Morphology Of Polymer Blends Research Articles

“Interface localization of reduced graphene oxide in polystyrene/polymethyl methacrylate blends with co-continuous morphology: Investigating the effects of polymer interface on nanoparticle network stabilization”

This study aimed to investigate the co-continuous morphology of polymer blends and determine whether nanoparticles can be localized at the interface of polymers to create a well-organized network and decrease the percolation threshold. The researchers chose solution-mixed polystyrene (PS)/polymethyl methacrylate (PMMA) blends containing reduced graphene oxide (rGO) for analysis of their rheological, electrical, dynamic-mechanic properties, topography, and morphology. Graphene oxide in varying degrees of thermal reduction was prepared, and surface tension measurements were used to detect the range at which the particles tend to reside at the interface. Based on electrical characterization, it was determined that the required amount of rGO to cover the total polymer interface in the co-continuous blend is approximately 0.1 wt% on a volume basis. The rheology time sweep revealed that, while the initial storage modulus of the nanocomposite containing interface-located particles is similar to that of the sample with randomly distributed particles, the increase in storage modulus over time is less steep, resulting in a lower final value. These findings confirm that the flocculation of rGO particles decreases when they are located at the interface.

Particle-size dependent stability of co-continuous polymer blends

The properties of polymer blend nanocomposites are typically associated with spatiotemporal distribution of nanoparticles within a polymer blend system. Here, we present in situ high-temperature confocal rheology studies to assess the effect of particle size on the extent of particle agglomeration, particle migration, and subsequently their influence on the coarsening dynamics of polymer blends filled with pristine silica particles. We investigate co-continuous polypropylene-poly(ethylene-co-vinyl acetate) blends filled with five different silica particles with a diameter ranging from 5 to 490 nm. While particle size does not play a role when particles are thermodynamically driven to their preferred polymer phase, a striking effect is achieved when particles are kinetically trapped at the interface. We find that the interparticle interaction largely driven by size dependent long-range repulsive forces governs their extent of agglomeration, severely affecting their ability to stabilize co-continuous morphology. Strikingly, the largest (490 nm) particles are more effective in suppressing coarsening than 5 nm particles, while 140 and 250 nm particles are found to be the most effective. We demonstrate that kinetic trapping of primary particles of either size is influenced by the interplay of interfacial folding during melt blending and Laplacian pressure exerted at the interface. These results extend our fundamental understanding of the stabilization of co-continuous morphology in polymer blends by particles.

Relationship Between The Co-Continuous Morphology of Immiscible Polymer Blends and the Structure of An In Situ Formed Graft Copolymer.

Suitable compatibilizers are essential to prepare immiscible polymer blends with stable co-continuous morphologies. From the thermodynamic point of view, such compatibilizer should not only reduce the interfacial tension, but also promote the formation of flat interface between different phases. Meanwhile, it must not hinder the coalescence of dispersed phase. Therefore, asymmetric structures are required for those block or graft copolymer compatibilizers. However, from the kinetic point of view, copolymers with asymmetric structures are prone to be dragged out from the interface and form micelles in one phase under the processing conditions, which will lose their compatibilization effects. The balance between such thermodynamic and kinetic factors remains unclear. In this paper, the relationship between the morphology of the compatibilized polystyrene/nylon 6/styrene-maleic anhydride copolymers (PS/PA6/SMA) immiscible polymer blends and the structures of the in-situ formed SMA-g-PA6 graft copolymers as well as the processing conditions are studied. Two kinds of SMA are used as compatibilizers: SMA28 (Mw = 110,000g/mol, MAH content 28wt.%) and SMA11 (Mw = 110,000g/mol, MAH content 11wt.%). After melt blending with PA6 into an internal mixer, the in-situ formed copolymer SMA28-g-PA6 has an average four PA6 side chains grafted on one SMA backbone, while that of SMA11-g-PA6 has only one PA6 side chain. Dissipative particle dynamics (DPD) simulation results indicate that both SMA28-g-PA6 copolymer and PS/PA6/SMA28 blends tend to form co-continuous structure, while SMA11-g-PA6 copolymer and PS/PA6/SMA11 blends form sea-island morphologies. However, these results are confirmed experimentally only at relatively low rotor speed of the internal mixer (60rpm). When the rotor speed of the mixer is higher (105rpm), sea-island morphologies are obtained in PS/PA6/SMA28 blends and co-continuous ones are found in PS/PA6/SMA11 systems. These results indicate that higher shear stress will favor to elongate the minor phase domains and form flat interfaces, which is benefit for the formation of co-continuous morphologies; meanwhile, high shear stress may pull the graft copolymers with asymmetric structures (SMA28-g-PA6) out from the interface of PS and PA6 and induce the formation of sea island morphologies. This article is protected by copyright. All rights reserved.

Rheological Characteristics of Starch-Based Biodegradable Blends.

Thermoplastic starch was blended with commercially available biodegradable polyesters of poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA) for its improved performance and processability. The morphology and elemental composition of these biodegradable polymer blends were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively, while their thermal properties were analyzed using thermogravimetric analysis and differential thermal calorimetry. For rheological analysis, the steady shear and dynamic oscillation tests of three samples at various temperatures were investigated using a rotational rheometer. All three samples exhibited significant shear thinning at all measured temperatures, and their shear viscosity behavior was plotted using the Carreau model. The frequency sweep tests showed that the thermoplastic starch sample exhibited a solid state at all temperatures tested, whereas both starch/PBAT and starch/PBAT/PLA blend samples exhibited viscoelastic liquid behavior after the melting temperature such that their loss modulus at low frequencies was greater than the storage modulus, and inversion occurred at high frequencies (storage modulus > loss modulus).

Employing impedance spectroscopy to investigate electrical conduction mechanism in polymer composite blends containing conductive masterbatch: PP/EVA/ (PP-g-MA/MWCNTS)

Impedance spectroscopy analysis has been employed to investigate the effect of melt mixing time on electrical conduction mechanism, direct contact or electron tunneling, of a polymer blend using a conductive masterbatch. A novel approach is proposed to correlate the dispersion/distribution states of conductive nanoparticles within the phases, achieved through kinetic control of the conductive masterbatch, and their impedance properties. A blend of polypropylene and ethylene-vinyl acetate copolymer (PP/EVA) was considered as a case study for the matrix. An electrically conductive masterbatch of multiwalled carbon nanotubes (MWCNTs) in polypropylene-grafted-maleic anhydride (PP-g-MA) was added to the blend. The masterbatch in varying amounts was mixed with PP/EVA in a range of 1 min–4.5 min. The co-continuous morphology of the ternary polymer blend was validated via scanning electron microscopy micrographs. The atomic force microscopy (AFM) results showed that as the mixing time of the masterbatch increases the interconnected structures within the conductive interphase decrease. Impedance spectroscopy using alternating current was employed to probe the conduction mechanism in the composite blends. The impedance spectroscopy results revealed that for samples with low mixing time, a dielectric relaxation peak occurs at high frequencies due to the existence of more conductive pathways as a consequence of the interconnected structures of the masterbatch phase. Also, the major contribution of conductance was direct contact in the samples with low mixing times while electron tunneling mechanism was considerable for the samples with high mixing times. Dielectric constant was increased as a result of interfacial polarization boosting with mixing time. The percolation threshold was considerably decreased from 0.95 v% for simultaneous direct mixing method to 0.16 v% for the masterbatch method.

Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

Interfacial rheology is crucial in dictating morphology and ultimate properties of particle-stabilized polymer blends, but is challenging to be determined. In this study, a fully polymeric dumbbell-shaped Janus nanoparticle (JNP) of polymethyl methacrylate (PMMA) and polystyrene (PS) spheres with equal sizes (∼80 nm) was prepared and used as an efficient compatibilizer for PMMA/PS blends. The JNPs were preferentially localized at the PMMA/PS interface, thereby reducing the interfacial tension and refining the morphology in both droplet-matrix and co-continuous type blends, whereby a JNP concentration ∼2.5 wt % is sufficient to reach a saturation in droplet size reduction due to compatibilization. Based on the linear viscoelastic moduli and corresponding relaxation spectra (H(τ)*τ) of JNP-compatibilized droplet-matrix blends, besides the droplet shape relaxation time (τF), a longer relaxation time (τβ), typically related to interfacial viscoelasticity, was readily identified. The dependence of τβ on the JNP concentration (WJNPs) was significantly dominated by the droplet size reduction induced by the JNP compatibilization, with τβ decreasing with increasing WJNPs. The viscoelastic properties extracted from τβ typically originate from a combination of gradients in interfacial tension due to the particle redistribution at the droplet interface (Marangoni stresses) and the deviatoric stresses of intrinsic rheological origin. The latter originate from the intrinsic viscoelasticity of the particle-laden interface, which is enhanced by particle jamming and particle–polymer interactions, such as entanglements between chains from the polymeric spheres and those penetrating from the bulk into the spheres. To address the challenge of isolating these contributions, a JNP-sandwiched PMMA/PS multilayer structure was designed to exclude the effect of Marangoni stresses and droplet curvature, thus having no τF but a new relaxation (τ′β), which characterizes the contribution of intrinsic interfacial viscoelasticity. The τ′β was observed to increase with JNP coverage (Σ) following the Vogel–Fulcher–Tammann model that is typically used to describe the divergent behavior of the “cage” effect in classical colloidal glasses. Moreover, a multimode Maxwell model fitting allows to split the interfacial relaxation into the confined diffusion of JNPs within their cage and the entanglements between the JNPs and the bulk.

Enabling quantitative analysis of complex polymer blends by infrared nanospectroscopy and isotopic deuteration.

Atomic-force microscopy coupled with infrared spectroscopy (AFM-IR) deciphers surface morphology of thin-film polymer blends and composites by simultaneously mapping physical topography and chemical composition. However, acquiring quantitative phase and composition information from multi-component blends can be challenging using AFM-IR due to the possible overlapping infrared absorption bands between different species. Isotope labeling one of the blend components introduces a new type of bond (carbon-deuterium vibration) that can be targeted using AFM-IR and responds at wavelengths sufficiently shifted toward unoccupied regions (around 2200 cm-1). In this project, AFM-IR was used to probe the surface morphology and chemical composition of three polymer blends containing deuterated polystyrene; each blend is expected to exhibit various degrees of miscibility. AFM-IR results successfully demonstrated that deuterium labeling prevents infrared spectral overlap and enables the visualization of blend phases that could not normally be distinguished by other scanning probe techniques. The nanoscale domain composition was resolved by fast infrared spectrum analysis. Overall, we presented isotope labeling as a robust approach for circumventing obstacles preventing the quantitative analysis of multiphase systems by AFM-IR.

An approach on reactive processing of plastic waste

AbstractAn approach on the reactive processing and compatibilization of plastic waste was simulated for the mixture of thermoplastics with the major content in municipal plastic waste: low‐density polyethylene, high‐density polyethylene, polypropylene, polystyrene, poly(vinyl chloride) (PVC), polyethylene terephthalate, polymethyl methacrylate, PA6, and acrylonitrile‐butadiene‐styrene. Peroxide initiators 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane (L101) and hydrogen peroxide (H2O2) and poly(styrene‐b‐ethylene‐b‐butylene‐b‐styrene) grafted with maleic anhydride (SEBS‐g‐MAH) were used for the reactive processing of polymer blend under optimized conditions (concentration, reaction temperature, and time). The compatibilization was evidenced by “online” monitoring of the melt viscosity during reactive processing of polymer blend and examined by melt volume rate, oscillatory rheology, mechanical testing, and scanning electron microscopy. The effect of selected peroxides on the type of radical reaction was also evidenced for individual thermoplastics. Both L101 and hydrogen peroxide modify the melt viscosity with different effectivity due to different miscibility, decomposition mechanism, and limited reactivity of individual thermoplastics toward primary radicals. Therefore, the efficiency of compatibilization is limited. On the other hand, SEBS‐g‐MAH acts is an “universal” and effective reactive compatibilizer for multicomponent polymeric blend due to combination of covalent and non‐covalent interactions with blended thermoplastics, resulting in the improvement of mechanical properties and morphology of polymer blend.

Facile production of binary polymer/carbonic nanofiller‐based biodegradable electromagnetic interference shield films with low electrical percolation threshold

AbstractInterference of electromagnetic (EM) radiation generated from different electronic gadgets produces noises diminishing their performance. So, shielding of EM interferences (EMI) is necessary to achieve noise‐free performance from electronic gadgets. In the present work, we have produced thermoplastic polyurethane (TPU)/polybutylene adipate‐co‐terephthalate (PBAT) based biodegradable binary polymeric blend and incorporated different carbonic nanofillers such as Vulcan XC‐72 conductive carbon black (VCB) and multiwalled carbon nanotube (MWCNT) into it employing solvent mixing and casting technique and studied the morphology of polymer blends, EMI shielding effectiveness in X‐band of the EM spectrum as well as mechanical performance, electrical performance, and biodegradability of polymer nanocomposites. The selective nanofiller distribution in the low viscous PBAT phase of the “co‐continuous” binary blend is found to achieve a “lower electrical percolation threshold” compared to neat polymer nanocomposites. For each of the TPU/PBAT/VCB and TPU/PBAT/MWCNT nanocomposites, electrical percolation threshold of around 12.5 and 5 wt% respectively has been achieved successfully. Nanocomposite sheets with a thickness of 1.0 mm and loading of 30 wt% of VCB and 15 wt% of MWCNT gave EMI shielding values of −25 dB and −28 dB respectively at a frequency of 8.4 GHz.

Influence of Asphaltene Modification on Structure of P3HT/Asphaltene Blends: Molecular Dynamics Simulations.

Further development and commercialization of bulk heterojunction (BHJ) solar cells require the search for novel low-cost materials. The present study addresses the relations between the asphaltenes’ chemical structure and the morphology of the poly(3-hexylthiohene) (P3HT)/asphaltene blends as potential materials for the design of BHJ solar cells. By means of all-atom molecular dynamics simulations, the formation of heterophase morphology is observed for the P3HT-based blends with carboxyl-containing asphaltenes, as well as the aggregation of the asphaltenes into highly ordered stacks. Although the π–π interactions between the polyaromatic cores of the asphaltenes in solutions are sufficient for the molecules to aggregate into ordered stacks, in a blend with a conjugated polymer, additional stabilizing factors are required, such as hydrogen bonding between carboxyl groups. It is found that the asphaltenes’ aliphatic side groups may improve significantly the miscibility between the polymer and the asphaltenes, thereby preventing the formation of heterophase morphology. The results also demonstrate that the carboxyl-containing asphaltenes/P3HT ratio should be at least 1:1, as a decrease in concentration of the asphaltenes leads to the folding of the polymer chains, lower ordering in the polymer phase and the destruction of the interpenetrating 3D structure formed by P3HT and the asphaltene phases. Overall, the results of the present study for the first time reveal the aggregation behavior of the asphaltenes of varying chemical structures in P3HT, as well the influence of their presence and concentration on the polymer phase structure and blend morphology, paving the way for future development of BHJ solar cells based on the conjugated polymer/asphaltene blends.

Observing the On-Site Generation of Excitons and Charges by Low-Temperature Spectroscopy.

Understanding the relation between phase morphology and physical processes in polymer blends is the key to the fabrication of reproducible and reliable polymer optoelectronic devices. In this work, taking the advantage of low-temperature spectroscopy, we have observed the on-site generation of excitons and long-lived charges in different phase morphology polymer/fullerene blends. Probing at 10K, the photo-generated species are localized to where they are generated. We found that the generation of excitons and long-lived charges is highly influenced by the local molecular phase morphology. We further demonstrated that although the influence of phase morphology is localized to the place that excitons and long-lived charges are generated, this influence can persist over sub-millisecond timescales. Thus, we believe that the fate of excitons and long-lived charges is determined by the location at which they are generated, which can in turn be controlled precisely by molecular phase morphology.

Fine-Tuning of Siloxane Pendant Distance for Achieving Highly Efficient Eco-Friendly Nonfullerene Solar Cells.

Side-chain engineering has been proved to show profound impact on polymer properties and blend morphology. Herein, the critical role of siloxane-terminated alkoxy side chains was revealed by a tiny decorating method through which the molar content of siloxane-terminated alkoxy side chain was fixed to 5 %, and its alkyl linker was the only tuning factor. The pentylene, heptylene, and nonylene linkers were designed and used to synthesize wide-bandgap polymers PQSi505, PQSi705, and PQSi905, respectively. Interestingly, the siloxane pendant of combinatory side chain exhibited a distinct impact on molecular packing when its branching position shifted slightly. Among the three polymers, PQSi705 had the strongest aggregation and the highest packing order. Finally, toluene-processed organic solar cells (OSCs) based on PQSi705 and Y6-BO achieved the best power conversion efficiency of 15.77 %. This work suggests that siloxane pendant can serve as a powerful modulator to enhance the photovoltaic performance of OSCs.

Microscopic Interface and Multiscale Failure Analysis of Proposed Molecular Chain Polymers Based on Aifantis Strain Gradient Theory.

A study on the microscopic morphology of real-world polymer blends and its mechanism of change showed that the microscopic morphology of equiproportional mixtures gradually changed from a dense body structure to a network structure with the addition of the total polymer concentration up to 20%; the microscopic morphology of mixtures with different proportions was characterized by the most uniform network structure of equiproportional mixtures when the total polymer concentration was 20%. The polymer acts as a defoamer in the mixed system. In this paper, the relationship between the microscopic morphology of each mixture and the physicochemical behavior of the two polymer chains in the mixed system was investigated on the basis of the Aifantis strain gradient theory. Molecular polymer microscopic interface and multiscale failure analysis are proposed. It is shown that for the dihedral angle distribution of four consecutive coarse-grained particles, the peaks obtained from all atomic-scale simulation data are reproduced in the coarse-grained model simulations. The deviation is within 2.5% in most places, except for the local area where the deviation exceeds 5%. Therefore, we have achieved good results for large-scale failures.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Numerical Modeling of the Blend Morphology Evolution in Twin‐Screw Extruders

Front Cover: The disperse polymer blend morphology evolution is described using a macroscopic model, which clusters individual droplets in droplet populations. The blend model is used to perform a particle tracking simulation of the morphology evolution inside a twin-screw extruder. The figure shows the size distribution of 1300 droplet populations along the cross-section of a twin-screw extruder. This is reported by Patrick D. Anderson and co-workers in article number 2100087.

Simulations of Structure and Morphology in Photoreactive Polymer Blends under Multibeam Irradiation

We present a theoretical study of the organization of photoreactive polymer blends under irradiation by multiple arrays of intersecting optical beams. In a simulated medium possessing an integrated intensity-dependent refractive index, optical beams undergo self-focusing and reduced divergence. A corresponding intensity-dependent increase in molecular weight induces polymer blend instability and consequent phase separation, whereby the medium can evolve into an intersecting waveguide lattice structure, comprising high refractive index cylindrical cores and a surrounding low refractive index medium (cladding). We conduct simulations for two propagation angles and a range of thermodynamic, kinetic, and polymer blend parameters to establish correlations to structure and morphology. We show that spatially correlated structures, namely, those that have a similar intersecting three-dimensional (3D) pattern as the arrays of intersecting optical beams, are achieved via a balance between the competitive processes of photopolymerization rate and phase separation dynamics. A greater intersection angle of the optical beams leads to higher correlations between structures and the optical beam pattern and a wider parameter space that achieves correlated structures. This work demonstrates the potential to employ complex propagating light patterns to create 3D organized structures in multicomponent photoreactive soft systems.

Thermodynamics, morphology, mechanics, and thermal transport of PMMA-PLA blends

Thermodynamics controls structure, function, stability, and morphology of polymer blends. However, obtaining the precise information about their mixing thermodynamics is a challenging task, especially when dealing with complex macromolecules. This is partially because of a delicate balance between the local concentration/composition fluctuations and the monomer level (multibody) interactions. In this context, the Kirkwood-Buff (KB) theory serves as a useful tool that connects the local pairwise fluid structure to the mixing thermodynamics. Using larger scale molecular dynamics simulations, within the framework of KB theory, we investigate a set of technologically relevant poly(methyl methacrylate)-poly(lactic acid) blends with the aim to elucidate the underlying microscopic picture of their phase behavior. Consistent with the existing experiments, we emphasize the importance of properly accounting for the entropic contribution to the mixing Gibbs free-energy change $\mathrm{\ensuremath{\Delta}}{\mathcal{G}}_{\mathrm{mix}}$ that controls the phase morphology. We further show how the relative microscopic interaction details and the molecular level structures between different mixing species can control the nonlinear mechanics, ductility, and heat flow. Therefore, this study provides a guiding principle for the design of light weight functional materials with extraordinary physical properties.

Numerical Modeling of the Blend Morphology Evolution in Twin‐Screw Extruders

AbstractThe blend morphology model developed by Wong et al., based on Peters et al., is used to investigate the development of the disperse polymer blend morphology in twin‐screw extruder flow. First, the model is written in a point‐wise form suitable for using in conjunction with particle tracking. Particle tracking methods are used to generate trajectories along the flow field. Macroscopic droplet populations are placed along these trajectories and the velocity gradient tensor is extracted and applied on the point‐wise blend morphology model. Very large morphology differences arise between trajectories that pass through the middle gap and those that do not. In the global distribution of (macroscopically averaged, monodisperse) droplet sizes, two distinct peaks appear due to these different trajectories. Given enough number of screw rotations, a droplet population can reach almost every position in the twin‐screw extruder and travel along both types of particle trajectories. The effect of varying the gap size is that the largest droplets are unaffected, but the smallest droplets are smaller for a smaller gap size due to the higher maximum shear rate. The effect of varying the viscosity ratio on the global droplet size distribution is found to be nonlinear and is strongly determined by the Grace curve. The effect on polydisperse droplet populations is found to be that trajectories that do not pass through the gap evolve toward a single peak, whereas trajectories that do pass through the gap lead to a split into two peaks that ultimately rejoin as one peak. It is concluded that the initial position of a population in the twin‐screw extruder has a very large effect on the developing transient blend morphology, though future work should be done on the importance of the initial position on the steady‐state blend morphology after a very large number of screw rotations.

Solid additive tuning of polymer blend morphology enables non-halogenated-solvent all-polymer solar cells with an efficiency of over 17%

The treatment of toluene solvent and DTT additive enables the PBQ6:PYF-T-o-based all-PSC devices with PCE up to 17.06%, which is one of the highest value in non-halogenated-processed all-PSCs to date.

Melt Spinning of Flexible and Conductive Immiscible Thermoplastic/Elastomer Monofilament for Water Detection.

In many textile fields, such as industrial structures or clothes, one way to detect a specific liquid leak is the electrical conductivity variation of a yarn. This yarn can be developed using melt spun of Conductive Polymer Composites (CPCs), which blend insulating polymer and electrically conductive fillers. This study examines the influence of the proportions of an immiscible thermoplastic/elastomer blend for its implementation and its water detection. The thermoplastic polymer used for the detection property is the polyamide 6.6 (PA6.6) filled with enough carbon nanotubes (CNT) to exceed the percolation threshold. However, the addition of fillers decreases the polymer fluidity, resulting in the difficulty to implement the CPC. Using an immiscible polymers blend with an elastomer, which is a propylene-based elastomer (PBE) permits to increase this fluidity and to create a flexible conductive monofilament. After characterizations (morphology, rheological and mechanical) of this blend (PA6.6CNT/PBE) in different proportions, two principles of water detection are established and carried out with the monofilaments: the principle of absorption and the short circuit. It is found that the morphology of the immiscible polymer blend had a significant role in the water detection.