Suspensions Of Rods Research Articles

Role of particle orientational order during shear thickening in suspensions of colloidal rods.

Rheology of dense anisotropic colloidal suspensions often exhibits unsteady flow at constant imposed shear stress and/or shear rate. Using simultaneous high-resolution confocal microscopy and rheology, we find that the temporal behavior arises due to a strong coupling between shear flow and particle orientation. At smaller applied stresses, the orientation of rods fluctuates around the flow direction. A transition to an intermittent disordered state is observed at higher stresses when the angle between the flow and the rod orientation reaches a critical value. This disordered state is associated with transient drop in shear rate and an increase in viscosity. Simultaneous visualization of boundary stresses and orientation shows that the disordered regions lead to heterogeneous stresses and positive normal forces at the boundary, indicating the formation of systems spanning disordered particle contact networks.

Numerical investigation of dilute suspensions of rigid rods in power-law fluids

Polymer melts filled with rod-like particles like glass and carbon fibers have high practical importance. Here we numerically investigate the properties of power-law fluids filled with rigid rods of different aspect ratios. For that we compute the rheological coefficients of the transversely isotropic fluid (TIF) equation and compare our results with analytical models, specifically with the model of Souloumiac and Vincent (1998). Here we found, that the additional orientation dependence predicted by the model for the nonlinear regime is too strong and overpredicts our numerical results. The rheological coefficient A in the TIF equation depends on the thinning exponent of the power-law model and decreases strongly with increasing nonlinearity. In the Newtonian case we found that Batchelor (1970, 1971) considerably underpredicts our numerical results. Comparing our current data with previous results for spheroids we found, that there is no similarity between the rheological coefficients for these particles at large aspect ratios. We further analyze the angular and translational velocities of the particles. We found that there are negligible differences in the angular velocities between the Newtonian and power-law matrix fluids, especially for large aspect ratios. The translational velocities are exactly the same for the Newtonian and power-law fluids.

Dispersion of magnetic susceptibility in a suspension of flexible ferromagnetic rods

The properties of suspensions of magnetosomes extracted from magnetotactic bacteria are investigated. By using dynamic light scattering and measuring the dispersion of magnetic susceptibility it is shown that sonicated samples with broken magnetosome chains have qualitatively different behavior in comparison with native samples. This is explained by the presence of flexible chains of magnetosomes in non-sonicated samples which have the qualitative features of magnetic susceptibility predicted by the model of flexible magnetic rods. • The model of flexible magnetic rods of magnetic susceptibility is proposed. • Broken magnetosome chains have qualitatively different behavior as native samples. • Frequency dependence of magnetosomes' complex susceptibility is analyzed.

Assessment of dynamic efforts taking into account of inertial and vibrating loads in deaxial pumping units

The choice of rational designs of pumping units for lifting fluid from a well and the modes of their operation is one of the most urgent tasks in oil production. Despite the large amount of theoretical and extreme research, the solution of the problem in this direction cannot be considered complete, given that the dynamic characteristics of the movement of the well product and the kinematics of the well pumping unit are extremely complex. This article discusses the issue of determining the dynamic forces acting at the rod suspension point, in the new constructive solution of a beamless pumping unit depending on the angle of rotation of the crank and dimensionless kinematic parameter characterizing the relationship of the length of the crank to the length of the working part of the rope and the relative eccentric. Analytical dependencies are proposed to determine the maximum load at the rods suspension point depending on inertial and vibration forces.

Investigation of the Hydrolytic Stability of Polyurethane Applied to Vehicle Suspension Components

Process parameters such as temperature and humidity, as well as formulation are the key factors in the manufacture of a polymeric component through a polyurethane prepolymer. These define the reaction kinetics, bonding and the resulting chemical interactions which determine the final characteristics of the material. One of the expected skills of polyurethane, when applied to components used in contact with water, is hydrolysis resistance. Consequently this research focused on exposure of a polymerized TDI (toluene diisocyanate) polyether polyurethane to different proportions of the curing agent, MOCA (4,4'-methylene-bis), in an environment susceptible to reactions with water at 70 °C. In this case, this material is applied in the manufacture of coil spring solid axle with trailing arms and Panhard rod suspension bushings. Mechanical tests and DSC (differential scanning calorimetry), TGA (thermogravimetry) and FT-IR (Fourier transform infrared) evaluations of the samples and prepolymer are conducted for the characterization of the different formulations, showing the negative relationship of the curing agent proportion parameters with the hydrolysis resistance. Here depolymerization of urethane and ether groups, as well as lower retention of yield stress are verified. These findings can subsidize developing predictive models for performance and lifetime of polyurethanes.

Sound Propagation in a Particle Suspension with a Rotational Degree of Freedom

Suspensions are often found in nature and in technological processes. Suspension particles can differ in density and compressibility from the parent medium and affect the speed and attenuation of sound. It is thought that particle suspensions with neutral buoyancy, i.e., the average density and compressibility of which do not differ from the parameters of the surrounding fluid, do not affect sound propagation. However, if a particle’s center of mass is displaced, i.e., it does not coincide with the point of the Archimedes force, in an acoustic field, such a particle executes rotational oscillations. Rotational oscillations are accompanied by viscous friction and lead to loss of acoustic wave energy. A particle’s center of mass can be displaced by a nonuniform density distribution of a body or a point uneven mass on its surface, which in the general case can be both positive and negative (a cavity). The article analyzes sound propagation in suspensions of rod- and disk-shaped particles characteristic of many media. The formulas describing acoustic wave energy losses in a particle suspension are obtained, and the magnitude of additional sound wave attenuation is estimated, which show that this mechanism can lead to appreciable attenuation.

Relaxation in two-dimensional suspensions of rods as driven by Brownian diffusion.

Relaxation in a two-dimensional suspensions containing rods was studied by using dynamic Monte Carlo simulations. An off-lattice model with continuous positional and orientational degrees of freedom was considered. The initial state was produced by using a random sequential adsorption model. During the relaxation, the rods underwent translational and rotational Brownian motions. The simulations were run at different values of number density ρ (the number of rods per unit area) and of the initial orientation order parameter S_{i}. The rods were assumed to have core-shell structures. The evolutions of both the connectivity and the order parameter have revealed different relaxation behavior.

Structure and rheology of liquid crystal hydroglass formed in aqueous nanocrystalline cellulose suspensions

HypothesisLiquid crystal hydroglass (LCH) is a biphasic soft material with flow programmable anisotropy that forms via phase separation in suspensions of charged colloidal rods upon increases in ionic strength. The unique structure and rheology of the LCH gel formed using nanocrystalline cellulose (NCC) is hypothesised to be dependent on colloidal stability that is modulated using specific ion effects arising from Hofmeister phenomena. ExperimentsLCHs are prepared in NCC suspensions in aqueous media containing varying levels of sodium chloride (NaCl) or sodium thiocyanate (NaSCN). The NCC suspensions are characterised using rheology and structural analysis techniques that includes polarised optical microscopy, zeta potential, dynamic light scattering and small-angle X-ray scattering. FindingsThe two salts have a profound effect on the formation process and structure of the LCH. Differences in network density and size of the liquid crystal domains are observed within the LCH for each of the salts, which is associated with the strength of interaction between NCC particles during LCH formation. In comparison to Cl− at the same salinity, the chaotropic nature of the weakly hydrated SCN− enhances colloidal stability by rendering NCC particles more hydrated and repulsive, but this also leads to weaker gel strength of the LCH. The results suggest that salts are a means in which to control the formation, structure and rheology of these anisotropic soft materials.

Fluid medium effect on stresses in suspensions of high-inertia rod-like particles

The rheology of suspensions of high-inertia (or granular) non-spherical particles characterized by high particle Stokes and Reynolds numbers is rarely investigated. In this study, we investigate the rheology of suspensions of inertial rod-like particles of aspect ratio 4 subjected to shear flow. In particular, the effect of fluid medium (air, water) against dry granular simulations on the developed stresses is assessed. CFD-DEM simulations are performed for a periodic shear box for a range of shear rates and volume fractions of particles. The dependence of rheological properties like shear stress, normal stress difference, pressure and relative viscosity on volume fraction, shear rate, granular temperature and the particle orientation are discussed. These results provide insight into the macroscopic rheology of suspensions of rods and demonstrate that the effect of particle shape and surrounding fluid cannot be completely ignored. Air as a fluid medium shows similar scaling as compared to dry granular simulations, but the stress values are generally lower. We observe drastic change in both scaling and values for water as fluid medium. In all cases, the rods show strong alignment in the direction of shear. This study can be further extended to develop stress closures for use in Eulerian flow models.

Settling dynamics of two spheres in a suspension of Brownian rods

We investigate via numerical simulations the settling dynamics of two non-Brownian rigid spheres in a dilute suspension of Brownian rods at low Reynolds numbers. Specifically, this work focuses on how the overall settling dynamics is affected by the coupling between the flow field around the spheres and the orientation of the rods. The Brownian motion introduces a finite relaxation time in the suspending medium which is modeled as a continuum. When the spheres fall along their centerline, the spheres experience two contributions: one Newtonian and a non-Newtonian contribution due to the presence of the Brownian rods. The interactions between the two settling spheres are evaluated as a function of Péclet number (Pe) and the distance between the centers of the spheres. Repulsive interactions are found, and these interactions are affected by Pe and the distance between the centers of the spheres. An analysis of the flow fields highlights the origin of these repulsive interactions in non-Newtonian elongational effects.

A versatile simulation method for studying phase behavior and dynamics in colloidal rod and rod-polymer suspensions.

Here, we present an implicit-solvent model for dynamic simulations of hard-rod and rod-polymer suspensions. Individual rods are represented by a rigid linear chain consisting of overlapping spheres which interact through a pseudohard-core potential based on the cut-and-shifted Mie (generalized Lennard-Jones) potential with exponents (50, 49). In the rod-polymer suspensions, the polymers are modeled as freely interpenetrable spheres with respect to each other, while there is the pseudohard-core repulsion between the polymer and rod spheres. Dynamic simulations with this model are carried out with a dissipative particle dynamics (DPD) thermostat-each sphere is put in a larger DPD sphere and thus interacts with others via additional pairwise frictional and random forces-which captures the effects of Brownian forces due to the solvent while conserving local momentum. The phase behavior of these models, obtained from continuous compression and expansion simulations, reproduces previous predictions based on theoretical calculations and Monte Carlo simulations. Our method is suited to study dynamic processes in these suspensions, including nucleation and self-assembly, and can be readily extended to colloidal particles of different shapes and chemistry.

Sedimentation of a suspension of rods: Monte Carlo simulation of a continuous two-dimensional problem.

The sedimentation of a two-dimensional suspension containing rods was studied by means of Monte Carlo (MC) simulations. An off-lattice model with continuous positional and orientational degrees of freedom was considered. The initial state before sedimentation was produced using a model of random sequential adsorption. During such sedimentation, the rods undergo translational and rotational Brownian motions. The MC simulations were run at different initial number densities (the numbers of rods per unit area), ρ_{i}, and sedimentation rates, u. For sediment films, the spatial distributions of the rods, the order parameters, and the electrical conductivities were examined. Different types of sedimentation-driven self-assembly and anisotropy of the electrical conductivity were revealed inside the sediment films. This anisotropy can be finely regulated by changes in the values of ρ_{i} and u.

Stress relaxation in a dilute bacterial suspension: the active–passive transition

This paper follows a recent article of Nambiar et al. (J. Fluid Mech., vol. 812, 2017, pp. 41–64) on the linear rheological response of a dilute bacterial suspension (e.g. E. coli) to impulsive starting and stopping of simple shear flow. Here, we analyse the time dependent nonlinear rheology for a pair of linear flows – simple shear (a canonical weak flow) and uniaxial extension (a canonical strong flow), again in response to impulsive initiation and cessation. The rheology is governed by the bacterium orientation distribution which satisfies a kinetic equation that includes rotation by the imposed flow, and relaxation to isotropy via rotary diffusion and tumbling. The relevant dimensionless parameters are the Péclet number $Pe\equiv \dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D70F}$, which dictates the importance of flow-induced orientation anisotropy, and $\unicode[STIX]{x1D70F}D_{r}$, which quantifies the relative importance of the two intrinsic orientation decorrelation mechanisms (tumbling and rotary diffusion). Here, $\unicode[STIX]{x1D70F}$ is the mean run duration of a bacterium that exhibits a run-and-tumble dynamics, $D_{r}$ is the intrinsic rotary diffusivity of the bacterium and $\dot{\unicode[STIX]{x1D6FE}}$ is the characteristic magnitude of the imposed velocity gradient. The solution of the kinetic equation is obtained numerically using a spectral Galerkin method, that yields the rheological properties (the shear viscosity, the first and second normal stress differences for simple shear, and the extensional viscosity for uniaxial extension) over the entire range of $Pe$. For simple shear, we find that the stress relaxation predicted by our analysis at small $Pe$ is in good agreement with the experimental observations of Lopez et al. (Phys. Rev. Lett., vol. 115, 2015, 028301). However, the analysis at large $Pe$ yields relaxations that are qualitatively different. Upon step initiation of shear, the rheological response in the experiments corresponds to a transition from a nearly isotropic suspension of active swimmers at small $Pe$, to an apparently (nearly) isotropic suspension of passive rods at large $Pe$. In contrast, the computations yield the expected transition to a nearly flow-aligned suspension of passive rigid rods at high $Pe$. We probe this active–passive transition systematically, complementing the numerical solution with analytical solutions obtained from perturbation expansions about appropriate base states. Our study suggests courses for future experimental and analytical studies that will help understand relaxation phenomena in active suspensions.

NMR of cellulose nanocrystals, mesoporous media, and liquid crystal assemblies

ABSTRACT This article gives an overview of cellulose nanocrystals (CNCs), liquid crystal templating based on suspensions of CNC rods, and their corresponding templated mesoporous materials. NMR cryoporometry was used to give pore size distributions in chiral nematic mesoporous silica (CNMS) and organosilica (CNMO) films, while NMR pulsed-field gradient technique was used to study diffusion anisotropy of water absorbed in these films. 14N-NMR was used to probe the orientation of a calamite liquid crystal (LC) confined in the pores of CNMO films. Effects due to confining hydrogen-bond assemblies (HBAs) in CNMS and CNMO films were investigated by means of 2H-NMR and 19F-NMR. These results were compared with the ordering in the corresponding neat HBA. The ability to tune/switch the film’s optical responses via orientation ordering of LCs in the pores of CNMO films was demonstrated by NMR.

Design and Modeling of Pull Rod and Push Rod Suspension System

Design and Modeling of Pull Rod and Push Rod Suspension System

Collective oscillation in dense suspension of self-propelled chiral rods.

Active particles capable of self-propulsion commonly exhibit rich collective dynamics and have attracted increasing attention due to their applications in biology, robotics, social transport, and biomedicine. However, it remains unclear how the geometric features of active particles affect their collective behaviors. In this paper, we explore the collective dynamics of L-shaped active rods. We show that a dense suspension of self-propelled L-shaped rods exhibits fascinating non-equilibrium oscillatory dynamic clustering. A new oscillation phase can form due to distinct collisions and aggregation mechanisms arising from the L-shaped chirality of elements. A generic diagram of emerging states is provided over a wide range of geometric parameters. Our findings show that the comparative strength between the periodic separation and proximity effect from chirality and the alignment effect from elongated geometry drive the formation and transition of dynamic patterns. This chirality-triggered oscillation phase suggests a new route to understand active matter and paves a way for emerging applications.

Diffusion of Rodlike Polymers: Pulsed Gradient Spin Echo NMR of Poly(γ-stearyl-α,l-glutamate) Solutions and the Importance of Helix Stability.

Many natural and synthetic polymers and particles have a rodlike shape, leading to important and intriguing solution behavior, such as high intrinsic viscosities and liquid crystalline phases. Much of what is known about suspensions of rods has been learned by studying helical polypeptides, even though such molecules are not perfectly rigid, smooth cylinders. Previous optical tracer self-diffusion studies of poly(γ-benzyl-α,l-glutamate) (PBLG) revealed that the molecule initially resists topological constraints imposed by neighboring molecules, but diffusion strongly decreases as concentration rises beyond a certain number density. In contrast, the tracer self-diffusion coefficient of truly rigid tobacco mosaic virus begins decreasing immediately with concentration. We used pulsed gradient spin echo NMR to measure another polypeptide, poly(γ-stearyl-α,l-glutamate) (PSLG), to gain physical insight into the question of polypeptide diffusion in crowded isotropic solutions. The PSLG molecule, with long alkyl sidechains, is semiflexible like PBLG but does not exhibit the same ability to evade topological constraints. Instead, PSLG follows a simple exponential decay, D/ DKR = A e(-κν/ν*) + B, where DKR is the Kirkwood-Riseman expectation for rod diffusion, ν is the number density of rods, ν* is the Onsager expectation for the number density at the onset of liquid crystal formation, A = 1 ± 0.1, B = 0.1 ± 0.01, and κ = 4.5 ± 0.5. The results emphasize the importance of helix stability when choosing rodlike polypeptides as model systems, particularly with regard to the chain ends.

Rod Construction of an Isotropic Elastic Suspension of Inertial Mass

In this article, the dynamics of a mechanical isotropic elastic rod suspension of inertial mass in the linear formulation is examined as one of the possible options for implementing an inertial information sensor.

Wireless and autonomous sensor for Integrated Engine Health Management

Providing the best availability of aircrafts is a main cause for concern in aeronautics industry. Integrated Engine Health Management (IEHM) is the up to date solution that is used by Aircraft Engine Manufacturers in order to maintain a fleet of engines operative. IEHM detect signs of failure before they happen is the key tool for improving the level of aircraft operability. There is a strong focus on the sensor part and particularly on a wireless autonomous load sensor. Measuring load can have a high value to estimate the remaining useful life of equipment’s like suspension rods or gears after a hard landing. Indeed, after such an event, aircraft companies need to know if suspension rods/gears are safe or could have been damaged. This paper presents the current CORALIE sensor development (autonomous wireless load recorder) that will enable maintenance operators to determine the load level seen by an engine link after a hard landing by simply setting a portable device near the mounting system. Interesting features are Energy Harvesting and RFID communication modules that have been developed for this sensor. Such autonomous SHM systems typically include embedded sensors, and elements for data acquisition, wireless communication, and energy harvesting. Among all of these components, this paper focuses on RFID technologies. Actually, low power sensors and wireless communication components are used in newer SHM systems, and a number of researchers have recently investigated such techniques to extract wirelessly communicate data stored in these stand-alone systems. The first part of the paper is dedicated to benchmark the different wireless communication protocols against RFID available for the project application (engine pods). The second part gives a presentation of the RFID communication system (Antenna, reader and RFID front end circuit) developed for transmitting local data stored in the memory of the system for analysis in a SHM maintenance strategy. The last part presents real test of RFID wireless communication and provide a maturity assessment on the technology.

Electric-Parameter-Based Inversion of Dynamometer Card Using Hybrid Modeling for Beam Pumping System

Conventional fault diagnosis and production calculation of an oil well can be conducted with the surface dynamometer cards, which are obtained by load sensor installed on the horse head. This method to measure the dynamometer cards is limited by the sensor maintenance and calibration, battery replacement, and safety hazards for staff. As the basic parameter of the oil extraction industry, electric parameters have the advantages of low cost and high efficiency. So the inversions of dynamometer card with electric parameters are attracting more and more attention. In order to solve the problem of insufficient data and consider the real-time performance in the actual oil extraction process, this paper proposes a novel hybrid model which consists of two parts: the mechanism model of polished rod load and the suspension displacement calculated with the space vector equations of motor and a data-dependent kernel online sequential extreme learning machine (DDKOS-ELM) model proposed to correct the output error of the mechanism model, which improves the kernel function selection and makes it real-time. Thus, the highlights of this paper can be summed up in two points: (1) under the circumstance of the bottom dead point detection without sensors, the mechanism modeling of the polished rod load and suspension displacement has been carried out from the perspective of mathematical model of AC motor; (2) a novel data-driven model based on data-dependent kernel online sequential extreme learning machine (DDKOS-ELM) has been proposed to improve the kernel functions selection. The coefficients in the data-dependent kernel function are optimized with improved free search algorithm (IFSA). The proposed hybrid model has been applied to a normal working oil well and the prediction results show better accuracy than the pure data-driven model and mechanism model.