Rheology Of Materials Research Articles

Aeration and rheology of buttercream icings

Buttercream icings – 4 phase materials comprising sugar, butter (an emulsion) and air – are widely used for coating and decorating sweet goods. The aeration of 2:1 w/w sugar-butter mixtures was investigated in 2 benchtop planetary mixers and the rheology of the resultant viscoplastic material was quantified using lubricated compressive testing (squeeze flow and upsetting) over extensional shear rates of 10−3–100 s−1. The aeration dynamics exhibited asymptotic behaviour which fitted a simple phenomenological model well. Optical microscopy and X-ray microtomography indicated that the air was incorporated as small bubbles of similar size to the sugar particles or as voids generated by the mixer wires. The measured yield stress was strongly dependent on the air volume fraction, φ. The flow behaviour for one batch could be reasonably described as a Herschel-Bulkley fluid whereas a second batch gave overall better agreement with a modified power-law description: in both cases the viscous friction term decreased strongly with φ.

Design and optimization of the magnetic field-driven spherical gripper with adjustable stiffness

This paper presents a new gripping technique that merges the variable stiffness characteristics of conventional magnet-controlled and negative-pressure spherical grippers to produce a spherical gripper capable of securely grasping large and structurally diverse objects. The proposed method incorporates the smart rheological material from magnet-controlled grippers with the particle-jamming smart structure used in negative-pressure grippers. The gripper comprises a magnetic control device and a spherical variable stiffness body. Simulation analysis was used to optimize its structure and enhance the efficiency ratio of the magnetic control device. The flexible variable stiffness body was initially designed to be cylindrical to increase interlocking with objects. Experiments were conducted to evaluate the gripping efficiency and adaptability of the magnetron spherical gripper, which were designed to simulate real-world application requirements. These results suggest that the magnetically controlled spherical gripper can achieve a gripping efficiency of approximately five and securely grasp objects with a relative bladder diameter ranging from 20 % to 130 %. Furthermore, it can stably grip objects up to an offset distance of 15 mm without requiring sensor assistance. The enhanced magnetic field-powered spherical gripper exhibits superior adaptability and efficiency in gripping compared to its counterpart. In addition, it boasts robust resistance against environmental interference.

Rheology of sheared polyhedral granular materials in inclined flows

An investigation of frictional, Platonic solid-shaped particle flows on inclined planes is performed using the discrete element method, and the effects of particle angular shape on rheological properties are analyzed. Higher shear stresses at a specified depth of particle bed are obtained for more angular particles. As particle angularity increases, rapid surges in the coordination number and solid-phase stresses occur at a smaller critical solid volume fraction. The friction and dilatancy laws of polyhedral particle flows are significantly different from those of spherical particle flows, due to particle angularity. Nevertheless, by applying a specific rolling friction to the spherical particles, their rheological properties can match those of the polyhedral particles, indicating that the angular particle shape plays a similar role to the rolling friction in preventing particle rotation. Thus, the flows of spherical particles with a rolling friction incorporated can be used to mimic the flows of angular polyhedral particles. At last, a scaling law is adopted to describe rheological relations for various polyhedral particles based on a bulk friction coefficient, a dimensionless granular temperature, and an inertial number.

Steady elongational flow from rotarance theory

The physics of macromolecular orientation has been used to explain the elasticity of polymeric liquids. Specifically, by first sculpting a rigid bead–rod likeness of the macromolecule, we can then derive its hydrodynamic resistance to orientation. The solution for the orientation distribution function has then been used, by integration in phase space, to get rheological material functions in both (i) small- and (ii) large-amplitude oscillatory shear flow, including its limiting case, and (iii) steady shear flow. However, rheological material functions in steady homogeneous extension from rigid bead–rod theory remain elusive. In this paper, we derive the orientation distribution function, and the rheological material functions, for suspensions of general rigid bead–rod structures. We focus on the time-steady viscosities in extension, and we first do so for general extensional kinematics. We then obtain the viscosities in steady extension for (iv) uniaxial extension, (v) planar extension, and (vi) biaxial extension. We close with a worked example, in which we use our new result for the steady uniaxial extensional viscosity to build a bridge between the macromolecular theory and the Oldroyd framework for rheological constitutive models. We, thus, arrive at a constitutive equation whose parameters are deducible from the moments of inertia of the macromolecule, and thus, deducible from macromolecular architecture alone. Our model is accurate up to third order for time-independent flows and is accurate to second order for time-dependent ones.

Smart materials for experimental tectonics: Viscous behavior of magnetorheological silicones

Magnetorheological (MR) materials are a relatively new class of materials whose mechanical properties can be controlled by a magnetic field. In this work, we investigate the viscous behavior of MR silicones, i.e., mixtures of Polydimethyl Siloxane (PDMS) and carbonyl iron powder, for analog modeling purposes. The rheological properties were determined using a parallel plate rheometer equipped with a variable strength electromagnet. We measured viscosity, yield stress and response time of MR silicone samples in a wide range of strain rates as a function of concentration of carbonyl iron powder and applied magnetic field. We find that MR silicones in the unmagnetized state show a transition from Newtonian to shear-thinning behavior for increasing strain rates. In the magnetized state, MR silicones behave as Herschel-Bulkley, shear-thinning fluids. Viscosity, yield stress and power-law exponent increase as a function of carbonyl iron powder concentration and magnetic field. A simple experiment is presented to demonstrate how the rheology of the analog material can be easily controlled during an experimental run, a condition that is challenging to achieve with other materials commonly used in experimental tectonics.

Chemically reactive Squeezed flow of Maxwell nanofluid confined by parallel stratified walls subjected to radiative flux

This study features numerical analysis of squeezing flow within a confined parallel-wall geometry subjected to chemical reactions, magnetohydrodynamics (MHD), transpiration, double stratification, heat generation and thermal radiation. The flow formulation in this research is based on the rheological expressions of a rate type (Maxwell) fluid capturing the non-Newtonian behavior. Such consideration enables the modeling of complex fluid behavior involving both viscous and elastic responses, making it applicable to a wide range of scenarios in materials science, rheology, and fluid dynamics. In addition, the Buongiorno two-component nanofluid model is opted to model the transport equations. Equations elaborating the dynamics of fluid flow and heat-mass transport are established, taking into account the specific assumptions like the presence of a lower magnetic Reynolds number and the insignificance of viscous dissipation. Following this, these equations are transformed into a dimensionless form by introducing similarity variables. The numerical simulations are carried out utilizing the MATLAB software package, employing the bvp4c scheme. Our findings indicate a rise in horizontal and vertical velocities subjected to higher squeezing parameter, however, contrasting results are found for temperature, where an increase in squeezing parameter led to a diminution in temperature, signifying a cooling effect.

Optimization on the mix design method of self-compacting concrete with recycled coarse aggregate based on paste rheological threshold theory and material packing characteristics

This study aims to use the mixture design method to optimize self-compacting concrete (SCC) and manufacture SCC with excellent workability using recycled coarse aggregate (RCA) and a ternary cementitious system. The influences of incorporated RCA on the rheological thresholds of SCC with a fixed content of fly ash (FA) and blast furnace slag (BFS) are investigated based on paste rheological threshold theory and material packing characteristics. The original rheological model is improved by introducing the volume of adhesive mortar and modifying the equivalent packing density and mortar film thickness. The improved model is incorporated into the original theoretical system to apply the optimized mix design method to SCC. Moreover, experiments are conducted with different volumes of water, water-powder ratios and RCA replacement levels to verify the applicability of the optimized method. The results indicate that the proposed models can accurately predict the yield strength threshold and plastic viscosity threshold of fresh SCC. Furthermore, compared to the original model, predictions are 53% more accurate with the modified model.

Influence of filler concentration and type on rheological and mechanical properties of liquid isoprene rubber for high-strength parts via material extrusion

This study investigates the rheological behavior and material extrusion performance of liquid isoprene rubber (LIR) compounds filled with carbon black (CB), silica (Si), and recycled crumb rubber (CR) fillers for potential additive manufacturing applications. The rheological properties of the LIR mixtures were characterized using flow curve analysis and temperature sweeps, identifying shear-thinning behavior and temperature-dependent viscosity ultimately reflecting the final dimensional tolerance of the prints. Vulcanization time (t90) was determined using oscillatory rheometry, and the effect of filler concentration on t90 was evaluated. Mechanical testing was conducted to assess the hardness and tensile properties. The results demonstrate the influence of filler concentration on the rheological properties, printability, and mechanical performance of the LIR compounds thus resulting in the printing of high-strength (σu > 5 MPa) isoprene rubber parts capable of being additively manufactured.

(Invited) Poly(lactic acid)-Nanodiamond Composites for Electroanalytical Applications

There has been an exponential increase in the popularity of 3D printing technology in the last few years, also in everyday life. Numerous applications are reported for poly(lactic acid) (PLA) based polymer composites with various conductive carbon fillers for electrochemical needs, such as sensors, batteries, water remediation, etc. The bulk of these reports is based on commercially available 3D printing filaments, with carbon black, graphene or carbon nanotubes as fillers. Regardless of good conductivity, these materials possess characteristics that are suboptimal for electrochemical applications, including charge transfer kinetics, stability to oxidation, electrolytic window, etc.3D printouts offer versatility in terms of ease of cheap and on-demand fabrication of free-standing multielectrode setups e.g. by dual-extruder printing. However, to fully embrace their advantages enhancement of charge transfer kinetics by removing an excess of PLA and uncovering the nanofillers, is needed. Recently we have demonstrated laser ablation for locally sculptured effective modification of the electrochemical response of these materials.There is a great focus on the development of new conductive filaments that exhibit better mechanical, electric, thermal, and electrochemical properties. We have evaluated for the first time various forms of conductive nanodiamonds (ND), i.e. detonation nanodiamonds and diamond-phase rich boron-doped carbon nanowalls, as fillers for PLA-based composites for 3D printing. The goal of the research was to investigate and thoroughly understand the interactions between composite components and those that affect the mechanical parameters and electrochemical characteristics of printed elements, studying how ND addition to PLA matrix affects material strength, rheology, and melting temperature. In particular, the enhancement of electrode kinetics and electrochemically available surface area by ND was revealed and discussed. The authors acknowledge the financial support by The National Science Centre (Republic of Poland) SONATA BIS 2020/38/E/ST8/00409.

On Applicability of the Relaxation Spectrum of Fractional Maxwell Model to Description of Unimodal Relaxation Spectra of Polymers.

The relaxation time and frequency spectra are vital for constitutive models and for insight into the viscoelastic properties of polymers, since, from the spectra, other material functions used to describe rheological properties of various polymers can be uniquely determined. In recent decades the non-integer order differential equations have attracted interest in the description of time-dependent processes concerning relaxation phenomena. The fractional Maxwell model (FMM) is probably the most known rheological model of non-integer order. However, the FMM spectrum has not yet been studied and used to describe rheological materials. Therefore, the goal of the present paper was to study the applicability of the relaxation spectrum of FMM to the description of the relaxation spectra of polymers. Based on the known integral representation of the Mittag-Leffler two-parameter function, analytical formulas describing relaxation time and frequency spectra of FMM model were derived. Monotonicity of the spectra was analyzed and asymptotic properties were established. Relaxation frequency spectrum grows for large frequencies with a positive power law, while the relaxation time spectrum decays for large times with a negative power of time. Necessary and sufficient conditions for the existence of the local extrema of the relaxation spectra were derived in the form of two trigonometric inequalities. A simple procedure for checking the existence or absence of the spectra extrema was developed. Direct analytical formulas for the local extrema, minima, and maxima are given in terms of model fractional and viscoelastic parameters. The fractional model parameters, non-integer orders of the stress and strain derivatives of FMM uniquely determine the existence of the spectrum extrema. However, the viscoelastic parameters of the FMM, elastic modulus, and relaxation time affect the maxima and minima of the relaxation spectra and the values of their local peaks. The influence of model parameters on their local extrema was examined. Next, the applicability of the continuous-discrete spectrum of FMM to describe Baumgaertel, Schausberger and Winter (BSW) and unimodal Gauss-like relaxation spectra, commonly used to describe rheological properties of various polymers, was examined. Numerical experiments have shown that by respective choice of the FMM parameters, in particular by respective choice of the orders of fractional derivatives of the stress and strain, a good fit for the relaxation modulus experiment data was obtained for polymers characterized both by BSW and Gauss-like relaxation spectra. As a result, a good approximation of the real spectra was reached. Thus, the viscoelastic relaxation spectrum of FMM, due to the availability of the two extra degrees of freedom (non-integer orders of the stress and strain derivatives), provides deep insights into the complex behavior of polymers and can be applied for a wide class of polymers with unimodal relaxation spectra.

Influence of Reinforcement Particle Parameters on the Homogeneity of Particle Distribution in Semi-Solid Formed Aluminium Matrix Composites

Aluminium matrix composites (AMCs) offer improved mechanical and tribological properties compared to monolithic materials and therefore provide great potential for various applications. This particularly applies to particle-reinforced AMCs revealing comparatively high contents of reinforcement particles. However, these types of composites are difficult to manufacture due to their abrasive characteristics as well as their complex rheological material behaviour. An approach to produce such AMCs is semi-solid powder processing, combining powder pressing and sintering in one step in order to produce fully dense composites with currently only cylindrical shapes. Therefore, the tools as well as the powder mixture are first heated into the semi-solid temperature range of the aluminium powder and subsequently formed using low pressures under 200 MPa. Due to the shear thinning behaviour of the semi-solid aluminium matrix the porous structure of the pressed powder is filled during compaction, resulting in homogenous particle distributions in the component. However, this process results in high process times as well as energy costs, due to the heating inside of the die. In contrast to the semi-solid powder processing in one step, in this paper, a novel process route combining cold uniaxial compaction of particle reinforced aluminium powders having up to 50 vol.% SiC with subsequent semi-solid forming is presented. Here, a particle reinforced and cylindrically shaped green body is utilized as raw material, in order to produce complex components through semi-solid forming. The parts produced in this way are featuring varying wall thicknesses and are used in order to determine the process limits for manufacturing particle reinforced components having up to 50 vol.% SiC. Thereby, the influence of reinforcement particle size as well as particle loading on the homogeneity of the resulting particle distribution of an academic component is investigated. Future main objective of the process route is the manufacturing of complex parts with homogenously distributed particles.

Semi-Analytical Results for the Linear Nonaging Viscoelastic Contact Behaviors

This paper investigates the importance of creep and relaxation functions in modeling the Hertzian contact problem between linear nonaging viscoelastic materials and viscoelastic rough surfaces. We provide novel analytical and semi-analytical solutions to these functions for various materials, including Generalized Maxwell, Generalized Kelvin, and Burgers’ rheological materials. Closed-form and semi-analytical solutions are developed for several specific cases with high practical applications, such as the contact between incompressible solids, a rigid material and an incompressible material, and two solids with no volumetric viscous strain. They are extensions of existing solutions given in the literature. A simple computation procedure based on the discretized integral technique is proposed for the general case of contact between linear nonaging viscoelastic materials. This proposed method is easy to implement in practical applications such as the interpretation of viscoelastic indentation tests for material characterization and the implementation of viscoelastic contact in finite/discrete element simulations.

Design optimization of 3D printed concrete elements considering buildability

In this paper, we propose an integration of 3D concrete printing buildability requirements into a formal structural optimization problem. The aim is to enable the design of a structural element while balancing between its performance as a load-bearing element and its stability during the printing process. Physical buildability is quantified by stress constraints imposed on the fresh concrete, whose time-dependent strength is determined according to a rheological material characterization. This is complemented by geometric buildability that is achieved by imposing constraints on the overlap between layers. The output of optimization is the shape of the structure and the time instance at which each layer is deposited. Several prototypes were printed for verifying the numerical buildability predictions, showing acceptable quantitative agreement between theory and experiments. A critical trade-off between structural performance and buildability is exposed, that emphasizes the need for further development of holistic methodologies that integrate structural design, material design and tooling limitations.

Smart superplasticizers based on redox-responsive polymers for rheology control of cementitious materials

A new concept is introduced for active rheology control of cementitious materials using stimuli-responsive polymers. RAFT polymerization of methacrylic acid (MAA) and 2,2,6,6, tetramethyl-4-piperidyl methacrylate (TMPMA) was employed to prepare poly(MAA-co-TMPMA) as precursor for the preparation of poly(MAA-co-TEMPO), a redox-responsive copolymer containing 2,2,6,6-tetramethylpiperidine-1-oxyl group. Poly(MAA-co-TEMPO) is soluble in alkaline water and undergoes a redox switch when electrically triggered, oxidizing the TEMPO group to the oxoammonium cations (TEMPO+). The observed active stiffening control is hypothesized to result from adsorption of the negatively charged copolymer with the TEMPO side chains on cement particles and (partial) desorption of the zwitterionic copolymer with the TEMPO+ side chains. The new chemical admixtures could enhance flowability of cement pastes at low W/C ratio and sharply increase storage modulus when applying an electric potential of 1 V. Poly(MAA-co-TEMPO) acts as smart superplasticizer that can actively alter the rheology of cementitious materials upon applying an electric voltage.

Microstructural and thermodynamic characterization of wormlike micelles formed by polydisperse ionic surfactant solutions.

For industrial applications of self-assembled wormlike micelles, measurement and characterization of a micellar material's microstructure and rheology are paramount for the development and deployment of new high-performing and cost-effective formulations. Within this workflow, there are significant bottlenecks associated with experimental delays and a lack of transferability of results from one chemistry to another. In this work, we outline a process to predict microscopic and thermodynamic characteristics of wormlike micelles directly from rheological data by combining a more robust and efficient fitting algorithm with a recently published constitutive model called the Toy Shuffling model [J. D. Peterson and M. E. Cates, J. Rheol. 64, 1465-1496 (2020) and J. D. Peterson and M. E. Cates, J. Rheol. 65, 633-662 (2021)]. To support this work, linear rheology measurements were taken for 143 samples comprising a common base formulation of commercial sodium lauryl ether sulfate, cocamidopropyl betaine, and salt (NaCl). The steady state zero shear viscosity evident in linear rheology was measured in duplicate via direct steady and oscillatory shear experiments. Fitting the collected data to the model, we found trends in the microstructural and thermodynamic characteristics that agree with molecular dynamics simulations. These trends validate our new perspective on the parameters that inform the study of the relationship between chemical formulation and rheology. This work, when implemented at scale, can potentially be used to inform and test strategies for predicting self-assembled micellar structures based on chemical formulation.

Statistical mix design method for self-compacting concrete with limestone fillers

This study presents a statistical mix design method for self-compacting concrete (SCC) with limestone fillers (LF) content that considers mortar rheological properties and material packing characteristics. The effect of LF on the rheological properties of SCC was investigated through seven SCC mixes with different LF replacement levels. A basic water demand experiment was designed to obtain the packing density of mortar, and the equivalent packing density was defined and calibrated to represent the effect of LF. The relative spread and relative flow formula were modified based on the equivalent packing density, and the bilinear interpolation method was used to analyses the mortar results.

Advances in large amplitude oscillatory shear Rheology of food materials

Molecular interactions determine the microstructure of food, as well as its response to deformation and flow. In order to design efficient processing equipment, to produce high-quality, stable end products, to predict textural and sensory properties, and to ensure consumer acceptance, the characterization of food rheology is essential. Deformations are rapid and large during the processing of foods and during consumption. In food studies, large amplitude oscillatory shear (LAOS) has become increasingly popular due to its ability to mimic real-life processes. When food is subjected to dynamic oscillatory shear tests, a sinusoidal deformation is applied, the mechanical stress (or strain) is probed, and the response is recorded. This chapter summarize main methods to extract meaningful rheological parameters from complex LAOS response of selected food materials. A time-resolved nonlinear rheology method, sequence of physical processes (SPP), gave detailed interpretations of transient microstructures, whereas the Fourier Transform coupled with Chebyshev decomposition (FTC) method provide static measurements at specific strains. LAOS behavior and its relationship to food microstructures and texture still needed to be studied in depth. By constructing more accurate mechanical models of complex food systems, the fundamental knowledge can be applied to evaluate the nonlinear rheology of food for consumer acceptance and efficient processing.

Effects of hydroxypropyl methylcellulose on anti-dispersion and rheology of alkali-activated materials in underwater engineering

To explore the feasibility of applying alkali-activated materials (AAM) to underwater engineering. The effects of hydroxypropyl methylcellulose (HPMC) on the anti-dispersion and rheological properties of AAM were investigated. NaOH was selected as the activator, and granulated blast furnace slag (GBFS) and fly ash (FA) were used as precursors. The characteristics of anti-dispersion, rheology, and hydration heat change of alkali-activated slurry with 6 kinds of HPMC content (0, 0.2%, 0.4%, 0.6%, 0.8%, and 1%) and 4 kinds of alkali content (Na2O: 3%, 5%, 7%, and 9%) were discussed. The anti-dispersion was characterized by turbidity. The fluidity, gel time, yield stress and plastic viscosity were obtained from rheological tests. The hydration heat was measured by isothermal calorimetry. The results show that HPMC can improve the anti-dispersion of alkali-activated slurry with alkali content (Na2O: 3%, 5%), and the effect was good when the content exceeded 0.6%. Compared with that without HPMC, the turbidity was reduced by 98.4% at 1% HPMC content. With the increase of HPMC, the fluidity and gel time decreased, and the yield stress and plastic viscosity increased at the initial stage. The fluidity of alkali-activated slurry decreased by 23% and the plastic viscosity increased by 916%. It is due to the thickening effect of HPMC, which can change the anti-dispersion and rheology of slurry. The mechanism of HPMC can increase the attraction between raw material particles, and the molecular chains overlap to form a network structure that can wrap the alkali-activated slurry. The evolution of shear stress and hydration heat show that HPMC can delay the hydration reaction of AAM. When the alkali content is high (Na2O: 7%, 9%), HPMC has no obvious improvement in the anti-dispersion of alkali-activated slurry. The increase of HPMC content has no effect on the yield shear stress and plastic viscosity at the initial stage. It shows that HPMC fails at high Na2O content, which leads to loss of thickening effect. The paper is expected to guide for using HPMC in underwater engineering to improve the anti-dispersion and workability of AAM.

A Sustainable Multi‐Dimensional Printable Material

AbstractPolymeric materials are usually tailored for specific functionality. A single polymer exhibiting multiple simultaneous functionalities often requires intricate molecular architecture, which is difficult to manufacture at scale because of its complex synthesis routes. Herein, a facile, partly renewable composition―prepared via reactive melt processing―that induces tunable functionalities such as 3D printability, shape recovery, and self‐healing while exhibiting satisfactory mechanical properties is reported. The system with a hydrogen‐bonded 3D network consists of thermally reversible nano‐scale agglomerates of sustainable, rigid phenolic oligomers and crystallizable flexible polymer. Local molecular mobility and temperature‐dependent relaxation and recovery of the non‐equilibrium networked states enable exploiting these simultaneous functionalities. Transitions involving solidification and structure stabilization at ambient temperature spanning several hours after preheating only at 70 °C directly contrast typical thermoplastic or thermoplastic elastomer behaviors. Results from this study can inform the design of future rheology modifiers and materials for soft robotics.

Investigations into the rheology and early-age properties of gypsum-based materials with different sticky rice contents

To use gypsum-based materials (GM) in a green manner, more natural starch derivatives are being developed as GM modifiers. In this paper, the effects of different sticky rice contents on the rheology and early-age properties of modified GM pastes were investigated. The results showed that the amylopectin in sticky rice was adsorbed on the hemihydrate gypsum surface, increasing the steric hindrance and reducing the particle size and spacing. In all dosage ranges (0.00 wt.%∼3.33 wt.%), relative to the control group, sticky rice increased the yield stress, maximum shear stress, and 28-day compressive strength of GM pastes by 2302.0%, 366.5%, and 134.9%, respectively, and decreased the fluidity by 64.5%. When the critical content exceeded 2.67 wt.%, the thixotropy, hydration heat, and compressive strength values of GM pastes were inhibited, decreasing by 25.4%, 24.8%, and 18.0%, respectively; the setting time was prolonged by 35.6%. This phenomenon was caused by the decrease in the Ca2+ complexation rate due to the overadsorption of amylopectin that led to the wrapping of hydration products. According to the above research, a model based on homogenization assumptions was speculated to describe the solidification mechanisms of GM pastes under sticky rice.