Solid-like Material Research Articles

Mechanical properties of glass forming systems

We address the interesting temperature range of a glass forming system where the mechanical properties are intermediate between those of a liquid and a solid. We employ an efficient Monte Carlo method to calculate the elastic moduli, and show that in this range of temperatures the moduli are finite for short times and vanish for long times, where short and long depend on the temperature. By invoking some exact results from statistical mechanics we offer an alternative method to compute shear moduli using molecular dynamics simulations, and compare those to the Monte Carlo method. The final conclusion is that these systems are not "viscous fluids" in the usual sense, as their actual time-dependence concatenates solid-like materials with varying local shear moduli.

Interfacial Rheology of Surface-Active Biopolymers: Acacia senegal Gum versus Hydrophobically Modifed Starch

Acacia gum is a hybrid polyelectrolyte containing both protein and polysaccharide subunits. We study the interfacial rheology of its adsorption layers at the oil/water interface and compare it with adsorbed layers of hydrophobically modified starch, which for economic and political reasons is often used as a substitute for Acacia gum in technological applications. Both the shear and the dilatational rheological responses of the interfaces are considered. In dilatational experiments, the viscoelastic response of the starch derivative is just slightly weaker than that for Acacia gum, whereas we found pronounced differences in shear flow: The interfaces covered with the plant gum flow like a rigid, solidlike material with large storage moduli and a linear viscoelastic regime limited to small shear deformations, above which we observe apparent yielding behavior. In contrast, the films formed by hydrophobically modified starch are predominantly viscous, and the shear moduli are only weakly dependent on the deformation. Concerning their most important technological use as emulsion stabilizers, the dynamic interfacial responses imply not only distinct interfacial dynamics but also different stabilizing mechanisms for these two biopolymers.

Commonality and Biosynthesis of the O-Methyl Phosphoramidate Capsule Modification in Campylobacter jejuni

In this study we investigated the commonality and biosynthesis of the O-methyl phosphoramidate (MeOPN) group found on the capsular polysaccharide (CPS) of Campylobacter jejuni. High resolution magic angle spinning NMR spectroscopy was used as a rapid, high throughput means to examine multiple isolates, analyze the cecal contents of colonized chickens, and screen a library of CPS mutants for the presence of MeOPN. Sixty eight percent of C. jejuni strains were found to express the MeOPN with a high prevalence among isolates from enteritis, Guillain Barré, and Miller-Fisher syndrome patients. In contrast, MeOPN was not observed for any of the Campylobacter coli strains examined. The MeOPN was detected on C. jejuni retrieved from cecal contents of colonized chickens demonstrating that the modification is expressed by bacteria inhabiting the avian gastrointestinal tract. In C. jejuni 11168H, the cj1415-cj1418 cluster was shown to be involved in the biosynthesis of MeOPN. Genetic complementation studies and NMR/mass spectrometric analyses of CPS from this strain also revealed that cj1421 and cj1422 encode MeOPN transferases. Cj1421 adds the MeOPN to C-3 of the beta-d-GalfNAc residue, whereas Cj1422 transfers the MeOPN to C-4 of D-glycero-alpha-L-gluco-heptopyranose. CPS produced by the 11168H strain was found to be extensively modified with variable MeOPN, methyl, ethanolamine, and N-glycerol groups. These findings establish the importance of the MeOPN as a diagnostic marker and therapeutic target for C. jejuni and set the groundwork for future studies aimed at the detailed elucidation of the MeOPN biosynthetic pathway.

Effect of flow history on the structure of a non-polar polymer/clay nanocomposite model system

The effect of flow history on the linear and non-linear viscoelastic properties of non-polar polymer nanocomposites (PNCs) has been investigated by means of a suitable model system based on a Newtonian matrix. The structural recovery of this model suspension after cessation of different pre-shear rates was monitored by measuring its linear viscoelastic properties while its structural evolution under shear flow was followed by using stepwise changes in shear rate including flow reversal measurements. To assess the kinetics of the structural evolution at rest and under flow, empirical relations of stretched exponential form were used. It is shown that for different pre-shear rates, different equilibrium structures were reached at rest but with a similar kinetics of recovery. As a result, the low frequency behaviour was typical of solid-like or weak gel material, strongly dependent on the flow history. After any given shear rate under steady state, only one reversible equilibrium structure was reached after a kinetics that was dependent on the pre-shear history. Finally, typical flow reversal responses as observed for PNCs are reported and interpreted in light of the microstructure evolution under flow.

Breakage mechanics—Part I: Theory

Different measures have been suggested for quantifying the amount of fragmentation in randomly compacted crushable aggregates. A most effective and popular measure is to adopt variants of Hardin's [1985. Crushing of soil particles. J. Geotech. Eng. ASCE 111(10), 1177–1192] definition of relative breakage ‘ B r ’. In this paper we further develop the concept of breakage to formulate a new continuum mechanics theory for crushable granular materials based on statistical and thermomechanical principles. Analogous to the damage internal variable ‘ D ’ which is used in continuum damage mechanics (CDM), here the breakage internal variable ‘ B ’ is adopted. This internal variable represents a particular form of the relative breakage ‘ B r ’ and measures the relative distance of the current grain size distribution from the initial and ultimate distributions. Similar to ‘ D ’, ‘ B ’ varies from zero to one and describes processes of micro-fractures and the growth of surface area. However, unlike damage that is most suitable to tensioned solid-like materials, the breakage is aimed towards compressed granular matter. While damage effectively represents the opening of micro-cavities and cracks, breakage represents comminution of particles. We term the new theory continuum breakage mechanics (CBM), reflecting the analogy with CDM. A focus is given to developing fundamental concepts and postulates, and identifying the physical meaning of the various variables. In this part of the paper we limit the study to describe an ideal dissipative process that includes breakage without plasticity. Plastic strains are essential, however, in representing aspects that relate to frictional dissipation, and this is covered in Part II of this paper together with model examples.

Rheological Behavior of the Melts for Polyethylene-based Montmorillonite Nanocomposites

The viscoelastic properties of melts of nanocomposites with partially exfoliated structures, which were composed of low-density polyethylene (LDPE), ethylene vinyl acetate copolymer (EVA), and montmorillonite and modified by cetyltrimethyl ammonium bromide and octadecyltrimethyl ammonium bromide, were studied. The results obtained through measurements of the dynamic storage modulus G', the dynamic loss modulus G”, and the transient stress relaxation modulus G(t) of the composites, reveal that the viscoelastic properties of the composites strongly depend on the amount of montmorillonite that is exfoliated into the composites. With the increase in montmorillonite content, the composites show an obvious property of pseudo solid-like materials within the region of lower frequencies (ω). The montmorillonite layers are aligned along the stress direction, and the dependence of dynamic modulus on ω, appears quite different for the composites before and after being exposed to a large amplitude oscillatory shears.

Production of ?-glucan and related glucan-hydrolases by Botryosphaeria rhodina

Characterization of beta-glucan production from Botryosphaeria rhodina DABAC-P82 by detecting simultaneously glucan-hydrolytic enzymes and their localization, culture medium rheology and oxygen transfer. Mycelium growth, beta-glucan production, substrate consumption and glucan-hydrolytic enzymes were monitored both in shaken flasks and in a 3-l stirred-tank bioreactor. Glucan production (19.7 and 15.2 g l(-1), in flask and bioreactor, respectively) was accompanied by extra-cellular and cell-bound beta-glucanase and beta-glucosidase activities. In the bioreactor scale, in the time interval of 0-78 h the apparent viscosity of the culture broth exhibited a general increase; thereafter, it began to reduce, probably because of the above glucan-hydrolytic activities. Moreover, the culture media collected after 45 h behaved as solid-like materials at shear rates smaller than 0.001 s(-1), as pseudo-plastic liquids in the middle shear rate range and as Newtonian ones at shear rates greater than 1000 s(-1). The greatest beta-glucan accumulation in the bioreactor was found to be associated with nitrogen and dissolved oxygen concentrations smaller than 0.15 g l(-1) and 25%, respectively, and with the peak points of the glucan-degrading enzymes. A careful analysis of the critical factors (such as, culture broth rheology, oxygen mass transfer and glucan-hydrolytic enzymes) limiting the beta-glucan production by B. rhodina is a prerequisite to maximize beta-glucan yield and production, as well as to define the process flow sheet capable of maximizing biopolymer recovery, solvent re-utilization and glucose consumption.

Computer Simulation of Formation and Collapse of Primary Thrombus due to Platelet Aggregation Using Particle Method

The purpose of this study is to propose a computer simulation method using particle method to analyze the formation and collapse of primary thrombus due to platelet aggregation in the blood flow. In the employed particle method, the blood region was discretized by particles that were assumed to have the characteristics of plasma and platelet. The MPS method that was developed for incompressible viscous flow was applied to the plasma flow. It was assumed that the platelets stochastically aggregate to the injured wall, and that the probability is expressed by hypothetic attractive force. In addition, spring force was introduced to express the deformation of the aggregated thrombus as a solid-like material. Two-dimensional simulations revealed that the proposed method reproduced initial thrombogenesis, growth of the thrombus, and its destruction. The blood flow rate influenced not only the amount of the aggregated platelets, but also the speed of the formation of a thrombus and the duration until a thrombus collapsed. These results demonstrated that the proposed method is useful to investigate the process of primary thrombogenesis which is regulated under the influence of fluid mechanical factors.

The effects of added nanoparticles on aqueous kaolinite suspensions: I. Structural effects

The results of an experimental study focused on the effect of added silica nanospheres on the structure of an aqueous suspension of disc-shaped kaolinite particles are presented. In the absence of any additives, kaolinite particles rapidly aggregate and settle. When only nanoparticles were added to a 14% vol. kaolinite suspension, some stabilization was observed, although a thick, fluid-like sediment still formed. Adding both nanoparticles and salt (NaCl or KCl), however, caused the entire suspension to transition into a solid material that was strong enough to actually be sliced. A phase diagram was constructed showing the concentration of salt and nanoparticles needed to produce this transition. With smaller nanoparticles, the transition occurred at much lower nanoparticle volume fractions. Scanning electron micrographs of both the sediment and solid-like material, obtained by cryogenic drying, showed that the latter consisted of a porous, ‘sponge-like’ structure. The characteristic size of the pores decreased as the number density of the added nanoparticles increased. Although the nanoparticles were not visible in the SEM images, it is believed that they had separated into the pores of the solid-like material. While a similar type of transition could be produced in suspensions containing only the silica nanospheres, the structure and flow behavior of this material were markedly different from that obtained with the added clay.

On canonical equations of continuum thermomechanics

It is shown that the canonical balance of momentum of continuum mechanics can be formulated in a general way, but not independently of the usual balance of linear momentum, even in the absence of specified constitutive equations. A parallel construct is made of necessity for the accompanying time-like canonical energy equation. On specifying the energy, previous particular cases can be deduced including pure elasticity, inhomogeneous thermoelasticity of conductors, and the case of dissipative solid-like materials described by means of a diffusive internal variable (such as in damage or weakly non-local plasticity). A redefinition of the entropy flux is necessarily accompanied by a redefinition of the Eshelby stress tensor.

Exponential stability and maximal attractors for a one-dimensional nonlinear thermoviscoelasticity

This paper is concerned with the global existence, exponential stability of solutions and associated nonlinear C0-semigroup as well as the existence of maximal attractors in Hi (i = 1, 2, 4) for a nonlinear one-dimensional thermoviscoelasticity describing a kind of solid-like material. Some new ideas and more delicated estimates are employed to prove the global existence and exponential stability of solutions. The important feature for the existence of maximal attractors in Hi+ (i = 1, 2, 4) is that the metric spaces H1+, H2+ and H4+ we work with are three incomplete metric spaces, as can be seen from the physical constraints, i.e. 𝛉 > 0 and u > 0, with 𝛉 and u being absolute temperature and deformation gradient (strain). For any positive parameters δ1, δ2, …, δ5 verifying some conditions, a sequence of closed subspaces Hiδ ⊂ Hi+ (i = 1, 2, 4) is found, and the existence of maximal attractors in Hiδ (i = 1, 2, 4) is established.

Structure of cubic phases in ternary systems Glucopone/water/hydrocarbon

Phase diagrams for the ternary systems of Glucopone, water and several hydrocarbons are reported. Four different types of hydrocarbon are used namely; heptane, octane, dodecane and tetradecane. Small angle X-ray scattering (SAXS) and polarizing microscope are used for phase identification and structure characterization. The ternary systems are shown to form different liquid crystalline phases with the increase of concentration in the following order—cubic, hexagonal, and lamellar. The liquid crystalline phases present in the ternary phase diagrams have been characterized by SAXS and further analyzed in terms of lattice parameters and area per surfactant head-group. An optical isotropic gel phase with strong elastic properties is found in these systems and identified as cubic phase. The cubic phase is optically isotropic, transparent and highly viscous phase with three-dimensional structure. The cubic samples showed several diffraction peaks and can be assigned to the Ia3 d space group. The rheological study on the cubic phase is performed. All cubic samples behave as solid-like material with storage modulus G′∼0.7×10 6 Pa typical of cubic lyotropic materials. The effect of the oil concentration and oil types on the storage and loss moduli for the cubic liquid crystalline phases is examined. For all systems, the elastic modulus and the complex viscosity are found to increase with oil concentration while decrease with increasing the length of hydrocarbon chain. Tetradecane ternary system shows completely opposite behaviors. The elastic modulus decreased when the oil content is increased. The effect of temperature on the dynamic moduli of the systems is also studied. The systems show very sharp melting transition. Both, storage and loss modulus are found to decrease as the temperature increased. It was possible to deduce the influence of the alkane chain lengths in the phase and rheological behaviors of the Glucopone surfactant. Generally, the ternary systems show similar rheological behaviors except for tetradecane system, which found to show completely opposite behaviors. The cubic phase region is found to shift to higher oil content with the increase in the alkane chain length of hydrocarbon. Finally, it is worth to mention that no cubic phases are found with toluene and cyclohexane as oil phase.

Mechanical relaxation in simple molecular liquids from the liquid to the supercooled state

Attenuation and velocity of acoustic waves have been revealed at ultrasonic frequencies (2, 5 and 10 MHz) in some glass-forming liquids. The mechanical response has been studied following continuously the materials from the liquid to the supercooled state, using an experimental set-up developed to this purpose. A peak in the attenuation of longitudinal acoustic waves has been observed in a temperature region in which the liquids are supercooled. Correspondingly, the sound velocity shows a dispersion, increasing from liquid-like to solid-like values for decreasing temperatures. Both features develop above the calorimetric glass transition temperature ( T g ). In the deeply supercooled liquids, nearly 10 K above their calorimetric T g , also the propagation of transverse wave sound (which is a characteristic behaviour of solid-like materials) has been experimentally detected. Shear and longitudinal relaxation times are not decoupled in the time–temperature region investigated. Compared to the mechanical one, the dielectric relaxation studied as a function of temperature at the same frequency of the ultrasonic experiments shows a loss peak centred at the same temperature. Depending on the liquid investigated, the mechanical relaxation spectrum can be broader than the dielectric one, specially in the low temperature flank, suggesting that some dissipative processes at lower energies can contribute to the mechanical loss, even though they do not couple to the electric probe field.

Rheology properties of dodecyl-β-d-maltoside stabilised mineral oil-in-water emulsions

Abstract Rheology properties of dodecyl-β- d -maltoside stabilized mineral oil–water (o–w) emulsions were studied. A strain controlled Rheometer was used for this purpose. Shear sweep was carried out to observe the η(γ) behavior, whereas oscillatory sweep was carried out to observe the G′(ϖ) and G″(ϖ) behaviors. All rheology properties examined in this work including η(γ), σ( γ ) G′(ϖ) and G″(ϖ) were found to be exhibiting typical non-linear power law dependence. η− γ profiles suggested that these sample do not exhibit zero shear rate limiting viscosity and terminal relaxation time, that η of these samples decays exponentially as a function of both the γ and surfactant concentration with a characteristic power law index, exponent of which decreases with surfactant concentration. Plot of σ( γ ) suggested that σ was not a linear function of γ at low-shear rate domain, but an exponentially growing function with a certain power exponent. At zero shear rate the stress response was not zero, implying that samples under investigation were shear thinning non-ideal plastic-like materials, with characteristic σY response. Much like η which increased with surfactant concentration at any given shear rate, both σY and η0 increased with surfactant concentration. Analysis of ϖ dependence of dynamic moduli suggested that at a very low ϖ domain below 1 Hz, the G′ response of these samples was dominant over G″ response, and that the G′ response was a more or less a linear function of ω, suggesting that these samples are solid-like materials. On the other hand, at higher ϖ domain beyond 1 Hz, the G″ response of these samples was dominant over G′ response, but neither G′(ϖ) was found to be a linear function of ϖ2, nor G″(ϖ) a linear function of ϖ, implying that the samples under examination were neither liquid-like nor solid-like materials. These in turn suggested that these samples cannot be characterized by Maxwell model type fluid flow behavior. Both the dynamic moduli decreased with surfactant concentration. Cole–Cole plot representing G″ response against G′ strongly deviated from the usual semi-circle characteristic of Maxwell model type fluid flow behavior, further confirming that these samples do not exhibit Maxwell model type fluid flow behavior. While tan δ grew linearly as a function of ϖ, it was comparably high in both the low and high ϖ domain, implying that these o–w emulsion exhibited more liquid-like viscous behavior than solid-like elastic behavior. The tan δ was both ϖ and surfactant concentration dependent. While it decreased with both the surfactant concentration and ϖ at low-frequency domain, it was almost independent of both the surfactant concentration and ϖ.

Study of Rheological Properties of Liquid and Solidlike Materials Using Burgers' Model

It was shown that the use of Burgers' model and introduction of the effective viscosity function make it possible to account for general trends in rheologic behavior of different isotropic liquid and solidlike materials: stress relaxation and strain delay, influence of loading or shear rate on a strain curve, curve hysteresis on loading and unloading, and the presence of a stress maximum and its shift at different shear rates for nonlinear-viscous systems. Generally, the rheological model consists of the binomial rheological equation and the modified Maxwell and Kelvin–Voigt differential equations. The model was tested for the case of tangential stresses when studying the polyacrylamide–aluminium acetate solutions and for the normal stresses, when studying the strain of the rock samples saturated with oil.

Quasistatic rheology and the origins of strain

Features of rheological laws applied to solid-like granular materials are recalled and confronted to microscopic approaches via discrete numerical simulations. We give examples of model systems with very similar equilibrium stress transport properties—the much-studied force chains and force distribution—but qualitatively different strain responses to stress increments. Results on the stability of elastoplastic contact networks lead to the definition of two different rheological regimes, according to whether a macroscopic fragility property (propensity to rearrange under arbitrary small stress increments in the thermodynamic limit) applies. Possible consequences are discussed. To cite this article: J.-N. Roux, G. Combe, C. R. Physique 3 (2002) 131–140.

Novel Process for Producing Cubic Liquid Crystalline Nanoparticles (Cubosomes)

A novel process for producing cubic liquid crystalline nanoparticles (cubosomes) has been developed. The process entails simple mixing of two waterlike solutions with a minimal input of energy. The key to this process is the inclusion of hydrotrope. Most lipids, such as monoolein, used to form cubic liquid crystals are essentially insoluble in water. The hydrotrope dissolves the lipid to create a waterlike solution. Water is added to the hydrotrope solution, resulting in a precipitous decrease in lipid solubility. Provided that the dilution trajectory falls into a cubic phase−water miscibility gap, nanometer-scale cubic liquid crystalline particles form spontaneously, presumably from a homogeneous nucleation mechanism. The process is versatile enough to accommodate any lipid and hydrotrope combination that forms cubic liquid crystalline material upon dilution. Actives and stabilizers can be formulated into either of the two solutions, allowing the production of colloidally stabilized, controlled-release dispersions. The phase diagram of the monoolein−ethanol−water system is determined to assess appropriate formulation of solutions and to develop dilution trajectories. This process replaces current processes that require long hold times, processing of solidlike materials, and very high-energy inputs to create cubosome nanoparticle dispersions. This process produces smaller, more stable cubosomes than by conventional bulk dispersion techniques.

Granular flow in partially filled slowly rotating drums

In many industrial processes granular materials are mixed together in partially filled slowly rotating drums. In this paper a general theoretical framework is developed for the quasi-two-dimensional motion of granular material in a rotating drum. The key assumption is that the body can be divided into a fluid-like and a solid-like region, that are separated by a non-material singular surface at which discontinuities occur. Experiments show that close to the free surface there is a thin rapidly moving fluid-like avalanche that flows downslope, and beneath it there is a large region of slowly rotating solid-like material. The solid region provides a net transport of material upslope and there is strong mass transfer between the two regions. In the theory the avalanche is treated as a shallow incompressible Mohr–Coulomb or inviscid material sliding on a moving bed at which there is erosion and deposition. The solid is treated as a rigid rotating body, and the two regions are coupled together using a mass jump condition. The theory has the potential to model time-dependent intermittent flow with shock waves, as well as steady-state continuous flow. An exact solution for the case of steady continuous flow is presented. This demonstrates that when the base of the avalanche lies above the axis of revolution a solid core develops in the centre of the drum. Experiments are presented to show how a mono-disperse granular material mixes in the drum, and the results are compared with the predictions using the exact solution.

Squeezing flow of a viscoelastic solid

We report an exact solution structure to the plane and axi-symmetric squeezing flows of a viscoelastic solid-like material modelled by a three-dimensional analogue of the Kelvin–Meyer–Voigt equation, consisting of the neo-Hookean rubber-like finite deformation and the Upper Convected Maxwell models. Although the solution is valid for any prescribed time function for the plate velocity, we choose to focus on the oscillatory squeezing flow, where the top plate is displaced sinusoidally with an arbitrary amplitude. It is found that the load can exhibit a significant degree of asymmetry. This is largely due to the rubber-like elasticity in the response, resulting in a larger force in the downward phase of the displacement. This, however, can be reversed at a higher Reynolds number, where material inertia dominates. This is the first time a non-trivial solution for this class of material is reported.

Multiple-time correlation functions in spin-3/2 solid-state NMR spectroscopy

Stimulated echo spectroscopy of nonselectively excitable I = 3/2 nuclei offers new perspectives for the investigation of ultraslow motions predominantly in inorganic solids and solid-like materials. Conditions for the generation of pure, quadrupole modulated multipolar spin orders and for the detection of two- and four-time correlation functions are discussed. The case of spins I > 3/2 is also briefly considered. Copyright 2000 Academic Press.