Equilibrium Morphology Research Articles

Equilibrium phase behavior of gyroid-forming diblock polymer thin films.

Thin-film confinement of self-assembling block polymers results in materials with myriad potential applications-including membranes and optical devices-and provides design parameters for altering phase behavior that are not available in the bulk, namely, film thickness and preferential wetting. However, most research has been limited to lamella- and cylinder-forming polymers; three-dimensional phases, such as double gyroid (DG), have been observed in thin films, but their phase behavior under confinement is not yet well understood. We use self-consistent field theory to predict the equilibrium morphology of bulk-gyroid-forming AB diblock polymers under thin-film confinement. Phase diagrams reveal that the (211) orientation of DG, often observed in experiments, is stable between nonpreferential boundaries at thicknesses as small as 1.2 times the bulk DG lattice parameter. The (001) orientation is stable between modestly B-preferential boundaries, where B is the majority block, while a different (211)-oriented termination plane is stabilized by strongly B-preferential boundaries, neither of which has been observed experimentally. We then describe two particularly important phenomena for explaining the phase behavior of DG thin films at low film thicknesses. The first is "constructive interference," which arises when distortions due to the top and bottom boundaries overlap and is significant for certain DG orientations. The second is a symmetry-dependent, in-plane unit-cell distortion that arises because the distorted morphology near the boundary has a different preferred unit-cell size and shape than the bulk. These results provide a thermodynamic portrait of the phase behavior of DG thin films.

Exploring the low-index surfaces of D52-La2O3 from the first-principles calculations

The surface relaxations, surface stability, electronic structures, and equilibrium morphology of D52-La2O3 were analyzed by means of first-principles calculations. The stoichiometric surfaces of D52-La2O3 possess thermodynamic energies of the following order: (001) < (110) < (100). Changes in temperature and the partial pressure of oxygen were employed to determine the energy of the non-stoichiometric surfaces. The results indicated that the energies of the (ns-1La1O)-terminated (100) and (ns-1La)-terminated (001) surfaces increased with increasing oxygen partial pressures and decreased with temperatures, whereas the (ns-1O)-terminated (001) and (ns-1O)-terminated (100) surfaces exhibited the reverse rule. According to the calculated density of states, surface relaxations primarily impact the surface electronic structures. The Gibbs-Wulff model was used to forecast the equilibrium morphology of D52-La2O3, which followed in comparison with other’s experimental findings.

A reduction-consistent phase field model for non-isothermal multiphase flows of N immiscible incompressible fluids

In this study, we developed a reduction-consistent phase field model for non-isothermal incompressible N-phase flows. The model is based on the high-order spectral element method. To account for thermocapillary effects, we reformulated the continuum surface force model specifically for N-phase flows. In order to enhance computational efficiency, time-independent coefficient matrices for all variables involved were reconstructed, and an unsymmetrized multifrontal LU factorization was employed to solve the linear algebraic equations, which is derived by discretization. To verify the model effectiveness in calculating surface tension and describing three-phase interfacial dynamics, we conducted several experiments, including the stationary two-droplet example, the three-phase droplet spreading, and the equilibrium morphology of double emulsion droplet. Through these experiments, both the reduction-consistency and robustness of our model were demonstrated. Moreover, we validated the proposed model's applicability to non-isothermal three-phase flows by investigating the thermocapillary migration of single droplet and two droplets of different phases. Notably, we explored the thermocapillary migration of three-phase double droplets, focusing particularly on how the encapsulation process affects overall thermocapillary motion. Our findings indicate that the interaction between the two vortices near the interfaces of the two droplets strongly influences their migration behavior.

Transient Interfacial Pattern Formation in Block Copolymer Thin Films via Sequential Thermal and Solvent Immersion Annealing.

A variety of structures encountered in nature only arise in materials under highly nonequilibrium conditions, suggesting to us that the scope for creating new functional block copolymer (BCP) structures might be significantly enlarged by embracing complex processing histories that allow for the fabrication of structures quite unlike those created under "near-equilibrium" conditions. The present work examines the creation of polymer film structures in which highly nonequilibrium processing conditions allow for the creation of entirely new types of transient BCP morphologies achieved by transitioning between different ordered states. Most previous studies of BCP materials have emphasized ordering them from their disordered state obtained from a solution film casting process, followed by a slow thermal annealing (TA) process at elevated temperatures normally well above room temperature. We have previously shown that achieving the equilibrium TA state can be accelerated by a direct solvent immersion annealing (DIA) preordering step that creates nascent ordered microstructures, followed by TA. In the present work, we examine the reverse nonequilibrium sequential processing in which we first thermally anneal the BCP film to different levels of partial (lamellar) order and then subject it to DIA to swell the lamellae. This sequential processing rapidly leads to a swelling-induced wrinkle pattern that initially grows with immersion time and can be quenched by solvent evaporation into its corresponding glassy state morphology. The article demonstrates the formation of wrinkling "defect" patterns in entangled BCP films by this sequential annealing that does not form under ordinary TA conditions. At long DIA times, these highly "defective" film structures evolve in favor of the equilibrium morphology of parallel lamellae observed with DIA alone. In conjunction with our previous study of sequential DIA + TA, the present TA + DIA study demonstrates that switching the order of these processing methods for block copolymer films gives the same final state morphology in the limit of long time as any one method alone, but with drastically different intermediate transient state morphologies. These transient morphologies could have many applications.

Thermodynamic Analysis of Silk Fibroin-Graphite Hybrid Materials and Their Morphology.

Silk fibroin (SF) is a β-sheet-rich protein that is responsible for the remarkable tensile strength of silk. In addition to its mechanical properties, SF is biocompatible and biodegradable, making it an attractive candidate for use in biotic/abiotic hybrid materials. A pairing of particular interest is the use of SF with graphene-based nanomaterials (GBNs). The properties of this interface drive the formation of well-ordered nanostructures and can improve the electronic properties of the resulting hybrid. It was previously demonstrated that SF can form lamellar nanostructures in the presence of graphite; however, the equilibrium morphology and associated driving interactions are not fully understood. In this study, we characterize these interactions between SF and SF lamellar with graphite using molecular dynamics (MD) simulations and umbrella sampling (US). We find that SF lamellar nanostructures have strong orientational and spatial preferences on graphite that are driven by the hydrophobic effect, destabilizing solvent-protein interactions and stabilizing protein-protein and protein-graphite interactions. Finally, we show how careful consideration of these underlying interactions can be applied to rationally modify the nanostructure morphology.

Anisotropic Magnetic Polymeric Particles with a Controllable Structure via Seeded Emulsion Polymerization.

Magnetic polymer composites have been widely utilized in potential applications in material science, such as reduction of dyes, immunodiagnostics, biomedicals, and magnetically controllable photonic crystals owing to large surface areas, fast separation, and recyclable performance. In this work, anisotropic magnetic particles were prepared by seeded emulsion polymerization, with morphologies of "Fe3O4-shell", "hemisphere-like", "raspberry-like", "multiple lobes-like", and "sandwich-like". Poly(styrene/divinylbenzene/mono-2-(methacryloxy)ethyl succinate)@ Fe3O4 (P(St/DVB/MMES)@Fe3O4) were the seed microspheres, and P(St/DVB/MMES)@Fe3O4@polymer particles are achieved by seeded emulsion polymerizations. The morphology of the particles depends on polymerization conditions (monomer ratios and surfactant), particle properties, and so on. Then, the minimum surface free energy change principles were used to predict the equilibrium morphologies of the magnetic polymer composites. Through theory, the model gives the correct tendency and good agreement with the equilibrium morphology which was in tandem with TEM results. Lastly, after in situ surface deposition of Ag nanoparticles, magnetic composite particles with sandwich-like morphology were applied for the catalytic degradation of 4-nitrophenol (4-NP) reacting with NaBH4. The apparent rate coefficient is 0.0069 s-1, and it can keep mainly about 80% efficiency in catalysis after five cycles.

Phase and Order Behavior of Charged Asymmetric Diblock‐Copolymer Melts in Bulk

AbstractThe phase and order behavior of charged asymmetric diblock‐copolymer melts is studied by using coarse‐grained molecular dynamics simulation. One of the blocks is made charged and other one is kept neutral, and the study systematically explores how the charged diblock‐coploymer responses as the charge fraction of the charged block is varied from 10% to 50%. When charge fraction increases, the study finds ordered transitions from interconnected cylinder‐like structures to lamellae, then to gyroid structures. It is also found that domain size of the obtained equilibrium morphology decreases slightly with the increase in charge fraction of the charged block.

Investigation of the equilibrium morphology of fcc [formula omitted] in Fe–Cu alloys using a non-local Allen–Cahn model

Cu-precipitation is one of the main concerns of the degradation of mechanical properties in reactor pressure vessel steels. It is especially prominent in the over-aged state, where the Cu-rich phase possesses an equilibrium face-centered cubic crystal structure. In this study, we develop and implement a non-local phase-field model to study the equilibrium morphology of precipitates in the over-aged state. The model reveals that the precipitates should possess oblate lath-like morphology, which is supported by novel experimental data. The orientation of the precipitates agrees well with the available literature. The mechanism of the morphology accommodation is explained using a theoretical framework of the invariant-line method. Also, morphology was analyzed quantitatively in the sense of its elongation. It was found that the equilibrium values deviate significantly from experimental data in this metric, which is assumed to be due to the metastable state of the precipitates during the coarsening process.

EQUILIBRIUM MORPHOLOGY MODEL APPLIED THROUGHOUT THE EXTENSIVE NAVIGATION CHANNEL NETWORK OF THE GOLD COAST WATERWAYS, AUSTRALIA

The prediction of sedimentation in waterways can preempt navigational hazards and support ongoing maintenance operations. The NCOS online software (Mortensen et al, 2018), used by port operators globally, has recently been upgraded to include the capability to predict sedimentation. This paper introduces the elegant but powerful equilibrium morphology model which would otherwise remain “behind the scenes” in the software.

Investigations on mechanical, thermodynamic and surface properties of U–Si alloys

The investigation of U–Si alloys as advanced technology fuels or accident tolerance fuels (ATFs) has gained momentum due to their higher uranium density and exceptional thermal conductivity. Density functional theory (DFT) calculations were used to examine the mechanical, thermodynamic and surface properties of U–Si alloys. Voigt-Reuss-Hill model was used to evaluate the mechanical properties such as Young's modulus, shear modulus, bulk modulus and so on. The results suggest that U3Si2 possesses an inherent brittleness, as opposed to the remaining U–Si alloys which demonstrate reliable ductility. In comparison to the hardness of other U–Si alloys (40–80 GPa), U3Si2 exhibits a significantly lower hardness (∼10 GPa). The results of anisotropy show that U3Si2 exhibits a lower anisotropy compared to USi2 (I41/amd) and U3Si (Pm-3m). Also, based on these mechanical properties, the sound velocity and Debye temperature are determined. Additionally, the study calculates the internal energy, Helmholtz free energy, entropy and heat capacity as a function of temperature, which is beneficial for fuel design and other applications. The surface energies and work function are investigated comprehensively for 161 surface slab models and used to obtain other surface properties, including equilibrium morphology, dominant surface orientations, area-weighted surface energy and area-weighted work function.

Regulating the self‐assembly of AB/CD diblock copolymer blends via secondary interactions

AbstractDesigned multiblock copolymers with complex architectures offer unlimited opportunities to obtain novel nanostructured phases, however, their synthesis could be challenging and expensive. An alternative approach to access desired nanostructures is to use blends of block copolymers with simple chain architectures and designed block‐block interactions. We use binary blends composed of AB and CD diblock copolymers as a model system to establish design principles of polymeric blends containing block copolymers. Specifically, we explore the phase behavior of AB/CD blends by using the polymeric self‐consistent field theory to construct phase diagrams of the blends focusing on the sphere‐forming regions in the phase space. We predict the formation of various spherical packing phases composed of either core‐shell‐structured spheres or binary spheres resembling metallic alloys. We demonstrate that the equilibrium morphology can be regulated by adjusting the blend composition and molecular parameters such as block fractions, conformational asymmetry, and segment‐segment interactions. The strategy of using secondary interaction in polymeric blends to control the phase behavior explored in the current study can also be generalized to other soft matter systems.

The surface and grain boundary properties of uranium boride: A DFT calculation

Uranium borides are currently being investigated as an accident tolerance fuel or advanced technology fuels (ATFs) to replace conventional UO2 fuel due to their high uranium density and high thermal conductivity. The surface properties of diverse facets of a crystal are pivotal for understanding different corrosion behaviors, fission gas bubble behaviors, and equilibrium morphologies. In this study, we employ density functional theory (DFT) calculations to investigate the surface properties of uranium borides. The surface orientations with maximum miller index up to 4, 1, and 2 for UB2, UB4 and UB12 were analyzed, respectively. Based on the calculated surface energies, the other surface properties of uranium borides were obtained through Wulff construction, including equilibrium morphology, dominant surface orientations, area-weighted surface energy and work function. Additionally, grain boundaries (GBs) have a significant impact on material properties, such as mechanical properties, corrosion behavior, and resistance to irradiation. Therefore, we use DFT calculations to determine the GB energies and work of separation for three low-Σ (7) symmetrical tilt GBs (STGB) and two twist GBs (TGB).

Morphological Differences of MnS Inclusions in Medium‐Carbon Steel with Different Manganese and Sulfur Contents

The morphology of MnS inclusion is one of the key elements influencing the machinability of steel. Herein, it is shown in the thermodynamic analysis results that the interaction coefficient causes a 1.2% deviation for the precipitation of MnS in low‐sulfur‐content steel (S1), while the deviation is 14% in high‐sulfur steel (S2), and the content of C and Si is the main element causing the deviation. The microstructure of medium‐carbon steel is mainly pearlite and ferrite. The increase of manganese and sulfur content leads to the decrease of ferrite content and increase of pearlite content. Almost all MnS inclusions in S1 are polyhedral, while S2 contains spherelike, cluster, and polyhedral MnS inclusions. Manganese and sulfur mainly affect the nucleation rate of MnS inclusion, where the number density of MnS in S2 is higher than that in S1, which increases the probability of viscous sintering of MnS inclusions in S2, and form spherelike‐ and rodlike‐polycrystalline MnS particles. Polyhedron inclusions are mostly octahedron, and it is the final equilibrium morphology of sulfide in S1 and S2.

Dynamic Motions of Topological Defects in Nematic Liquid Crystals under Spatial Confinement

AbstractTopological defects (TDs) have become a sensational topic due to their significant influence on the unusual optical and physiochemical characteristics of the material. To facilitate their application across a wide range of disciplines it is desirable to analyze and gain fundamental understanding of TDs in both equilibrium and nonequilibrium systems. Liquid crystals (LCs) are considered an ideal system for study given the direct visualization of TDs and a straightforward analyzation process. In addition to the equilibrium morphology of LC TDs, it is also of great interest to track and control the formation and annihilation of defects during thermodynamic processes. However, controlling the dynamic behavior of formed defects remains a challenge. Here, nematic LCs confined in a cell exhibiting surfaces with periodic anchoring conditions containing surface topography are relied on. The effects of patterned surface characteristics such as width, periodicity, and degree of curvature on defects dynamic motion, stabilization, and annihilation are explored. The computational experiments recapitulate the TDs transition path and provide free energy‐based predictions of critical distances for defect annihilation. Taken together, this simple approach offers a promising opportunity to control the dynamics of TDs in LCs through chemical patterned surfaces with topography.

Morphodynamic Resilience of the Tide‐Dominated Estuary With Interference From Tidal Flat Reclamations

AbstractMost tide‐dominated estuaries worldwide are among the morphodynamic shrinking types heavily disturbed by anthropogenic interventions like embankments and reclamations. A typical example is North Branch (NB), the northern first‐order distributary of Yangtze (Changjiang) Estuary, showed a rapid alteration from river‐dominated to tide‐dominated character in less than 50 years after intensive reclamations, resulting in serious morphodynamic shrinkage, thus attracted great concern of its evolutionary fate. Here, we explored this issue based on historical bathymetry data and hydro‐morphodynamic modeling to examine the morphology‐hydrology interactions and the suggested equilibrium re‐adjustment mechanism after intensive reclamations. Results demonstrated a mechanism of geomorphological resilience for the tide‐dominated estuary, evolving from preliminary estuarine shrinking to dynamic equilibrium after reclamations. Although reclamation could destabilize the system, leading to temporary positive feedback between tidal pumping and morphology shrinking, driving the estuary vanishing quickly in a short time. A substantial loss in the intertidal areas, changing the estuary geometry from a highly‐curved bank to a highly‐constrained channel, weakened flood tidal asymmetry of NB, which in turn altered sediment dynamics from deposition to erosion. Such negative feedback process tends to drive the estuary toward a new dynamic equilibrium morphology. The discovered nonlinear feedback mechanism is supported by the evidence of system efficiency adjustment, which was substantially gained during the first 30 years, then stayed in a low entropy production and minimum work state, indicating a more efficient dynamic equilibrium. If further estuary preservation policies are implemented, the dynamic equilibrium of NB is expected to continue for a long time in the future.

Interaction between a rising bubble and a stationary droplet immersed in a liquid pool using a ternary conservative phase-field lattice Boltzmann method.

When a stationary bubble and a stationary droplet immersed in a liquid pool are brought into contact, they form a bubble-droplet aggregate. Its equilibrium morphology and stability largely depend on the combination of different components' surface tensions, known as the "spreading factor." In this study, we look at the interaction between a rising bubble and a stationary droplet to better understand the dynamics of coalescence and rising and morphological changes for the bubble-droplet aggregate. A systematic study is conducted on the interaction processes with various bubble sizes and spreading factors in two dimensions. The current simulation framework consists of the ternary conservative phase-field lattice Boltzmann method (LBM) for interface tracking and the velocity-pressure LBM for hydrodynamics, which is validated by benchmark cases such as the liquid lens and parasitic currents around a static droplet with several popular surface tension formulations. We further test our LBM for the morphology changes of two droplets initially in contact with various spreading factors and depict the final morphologies in a phase diagram. The separated, partially engulfed, and completely engulfed morphologies can be replicated by systematically altering the sign of the spreading factors. The rising bubble and stationary droplet interaction are simulated based on the final morphologies obtained under stationary conditions by imposing an imaginary buoyancy force on the rising bubble. The results indicate that the bubble-droplet aggregate with double emulsion morphology can minimize the distortion of the bubble-droplet aggregate and achieve a greater terminal velocity than the aggregate with partially engulfed morphology.

The Sensitivity of Tidal Channel Systems to Initial Bed Conditions, Vegetation, and Tidal Asymmetry

AbstractIn tidal environments, channel networks act as essential drainage pathways. Although the complex interactions between environmental factors have been studied extensively, the effects of the initial bathymetry on tidal network ontogeny are poorly understood. In this contribution, we used a numerical model to mimic a schematic tidal basin subjected to tidal forcing. The effects of the initial bathymetry and vegetation growth are analyzed by changing the features of randomly generated bed perturbation and the intertidal platform slope. Different perturbation densities mildly affect the growth of tidal networks, which, at equilibrium, share similar values in terms of channel length, tidal prism, and cross‐sectional area. The complexity and structure of channel networks are more sensitive to variations in the perturbation distribution. Increasing the initial bathymetry slope can shorten channels and reduce the tidal prism and drainage efficiency. Vegetation growth is found to invariably promote channel lengthening and narrowing, increasing the complexity and drainage efficiency of the system. An asymmetrical tidal forcing generally leads to longer channels and smaller unchanneled lengths. Under ebb‐dominant conditions, channels get deeper, and the increased channel length ensures a higher drainage efficiency. The insights of our study provide a deeper understanding of the environmental factors controlling the equilibrium morphology of tidal channel systems and their overall resilience. Further implications concern the restoration and management of coastal areas through the informed use of topographic changes and planting arrangements. Finally, accounting for the uncertainties associated with initial conditions is relevant when modeling other earth systems and comparing them with real systems.

MTBE adsorption on surface modified adsorbent Kaolin-KOH – A study on Kinetic equilibrium and surface morphology

&lt;p&gt;The purpose of this research was to evaluate the effectiveness of low-cost adsorbents for the removal of MTBE by employing natural kaolin clay with surface modification by KOH. The feasibility of MTBE examination by High Pressure Liquid Chromatography (HPLC) in aqueous solution was investigated. To get rid of impurities, the kaolin clay goes through a beneficiated process. Then, the thermal procedure was carried out at 990°C to prepare the adsorbent. XRD, SEM, and FTIR were used to characterize the geochemical and surface characteristics of the kaolin adsorbent. Basic operation parameters were evaluated in the batch experiment, including beginning MTBE concentrations, pH, contact time, and adsorbent dosage. For three different sized columns that were 12cm, 8cm, and 4cm, respectively, the percentage removal efficiency for MTBE was recorded as 97.79%, 99.08%, and 98.13%. This study demonstrated that the adsorbent's contact time and retention period are crucial for the elimination of MTBE, as demonstrated by the Thomas model and Thomson model with R2 values of 97.81, 99.21, and 98.36.&lt;/p&gt;&#x0D;

Fabricating SU-8 Photoresist Microstructures with Controlled Convexity–Concavity and Curvature through Thermally Manipulating Capillary Action in Poly(dimethylsiloxane) Microholes

We present a simple, robust, and cheap microfabrication method, based on thermally manipulating capillary action in poly(dimethylsiloxane) (PDMS) microholes, for preparing SU-8 curved microstructures. The microstructure morphology including convexity-concavity and curvature can be controlled via tuning the formation temperature. The convex SU-8 microspherical crowns with a height of 40 μm were formed at 10 °C, whereas the concave SU-8 microspherical crowns with a height of 90 μm were formed at 100 °C. The morphology of the microstructures is dictated by the thermally controlled combination of the pressure difference across the interface, contact angle, and surface tension. The fabricated microstructures with a spherical surface can be used as a microlens array or a mold for producing a microlens array. The clear and uniform images were observed using the generated microlens arrays. The equilibrium morphology of the microstructures can be predicted by numerical simulation, which can lessen the number of experiments and thus the design cost. The proposed method has the potential to find applications in industrial fields.

Toward predicting surface energy of rutile TiO2with machine learning

A database of rutile TiO2containing 3000 morphologies was established. With this database, the surface energy was predicted from the experimentally observed crystal equilibrium morphology using the KNN model.