Oscillatory Shear Rheometry Research Articles

Strain hardening of acid-induced sodium caseinate gels as a function of pH and temperature

Strain hardening is a type of rheological behaviour that can be observed in large deformation tests of various materials. In oscillatory shear rheometry, it is characterised by an increase in storage and loss modulus (G′ and G″) with increasing oscillation amplitude (i.e, shear strain) until the material fractures and the moduli drop again. Acid-induced caseinate gels were previously shown to exhibit such a strain hardening behaviour. However, it has not been studied in much detailed how the extent of strain hardening is affected by pH and acidification temperature. In this work, the strain hardening of acid-induced caseinate gels was characterised as a function of pH by starting strain sweeps at various time points during acidification with glucono-delta-lactone, and the experiments were conducted at either 20, 30 or 40 °C to investigate the impact of temperature. The results demonstrate that the strain at fracture and the extent by which G′ increases with the strain amplitude change throughout acid-induced gelation of sodium caseinate in a complex manner with characteristic minima and maxima being barely related to the parameters observed in small strain experiments. The findings demonstrate the importance of considering the pH and temperature when characterising the strain hardening of caseinate gels as previous work showed that the strain hardening properties are related to water expression in forced syneresis experiments.

Optimizing the injection molding process for thermally and electrically conductive, carbon fiber and carbon nanotube‐reinforced poly(lactic acid) hybrid composites with enhanced mechanical properties

AbstractWe produced poly(lactic acid) (PLA) matrix carbon fiber and carbon nanotube‐reinforced hybrid composites with enhanced thermal conductivity (0.48–0.59 W/mK) and electrical conductivity (0.35–0.97 S/cm). The conductive fillers greatly decreased the toughness, which was compensated with oligomeric lactic acid (OLA). Since fillers and plasticizers greatly alter the flow and thermal properties of the material as well, it was necessary to optimize several parameters of the injection molding process that were predetermined based on theoretical considerations. Based on oscillatory shear rheometry, we explored the rheological behavior of the materials in a wide temperature and shear rate range for the optimum injection molding temperatures, injection volume rates. We showed that by adding 15 wt% OLA as a plasticizer to the composites, the optimal processing temperature decreased by 45–135°C. This remarkable change illustrates the need for rheological studies of PLA compounds. The injection molded hybrid composites containing 5% oligomeric lactic had a tensile strength, modulus of elasticity, and work of fracture higher by 41%, 10%, and 150%, respectively, compared to samples without OLA.

Dairy versus non-dairy cheese texture: Sensory and instrumental contrasts.

With growing consumer demand for plant-based products that mimic the eating experience of animal-based products, there is a need for improvement in instrumental measurements of sensory texture. This study aimed to characterize textural differences between dairy and non-dairy cheeses, and to investigate whether Large Amplitude Oscillatory Shear (LAOS) rheometry could discriminate sensory texture better than Texture profile analysis. Commercial dairy and non-dairy cheddar, mozzarella, and cream cheese were selected to provide a wide range of textures. Sensory evaluation used the check-all-that-apply methodology with 73 consumers. Texture profile analysis force-distance data were analyzed empirically, and also converted to stress and strain (see https://shiny.csiro.au/texture_dash). The major textural differences between dairy and non-dairy cheddar were related to structural cohesion, according to both instrumental measures (dairy cheddar had 1.5-fold higher failure stress and 2.2-fold higher failure strain) and sensory measurements (dairy cheddar was more chewy and less crumbly). In contrast, cream cheeses showed similar textural properties using sensory testing but significant instrumental differences (non-dairy cream cheese had 5.7-fold higher modulus of deformability, 4.7-fold higher failure stress). For mozzarella, there were large differences in both sensory attributes (chewy, crumbly, jelly-like, stretchy) and instrumental parameters (13.6-fold difference in modulus, 2.7-fold difference in failure stress). LAOS rheometry gave insights into the mechanisms by which samples absorbed or dissipated mechanical energy at nonlinear strains. The LAOS parameter correlated well with sensory attributes creamy, fatty/oily, and moist, indicating the potential of this technique to measure structural phenomena linked to sensory attributes that resonate with consumers.

Combining oscillatory shear rheometry and dynamic mechanical analysis to obtain wide-frequency master curves

In this paper, we present a novel approach combining widely available techniques, oscillatory shear rheometry and dynamic mechanical analysis to obtain wide-frequency range master curves. We carried out finite element analysis to investigate the influence of the specimen thickness and Poisson's ratio on the moduli measured with a shear sandwich clamp in solid-state. We demonstrated that the thickness/height ratio of the specimen greatly influences its shear stress state. Using polystyrene, which is a thermorheologically simple thermoplastic, we showed that continuous master curves can be generated from melt-state torsion and solid-state shear tests. Our results can facilitate the characterisation of polymers from viscous to elastic state and the development of test methods that use more accurate calculations.

Kinetic model-aided process optimization via integrated in-situ FTIR and real-time oscillatory shear rheometry: A case study on impurity control and gelation mitigation for a solid phase peptide cleavage process

Solid phase peptide synthesis is a widely used technique for the production of medicinal peptides, particularly when using unnatural amino acids. In such processes, when the synthesis is complete and the designed peptide sequence is obtained, a subsequent peptide isolation technique is often employed using a trifluoroacetic acid (TFA)/dichloromethane (DCM) solution mixture to promote the cleavage of the peptide from the resin while retaining the protecting groups on the peptide (soft cleavage). The peptide is then isolated via distillation, precipitation/crystallization, and drying unit operations. Throughout these processes, the reaction conditions must be optimized to minimize peptide degradation in the acidic cleavage solution. Furthermore, any peptide network formation during cleavage can dramatically increase the solution viscosity which poses significant operating risks in manufacturing. In this study, a systematic model-aided kinetics and rheology analysis is performed to rapidly identify optimal reaction conditions using the minimum number of screening experiments. The reaction kinetics investigation was conducted with the aid of a mid-FTIR probe to track peptide and TFA solution concentrations during the reaction in real-time. A detailed kinetics model of peptide cleavage and impurity formation is proposed and the adsorption isotherm of TFA is also considered. To confirm that an acceptable solution viscosity can be maintained at the specified reaction conditions over the duration of the projected process time, in-situ oscillatory rheometry was conducted to monitor any viscosity and modulus increase in the soft-cleavage reaction medium. The novel combination of reaction kinetics modeling, impurity control techniques, and the development of a peptide network phase diagram provides a layered approach that can be utilized in the rapid rational design of any solid phase peptide isolation processes.

Effect of caseinate salt addition on the structural characteristics of kefiran systems.

Sodium caseinates-kefiran systems were studied to explore whether any potential interactions between them might exist. The study was performed using low-deformation rheological techniques, which were dynamic and creep tests. The systems were prepared under various experimental conditions such as heating and acidification. Besides, the structure development of the systems in relation to time was also monitored using oscillatory shear rheometry. The results indicated that the structural characteristics of the systems were mainly affected by the state of the caseinates such as the formation of aggregates and to a lesser degree by the interactions of kefiran molecules with the caseinates. Freeze-thaw treatment produced cryogels with good thermal stability and fairly satisfactory mechanical properties. The morphology of the caseinate-kefiran systems was also investigated by means of confocal laser scanning microscopy.

Star-to-Bottlebrush Transition in Extensional and Shear Deformation of Unentangled Polymer Melts

A series of model poly((±)-lactide) (PLA) graft copolymers was synthesized by ring-opening metathesis polymerization and used to probe the star-to-bottlebrush transition in shear and extensional flows. Ten samples with backbone degrees of polymerization 11 ≤ Nbb ≤ 420 were investigated using small-amplitude oscillatory shear (SAOS) and extensional rheometry measurements. Each contained one PLA side chain of length Nsc = 72 per two backbone repeating units on average (graft density of z = 0.5). The star-like to bottlebrush transition was identified at Nbb = 50–69 using SAOS. In extension, melt strain hardening is absent in the star-like melts (Nbb ≤ 50) but is prominent in the bottlebrush limit (Nbb > 69). The onset of melt strain hardening occurs at a time scale equivalent to the Rouse time of the backbone. A molecular interpretation of these results builds upon recent conjectures related to strain-induced increases in interchain friction in bottlebrush polymers. These findings will be useful in designing bottlebrush melts that strain harden, which is critical in various types of processing methods involving extensional flows, including foaming, 3D printing, and film-blowing.

Gaborheometry: Applications of the discrete Gabor transform for time resolved oscillatory rheometry

Oscillatory rheometric techniques such as small amplitude oscillatory shear (SAOS) and, more recently, medium amplitude oscillatory shear and large amplitude oscillatory shear (LAOS) are widely used for rheological characterization of the viscoelastic properties of complex fluids. However, in a time-evolving or mutating material, the build-up or breakdown of microstructure is commonly both time- and shear-rate (or shear-stress) dependent, and thixotropic phenomena are observed in many complex fluids including drilling fluids, biopolymer gels, and many food products. Conventional applications of Fourier transforms for analyzing oscillatory data assume the signals are time-translation invariant, which constrains the mutation number of the material to be extremely small. This constraint makes it difficult to accurately study shear-induced microstructural changes in thixotropic and gelling materials, and it is becoming increasingly important to develop more advanced signal processing techniques capable of robustly extracting time-resolved frequency information from oscillatory data. In this work, we explore applications of the Gabor transform (a short-time Fourier transform combined with a Gaussian window), for providing optimal joint time-frequency resolution of a mutating material’s viscoelastic properties. First, we show using simple analytic models and measurements on a bentonite clay that the Gabor transform enables us to accurately measure rapid changes in both the storage and/or loss modulus with time as well as extract a characteristic thixotropic/aging time scale for the material. Second, using the Gabor transform we demonstrate the extraction of useful viscoelastic data from the initial transient response following the inception of oscillatory flow. Finally, we consider extension of the Gabor transform to nonlinear oscillatory deformations using an amplitude-modulated input strain signal, in order to track the evolution of the Fourier–Tschebyshev coefficients of thixotropic fluids at a specified deformation frequency. We refer to the resulting test protocol as Gaborheometry (Gabor-transformed oscillatory shear rheometry). This unconventional, but easily implemented, rheometric approach facilitates both SAOS and LAOS studies of time-evolving materials, reducing the number of required experiments and the data postprocessing time significantly.

Effect of the double heating cycle on the thermal gelling properties of vicilin fractions from soy, mung bean, red bean and their mixture with soy glycinin

This study investigated the effect of a double heating cycle (90 °C) on the thermal gelling behavior of fractionated vicilins from soybean (SV), mung bean (MV) and red bean (RV) with and without soy glycinin (SG). Both MV and RV consisted of peptides with relatively low Mw comparing to those of SV. Differential scanning calorimetry (DSC) indicated that MV and RV had a greater thermal stability than those of SV. Based on oscillatory shear rheometry, the first heating could not cause the gelation of MV and RV, but the thermal gel of both vicilins could be formed by the second heating stage. The stiffness of the RV gel was lower than that of MV. Based on texture profile analysis (TPA), the hardness and springiness of gel prepared by MV did not differ from those of SV, whereas RV gel showed high cohesiveness but low hardness and springiness compared to that of SV (p < 0.05). The gumminess of MV and RV gels was lower than that of SV gel (p < 0.05). The differences in TPA parameters between MV and RV were mainly due to different contributions of hydrophobic and electrostatic interactions, which also affected their microstructures. However, their gel characteristics disappeared when SG was mixed with these vicilins. The results indicated that both MV and RV had a potential to regulate the textural properties of soy protein-based gel matrix, and double heating was necessary to form a viscoelastic thermal gel containing vicilin fractions.

Secondary structure and stability of a gel-forming tardigrade desiccation-tolerance protein.

Protein-based pharmaceuticals are increasingly important, but their inherent instability necessitates a "cold chain" requiring costly refrigeration during production, shipment, and storage. Drying can overcome this problem, but most proteins need the addition of stabilizers, and some cannot be successfully formulated. Thus, there is a need for new, more effective protective molecules. Cytosolically, abundant heat-soluble proteins from tardigrades are both fundamentally interesting and a promising source of inspiration; these disordered, monodisperse polymers form hydrogels whose structure may protect client proteins during drying. We used attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, and small-amplitude oscillatory shear rheometry to characterize gelation. A 5% (wt/vol) gel has a strength comparable with human skin, and melts cooperatively and reversibly near body temperature with an enthalpy comparable with globular proteins. We suggest that the dilute protein forms α-helical coiled coils and increasing their concentration drives gelation via intermolecular β-sheet formation.

Dynamics of entangled metallosupramolecular polymer networks combining stickers with different lifetimes

We study the linear viscoelastic properties of polymeric networks formed by poly(n-butyl acrylate) telechelic stars end-capped with 2,2:6,2″-terpyridine (Star-PnBA-tpy4) and two types of metal-ligand cross-links with different lifetimes. The influence of interactions, mediated by temperature, nature of metal ions, and ion content, on the linear viscoelastic behavior of both single and double dynamics transient networks is systematically investigated by small amplitude oscillatory shear and creep rheometry. The experimental results reveal that the dynamics of networks with two different metal-ligand cross-links is much faster than expected, characterized by the average sticker lifetime rather than a discrete contribution of each metal-ligand complex. We model the dynamics with the help of our modified tube-based time marching algorithm by accounting for both association/dissociation dynamics of metal-ligand coordination and the entanglement dynamics. Two parameters are defined in the model, namely, the proportion of dangling ends and the average time during which a sticker is free. This allows us to quantify the transient dynamics of the network and, in particular, to determine how the sticker dynamics depend on temperature and ion content.

Modulation of Biofilm Mechanics by DNA Structure and Cell Type.

Deoxyribonucleic acid (DNA) evolved as a tool for storing and transmitting genetic information within cells, but outside the cell, DNA can also serve as "construction material" present in microbial biofilms or various body fluids, such as cystic fibrosis, sputum, and pus. In the present work, we investigate the mechanics of biofilms formed from Pseudomonas aeruginosa Xen 5, Staphylococcus aureus Xen 30, and Candida albicans 1408 using oscillatory shear rheometry at different levels of compression and recreate these mechanics in systems of entangled DNA and cells. The results show that the compression-stiffening and shear-softening effects observed in biofilms can be reproduced in DNA networks with the addition of an appropriate number of microbial cells. Additionally, we observe that these effects are cell-type dependent. We also identify other mechanisms that may significantly impact the viscoelastic behavior of biofilms, such as the compression-stiffening effect of DNA cross-linking by bivalent cations (Mg2+, Ca2+, and Cu2+) and the stiffness-increasing interactions of P. aeruginosa Xen 5 biofilm with Pf1 bacteriophage produced by P. aeruginosa. This work extends the knowledge of biofilm mechanobiology and demonstrates the possibility of modifying biopolymers toward obtaining the desired biophysical properties.

The role of molecular architecture on the viscoelastic properties of thermoreversible polyurethane adhesives

New polyurethane (PUR) adhesives containing covalent Diels-Alder (DA) bonds that can break and form with temperature have been recently developed for sustainable multilayer packaging. The understanding of the mechanical properties and in particular of creep in terms of molecular architecture appears of outmost importance in view of their applications and potential reutilization. Oscillatory shear rheometry shows a modulus decrease with temperature associated to bond breakage and the enhancement found upon cooling can be associated with network reconstruction. Analysis of storage modulus values above the glass transition and below the retro-DA reaction suggests a lower network crosslinking density with increasing adduct content. Room temperature indentation and shear rheometry tests reveal that DA bonds improve the modulus and reduce the resistance to linear viscoelastic flow. The modulus improvement can be associated to the enhanced chain rigidity introduced by the DA moieties and the reduced creep resistance seems to be related to the decrease of crosslinking density.

Rheological analysis of a novel phenylboronic acid-closomer gel

This study aims to characterize the rheological behavior of a novel phenylboronic acid (PBA)-based closomer nanoconjugate (Closogel) with potential application in pharmaceutical formulation. PBA was used as a cross-linking agent and model (antiviral) drug. The PBA loaded Closogel chemical structure was analyzed by boron (11B) NMR and Fourier transform infrared (FTIR) spectroscopy. The Closogel and control hydroxyethyl cellulose (HEC) gel were analyzed under oscillatory and continuous shear rheometry followed by mathematical modeling to characterize the gel flow behavior. The chemical analysis confirmed the existence of characteristic borate esters peaks and Boron chemical shifts within Closogel spectra. Due to its more flexible molecular structure, undiluted Closogel exhibited lower, yield stress, viscosity and relaxation time (30 Pa &163 Pa.s & 0.21 s vs 45 Pa &301 Pa.s & 0.39 s for HEC). Both Closogel and HEC gels exhibited a thixotropic behavior. The plastic undiluted and pseudoplastic 2.5 % w/v aqueous Closogels were more viscous than elastic (tan (δ) > 1) in the linear viscoelastic range. The Herschel-Bulkley model showed a significant fitting to all experimental data (R2 > 0.95). The 0.25 % w/v aqueous Closogel nearly exhibited a Newtonian behavior with a flow index of 0.93. These data suggest that PBA loaded Closomer-based gels have similar rheological behavior, with lower complex modulus than that of HEC gels, and they can be a promising platform used for delivery of topical antiviral or other bioactive agents.

Rheology of supercooled P-Se glass-forming liquids: From networks to molecules and the emergence of power-law relaxation behavior.

The effect of the network-to-molecular structural transformation with increasing phosphorus content in PxSe100-x (30 ≤ x ≤ 67) supercooled liquids on their shear-mechanical response is investigated using oscillatory shear rheometry. While network liquids with 30 ≤ x ≤ 40 are characterized by shear relaxation via a network bond scission/renewal process, a Maxwell scaling of the storage (G') and loss (G″) shear moduli, and a frequency-independent viscosity at low frequencies, a new relaxation process emerges in liquids with intermediate compositions (45 ≤ x ≤ 50). This process is attributed to an interconversion between network and molecular structural moieties. Predominantly molecular liquids with x ≥ 63, on the other hand, are characterized by a departure from Maxwell behavior as the storage modulus shows a linear frequency scaling G'(ω) ∼ ω over nearly the entire frequency range below the G'-G″ crossover and a nearly constant ratio of G″/G' in the terminal region. Moreover, the dynamic viscosity of these rather fragile molecular liquids shows significant enhancement over that of network liquids at frequencies below the dynamical onset and does not reach a frequency-independent regime even at frequencies that are four orders of magnitude lower than that of the onset. Such power-law relaxation behavior of the molecular liquids is ascribed to an extremely broad distribution of relaxation timescales with the coexistence of rapid rotational motion of individual molecules and cooperative dynamics of transient molecular clusters, with the latter being significantly slower than the shear relaxation timescale.

A theory of finite tensile deformation of double‐network hydrogels

AbstractA continuum damage model was developed to describe the finite tensile deformation of tough double‐network (DN) hydrogels synthesized by polymerization of a water‐soluble monomer inside a highly crosslinked rigid polyelectrolyte network. Damage evolution in DN hydrogels was characterized by performing loading‐unloading tensile tests and oscillatory shear rheometry on DN hydrogels synthesized from 3‐sulfopropyl acrylate potassium salt (SAPS) and acrylamide (AAm). The model can explain all the mechanical features of finite tensile deformation of DN hydrogels, including idealized Mullins effect and permanent set observed after unloading, qualitatively and quantitatively. The constitutive equation can describe the finite elasto‐plastic tensile behavior of DN hydrogels without resorting to a yield function. It was showed that tensile mechanics of DN hydrogels in the model is controlled by two material parameters which are related to the elastic moduli of first and second networks. In effect, the ratio of these two parameters is a dimensionless number that controls the behavior of material. The model can capture the stable branch of material response during neck propagation where engineering stress becomes constant. Consistent with experimental data, by increasing the elastic modulus of the second network the finite tensile behavior of the DN hydrogel changes from necking to strain hardening.

The rheology of ultra-high molecular weight poly(ethylene oxide) dispersed in a low molecular weight carrier.

Gel spinning is the industrial method of choice for combining hydrophilic ultra-high molecular weight (UHMW) polymer resins with a hydrophobic support polymer to produce composite filaments for cytapheresis. Cytapheresis is a medical technique for removal of leukocytes from blood. Gel spinning is used to avoid high melt viscosity and thermal sensitivity of UHMW resins and the high melt temperature of the substrate resin but requires the recovery of toxic solvents. The UHMW resin is used because it forms a stable gel phase in the presence of water; a lower molecular weight resin (LMW) simply dissolves. UHMW and LMW resins were both poly(ethylene oxide) (PEO) and the substrate was polyarylsulfone (PAS). The literature indicated PEO undergoes non-oxidative thermal degradation above 200 °C and PAS is processed up to 350 °C. Dynamic oscillatory shear rheometry was used to study 0, 25, 40, 50, 60, and 75 wt. % UHMW PEO in LMW PEO to take advantage of the sensitivity of viscosity to changes in molecular weight and material configuration, indicating degradation. Samples were exposed to 220 °C, 230 °C, 240 °C, 250 °C, 275 °C, and 300 °C temperatures for 5 min to explore conditions that could result in sample degradation. The viscosity decreased less with increasing UHMW PEO content for samples exposed to the same temperature and the viscosity decreased more with increasing exposure temperature for samples with the same UHMW PEO content. Parameters were regressed from observed data to predict the change in molecular weight via empiricisms relating the viscosity to molecular weight, shear rate, temperature, and time.

Oscillatory shear rheometry of hybrid polymer-modified bitumen using multiple stress creep and recovery and linear amplitude sweep tests

Modifying bitumen by combining elastomers and plastomers has been reported to result in improved overall performance. However, the assessment of the rheological properties is commonly done in the linear visco-elastic region at low strain levels. In this paper, the rutting and fatigue resistance of modified bitumen was evaluated using multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests. A base bitumen was modified with styrene butadiene styrene (SBS), crumb rubber (CR), ethylene–vinyl acetate (EVA) and various polyethylene to study the effects of these modifiers on the rheological behaviour of hybrid polymer-modified bitumen (PMB). These effects were measured using the non-recoverable creep compliance (Jnr) and percentage recovery (R%) in MSCR tests and by evaluating the fatigue damage using Viscoelastic Continuum Damage (VECD) analysis in LAS tests. Results showed that combining SBS, recycled polyethylene and sulphur resulted in the highest percentage recovery value, whereas using CR with SBS did not significantly affect the rheological results. Sulphur played an important role as a cross-linking agent. Concerning Jnr, the addition of sulphur help lowers the MSCR characteristic values, hence indicating better rutting performance. From the VECD analysis, the utilization of hybrid polymers improved the fatigue performance when compared with unmodified bitumen. Based on the overall MSCR and LAS results, the utilization of waste polymers such as recycled polyethylene and CR has resulted in highly satisfactory performance for both rutting and fatigue resistance. Hence, the usage of waste polymers can be considered a suitable alternative to replace virgin polymers.

Enzyme cross-linked pectin microgel particles for use in foods

We report on a new enzyme-based method for producing permanently cross-linked pectin microgels. We investigate the shape, size and rheological properties of these microgel particles making comparisons with the more traditional design of calcium cross-linked pectin microgels. Both sets of microgel particles were prepared via the ‘top-down’ mechanical disruption of parent pectin hydrogels. The first hydrogel was prepared from low methoxyl pectin (LMP) (2 wt% pectin) cross-linked using Ca2+ (8.3 mM CaCl2). The LMP microgels show particle sizes ca. 1–100 μm, but are stable only in [Ca2+] = 8.3 mM or above, swelling and/or dissolving rapidly in pure water. The second type of microgel was prepared from sugar beet pectin (SBP) hydrogels covalently cross-linked via laccase. Gelation kinetics were investigated by small amplitude oscillatory shear rheometry. The SBP microgels resisted dissolution in water for several months. Light scattering measurements suggested that the SBP microgel particle sizes were related to the mechanical properties of the parent hydrogels. Various imaging techniques all suggested that SBP microgels have highly irregular shapes, perhaps due to the top-down technique used for their manufacture and their inherent mechanical properties. Concentrating the SBP microgels (to 35–50 wt% microgel, or 0.6–0.8 wt% overall pectin concentration) resulted in suspensions with rheological properties typical of yield stress fluids. When compared at similar overall SBP concentrations, the SBP microgel suspensions offer distinct advantages as bulk rheology modifiers compared to SBP solutions.

Colloidal Physicochemical Properties and Variation Mechanisms of Lithium Complex Grease under Limited Operating Temperature

Abstract This study aims to investigate the colloidal physicochemical properties and variation mechanisms of lithium complex grease after heating at a limited operating temperature (180°C). Experimental lubricating grease samples were prepared by static heating in the laboratory for different times to simulate the limited operating temperature. The variations in grease mass loss and consistence were studied. Rheological behavior tests were carried out to explore the structural strength and structural recovery properties of all grease samples by using a continuous shear and oscillatory shear rheometry model of rotational rheometer. The fibrous microstructure was investigated by field emission scanning electron microscope, and infrared spectra were recorded using a Fourier transform infrared spectrometer. A structural evolution model of grease colloidal dispersion system was established and used to elucidate the variation mechanism of grease colloidal physicochemical properties under limited operating temperature conditions. The colloidal property of lithium complex grease gradually changed with prolonged heating time. The consistence of grease increased with increasing heating time. The typical shear yield phenomenon became less obvious, and the structural recovery property evidently weakened obviously with prolonged heating time. The variation mechanism of grease colloidal physicochemical properties could be mainly attributed to the thickener oxidation of grease. Results provide experimental support for grease application and failure analysis under harsh conditions.