Cessation Of Shear Research Articles

On the banded texture and nematic elasticity in a thermotropic liquid crystalline polymer. In situ optical microscopy and light scattering

Optical banded texture after cessation of shear was investigated in a semi‐flexible thermotropic liquid crystalline polymer (LCP) by in situ polarized optical microscopy (POM) and small‐angle light scattering (SALS). The LCP is a random copolymer consisting of mesogenic units separated by alkyl spacers. The quiescent state of the nematic phase exhibited a polydomain texture, with microdomains randomly oriented. Upon application of shear the texture aligned along the shear axis. In situ X‐ray scattering demonstrated that the texture alignment corresponded to macromolecular alignment along the shear axis. Above certain shear rate the aligned texture relaxed and produced a banded texture upon cessation of shear. Shearing at higher shear rate further aligned the texture to produce a monodomain. Stopping the shear spatially uncorrelated structures orthogonal to the shear direction were developed with incubation time in the 100 seconds of second. Hence, there is a threshold of texture alignment to produce banded texture. Shear rheometry showed that the liquid crystalline phase is viscoelastic with features akin to entangled linear polymer melts, for example, a minimum in mechanical damping tan δ [=G”/G']. Furthermore, the nematic phase exhibited considerable recoverable strain after creep. The elastic recoil after cessation of flow would be responsible to produce banded texture. Increasing the creep time reduced the recoverable strain, correlating with longer time to produced banded texture. In contrast, wholly aromatic LCPs exhibit much shorter recovery times after creep and shorter incubation time for banded texture formation.

A charged finitely extensible dumbbell model: Explaining rheology of dilute polyelectrolyte solutions

A robust non-Newtonian fluid model of dilute polyelectrolyte solutions is derived from kinetic theory arguments. Polyelectrolyte molecules are modeled as finitely elongated nonlinear elastic dumbbells, where effective charges (interacting through a simple Coulomb force) are added to the beads in order to model the repulsion between the charged sections of polyelectrolyte chains. It is shown that the relative strength of this repulsion is regulated by the electric-to-elastic energy ratio, E, which is one of the key parameters of the model. In particular, E accounts for the intrinsic rigidity of polyelectrolyte molecules and can be used to explain the impact of solvent salinity on polyelectrolyte rheology. With two preaveraging approximations, the constitutive equations of the resulting fluid model are formulated in closed form. Material functions predicted by the model for steady shear flow, steady extensional flow, small-amplitude oscillatory shear flow, and start-up and cessation of steady shear flow are obtained and investigated using a combination of analytical and numerical methods. In particular, it is shown how these material functions depend on E. The two limiting cases of the model—uncharged dumbbells (E = 0) and rigid dumbbells (E → ∞)—are included in the analysis. It is found that despite its simplicity, the model predicts most of the experimentally observed rheological features of polyelectrolyte solutions.

Micro-Mechanism Research into Molecular Chains Orientation Synergistically Induced by Carbon Nanotube and Shear Flow in Injection Molding

For the degree of orderly arrangement of the molecular chains at the interface of nanocomposites, the static and sheared polyethylene (PE)/carbon nanotube (CNT) models and the sheared pure PE model were constructed, and molecular simulation experiments were carried out in comparison. The micro-mechanism of molecular chains orientation, synergistically induced by the carbon nanotube and shear flow in injection molding, was discussed by analyzing the radius of gyration, molecular chain motion, conformation evolution of molecular chains, bond orientation parameter, interface binding energy and atom distribution. The results show that, for the static composite system, the conformation adjustment of PE molecular chains induced by CNT is limited due to the hindrance from the surrounding chains. Thus, the orientation and radius of gyration of molecular chains increase slightly. For the sheared pure PE system, the orientation induced by shear flow is unstable. After the cessation of shear, the molecular chains undergo intense thermal movement and relax quickly. The disorientation is obvious, and the radius of gyration decreases considerably. It is worth noting that for the sheared composite system, shear flow and the CNT have a synergistic effect on the orientation of the molecular chains, which is due to the adsorption effect of the CNT on shear-induced oriented chains and the inhibition effect of CNT on the relaxation of shear-induced oriented chains. Thus, the orientation stability of PE chains is greatly improved, and interface crystallization is promoted. Moreover, because of the more regular arrangement of molecular chains in the sheared composite system, more H atoms and C atoms are close to the surface of the CNT, which increases the van der Waals force, and correspondingly increases the interface binding energy.

POSS-Induced Dynamic Cross-Links Produced Self-Healing and Shape Memory Physical Hydrogels When Copolymerized with N-Isopropyl acrylamide.

The hydrogel morphology and viscoelasticity and the two-way shape memory behavior of copolymers of N-isopropyl acrylamide-polyhedral oligomeric silsesquioxane (PNIPAm-POSS) were investigated. NIPAm-POSS copolymers are unentangled and exhibit a thermoplastic and thermoresponsive hydrogel behavior ( Romo-Uribe ; ; Albanil , Eur. Polym. J. 2018 , 99 , 350 - 360 ). Here, we demonstrated by high-resolution transmission electron microscopy that POSS segregated into crystals to form physical cross-links. The hydrogels exhibited significant swelling, higher than chemical hydrogels at the same POSS content. The morphology of the hydrogels consisted of a honeycomb structure, and the pore size and swelling were a decreasing function of POSS. Moreover, the hydrogels were self-healing, exhibiting a liquid-like behavior under large amplitude shear and rubber-like behavior immediately after cessation of shear, that is, the POSS aggregates break and re-form, acting as dynamic cross-linkers. Strikingly, the physical networks behaved as perfect networks, thus matching chemically cross-linked networks and holding the scaling |η*| ∼ ω-1. Furthermore, the physical hydrogels exhibited a thermally activated shape memory (SM) behavior, without external stress and the lower critical solution temperature (LCST) being the only stimulus. The SM process involved swelling-deswelling, effectively opening opportunities for drug delivery. Furthermore, the SM was reversible, and no external stress was involved, therefore behaving as the two-way SM. Finally, POSS modulated the shear elastic modulus G' and LCST; therefore, the PNIPAm-POSS copolymers open opportunities for reusable, thermoformable SM hydrogels with tuned mechanical modulus and activation temperature.

Nonlinear Rheological Behaviors in Polymer Melts after Step Shear

Using molecular dynamics simulation, we investigate the evolution of chain conformation, stress relaxation, and fracture for a polymer melt between two walls after step shear. We find that the characteristic overlap time for the reduced relaxation moduli and the time that the stretched primitive chain retracts to its equilibrium length are both much longer than the Rouse time. Importantly, we observe significant fracture-like flow after shear cessation. While there is considerable randomness in the location of the fracture plane and the magnitude of displacement from sample to sample, our analysis suggests that the randomness is not due to thermal noise, but may reflect inherent structural and dynamic heterogeneity in the entangled polymer network.

Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution.

Reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate)x–poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diameter (or worm width) ranging from 11 to 20 nm as the mean degree of polymerization (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examined using variable temperature DLS, oscillatory rheology, and SAXS. A 10% w/w G37-H80 worm dispersion dissociated to afford an aqueous solution of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temperature, these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being observed in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temperature SAXS: these experiments indicated the gradual formation of longer worms at higher temperature, with a concomitant reduction in the number of spheres, suggesting worm growth via multiple 1D sphere–sphere fusion events. DLS studies indicated that a 0.1% w/w aqueous dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the experiment was also observed during rheological studies of a 10% w/w G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qualitatively different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was observed at a shear rate of 10 s–1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s–1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain critical temperature since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were observed. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer molecular weight.

Effect of Shear Rate on the Orientation and Relaxation of a Vanillic Acid Based Liquid Crystalline Polymer

In this study, we report on the visco-elastic response during start-up and cessation of shear of a novel bio-based liquid crystal polymer. The ensuing morphological changes are analyzed at different length scales by in-situ polarized optical microscopy and wide-angle X-ray diffraction. Upon inception of shear, the polydomain texture is initially stretched, at larger strain break up processes become increasingly important, and eventually a steady state texture is obtained. The shear stress response showed good coherence between optical and rheo-X-ray data. The evolution of the orientation parameter coincides with the evolution of the texture: the order parameter increases as the texture stretches, drops slightly in the break up regime, and reaches a constant value in the plateau regime. The relaxation of the shear stress and the polydomain texture showed two distinct processes with different timescales: The first is fast contraction of the stretched domain texture; the second is the slow coalescence of the polydomain texture. The timescale of the orientation parameter’s relaxation matched with that of the slow coalescence process. All processes were found to scale with shear rate in the tested regime. These observations can have far reaching implications for the processing of liquid crystal polymers as they indicate that increased shear rates during processing can correspond to an increased relaxation rate of the orientation parameter and, therefore, a decrease in anisotropy and material properties after cooling.

Genetically Engineered Supercharged Polypeptide Fluids: Fast and Persistent Self-Ordering Induced by Touch.

Mechanically induced disorder-order transitions have been studied in fluid surfactant solutions or polymer thermotropic liquid crystals. However, isothermally induced ordered phases do not persist after cessation of shear, which limits their technological applicability. Moreover, no such stimuli-responsive materials involving biomacromolecules have been reported although biopolymer liquids are gaining a lot of attention. A biological fluid system is introduced in which anionic polypeptides are complexed with cationic surfactants. The resulting fluids exhibited very sensitive isotropic-nematic transition triggered by shear. The formed liquid crystal was preserved after cessation of mechanical stimulus. Self-ordering behavior of the material was achieved through water flow and finger pressing. The latter mechanical induction resulted in the formation of complex pattern that can be read out by birefringence, allowing the recording of fingerprint information.

Genetically Engineered Supercharged Polypeptide Fluids: Fast and Persistent Self‐Ordering Induced by Touch

AbstractMechanically induced disorder–order transitions have been studied in fluid surfactant solutions or polymer thermotropic liquid crystals. However, isothermally induced ordered phases do not persist after cessation of shear, which limits their technological applicability. Moreover, no such stimuli‐responsive materials involving biomacromolecules have been reported although biopolymer liquids are gaining a lot of attention. A biological fluid system is introduced in which anionic polypeptides are complexed with cationic surfactants. The resulting fluids exhibited very sensitive isotropic–nematic transition triggered by shear. The formed liquid crystal was preserved after cessation of mechanical stimulus. Self‐ordering behavior of the material was achieved through water flow and finger pressing. The latter mechanical induction resulted in the formation of complex pattern that can be read out by birefringence, allowing the recording of fingerprint information.

A singular perturbation study of the Rolie-Poly model

A singular perturbation analysis for the Rolie-Poly model is presented for the limit of large relaxation time. The model describes entangled linear polymer melts and time scales for a Rouse time and reptation time. First, the case of the Rouse time approaching zero is named the nonstretching model, and the addition of a solvent model gives the small parameter to be the ratio of the retardation time to the slow reptation time. This analysis is instructive in formulating the perturbation analysis for the full Rolie-Poly model without the solvent, where the small parameter is the ratio of Rouse time to reptation time. The resulting formulae elucidate the characteristic features of thixotropic yield stress fluids, including yield stress hysteresis, delayed yielding and long term persistence of a decreased viscosity after cessation of flow. Two fundamental initial value problems are solved: startup of shear flow and cessation of shear flow. The scalings lead naturally to simplified dynamical systems that describe regimes of fast, slow and yielded dynamics, and show how the combination of these regimes can be used to describe the entire flow evolution.

Inelastic behaviour of cellulose microfibril networks.

Cellulose microfibrils (CMF) are a unique class of shape anisotropic bio-nanomaterials, already finding many applications in diverse fields owing to their advantageous material properties and abundant availability. The rich non-linear mechanical behaviour of CMF networks has been under-studied due to the complex nature of this system, being influenced by many factors such as strong inter-fibril interactions, a heterogeneous microstructure, and process conditions. In this work, we systematically explore the non-linear rheological behaviour of these networks using a CMF model system with controlled process conditions and fibril interactions. The microfibrils were dispersed in dimethyl sulfoxide to minimise the attractive van der Waals interactions and thereby also the network heterogeneity. We show that the networks exhibit a transition with increasing shear stress from a predominantly elastic to a plastic deformation where they undergo softening. We find that the network stiffness and plasticity are dependent on the loading rate. Finally, we observed that the networks regain their original viscoelastic moduli on cessation of shear. These findings form a basis towards understanding and ultimately modelling the mechanics of CMF networks, which is a prerequisite for the rational design of novel bio-based materials.

Shear-induced precursors in polyethylene: An in-situ synchrotron radiation scanning X-ray microdiffraction study

Localized shear flow was imposed by pulling glass fiber in polyethylene (PE) melt below and above its equilibrium melting point (141.6 °C). Immediately after the cessation of shear, the structure around the fiber was investigated with in-situ synchrotron radiation scanning X-ray microdiffraction (SR-μSXRD), which had spot area of 4.2 × 4.5 μm2 and step size of 6 μm. Results indicate that crystalline precursors are induced below equilibrium melting point, as evidenced by the occurrence of crystalline diffractions. Whilst at temperature above equilibrium melting point, no crystalline diffraction is observed. SR-μSXRD measurements on the crystallization behaviors at 127 °C after shearing at 145 °C suggest that non-crystalline precursors are induced, which is supported by three evidences. (i) The occurrence of crystallization near the fiber surface implies shear-induced formation of precursors at 145 °C since the fiber has no ability to induce crystallization at quiescent condition; (ii) No crystalline diffraction is detected immediately after cessation of shear at 145 °C; (iii) The necessity of induction time for the precursors to transform into crystalline nuclei further demonstrates the non-crystalline nature of precursors. The concentration of precursors is observed to reduce with increasing shearing temperature, as evidenced by twisting degree of lamellar crystals after isothermally crystallized at 127 °C.

The structure recovery capacity of highly concentrated emulsions under shear flow via studying their rheopexy

ABSTRACTAn investigation was performed into the structure recovery of highly concentrated water-in-oil emulsions (HCEs) under shear flow via studying their rheopexy. Experiments with the shear rate sweep in the up and down modes demonstrate that HCE has rheopexy. Restoration of the initial structure after cessation of shearing needs a period of time. The recovery time and ratio depend on the shear rate and the droplet size of the dispersed phase. A high shear rate results in a high probability of structure break of HCE. Thus, it is difficult to return to its initial structure. The structure of HCE that underwent shearing is closer to its original situation when the droplet size is small.

Heat-set emulsion gels of casein micelles in mixtures with whey protein isolate

Emulsion gels, also called emulgels, were formed by heating homogenized suspensions of micellar casein (MC) mixed with sunflower oil at pH < 6.5. The shear moduli of the emulgels were determined during heating and their microstructure was investigated by confocal laser scanning microscopy. The gel stiffness was studied as a function of the MC concentration at three pH values (5.8, 6.0 and 6.3) and three weight fractions of oil (5, 10 and 15%). Emulgels were compared with gels formed by heating MC suspensions without oil. After homogenization the oil droplets were found to be surrounded by a layer of MC and when MC formed a gel during heating the oil droplets were incorporated within the MC network. The oil droplets were active fillers that allowed formation of self-supporting gels at lower MC concentrations in the aqueous phase compared to gels formed by MC suspensions without oil. At a given MC concentration in the aqueous phase, emulgels showed reduced syneresis and were stiffer. Replacement of 20% or 40% MC by whey protein isolate (WPI) led to formation of more homogeneous networks and reduced syneresis, but had little effect on the stiffness of the emulgels. Shear flow caused break-up in macroscopic parts which behaved after cessation of shear as gels with reduced stiffness and a low yield stress.

Time-dependent viscoelastic properties of Oldroyd-B fluid studied by advection-diffusion lattice Boltzmann method

Time-dependent viscoelastic properties of Oldroyd-B fluid were investigated by lattice Boltzmann method (LBM) coupled with advection-diffusion model. To investigate the viscoelastic properties of Oldroyd-B fluid, realistic rheometries including step shear and oscillatory shear tests were implemented in wide ranges of Weissenberg number (Wi) and Deborah number (De). First, transient behavior of Oldroyd-B fluid was studied in both start up shear and cessation of shear. Stress relaxation was correctly captured, and calculated shear and normal stresses agreed well with analytical solutions. Second, the oscillatory shear test was implemented. Dynamic moduli were obtained for various De regime, and they showed a good agreement with analytical solutions. Complex viscosity derived from dynamic moduli showed two plateau regions at both low and high De limits, and it was confirmed that the polymer contribution becomes weakened as De increases. Finally, the viscoelastic properties related to the first normal stress difference were carefully investigated, and their validity was confirmed by comparison with the analytical solutions. From this study, we conclude that the LBM with advection-diffusion model can accurately predict time-dependent viscoelastic properties of Oldroyd-B fluid.

Mechanical History Dependence in Carbon Black Suspensions for Flow Batteries: A Rheo-Impedance Study.

We studied the effects of shear and its history on suspensions of carbon black (CB) in lithium ion battery electrolyte via simultaneous rheometry and electrical impedance spectroscopy. Ketjen black (KB) suspensions showed shear thinning and rheopexy and exhibited a yield stress. Shear step experiments revealed a two time scale response. The immediate effect of decreasing the shear rate is an increase in both viscosity and electronic conductivity. In a much slower secondary response, both quantities change in the opposite direction, leading to a reversal of the initial change in the conductivity. Stepwise increases in the shear rate lead to similar responses in the opposite direction. This remarkable behavior is consistent with a picture in which agglomerating KB particles can stick directly on contact, forming open structures, and then slowly interpenetrate and densify. The fact that spherical CB particles show the opposite slow response suggests that the fractal structure of the KB primary units plays an important role. A theoretical scheme was used to analyze the shear and time-dependent viscosity and conductivity. Describing the agglomerates as effective hard spheres with a fractal architecture and using an effective medium approximation for the conductivity, we found the changes in the derived suspension structure to be in agreement with our qualitative mechanistic picture. This behavior of KB in flow has consequences for the properties of the gel network that is formed immediately after the cessation of shear: both the yield stress and the electronic conductivity increase with the previously applied shear rate. Our findings thus have clear implications for the operation and filling strategies of semisolid flow batteries.

Nonlinear relaxation modulus via dual-frequency medium amplitude oscillatory shear (MAOS): General framework and case study for a dilute suspension of Brownian spheroids

A framework for determining the first nonlinear relaxation modulus of a viscoelastic fluid from a medium-amplitude oscillatory shear (MAOS) deformation is constructed. Knowledge of this “MAOS relaxation modulus” allows one to predict the weakly nonlinear stress response of a material under an arbitrary transient deformation via a memory integral expansion. Our framework is demonstrated by explicitly determining the MAOS relaxation modulus for a dilute suspension of Brownian spheroids subject to a dual-frequency oscillatory shear flow. Specifically, we first calculate the second normal stress difference for such a deformation from a corotational memory integral expansion. Second, the microstructural stress response of the model system of Brownian spheroids is determined via a regular perturbation expansion of the orientation distribution function at small dimensionless strain-rate amplitude, or Weissenberg number. An analytical expression for the MAOS relaxation modulus is resolved by comparing the second normal stress difference results of the memory integral expansion and microstructural stress calculation. Finally, using the MAOS relaxation modulus, we reconstruct the stress response of the model system for the start-up and cessation of simple shear and uniaxial extension. In summary, our work offers an approach to utilizing medium (and large) amplitude oscillatory shear results to predict stress dynamics of viscoelastic fluids in other transient, nonlinear flows.

Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

We present unique nonlinear rheological data of well-defined symmetric Cayley-tree poly(methyl methacrylates) in shear and uniaxial extension. Earlier work has shown that their linear viscoelasticity is governed by the hierarchical relaxation of different generations, whereas the segments between branch points are responsible for their substantial strain hardening as compared to linear homopolymers of the same total molar mass at the same value of imposed stretch rate. Here, we extend that work in order to obtain further experimental evidence that will help understanding the molecular origin of the remarkable properties of these highly branched macromolecules. In particular, we address three questions pertinent to the specific molecular structure: (i) Is steady state attainable during uniaxial extension? (ii) What is the respective transient response in simple shear? and (iii) How does stress relax upon cessation of extension or shear? To accomplish our goal, we utilize state-of-the-art instrumentation, i.e., filament stretching rheometry and cone-partitioned plate shear rheometry for polymers with 3 and 4 generations, and complement it with state-of-the-art modeling predictions using the branch-on-branch (BoB) algorithm. The data indicate that the extensional viscosity reaches a steady state value, whose dependence on extensional rate is identical to that of entangled linear and other branched polymer melts. Nonlinear shear is characterized by transient stress overshoots and the validity of the Cox–Merz rule. Remarkably, nonlinear stress relaxation is much broader and slower in extension compared to shear. It is also slower at higher generation, and rate-independent for rates below the Rouse rate of the outer segment. For extension, the relaxation time is longer than that of the linear stress relaxation, suggesting a strong “elastic memory” of the material. These results are described by BoB semiquantitatively, both in linear and nonlinear shear and extensional regimes. Given the fact that the segments between branch points are less than three entanglements long, this is a very promising outcome that gives confidence in using BoB for understanding the key features. Moreover, the response of the segments between generations controls the rheology of the Cayley trees. Their substantial stretching in uniaxial extension appears responsible for strain hardening, whereas coupling of stretches of different parts of the polymer appears to be the origin of the slower subsequent relaxation of extensional stress. Concerning the latter effect, for which predictions are not available, it is hoped that the present experimental findings and proposed framework of analysis will motivate further developments in the direction of molecular constitutive models for branched and hyperbranched polymers.

Effects of liquid crystalline and shear alignment on the optical properties of cellulose nanocrystal films

Rheo-optics, microspectrophotometry, and optical contrast measurements were used to gain new insights into the interrelated effects of liquid crystalline phase behavior, flow alignment, and microstructural relaxation on cellulose nanocrystal (CNC) films’ alignment and optical properties. Optical contrast measurements were found to be an effective and facile way of determining changes in anisotropy directly from cross-polarized microscopy images. This method was used to continuously measure microstructural relaxation after the cessation of shear as well as the anisotropy of dried CNC films. Aqueous liquid crystalline CNC dispersions showed greater alignment after shear than isotropic or biphasic dispersions. However, CNC gels exhibited lower alignment at equivalent shear rates. The combination of greater initial alignment and slower relaxation of sheared liquid crystalline dispersions resulted in the most optically anisotropic films. Depending on their thickness, the CNC films were optically transparent in the visible regime or exhibited tunable interference colors. The results of this work highlight the tunability of CNC dispersion processing for producing color filters and other optical materials with controlled properties.

Influence of electric field and shear on the rheology of fumed alumina in silicone oil suspensions

We investigate the effect of shear and electric field (E) on the rheology of fumed alumina (Al2O3) − in − silicone oil suspensions (Al2O3/silicone oil) at varying Al2O3 nanoparticle loadings of 0.5wt%–15wt%. 0.5wt% and 2.5wt% Al2O3/silicone oil suspensions behave as Newtonian fluids and form gel − like suspensions at a nanoparticle loading of 10wt% and above; attributed to the formation of a particulate network of fumed Al2O3 nanoparticles. Transient step − down experiments with 5wt% and 15wt% Al2O3/silicone oil suspensions indicate shear thinning and thixotropy. We also show that the dynamic rheology of gel − like 15wt% Al2O3/silicone oil suspensions is extremely sensitive to the preshearing protocols. Depending on the preshear, partial or complete breakdown of the network structure in 15wt% Al2O3/silicone oil suspensions is observed. Once the network structure breaks, the structural recovery doesn’t ensue at rest after the cessation of shear. On application of E, Al2O3/silicone oil suspensions with 0.5wt%–5wt% Al2O3 nanoparticle loading exhibit diverging low shear viscosity, frequency independent G′ along with the presence of a yield stress. The electrorheological response of 5wt% Al2O3/silicone oil suspensions is independent of the preshearing protocols at an applied E=1kV/mm. Furthermore, the shear rheology with applied E does not scale with γ˙E2, instead linear and sub-linear scaling with applied E is observed.