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The mechanism of the development of solutal Marangoni instability in a thin layer of polymer solution, by rapid evaporation of volatile solvent, is studied numerically. By considering the conservation of mass, momentum, and concentration across the evaporating surface, physically reliable kinematic and boundary conditions are derived and implemented in numerical simulations. To simulate the drying of a polymer solution more realistically up to the point where 80% of solvent was evaporated, the concentration-dependent evaporation rate, viscosity, and diffusivity and the movement of the interface are taken into account. Numerical simulations demonstrate that the generation and merging of convective cell motions in a layer during drying lead to surface patterns as the drying process continues. The drying of a polymer film and the development of the surface topography including thickness deviation depend on various physical phenomena such as Marangoni stress, surface tension, vapor recoil pressure, evaporation rate, initial concentration of polymer, and variation of viscosity and diffusivity with concentration. Meanwhile, the vapor recoil force plays little role in the onset of instability motion and the irregularity of the evaporation surface. Furthermore, both the diffusivity reduction and the viscosity thickening due to evaporative concentration play a critical role in the formation of the skin layer, because they suppress the Marangoni instability motion and therefore impede the convective transport of concentrated polymeric solute. [ABSTRACT FROM AUTHOR]

We investigate the onset and growth of viscous fingering (VF) of miscible annulus in a radial Hele-Shaw cell. Systematic numerical study on a finite annulus domain is performed by employing finite element method solver in COMSOL Multiphysics software. We justify that concentration field analysis is not a good choice for dynamic study in radial flows. Instead, velocity magnitude is a better tool to understand the dynamics. Therefore, we propose velocity field analysis to better differentiate the stable and unstable states and present a new stability criterion using the velocity field method. Most interestingly, using the velocity field analysis and the new stability criterion, we show a restabilization of the VF at a critical time when the system becomes diffusion dominant and able to provide both the onset time, τon (time at which instability develops), and the time at which the interface returns to the stable state, τd. Furthermore, the study successfully suggests the critical values for several dimensionless parameters, the Péclet number (Pe), log-viscosity ratio (R), and volumetric ratio (ra) and time (τ), to induce instability. When Pe is higher than 103, the evolution of VF instability is no longer enhanced by Pe, and Rc converges to a certain value. In particular, for the transiently unstable system of low Pe, the restabilization of VF instability is identified even though R is higher than Rc. The unstable system (τ > τ o n) returns to the stable state as injection time increases further. Moreover, we obtained a critical value of the volumetric ratio ( r c , a ). [ABSTRACT FROM AUTHOR]

The onset of solutal-capillary instability driven by evaporation through the solution–air interface is investigated theoretically and numerically in thin saline water. A scaling analysis shows that the development of the surface tension gradient is mainly driven by evaporative mass flux rather than evaporative heat flux, leading to the onset of solutal-capillary instability. The onset time of instability is theoretically analyzed through a linear stability analysis with newly derived stability equations that consider variations in the evaporative concentration, concluding that Ma · α is the most important parameter governing the onset of solutal-capillary convection, rather than Ma or α. Correspondingly, a nonlinear numerical simulation demonstrates that as evaporation proceeds, a nonvolatile salt accumulates near the evaporating interface and inhomogeneity of the concentration along the interface, which induces solutal-capillary motion, develops. The critical onset time determined from the linear stability analysis is in good agreement with the numerical simulation outcomes. The present theoretical and numerical study provides a better understanding of the evaporation-driven instability that develops in thin liquid films under the given temperature variation. [ABSTRACT FROM AUTHOR]

The coupled effects of thermodynamic and hydrodynamic instabilities are studied during viscous fingering (VF). We introduced a modified Cahn–Hilliard phase-field model in conjunction with the Korteweg force in the classical VF model and derived consistent governing equations. The free energy of the partially miscible system is described using a modified Flory–Huggins model, which allows us to investigate the temporal evolution of spatial inhomogeneities. The mass flux in the Cahn–Hilliard equations is modified according to modern diffusion theory. The governing equations have been solved through an in-house model implementation using the COMSOL multiphysics software. We successfully demonstrated the transition from the finger-like structures to the droplet formation during spinodal decomposition as demonstrated experimentally in the literature. Our results are also in agreement with earlier numerical results obtained using a classical Landau type mixing energy. We further systematically studied the effects of the Margules parameter (interaction parameter) and the gradient parameter, which is associated to the thermodynamic length scale and capillary number on the VF. Aysmmetric features of the binary mixture are also investigated showing a stronger thermodynamic effect on the system with increasing phase separation and, hence, droplet formation. [ABSTRACT FROM AUTHOR]

Characterized by high strength to unit weight, poly(ethylene terephthalate) (PET) remains one of the most widely used engineering plastics, hence the attention to its associated waste and recycling technology development has been paid from academic and industrial perspectives. Herein, we investigate the mechanical degradation of PET through degradative compounding process cycles and the effect of chain extender (Joncryl® ADR 4468) to prevent molecular degradation of PET during melt processing. They are characterized based on rheological and mechanical measurements. Characterization of the bottle-grade PET samples reveals low viscosity and crystallinity owing to isophthalic acid units within the PET copolymer structure over PET homopolymer. Mechanical shear and thermal impact by virtue of the increase in rotor speed and temperature are employed to study the degradation of the PET samples. Both samples respond to degradation in successive processing cycles with as much as 70% decrease in their complex viscosity and moduli. The molecular weight of PET copolymer accordingly decreases from 23,400 to 8010 g/mol. Chain scission arising from thermo-mechanical degradation results in high crystallinity by more than five folds in the processed PETs. Attributed to recoupling of the degraded short chains, the chain extender compensates with the increase in viscosity and moduli up to 20% whilst serving to increase crystallinity but almost ineffective in appreciating mechanical performance with barely any significant variation in tensile strength and elongation at break. This study shows that mechanical shear is verified to impact a pronounced degradation on PET more than thermal action on the samples. [ABSTRACT FROM AUTHOR]

The drying of the thin liquid film of polymer solution is a complex process accompanying instabilities induced by concentration gradients that develop during the evaporation. This study investigates evaporation-driven gravitational instabilities (Rayleigh–Taylor instability) in the thin liquid film of a polymer solution based on theoretical and numerical analyses, specifically focusing on the onset of instability at the early stage of the drying process. Evaporation-driven convection is taken into account by employing a dynamic moving boundary condition and concentration-dependent material functions (dynamic viscosity and diffusivity). A theoretical analysis predicts the onset of gravitational instability ( τ c) , showing good agreement with the results of a numerical simulation analysis ( τ d) , suggesting scaling relationships between the onset of instability and the initial concentration (Ci), τ c ∼ C i − 1 / 2 , for a slow evaporation rate and dilute concentration range, which rapidly increases with an increase in the concentration due to an instability-retardation effect. A nonlinear two-dimensional numerical simulation visualizes the development of a polymer-dense layer, pluming, and a convection–diffusion flow throughout the liquid film under transient evaporation. The concentration-gradient-driven convection–diffusion flow enhances the gravitational instability and pluming further at higher frequencies. Meanwhile, for a polymer solution with high viscosity, viscosity thickening delays the onset of instability, retarding the development of instability. This study provides a fundamental understanding of the mechanism behind how convective instability develops in a drying polymer solution during evaporation and information on how to develop pluming of a polymer-dense skin layer at early stages of drying of a polymer solution film. The findings suggest that the proper control of hydrodynamic instability induced by a concentration gradient in a thin polymer solution film is important to prevent or enhance the formation of a convection pattern in the thin polymer film. [ABSTRACT FROM AUTHOR]

The dissolution of a horizontal salt body is theoretically and numerically investigated by considering the coupled dynamics of the dissolution reaction and the diffusive and convective mass transfer at the salt surface. To take into account the nature of the recessing salt surface and the dissolution-driven convection, a dynamic moving boundary condition coupled with a dissolution reaction are employed By employing a newly derived moving interface condition and parameters, a theoretical analysis predicts the onset of gravitational instability, suggesting scaling relationships between parameters to describe the onset of instability (in transport-dominant (Damkholer number $Da \to \infty $ and Rayleigh number $Ra > {10^5}$), onset time ${\tau _d}\sim R{a^{ - 2/3}}$ and ${\tau _d}\sim (RaDa)^{1/4}$ for reaction-dominant regimes $(Da \to 0)$). The scaling relationships on dissolution (the average height change, $\Delta {h_{avg}}\sim \sqrt \tau $ for the diffusion-dominant regime and $\Delta {h_{avg}}\sim R{a^{0.79/3}}{\tau ^{0.86}}$ for the convection-dominant regime) are also suggested to explain the pattern formation. Under a convective mass transfer condition, the concentration gradient of the solute developed during the recession of the salt surface results in an adverse density gradient, which causes gravitational instability motion and finally determines the formation of a dissolution pattern. In addition, two-dimensional and three-dimensional numerical simulations visualize dissolution-driven convective flow fields, the recession of the liquid-solid interface and pattern formation on the dissolving interface. Theoretical and numerical analyses of the dissolution process suggest that the control of gravitational instability is important to prevent or enhance dissolution pattern formation. This systematic parameter study provides a deep understanding of the effect of gravitational instability on convection-driven dissolution in a horizontal geometry. [ABSTRACT FROM AUTHOR]

In this study, the poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate)(PBAT) blend is investigated to improve rheological and mechanical performances of PBAT based on rheological, mechanical, and thermal behavior analyses. The multi‐step mixing method is developed to fabricate the blend with non‐spherical morphology. In the multi‐step mixing method, blends with a wide composition range (25/75–75/25) are mixed with additional PBAT at a mixing temperature between the melting temperatures of PBAT and PLA to produce the PBAT blend embedded with non‐spherical PLA particles (10 wt%). The embedding of non‐spherical PLA particles in PBAT increases the resistance against deformation, resulting in strain hardening behavior and an increase in the yield strength as well as the tear resistance of the PBAT. The presence of stiff PLA particles enhances the crystallization behavior of PBAT, meaning that polymer chains may interpenetrate. The findings of this study suggest that the multi‐step mixing method is beneficial for embedding non‐spherical PLA particles into a PBAT matrix, which in turn facilitates the maintenance of good interfacial adhesion to increase the melt strength, yield strength, and tear resistance. [ABSTRACT FROM AUTHOR]

This study investigates unfractionated microalgae (Chlorella sp. HS2 (HS2)) as a new resource of biomass to develop microalgae-based bioplastic materials. For the fabrication of microalgae-based bioplastics, HS2 is melt-compounded with various polymers with different solubility. In addition, lipid-extracted HS2 (HS2-LE) is tested to compare the dispersion of unfractionated microalgae. Dispersion of HS2 in the polymer is assessed with morphological observations and image analysis, further evaluated based on mechanical, thermal, FT-IR spectroscopic, and rheological measurements. HS2 disperses in polymer with broad size distribution and forms large millimeter-sized agglomerates throughout the composite regardless of type of polymers. Meanwhile, size distribution of HS2 aggregates is shifting to smaller region at mixing condition realizing strong stress transfer. For poly(ethylene–vinyl acetate) (EVA)/HS2 showing smaller size distribution, the addition of 10% HS2 increases elongation at break of EVA. Moreover, lipid-extracted HS2 (HS2-LE) increases further ductility and strength of EVA composite due to better dispersion of HS2-LE. This preliminary study to screen out of several polymers to develop microalgae-based bioplastics has brought out a potential of HS2 for bioplastic application. [ABSTRACT FROM AUTHOR]

In order to develop conductive‐biocompatible 3D parts, poly(lactic acid) (PLA) is mixed with a hybrid of carbon black (CB, 4%) and graphene (GP, 0.1–0.5%) and the change of the particle dispersion under a flow is investigated based on rheological and electrical characterizations. In CB/PLA composite, CB aggregates are rearranged and percolation structure is disrupted under the given flow, resulting in a decrease in the modulus of the composite and lower electrical conductivity. During the 3D printing process, assemblies of CB aggregates do not remain close enough to maintain the percolation structure. When CB/PLA composite is mixed with GP, CB aggregates come into contact with GP aggregates to form percolation, maintaining a durable particle percolation against a flow and realizing electrical conductivity in 3D part. Despite the orientation effect of GP, the presence of GP enhances connectivity between the aggregates under a flow and maintains electrical percolation. A cell viability test of a 3D composite part shows good adsorption and growth of the cell due to the rough surface and biocompatibility of PLA. The addition of CB and GP to PLA improves not only the electrical properties of the 3D printing part but also enhances the cell viability. [ABSTRACT FROM AUTHOR]

In this study, clays (C30B, C20A, and CNa+) with different interlayer modifier and localization are investigated to improve mechanical properties of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blend based on crystallization, morphology, and rheology analyses. The mechanical properties of the PLA/TPU 70/30 blend (elongation at break: 229%, impact strength: 55 J/m) are additionally increased by the clay particles. Depending on modifiers within the particles localized at the interface, 0.1 wt% of the C30B maximizes elongation at break (289%) while 0.1 wt% of the C20A maximizes impact strength (81 J/m) due to its influence on crystal structure of PLA. Thermal analysis through differential scanning calorimeter shows that hydrophilic C30B induces ductile α' PLA crystal formation while less hydrophilic C20A induces stiff α crystal formation, which is reflected on the mechanical properties. In addition, there exists optimum degree of crystallinity for the desired mechanical properties. The excessive interfacial‐localized clay is found to interfere PLA/TPU interaction. Meanwhile, natural clay, CNa+ enhances mechanical properties of blend with the reduced distance between the TPU droplets with a 0.3–3 wt% addition. In addition, rheological properties help us to design the blend and annealing condition for the desirable mechanical properties. [ABSTRACT FROM AUTHOR]

Microalgae (Chlorella sp. HS2) have a high potential as a new biomass filler resource. Microalgae suspension is investigated depending on pH condition, focusing on microscopic sedimentation and a rheological behavior in order to understand in-depth the behavior of Chlorella sp. HS2 for harvesting process design. In terms of sedimentation analysis, it is found that Chlorella sp. HS2 cells settle down due to high density of 1.56 gcm−3. Meanwhile due to its small size and dilute concentration, the settling velocity is too slow for harvesting by natural sedimentation. Chlorella sp. HS2 cells undergo weak aggregation in the medium depending on pH condition. When the Chlorella sp. HS2 suspension (pH 5.4) is adjusted at pH 2.5, the surfaces of the microalgal cells turn neutral and cells are aggregated by van der Waals force between cells, leading to relatively faster sedimentation compared to Chlorella sp. HS2 cells without pH adjustment. The aggregation of Chlorella sp. HS2 cells depending on pH condition is reflected in rheological properties of the suspension. At pH 2.5, shear viscosity of the Chlorella sp. HS2 suspension increases and the suspension shows shear thinning behavior, meaning that the neutralized surface of Chlorella sp. HS2 makes cells aggregation. However, the aggregation of microalgal HS2 cells is easily dissociated and aligned along shear flow. Therefore, for the successful harvesting of biomass Chlorella sp. HS2, the flow and colloidal condition must be considered along with coagulation for rapid harvesting of cells. [ABSTRACT FROM AUTHOR]

In order to fabricate electrically and mechanically reinforced biopolymer-based composites, we control the dispersion of the particles through the addition of a secondary polymer with high affinity to carbon black (CB) particles. The addition of a small amount of the secondary polymer induces the aggregation of CB particles beyond interfacial localization in a ternary composite. The aggregation and percolation network in poly(lactic acid) (PLA)-based ternary systems are investigated through a scaling analysis. According to rheological and geometric fractal analyses, the secondary polymer induces an aggregation of CB particles to form a percolation network because the induced-diffusion effect is stronger than the interaction between the particles, leading to a particle aggregate with a high-order structure. The modulus (G 0 ′ ) of the CB/PLA binary composite has a scaling relationship with the particle volume fraction (φ), G 0 ′ ∼ φ 1.92 (φ c , G ′ = 2.2 %). In the CB/PLA binary composite, the addition of a small amount of secondary polymer having strong chemical affinity to CB changes the scaling relationship significantly depending on the type of the secondary polymer (G 0 ′ ∼ φ 2.17 ∼ 2.53 ) with a lower percolation threshold (φ c , G ′ ) (φ c , G ′ = 0.96 %). It also enhances the electrical percolation (electrical conductivity, σ d c ∼ φ 3.23 ∼ 3.78 φ c , σ = 1.50 % − 1.86 % for ternary composites) with an increase in the exponent and a lower percolation threshold (φ c , σ ). The secondary polymer serves as a binder and causes the aggregates to be well dispersed, leading to a brittle-ductile transition and significant enhancement of the ductility. [ABSTRACT FROM AUTHOR]

In this study, poly(lactic acid) (PLA) is toughened by blending with natural rubber (NR). In order to induce additional toughening, the hybrid of two clays (natural clay (CNa+) and organically‐modified clay (C20A)) showing different localization in the blend is added to the PLA/NR 70/30 blend. For the blend with CNa+ localized in the PLA matrix, linear viscoelastic response (G′, G″) of the blend does slightly change with the decreased drop size or the coarsening of NR as CNa+ content increases. On the other hand, the addition of C20A brings notable rheological response with a significant change in morphology from co‐continuous structure (< 0.5 wt%) to compatibilized morphology (> 0.5 wt%). With a small amount of clay (0.75 wt%) where G′ and G″ crossover, the mixture of two clays (CNa+/C20A 0.3/0.45 wt%) inducing different morphologies to the blend causes a synergistic effect to form cocontinuous structure, leading to a synergistic elongation at break over 100%. This study shows that the addition of a small amount of clays less than 1 wt% can induce toughening of PLA/NR by morphology control of well‐designed particle localization. Also, linear viscoelasticity analysis is useful to detect a subtle change in blend morphology. [ABSTRACT FROM AUTHOR]

The electrical conductivity of ternary composites composed of a biopolymer blend with conductive particles (carbon black [CB]) is induced by the control of particle dispersion in the dispersed phase. If the CB particles have higher chemical affinity for the secondary phase (poly(caprolactone) [PCL]]) than the matrix (poly(lactic acid) [PLA]), especially as the concentration of the PCL phase decreases significantly to 4 wt%, the PCL phase induces the aggregation of CB particles beyond the selective localization, resulting in a shift of the particle percolation threshold to a lower concentration of particles (2.44 wt% CB). Moreover, the mixing ratio between the CB and the PCL phase significantly affects the formation of percolation of particles. When the mixing ratio of CB to PCL is equivalent (1:1), the ternary composite shows high electrical DC conductivity above 1 S/m with 10 wt% CB. The addition of a small amount of PCL induces the formation of particle aggregates with a high aspect ratio, providing more electron transfer pathways due to the multiple points of contact between the particle aggregates (power law scaling exponent of the composites ~2.14). Meanwhile, a binary composite (PLA/CB) never reaches high electrical conductivity of 1 S/m and even requires a greater concentration of CB (13 wt% CB for 10−3 S/m) to accomplish electron transfer because of the small aspect ratio of randomly dispersed particle aggregates (power law scaling exponent ~3.20). [ABSTRACT FROM AUTHOR]

In this study, poly(lactic acid) (PLA) is blended with natural rubber (NR) to improve a brittleness of PLA. Surface‐modified inorganic particles of calcium carbonate are incorporated to this polymer blend not only to mitigate the strength loss but also to induce toughening of the PLA. Specifically, in order to toughen the PLA, the influence of NR as a second phase on the particle dispersion characteristics is examined while varying the concentration of the particles or the second phase and undertaking rheological measurements and morphological observations. With the surface‐modified particles, the secondary phase was found to induce the aggregation of particles along the interface as opposed to creating a homogeneous dispersion of particles. In addition, it enhanced the particle percolation throughout the blend and improved the brittleness of the PLA. With regard to elongation at break of the PLA/particle, it was increased from 12 to 86% by the addition of NR (19 vol%). On the other hand, for a composite with uncoated particles, the second phase of NR did not induce particle aggregation. Elongation at break of this composite decreased as the particle concentration increased. POLYM. COMPOS., 40:4023–4032, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Clay particles (montmorillonite) induced stabilization in oil–water emulsions in different ways depending on their localization. Regardless of the localization, an emulsion showed a plateau in G′ and a local peak in G″ under small strain. During large-amplitude shear tests, an emulsion with clays selectively localized in the oil phase demonstrated local minima in G′ and G″ while an emulsion with an interfacial layer of clays showed a strain thinning behavior. The strain thinning behavior of the emulsion substantially occurred due to strain thinning behavior of the viscoelastic interfacial layer. The interfacial layer of particles of high concentration provided higher yield stress and shear thinning in the emulsion because it had a higher modulus and rapid thinning behavior compared to a layer of particles of low concentration. Using interfacial rheology, the bulk rheological response of the emulsion could be linked to the mechanical properties of the interfacial layer. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of clay particles on the coalescence of oil droplets, a typical head-on experiment was carried out. The coalescence of two oil drops containing clay was observed depending on the clay types. The influence of clay on the coalescence of oil droplets is successfully distinguished from the coalescence of pure oil droplets. When two oil droplets make direct contact, pure oil droplets never coalesce due to a lack of compressive stress against the colloidal force. Meanwhile, when oil drops with hydrophobic types of clay make contact, the oil drops quickly merge despite the fact that there is no change in colloidal interaction and capillary force relative to those of the pure oil droplet. Hydrophobic clay particles in the oil drop are able to pierce through the medium film to enhance the coalescence because particles in the oil drop have also hydrophobic attraction with the other oil drop. With the natural clay, the coalescence of two oil droplets is still enhanced despite the slight delay due to the balanced wetting behavior of the natural clay between the oil and the water. Thus, regardless of the wetting behavior of clay between oil and water, clay can enhance the coalescence of the oil drops by transporting particles through the medium between two oil droplets when they come into contact. [ABSTRACT FROM AUTHOR]

ABSTRACT: In order to investigate the influence of mixing flow condition on particle generation, poly(lactic acid) (PLA) particles were fabricated at different mixing velocities (10–50 m s−1) using a nanomixer through either the nanoprecipitation or the emulsion diffusion method. With a nanomixer (Couette–Taylor mixing geometry modified with cavitations), particles became smaller as the mixing velocity increased as long as the temperature was kept below the glass transition temperature (Tg) of PLA. Even in the emulsion diffusion method, it led to the formation of PLA nanoparticles in a short emulsification time (∼1 min) and the mean diameter was less than 100 nm with deviation less than 10% (100 nm ± 10%). However, at high mixing velocity, the particle size was rapidly increased which was enhanced as mixing time increased. Dissipation rapidly increased the temperature inside the mixer above Tg of PLA, which caused smaller particles to agglomerate to form larger micron‐sized particles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46199. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effects of cation exchange capacity (CEC) and location of clay nanoplatelets on the structure and performance of clay-embedded polyelectrolyte multilayer (c-PEM) membranes for wastewater effluent treatment. Two kinds of clay nanoplatelets, montmorillonite and kaolin, were deposited on the ultrafiltration membrane by employing layer-by-layer (LbL) assembly with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). Negatively charged clay platelets or PAA interacted with positively charged PAH to form a bilayer in the c-PEM membrane. The filtration effect of clay platelets was successively distinguished from PEM by reducing the number of (PAH/PAA) bilayers from four to one, while keeping the clay layer at the outermost layer of assembly. When the clay platelets were deposited only as the outermost layer of the LbL multilayers, the c-PEM membrane with one clay layer and one bilayer assembly showed significant flux barrier and fouling resistance. Clay platelets as the outermost layer physically increased the flow path length and decreased the number of pores, as well as effectively blocked the organic contaminants in the wastewater. Meanwhile, when the clay layer was embedded in the middle of the PEM, the synergistic effect of clay platelets and PEM for wastewater treatment was difficult to obtain because the presence of clay platelets defected the buildup of fully interdigitated c-PEM and the adsorption of clay platelets was decreased. For the clays having low CEC, a higher number of LbL multilayers were required to deposit the clay platelets and to improve the performance of membrane. The high CEC clays (montmorillonite) turned out to be better than the low CEC clays (kaolin) in the structure and performance of the c-PEM membrane for wastewater effluent treatment. [ABSTRACT FROM PUBLISHER]

We fabricated a carbon nanotube (CNT)/adhesive polydimethylsiloxane (aPDMS) composite-based dry electroencephalograph (EEG) electrode for capacitive measuring of EEG signals. As research related to brain–computer interface applications has advanced, the presence of hairs on a patient's scalp has continued to present an obstacle to recorder EEG signals using dry electrodes. The CNT/aPDMS electrode developed here is elastic, highly conductive, self-adhesive, and capable of making conformal contact with and attaching to a hairy scalp. Onto the conductive disk, hundreds of conductive pillars coated with Parylene C insulation layer were fabricated. A CNT/aPDMS layer was attached on the disk to transmit biosignals to the pillar. The top of disk was designed to be solderable, which enables the electrode to connect with a variety of commercial EEG acquisition systems. The mechanical and electrical characteristics of the electrode were tested, and the performances of the electrodes were evaluated by recording EEGs, including alpha rhythms, auditory-evoked potentials, and steady-state visually-evoked potentials. The results revealed that the electrode provided a high signal-to-noise ratio with good tolerance for motion. Almost no leakage current was observed. Although preamplifiers with ultrahigh input impedance have been essential for previous capacitive electrodes, the EEGs were recorded here by directly connecting a commercially available EEG acquisition system to the electrode to yield high-quality signals comparable to those obtained using conventional wet electrodes. [ABSTRACT FROM PUBLISHER]

To investigate whether nanoclay particles vary with the interfacial tension of oil-in water emulsion, interfacial tension is measured using dynamic drop volume method. From the critical volume of a single droplet at the moment of detachment, interfacial tension is calculated based on the force balance between gravity force and capillary force. The interfacial tension of a droplet is reduced by the addition of nanoclay and the interfacial tension reduction is further varied depending on nanoclay type. The addition of hydrophilic nanoclay particles (5000 ppm) in an oil drop reduces the interfacial tension from 31.4 to 19.6 mN/m by interfacial localization. In the case of organically modified nanoclay (5000 ppm), interfacial tension is only slightly reduced from 31.4 to 26 mN/m. This study shows that nanoclay effectively reduces the interfacial tension of a droplet when nanoclay is located at the interface. [ABSTRACT FROM PUBLISHER]

In this study, the nonlinear response of polymer nanocomposites under large amplitude oscillatory shear (LAOS) flow was investigated. We first investigated polycaprolactone (PCL)/multiwall nanotube (MWNT) composites under LAOS flow using different analyzing methods including Lissajous plot analysis, stress decomposition, and Fourier transform rheology (FT-rheology). The nonlinear parameter Q (≡I3/1/γ02) was obtained from the FT-rheology as a function of strain amplitude, and the zero-strain nonlinearity Q0 (≡limγ0→0Q) was also calculated. We compared the linear and nonlinear viscoelastic properties as we increase MWNT concentration ([lowercase_phi_synonym]). It was found that the zero-strain nonlinearity (Q0) was more sensitive to detect the effect of MWNT concentration than the linear viscoelastic properties. We also investigated the effect of particle shape on nonlinear viscoelastic properties of the polymer composites containing particles of different shape, e.g., PCL/MWNT (one-dimensional thread shape), PCL/organomodified montmorillonite (two-dimensional plate shape), PCL/precipitated calcium carbonate (three-dimensional cubic shape). Furthermore, we introduced a new parameter, nonlinear-linear viscoelastic ratio, to compare linear and nonlinear viscoelasticity. [ABSTRACT FROM AUTHOR]

We fabricated a carbon nanotube (CNT)/ polydimethylsiloxane (PDMS) composite-based dry ECG electrode that can be readily connected to conventional ECG devices, and showed its long-term wearable monitoring capability and robustness to motion and sweat. While the dispersion of CNTs in PDMS is challenging, we optimized the process to disperse untreated CNTs within PDMS by mechanical force only. The electrical and mechanical characteristics of the CNT/PDMS electrode were tested according to the concentration of CNTs and its thickness. The performances of ECG electrodes were evaluated by using 36 types of electrodes which were fabricated with different concentrations of CNTs, and with a differing diameter and thickness. The ECG signals were obtained by using electrodes of diverse sizes to observe the effects of motion and sweat, and the proposed electrode was shown to be robust to both factors. The CNT concentration and diameter of the electrodes were critical parameters in obtaining high-quality ECG signals. The electrode was shown to be biocompatible from the cytotoxicity test. A seven-day continuous wearability test showed that the quality of the ECG signal did not degrade over time, and skin reactions such as itching or erythema were not observed. This electrode could be used for the long-term measurement of other electrical biosignals for ubiquitous health monitoring including EMG, EEG, and ERG. [ABSTRACT FROM PUBLISHER]

The article offers information on a study which explored clay migration and its localization in multiphase blend nanocomposite systems during the emergence of blend morphology to further determine how a hydrodynamic stress and chemical affinity between the polymer and clay influence them. Methods utilized include scanning electron microscopy (SEM) and transmission electron microscopy (TEM), among others. A detailed discussion on the research findings is given.

A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 × 10−2 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeter~aggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G′), high Young's modulus, high dielectric loss (ε″), and negative–positive switching of dielectric constant at high frequency (of 103 Hz) of composite. [ABSTRACT FROM AUTHOR]