Phase-separated Microstructure Research Articles

Thermal and Optical Properties, and Aggregated Structure of Poly(substituted methylene)s Produced by Radical Polymerization of Fumarates Containing Fluorine-Substituted Alkyl Ester Groups

Fluoropolymers have excellent heat, oxidation, and chemical resistances as well as low dielectric constant and dielectric loss, and are often used as highly functional optical polymer materials. In this study, we conducted the radical polymerization and copolymerization of asymmetric dialkyl fumarates, in which a bulky alkyl group is introduced into one ester group and a trifluoroethyl or hexafluoroisopropyl group is into another ester group. We successfully synthesized poly(dialkyl fumarate)s (PDRF) with a poly(substituted methylene) structure containing fluorine atoms in the side chain, and evaluated their structure and physical properties. First, the effect of fluorine substitution on the radical polymerization and copolymerization reactivity was examined. We also evaluated the thermal and optical properties of the fluorine-containing PDRFs and clarified the role of the fluorine substitution for increasing the β transition temperatures and reducing the refractive indices. Furthermore, the higher-order structure of the PDRFs in the solid state was analyzed by wide-angle X-ray scattering (WAXS) measurement in order to discuss the aggregation of the rigid PDRF chains and a possibility for the formation of a phase-separated microstructure by the fluorine-containing side chains.

Thermo-Mechanical Properties and Phase-Separated Morphology of Warm-Mix Epoxy Asphalt Binders with Different Epoxy Resin Concentrations.

The performance and phase-separated microstructures of epoxy asphalt binders greatly depend on the concentration of epoxy resin or bitumen. In this paper, the effect of the epoxy resin (ER) concentration (10-90%) on the viscosity, thermo-mechanical properties, and phase-separated morphology of warm-mix epoxy asphalt binders (WEABs) was investigated using the Brookfield rotational viscometer, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and laser scanning confocal microscopy (LSCM). Due to the high reactivity of epoxy resin, the viscosity of WEABs increases with time. Furthermore, the initial viscosity of WEABs decreases with the ER concentration. Depending on the ER concentration, the viscosity-time behavior of WEABs is divided into three stages: slow (10-40%), fast (50-80%), and extremely slow (90%). In the slow stage, the viscosity slightly increases with the ER concentration, while the fast stage shows an opposite trend. DSC and DMA results reveal that WEABs with 10-80% ER exhibit two glass transition temperatures (Tgs) for cured epoxy resin and bitumen. Moreover, the Tgs of epoxy resin and bitumen increase with the ER concentration. However, WEAB with 90 % ER has only one Tg. LSCM observation shows that phase separation occurs in all WEABs. For WEABs containing 10-40% ER, spherical epoxy particles act as the discontinuous phase and disperse in the continuous bitumen phase. However, in WEABs with 50-90% ER, phase inversion takes place. Contrarily, bitumen particles disperse in the continuous epoxy phase. The damping properties of WEABs with the continuous epoxy phases increase with the ER concentration, while the crosslinking density shows an opposite trend. The occurrence of phase inversion results in a sharp increase in the tensile strength of WEABs. For WEABs with the continuous epoxy phases, the elongation at break increases with the ER concentration. The toughness first increases and then decreases with the ER concentration. A maximum toughness value shows at 70% ER.

Recent Developments in Polyurea Research for Enhanced Impact Penetration Resistance and Blast Mitigation.

Polyurea has gained significant attention in recent years as a functional polymer material, specifically regarding blast and impact protection. The molecular structure of polyurea is characterized by the rapid reaction between isocyanate and the terminal amine component, and forms an elastomeric copolymer that enhances substrate protection against blast impact and fragmentation penetration. At the nanoscale, a phase-separated microstructure emerges, with dispersed hard segment microregions within a continuous matrix of soft segments. This unique microstructure contributes to the remarkable mechanical properties of polyurea. To maximize these properties, it is crucial to analyze the molecular structure and explore methods like formulation optimization and the incorporation of reinforcing materials or fibers. Current research efforts in polyurea applications for protective purposes primarily concentrate on construction, infrastructure, military, transportation and industrial products and facilities. Future research directions should encompass deliberate formulation design and modification, systematic exploration of factors influencing protective performance across various applications and the integration of numerical simulations and experiments to reveal the protective mechanisms of polyurea. This paper provides an extensive literature review that specifically examines the utilization of polyurea for blast and impact protection. It encompasses discussions on material optimization, protective mechanisms and its applications in blast and impact protection.

Regulated Phase Separation in Al-Ti-Cu-Co Alloys through Spark Plasma Sintering Process.

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al-Ti-Cu-Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al-Ti-Cu-Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8-5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

Substrate interaction mediated control of phase separation in FIB milled Ag–Cu thin films

Nanofabrication is an integral part of the realization of advanced functional devices ranging from optical displays to memory devices. Focused-ion beam (FIB) milling is one of the most widely used nanofabrication methods. Conventionally, FIB milling has been carried out for patterning single-phase stable thin films. However, the influence of FIB milling on the phase separation of metastable alloy films during subsequent treatments has not been reported. Here, we show how FIB milling of Ag–Cu thin films influences the separation process and microstructure formation during post-milling annealing. The phase-separated microstructure of the film consists of fine, randomly distributed Ag-rich and Cu-rich domains, whereas adjacent to milled apertures (cylindrical holes), we observe two distinctly coarser rings. A combination of imaging and analysis techniques reveals Cu-rich islands dispersed in Ag-rich domains in the first ring next to the aperture, while the second ring constitutes mostly of Ag-rich grains. Copper silicide is observed to form in and around apertures through reaction with the Si-substrate. This substrate interaction, in addition to known variables like composition, temperature, and capillarity, appears to be a key element in drastically changing the local microstructure around apertures. Thus, the current study introduces new avenues to locally modulate the composition and microstructure through an appropriate choice of the film-substrate system. Such an ability can be exploited further to tune device functionalities for possible applications in plasmonics, catalysis, microelectronics, and magnetics.

High-performance supramolecular ionogel synthesized via click chemistry

The development of high-strength ionogels is of great significance for high-performance flexible sensing and soft robots. However, the introduction of ionic liquids will cause a decrease in the modulus and strength of ionogels and can cause unnecessary leakage problems. This poses a challenge for designing high-strength ionogels. In this work, based on the design concept of click chemistry, a modular polymer is constructed. The polymer self-assembled a phase-separated microstructure between soft phase and hard phase, exhibiting an ionic liquid-free, flexible, high-strength characteristic. By adjusting the molar ratio of the hard segment and the soft segment, it endows ionogels with various mechanical properties. When the content of hard segment increases from 5mol% to 20mol%, the Young’s modulus of the ionogel increases from 4.37 MPa, 25.17 MPa to 129.94 MPa, the strength increases from 4.34 MPa, 9.67 MPa to 18.39 MPa, and the elongation at break decreases from 1129%, 1063% to 797%, respectively. Meanwhile, the supramolecular ionogel shows good stress-sensing ability and stability, which has promoted the development of high-performance flexible sensing and soft robots.

Solution‐Doped Donor–Acceptor Copolymers Based on Diketopyrrolopyrrole and 3, 3′‐Bis (2‐(2‐(2‐Methoxyethoxy) Ethoxy) ethoxy)‐2, 2′‐Bithiophene Exhibiting Outstanding Thermoelectric Power Factors with p‐Dopants

AbstractThe design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large‐area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3‐dihydrothieno[3,4‐b][1,4]dioxine (EDOT), thieno[3,2‐b]thiophene (TT), and 3, 3′‐bis (2‐(2‐(2‐methoxyethoxy) ethoxy) ethoxy)‐2, 2′‐bithiophene (MEET) are investigated as side‐chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F4TCNQ), CF3SO3H, and the synthesized dopant Cp(CN)3‐(COOMe)3, differing in geometry and electron affinity. The DPP‐EDOT‐based polymer containing MEET as side‐chains exhibits the highest conductivity (σ) ≈700 S cm−1 in this series with the acidic dopant (CF3SO3H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen‐based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm−1 and power factor up to 300 µW m−1 K−2. The mechanism of conductivity is predominantly electronic, as validated by time‐dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. These materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM‐EDS) and x‐ray diffraction, provides insight into the solid‐state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant.

Exploiting the use of deep learning techniques to identify phase separation in self-assembled microstructures with localized graphene domains in epoxy blends

In this study for the first time, convolutional neural networks (CNN) are applied to identify phase-separated microstructures in a novel nano-modified polymer composite. The input data consist of a mixed labelled dataset of homogeneous microstructure and phase-separated microstructure images collected using an optical microscope; the problem is modelled as a binary classification. The initial dataset consisted of microstructural images collected in house from past experiments, expanded in number using the data augmentation method, and upon testing, the model showed an accuracy of 65.4% and a 0.5 F1 score. Additional experiments were performed to generate more ground truth images and the CNN model built on this second data set showed improved accuracy of 80.1% and a 0.9 F1 score; The CNN classifier mimicked the receiver operating characteristic (ROC) curve of perfect classifier. Using the trained model, the phase separated microstructure is distinguished from homogeneous microstructure in a matter of minutes, saving hours of manual screening and cost intensive characterisation.

Nanoscale Structure–Property Relations in Self-Regulated Polymer-Grafted Nanoparticle Composite Structures

Using a model system of poly(methyl methacrylate)-grafted silica nanoparticles (PMMA-NP) and poly(styrene-ran-acrylonitrile) (SAN), we generate unique polymer nanocomposite (PNC) morphologies by balancing the degree of surface enrichment, phase separation, and wetting within the films. Depending on the annealing temperature and time, thin films undergo different stages of phase evolution, resulting in homogeneously dispersed systems at low temperatures, enriched PMMA-NP layers at the PNC interfaces at intermediate temperatures, and three-dimensional bicontinuous structures of PMMA-NP pillars sandwiched between two PMMA-NP wetting layers at high temperatures. Using a combination of atomic force microscopy (AFM), AFM nanoindentation, contact angle goniometry, and optical microscopy, we show that these self-regulated structures lead to nanocomposites with increased elastic modulus, hardness, and thermal stability compared to analogous PMMA/SAN blends. These studies demonstrate the ability to reliably control the size and spatial correlations of both the surface-enriched and phase-separated nanocomposite microstructures, which have attractive technological applications where properties such as wettability, toughness, and wear resistance are important. In addition, these morphologies lend themselves to substantially broader applications, including: (1) structural color applications, (2) tuning optical adsorption, and (3) barrier coatings.

Phase-separated microstructures and viscosity-time behavior of graphene nanoplatelet modified warm-mix epoxy asphalt binders

Phase-separated microstructures and viscosity-time behavior of graphene nanoplatelet modified warm-mix epoxy asphalt binders

Self-assembled microstructures with localized graphene domains in an epoxy blend and their related properties

Locating nanoparticles in selected areas via the mixing of two immiscible polymers is widely studied for achieving nanocomposites with next-level performance, however, the formation of a phase-separated domain constructed with nanofillers from entirely miscible molecules is rarely achieved in the literature. Here we demonstrate a method to fabricate a self-constructed bi-continuous phase structure with localized amine-functionalized graphene nanoplatelets (A-GNPs) in a liquid processable multi-component epoxy blend. Atomic force microscopy infrared spectroscopy (AFM-IR) was employed to identify the compositions of the phase-separated microdomains formed during self-assembly by A-GNP in the multi-component epoxy blend, with incorporating 1-(2-aminoethyl) piperazine (AEPIP) found to be the driving force for the formation of the graphene microdomains. Nanoindentation measurements show that a Young’s modulus of 6.3 GPa for the graphene domain was achieved, which is nearly twice that of the epoxy resin (3.2 GPa). Transient thermoreflectance results indicate that the thermal conductivity of nanocomposite with phase-separated graphene domain reached 0.48 W/mK, exhibiting a significant enhancement (70%) when compared to epoxy resin, while maintaining excellent dielectric properties. Overall, this study provides a simple and effective route to fabricate phase-separated microstructure with nanoparticles from a liquid processable nanocomposite blend, which shows the great potential of this promising new approach to fabricate nanocomposite films with excellent performance for microelectronics applications.

Modeling Oxidation of AlCoCrFeNi High-Entropy Alloy Using Stochastic Cellular Automata.

Together with the thermodynamics and kinetics, the complex microstructure of high-entropy alloys (HEAs) exerts a significant influence on the associated oxidation mechanisms in these concentrated solid solutions. To describe the surface oxidation in AlCoCrFeNi HEA, we employed a stochastic cellular automata model that replicates the mesoscale structures that form. The model benefits from diffusion coefficients of the principal elements through the native oxides predicted by using molecular simulations. Through our examination of the oxidation behavior as a function of the alloy composition, we corroborated that the oxide scale growth is a function of the complex chemistry and resultant microstructures. The effect of heat treatment on these alloys is also simulated by using reconstructed experimental micrographs. When they are in a single-crystal structure, no segregation is noted for α-Al2O3 and Cr2O3, which are the primary scale-forming oxides. However, a coexistent separation between Al2O3 and Cr2O3 oxide scales with the Al-Ni- and Cr-Fe-rich regions is predicted when phase-separated microstructures are incorporated into the model.

Steric group-based polymer dispersed liquid crystal composite films with high contrast ratio, low driving voltage and small hysteresis

The unique phase-separated microstructure has endowed polymer dispersed liquid crystals (PDLCs) with outstanding electro-optical performances. However, their applications are hampered by the high driving voltage and low contrast ratio. Attempts to optimize the materials have been made in order to reduce the driving voltage without sacrificing the contrast ratio and other features. Herein, acrylate monomers with different steric end groups were introduced to fabricate PDLCs and their effects on the electro-optical properties and microstructure were investigated. Bipolar droplet configuration was observed in all samples implying tangential anchoring conditions. It was found that the steric end group could affect the morphology of polymer matrix and the electro-optical properties. By carefully adjusting the steric group and doping concentration, the contrast ratio could be enhanced and the driving voltage could be reduced. Besides, hysteresis could also be decreased. The research offers more choices for the construction of PDLCs from material perspective, promoting their potential applications.

Microstructural evolution and kinetics of phase separation in binary polymer blends under electric fields

Temporal evolution of microstructure and kinetics of phase separation under electric fields (E-fields) were numerically investigated for binary polymer blends at both off-critical and critical compositions, where the morphology, structure factor, characteristic size, and anisotropy parameter were adopted. The results show that the E-field can significantly influence morphological development and kinetic process of phase separation, and the influence rule at the off-critical composition is distinctly different from the rule at the critical composition. With the enhancement of E-field strength, the growth exponent in the x direction (perpendicular to the E-field) decreases and the growth exponent in the y direction (parallel to the E-field) increases. Moreover, as initial composition raises, anisotropy parameter firstly increases and then decreases, and reaches to a maximum at the critical composition. The simulation results were also compared with existing experimental results, and exhibit several different aspects. This study reveals the influence rule of E-fields on phase separation process of binary polymer blends. On the other hand, it can provide a scheme to predict and design anisotropic microstructures by E-fields, and further guide to produce polymeric composite materials with superior mechanical and physical properties.

A phase separation strategy for enhanced toughness self-assembly graphene-network composites

The toughness of three unsaturated polyester resins modified with different quantities of polycaprolactone (PCL) and few-layer graphene microsheets was evaluated by single-edge-notch bending (SENB). The addition of PCL to the resin systems created phase-separated microstructures with different critical compositions at phase inversion (7, 15 and 16.5 wt%PCL). The addition of PCL in quantities lower than the critical compositions showed increases up to 90% in toughness. A similar effect was observed by the addition of graphene to the neat resin increasing the toughness by up to 96% with 6 wt% of graphene. The incorporation of graphene to a phase separating system was found to form a self-assembly graphene-network at the unsaturated polyester-rich phase of the microstructure. When such network showed an appreciable effect of the toughness compared to the system without the PCL (114% increase at 6 wt% graphene and 2 wt% PCL), it also positively impacted the electrical conductivity. A shift of the percolation threshold towards a lower quantity of graphene was achieved by the creation of such graphene-rich network, reducing by 2 wt% the quantity of graphene needed for conduction.

Cyclopeptide-β-cyclodextrin/γ-glycerol methoxytrimethoxysilane film for potential vascular tissue engineering scaffolds

The mortality rate of cardiovascular diseases is the highest among all mortality rates worldwide. Allotransplantation and autotransplantation are limited by rejection reaction and availability. Tissue engineering provides new avenues for the treatment of cardiovascular diseases. However, the current small-diameter (<6 mm) vascular tissue-engineered scaffolds have many challenges, including thrombosis, stenosis, and infection. Small-diameter vascular scaffolds have structural and compositional requirements such as biocompatibility, porosity, and appropriate phase separation. We used liquid-crystal cyclopeptide（CYC）to modify β-cyclodextrin and mixed it with γ-glycerol methoxytrimethoxysilane (GPTMS) to prepare CYC-β-cyclodextrin (βCD)/GPTMS film by sol-gel. The chemical structure of CYC-βCD was confirmed by Fourier transform infrared spectroscopy and 1H-nuclear magnetic resonance. The chemical characterization of CYC-βCD/GPTMS film was performed by differential scanning calorimetry, X-ray diffraction, and small-angle X-ray scattering. The surface morphology and phase separation microstructure of the film were determined by scanning electron microscopy and atomic force microscopy, and the image of polarizing microscopy showed the liquid-crystal structure of the film. Cell culture experiments showed that CYC-βCD/GPTMS film had good cytocompatibility and induced growth and proliferation of cells. These results indicated the potential applications of CYC-βCD/GPTMS film in tissue engineering scaffolds.

Phase structure characterization and compatibilization mechanism of epoxy asphalt modified by thermoplastic elastomer (SBS)

Epoxy resin is widely used in thermosetting polymer modified asphalt. However, the delamination and segregation will occur owing to the poor compatibility between epoxy resin and asphalt. The rigid molecular structure of epoxy resin also leads to insufficient toughness of epoxy asphalt (EA) at low temperature. In order to solve these problems of EA, styrene butadiene styrene block copolymer (SBS) is used to prepare modified epoxy asphalt (SBS-EA). The phase separation microstructure, rheological properties, mechanical properties and compatibilization mechanism of SBS-EAs are investigated. The initial viscosity of EA is increased by introducing SBS, but it still satisfies the requirement of pavement. The results of fluorescence microscopy and micro-computed tomography reveal that the compatibility of EA can be significantly improved by 3 wt% SBS. The average particle size of dispersed phase asphalt can be reduced with the content of SBS. Micro-infrared and gel permeation chromatography quantitative analysis turn out that SBS will migrate from the base asphalt to epoxy resin crosslinking network. The tensile strength, elongation at break and toughness of 3%SBS-EA are 12%, 67% and 78% higher than those of EA due to the good phase separation structure. Furthermore, the dispersed asphalt phase size is closely correlated with the mechanical properties of SBS-EA.

Phase separation of a milk protein and guar gum: The effect of guar gum molecular weight and oil addition on the phase diagram

Skimmed milk powder (SMP), and low and high molecular weight guar gum (GG), were used to establish phase diagrams at 5 °C and pH 6.5 to better understand the phase behaviours of the milk protein/guar gum systems. As expected, the compatibility of SMP-GG system was found to increase with decrease in molecular weight of the GG. Confocal laser scanning microscopy (CLSM) clearly shows that the microstructure was dependant upon starting composition which in turn determines the relative phase volumes of the two phases. This phase separated microstructure of SMP-GG can be considered as a water-in water (W/W) emulsion. Through the incorporation of oil into these systems with designed microstructures based on the phase diagram, it is possible to form a model systems of SMP-GG-OIL, showing a lipid phase within a protein phase within a polysaccharide phase, which can be described as ‘Matryoshka Composites’ and therefore being viewed as ‘O/W/W’ emulsion when the starting aqueous phase is either polysaccharide continuous or bi-continuous. The addition of low volume fraction of oil has indicated an influence on the thermodynamic equilibrium of SMP-GG system, through chemical analysis and rheological measurement. This probably leads to a tie-line change in the established phase diagram of SMP-GG system.

Novel polyurethane network/organoclay nanocomposites: Microstructure and physicochemical properties

A series of novel polyurethane network/organoclay nanocomposites (PUN-NCs) with different soft segment contents (30–60 wt%) was prepared by in situ polymerization in solution and characterized. PU network (PUN) was made from poly(dimethylsiloxane)-based macrodiol as the soft segment and 4,4′-methylenediphenyldiisocyanate and hyperbranched polyester of the third pseudo generation as the hard segment. Nanocomposites were obtained by dispersion of organically modified montmorillonite (Cloisite 30B) nanofiller (0.5 wt%). The influence of the soft segment content on the functional properties of PUN-NCs was studied by Fourier transform infrared (FTIR), small-angle and near wide-angle X-ray scattering (SWAXS), thermogravimetric analysis (TGA), dynamic mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), nanoindentation, atomic force microscopy (AFM), scanning electron microscopy (SEM), and swelling behavior, water absorption and contact angle measurements. The biodegradation process was evaluated using mixed cultures of microorganisms that originated from soil. Mechanically strong PUN-NC materials in the form of films were obtained, pointing to good dispersion and the existence of exfoliated morphology of Cloisite 30B within the PUN matrix, and the nanocomposites with the abovementioned characteristics were obtained as a function of the soft segment content. The decrease of the soft segment content induced a higher degree of phase separated microstructure, increase of Young's modulus, hardness, plasticity, storage modulus, glass transition temperature, surface free energy and swelling ability in tetrahydrofuran, but at the same time, it is responsible for the decrease of crosslinking density and hydrophobicity of PUN-NCs. By choosing adequate soft segment content, the prepared materials can potentially be designed for coating applications, such as top coating materials in environmental conditions.

Putting the Squeeze on Phase Separation.

Phase separation is a ubiquitous process and finds applications in a variety of biological, organic, and inorganic systems. Nature has evolved the ability to control phase separation to both regulate cellular processes and make composite materials with outstanding mechanical and optical properties. Striking examples of the latter are the vibrant blue and green feathers of many bird species, which are thought to result from an exquisite control of the size and spatial correlations of their phase-separated microstructures. By contrast, it is much harder for material scientists to arrest and control phase separation in synthetic materials with such a high level of precision at these length scales. In this Perspective, we briefly review some established methods to control liquid–liquid phase separation processes and then highlight the emergence of a promising arrest method based on phase separation in an elastic polymer network. Finally, we discuss upcoming challenges and opportunities for fabricating microstructured materials via mechanically controlled phase separation.