Two-phase Morphology Research Articles

Studies on mechanical, thermal, rheological and impact properties of polyamide 6 and thermoplastic copoly(ether-ester) elastomer blends

A series of blends of polyamide 6 (PA-6) (nylon-6) and a copoly(ether-ester) (HYTREL) were prepared by the melt-mixing method using a twin-screw extruder. The HYTREL content was varied from 0% to 25% by weight of the blends. Thermal and rheological studies on the blends using differential scanning calorimetry, dynamic mechanical analysis (DMA) and capillary rheometer showed that the blends are semi-compatible in nature. A two-phase globular morphology of the blends was established by scanning electron microscope (SEM) analysis. The matrix ligament thickness (interparticle distance) in each blend composition was measured from SEM images and compared with those calculated using Wu’s equation. The impact strength of the blends as measured by the Izod impact test was found to be substantially improved as a result of the incorporation of HYTREL. The toughness determined by loss area calculation from the DMA spectrum showed similar trends. The toughness was found to be optimal in a blend having 15 wt.% HYTREL with an average dispersed particle size of around 450 nm. The yield stress of the blend decreased in comparison to PA-6 on addition of HYTREL, while the thermal stability of PA-6 remained unaffected.

Multiscale study on fatigue healing performance and molecular healing behavior of self-healing SBS modified bitumen

Self-healing polymer modified bitumen based on dynamic chemical bonds is a potential approach to improve the durability of bitumen pavement and save fossil energy. Herein, a novel self-healing SBS modified bitumen on the basis of dynamic disulfide bonds and hydrogen bonds was prepared. Firstly, an aliphatic disulfide (A-ALD) with disulfide bonds and hydrogen bonds was synthesized. Then A-ALD/SBS modified bitumen (A-ALD/SMB) was prepared by blending A-ALD and SBS modified bitumen. The chemical structure and microstructure of A-ALD/SMB were evaluated. In addition, the self-healing performance of A-ALD/SMB at the macroscopic scale and the self-healing behavior at the molecular scale were investigated by a combination of fatigue healing test and molecular dynamics (MD) simulation. The chemical structure analysis showed the formation of disulfide bonds and hydrogen bonds in A-ALD, and A-ALD was successfully attached to the CC bonds in SBS. Fluorescent images revealed that a better network structure appeared in A-ALD/SMB and formed a two-phase continuous morphology. The optimal dosage of A-ALD in SBS modified bitumen was 0.6 %. The fatigue healing test results indicated that A-ALD markedly enhanced the self-healing ability of SBS modified bitumen, and prolonging resting time and raising healing temperature can increase the self-healing performance of A-ALD/SMB. When the damage degree, healing temperature, and resting time were 30 %, 30 °C, and 60 min, respectively, the healing rate of A-ALD/SMB was 98.5 %, which was 30.2 % higher than SMB. The MD simulation results showed that the A-ALD enhanced the molecular diffusion capacity of SBS modified bitumen, and crack healing time of A-ALD/SMB was earlier than that of SMB under the same conditions. When the healing temperature was 40 °C, the time for the A-ALD/SMB and SMB molecular chain segments to start contacting and healing was 27 ps and 49 ps, respectively, which was improved by 44.9 % for A-ALD/SMB compared to SMB. Furthermore, the self-healing behavior of A-ALD/SMB at the molecular scale was consistent with the self-healing performance at the macroscopic scale under different healing temperatures and damage degrees. This study provided a theoretical basis for exploring the self-healing mechanism of SBS modified bitumen.

Effect of Fe content on wetting behaviors and interfacial characteristics of TiZr-based bulk metallic glass/W substrate

The wetting characteristics of Ti32.8Zr30.2FexCu14.3-xBe22.7 (at.%, x = 0, 2.5, 5.3) bulk metallic glasses (BMGs) with W substrate are conducted using the sessile drop method at different temperatures. The effect of Fe content on wettability is systematically studied. At a given temperature, contact angle initially rises and subsequently declines as the Fe content increases from 0 at.% to 5.3 at.%. Optimal wettability is observed in BMGs devoid of the Fe element. This is attributed to the influence of Fe addition on the elemental diffusion behaviors and two-phase interfacial morphologies during wetting. The addition of 2.5 at.% Fe leads to a significant accumulation of Ti element at the wetting interface and prevents the wetting process. As the Fe content increases to 5.3 at.%, the conspicuous abundance of Fe in the glass phase together with the diffused Cu in W substrate determines the wettability of the system. These findings not only reveal the influence of Fe content on the wetting properties of the TiZr-based BMGs/W system but also provide a theoretical basis for the preparation of ex-situ BMG composites.

Local Rotational Jamming and Multi-Stage Hyperuniformities in an Active Spinner System

An active system consisting of many self-spinning dimers is simulated, and a distinct local rotational jamming transition is observed as the density increases. In the low density regime, the system stays in an absorbing state, in which each dimer rotates independently subject to the applied torque; while in the high density regime, a fraction of the dimers become rotationally jammed into local clusters, and the system exhibits microphase-separation like two-phase morphologies. For high enough densities, the system becomes completely jammed in both rotational and translational degrees of freedom. Such a simple system is found to exhibit rich and multiscale disordered hyperuniformities among the above phases: the absorbing state shows a critical hyperuniformity of the strongest class and subcritically preserves the vanishing density fluctuation scaling up to some length scale; the locally jammed state shows a two-phase hyperuniformity conversely beyond some length scale with respect to the phase cluster sizes; the totally jammed state appears to be a monomer crystal, but intrinsically loses large-scale hyperuniformity. These results are inspiring for designing novel phase-separation and disordered hyperuniform systems through dynamical organization.

Two-phase flow and morphology of the gas–liquid interface for bubbles or droplets in different microchannels

Two-phase interface fluid, bubble or droplet, has shown broad application potential in oil and gas field development, contaminated soil remediation, and medical treatment. These applications are particularly concerned about the flow characteristics of the two-phase fluid in different channels. Herein, we summarize and analyze the research progress in the flow of bubbles (or droplets) in different channels, mainly including simple, Y-junction/T-junction, and obstructed microchannels. At present, there is no systematic theory about the structure and mechanical evolution of the two-phase interface fluid, and therefore, the comprehensive study is still insufficient. Especially, current studies on the breakup of the two-phase interface in bifurcated channels mainly focus on a few of specific perspectives and a general conclusion is not achieved. In addition, to systematically verify the mechanism of bubble (or droplet) breakup, extensive studies on the three-dimensional physical model of bubbles (or droplets) are needed. Furthermore, we have also sorted out the involved influencing factors, as well as the prediction models for bubble (or droplet) breakup and retention in different channels, and in the end, we provide suggestions for the potential research and development of the two-phase interface fluid.

Thermally-triggered multi-shape-memory behavior of binary blends of cross-linked EPDM with various thermoplastic polyethylenes and their potential applications as temperature indicators

Shape-memory polymers (SMPs) are smart materials that can alter their configuration in response to external stimuli. They have shown promise in a number of application areas, including soft robotics or biomedical devices. Frequently, however, the materials needed are expensive, or labor-intensive synthetic processes are involved. In this contribution, we report a versatile and cost-effective manufacturing method for SMPs based on binary elastomer-thermoplastic-blends. These were produced from ethylene-propylene-diene monomer rubber (EPDM) combined with ultra-low-density polyethylene (ULDPE), propylene-ethylene copolymer (PP-c-PE), or high-density polyethylene (HDPE) as thermoplastic components. Atomic force microscopy revealed an immiscible two-phase morphology. Results of dynamic-mechanical thermal analysis showed that all polymer blends with a high thermoplastic load had efficient thermo-responsive dual-shape-memory, also demonstrated on macroscopic specimens. Furthermore, multi-shape-memory of elastomer/thermoplastic (40/60)-blends was investigated. Especially ULDPE-containing blends exhibited particularly promising multi-shape-memory features and stepless, controllable temperature response. Mechanistically, this is based upon the synergistic interaction of the cross-linked elastomer and the thermoplastic switching phase, consisting of different crystalline segments melting over a wide range from 60 to 125 °C. The continuous shape recovery over a broad temperature range could be used to create reusable test strips, e.g., for indicating exposure temperature in transportation chains or overheating protection.

Thermogravimetric, Morphological and Infrared Analysis of Blends Involving Thermoplastic Starch and Poly(ethylene-co-methacrylic acid) and Its Ionomer Form.

This study focuses on the thermal properties and structural features of blends consisting of thermoplastic starch (TPS) and poly(ethylene-co-methacrylic acid) copolymer (EMAA) or its ionomer form (EMAA-54Na). The aim is to investigate how carboxylate functional groups of the ionomer form intervene in blends compatibility at the interface of the two materials and how this impacts their properties. Two series of blends (TPS/EMAA and TPS/EMAA-54Na) were produced with an internal mixer, with TPS compositions between 5 and 90 wt%. Thermogravimetry shows two main weight losses, indicating that TPS and the two copolymers are primarily immiscible. However, a small weight loss existing at intermediate degradation temperature between those of the two pristine components reveals specific interactions at the interface. At a mesoscale level, scanning electron microscopy confirmed thermogravimetry results and showed a two-phase domain morphology, with a phase inversion at around 80 wt% TPS, but also revealed a different surface appearance evolution between the two series. Fourier-transformed infrared spectroscopy analysis also revealed discrepancies in fingerprint between the two series of blends, analysed in terms of additional interactions in TPS/EMAA-54Na coming from the supplementary sodium neutralized carboxylate functions of the ionomer.

Bio-based semi-interpenetrating networks with nanoscale morphology and interconnected microporous structure

Creating new bio-based sustainable polymeric materials with similar or better performance than the petroleum-based counterparts has recently received considerable attention. It will have a significant positive impact on the environment and the sustainable polymer industry. This review article shows a relatively new method based on simultaneous in-situ polymerization and compatibilization of bio-based plant oil and biodegradable thermoplastic polymer to prepare semi-interpenetrating polymer networks (SINs) with unusual nano-scale morphology and interconnected porous structure will be summarized. The SINs were synthesized via cationic polymerization of tung oil in a homogenous solution of poly(ε-caprolactone) as a biodegradable, semi-crystalline, and biocompatible thermoplastic polymer. The degrees of miscibility, nanostructure morphology, and crystallinity was found to be composition-dependent. This relatively new blending method created a two-phase nanoscale morphology as small as 100 nm for blends with PCL contents of 20 and 30 wt.%. For higher PCL contents (e.g., 50 wt.% PCL blend), a co-continuous, interconnected microscale two-phase morphology was detected. The microporous structure of the SINs was also changed as a function of composition. For example, the interconnectivity and pore size was considerably decreased with increasing PCL content. Furthermore, a considerable decrease in the crystallization kinetics of PCL was observed as the PCL content is higher than or equal to 30 wt.%. While on the other hand, the crystallization kinetics accelerated significantly for 50 wt.%. This novel, low-cost strategy for preparing bio-based SINs with nanoscale morphology and interconnected three-dimensional cluster structures and desired properties should be widely used for creating new polymer systems.

Crystallization Kinetics in an Immiscible Polyolefin Blend.

Motivated by the problem of brittle mechanical behavior in recycled blends of high density polyethylene (HDPE) and isotactic polypropylene (iPP), we employ optical microscopy, rheo-Raman, and differential scanning calorimetry (DSC) to measure the composition dependence of their crystallization kinetics. Raman spectra are analyzed via multivariate curve resolution with alternating least-squares (MCR-ALS) to provide component crystallization values. We find that iPP crystallization behavior varies strongly with blend composition. Optical microscopy shows that three crystallization kinetic regimes correspond to three underlying two-phase morphologies: HDPE droplets in iPP, the inverse, and cocontinuous structures. In the HDPE droplet regime, iPP crystallization temperature decreases sharply with increasing HDPE composition. For cocontinuous morphologies, iPP crystallization is delayed, but the onset temperature changes little with the exact blend composition. In the iPP droplet regime, the two components crystallize nearly concurrently. Rheological measurements are consistent with these observations. DSC indicates that the enthalpy of crystallization of the blends is less than the weighted values of the individual components, providing a possible clue for the decreased iPP crystallization temperatures.

Self-Organization of Graft Copolymers and Retortable iPP-Based Nanoporous Films Thereof

Polyolefins might become inexpensive alternatives to the existing membranes based on polyethersulfone. Here, we disclose the production of retortable, well-defined polypropylene (PP)-based nanoporous films derived from amphiphilic graft copolymer precursors. The graft copolymers, containing a polypropylene backbone and polyester grafts, were obtained by grafting lactones, specifically δ-valerolactone and ε-caprolactone, from well-defined randomly functionalized poly(propylene-co-10-undecen-1-ol) as a macroinitiator. Depending on the composition, the graft copolymers self-assemble into droplet, cylindrical, lamellar, or interconnected two-phase morphologies. Functional mesoporous iPP-based films were fabricated by the selective degradation of the polyester blocks of the copolymers. Their structure and morphology were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and solid-state NMR, while the mesoporosity was assessed by nitrogen sorption experiments. The pore size of the films is strongly influenced not only by the volume fraction of the copolymer blocks but unexpectedly also by the topology (i.e., number of grafts) of the graft copolymer, as was confirmed by computational modeling studies using the dynamic density functional theory (DDFT) engine within the Culgi software. This work provides a conclusive answer on how the morphology of iPP-based graft copolymers is tuned by the copolymer composition and the amount and length of the grafted polyester blocks. Filtration tests and flux determination demonstrated that such structurally well-defined mesoporous products could be considered for the development of ultrafiltration membranes while the chemical resistance and sterilization tests revealed their robust performance and suitability for water purification applications.

Synergistic toughening on hybrid epoxy nanocomposites by introducing engineering thermoplastic and carbon-based nanomaterials

In this study, epoxy-anhydride thermoset was initially modified with polyethersulfone (PESU) at 0‐15 wt% loading. The various mass ratios at 0.50 wt% total content of graphene nanoplatelets (GNPs)/carbon nanotubes (CNTs) were further introduced to comprehensively study the simultaneous incorporation of different tougheners on morphological, thermal, and mechanical properties of engineering thermoplastic modified epoxy. The binary blend of PESU/epoxy reveals two-phase morphologies due to reaction induced phase separation, showing particulate morphology at 5 wt% PESU and co-continuous morphology at 10‐15 wt% PESU. It was found that the presence of PESU at 5 wt% not only improved thermal stability but also provide the optimum mechanical properties, showing 35% and 40% increasing in tensile strength and fracture toughness, respectively. From fracture surface analysis, crack deflection from the PESU dispersed particles was observed as a main toughening mechanism for this binary blend. With introducing GNPs and/or CNTs, hybrid nanocomposite based on 5 wt% PESU modified epoxy matrix showed similar morphology and thermo-mechanical properties to the binary blends. Additionally, the remarkable Young's modulus were observed in all hybrid PESU/carbon-based nanofillers toughened epoxy composites. PESU and GNPs dispersed phase contribute greatly in enhancing fracture toughness (KIc) of hybrid PESU/nanofillers system. KIc of PESU/epoxy blends with 0.5 wt% GNPs was measured at 0.86 MPa m1/2, counting as ∼60% and ∼18% improvement from pristine epoxy and 0.5 wt% GNPs modified neat epoxy, respectively. Apart from crack deflection of PESU, GNPs cluster effectively deviates and bifurcates the crack path, indicating the synergistic effect on PESU/GNPs epoxy nanocomposite. Interestingly, these two tougheners also dominates the toughening mechanism in PESU/GNPs/CNTs epoxy nanocomposites. Meanwhile, the influence of CNTs on fracture toughness was not clearly demonstrated on hybrid nanocomposite system.

CFD-modelling of boiling in a heated pipe including flow pattern transition

Flow boiling occurs when a subcooled liquid enters a heating pipe and its temperature near the heating wall exceeds the boiling onset temperature. Bubbles are generated on the heating wall and the more downstream the larger the average bubble size due to progressing evaporation and coalescence. Further downstream, the two-phase flow morphologies may change from bubbly to slug, plug, and annular flow. Since these flow patterns have a great impact on the heat and mass transfer rates, an accurate prediction of them becomes critical. In this work, the recently developed GENeralized-TwO Phase concept (GENTOP) was used for flow patterns transition modelling and their effects on the wall heat transfer during the upward subcooled flow boiling inside a vertical heating pipe. Furthermore, a previously developed mechanistic bubble dynamics model was implemented in the GENTOP framework as a sub-model. This model is based on the force balance on a single growing bubble considering evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble as well as the dynamic inclination and contact angles. It does not require a recalibration of parameters to predict the bubble dynamics. For implementing this model in the Euler-Euler (E-E) framework an extension of the current nucleation site density and heat partitioning model was required. Eventually, for a generic test case, flow boiling regimes of water in a vertical heating pipe were simulated using ANSYS CFX 18.2.

Transparent PC/PMMA Blends with Enhanced Mechanical Properties via Reactive Compounding of Functionalized Polymers.

Reactive compounding of terminally phenolic OH-functionalized polycarbonate (PC) with epoxy-functionalized polymethylmethacrylate (PMMA) prepared by copolymerization with glycidyl methacrylate was investigated. It was spectroscopically demonstrated that a PC/PMMA copolymer was formed during the melt reaction of the functional groups. Zirconium acetylacetonate could catalytically accelerate this reaction. Correlations of the phenomenological (optical and mechanical) properties with the molecular level and mesoscopic (morphological) structure were discussed. By the investigated reactive compounding process, transparent PC/PMMA blends with two-phase morphologies were obtained in a continuous twin-screw extruder, which, for the first time, combined the high transmission of visible light with excellent mechanical performance (e.g., synergistically improved tensile and flexural strength and high scratch resistance). The transparency strongly depended on (a) the degree of functionalization in both PC and PMMA, (b) the presence of the catalyst, and (c) the residence time of the compounding process. The in-situ-formed PC/PMMA copolymer influenced the observed macroscopic properties by (a) a decrease in the interphase tension, leading to improved and stabilized phase dispersion, (b) the formation of a continuous gradient of the polymer composition and thus of the optical refractive indices in a diffuse mesoscopic interphase layer separating the PC and PMMA phases, and (c) an increase in the phase adhesion between PC and PMMA due to mechanical polymer chain entanglement in this interphase.

Melting and Re-Freezing Leads to Irreversible Changes in the Morphology and Molecular-Level Dynamics of Pfizer-BioNTech COVID-19 Vaccine.

Background and Objectives: As an mRNA-based vaccine, the Pfizer-BioNTech COVID-19 vaccine has stringent cold storage requirements to preserve functionality of the mRNA active ingredient. To this end, lipid components of the vaccine formulation play an important role in stabilizing and protecting the mRNA molecule for long-term storage. The purpose of the current study was to measure molecular-level dynamics as a function of temperature in the Pfizer-BioNTech COVID-19 vaccine to gain microscopic insight into its thermal stability. Materials and Methods: We used quasielastic and inelastic neutron scattering to probe (1) the vaccine extracted from the manufacturer-supplied vials and (2) unperturbed vaccine in the original manufacturer-supplied vials. The latter measurement was possible due to the high penetrative power of neutrons. Results: Upon warming from the low-temperature frozen state, the vaccine in its original form exhibits two-step melting, indicative of a two-phase morphology. Once the melting is completed (above 0 °C), vaccine re-freezing cannot restore its original two-phase state. This observation is corroborated by the changes in the molecular vibrational spectra. The molecular-level mobility measured in the resulting single-phase state of the re-frozen vaccine greatly exceeds the mobility measured in the original vaccine. Conclusions: Even a brief melting (above 0 °C) leads to an irreversible alteration of the two-phase morphology of the original vaccine formulation. Re-freezing of the vaccine results in a one-phase morphology with much increased molecular-level mobility compared to that in the original vaccine, suggesting irreversible deterioration of the vaccine’s in-storage stability. Neutron scattering can be used to distinguish between the vibrational spectra characteristic of the original and deteriorated vaccines contained in the unperturbed original manufacturer-supplied vials.

Relative permeability measurement of coal microchannels using advanced microchip technology

The gas–water flow in coal cleats is an important factor affecting coalbed methane production. However, difficulties are often encountered in the prediction of gas production. Limited understanding of two-phase flow behaviour in microchannels reduces prediction accuracy, often leading to overestimation. In this study, based on micro-computed tomography, advanced microchip technology is used to predict the optimal coal cleat in the polydimethylsiloxane chip. Gas and liquid injection experiments are carried out on the microchannels through the syringe pumps, as the two-phase flow morphology in the system can obtain flow information that cannot be provided by conventional laboratory measurements. The flow capacities of single-phase gas, water, and wetting liquid in the microchannels are compared, alongside determining the flow laws under different wettability and flow rates. The results show that in the single-phase fluid injection experiment, gas is more sensitive to the microchannel size effect than the liquid phase, and hydrophilic liquids flow readily. The gas–water relative permeability value in this study is significantly smaller than that obtained from conventional experiments, based on the steady-state method. This is a result of the gas–water forming a discontinuous plug flow in the microchannel, which produces higher resistance and reduces flow capacity. The occurrence of discontinuous flow regimes challenges the laminar flow assumption adopted in the steady-state method and suggests that conventional laboratory measurements of relative permeability measurements may misrepresent the physics of fluid flows in microchannels. The results also reveal that a hydrophilic environment and a suitable flow rate can increase the two-phase relative permeability. The results of this study enhance our understanding of and approach to core flooding measurement, with the differences in the relative permeability curves indicating that data uncertainty associated with the steady-state method is worthy of further research.

Pore-resolved volume-of-fluid simulations of two-phase flow in porous media: Pore-scale flow mechanisms and regime map

Two-phase flow through porous media is important to the development of secondary and tertiary oil recovery. In the present work, we have simulated oil recovery through a pore-resolved three-dimensional medium using volume-of-fluid method. The effects of wettability and interfacial tension (IFT) on two-phase flow mechanisms are investigated using pore-scale events, oil-phase morphology, forces acting on oil ganglia surfaces, and oil recovery curves, for Capillary numbers (Ca) in the range of 1.2 × 10−3 to 6 × 10−1. We found that the two-phase flow through oil-wet medium is governed by pore-by-pore filling mechanism dominated by the Haines-jumps. At low Ca values, a change in the wettability from oil- to neutrally wet resulted into the change of pore-by-pore filling mechanism to co-operative pore filling and as the medium wettability changes from the neutrally to the weakly water-wet, the corner flow events begin to emerge. At low Ca values, the invasion through weakly water-wet porous medium is dominated by co-operative filling and results into an increased oil recovery, whereas the two-phase flow through strongly water-wet medium is governed by corner flow events resulting in a low oil recovery. The corner flow events are found to be a function of not only the medium wettability, but also of Ca and are a characteristic of controlled imbibition. Further, we show that a substantial decrease in the IFT results in a fingerlike invasion at pore-scale, irrespective of the medium wettability. Finally, a two-phase flow regime map is proposed in terms of Ca and contact angle based on the two-phase interface morphology.

Insights into PU/EVA Blends Produced Using Industrial Residues Towards Eco-efficient Materials

Aiming at minimizing the issues associated with the disposal of polymers, in this study, elastomeric materials derived from 100% recycled feedstocks were produced. Residues of polyurethane (PU) foams (from 0 to 100%) were blended with residues of ethylene–vinyl acetate (EVA) derived from the shoe-soles industry (from 0 to 100%) to produce films by hot compression. The experimental values obtained by the characterization of the blends were compared with the predicted values derived from the rule of mixtures. Despite of the two-phase morphology observed, the high correlation between the experimental and predicted values suggest that phase segregation did not have a significant effect on the properties of the blends. Voids were also observed on the PU derived materials, due to the source of PU (foams), which reduced their density and increased the water absorption. Yet, this did not jeopardize the mechanical performance of the ensuing materials. In addition, higher amounts of PU resulted in stiffer materials, while higher amounts of EVA induced higher thermal stability. From the results, it was demonstrated that the PU/EVA blends, produced from 100% recycled feedstock, presented suitable properties to be used in shoe-soles applications.

Rheological behavior of a low crystallinity polyolefin-modified asphalt binder for flexible pavements

An asphalt binder (PG 64−22) is modified with a crystallizable copolymer of polypropylene (PP) and polyethylene (PE) to enhance its ability to resist rutting in flexible pavements during periods of warm weather. After cooling of binders from the mixing temperature at a controlled rate of 3 °C/min, their microstructure and rheological behavior are characterized. The modified asphalts exhibit two-phase morphology with droplets of a maltene-rich polymer phase less than 50 μm in size dispersed in an asphaltene-rich, continuous phase. X-ray diffraction patterns and optical birefringence microscopy indicate that the PP/PE copolymer segregates from the matrix during cooling, forming a network of interconnected, crystalline fibrils. At temperatures of (50–80) °C, at which rutting is an issue in pavements, addition of PP/PE copolymer substantially increases the rutting factor by a factor of 2–6, depending on temperature and concentration. At temperatures of (―20 to 0) °C, addition of 5 wt.% or less of the PP/PE modifier has a minimal impact on performance based on both s-value and m-value. The modified asphalts are s-controlled, with ΔTc less than about 6.4 °C, suggesting that the PP/PE copolymer is an effective modifier for reducing rutting in flexible pavements.

Influence of morphology on high-temperature rheological properties of bitumen modified with styrene-butadiene-styrene (SBS) copolymer

Different microstructures of the same polymer-modified bitumen (PMB) were obtained by subjecting the bitumen modified with styrene-butadiene-styrene (SBS) copolymer to isothermal annealing at various temperatures. The effects of the morphology on the rheological properties of SBS-modified bitumen were investigated within the high-temperature range. The PMB microstructures were quantitatively evaluated using image analysis. A dynamic shear rheometer was used to measure the rheological parameters of the PMB samples and perform the multiple stress creep and recovery (MSCR) test. A quantitative basis could be established on which to discuss the relationship between the PMB morphology and rheology. The image analysis indicated that conditioning by isothermal annealing evidently led to a difference in the microstructure of the samples. Variation of the thermal history is demonstrated to be a practical way to vary the morphology of the PMB with the same raw materials and formulation. Compared with the two-phase morphology, the single-phase microstructure tended to have a narrower linear viscoelastic (LVE) region of the PMB. Within the LVE region, especially at low frequencies, the homogenous PMB can store more energy when experiencing loadings and is more elastic. Outside the LVE region, based on the MSCR test results, the homogenous morphology could assist in reaching a higher percentage of strain recovery after the creep period.

Fast inverse design of microstructures via generative invariance networks.

The problem of the efficient design of material microstructures exhibiting desired properties spans a variety of engineering and science applications. The ability to rapidly generate microstructures that exhibit user-specified property distributions can transform the iterative process of traditional microstructure-sensitive design. We reformulate the microstructure design process using a constrained generative adversarial network (GAN) model. This approach explicitly encodes invariance constraints within GANs to generate two-phase morphologies for photovoltaic applications obeying design specifications: specifically, user-defined short-circuit current density and fill factor combinations. Such invariance constraints can be represented by differentiable, deep learning-based surrogates of full physics models mapping microstructures to photovoltaic properties. Furthermore, we propose a multi-fidelity surrogate that reduces expensive label requirements by a factor of five. Our framework enables the incorporation of expensive or non-differentiable constraints for the fast generation of microstructures (in 190 ms) with user-defined properties. Such proposed physics-aware data-driven methods for inverse design problems can be used to considerably accelerate the field of microstructure-sensitive design.