Local Structural Order Research Articles

Measuring Oxygen Solubility in Amorphous and Semicrystalline Polyolefins Using Test Particle Insertion: A Comparative Study of Polyethylene and Isotactic Polypropylene.

The test particle insertion method is used to study the solubility of oxygen in two commonly used polymers: polyethylene (PE) and isotactic polypropylene (iPP). Amorphous samples for both polymers were prepared by means of Monte Carlo and molecular dynamics simulations, and the oxygen solubility was measured across different temperatures. The solubility-temperature dependence for iPP proved to be nonmonotonic due to the interplay between binding and reorganizational enthalpy, while for PE, it appeared to be monotonic based on the available data in the studied temperature range. A broad comparison to experiments and simulations is included. Further oxygen insertions were also performed in semicrystalline PE and iPP samples at ambient temperature, and the obtained values were compared to a linear relationship which correlates the solubility in the purely amorphous phase with the solubility in the crystalline phase. The solubility of PE closely follows the linear relationship, while iPP exhibits some divergence. All the semicrystalline samples were previously annealed at elevated temperatures for long periods (a few μs), and a strong effect of annealing was observed on the structure and the solubility of iPP. A well-developed iPP lamellar structure emerged at longer annealing times, while PE develops that structure already in the early crystallization stages. The solubility of semicrystalline iPP samples with lamellar morphology exhibited better agreement with extrapolated solubility values of the amorphous state─the extrapolation was made using a linear relationship connecting solubility in the purely amorphous phase and solubility in mixed phases (amorphous and crystalline). Results on the correlation of the solubility with the local structural ordering are also present.

Synergistic effects of zinc thiocyanate on the performance of cesium lead bromide perovskite phosphors for solid-state lighting applications

All inorganic lead halide perovskites have led to a new paradigm shift in display and lighting technologies because of significant cost and performance advantage over the current state-of-the-art optoelectronics. However, the applications of these perovskites are undermined due to the toxicity and severe degradation of the materials in response to external stimuli. This research highlights the synergetic effects of co-doping of CsPbBr3 nanocrystals (NCs) at its B- and X-site using zinc thiocyanate (Zn(SCN)2). The adopted doping strategy helps to improve the photoluminescence stability of the pristine NCs when stored under ambient conditions for 156 days. This is attributed to the enhanced local structural order and reduced inhomogeneous strain between the lattices of the NCs due to the synchronized effect of Zn2+ and SCN–. The composite NCs are integrated as color-converting layers (thin 3D printing layer coated with NCs) with a blue LED chip to obtain the white light. It exhibits bright white emissions with a color rendering index of 86, correlated color temperature of 6046 K, and color coordinates close to standard white light. This work emphasizes the strong potential of inexpensive and earth-abundant Zn(SCN)2-based CsPbBr3 composites to meet consumer needs.

Nitrogen doping in carbon xerogels via ammonia pyrolysis: A case study

Nitrogen-doped carbon xerogels (CXNs) were carbonized across a range of temperatures (400 °C–800 °C) using sol-gel derived resorcinol-formaldehyde xerogel to elucidate their structural evolution during carbonization in ammonia. The investigation extensively probed chemical and structural changes in CXNs at varying carbonization temperatures, employing analytical methods such as X-ray photoelectron spectroscopy, infrared spectroscopy, and energy-dispersive X-ray spectroscopy. These findings were thoroughly compared with the local structure derived from total X-ray scattering and Raman spectroscopy. The results showed a transformation in the local ordering and chemical structure of CXNs, characterized by a reduction in oxidation sites, expansion of C sp2 network structures, leading to the growth of aromatic domains, and the incorporation of nitrogen into the carbon backbone structure. Pyrolysis in ammonia notably influenced the textural structure, resulting in a partial loss of mesopores and an increased micropore volume.

Designing athermal disordered solids with automatic differentiation

The ability to control forces between sub-micron-scale building blocks offers significant potential for designing new materials through self-assembly. Traditionally, this involves identifying a crystal structure with a desired property and then designing building-block interactions so that it assembles spontaneously. However, this paradigm fails for structurally disordered solids, which lack a well-defined structure. Here, we show that disordered solids can still be treated from an inverse self-assembly perspective by bypassing structure and directly targeting material properties. Using the Poisson’s ratio as a primary example, we demonstrate how differentiable programming links interaction parameters with emergent behavior, enabling iterative training to achieve the desired Poisson’s ratio. We also tune other properties, including pressure and local 8-fold structural order, and can even control multiple properties simultaneously. This robust, transferable, and scalable approach can handle a wide variety of systems and properties, demonstrating the utility of disordered solids as a practical avenue for self-assembly platforms.

α-Hydrazino Acid Insertion Governs Peptide Organization in Solution by Local Structure Ordering.

In this work, we have applied the concept of α-hydrazino acid insertion in a peptide sequence as a means of structurally organizing a potential protein-protein interactions (PPI) inhibitor. Hydrazino peptides characterized by the incorporation of an α-hydrazino acid at specific positions introduce an additional nitrogen atom into their backbone. This modification leads to a change in the electrostatic properties of the peptide and induces the restructuring of its hydrogen bonding network, resulting in conformational changes toward more stable structural motifs. Despite the successful use of synthetic hydrazino oligomers in binding to nucleic acids, the structural changes due to the incorporation of α-hydrazino acid into short natural peptides in solution are still poorly understood. Based on NMR data, we report structural models of p53-derived hydrazino peptides with elements of localized peptide structuring in the form of an α-, β-, or γ-turn as a result of hydrazino modification in the peptide backbone. The modifications could potentially lead to the preorganization of a helical secondary peptide structure in a solution that is favorable for binding to a biological receptor. Spectroscopically, we observed that the ensemble averaged rapidly interconverting conformations, including isomerization of the E-Z hydrazide bond. This further increases the adaptability by expanding the conformational space of hydrazine peptides as potential protein-protein interaction antagonists.

Ultrabroad distribution of multiple anelasticities in O-doped refractory multiprincipal element alloys

The Snoek anelastic internal friction (IF) peak due to stress-induced dipole ordering associated with interstitial atoms was well observed in IF curves of single-principal element alloys (SPEAs) as early as in the 1950s, however, its behavior remains elusive in multi-principal element alloys (MPEAs) to date. Here the temperature-dependent IF spectra of NbTiV0.5Zr refractory MPEAs with varying O contents were presented, and the analysis of these data indicates that for O-doped NbTiV0.5Zr MPEAs, the O addition triggers two anelastic IF peaks (the PO1 and PO2), corresponding to the O-Snoek-type relaxation in random solid solution (RSS) and local chemical ordering (LCO) structures, respectively. The half-peak width of the PO1 is 2–3 times broader than that for SPEAs, associated with the wide O migration energy barrier distribution in MPEAs. These phenomena show a striking contrast to the single and narrow Snoek-type peak observed for SPEAs. Our analysis further reveals an approximate linear correlation between the half-peak width of the Snoek-type peak and the mixing entropy. The introduction of O also shifts grain boundary relaxation peaks (PG) towards higher temperatures. Interestingly, high-temperature anomalous modulus changes were observed for the first time in TiV-based lightweight refractory MPEAs, which is suggested to be originated from the order reduction of the body-centered cubic (bcc) structure at elevated temperatures. Moreover, the 1 at.%O doped NbTiV0.5Zr MPEA with a favorable balance between the peak heights of the PO2 and PG, exhibits outstanding specific yield stress (SYS) among refractory MPEAs while maintaining an elongation as high as 20 %. This work provides not only a bridge between the anelastic behavior of SPEAs and MPEAs for upcoming studies and theories concerning bcc MPEAs with interstitial atoms, but contributes to the holistic design of bcc MPEAs with high strength and excellent ductility.

Electrodeless method for ultra-low mobility with carrier-resolution of nanochannel

As the channel lengths of electronic devices are scaled down to the nanometer range, the conventional methods to evaluate charge-carrier mobility approach a technical limit that is imposed by interfering effects of the electrode and forcing field. In this study, we demonstrate that electron spectroscopy provides additional (yet hidden) information on unipolar charge transport, which is free from conventional problems. We demonstrate that the estimated effective diffusion current through the target sample allows the measurement that is precise enough (10−4 cm2/V s) to obtain the mobility of electrons μelectron and holes μhole in nanolength organic channels. Using this method, we show how μelectron and μhole are correlated with the local structural order of poly(3-hexylthiophene) at the nanoscale. This method enables in situ charge-resolved observations of μelectron and μhole by eliminating the need for electrode and forcing field and will help to expand our understanding of charge conduction in nanoscale materials.

Ring-originated anisotropy of local structural ordering in amorphous and crystalline silicon dioxide

Rings comprising chemically bonded atoms are essential topological motifs for the structural ordering of network-forming materials. Quantification of such larger motifs beyond short-range pair correlation is essential for understanding the linkages between the orderings and macroscopic behaviors. Here, we propose two quantitative analysis methods based on rings. The first method quantifies rings by two geometric indicators: roundness and roughness. These indicators reveal the linkages between highly symmetric rings and crystal symmetry in silica and that the structure of amorphous silica mainly consists of distorted rings. The second method quantifies a spatial correlation function that describes three-dimensional atomic densities around rings. A comparative analysis among the functions for different degrees of ring symmetries reveals that symmetric rings contribute to the local structural order in amorphous silica. Another analysis of amorphous models with different orderings reveals anisotropy of the local structural ordering around rings; this contributes to building the intermediate-range ordering.

Orientational Order in Dense Colloidal Liquids and Glasses.

We construct structural order parameters based on local angular and radial distribution functions in dense colloidal suspensions. All the order parameters show significant correlations to local dynamics in the supercooled and glass regime. In particular, the correlations between the orientational order and dynamical heterogeneity are consistently higher than those between the conventional two-body structural entropy and local dynamics. The structure-dynamics correlations can be explained by a excitation model with the energy barrier depending on local structural order. Our results suggest that in dense disordered packings, local orientational order is higher than translational order, and plays a more important role in determining the dynamics in glassy systems.

Local structural ordering determines the mechanical damage tolerance of amorphous grain boundary complexions

Amorphous grain boundary complexions act as toughening features within a microstructure because they can absorb dislocations more efficiently than traditional grain boundaries. This toughening effect should be a strong function of the local internal structure of the complexion, which has recently been shown to be determined by grain boundary crystallography. To test this hypothesis, molecular dynamics are used here to simulate dislocation absorption and damage nucleation for complexions with different distributions of structural short-range order. The complexion with a more disordered structure away from the dislocation absorption site is actually found to better resist crack nucleation, as damage tolerance requires delocalized deformation and the operation of shear-transformation zones through the complexion thickness. The more damage tolerant complexion accommodates plastic strain efficiently within the entire complexion, providing the key mechanistic insight that local patterning and asymmetry of structural short-range order controls the toughening effect of amorphous complexions.

Inhibition effect of segregation and chemical order on grain boundary migration in NbMoTaW multi-principal element alloy

The impacts of solute segregation and chemical order on grain boundary (GB) migration are investigated by atomistic simulations in the NbMoTaW multi-principal element alloy (MPEA). Assisted by a contrived Nb-rich model, it is found that solute segregation and chemical order synergistically inhibit GB migration. Nb segregation increases the critical stress for GB migration, and the presence of chemical order further enhances the resistance of GB to plastic deformation. The destruction of local ordering structures is responsible for the difficult GB migration. Transition pathway analyses show that GB modified with both Nb segregation and chemical order requires high migration barrier, and the prior migration of GB sites tends to avoid regions with heavier chemical order. These results provide new insight into how chemical complexity affects elementary GB motion and contribute to manipulating the stability of MPEAs.

Structural transitions in jammed asymmetric bidisperse granular packings

We study the local structural changes along the jamming transitions in asymmetric bidisperse granular packings. The local structure of the packing is assessed by the contact orientational order, tilde{Q}_{ell }, that quantifies the contribution of each contact configuration (Large–Large, Small–Small, Large–Small, Small–Large) in the jammed structure. The partial values of tilde{Q}_{ell } are calculated with respect to known ordered lattices that are fixed by the size ratio, delta , of the particles. We find that the packing undergoes a structural transition at phi _J, manifested by a sudden jump in the partial tilde{Q}_{ell }. Each contact configuration contributes to the jammed structure in a different way, changing with delta and concentration of small particles, X_{textrm{S}}. The results show not only that the packing undergoes a structural change upon jamming, but also that bidisperse packings exhibit local HCP and FCC structures also found in monodisperse packings. This suggests that the jammed structure of bidisperse systems is inherently endowed with local structural order. These results are relevant in understanding how the arrangement of particles determines the strength of bidisperse granular packings.Graphic abstract

Percolation transitions of confinement-induced layering and intralayer structural orders in three-dimensional Yukawa liquids.

The disorder-order transitions of layering and intralayer structural orders of three-dimensional Yukawa liquids, under the enhanced confinement effect with decreasing normal distance z to the confinement boundary, is investigated numerically. The liquid between the two flat boundaries is segmented into many slabs parallel to the boundary, with the same slab width as the layer width. In each slab, particle sites are binarized into sites with layering order (LOSs)/ layering disorder (LDSs) and with intralayer structural order (SOSs)/disorder (SDSs). It is found that with decreasing z, a small fraction of LOSs starts to heterogeneously emerge in the form of small clusters in the slab, followed by the emergence of the large percolating LOS clusters spanning over the system. The smooth rapid rise of the fraction of LOSs from small values followed by their gradual saturations, and the scaling behavior of multiscale LOS clustering, are similar to those of the nonequilibrium systems governed by the percolation theory. The disorder-order transition of intraslab structural ordering also exhibits a similar generic behavior as that of layering with the same transition slab number. The spatial fluctuations of local layering order and local intralayer structural order are uncorrelated in the bulk liquid and the outmost layer next to the boundary. Approaching the percolating transition slab, their correlation gradually increases to the maximum.

Hydrogen segregation by local chemical ordering structure in CrCoNi medium-entropy alloys: A first principle study

Hydrogen segregation by local chemical ordering structure in CrCoNi medium-entropy alloys: A first principle study

Singlet Molecular Oxygen Generation via Unexpected Emission Color-Tunable CdSe/ZnS Nanocrystals for Applications in Photodynamic Therapy

It is highly desirable in biomedical sciences to utilize the multifunctional nanoparticles of similar size with tunable emission. Since the optoelectronic properties of quantum dots (QDs) originate from size-dependent quantum confinement effects, we developed an alternate approach to synthesize color-tunable CdSe/ZnS QDs based on interfacial ion exchange (predominantly exchange of Se2– by S2– anions), using 1-dodecanethiol and oleylamine solvent systems as a sensitive parameter. The wide-range color-tunability (490–570 nm) was achieved unexpectedly as a result of interfacial alloying without inducing a significant change in the size (from 4.45 to 4.81 nm) of QDs. The local atomic structure order, chemical composition, and nature of alloying in QDs were unraveled by XAFS data analysis. Owing to the molecular-like sensitization behavior, the QDs were evaluated for singlet molecular oxygen (1O2) efficiency. They were further studied in RAW 264.7 macrophages for biocompatibility, bioimaging, and delivering pathways for use in future photodynamic therapy (PDT). The QDs demonstrated efficient singlet molecular oxygen (1O2) quantum yields (ΦQDs) of 14, 12, and 18% for QDs (I), QDs (II), and QDs (III), respectively. The QD-treated cells presented high cell viability above 85% and induced no cell activation. Fluorescence and transmission electron microscopy (TEM) images of cells manifested a considerable amount of QDs in the vicinity of the cell membrane and intracellular regions. The pathway-specific inhibition measurements revealed that the QDs were internalized by cells via energy-dependent endocytosis, predominantly macropinocytosis and other receptor-mediated endocytic pathways, and accumulated them presumably in endosome/lysosomes. This study will open new possibilities for engineering interfacial alloying-based tunable emission QDs and pathway-specific delivery of QD-based theranostics into a site of interest for simultaneous bioimaging and PDT.

Combining reverse Monte Carlo analysis of X-ray scattering and extended X-ray absorption fine structure spectra of very small nanoparticles.

Finite size effects in partial pair distribution functions generate artefacts in the scattering structure factor and scattering intensity. It is shown how they can be overcome using a binned version of the Debye scattering equation. Accordingly, reverse Monte Carlo simulations are used for very small nanoparticles of LaFeO3 with diameters below 10 nm to simultaneously analyse X-ray scattering data and extended X-ray absorption fine structure spectra at the La K and Fe K edges. The structural information obtained is consistent regarding local structure and long-range order.

Spatially resolved structural order in low-temperature liquid electrolyte.

Determining the degree and the spatial extent of structural order in liquids is a grand challenge. Here, we are able to resolve the structural order in a model organic electrolyte of 1 M lithium hexafluorophosphate (LiPF6) dissolved in 1:1 (v/v) ethylene carbonate:diethylcarbonate by developing an integrated method of liquid-phase transmission electron microscopy (TEM), cryo-TEM operated at -30°C, four-dimensional scanning TEM, and data analysis based on deep learning. This study reveals the presence of short-range order (SRO) in the high-salt concentration domains of the liquid electrolyte from liquid phase separation at the low temperature. Molecular dynamics simulations suggest the SRO originates from the Li+-(PF6-)n (n>2) local structural order induced by high LiPF6 salt concentration.

Vibrational dynamics of liquid water in an external electric field.

In our present study, we have investigated the effects of an externally applied static electric field on the vibrational dynamics of liquid water (D2O) using ab initio molecular dynamics. The rate of vibrational spectral diffusion is obtained from simulated two-dimensional infrared spectra, three-pulse photon echo intensity, and frequency correlation functions and distributions. We find that the static vibrational frequency distribution undergoes a redshift of 90 cm-1 whereas the overall vibrational dynamics get slower with the relaxation time constant to be around 4.9 ps. Thus we infer that the local hydrogen bond network tends to reorganize in the presence of an external field with an increase in local structural order as evident from the overall slower vibrational dynamics and reduced molar entropy.

Homogenization modelling of antibiotic diffusion and adsorption in viral liquid crystals.

Systems of rod-shaped viruses have long been important to the science of living liquid crystals, as their monodispersity and uniform charge make them convenient model systems. Recently, it was shown that, upon the addition of polymers, suspensions of rod-shaped viruses form liquid crystals that are linked with increased tolerance of bacteria against antibiotics. We use homogenization to obtain effective equations describing antibiotic diffusion through these liquid crystals. The analytical results of homogenization are compared with numerical results from an exact microscopic model, showing good agreement and thus allowing us to identify the key parameters behind the process. Our modelling shows that the adsorption plays a key role in increasing antibiotic diffusion time and therefore the presence of nematic rod-shaped viruses may increase antibiotic tolerance through physical mechanisms alone. These results demonstrate the applicability of homogenization as an analytical tool to systems of liquid crystalline viruses, with relatively straightforward extension to more complex problems such as liquid crystalline biofilms, other biological liquid crystals and biological systems with different types of local structural order.

Structure of jammed ellipse packings with a wide range of aspect ratios.

Motivated in part by the recent observation of liquid glass in suspensions of ellipsoidal colloids, we examine the structure of jammed two-dimensional ellipse packings over a much wider range of particle aspect ratios (α, the ratio of the major and minor axis lengths) than has been previously attempted. We determine the jamming densities ϕJ(α) to high precision, and find empirical analytic formulae that predict ϕJ(α) to within less than 0.1% for all 1≤α≤10, for three different particle dispersities. Then we explore how these packings' local structural order varies with α. We find that the densest packings possess unusually-well-defined nearest-neighbor shells, including both a higher fraction fZ=6 of particles with exactly six contacts and a previously-unreported short-range order marked by "kinetically suppressed" regions in their positional-orientational pair correlation function g(r,Δθ). We also show that the previously-reported approach to isostaticity (coordination number ZJ → Ziso ≡ 6) with increasing α is interrupted and then reversed as local nematic order increases: ZJ(α) drops towards 4 as ellipses are more often trapped by contacts with a parallel-oriented neighbor on either side and a perpendicularly-oriented neighbor on either end. Finally we show that ϕJ/ϕs (where ϕs is the saturated RSA packing density) is nearly α-independent for systems that do not develop substantial local hexatic or nematic order during compression.