Unraveling the Rheology of Nanocellulose Aqueous Suspensions:A Comprehensive Study on Biomass-Derived Nanofibrillated Cellulose

The rheological properties of nanocellulose aqueous suspensions play a critical role in the development of nanocellulose-based bulk materials.High-crystalline,high-aspect ratio,and slender nanofibrillated cellulose(NFC)were extracted from four biomass resources.The cellulose nanofibrils and nanofibril bundles formed inter-connected networks in the NFC aqueous suspensions.The storage moduli of the suspensions with different concentrations were higher than their corresponding loss moduli.As the concentration increased,the storage and loss modulus of NFC dispersion increased.When the shear rate increased to a certain value,there were differences in the changing trend of the rheological behavior of NFC aqueous suspensions derived from different biomass resources and the suspensions with different solid concentrations.NFC dispersion’s storage and loss modulus increased when the temperature rose to nearly 80℃.We hope this study can deepen the understanding of the rheological properties of NFC colloids derived from different biomass resources.

The stress-microstructure relationship in an evolving mixing layer of fiber suspensions

The equations for fiber suspensions in an evolving mixing layer were solved by the spectral method, and the trajectory and orientation of fibers were calculated based on the slender body theory. The calculated spatial and orientation distributions of fibers are consistent with the experimental ones that were performed in this paper. The relationship between the microstructure of fibers and additional stress was examined. The results show that the spatial and orientation distributions of fibers are heterogeneous because of the influence of coherent vortices in the flow, which leads to the heterogeneity of the additional stress. The degree of heterogeneity increases with the increasing of St number and fiber aspect ratio. The fibers in the flow make the momentum loss thickness of the mixing layer thicker and accelerate the vorticity dispersion.

Development and validation of RP-HPLC method for determination of acetazolamide, furosemide and phenytoin extemporaneous suspensions

The development of the extemporaneous preparations allows physicians to adjust the dose for pediatric patients and provides for a more convenient dosage vehicle for those patients with difficulty swallowing tablets[1].As such,the production unit of pharmacy division,Sappasit Prasong Hospital,Ubon Ratchathani province,prepared the extemporaneous formulations such as Acetazolamide(AM),Furosemide(FM)and Phenytoin(PT)powder for suspensions.The extemporaneous suspensions of 10 mg/mL AM,2 mg/mL FM and 10 mg/mL PT were prepared from 250 mg Diamox?,40 mg Lasix?and 50 mg Dilantin?tablets,respectively and diluted with syrup vehicle.

Flow Behavior of Clay-Silt to Sand-Silt Water-Rich Suspensions at Low to High Shear Rates: Implications for Slurries, Transitional Flows, and Submarine Debris-Flows

Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.

CAPTURE EFFECT OF ELECTRORHEOLOGICAL SUSPENSIONS IN FLOW FIELD

According to the results of experiments and theoretical analysis, a phenomenon called ＂capture effect＂ is put forward, which could be used to describe the particles dynamic behavior of electrorheological （ER） suspensions. Then a ＂structure-force＂ mathematical model is established to explain this effect based on electrostatic energy density equation. The analysis results show that the dynamic coupling process of ER suspensions under an external electric filed is the function not only of the electric intensity, but also of the dielectric properties and the structure form.

STABILITY ANALYSIS IN SPATIAL MODE FOR CHANNEL FLOW OF FIBER SUSPENSIONS

Different from previous temporal evolution assumption, the spatially growing mode was employed to analyze the linear stability for the channel flow of fiber suspensions. The stability equation applicable to fiber suspensions was established and solutions for a wide range of Reynolds number and angular frequency were given numerically . The results show that, the flow instability is governed by a parameter H which represents a ratio between the axial stretching resistance of fiber and the inertial force of the fluid. An increase of H leads to a raise of the critical Reynolds number, a decrease of corresponding wave number, a slowdown of the decreasing of phase velocity , a growth of the spatial attenuation rate and a diminishment of the peak value of disturbance velocity. Although the unstable region is reduced on the whole, long wave disturbances are susceptible to fibers.

Modeling effective viscosity reduction behaviour of solid suspensions

Under a simple shearing flow, the effective viscosity of solid suspensions can be reduced by controlling the inclusion particle size or the number of inclusion particles in a unit volume. Based on the Stokes equation, the transformation field method is used to model the reduction behaviour of effective viscosity of solid suspensions theoretically by enlarging the particle size at a given high concentration of particles. With a lot of samples of random cubic particles in a unit cell, our statistical results show that at the same higher concentration, the effective viscosity of solid suspensions can be reduced by increasing the particle size or reducing the number of inclusion particles in a unit volume. This work discloses the viscosity reduction mechanism of increasing particle size, which is observed experimentally.

NUMERICAL SIMULATION OF FLOW OF PULP FIBER SUSPENSIONS IN STOCK PUMP WITH SEMI-OPEN IMPELLER

The flow of pulp fiber suspensions with a consistency below 5% through a pump falls into the turbulent region. The 2-phase 3D turbulent flow of the mixture is simulated in the hydraulic components composed by suction chamber, front board, semi-impeller and volute casing for the first time. The pseudo-fluid model and the k-ε turbulent model are modified. Phase coupled SIMPLE algorithm is applied to make pressure-velocity correction equation. Based on the results of the numerical simulation, the distribution of velocity, pressure and density of liquid and particle phase are compared and analyzed. The flow analysis in the tip between front board and impeller is emphasized, which reflects the advantage of semi-open impeller when it transports 2-phase medium. This calculation result will be helpful for the design of pump impeller and the establishment of design method of centrifugal stock pump.

Effect of surface treatment on rheological behaviors of glass bead/hydroxyl terminated polybutadiene suspensions

Surface treatment of glass bead(GB) was carried out by using γ-glycidoxypropyltrimethoxy silane(GPTES) and γ-methacryloxypropyltrimethoxy silane(MPTMS) as coupling agents,respectively.The steady viscosity and yield stress of the GB/hydroxyl terminated polybutadiene(HTPB) suspensions were determined by Brookfield R/S rheometer.The effect of surface treatment on the viscosity and yield stress of GB/HTPB suspension was investigated.The results indicate that the viscosity of the pristine GB/HTPB suspension increases with increasing GB,and the relationship between its viscosity and volume fraction of GB depends on the shear rate.The modification of GB by MPTMS changes the viscosity of the MPTMS@GB/HTPB suspension,and its viscosity is the minimum at the MPTMS dosage of 0.3 g per 1 g GB.Additionally,the modification of GB by MPTMS increases the yield stress of the GB/HTPB suspension,and its yield stress is the maximum at the MPTMS dosage of 0.1 g per 1 g GB.The GPTES modified GB/HTPB suspension behaves lower viscosity and weaker shear thinning than the MPTMS modified GB/HTPB suspension within the range of experimental shear rate.

Dynamics simulation of electrorheological suspensions in poiseuille flow field

Based on a modified Maxwell-Wagner model,molecular dynamics is carried out to simulate the structural changes of ER(electrorheological) suspensions in a poiseuille flow field.The simulation results show that the flow assists in the collection of particles at the electrodes under a low pressure gradient,and the negative ER effect will show under a high pressure gradient.By analyzing the relationship curves of the shear stress and the pressure gradient in different relaxation time,it is found that for the same kind of ER suspensions materials,there is an optimal dielectric relaxation frequency.

Orientation distribution of fibers and rheological property in fiber suspensions flowing in a turbulent boundary layer

A model relating the translational and rotational transport of orientation distribution function （ODF） of fibers to the gradient of mean ODF and the dispersion coefficients is proposed to derive the mean equation for the ODE Then the ODF of fibers is predicted by numerically solving the mean equation for the ODF together with the equations of turbulent boundary layer flow. Finally the shear stress and first normal stress difference of fiber suspensions are obtained. The results, some of which agree with the available relevant experimental data, show that the most fibers tend to orient to the flow direction. The fiber aspect ratio and Reynolds number have significant and negligible effects on the orientation dis- tribution of fibers, respectively. The additional normal stress due to the presence of fibers is anisotropic. The shear stress of fiber suspension is larger than that of Newtonian solvent, and the first normal stress difference is much less than the shear stress. Both the additional shear stress and the first normal stress difference increase with increasing the fiber concentration and decreasing fiber aspect ratio.

Study on ER Suspensions of Polyparapheneylene Doped with Rare Earth

Polyparapheneylene (PPP) was doped by CeCl 4 and FeCl 3, and then electrorheological (ER) suspensions were prepared by polymer powder with high dielectric constants and silicone oil. Under electric field, the change of viscosity, leakage current density and relative physical constants were measured. The relationships among electric field strength, particle concentration, viscosity and leakage current density were discussed. The speed of electrorheological response and the recovery time were studied and corresponding mechanisms were investigated.

Effects of heat transfer in a growing particle layer on microstructural evolution during solidification of colloidal suspensions

Heat transfer is the foundation of freezing colloidal suspensions and a key factor for the interface movement.However,how the thermal conductivity of particles affects freezing microstructural evolution remains unknown.Here in this work,a mathematical model is built up to investigate thermal interactions among a growing particle layer,pulling speeds,and the freezing interface under a thermal gradient.Experiments are conducted to confirm the tendency predictions of the model.With the increase of pulling speeds,the drifting distance of the freezing interface increases and the time to finish drifting decreases.When the thermal conductivity of particles(k_(p))is smaller than that of the surrounding(kw),the freezing interface tends to go forward to the warm side.Contrarily,the freezing interface tends to go back to the cold side when the thermal conductivity of particles is larger than that of the surrounding(α=k_(p)/k_(w)>1).It originates from the shape of the local freezing interface:convex(α<1)or concave(α>1).These morphological changes in the local interface modify the premelting drag force F_(f).Whenα<1,F_(f)decreases and the freezing morphology tends to be the frozen fringe.Whenα>1,F_(f)increases and the freezing morphologies tend to be ice spears.These understandings of how the thermal conductivity of particles affect microstructural evolution may optimize the production of freeze-casting materials and their structural-functional properties.

Dielectric Polarization of Electrorheological Suspensions

The relation between electrorheological(ER)effect and dielectric properties of Polymer-based and inorganic-based suspensions were investigated.It is found that ER effect is determined not only by the dielectric constant of the suspended particles,but also by the dielectric loss,which provides a criterion whether suspension exhibits ER effect.The wagner model,which describes the interfacial polarization occurring in multiphase systems,was introduced to predict the dielectric behaviours of ER suspensions.A good agreement is found between experiments and theoretical predictions.The conductivity of the dispersed particles,the working temperature range and working frequency range of ER suspension can be optimized with Wagner model.The other ER phenomena such as the effect of water content were also explained by using this model.

A New Method of Simulating Fiber Suspensions and Applications to Channel Flows

A successive iteration method is proposed to numerically simulate fiber suspensions.The computational field is discretized with the collocated finite volume method,and an ergodic hypothesis is adopted to gready accelerate the solution to the Fokker-Planck equation.The method is employed in channel flows with different fiber volume fractions and aspect ratios,and its effectiveness is proved.The numerical results show that the existence of fibers significantly changes the pressure distribution,and the fiber aspect ratio has a greater effect on the velocity profile than on the volume faction.At the center of the channel,the velocity increases along the streamwise direction,while the velocity near the wall decreases slightly.The uncoupling and coupling solutions of the additional stress of the fiber suspensions are quite different.

Novel Magnetorheological Suspensions Based on Co-Phthalocyanine/Fe Nanocomposite Particles

A novel magnetorheological (MR) suspension was based on methyl silicone oil and cobaltphthalocyanine (Co-Pc)/Fe nanocomposite particles, which were synthesized by thermally decomposing liquid carbonyl Fe in the solution of Co-Pc in N, N-dimethyl formamide. The nanocomposite particles were fully characterized by XRD, SEM and HREM, and the thermal, magnetic and MR properties of nanocomposite particles were measured. Such factors as weight percent of particles (w), magnetic field strength (H), temperature (T) and shear rate (γ) etc influencing on MR properties were investigated. The results indicated that Co-Pc/Fe nanocomposite with density of 3.66 g/cm3 was almost micro-sized regular spheroids consisting of tens of Co-Pc coated α-Fe nanoparticles in inner and Co-Pc layers on surface of the spheroids. They showed good characteristics of anti-oxidation and soft magnetic. Increment of ω increased field-induced shear stress and zero-field viscosity (η0) of MR suspensions monotonously, and improved anti-settlement stability, butη0 increased more markedly than with increasing ω. was basically independent on T and γ while increased obviously with increasing H. With increasing T, response time of the MR suspension to external magnetic field seemed to decrease. As a result, MR suspensions with satisfactory stability and rapid, completely reversible and significant MR effect can be obtained from Co-Pc/Fe nanocomposite particles.

ELECTRORHEOLOGICAL PROPERTIES OF DIATOMITE/SILICONE OIL SUSPENSIONS UNDER DC FIELDS

In this study, electrorheological （ER） behavior of suspensions prepared from 3.0 and 9.0 μm diatomite particulate, dispersed in insulating silicone oil （SO） medium was investigated. Sedimentation stabilities of suspensions （c = 5 wt%） prepared using these diatomite powders were determined to be 32 days （d = 3 μm） and 24 days （d = 9 μm）, respectively. ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Shear stress of diatomite suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and particle size, showing a typical shear thinning non-Newtonian visco-elastic behavior. Effects of high temperature and polar promoter onto ER activity ofdiatomite/SO system were also investigated.

Data-Driven Upscaling of Orientation Kinematics in Suspensions of Rigid Fibres

Describing the orientation state of the particles is often critical in fibre suspension applications.Macroscopic descriptors,the so-called second-order orientation tensor(or moment)leading the way,are often preferred due to their low computational cost.Closure problems however arise when evolution equations for the moments are derived from the orientation distribution functions and the impact of the chosen closure is often unpredictable.In this work,our aim is to provide macroscopic simulations of orientation that are cheap,accurate and closure-free.To this end,we propose an innovative data-based approach to the upscaling of orientation kinematics in the context of fibre suspensions.Since the physics at the microscopic scale can be modelled reasonably enough,the idea is to conduct accurate offline direct numerical simulations at that scale and to extract the corresponding macroscopic descriptors in order to build a database of scenarios.During the online stage,the macroscopic descriptors can then be updated quickly by combining adequately the items from the database instead of relying on an imprecise macroscopic model.This methodology is presented in the well-known case of dilute fibre suspensions(where it can be compared against closure-based macroscopic models)and in the case of suspensions of confined or electrically-charged fibres,for which state-of-the-art closures proved to be inadequate or simply do not exist.

ELECTRORHEOLOGICAL PROPERTIES OF TALC POWDER/SILICONE OIL SUSPENSIONS UNDER DC FIELDS

In this study, the electrorheological （ER） behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil （SO） medium was investigated. Sedimentation stabilities of suspensions （c = 5 wt%） prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated.