Pendular State Research Articles

Structure-rheological relationship of capillary protein oleogels: The role of particle wettability

The design of well-structured food colloids and functional interfaces provides new perspectives for developing healthy and sustainable foods in the future. In this study, we show how particle wettability affects the structural features and rheological properties of capillary oleogels, which are formed using colloidal zein particles with varying wettability from 77.8° to 106.7° as building blocks, creating a space-spanning network in oil via capillary attraction. Confocal microscopy was utilized to image the structural heterogeneities in the oleogels caused by variations in particle wettability, while rheological scaling analysis was used to describe the multiscale structural contributions of protein particles within the network. These changes in particle wettability led to large-scale structural heterogeneity and differences in the mechanical strength of the oleogels. As particle wettability increases, both structural homogeneity and mechanical strength improve, forming adjustable network structures from the capillary state (θ > 90°) to the pendular state (θ < 90°). The fractal dimensions of these oleogels also increases, suggesting that the fractal structural features within both inter- and intra-floc clusters become more densely packed. The results indicate that the structural features and mechanical properties of capillary oleogels can be tailored by modifying the wettability of protein particles to suit specific applications.

Formation of small-granule starch oleogels based on capillary force: Impact of starch surface lipids on lubrication performance

Starch granule oleogels were prepared and their rheological properties were precisely tuned using the capillary bridging phenomenon. The addition of a small amount of water to an oily suspension of starch granules can lead to starch granule bridging and network formation, transitioning it from a fluid-like to a gel-like state. Small-granule starches with high specific surface area and interfacial area exhibited a greater number of liquid bridges and stronger starch granules interactions, making them more prone to forming structurally stable oleogel systems. By increasing the content of water and starch granule, the starch oleogels exhibited three distinct structural states: pendular state (water ≤ 3.28 %, starch ≤ 17.85 %), pendular bridging network (water: 4.92 %, starch: 24.59 %), and capillary aggregates (water ≥ 6.56 %, starch > 24.59 %). Furthermore, the influence of starch granule surface lipids on the lubrication performance of the oleogel system was investigated. Surface roughness increased after extraction of surface lipids, and the friction coefficient also showed a significant increase. Overall, capillary suspension system can potentially be used to design novel fat food products, and our findings have established the correlation between starch granule surface properties and sensory perception in food, providing valuable insights for adjusting the oral processing characteristics of food.

Capillary force-driven formation of native starch granule oleogels for 3D printing

3D printing has extremely high requirements for the design of food matrices with suitable rheological properties. Starch exhibits considerable potential as a material for 3D printing. However, there is limited research available on the direct fabrication of oleogels using starch granules as building blocks. In this study, we developed a simple approach to fabricate plant-based oleogels as edible 3D printable materials by exploiting capillary forces between starch granules. When a small amount of water (less than 5 wt%) was added to starch granules dispersed in an oil phase, a pendular bridging network was formed between the starch granules. The rheological properties of the starch-oil suspension were significantly changed, transitioning it from a fluid-like to a gel-like state. The rheological properties of the oleogel could be altered by varying the starch granule volume fraction, the amount of water added, the structure of starch granules, and the oil-water interfacial tension. Confocal laser microscopy imaging demonstrated that starch granule oleogels exhibit three distinct structural states: pendular state, pendular bridge network, and capillary aggregation. Furthermore, the presence of water was identified as a liquid bridge between starch granules. Additionally, starch granule oleogels exhibited excellent thermal stability and freeze-thaw stability. Overall, this approach enhances the feasibility of preparing starch oleogels and provides valuable insights for the personalized 3D printing of oleogels.

Impact of drying-wetting cycles on the small strain behaviour of compacted clay

Small strain shear modulus (Gmax) is an important parameter for assessing the performance of compacted soils that underlie typical transport infrastructure assets such as railway tracks. This is particularly important when considering changes in climate patterns, which are expected to yield larger seasonal soil-atmosphere moisture fluctuations. This in turn results in the progressive variation of the small strain properties of compacted soils during their service life (i.e. drying and wetting). In this study, the small strain shear behaviour was evaluated for an intermediate plasticity clay (i.e. kaolin) in a series of drying and wetting cycles. Four different dying and wetting boundaries were considered to explore a wide range of moisture amplitudes during 10 drying-wetting cycles. Drying and wetting was controlled using gravimetric water content in order to mimic realistic field conditions typically observed at substructure level. An ultrasonic pulse transmission method was used to capture the change in small strain stiffness and volume at discrete points during the drying-wetting cycles. The results reveal clear distinctions in behaviour for all four boundaries considered, with wetting boundaries having the greatest influence on behaviour. In this instance, specimens brought to full saturation during wetting exhibited an increase in the small strain shear modulus during progressive drying-wetting cycles. However, a reduction was observed when the wetting boundary was restricted to the compacted state. Measured volume changes were also in agreement with these findings, however there was some evidence of volume increase when drying to residual conditions. The results suggest that this is associated with the formation of the partial pendular state where a loss of capillary contacts between particles occurs. Furthermore, when all data for 10 drying-wetting cycles is plotted in the e-Gmax space, a linear relationship is observed for different constant water content levels. Remarkably, this trend is shown to be independent of the boundary conditions considered in this study or number of drying-wetting cycles.

All-optical control of pendular qubit states with nonresonant two-color laser pulses

Practical methodologies for qubit controls are established by two prerequisites, i.e., preparation of a well-defined initial quantum state and coherent control of that quantum state. Here we propose a quantum control method, realized by irradiating nonresonant nanosecond two-color (ω and 2ω) laser pulses to molecules in the pendular (field-dressed) ground state. The two-color field nonadiabatically splits the initial pendular ground state |tilde{0},tilde{0}rangle to a superposition state of |tilde{0},tilde{0}rangle and |tilde{1},tilde{0}rangle , whose relative probability amplitudes can be controlled by the peak intensity of one wavelength component (ω) while the peak intensity of the other component (2ω) is fixed. The splitting of the quantum paths is evidenced by observing degrees of orientation of ground-state-selected OCS molecules by the velocity map imaging technique. This quantum control method is highly advantageous because any polar molecule can be controlled regardless of the molecular energy structures.

Unchannelized collapse of wet granular columns in the pendular state: Dynamics and morphology scaling

Different regimes are observed in the unchannelized collapse of wet granular columns. The initial aspect ratio of the column and the dimensionless macroscopic cohesion, which contains the particle size and the water content, are two relevant variables in the formation of different regimes and in the collapse dynamics. Generalized scaling laws are developed to characterize the deposit of wet collapsing material for which morphological quantities may be conveniently expressed by adding variations caused by the cohesion effect to the results of dry granular material.

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (CSC) region (CSC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower CSC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at CSC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at CSC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at CSC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at CSC = 85 wt.% in rheological measurements.

Microstructure and rheological behavior of capillary suspension prepared with plate-shaped particles

Capillary suspension is a unique strategy to prepare high-yield-stress fluids, in which particle-to-particle interaction caused by capillary bridges results in a substantial change in fluidity. The capillary suspension with plate-shaped particles have recently been considered useful in various applications, including Li-battery electrodes and conductive elastomers, due to their large specific surface area, which results in a rigid sample-spanning capillary network. However, there is a poor understanding of the relationship between the dimensions of plate-shaped particles and the fluidity of the capillary suspensions.In this study, the yield stress of the capillary suspension prepared with plate-shaped particles of various diameters and thicknesses was investigated to establish a correlation equation. Additionally, the conformation of the particles in the capillary suspension was also determined by microscopic analysis. As a result, it was discovered that when the secondary fluid is added, plate-shaped particles form a laminated structure supported by capillary bridges generated between their largest faces (pendular state). Furthermore, rheological measurements revealed that the yield stress of the capillary suspension was determined by the number density of particles, cross-sectional area of the particle, and volume fraction of the secondary fluid. Based on these findings, we established a power-law-based correlation equation that accurately predicted (20% error at most) the yield stress of the capillary suspension regardless of the size of the particles.

Experimental study on the collapse of wet granular column in the pendular state

The collapse of wet granular columns in the pendular state is experimentally investigated, where the effects of the initial aspect ratio, the water content, and the particle size on the dynamics and the deposit of collapsing material are mainly considered. Three typical regimes are observed in our experiments, and a phase diagram is then proposed for describing different flow states. Furthermore, the velocity field of collapsing material exhibits distinct evolving features in two collapse regimes, and the transition between different regimes is also discussed, where the capillary effect plays different roles. On this basis, the influence of the water content on the flow duration and the final deposit morphology of collapsing material are further analyzed. Finally, a simplified theoretical model is put forward, which has been proved to be able to describe the dependence of the runout distance on the particle diameter in the collapse of wet granular material.

Transitioning from the funicular to the pendular regime in granular soils

The simulation of granular soils partially saturated by two immiscible fluids – say, water and air – has long been restricted to the so-called ‘pendular regime’, in which the wetting phase (i.e. water in air/water systems) is discontinuous and its presence is restricted to bridges connecting grain pairs. In this work the pendular model is combined with the recently developed two-phase pore-scale finite volumes (2PFV) method for the first time in order to simulate complete drainage from a saturated state to a residual pendular state. The contribution of pendular bridges in terms of water retention and induced internal stress is examined. It is shown that although the presence of a bridge does not significantly affect the soil water retention curve, its induced stress indeed plays a major role in the capillary effects for low saturation (lower than 0·10).

Navigating Social Spaces: Armed Mobilization and Circular Return in Eastern DR Congo

AbstractThis article discusses the social mobility of combatants and introduces the notion of circular return to explain their pendular state of movement between civilian and combatant life. This phenomenon is widely observed in eastern Democratic Republic of Congo (DRC), where Congolese youth have been going in and out of armed groups for several decades now. While the notion of circular return has its origins in migration and refugee studies, we show that it also serves as a useful lens to understand the navigation capacity between different social spaces of combatants and to describe and understand processes of incessant armed mobilization and demobilization. In conceptualizing these processes as forms of circular return, we want to move beyond the remobilization discourse, which is too often connected to an assumed failure of disarmament, demobilization, and reintegration processes. We argue that this discourse tends to ignore combatants’ agency and larger processes of socialization and social rupture as part of armed mobilization.

Semiphenomenological model to predict hardening of solid–liquid–liquid systems by liquid bridges

In this study, we developed two semiphenomenological models to quantitatively predict the rheological properties of capillary suspensions. These models can be used to estimate the critical volume fraction of an additional immiscible fluid above which liquid bridges have formed between all neighboring particles, causing gelation. The models can also be used to estimate the numerical value of the yield stress. This model was derived from the mass balance between the net volume of the liquid bridge and the volume fraction of the secondary fluid assuming monodisperse particles and a cylindrical liquid bridge. The yield stress was constructed based on Rumpf’s equation. The calculation results demonstrated good agreement with the experimental data. We also used the developed model to investigate the effect of particle size on the yield stress. This model qualitatively described the experimental data and reference data, and revealed the mechanism of the particle size dependence of the yield stress. The model applies to capillary suspensions in the pendular state.

Rheology and microstructure of unsaturated wet granular materials: Experiments and simulations

When dealing with unsaturated wet granular materials, a fundamental question is: What is the effect of capillary cohesion on the bulk flow and yield behavior? We investigate the dense-flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesive, spherical particles. Dense shear flows of dry, cohesionless granular materials exhibit three regimes: Quasistatic, inertial, and intermediate [B. Andreotti et al., Contemp. Phys. 55, 151–152 (2013)]. Herewith, we show that the quasistatic and the intermediate regimes persist for unsaturated materials and that the rheology is essentially described by two dimensionless numbers: The reduced pressure P* comparing the cohesive to confining forces and the inertial number I, for a wide range of liquid content. This is consistent with recent numerical simulations [S. Khamseh et al., Phys. Rev. E 92, 022201 (2015)]. Finally, we measure the effective friction coefficient and the solid fraction variation throughout the wet bed. From this, we show that, in the quasistatic regime, the Mohr–Coulomb yield criterion is a good approximation for large enough P*. The experimental results agree quantitatively with the numerical simulation ones, provided the intergranular friction coefficient μ is set to its physical value identified from dry material rheology [M. Badetti et al., Eur. Phys. J. E 41, 68 (2018)]. To directly and quantitatively determine what happens inside the sheared granular bed, x-ray tomography measurements are carried out in a custom-made setup that enables imaging of a wet granular material after different shear histories. For the explored range of liquid content, samples remain homogeneous but exhibit some complex microscopic morphologies far from simple capillary bridges. From the x-ray microtomographic images, we can clearly distinguish liquid capillary bridges and liquid clusters by their morphologies. We see that the total number of capillary bridges decreases when one increases the liquid content and interestingly increases, at the expense of other morphologies, when we increase the shear strain. This explains the concordance between the experimental and numerical measurements since the numerical model is restricted to the pendular state, for which the liquid phase is completely discontinuous and no coalescence occurs between liquid bridges.

Suppression of MIF-induced neuronal apoptosis may underlie the therapeutic effects of effective components of Fufang Danshen in the treatment of Alzheimer's disease.

Fufang Danshen (FFDS or Compound Danshen) consists of three Chinese herbs Danshen (Salviae miltiorrhizae radix et rhizome), Sanqi (Notoginseng radix et rhizome) and Tianranbingpian (Borneolum, or D-borneol), which has been show to significantly improve the function of the nervous system and brain metabolism. In this study we explored the possible mechanisms underlying the therapeutic effects of the combination of the effective components of FFDS (Tan IIA, NG-R1 and Borneol) in the treatment of Alzheimer's disease (AD) based on network pharmacology. We firstly constructed AD-related FFDS component protein interaction networks, and revealed that macrophage migration inhibitory factor (MIF) might regulate neuronal apoptosis through Bad in the progression of AD. Then we investigated the apoptosis-inducing effects of MIF and the impact of the effective components of FFDS in human neuroblastoma SH-SY5Y cells. We observed the characteristics of a "Pendular state" of MIF, where MIF (8 ng/mL) increased the ratio of p-Bad/Bad by activating Akt and the IKKα/β signaling pathway to assure cell survival, whereas MIF (50 ng/mL) up-regulated the expression of Bad to trigger apoptosis of SH-SY5Y cells. MIF displayed neurotoxicity similar to Aβ1-42, which was associated with the MIF-induced increased expression of Bad. Application of the FFDS composite solution significantly decreased the expression levels of Bad, suppressed MIF-induced apoptosis in SH-SY5Y cells. In a D-galactose- and AlCl3-induced AD mouse model, administration of the FFDS composite solution significantly improved the learning and memory, as well as neuronal morphology, and decreased the serum levels of INF-γ. Therefore, the FFDS composite solution exerts neuroprotective effects through down-regulating the level of Bad stimulated by MIF.

Electric Field Effect on Condensed-Phase Molecular Systems. VI. Field-Driven Orientation of Hydrogen Chloride in an Argon Matrix.

The orientation state of hydrogen chloride (HCl) molecules in a solid argon matrix was reversibly controlled by applying an external electric field of up to 4 × 108 V·m-1 using the ice film capacitor method. The rovibrational transitions of the field-oriented HCl were measured by reflection absorption infrared spectroscopy with p-polarized light. Upon application of the external field, free rotation of HCl inside the matrix gradually changed to perturbed rotation and then to a pendular state harmonically bound in the Stark potential well. Further increase in the field strength increased the degree of dipole alignment along the field direction, approaching an asymptotically perfect orientation of the molecules with an average tilt angle of <30° at a field strength above 1 × 108 V·m-1.

A micro–macro investigation of the capillary strengthening effect in wet granular materials

Wet granular materials are three-dimensionally simulated by the discrete element method with water bridges incorporated between particles. The water bridges are simplified as toroidal shapes, and the matric suction is constantly maintained in the material. A comparison with experimental tests in the literature indicates that the toroidal shape approximation may be one of the best choices with high practicability and decent accuracy. Mechanical behaviours of wet granular materials are studied by triaxial tests. Effects of particle size distributions and void ratios are investigated systematically in this study. The hydraulic limit of the pendular state is also discussed. It gives the capillary cohesion function which is not only determined by the degree of saturation but also positively correlated to relative density and particle size polydispersity and inversely proportional to mean particle size. Furthermore, the capillary strengthening effect is also analysed microscopically in aid of the Stress–Force–Fabric relationship, mainly in fabric anisotropy, coordination number and stress transmission pattern, which revealed the micro-mechanisms of the additional effective stress induced by capillary effect.

Rheology of particle/water/oil three-phase dispersions: Electrostatic vs. capillary bridge forces

HypothesisParticle/water/oil three-phase capillary suspensions possess the remarkable property to solidify upon the addition of minimal amount of the second (dispersed) liquid. The hardening of these suspensions is due to capillary bridges, which interconnect the particles (pendular state). Electrostatic repulsion across the oily phase, where Debye screening by electrolyte is missing, could also influence the hardness of these suspensions. ExperimentsWe present data for oil-continuous suspensions with aqueous capillary bridges between hydrophilic SiO2 particles at particle volume fractions 35–45%. The hardness is characterized by the yield stress Y for two different oils: mineral (hexadecane) and vegetable (soybean oil). Findings and modellingThe comparison of data for the “mirror” systems of water- and oil-continuous capillary suspensions shows that Y is lower for the oil-continuous ones. The theoretical model of yield stress is upgraded by including a contribution from electrostatic repulsion, which partially counterbalances the capillary-bridge attraction and renders the suspensions softer. The particle charge density determined from data fits is close to that obtained in experiments with monolayers from charged colloid particles at oil/water interfaces. The results could contribute for better understanding, quantitative prediction and control of the mechanical properties of solid/liquid/liquid capillary suspensions.

Effect of the particle size and the liquid content on the shear behaviour of wet granular material

The size of particle is a relevant parameter in the study of the granular material behaviour. For wet granular materials, it affects the capillary force and the number of liquid bridges. We present quantitative and qualitative investigations of the effect of the particle size on the steady-state shear behaviour of partially wet granular material. Two sizes of glass beads have been used: 12–40μm and 70–110μm in diameter and the shear behaviour was studied using an annular shear cell. The results show different regimes of the shear-normal stresses relationship depending on the particle size, with a general increase of the magnitude of the shear stress for a decrease in the particle size.Most studies of wet granular material behaviour have focused on the pendular state of saturation with liquid bridge formed between particles. In this study, the states of saturation are explored going up to completely filling the space between beads of 70–110μm. Different regimes are identified depending on the liquid fraction and the applied normal stress. A theoretical approach was used to estimate the tensile strength for the different states of saturation. An agreement between both experimental and theoretical data was observed and discussed.

Influence of mixing conditions on the rheological properties and structure of capillary suspensions

The rheological properties of a suspension can be dramatically altered by adding a small amount of a secondary fluid that is immiscible with the bulk liquid. These capillary suspensions exist either in the pendular state where the secondary fluid preferentially wets the particles or the capillary state where the bulk fluid is preferentially wetting. The yield stress, as well as storage and loss moduli, depends on the size and distribution of secondary phase droplets created during sample preparation. Enhanced droplet breakup leads to stronger sample structures. In capillary state systems, this can be achieved by increasing the mixing speed and time of turbulent mixing using a dissolver stirrer. In the pendular state, increased mixing speed also leads to better droplet breakup, but spherical agglomeration is favored at longer times decreasing the yield stress. Additional mixing with a ball mill is shown to be beneficial to sample strength. The influence of viscosity variance between the bulk and second fluid on the droplet breakup is excluded by performing experiments with viscosity-matched fluids. These experiments show that the capillary state competes with the formation of Pickering emulsion droplets and is often more difficult to achieve than the pendular state.

Enhanced conductivity induced by attractive capillary force in ternary conductive adhesive

Materials with advanced conductive properties are in high demand to fulfill the requirements of energy transport in many fields. Here, we present a simple, efficient yet low cost method to produce highly conductive polymer based composites at low filler concentration of 10 vol%. A particle-wetting fluid as a secondary fluid is introduced to bridge plate-shape silver particles within an epoxy base. The electrical and thermal conductivity dependence on network structure in ternary silver adhesive presenting strong capillary attraction was first reported. Both electrical and thermal conductivities are greatly enhanced by introducing the secondary fluid at a low particle volume fraction of 10%. A non-monotonic dependence of the conductivities on secondary fluid content was observed. The maximum electrical and thermal conductivities correspond to the formation of full pendular network and funicular network, respectively. Gradually increasing the secondary fluid content leads to a microstructure evolution from highly dispersed particles, weak gel network, full pendular network, funicular network and ultimately to compact capillary aggregates network. Such structural transition appears to result from a pendular bridge formation and bridges coalescence. Face-face configuration of plate-shaped silver particles was observed in the pendular state. Taking account of the highly non-spherical shape of silver flake, a bridging gelation model is proposed to explain the underlying mechanism of microstructure transition.