Search Results (11)

The morphology of CVD-grown molybdenum disulfide (MoS₂) is sensitive to the local precursor environment, which governs nucleation density, edge stability, and growth kinetics. In this work, we systematically investigate the effect of precursor ratio on the morphological evolution of MoS₂ microstructures synthesized by atmospheric-pressure chemical vapor deposition on SiO₂/Si substrates. By varying the relative amounts of MoO₃ and sulfur precursors, distinct growth regimes were obtained, ranging from compact hexagonal and quasi-circular domains to multilayer hexagonal structures, triangular domains, and dendritic morphologies. At higher MoO₃ loading, growth is dominated by dense nucleation, leading to isolated few-layer hexagonal domains. A moderate reduction in Mo precursor concentration promotes diffusion-assisted growth and secondary nucleation, resulting in multilayer hexagonal structures with aligned or slightly rotated stacked layers. Under sulfur-rich conditions, morphology evolves into triangular domains due to anisotropic edge stabilization, while further increase in sulfur concentration gives rise to branched dendritic structures through kinetically limited, diffusion-dominated growth. Cross-sectional FIB analysis reveals dense vertical stacking and lateral displacement of upper layers in the multilayer hexagonal domains. Raman and photoluminescence measurements confirm strong correlations between morphology, layer thickness, and optical response, with thinner regions exhibiting reduced Raman peak separation, enhanced photoluminescence intensity, and blue-shifted excitonic transitions. The results show that, under fixed APCVD reactor geometry, source positions, temperature profile, carrier-gas flow, and nominal growth duration, the nominal MoO₃ to sulfur source-loading ratio reproducibly correlates with the transition between compact hexagonal, multilayer hexagonal, triangular, and dendritic MoS₂ morphologies on amorphous SiO₂/Si substrates. Because vapor-phase Mo- and S-containing partial pressures were not directly measured, this ratio is treated as a nominal source-inventory descriptor rather than as a direct vapor-phase stoichiometric ratio. The observed trends are interpreted using a qualitative thermodynamic and kinetic framework based on precursor fluence, nucleation density, edge stability, and diffusion-limited growth. Full article

Molecular transport membranes are promising alternatives to conventional cryogenic separation processes. Here, solvent polarity effects were investigated by varying the DMF/MeOH ratio during the solvothermal synthesis of supported ZIF-7 membranes. A DMF:MeOH ratio of 1:3 preserved the characteristic sodalite topology while suppressing dense-phase formation. Methanol incorporation modified heterogeneous crystallization behavior, intercrystalline organization, membrane morphology, and film densification on α-alumina supports while reducing DMF consumption by approximately 75%. These effects are associated with solvent-mediated precursor solvation, Zn²⁺–benzimidazole coordination equilibria, and heterogeneous nucleation at the support–solution interface. Although low BET surface areas were obtained from N₂ adsorption at 77 K, these values were interpreted cautiously considering the known limitations of nitrogen physisorption in flexible ultramicroporous frameworks. Overall, the results support solvent polarity engineering as a physicochemical strategy for regulating membrane microstructural evolution under reduced DMF conditions. Accordingly, the transport behavior discussed herein is interpreted primarily from a solvent-mediated microstructural perspective rather than as a direct quantitative descriptor of accessible porosity. Full article

Background: Daptomycin, a lipopeptide antibiotic with critical clinical applications, presents a formidable crystallization challenge due to its high conformational flexibility and complex ionization equilibrium. Current literature lacks reports on single crystals or highly crystalline powders of this molecule. This study aims to elucidate the thermodynamic and kinetic mechanisms governing daptomycin solubility and crystallization to establish a rational screening pathway. Methods: In this study, the solubility of daptomycin was systematically measured across eight pure solvents using a static gravimetric method. Molecular-level insights were obtained by integrating experimental data with the Conductor-like Screening Model for Real Solvents (COSMO-RS) and molecular dynamics (MD) simulations. Results: Solubility trends correlated strongly with solvent electrostatic and hydrogen-bonding capabilities. MD simulations revealed that the solvent’s ability to modulate conformational diversity—quantified by the number of dominant conformational clusters—is the decisive factor governing crystallization. For instance, aqueous systems exhibited strong Coulombic stabilization (−1126.61 kJ/mol). Crucially, solvents like acetone restricted daptomycin to a limited number of conformers (12 clusters), significantly lowering the nucleation barrier and yielding crystalline powders with distinct PXRD peaks. Conversely, solvents like methanol induced high conformational diversity (53 clusters), resulting exclusively in amorphous precipitates. Conclusions: The “number of conformational clusters” serves as a robust descriptor for rapidly screening crystallization solvents, effectively bridging thermodynamics and kinetics. This strategy provides a rational, reduced-trial-and-error framework for crystallizing complex, flexible macromolecules with multiple dissociation sites, moving beyond traditional trial-and-error approaches. Full article

The understanding and control of protein crystallization are crucial in structural biology, drug development, and biomaterial design. This study introduces a unified framework for modeling and comparing crystallization kinetics using selected growth functions. Experimental datasets from the literature for four proteins, Lysozyme, Thaumatin, Ribonuclease A, and Proteinase K, under Hanging Drop and Langmuir–Blodgett conditions were analyzed. Five kinetic models, Avrami, Kashchiev, Hill, Logistic, and Generalized Sigmoid (GSM), were fitted to size–time data of the four benchmark proteins. From each fit, four descriptors were extracted: crystallization half-time, time of maximum growth, width at half-maximum, and peak growth rate. These metrics summarize crystallization dynamics and enable cross-comparison of proteins and methods. Langmuir–Blodgett templating accelerated onset and improved synchrony, though the effect varied by protein and model. Logistic, Hill, and GSM models provided consistent fits across most conditions, while Avrami and Kashchiev were more sensitive to early or late deviations. Notably, descriptor extraction remained reliable even with limited or uneven sampling, revealing kinetic regimes such as synchrony, asymmetry, or prolonged nucleation, not evident in raw data. This transferable analytical framework supports quantitative evaluation of crystallization behavior, aiding screening, process optimization, and time-resolved structural studies. Full article

Melt-spun PA6/TiO₂ fibers with TiO₂ modified by silane coupling agents KH550 and KH570 at 0, 1.6, and 4 wt% provide a practical testbed to address three fiber-centric gaps: transferable interphase quantification, interphase-resolved indications of compatibility, and a reproducible kinetics–structure–property link. This work proposes, for the first time at fiber scale, a four-phase partition into crystal (c), crystal-adjacent rigid amorphous fraction (RAF-c), interfacial rigid amorphous fraction (RAF-i), and mobile amorphous fraction (MAF), and extracts an interfacial triad consisting of the specific interfacial area (S_v), polymer-only RAF-i fraction expressed per composite volume (Γ_i), and interphase thickness (t_i) from SAXS invariants to establish a quantitative interphase-structure–property framework. A documented SAXS/DSC/WAXS workflow partitions the polymer into the above four components on a polymer-only basis. Upon filling, Γ_i increases while RAF-c decreases, leaving the total RAF approximately conserved. Under identical cooling, DSC shows the crystallization peak temperature is higher by 1.6–4.3 °C and has longer half-times, indicating enhanced heterogeneous nucleation together with growth are increasingly limited by interphase confinement. At 4 wt% loading, KH570-modified fibers versus KH550-modified fibers exhibit higher α-phase orientation (Hermans factor f(α): 0.697 vs. 0.414) but an ~89.4% lower α/γ ratio. At the macroscale, compared to pure (neat) PA6, 4 wt% KH550- and KH570-modified fibers show tenacity enhancements of ~9.5% and ~33.3%, with elongation decreased by ~31–68%. These trends reflect orientation-driven stiffening accompanied by a reduction in the mobile amorphous fraction and stronger interphase constraints on chain mobility. Knitted fabrics achieve a UV protection factor (UPF) of at least 50, whereas pure PA6 fabrics show only ~5.0, corresponding to ≥16-fold improvement. Taken together, the SAXS-derived descriptors (S_v, Γ_i, t_i) provide transferable interphase quantification and, together with WAXS and DSC, yield a reproducible link from interfacial geometry to kinetics, structure, and properties, revealing two limiting regimes—orientation-dominated and phase-fraction-dominated. Full article

Molecular dynamics (MD) simulations provide atomistic insights into nucleation and crystallization in polymers, yet interpreting their complex spatiotemporal data remains a challenge. Existing order parameters face limitations, such as failing to account for directional alignment or lacking sufficient spatial resolution, preventing them from accurately capturing the anisotropic and heterogeneous characteristics of nucleation or the surface phenomena of polymer crystallization. We introduce a novel set of local order parameters—namely, directional entropy bands— that extend scalar entropy-based descriptors by capturing first-order angular moments of the local entropy field around each particle. We compare these against conventional metrics (entropy, the crystallinity index, and smooth overlap of atomic positions (SOAP) descriptors) in equilibrium MD simulations of polymer crystallization. We show that (i) scalar entropy bands demonstrate advantages compared to SOAP in polymer phase separation at single-snapshot resolution and (ii) directional extensions (dipole projections and gradient estimates) robustly highlight the evolving crystal–melt interface, enabling earlier nucleation detection and quantitative surface profiling. UMAP embeddings of these 24–30D feature vectors reveal a continuous melt–surface–core manifold, as confirmed by supervised boundary classification. Our approach is efficient and directly interpretable, offering a practical framework for studying polymer crystallization kinetics and surface growth phenomena. Full article

In the present work, the structure and properties of Ti_nB_n (n = 2–12) clusters were studied, and the microstructure of a Al-Ti-B system was simulated by molecular dynamics to determine the grain refinement mechanism of an Al-Ti-B master alloy in Al alloy. Based on the density functional theory method, the structural optimization and property calculations of Ti_nB_n (n = 2–12) clusters were carried out. The clusters at the lowest energy levels indicated that the Ti and B atoms were prone to form TiB₂ structures, and the TiB₂ structures tended to be on the surface of the clusters. The Ti₁₀B₁₀ cluster was determined to be the most stable structure in the range of n from 2 to 12 by average binding energy and second-order difference energy. The analysis of HOMOs and LUMOs suggested that TiB₂ was the active center in the cluster; the activity of Ti was high, but the activity of B atoms decreased as the cluster size n increased. Meanwhile, the prediction of reaction sites by Fukui function, condensed Fukui function, and condensed dual descriptor identify that Ti atoms were more active than B atoms. Furthermore, TiB₂ structures were found in the Al-Ti-B system simulated by the ab initio molecular dynamics method, and there were Al atoms growing on the Ti atoms in the TiB₂. Based on the above analysis, this study suggests that TiB₂ may be a heterogeneous nucleation center of α-Al. This work helps to further understand the mechanism of Al-Ti-B induced heterogeneous nucleation in Al alloys, which can provide theoretical guidance for related experiments. Full article

This paper presents a computational study of the mechanistic models for the laydown of carbon species on nickel surface facets and the burn-off models for their gasification mechanism in methane steam reforming based on density functional theory. Insights into catalyst design strategies for achieving the simultaneous inhibition of the laydown of polymeric carbon and the promotion of its burn-off are obtained by investigating the influence of single atom dopants on nickel surfaces. The effects of single atom dopants on adsorption energies are determined at both low and high carbon coverages on nickel and used to introduce appropriate thermodynamic descriptors of the associated surface reactions. It is found that the critical size of the nucleating polymeric carbon adatom contains three atoms, i.e., C₃. The results show that the burn-off reaction of a polymeric carbon species is thermodynamically limited and hard to promote when the deposited carbon cluster grows beyond a critical size, C₄. The introduction of single atom dopants into nickel surfaces is found to modify the structural stability and adsorption energies of carbon adatom species, as well as the free energy profiles of surface reactions for the burn-off reactions when CH₄, H₂O, H₂, and CO species react to form hydrogen. The results reveal that materials development strategies that modify the sub-surface of the catalyst with potassium, strontium, or barium will inhibit carbon nucleation and promote burn-off, while surface doping with niobium, tungsten, or molybdenum will promote the laydown of polymeric carbon. This study provides underpinning insights into the reaction mechanisms for the coking of a nickel catalyst and the gasification routes that are possible for the recovery of a nickel catalyst during the steam reforming of methane for large-scale production of hydrogen. Full article

We investigate, through Monte Carlo simulations, the heterogeneous crystallization of linear chains of tangent hard spheres under confinement in one dimension. Confinement is realized through flat, impenetrable, and parallel walls. A wide range of systems is studied with respect to their average chain lengths (N = 12 to 100) and packing densities (φ = 0.50 to 0.61). The local structure is quantified through the Characteristic Crystallographic Element (CCE) norm descriptor. Here, we split the phenomenon into the bulk crystallization, far from the walls, and the projected surface crystallization in layers adjacent to the confining surfaces. Once a critical volume fraction is met, the chains show a phase transition, starting from regions near the hard walls. The established crystal morphologies consist of alternating hexagonal close-packed or face-centered cubic layers with a stacking direction perpendicular to the confining walls. Crystal layer perfection is observed with an increasing concentration. As in the case of the unconstrained phase transition of athermal polymers at high densities, crystal nucleation and growth compete with the formation of sites of a fivefold local symmetry. While surface crystallites show perfection with a predominantly triangular character, the morphologies of square crystals or of a mixed type are also formed. The simulation results show that the rate of perfection of the surface crystallization is not significantly faster than that of the bulk crystallization. Full article

Driven by the rapid development of additive manufacturing technologies and the trend towards mass customization, the development of new feedstock materials has become a key aspect. Additivation of the feedstock with nanoparticles is a possible route for tailoring the feedstock material to the printing process and to modify the properties of the printed parts. This study demonstrates the colloidal additivation of PA12 powder with laser-synthesized carbon nanoparticles at >95% yield, focusing on the dispersion of the nanoparticles on the polymer microparticle surface at nanoparticle loadings below 0.05 vol%. In addition to the descriptors “wt%” and “vol%”, the descriptor “surf%” is discussed for characterizing the quantity and quality of nanoparticle loading based on scanning electron microscopy. The functionalized powders are further characterized by confocal dark field scattering, differential scanning calorimetry, powder rheology measurements (avalanche angle and Hausner ratio), and regarding their processability in laser powder bed fusion (PBF-LB). We find that heterogeneous nucleation is induced even at a nanoparticle loading of just 0.005 vol%. Finally, analysis of the effect of low nanoparticle loadings on the final parts’ microstructure by polarization microscopy shows a nanoparticle loading-dependent change of the dimensions of the lamellar microstructures within the printed part. Full article

Duplex stainless steels (DSS) and superduplex stainless steels (SDSS) are important classes of stainless steels, because they combine the benefits of austenite and ferrite phases. This results in steels with better mechanical properties and higher corrosion resistance. Owing to these characteristics, DSS and SDSS are widely employed in industry. However, the appearance of undesirable intermetallic phases in their microstructure impairs the properties of DSS and SDSS. Among the undesirable intermetallic phases, the main one is the sigma phase (σ), which can be nucleated when the steel is exposed to the temperature range between 650 °C and 900 °C, reducing the steel’s toughness and resistance to corrosion. In a previous work, Fonseca and collaborators used two descriptors of the microstructural path to analyze the formation of sigma phase (σ), the interfacial area per unit volume between sigma phase and austenite (S_V), and the mean chord length of sigma (<λ>), both as a function of V_V, the volume fraction of sigma, known in the literature as the microstructural partial path (MP). In this work, the contiguity ratio is applied for the first time to describe the microstructural path in the study of sigma phase precipitation in SDSS. The contiguity ratio shows that the distribution of the ferrite/sigma boundaries is homogeneous. Thus, it is reasonable to infer that one has a uniform distribution of sigma phase nuclei within the ferrite. About the kinetics of sigma phase formation, the DSS can be described by the classical Johnson-Mehl, Avrami, and Kolmogorov (JMAK) equation, whereas for the SDSS, the kinetics tend to follow the Cahn model for grain edge nucleation. Finally, we present the three-dimensional (3D) reconstruction of the sigma phase in SDSS. The results demonstrate that the sigma phase nucleates at the edges of the ferrite/austenite interfaces. Moreover, the sigma phase grows and consumes the ferrite, but is not fully interconnected. Full article