Search

In order to investigate the two-dimensional flow of a non-Newtonian fluid, such as an elastomer liquid over a cylinder, a simplified model is applied. The analysis is carried out to study the thermophysical properties of the melt elastomer flow with Prandtl variable in the presence of internal heat generation. The temperature-dependent physical properties such as velocity, contour temperature, surface temperature as a function of contour velocity, and pressure are considered and discussed. Moreover, the exchange of energy from the surface to the fluids is examined through the variation in the Rayleigh number.

Radiostereometric analysis (RSA) is an accurate and precise radiographic method that can be used to measure micromotion of implants and study joint kinematics in vivo. A calibration cage with radiopaque markers is used to calibrate the RSA images; however, the thickness (250 mm) of the calibration cage restricts the available area for the patient and equipment during RSA recordings. A thinner calibration cage would increase the recording area, facilitate handling of the cage, and ease integration of the cage with the RSA system. We developed a thinner calibration cage without compromise of accuracy and precision. First, we performed numerical simulations of an RSA system, and showed that the calibration cage thickness could be decreased to 140 mm maintaining accuracy and precision using 40 fiducial and 30 control markers. Second, we constructed a new calibration cage (NRT cage) according to the simulation results. Third, we validated the new calibration cage against two state-of-the-art calibration cages (Umeaa cage and Leiden cage) in a phantom study. All cages performed similar for marker-based analysis, except for y-rotation, where the Umeaa cage (SD = 0.064 mm) was less precise compared to the NRT (SD = 0.038 mm) and Leiden cages (0.042 mm) (p =.01). For model-based analysis the NRT cage had superior precision for translations (SD ≤ 0.054 mm) over the Leiden cage (SD ≤ 0.118 mm) and Umeaa cage (SD ≤ 0.093 mm) (p

In this contribution, we present a partitioned‐domain method coupling a particle domain and a continuum domain for multiscale simulations of inelastic amorphous polymers under isothermal conditions. In the continuum domain, a viscoelastic–viscoplastic constitutive model calibrated from previous molecular dynamics (MD) simulations is employed to capture the inelastic properties of the polymer. Due to the material's rate‐dependence, a temporal coupling scheme is introduced. The influence of the time‐related parameters on the computational cost and accuracy is discussed. With appropriate parameters, multiscale simulations of glassy polystyrene under various loading conditions are implemented to showcase the method's capabilities to capture the mechanical behavior of polymers with different strain rates and with non‐affine deformations of the MD domain.

Equilibrium sediment transport is the condition of zero net entrainment and deposition by sediment-transporting flow (i.e. grade or regime). Here criteria for equilibrium sediment transport, or those used as proxies for equilibrium (for example, onset of erosion, onset of particle setting or suppression of turbulence) for dilute, suspended-load-dominated, turbidity currents, are tested against laboratory and natural data. The examined criteria are restricted to those describing flow over a bed of loose particulate material involving non-cohesive sediment. Models include both monodisperse and polydisperse formulations that represent sediment non-uniformity by using a single characteristic grain size or discretization of the grain-size distribution, respectively. Analysis shows that a polydisperse-type flux-balance model, that equates erosional and depositional fluxes and where erosion is related to the power used to lift sediment mass from the bed (the ‘Flow-Power Flux-Balance’ model) provides predictions most consistent with observational data. Other equilibrium models tested, monodisperse or polydisperse, fail to predict realistic bed slopes and/or flow durations for concentrations, velocities and depths within limits for natural flows. Results of the Flow-Power Flux-Balance model are used to quantify sediment transport fields, equilibrium Shields numbers and slopes for turbidity currents of variable flow and particle properties.

Electrophoresis of core-shell composite soft particles possessing hydrophobic inner core grafted with highly charged polyelectrolyte layer (PEL) has been studied analytically. The PEL bears pH-dependent charge properties due to the presence of zwitterionic functional groups. The dielectric permittivity of the PEL and bulk aqueous medium were taken to be different, which resulted in the ion-partitioning effect. Objective of this study was to provide a simple expression for the mobility of such core-shell soft particles under Donnan limit where the thickness of the PEL well exceeds the electric double layer thickness. Going beyond the widely used Debye-Hückel linearization, the nonlinear Poisson-Boltzmann equation coupled with Stokes-Darcy-Brinkman equations was solved to determine the electrophoretic mobility. The derived expression further recovers all the existing results for the electrophoretic mobility under various simplified cases. The graphical presentation of the results illustrated the impact of pertinent parameters on the electrophoretic mobility of such a soft particle.

Crystal structure of conjugated molecules and polymers is fundamentally critical to understand their multilevel microstructures, carrier transport, and diverse functions. However, to determine the crystal structure of conjugated polymers is a significant challenge, mainly due to the poor crystallinity, weak diffraction, and instability under high‐energy radiation. Here, we build the possible crystal structures of eight typical conjugated polymers, covering several widely used molecular segments in organic optoelectronics. We model the packing structures of these seed polymers based on synchrotron X‐ray diffractions and molecular simulations. These crystal structures provide a new platform to predict the packing structures of more related polymer systems, extending the molecular scope. Based on this polymer crystal structure database, the multiscale microstructures and charge transport properties of conjugated polymers can be predicted before experiments. This study sets up a polymer crystal structure database to eliminate the current trial‐and‐error approaches and accelerating the design of high‐performance conjugated polymers.

The dielectric constant is a crucial physicochemical property of liquids in tuning solute-solvent interactions and solvation microstructures. Herein the dielectric constant variation of liquid electrolytes regarding to temperatures and electrolyte compositions is probed by molecular dynamics simulations. Dielectric constants of solvents reduce as temperatures increase due to accelerated mobility of molecules. For solvent mixtures with different mixing ratios, their dielectric constants either follow a linear superposition rule or satisfy a polynomial function, depending on weak or strong intermolecular interactions. Dielectric constants of electrolytes exhibit a volcano trend with increasing salt concentrations, which can be attributed to dielectric contributions from salts and formation of solvation structures. This work affords an atomic insight into the dielectric constant variation and its chemical origin, which can deepen the fundamental understanding of solution chemistry.

In this work, the shear bands formed during the stretching of isotactic polypropylene fibers are studied. The digital photoelasticity technique is applied to provide full-field visualization of the stress of the shear bands regions. The mechanical testing device is modified to be suitable for mechanical measurements. The effect of different parameters, that is, the stretching rates and the ambient temperature on the formation of shear bands is investigated. Finally, the influence of heating pre-existed shear bands is studied. Photoelastic patterns of the shear bands at these conditions are included for illustration.

The electrophoresis and electric conduction of a suspension of charged spherical particles in a salt-free solution are analyzed by using a unit cell model. The linearized Poisson-Boltzmann equation (valid for the cases of relatively low surface charge density or high volume fraction of the particles) and Laplace equation are solved for the equilibrium electric potential profile and its perturbation caused by the imposed electric field, respectively, in the fluid containing the counterions only around the particle, and the ionic continuity equation and modified Stokes equations are solved for the electrochemical potential energy and fluid flow fields, respectively. Explicit analytical formulas for the electrophoretic mobility of the particles and effective electric conductivity of the suspension are obtained, and the particle interaction effects on these transport properties are significant and interesting. The scaled zeta potential, electrophoretic mobility, and effective electric conductivity increase monotonically with an increase in the scaled surface charge density of the particles and in general decrease with an increase in the particle volume fraction, keeping each other parameter unchanged. Under the Debye-Hückel approximation, the dependence of the electrophoretic mobility normalized with the surface charge density on the ratio of the particle radius to the Debye screening length and particle volume fraction in a salt-free suspension is same as that in a salt-containing suspension, but the variation of the effective electric conductivity with the particle volume fraction in a salt-free suspension is found to be quite different from that in a suspension containing added electrolyte.

Organic cages are fascinating because of their well-defined 3D cavities, excellent stability, and accessible post-modification. However, the synthesis is normally realized by fragment coupling approach in low yields. Herein, we report one-pot, gram-scale and shape-controlled synthesis of two covalent organic cages (box-shaped [4]cage and triangular prism-shaped [2]cage) in yields of 46 % and 52 %, involving direct condensation of triangular 1,3,5-tris(2,4-dimethoxyphenyl)benzene monomer with paraformaldehyde and isobutyraldehyde, respectively. The cages can convert into high-yielding per-hydroxylated analogues. The [2]cage can be utilized as gas chromatographic stationary phase for high-resolution separation of benzene/cyclohexane and toluene/methylcyclohexane. By changing the central moiety of the triangular monomer and/or aldehyde, this synthetic method would have the potential to be a general strategy to access diverse cages with tunable shape, size, and electronic properties.

The contact number of a packing of finitely many balls in Euclidean $d$-space is the number of touching pairs of balls in the packing. A prominent subfamily of sphere packings is formed by the so-called totally separable sphere packings: here, a packing of balls in Euclidean $d$-space is called totally separable if any two balls can be separated by a hyperplane such that it is disjoint from the interior of each ball in the packing. Bezdek, Szalkai and Szalkai (Discrete Math. 339(2): 668-676, 2016) upper bounded the contact numbers of totally separable packings of $n$ unit balls in Euclidean $d$-space in terms of $n$ and $d$. In this paper we improve their upper bound and extend that new upper bound to the so-called locally separable packings of unit balls. We call a packing of unit balls a locally separable packing if each unit ball of the packing together with the unit balls that are tangent to it form a totally separable packing. In the plane, we prove a crystallization result by characterizing all locally separable packings of $n$ unit disks having maximum contact number.

The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large‐scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large‐scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood‐ and ebb‐oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune‐induced directional bed roughness in numerical models of estuarine and tidal environments., Estuarine tidal asymmetry is found to depend on directional dune‐induced flow resistance interacting on spatiotemporal scales with the combined influence of fluvial discharge and tidal forcing. The nonequilibrium nature of asymmetric dunes in tidal flow is critical to large‐scale hydrodynamics and bed load sediment fluxes and needs to be addressed through inter‐tidal‐phase variable bedform roughness in numerical models of tidal environments., Federal Waterways Engineering and Research Institute (BAW), Hamburg, Germany, Kiel Marine Science (KMS), German Research Foundation (DFG) http://dx.doi.org/10.13039/501100001659

The effect of gravity on directional solidification was investigated in solution-based freeze casting. A preceramic siloxane-based polymer was freeze-cast with a cyclohexene solvent from two different directions: that against the direction of the gravitational force and that in concert with the gravitational force. Because the density of preceramic polymer is higher than the solvent, the segregated polymer creates a denser solution ahead of the freezing front than the underlying solution when the freezing direction is the same as the gravity direction. This results in convective flow in the liquid phase. This convective flow influences constitutional supercooling, which changes not only the pore size of freeze-cast structure but also the pore morphology from dendritic to cellular pores.

We study the propagation of a plane‐strain hydraulic fracture driven by a shear thinning fluid following a Carreau rheology. We restrict to the impermeable medium case and quantify in details the impact on fracture growth of the shear‐thinning properties of the fluid between the low and high shear‐rates Newtonian limits. We derive several dimensionless numbers governing the evolution of the solution. The propagation notably depends on the ratio between the two limiting viscosities, the fluid shear‐thinning index, a dimensionless fracture toughness and a characteristic time‐scale capturing the instant at which the fluid inside the fracture reaches the low‐shear rate Newtonian plateau. We solve the problem numerically using Gauss‐Chebyshev methods for the spatial discretization of the coupled hydro‐mechanical problem and a fully implicit time integration scheme. The solution evolves from an early time self‐similar solution equals to the Newtonian one for the large‐shear rate viscosity to a late time self‐similar solution equals to the low‐shear rate Newtonian solution. The transition period (corresponding to the shear thinning part of the rheology) exhibits features similar to the power law rheology, albeit quantitatively different. Comparisons of hydraulic fracture growth predictions obtained with a power‐law model confirm its inadequacy for realistic fluids used in practice compared to the more physical Carreau rheology: the Newtonian plateau at high and low shear rates cannot be neglected.

Chiral sulfones extensively exist in drugs, agricultural chemicals, chiral organic intermediates, and functional materials. Their importance causes the rapid development of their synthetic methods in recent years. Many transition metal complex catalysts with chiral ligands and chiral organocatalysts are adopted in synthesis of chiral sulfones. Most of the methods to construct chiral sulfones are based on the reduction of unsaturated sulfones and the introduction of sulfone groups into unsaturated hydrocarbons. This review describes all classes of asymmetric reactions for synthesis of chiral sulfones.

Condensation of an inherently C3 -symmetric polychlorotriphenylmethyl (PTM) radical trisaldehyde with tris(2-aminoethyl)amine (TREN) yields a [4+4] tetrahedral radical cage as a racemic pair of homochiral enantiomers in 75 % isolated yield. The structure was characterized by X-ray crystallography, confirming the homochirality of each cage framework. The homochirality results from intramolecular [CH⋅⋅⋅π] and hydrogen-bonding interactions within the cage framework. The four PTM radicals in a cage undergo weak through-space coupling. Magnetic measurements demonstrated that each cage bears 3.58 spins.

The performed investigations have shown that the basis of the local laser heating/“drilling” of composite coarse‐pored ceramics consisting of aluminosilicates and a glass phase is the melting and ablation processes that lead to the formation of a hole. The interaction of the components of the composite in the zone of high‐temperature heating is accompanied by the formation of melt of a glass phase of new composition. The motion of the metal to the depth of a sample through pore channels‐clusters of the main ceramic material depends on the viscosity of melt (ie, on the radiation regime) and the cooling rate of the melt (ie, the thermo physical properties of the ceramics and glass phase). The development of hydrodynamic pressure in the zone of laser heating leads not only to the ejection of a part of the melt from the channel, but also to the densification of the ceramics adjacent to the walls of the vitrified channel. These effects depend to a great extent on the ceramics/glass phase ratio and on the porosity of the initial ceramics.

A comprehensive study into the effects of mobile phase composition and column temperature on enantiomer elution order was conducted with a set of chiral rod-like liquid crystalline materials. The analytes were structurally similar and comprised variances such as length of terminal alkyl chain, presence of chlorine, number of phenyl rings, and type of chiral center. Experiments were carried out in polar organic and reversed-phase modes using amylose tris(3-chloro-5-methylphenylcarbamate) immobilized on silica gel as the chiral stationary phase. For all liquid crystals, reversal of elution order of enantiomers was observed based on type of used cosolvent and/or its content in the mobile phase; for some of the liquid crystals a temperature-induced reversal was also observed. Both linear and nonlinear dependencies of natural logarithm of enantioselectivity on temperature were found. Tested mobile phases comprised pure organic solvents and binary and tertiary mixtures of acetonitrile with organic solvents and/or water. Effect of acidic/basic mobile phase additives was also tested. Effect of structure of chiral selector is briefly discussed.

The startup of electrophoretic motion in a suspension of spherical colloidal particles, which may be charged with constant zeta potential or constant surface charge density, due to the sudden application of an electric field is analytically examined. The unsteady modified Stokes equation governing the fluid velocity field is solved with unit cell models. Explicit formulas for the transient electrophoretic velocity of the particle in a cell in the Laplace transforms are obtained as functions of relevant parameters. The transient electrophoretic mobility is a monotonic decreasing function of the particle-to-fluid density ratio and in general a decreasing function of the particle volume fraction, but it increases and decreases with a raise in the ratio of the particle radius to the Debye length for the particles with constant zeta potential and constant surface charge density, respectively. On the other hand, the relaxation time in the growth of the electrophoretic mobility increases substantially with an increase in the particle-to-fluid density ratio and with a decrease in the particle volume fraction but is not a sensitive function of the ratio of the particle radius to the Debye length. For specified values of the particle volume fraction and particle-to-fluid density ratio in a suspension, the relaxation times in the growth of the particle mobility in transient electrophoresis and transient sedimentation are equivalent.

Knowledge of relaxation processes is fundamental in glass science and technology because relaxation is intrinsically related to vitrification, tempering as well as to annealing and sev-eral applications of glasses. However, there are conflicting reports -- summarized here for different glasses -- on whether the structural relaxation time of glass can be calculated using the Maxwell equation, which relates relaxation time with shear viscosity and shear modulus. Hence, this study aimed to verify whether these two relaxation times are comparable. The structural relaxation kinetics of a lead metasilicate glass were studied by measuring the re-fractive index variation over time at temperatures between 5 and 25 K below the fictive temperature, which was initially set 5 K below the glass transition temperature. Equilibrium shear viscosity was measured above and below the glass transition range, expanding the current knowledge by one order of magnitude. The Kohlrausch equation described very well the experimental structural relaxation kinetics throughout the investigated temperature range and the Kohlrausch exponent increased with temperature, in agreement with studies on other glasses. The experimental average structural relaxation times were much longer than the values computed from isostructural viscosity, as expected. Still, they were less than one order of magnitude higher than the average relaxation time computed through the Maxwell equation, which relies on equilibrium shear viscosity. Thus, these results demon-strate that the structural relaxation process is not controlled by isostructural viscosity, and that equilibrium shear viscosity only provides a lower boundary for structural relaxation kinetics., 19 pages, 8 figures. Changed title. Minor updates to the text

The use of the biphasic isotropic/nematic region in a bisperylene imide-based lyotropic liquid crystal system allows the extraction of proton-carbon 1 DCH residual dipolar couplings in aqueous solution from a single F1-coupled HSQC experiment. The method was successfully applied to the RDC-based conformational analysis of sucrose.

The structure of the double layer on the boundary between solid and liquid phases is described by various models, of which the Stern-Gouy-Chapman model is still commonly accepted. Generally, the solid phase is charged, which also causes the distribution of the electric charge in the adjacent diffuse layer in the liquid phase. We propose a new mathematical model of electromigration considering the high deviation from electroneutrality in the diffuse layer of the double layer when the liquid phase is composed of solution of weak multivalent electrolytes of any valence and of any complexity. The mathematical model joins together the Poisson equation, the continuity equation for electric charge, the mass continuity equations, and the modified G-function. The model is able to calculate the volume charge density, electric potential, and concentration profiles of all ionic forms of all electrolytes in the diffuse part of the double layer, which consequently enables to calculate conductivity, pH, and deviation from electroneutrality. The model can easily be implemented into the numerical simulation software such as Comsol. Its outcome is demonstrated by the numerical simulation of the double layer composed of a charged silica surface and an adjacent liquid solution composed of weak multivalent electrolytes. The validity of the model is not limited only to the diffuse part of the double layer but is valid for electromigration of electrolytes in general.

Spontaneous development of chirality in systems composed of achiral molecules is important for new routes to asymmetric synthesis, chiral superstructures and materials, as well as for the understanding of the mechanisms of emergence of prebiotic chirality. Herein, it is shown that the 4,4′‐diphenylbenzil unit is a universal transiently chiral bent building block for the design of multi‐chained (polycatenar) rod‐like molecules capable of forming a wide variety of helically twisted network structures in the liquid, the liquid crystalline (LC) and the crystalline state. Single polar substituents at the apex of tricatenar molecules support the formation of the achiral (racemic) cubic double network phase with Ia 3‾ d symmetry and relatively small twist along the networks. The combination of an alkyl chain with fluorine substitution leads to the homogeneously chiral triple network phase with I23 space group, and in addition, provides a mirror symmetry broken liquid. Replacing F by Cl or Br further increases the twist, leading to a short pitch double gyroid Ia 3‾ d phase, which is achiral again. The effects of the structural variations on the network structures, either leading to achiral phases or chiral conglomerates are analyzed., Soft helical networks: Achiral benzil‐based multi‐chained molecules form a series of spontaneously mirror‐symmetry‐broken soft matter structures; the steric and electronic effects of polar substituents on helical self‐assembly, local and long range network formation as well as through‐space interhelical interactions are discussed.

Numerous studies have addressed the influence of the surrounding frame members on the in‐plane properties of steel shear walls with stiffeners. However, the effect of the out‐of‐plane stiffness on the buckling strength of stiffening plates has not been elucidated. Herein, the influence of surrounding frame members on the buckling behavior of steel shear walls reinforced by cross stiffeners was investigated. A calculation formula for the elastic buckling strength of the stiffened plate was proposed by eigenvalue analysis. In addition, the relationship between the buckling strength and out‐of‐plane stiffness of the surrounding frame members was revealed and a calculation formula for the buckling strength considering the out‐of‐plane stiffness was put forward. Finally, through experimental tests and large deformation analysis, the effect of vertical frame members on the elasto‐plastic property of the stiffened plate was shown. The results obtained are as follows. This study proposes an elastic buckling strength calculation formula for a stiffened plate by correcting the elastic buckling strength calculation formula of an orthotropic plate using the ratio between the torsional rigidity of an actual stiffened plate and that of the plate regarded as anisotropic. The rate of decrease in elastic buckling strength of the stiffened plate due to the out‐of‐plane stiffness of the surrounding frame member can be evaluated by the flexural rigidity ratio between the surrounding member and the stiffened plate. The rate of decrease in elastic buckling strength of stiffened plates due to the out‐of‐plane stiffness of the left and right surrounding vertical frame members with different bending stiffnesses and intermediate vertical frame members can be evaluated by the buckling stress ratio determined from the out‐of‐plane stiffness of the surrounding vertical frame members. It is possible to obtain a stable behavior even if the out‐of‐plane stiffness of the surrounding member is relatively small, if the elastic buckling strength is higher than the shear yield strength of the stiffened plate. It was confirmed that the effect of the end constraint condition on the elasto‐plastic behavior of a stiffened plate was negligible. The results obtained in this study can facilitate the construction of novel earthquake‐resistant steel shear walls.

In this study, the effects of impeller rotation speed, off‐bottom clearance, blade angle, types of solid and liquid, etc., on the suspension pattern of sedimentary particles and particle rise height in liquid were investigated with a hemispherical vessel without baffles under low particle concentration. The transition conditions of suspension pattern between regimes I and II, and regimes II and III, were observed visually, and their non‐dimensional equations were expressed with an acceptable correlation by varying the above operation factors a great deal. Here, regime I is stagnation of particles on a vessel bottom, II is partial suspension, and III is complete suspension in liquid. The non‐dimensional equation of the maximum particle rise height was also successfully obtained. The combination of the non‐dimensional equations of transition and maximum particle rise height permitted us to determine the adequate solid/liquid mixing operation conditions without collision of particles with device parts.

The freezing of sulfate saline soil involves the coupling effect of heat and mass transfer and crystallization deformation. The influence of salt content and temperature on the crystallization of ice and salt was analyzed by using a one‐side freezing experiment. Based on the effect of solute and temperature on water activity, a crystallization kinetics model of ice–water phase change in saline soil was established. The application of supersaturation in the crystallization kinetics model of solution–crystal phase change is improved with the Frezchem model. The calculated results are compared with experimental data to validate the effectiveness of the proposed model. the study shows that: (a) crystallization can be well illustrated by the proposed model based on the concepts of the formation factor of ice crystals and solution supersaturation; (b) convection and diffusion are the main means of salt redistribution, which cause the accumulation of salt above the freezing front and the formation of discontinuously distributed–layered salt crystal zones; and (c) the alternate crystallization of ice and salt increases variation i solute concentration and then increases crystallization pressure, which leads to the deformation of salt expansion.

It is known that interfaces have various impacts on crystallization from a solution. Here, we describe crystallization of acetaminophen using a microflow channel, in which two liquids meet and form a liquid–liquid interface due to laminar flow, resulting in uniform mixing of solvents on the molecular scale. In the anti‐solvent method, the microflow mixing promoted the crystallization more than bulk mixing. Furthermore, increased flow rate encouraged crystal formation, and a metastable form appeared under a certain flow condition. This means that interface management by the microchannel could be a beneficial tool for crystallization and polymorph control.

Toroids and helices are fundamental geometrical structures in nature. Polymers can self-assemble into various nanostructures, including both toroids and helices; however, nanostructures combining toroidal and helical morphologies (that is, helical toroids) are rarely observed. A binary system is reported containing polypeptide homopolymer and its block copolymer, which can hierarchically self-assemble into uniform helical nanotoroids in solution. The formation of the helical toroids is a successive two-step process. First, the homopolymers aggregate into fibrils and convolve into toroids, thereby resembling the toroidal condensation of deoxyribonucleic acid (DNA) chains. Second, the block copolymers self-assemble on the homopolymer toroids and result in helical surface patterns. Additionally, the chirality of the surface helical patterns can be varied by the chirality of the polypeptide block copolymers.

There is a need to better understand the influence of shear flow on the crystallization of a molten oil phase in an oil/water emulsion due to its high relevance for industrial processes. The present study focuses on the influence of laminar shear flow on the crystallization kinetics of polydisperse n ‐hexadecane‐in‐water emulsions. The investigation was carried out by rheo‐nuclear magnetic resonance (NMR) spectroscopy in a Taylor‐Couette geometry. An accelerating impact of the shear rate on the overall crystallization kinetics was verified. This effect stems from an increase of the collision frequency of already crystallized droplets with not yet crystallized droplets. Nevertheless, the collision efficiency decreased with higher shear rate.

Author(s): Cheng, S; Song, C; Ercius, P | Abstract: To investigate the possible structural differences between silica glass fibers and bulk silica glasses, electron energy loss spectroscopy (EELS) has been used to study the short-range and medium-range structures of both forms of silica glasses. The short-range structure of silica glass, such as the coordination and symmetry, was investigated by the energy loss near edge structure (ELNES) of Si L2,3-edges. The ordering structure in the medium-range was analyzed by the exponential optical absorption edge also known as the Urbach edge of the glasses. The optical absorption data were obtained from the low energy loss spectrum of EELS through Kramers-Kronig analysis. The results show that silica fiber has the same short-range structure as the bulk specimen, but is significantly more disordered than the bulk glasses.

Amphiphiles alter the energy of surfaces, but the extent of this feature is typically constant. Smart systems with amphiphilicity as a function of an external, physical trigger are desirable. As a trigger, the exposure to a magnetic field, in particular, is attractive because it is not shielded in water. Amphiphiles like surfactants are well known, but the magnetic response of molecules is typically weak. Vice‐versa, magnetic particles with strong response to magnetic triggers are fully established in nanoscience, but they are not amphiphilic. In this work colloids with Janus architecture and ultra‐small dimensions (25 nm) have been prepared by spatial control over the thiol‐yne click modification of organosilica‐magnetite core–shell nanoparticles. The amphiphilic properties of these anisotropically modified particles are proven. Finally, a pronounced and reversible change in interfacial stabilization results from the application of a weak (, Particle‐based amphiphiles: Ultra‐small Janus particles (JPs) have been prepared using magnetite/organosilica particles in a click reaction with spatial control. The JPs show a pronounced and reversible magnetic response when applying a weak magnetic field to a dispersion which results in a difference in the interfacial energy.

There are two categories of coordination polymers (CPs): inorganic CPs (i-CPs) and organic ligand bridged CPs (o-CPs). Based on the successful crystal engineering of CPs, we here propose noncrystalline states and functionalities as a new research direction for CPs. Control over the liquid or glassy states in materials is essential to obtain specific properties and functions. Several studies suggest the feasibility of obtaining liquid/glassy states in o-CPs by design principles. The combination of metal ions and organic bridging ligands, together with the liquid/glass phase transformation, offer the possibility to transform o-CPs into ionic liquids and other ionic soft materials. Synchrotron measurements and computational approaches contribute to elucidating the structures and dynamics of the liquid/glassy states of o-CPs. This offers the opportunity to tune the porosity, conductivity, transparency, and other material properties. The unique energy landscape of liquid/glass o-CPs offers opportunities for properties and functions that are complementary to those of the crystalline state.

Non-Newtonian fluids are ubiquitous in daily life and industrial applications. Herein, we report an intelligent fluidic system integrating two distinct non-Newtonian rheological properties mediated by an autocatalytic enzyme reaction. Associative polyelectrolytes bearing a small amount of ionic and alkyl groups are engineered: by carefully balancing the charge density and the hydrophobic effect, the polymer solutions demonstrate a unique shear thickening property at low pH while shear thinning at high pH. The urea-urease clock reaction is utilized to program a feedback-induced pH change, leading to a strong upturn of the nonlinear viscoelastic properties. As long as the chemical fuel is supplied, two distinct non-Newtonian states can be achieved with a tunable lifetime span. As a proof of concept, we demonstrate how the physical energy-driven nonequilibrium properties can be manipulated by a chemical-fueled process.

The nitroaldol reaction is demonstrated as an efficient dynamic covalent reaction in phosphate buffers at neutral pH. Rapid equilibration was recorded with pyridine-based aldehydes, and dynamic oligomerization could be achieved, leading to nitroaldol dynamers of up to 17 repeating units. The dynamers were applied in a coherent stimuli-responsive molecular system in which larger dynamers transiently existed out-of-equilibrium in a neutral aqueous system rich in formaldehyde, controlled by nitromethane.

We present a new brittle rheology and an accompanying numerical framework for large-scale sea-ice modelling. We have based this rheology on a Bingham-Maxwell constitutive model and the Maxwell-Elasto-Brittle (MEB) rheology for sea ice. The key strength of the MEB rheology is its ability to represent the scaling properties of simulated sea-ice deformation in space and time. The new rheology we propose here, which we refer to as the brittle Bingham-Maxwell rheology (BBM), represents a further evolution of the MEB rheology. We developed BBM to address two main shortcomings of the MEB rheology and numerical implementation: excessive thickening of the ice in model runs longer than about one winter and a relatively high computational cost. The BBM addresses these shortcomings by demanding that the ice deforms under convergence in a purely elastic manner when internal stresses lie below a given compressive threshold. It also improves numerical performance by introducing an explicit scheme to solve the ice momentum equation. We show that using an implementation of BBM in the neXtSIM sea-ice model, the model gives reasonable long-term evolution of the Arctic sea-ice cover. It also gives very good deformation fields and statistics compared to satellite observations.

Colloidal micromotors are important candidates for a wide spectrum of applications, ranging from medicine to environmental remediation. Thus far, the propulsion force determination has been obtained from the colloidal motor motion speed and surrounding viscosity via the Stokes drag. Herein, a precise force measurement method and detailed analysis of the fundamental propulsion mechanisms of colloidal Janus micromotors propelled by thermophoretic and steam bubble force vectors, revealing findings uninvestigated to date, are presented. Optical tweezers provide fast and high-precision force measurements in all three orthogonal dimensions simultaneously. Colloidal Janus micromotors are compared with isotropic hot Brownian reference microparticles, which have no defined force vector that propels them perpendicular to the direction of the laser beam. Janus micromotors display a defined laser power intensity-dependent thermophoretic propulsion, as well as bubble force-based propulsion, after surpassing the threshold value for the water boiling. The steam bubble propulsion force vector and the thermophorethic force vectors sum up for the Janus micromotor propulsion direction. On the contrary, the bubble force counteracts photophoretic force in propagation direction of light. Moreover, the thermal-based reduction of viscosity around the Janus colloidal motor contributes significantly to its speed and guidance abilities., Advanced Photonics Research, 3 (1)

Single-particle tracking and optical tweezers are powerful techniques for studying diverse processes at the microscopic scale. The stochastic behavior of a microscopically observable particle contains information about its interaction with surrounding molecules, and an optical tweezer can further facilitate this observation with its ability to constrain the particle to an area of interest. Although these techniques found their initial applications in biology, they can also shed new light on colloid and interface phenomena by unveiling nanoscale morphologies and molecular-level interactions in real time, which have been obscured in traditional ensemble analysis. Here we demonstrate the application of single-particle tracking and optical tweezers for studying molecular interactions at solid-liquid interfaces. Specifically, we investigate the behavior of surfactants at the water-glass interface by tracing their interactions with gold nanoparticles that are optically trapped on these molecules. We discover the underlying mechanisms governing the particle motion, which can be explained by hydrophobic interactions, disruptions, and rearrangements among surfactant monomers at the interfaces. Such interpretations are further supported by statistical analysis of an individual trajectory and comparison to theoretical predictions. Our findings provide new insights into the surfactant dynamics in this specific system but also illustrate the promise of single-particle tracking and optical manipulation in studying nanoscale physics and chemistry of surfaces and interfaces.

The formation and development of tidal channels and salt marshes are controlled by complex interactions between hydrodynamics, sediment transport, and vegetation dynamics. Tidal channels affect and...

In single‐molecule force spectroscopy (SMFS), many studies have focused on the elasticity and conformation of polymer chains, but little attention has been devoted to the dynamic properties of single polymer chains. In this study, we measured the energy dissipation and elastic properties of single polystyrene (PS) chains in toluene, methanol, and N,N‐dimethylformamide using a homemade piezo‐control and data acquisition system externally coupled to a commercial atomic force microscope (AFM), which provided more accurate information regarding the dynamic properties of the PS chains. We quantitatively measured the chain length‐dependent changes in the stiffness and viscosity of a single chain using a phenomenological model consistent with the theory of viscoelasticity for polymer chains in dilute solution. The effective viscosity of a polymer chain can be determined using the Kirkwood model, which is independent of the intrinsic viscosity of the solvent and dependent on the interaction between the polymer and solvent. The results indicated that the viscosity of a single PS chain is dominated by the interaction between the polymer and solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1736–1743

We report, for the first time, the observation of a Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface. The potential of zero charge of 0.3 V vs. NHE agrees very well with earlier values obtained by different methods. The observation of the potential of zero charge of this interface requires a specific pH (pH 4) and anomalously low electrolyte concentrations (, A Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface is reported. Compared to the gold and mercury double‐layer data, the diffuse double layer structure at the Pt(111)‐electrolyte interface deviates significantly from the Gouy–Chapman theory in the sense that the electrostatic screening is much better than predicted by purely electrostatic mean‐field Poisson–Boltzmann theory.

Plateau-Rayleigh (P-R) instability occurring on Brownian colloidal particles is presented. This instability can be used for the surface patterning of Brownian colloidal rings. This idea was realized by employing polystyrene(PS)/SiO2 core/shell rings, for which PS layer was selectively grown onto the interior surface of SiO2 rings. The P-R instability was initiated in the ring's dispersion by adding a good solvent of PS. By using both experiments and theory, it is shown that the number of patches is tunable and that it is linearly related to a function of two variables, namely, solvent quantity and contact angle. In particular, one-patch Janus rings and patchy disks were also synthesized at high yields. The patch size of all particles is tunable by step-by-step polymerization and the patches can be functionalized, for example by ATRP grafting with pH-sensitive polymers. This approach can be adapted for the synthesis of other patchy colloids with designated complexity.

The electronic performance of conjugated polymers depends on the microstructure of the polymer films. A percolated network morphology with high crystallinity, ordered intermolecular packing and long‐range order is beneficial for charge transport. In recent reports, some conjugated polymers have been shown to exhibit liquid crystallinity. The appearance of liquid crystalline ordering provides a new solution to solve the difficulties in microstructure manipulation. In this review, we summarize how liquid crystallinity can assist molecular arrangement and guide long‐range orientation during film processing, leading to high charge mobility. We expect that this article could draw more attention to the liquid crystallinity of conjugated polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1572–1591

Mach-Zehnder interferometer technique is utilized to study the impact of grafting of the nylon-6 fibers with poly (methyl methacrylate) (PMMA) polymer on the optical, geometrical, and structural properties. He-Ne laser diffraction technique is applied to study the changes in the fiber thickness of two samples (nylon-6 blank and nylon-6 grafted with PMMA) at different positions along the fiber length. The geometrical parameters are investigated by determining the cross-sectional shape of the two samples. The results of the interferometric and the diffraction techniques show that there is no variation in the thickness of nylon-6 fiber but variations in the thickness of the grafted nylon-6 fiber are obvious. The optical and physical properties along the axis of these fibers are characterized by measuring their refractive indices, birefringence, polarizability per unit volume, dielectric constant, surface reflectivity and the refractive index profile. The results show that PMMA polymer changed the optical, geometrical, and structural properties of the nylon-6 blank fiber. Microinterferograms are given for illustrations.

We report a methodology to calculate the free energy of a shape transformation in a lipid membrane directly from a molecular dynamics simulation. The bilayer need not be homogeneous or symmetric and can be atomically detailed or coarse grained. The method is based on a collective variable that quantifies the similarity between the membrane and a set of predefined density distributions. Enhanced sampling of this "Multi-Map" variable re-shapes the bilayer and permits the derivation of the corresponding potential of mean force. Calculated energies thus reflect the dynamic interplay of atoms and molecules, rather than postulated effects. Evaluation of deformations of different shape, amplitude, and range demonstrates that the macroscopic bending modulus assumed by the Helfrich-Canham model is increasingly unsuitable below the 100-Å scale. In this range of major biological significance, direct free-energy calculations reveal a much greater plasticity. We also quantify the stiffening effect of cholesterol on bilayers of different composition and compare with experiments. Lastly, we illustrate how this approach facilitates analysis of other solvent reorganization processes, such as hydrophobic hydration. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.

Gas‐liquid‐liquid slug flow in a capillary reactor is a promising new concept that allows one to incorporate gas‐liquid reaction, liquid‐liquid extraction, and facile catalyst separation in a single unit. In order to assess the performance of a gas‐liquid‐liquid slug flow reactor, it is necessary to predict the slug velocity and pressure drop to ascertain residence times and reaction rates. New empirical models for velocity and pressure drop were developed based on existing models for two‐phase gas‐liquid and liquid‐liquid slug flows, and these were validated experimentally., Chem. Eng. Technol.;42(10)

Competition between supramolecular polymers for the same monomers can lead to strong responses in these systems. Using numerical simulations, we show that the sharpness and asymmetry of the transition from one thermodynamically stable polymer to another upon changing temperature is determined by the most unstable rather than the most stable supramolecular polymer. The width and asymmetry of the transitions are shown to depend on the relative and absolute nucleation penalties of the competing supramolecular polymerizations.

The diffusion of small molecules through amorphous polymers proceeds by the thermally activated jumps whose rate changes from one region to another due to polymer heterogeneity. Little is known at present about the origin of diffusion heterogeneity. The oxidation of triplet nitrene and quenching of phenanthrene phosphorescence have been used to study the movement of molecular oxygen on a nanometer length scale in glassy poly(ethyl methacrylate) and poly(n‐butyl methacrylate) far below the glass transition temperature. It has been found that, as temperature increases, the jump rates in all regions increase by the same factor. This finding points to the equality of the activation energies of oxygen jumps in different regions of the polymers. We conclude that the correlated elastic displacements of polymer chains inside regions about several nanometers in size provide molecules jumps. Due to the large size of these regions, the activation energy of jump does not depend on local polymer structure. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1097–1104

Although clay is composed of disconnected anisotropic clay platelets, many rock physics models treat the clay platelets in shale as interconnected. However, the clay matrix in shales can be modelled as anisotropic clay platelets embedded within a soft isotropic interplatelet region, allowing the influence of disconnected clay platelets on the elastic properties of the clay matrix to be analysed. In this model, properties of the interplatelet region are governed by its effective bulk and shear moduli, whereas the effective properties of the clay platelets are governed by their volume fraction, aspect ratio and elastic stiffness tensor. Together, these parameters implicitly account for variations in clay and fluid properties, as well as fluid saturation. Elastic stiffnesses of clay platelets are obtained from the literature, including both experimental measurements and first‐principles calculations of the full anisotropic (monoclinic or triclinic) elastic stiffness tensors of layered silicates. These published elastic stiffness tensors are used to compile a database of equivalent transverse isotropic elastic stiffness tensors, and other physical properties, for eight common varieties of layered silicates. Clay matrix anisotropy is then investigated by examining the influence of these different elastic stiffnesses, and of varying model parameters, upon the effective transverse isotropic elastic stiffness tensor of the clay matrix. The relationship between the different clay minerals and their associated anisotropy parameters is studied, and their impact on the resulting anisotropy of the clay matrix is analysed.

The effect of viscosity on the diffusion efficiency (Fdif ) of an organic radical pair in a solvent cage and the termination mechanism, that is, the selectivity of disproportionation (Disp) and combination (Comb) of the geminated caged radical pair and the diffused radicals encountered, were investigated quantitatively by following the photolysis of dimethyl 2,2'-azobis(2-methylpropionate) (V-601) in the absence and presence of PhSD. Fdif and Disp/Comb selectivity outside the cage [Disp(dif) /Comb(dif) ] are highly sensitive to the viscosity. In contrast, the Disp/Comb selectivity inside the cage [Disp(cage) /Comb(cage) ] is rather insensitive. The difference in viscosity dependence between Disp(cage) /Comb(cage) and Disp(dif) /Comb(dif) is explained by the spin state of the radical pair inside and outside the cage and the spin state dependent configurational changes of the radical pair upon their collision. Given that the configurational change of the radicals associates the displacement and reorganization of solvents around the radicals, the termination outside the cage, which requires larger change than that inside the cage, is highly viscosity dependent. Furthermore, while the bulk viscosity of each solvent shows good correlation with Fdif and Disp/Comb selectivity, microviscosity is the better parameter predicting Fdif and Disp(dif) /Comb(dif) selectivity regardless of the solvents.