Effect of liquid volume fraction and shear rate on rheological properties and microstructure formation in ternary particle/oil/water dispersion systems under shear flow: two-dimensional direct numerical simulation.

We numerically studied the rheological properties and microstructure formation under shear flow in a ternary particle/oil/water dispersion system. Our numerical simulation method was based on a phase-field model for capturing a free interface, the discrete element method for tracking particle motion, the immersed boundary method for calculating fluid-particle interactions, and a wetting model that assigns an order parameter to the solid surface according to the wettability. The effects of the water-phase volume fraction and shear rate on the microstructure and apparent viscosity were investigated. When the water-phase volume fraction was low, a pendular state was formed, and with an increase in the water-phase volume fraction, the state transitioned into a co-continuous state and a Pickering emulsion. This change in the microstructure state is qualitatively consistent with the results of previous experimental studies. In the pendular state, the viscosity increased with an increase in the water-phase volume fraction. This was due to the development of a network structure connected by liquid bridges, and the increase in the coordination number was quantitatively confirmed. In the case of the pendular state, significant shear thinning was observed, but in the case of the Pickering emulsion, no significant shear thinning was observed. It is concluded that this is due to the difference in the manner in which the microstructure changes with the shear rate. This is the first study to numerically demonstrate the microstructure formation of a ternary dispersion under shear flow and its correlation with the apparent viscosity.

High-Resolution Numerical Simulation of Microfiltration of Oil-in-Water Emulsion Permeating through a Realistic Membrane Microporous Structure Generated by Focused Ion Beam Scanning Electron Microscopy Images.

Owing to the limitations of visualization techniques in experimental studies and low-resolution numerical models based on computational fluid dynamics (CFD), the detailed behavior of oil droplets during microfiltration is not well understood. Hence, a high-resolution CFD model based on an in-house direct numerical simulation (DNS) code was constructed in this study to analyze the detailed dynamics of an oil-in-water (O/W) emulsion using a microfiltration membrane. The realistic microporous structure of commercial ceramic microfiltration membranes (mullite and α-alumina membranes) was obtained using an image processing technique based on focused ion beam scanning electron microscopy (FIB-SEM). Numerical simulations of microfiltration of O/W emulsions on the membrane microstructure obtained by FIB-SEM were performed, and the effects of different parameters, including contact angle, transmembrane pressure, and membrane microporous structure, on filtration performance were studied. Droplet deformation had a strong impact on filtration behavior because coalesced droplets with diameters larger than the pore diameter permeated the membrane pores. The permeability, oil hold-up fraction inside the pores, and rejection were considerably influenced by the contact angle, while the transmembrane pressure had a little impact on the permeability and oil hold-up fraction. The membrane structure, especially the pore size distribution, also had a significant effect on the microfiltration behavior and performance.

Phase-Field Simulation of the Coalescence of Droplets Permeating through a Fibrous Filter Obtained from X-ray Computed Tomography Images: Effect of the Filter Microstructure.

We numerically study the droplet coalescence of an oil-in-water (O/W) emulsion permeating through a fibrous filter. Our numerical simulation method is based on the phase-field model for capturing a free interface, the immersed boundary method used to calculate fluid-solid interactions, and the wetting model that assigns an order parameter to the solid surface according to the wettability. To represent realistic flow inside the filter during simulation, the voxel data obtained from X-ray computed tomography (CT) images of the filter microstructure are used in the simulation. The effects of the filter microstructure, such as fiber arrangement and orientation of the droplet coalescence, are investigated by using several filter domains. Our simulations demonstrate that the arrangement of closely attached fibers placed at the permeate-side surface enhances droplet coalescence. In addition, the parallel orientation of the fiber to the main flow direction suppresses droplet enlargement due to the coalescence but reduces the number of droplet passages without coalescence in the filter.

Micro-transfer patterning of dense nanoparticle layers: roles of rheology, adhesion and fracture in transfer dynamics.

Liquid inks deposited on substrates undergo spreading, coalescence, dewetting and subsequent drying kinetics, which limit the controllability of the cross-sectional shape and resolution of the printed patterns. By contrast, when the ink layers are previously semidried (highly-concentrated) and patterned on a polydimethylsiloxane sheet, single-micrometer features are resolved. Here we present the rheological, fracture and adhesive properties of semidried nanoparticle dispersion ink layers, which optimize the patterning of reverse offset printing with 5 µm spatial resolution. Under the appropriate patterning conditions, when the volume fraction φ of the particles in the semidried layers was approximately 46 v/v%, the layer elasticity was dominant in the linear viscoelastic region and a Burgers-type creeping property appeared. Under tensile strain, the semidried layers suddenly fractured at the sites of patterns with sharply defined sidewalls. In the semidried thin layers dominated by viscosity (lower φ), the pattern edges were degraded owing to local transfer instability and possible subsequent spreading. Over-drying reduced the adhesiveness of the ink layers, implying an upper limit of φ for successful patterning. The characteristics of semidried inks contribute to establishing a versatile ink-formulation scheme of various functional nanomaterials for high-resolution printed applications.

Mechanisms of Adhesive Micropatterning of Functional Colloid Thin Layers.

Thin-film layers of nanoparticles exhibit mechanical fragility that depends on their interactions. Balancing the cohesive force of particles with their interfacial adhesion to a substrate enables the selective transfer of micrometer-scale layer features. Here, the versatility of this adhesion-based transfer approach from poly(dimethylsiloxane) (PDMS) is presented by demonstrating micropatterns of various functional nanoparticulate materials, including Ag, Cu, indium tin oxide, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and dielectric silica. With the attachment of the Johnson-Kendall-Roberts interaction to a simple strain model of particle layers during the patterning process, the patterning criteria for successful printing at both macroscale and nanoscale levels are deduced. Discrete element modeling analysis was used to validate the scaling laws and to highlight the fracture modes of particle layers during the patterning process. In particular, the balance among cohesive forces in the tensile direction and in the shear direction and the adhesion force at the layer-PDMS interface mainly regulates the patterning quality of adhesion patterning.

Host manipulation by an ichneumonid spider ectoparasitoid that takes advantage of preprogrammed web-building behaviour for its cocoon protection.

Host manipulation by parasites and parasitoids is a fascinating phenomenon within evolutionary ecology, representing an example of extended phenotypes. To elucidate the mechanism of host manipulation, revealing the origin and function of the invoked actions is essential. Our study focused on the ichneumonid spider ectoparasitoid Reclinervellus nielseni, which turns its host spider (Cyclosa argenteoalba) into a drugged navvy, to modify the web structure into a more persistent cocoon web so that the wasp can pupate safely on this web after the spider's death. We focused on whether the cocoon web originated from the resting web that an unparasitized spider builds before moulting, by comparing web structures, building behaviour and silk spectral/tensile properties. We found that both resting and cocoon webs have reduced numbers of radii decorated by numerous fibrous threads and specific decorating behaviour was identical, suggesting that the cocoon web in this system has roots in the innate resting web and ecdysteroid-related components may be responsible for the manipulation. We also show that these decorations reflect UV light, possibly to prevent damage by flying web-destroyers such as birds or large insects. Furthermore, the tensile test revealed that the spider is induced to repeat certain behavioural steps in addition to resting web construction so that many more threads are laid down for web reinforcement.

Permeation of concentrated oil-in-water emulsions through a membrane pore: numerical simulation using a coupled level set and the volume-of-fluid method.

In this paper, we investigated the demulsification behavior of oil-in-water (O/W) emulsions during membrane permeation in the oil-water separation process using a numerical simulation approach. To accurately deal with the large deformation of the oil-water interface by coalescence and wetting, and to estimate the volume of the coalesced oil droplet, the coupled level set and volume-of-fluid method was used as the interface capturing method. We applied the simulation model to the permeation of O/W emulsions through a membrane pore, and then investigated the effects of the wettability of the membrane surface, filtration flux, and pore size on the demulsification efficiency. The results showed that oil droplets were likely to coalesce on the outlet membrane surface. High wettability on the membrane surface and low fluid velocity inside the pore increased the demulsification efficiency. This is the first work to numerically simulate the demulsification behavior of emulsions through membranes in the oil-water separation process.

Solidification Behavior of Polymer Solution during Membrane Preparation by Thermally Induced Phase Separation.

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed on a stage, is moved upwards and the surface of the polymer solution contacts a sphere attached to the tip of a needle. The displacement of a blade spring attached to the needle is then measured by a laser displacement sensor. Different phase separation modes, such as liquid-liquid (L-L) phase separation and solid-liquid (S-L) phase separation (polymer crystallization) were investigated. In the case of S-L phase separation, the stiffness of the solution surface began to increase significantly just before termination of crystallization. In contrast, L-L phase separation delayed solidification of the solution. This was because mutual contact of the spherulites was obstructed by droplets of polymer-lean phase formed during L-L phase separation. Thus, the solidification rate was slower for the L-L phase separation system than for the S-L phase separation system.

Amino acid ionic liquid-based facilitated transport membranes for CO2 separation.

Supported liquid membranes incorporating amino acid ionic liquids remarkably facilitate CO(2) permeation under dry and low humid conditions.