Solid-like Material Research Articles

Non-linear oscillatory flow of a soft solid-like viscoelastic material

Large-amplitude oscillatory shearing flow data are reported for a wheat-flour dough, which is highly shear-thinning in its dynamic data. The large-amplitude data are analysed using a recently proposed constitutive equation for bread dough, in which dough is considered as a solid-like material. It is found that the model predictions agree well with experimental data, giving a certain degree of confidence in the constitutive equation. Furthermore, the markedly non-linear response of the material, even at as low an amplitude as 0.05, is mainly due to the strain softening behaviour of the material; and this non-linearity cannot be predicted by a model with shear rate dependent parameters alone.

Interface between fluid- and solid-like behaviour in rapid granular flows down bumpy inclines

Gravity-driven granular flows down bumpy inclined surfaces were investigated. The flows consist of a bottom region of an amorphous solid-like granular material interacting with a top region of rapidly agitated grains. Chou theoretically analysed these granular flows by employing the constitutive theory, the corresponding boundary conditions and the continuity conditions at the interface. By making use of Chou's model, the research work reported here investigated the effects of the inclination, coefficient of restitution and boundary geometry on the profiles of solid concentration, mean velocity and granular temperature. The direction of the energy flux at the bumpy surfaces, as well as the flow depth for both the active and passive layers were also observed.

Global Existence of Smooth Solution to¶Non-Linear Thermoviscoelastic System with¶Clamped Boundary Conditions in Solid-like Materials

In this paper, we prove the global existence and uniqueness of smooth solution to a system of one-dimensional non-linear thermoviscoelasticity which describes the thermomechanical processes in a class of solid-like materials, such as rubber, etc. The materials satisfy that both ends of the rod are fixed. This assumption was proposed by Dafermos in 1982 (see [6]). A new approach is developed to obtain the crucial estimate of the L∞-norm of the strain u.

Physical Characterization of Polymer Electrolytes as Novel Iontophoretic Drug Delivery Devices

Polymer electrolytes are solidlike materials formed by dispersing a salt at the molecular level in a high molecular weight polymer such as poly(ethylene oxide) (PEO). They have been extensively studied for use in electrochemical applications such as batteries and display devices. This paper considers a novel application of polymer electrolytes as the basis of iontophoretic drug delivery systems. Polymer electrolyte films were cast from solutions of PEO and various drug salts using either water or an acetonitrile/ethanol mixture as the solvent. These films were characterized by variable-temperature polarizing microscopy (VTPM), differential scanning calorimetry (DSC), and alternating current (AC) impedance analysis. The films were around 100-μm thick and mechanically strong; the optical and thermal methods provided evidence that the polymer electrolytes had crystalline and amorphous phases, although some drugs may exist in films as nanodispersions. The amorphous phase is important as ions have greater mobility in this phase and therefore allow a current to be passed when the material is incorporated into a device such as one suitable for drug delivery by iontophoresis. The AC impedance analysis showed that the conductivity of the films varied between 10−6 and 10−3 S cm−1, depending on the salt, casting solvent, and temperature. Two drugs in particular were shown to be promising candidates in these systems: lidocaine hydrochloride and lithium chloride.

Small Molecular Luminescent Gelling Agent 2,3-Bis-n-decyloxyanthracene: Rheological and Structural Study

Luminescent organogels in decane and alcohol solvents of a small molecule, 2,3-bis-n-decyloxyanthracene (DDOA), have been studied by rheology and small-angle neutron scattering techniques. When the temperature of a binary DDOA/hydrocarbon or alcoholic solution is lowered, a sharp sol-to-gel transition is observed during the kinetics of DDOA aggregation. A thermoreversible solid-like viscoelastic material with a large yield stress (σ ≈ 550 Pa at C = 1% wt) is obtained. The elasticity of the 3D network (G′ ≈ 104 Pa at C = 1% wt) suggests the existence of numerous and/or strong junction zones as found in some crystalline gels. The scattering experiments have demonstrated the existence of an interface of large bundles of particles with the solvents. If a fiber morphology is considered, the diameters range from ca. 100 to at least 500 Å, in agreement with previous electron microscopy experiments. The DDOA gel crystallinity is correlated with the hexagonal ordering of the related crystalline powder.

Towards a phenomenological definition of the term ‘gel’

Abstract The term ‘gel’ is used so indiscriminately that it has become ambiguous. Existing definitions are reviewed, examples of unfortunate uses of the term are discussed, and important phenomenological characteristics of gels are identified. We propose that the term ‘gel’ should be limited to systems which fulfil the following phenomenological characteristics: (a) they consist of two or more components one of which is a liquid, present in substantial quantity and (b) they are soft, solid, or solid-like materials. We further propose a definition of the solid-like characteristics of gels in terms of the dynamic mechanical properties, viz. a storage modulus, G′(ω), which exhibits a pronounced plateau extending to times at least of the order of seconds and a loss modulus, G″(ω), which is considerably smaller thatn the storage modulus in the plateau region.

The measurement of ultrasonic shear wave properties in electrorheological fluids

Electrorheological (ER) fluid systems acquire reversible solid-like material properties upon the influence of a strong electric field. Prior efforts to study ER system properties acoustically have employed compressional waves. In this work, three ER systems have been studied by means of an ultrasonic shear wave reflectometry technique. In each case, a moderate to substantial increase in the shear wave velocity, storage modulus, and loss modulus was observed at the ER transition at 3 MHz. These results are interpreted in light of limited dynamic shear data at lower frequencies found in the literature, recent theoretical calculations, and direct observations using optical microscopy.

The interface between fluid-like and solid-like behaviour in two-dimensional granular flows

The effective phase change from fluid behaviour to solid behaviour, that too often occurs in granular flow and brings with it such unwelcome events as funnel flows in hoppers and clogging of other material handling devices, is studied using a discrete particle computer simulation of a Couette flow with gravity. This simulation exhibits the full range of granular flow behaviour, from a stagnant solid-like material, through a quasi-static transition zone, to a rapid granular flow. The most important result is that the first movement in the material just above the static bed occurs in a quasi-static mode at a fixed value of the stress ratio τxy/τyy. Thus, it appears that the primary transition from solid to fluid behaviour is a yield-like phenomenon and can be described by a Mohr-Coulomb-type failure criterion.

Propagation of Weak Shock Waves in Materials with Memory

The propagation of longitudinal shock waves is studied for Green-Rivlin viscoelastic materials. Significant results can be obtained only for a class of materials, almost-elastic materials. Using the integral-expansion method along with the derivative-expansion method, well-known Burgers' equation is derived as a far field equation for solid-like materials with a normal memory. For both solid-like and fluid-like materials with an anomalous memory, a far field equation becomes a new type of integro-partially differential equation. In practice, the mechanical models consisting of spring and dashpot elements are considered as concrete and manifest examples. The structure of steady shocks is examined by solving the far field equations thus obtained.