multiple components can offer unique opportunities for understanding the nanoscale mechanism and advanced material applications. Here, we report the synthesis of heterodimeric silver-carbon dot nanoparticles (Ag-CD NPs) where the Ag NP is grown on the surface of CDs derived from polysaccharides, such as chitosan and alginate, through the photoelectron transfer reaction between CD and Ag(+) ions. The nanoscale interface between the Ag NPs and the CDs is highly tunable depending on the precursor of the CDs and the amount of additives, resulting in fine modification of photoluminescence of the CDs as well as the related surface plasmon resonance of the Ag NPs. This result demonstrates the critical role of the interface between the hybrid nanoparticles in governing the electrical and optical properties of respective nanoparticles.

Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer.

Organic light-emitting diodes have been recently focused for flexible display and solid-state lighting applications and so much effort has been devoted to achieve highly efficient organic light-emitting diodes. Here, we improve the efficiency of inverted polymer light-emitting diodes by introducing a spontaneously formed ripple-shaped nanostructure of ZnO and applying an amine-based polar solvent treatment to the nanostructure of ZnO. The nanostructure of the ZnO layer improves the extraction of the waveguide modes inside the device structure, and a 2-ME+EA interlayer enhances the electron injection and hole blocking in addition to reducing exciton quenching between the polar-solvent-treated ZnO and the emissive layer. Therefore, our optimized inverted polymer light-emitting diodes have a luminous efficiency of 61.6 cd A(-1) and an external quantum efficiency of 17.8%, which are the highest efficiency values among polymer-based fluorescent light-emitting diodes that contain a single emissive layer.

Preparation of mesoporous nanofibers by vapor phase synthesis: control of mesopore structures with the aid of co-surfactants.

Mesoporous nanofibers (MSNFs) can be fabricated in the pores of anodic aluminum oxide (AAO) membrane using diverse methods. Among them vapor phase synthesis (VPS) provides several advantages over sol-gel or evaporation-induced self-assembly (EISA) based methods. One powerful advantage is that we can employ multiple surfactants as structural directing agents (SDAs) simultaneously. By adopting diverse pairs of SDAs, we can control the mesopore structures, i.e. pore size, surface area, and even the morphology of mesostructures. Here, we used F127 as a main SDA, which is relatively robust (thus, difficult to change the mesopore structures), and added a series of cationic co-surfactants to observe the systematical changes in their mesostructure with respect to the chain length of the co-surfactant.

Fabrication of polymer nanotubes containing nanoparticles and inside functionalization.

A polypyrrole nanotube containing nanoparticles is prepared by a dual template approach, and the inside of the nanotube is selectively functionalized with carboxyl and amine groups.

Mesoporous nanofibers from dual structure-directing agents in AAO: Mesostructural control and their catalytic applications.

Control yourself! The mesoporous silica nanofibers (MSNFs) from dual structure-directing agents were fabricated inside the pores of porous alumina (AAO, see figure) by using vapor phase synthesis. The pore structures could be controlled to form a range of structures from mesocellular foams to cylindrical mesopores with long-range order by adding cationic cosurfactants.