Anisotropy Kinetics Research Articles

A novel interferometry-based optical sensor to study the coagulation of human plasma

We propose and demonstrate a Twin-interferometry (TIM) based optical approach for studying and exploring anisotropy and directional dependent coagulation kinetics in human plasma under isothermal condition. Human plasma is obtained by centrifuging blood samples collected in Ethylenediamine tetra acetic acid (EDTA) coated vials at 6000 RPM in a laminar flow unit. 0.5 ml of plasma is collected in an optically flat disposable glass cuvette and subjected to induced coagulation by adding equal amounts of CaCl2 solution as coagulant at seven different concentrations. A Twin-interferometer is designed to record the rate of shift in Michelson’s fringes caused by rate of change of optical path difference of coagulating plasma in two orthogonal directions. A pair of interferograms, referred to as the Twin- interferogram (TIG), are recorded for all plasma samples with different CaCl2 concentration during its coagulation. A new approach for extracting various coagulation parameters from TIG, such as anisotropy, half coagulation time, constants governing the rate and dimensionality of coagulation, and their variation along distinct direction is demonstrated. TIG results are validated using polarizing optical microscopic (POM) and optical extinction techniques.

Stable cycling and low-temperature operation utilizing amorphous carbon-coated graphite anodes for lithium-ion batteries.

With the continuous expansion of the lithium-ion battery market, addressing the critical issues of stable cycling and low-temperature operation of lithium-ion batteries (LIBs) has become an urgent necessity. The high anisotropy and poor kinetics of pristine graphite in LIBs contribute to the formation of precipitated lithium dendrites, especially during rapid charging or low-temperature operation. In this study, we design a graphite coated with amorphous carbon (GC) through the Chemical Vapor Deposition (CVD) method. The coated carbon layer at the graphite interface exhibits enhanced reaction kinetics and expanded lithium-ion diffusion pathways, thereby reduction in polarization effectively alleviates the risk of lithium precipitation during rapid charging and low-temperature operation. The pouch cell incorporating GC‖LiCoO2 exhibits exceptional durability, retaining 87% of its capacity even after 1200 cycles at a high charge/discharge rate of 5C/5C. Remarkably, at -20 °C, the GC-2 maintains a specific capacity of 163 mA h g-1 at 0.5C, higher than that of pristine graphite (65 mA h g-1). Even at -40 °C, the GC-2‖LiCoO2 pouch cell still shows excellent capacity retention. This design realizes the practical application of graphite anode in extreme environments, and have a promising prospect of application.

Photochromic polymers: Structural engineering driving individual NLO response

Photochromic polymers have attracted a lot of attention in the last few decades because of their useful properties related to color change and optical data storage. In this contribution we present a macromolecular structure influence on the output spectroscopic properties in the manner of all-optical switching and harmonics of light generation. Slight chemical architecture changes make significant difference if we consider generated optical anisotropy magnitude and kinetics of photoinduced process but also force diversified nonlinear optical response. We have placed a strong electron acceptor unit, fluorine atom, in a few alternate substitution patterns. One of them (1,4-) activates the phenyl unit, the other one (1,3-) works opposite. Finally, a joined form was also investigated, which led to appealing results making materials engineering field of studies a useful tool dedicated for advanced functional materials fabrication. Moreover, experimental achievements presented here indicate that investigated materials are perfect candidates for opto-electronics, photonics and spectroscopy fields and can be easily implemented into individual optical processing solutions.

Effect of steel slag on 3D concrete printing of geopolymer with quaternary binders

A new type of 3D-printable ‘one-part’ geopolymer was synthesized with fly ash (FA), granulated blast furnace slag (GBFS), steel slag (SS) and flue gas desulfurization gypsum (FGD). The effects of SS content (0–40%) on the rheological properties, 3D-printability, mechanical anisotropy and reaction kinetics of geopolymer were investigated. The yield stress and plastic viscosity monotonically decreased with the increasing SS content. Contrarily, the geopolymer with 10% of SS presented better extrudability, buildability and mechanical strength than those with 0, 20%, 30% and 40% of SS. This was mainly attributed to the conflicting influence of SS on geopolymerization, of which the OH− produced by hydration of SS raised the alkalinity of the reaction system and accelerated the dissolution of SiO44− and AlO45−, while the low reactivity prohibited the following polymerization process. Furthermore, the 3D-printed geopolymer presented more compact microstructure and less mechanical anisotropy thanks to the crosslinking of morphologically complementary products, including N(C)-A-S-H, C–S–H, AFt and CH, formed via synergistic reaction of FA-GBFS-SS-FGD system.

A functional family of fluorescent nucleotide analogues to investigate actin dynamics and energetics

Actin polymerization provides force for vital processes of the eukaryotic cell, but our understanding of actin dynamics and energetics remains limited due to the lack of high-quality probes. Most current probes affect dynamics of actin or its interactions with actin-binding proteins (ABPs), and cannot track the bound nucleotide. Here, we identify a family of highly sensitive fluorescent nucleotide analogues structurally compatible with actin. We demonstrate that these fluorescent nucleotides bind to actin, maintain functional interactions with a number of essential ABPs, are hydrolyzed within actin filaments, and provide energy to power actin-based processes. These probes also enable monitoring actin assembly and nucleotide exchange with single-molecule microscopy and fluorescence anisotropy kinetics, therefore providing robust and highly versatile tools to study actin dynamics and functions of ABPs.

Cobalt-Induced Performance Instabilities of Mn–Zn Ferrite Cores

Stability and reliability of transformers and inductors in power applications strongly depend on the quality of the employed ferrite cores. Given the critical role of cores, Mn–Zn ferrites’ sensitivity to their magnetic history and environmental storage conditions is investigated. To this end, Co-doped and Co-free Mn–Zn ferrites are prepared and primarily characterized in terms of structural, microstructural, and magnetic properties. The produced cores are subjected to endurance tests of technical interest comprising the response to a saturating magnetic bias and longtime storage under elevated temperature or humidity levels. With the exception of the damp heat test, prior imposition of a strong field or thermal aging process are found to induce significant instabilities to the power loss density of the Co-containing Mn–Zn ferrite cores in particular. Depending on the excitation, power loss may notably increase in the low- or high-frequency regime, whereas the effects can be either reversed with time or time independent. The proposed underlying mechanisms are based on the magnetically and thermally induced reorientation of Co2+ cations, which affects magnetocrystalline anisotropy and domain wall kinetics. Studies of different stress tests are supported by analysis of complex permeability spectra and electrical characteristics.

Mutual orientation of the n → π * and π → π * transition dipole moments in azo compounds: Determination by light-induced optical anisotropy

Abstract Photonic applications of azo compounds often require to know the polarization of molecular absorption bands. In this study, we demonstrate how the kinetics of light-induced anisotropy can be used to determine the mutual orientation of transition dipole moments pertaining to different absorption bands of an azo compound. The time profiles of light-induced anisotropy of the polymeric films doped with azo compounds p-azotoluene (AT) and 1-naphthyl-p-azo-methoxybenzene (NAMB) are analysed using commonly accepted models of photo-orientation. It is found that under irradiation of the films containing NAMB in the n → π* band of NAMB, the anisotropy level is too low compared to the anisotropy formed under irradiation in the π → π* band. The data are interpreted as demonstrating that the dipole moments of the n → π* and π → π* transitions of the NAMB molecule are not collinear. The angle between them was estimated to be 32.5 ± 5°.

(Invited) Direct Template-Less Synthesis of Oriented Sub-10 Nm Semiconducting Graphene Nanoribbons with Smooth Armchair Edges on Ge(001)

The rational synthesis of graphene nanoribbons that are semiconducting with sub-10 nm width, controlled crystallographic orientation, and well-defined edges on non-metallic substrates has been a significant challenge. The growth of nanoribbons on metal substrates precludes their direct use in semiconducting electronics due to the conductive substrate, and the direct synthesis of nanoribbons in solution is complicated by challenges of their post-synthetic assembly. In this talk, we demonstrate the direct, scalable synthesis of graphene nanoribbons via chemical vapor deposition (CVD) on Ge(001).[1] Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show that the ribbons are self-orienting ±2.9° from the Ge[110] directions and are self-defining. The nanoribbons have predominately smooth armchair edges that give rise to electron interference patterns indicative of high quality edges. By tuning the precursor flux, growth time, and growth temperature, the ribbon anisotropy and growth kinetics can be tailored to yield ribbons with controlled width < 10 nm and aspect ratio > 60. Compared to previous low aspect ratio crystals of graphene obtained on Ge, we find that in order to realize high aspect ratio nanoribbons, it is critical to operate in a regime in which the growth rate is especially slow, on the order of 5 nm/h in the width direction. This work is important because unlike continuous two-dimensional graphene, which is semimetallic, one-dimensional graphene nanoribbons can be semiconducting, allowing for the substantial modulation of their conductance and enabling their application in semiconductor logic, optoelectronics, photonics, and sensors. Moreover, the direct synthesis of ultranarrow and smooth graphene nanoribbons on Ge demonstrated here provides a scalable, high throughput pathway for integrating semiconducting graphene directly on conventional large-area semiconductor wafer platforms that are compatible with planar processing. [1] Jacobberger RM, Kiraly B, Fortin-Deschenes M, Levesque PL, McElhinny KM, Brady GJ, Rojas Delgado R, Singha Roy S, Mannix A, Lagally MG, Evans PG, Desjardins P, Martel R, Hersam MC, Guisinger NP, Arnold MS, Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015)

Characterization of Low EW Ionomers in Fuel Cells

Perfluorosulfonic-acid (PFSA) ionomers play a key role in the polymer-electrolyte fuel-cell (PEFC), in which they are primarily used as the proton-exchange membrane (PEM) with their remarkable transport properties and chemical/mechanical stability, but they also function as the nanometer thick "thin" electrolyte film in the catalyst layers binding the catalytic sites and providing proton transport pathways. In the thin-film regime, an ionomer exhibits vast deviations in its properties which are controlled by its interfaces with the air and the catalytic particles, i.e., carbon and platinum. While bulk membrane is responsible mainly for the ohmic resistances, in the catalyst layers, transport resistance in the ionomer film resulting from its interfacial interactions has direct implication on the mass-transport limitations in the PEFC, especially at higher current densities. Thus, it is imperative to understand the origins of ionomer-related transport resistances in fuel-cell catalysts, and how they changes with ionomer's chemistry and equivalent weight (EW). In this talk, we present our findings on the impact of EW and hygrothermal environmental stressors the structure and properties of ionomers across the lengthscales, i.e., from bulk membrane (PEM) to catalyst ionomer film in CLs. It will be shown through X-Ray scattering studies how hygrothermal ageing induces morphological changes in the catalyst ionomer films, and subsequently alters their swelling and sorption behavior as investigated by ellipsometry and quartz crystal microbalance (QCM). From the collected data, structure-swelling-uptake correlations are generated for PFSA ionomers of various EWs, both as bulk membrane and thin films. From the grazing-incidence X-ray scattering (GIXS), changes in the size and orientation of water domains in the ionomer film are determined in response to humidity, heat-treatments and hygrothermal ageing, which result in substantial changes in these morphological features. Nanostructrual anisotropy, phase-separation and sorption kinetics are all found to be related and affected by the substrates the ionomer film is interacting with. The investigation on the impact of equivalent weights (EWs) and PFSA side-chain chemistries on ionomer’s response demonstrated a key role EW plays in controlling the structure/transport relationship of the ionomer, especially in the catalyst layers. Impact of ageing and heat-treatments on ionomer’s structure and properties are similar for both bulk and thin films, but found to be more pronounced for the latter. Our results provide new insights into the environmental and operational stressors controlling ionomer's functionalities, especially as thin-films in fuel-cell catalysts.

Bottom-up Synthesis of Sub-10 Nm Semiconducting Graphene Nanoribbons with Smooth Armchair Edges on Ge(001)

The rational synthesis of graphene nanoribbons that are semiconducting with sub-10 nm width, controlled crystallographic orientation, and well-defined edges on non-metallic substrates has been a significant challenge. The growth of nanoribbons on metal substrates precludes their direct use in semiconducting electronics due to the conducting substrate, and the direct synthesis of nanoribbons in solution is complicated by challenges of their post-synthetic assembly. In this talk, we demonstrate the scalable synthesis of graphene nanoribbons from the bottom-up via chemical vapor deposition (CVD) on Ge(001). Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show that the ribbons are self-orienting ±2.9° from the Ge[110] directions and are self-defining. The nanoribbons have predominately smooth armchair edges that give rise to electron interference patterns that are indicative of the high quality of the edges. By tuning the precursor flux, growth time, and growth temperature, the ribbon anisotropy and growth kinetics can be tailored to yield ribbons with controlled width < 10 nm and aspect ratio > 60. Compared to previous reports of the growth of low aspect ratio crystals of graphene on Ge, we find that in order to realize high aspect ratio nanoribbons, it is critical to operate in a regime in which the growth rate is especially slow, on the order of 5 nm/h for growth in the width direction. Scanning tunneling spectroscopy shows that the ribbons have electronic structures that are consistent with semiconductors with bandgaps that are > 500 meV and that vary inversely with width. This work is important because unlike continuous two-dimensional graphene, which is semimetallic, one-dimensional graphene nanoribbons can be semiconducting, allowing for the substantial modulation of their conductance and enabling their application in semiconductor logic, optoelectronics, photonics, and sensors. Moreover, the direct synthesis of ultranarrow and smooth graphene nanoribbons on Ge demonstrated here provides a scalable, high throughput pathway for integrating semiconducting graphene directly on conventional large-area semiconductor wafer platforms that are compatible with planar processing.

Faceted–nonfaceted growth transition and 3-D morphological evolution of primary Al6Mn microcrystals in directionally solidified Al–3 at.% Mn alloy

Abstract

Investigation of Photoinduced Orientation Ordering in Polymethacrylates with Side-Chain Azobenzene Moieties

The initial and the photoinduced 3D orientational order in the films of two methacrylic polymers containing azobenzene groups with electron-donor or electron-acceptor substituents was studied by using null ellipsometry and UV/Vis absorption spectroscopy. The 3D order was induced by monochromatic polarized light of two different wavelengths corresponding to ππ* and nπ* absorption bands of azochromophores. We found that, depending on the excitation wavelength and terminal substituents of azochromophores, recording kinetics of photoinduced anisotropy in the polymers is dominated by either angular redistribution or angularly selective trans-cis isomerization of the chromophores originally being mainly in the trans-form. Before irradiation, the azobenzene groups in the films of all polymers show preference to the out-ofplane ordering. Scenario of the order transformation under irradiation depends on the prevailing mechanism of the photoinduced anisotropy. In case of angular redistribution,initial positive uniaxial order of azochromophores is transformed into the negative uniaxial order characterized by random orientation of these units in the plane perpendicular to the polarization direction of the exciting light. In turn, in case of photoselection, the chromophores approach a zero-order (spatially isotropic) state due to exhaustion of the anisotropic trans-isomers in all directions. The transient orientational structures in these kinetic processes are biaxial. Вивчено кінетику фотоіндукованого впорядкування двох метакрилових полімерів, що містять азобензольні групи з електрон-донорними або електрон-акцепторними замісниками, при їх опроміненні за різних довжин хвиль. Експериментальні дослідження було проведено з використанням методів нуль-еліпсометрії та спектроскопії. Показано, що азофрагменти орієнтуються в залежності від довжини хвилі за механізмом фотоорієнтації або фотоселекції. За механізмом фотоорієнтації азохромофори спонтанно розміщуються в площині, перпендикулярній вектору поляризації світла Eex. У випадку, коли переважає механізм фотоселекції, 3-мірний розподіл азохромофорів у стані насичення є ізотропним завдяки суттєвому вичерпанню анізотропних транс-ізомерів.

Molecular modeling of the relationship between nanoparticle shape anisotropy and endocytosis kinetics

In this work, an N-varied dissipative particle dynamics (DPD) simulation technique is applied to investigate detailed endocytosis kinetics for ligand-coated nanoparticles with different shapes, including sphere-, rod- and disk-shaped nanoparticles. Our results indicate that the rotation of nanoparticles, which is one of the most important mechanisms for endocytosis of shaped nanoparticle, regulates the competition between ligand–receptor binding and membrane deformation. Shape anisotropy of nanoparticles divides the whole internalization process into two stages: membrane invagination and nanoparticle wrapping. Due to the strong ligand–receptor binding energy, the membrane invagination stage is featured by the rotation of nanoparticles to maximize their contact area with the membrane. While the kinetics of the wrapping stage is mainly dominated by the part of nanoparticles with the largest local mean curvature, at which the membrane is most strongly bent. Therefore, nanoparticles with various shapes display different favorable orientations for the two stages, and one or two orientation rearrangement may be required during the endocytosis process. Our simulation results also demonstrate that the shape anisotropy of nanoparticles generates a heterogeneous membrane curvature distribution and might break the symmetry of the internalization pathway, and hence induce an asymmetric endocytosis.

Stochastic model for photoinduced anisotropy

We present a stochastic model for the kinetics of photoinduced anisotropy in a sample of molecular chromophores that may undergo photoisomerization. It is assumed that the chromophores do not interact among them, but are embedded in a medium that slows down the rotational diffusion. The model makes use of data about the photoinduced reorientation of the single chromophore, its photoisomerization and its rotational diffusion, that are made available by molecular dynamics simulations. For the first time such molecular scale processes are computationally connected to the development of anisotropy in a large sample and on a long time scale. A test on azobenzene shows the potentiality of the method and the interplay between photoinduced anisotropy and photoisomerization.

Oligomerization of DNMT3A controls the mechanism of de novo DNA methylation.

DNMT3A is one of two human de novo DNA methyltransferases essential for regulating gene expression through cellular development and differentiation. Here we describe the consequences of single amino acid mutations, including those implicated in the development of acute myeloid leukemia (AML) and myelodysplastic syndromes, at the DNMT3A·DNMT3A homotetramer and DNMT3A·DNMT3L heterotetramer interfaces. A model for the DNMT3A homotetramer was developed via computational interface scanning and tested using light scattering and electrophoretic mobility shift assays. Distinct oligomeric states were functionally characterized using fluorescence anisotropy and steady-state kinetics. Replacement of residues that result in DNMT3A dimers, including those identified in AML patients, show minor changes in methylation activity but lose the capacity for processive catalysis on multisite DNA substrates, unlike the highly processive wild-type enzyme. Our results are consistent with the bimodal distribution of DNA methylation in vivo and the loss of clustered methylation in AML patients. Tetramerization with the known interacting partner DNMT3L rescues processive catalysis, demonstrating that protein binding at the DNMT3A tetramer interface can modulate methylation patterning. Our results provide a structural mechanism for the regulation of DNMT3A activity and epigenetic imprinting.

Effects of Aggregation on the Excitation Dynamics of LH2 from Thermochromatium tepidum in Aqueous Phase and in Chromatophores

We carried out femtosecond magic-angle and polarized pump-probe spectroscopies for the light-harvesting complex 2 (LH2) from Thermochromatium (Tch.) tepidum in aqueous phase and in chromatophores. To examine the effects of LH2 aggregation on the dynamics of excitation energy transfer, dominant monodispersed and aggregated LH2s were prepared by controlling the surfactant concentrations. The aqueous preparations solubilized with different concentrations of n-dodecyl-β-D-maltoside (DDM) show similar visible-to-near-infrared absorption spectra, but distinctively different aggregation states, as revealed by using dynamic light scattering. The B800 → B850 intra-LH2 energy transfer time was determined to be 1.3 ps for isolated LH2, which, upon aggregation in aqueous phase or clustering in chromatophores, shortened to 1.1 or 0.9 ps, respectively. The light-harvesting complex 1 (LH1) of this thermophilic purple sulfur bacterium contains bacteriochlorophyll a absorbing at 915 nm (B915), and the LH2(B850) → LH1(B915) intercomplex transfer time in chromatophores was found to be 6.6 ps. For chromatophores, a depolarization time of 21 ps was derived from the anisotropy kinetics of B850*, which is attributed to the migration of B850* excitation before being trapped by LH1. In addition, the B850* annihilation is accelerated upon LH2 aggregation in aqueous phase, but it is much less severe upon LH2 clustering in the intracytoplasmic membrane. These results are helpful in understanding the light-harvesting function of a bacterial photosynthetic membrane incorporating different types of antenna complexes.

Kinetics of Surfactant-induced Aggregation of Lysozyme Studied by Fluorescence Spectroscopy

The study of protein conformational changes in the presence of surfactants and lipids is important in the context of protein folding and misfolding. In the present study, we have investigated the mechanism of the protein conformational change coupled with aggregation leading to size growth of Hen Egg White Lysozyme (HEWL) in the presence of an anionic detergent such as sodium dodecyl sulphate (SDS) in alkaline pH. We have utilized intrinsic protein fluorescence (tryptophan) and extrinsic fluorescent reporters such as 8-anilinonaphthalene-1-sulfonic acid (ANS), dansyl and fluorescein to follow the protein conformational change in real-time. By analyzing the kinetics of fluorescence intensity and anisotropy of multiple fluorescent reporters, we have been able to delineate the mechanism of surfactant-induced aggregation of lysozyme. The kinetic parameters reveal that aggregation proceeds with an initial fast-phase (conformational change) followed by a slow-phase (self-assembly). Our results indicate that SDS, below critical micelle concentration, induces conformational expansion that triggers the aggregation process at a micromolar protein concentration range.

Necking in glassy polymers: Effects of intrinsic anisotropy and structural evolution kinetics in their viscoplastic flow

Two recently proposed developments of the Glass–Rubber constitutive model for glassy polymers treat the viscoplastic deformation as intrinsically anisotropic, and incorporate the kinetics of structural evolution. These features enable the model to capture better the distinctive features of glassy polymers’ constitutive response: post-yield strain-softening and strain-hardening and effects of pre-existing molecular orientation. They have been combined to form a new variant of the model, and the consequences for necking have been explored. Uniaxial extension of prismatic bars was simulated using the finite element method, employing a numerical implementation of the new model, with material parameters of polystyrene. Strain localization predicted with the new model was found to be systematically retarded as compared to predictions with the original (intrinsically isotropic) version of the model, for the same conditions. In particular, the effect of frozen-in molecular orientation was examined. This was found to retard strain localization for stretching parallel to the orientation direction, for both models. But the localization predicted with the new model was always significantly less pronounced than with the original model. Indeed, for sufficiently high pre-orientation (e.g. a uniaxial stretch of 2.2), localization could be effectively prevented with the new model, under conditions when otherwise failure by necking is predicted. Such results can all be explained in terms of a linear stability analysis. They suggest that all previous simulations of necking in glassy polymers made using intrinsically isotropic representations of polymer viscoplasticity may have over-predicted the rate of strain localization.

Kinetic characterization of photoinduced anisotropy in diarylethene film

Based on the theoretical model we have proposed, a complete study on the kinetics of photoinduced anisotropy in diarylethene films is performed. The kinetic curves of molecular concentration, photoinduced dichroism and birefringence are calculated, respectively. It is found that the colored molecular concentration decreases with the increase of the excitation exposure until saturation, and the photoinduced anisotropy increases to a maximum and then decreases gradually. The optimal exposure is 260J/cm2. In addition, the transmittance of probe beam reflecting the anisotropy is measured by experiment. The theoretical results are compared with experimental data, and basic concordance is found between both sets of data.

Kinetics of photoinduced anisotropy in bacteriorhodopsin film under two pumping beams

Photoinduced anisotropy in bacteriorhodopsin (BR) film arises from the selective bleaching of BR molecules to linearly polarized light. The kinetics of photoinduced anisotropy excited by single and two pumping beams are investigated theoretically and experimentally. Compared with a single pumping beam (650 nm), which produces comparatively small photoinduced anisotropy, dual-wavelength linearly polarized pumping beams (650 and 405 nm) can obviously change the photoinduced anisotropy. When the polarization orientation of the 405 nm pumping beam is perpendicular to that of the 650 nm pumping beam, the peak and steady values of the photoinduced anisotropy kinetic curves are remarkably enhanced. But when the two pumping beams have parallel polarization orientation, the peak and steady values are restrained. At a fixed intensity of the 650 nm pumping beam, there exists an optimal intensity for the 405 nm pumping beam to maximize the value of the photoinduced anisotropy. The photoinduced transmittance of the polarizer-BR-analyzer system is modulated by the polarization angle of the 405 nm pumping beam in an approximate-cosine form.