Effect Of Oscillatory Shear Research Articles

Modifying the microstructure and mechanical properties of whey protein isolate gels using large deformation oscillatory strain

The effect of oscillatory shear during heat-induced gelation of whey protein isolate has been investigated. For each gel sample, a single oscillating strain was applied during the gelation process from within the range of 0-1.0. A strain sweep was then used to evaluate the linear viscoelastic region as well as the fracturing properties of each gel. The application of strains lower than ∼0.01 during gelation did not affect the storage modulus while larger strains resulted in lower storage moduli in the linear viscoelastic region. Furthermore, gels produced under small (<0.01) strain amplitudes showed a single fracture point, while gels produced under high (>0.01) amplitude strain were characterised by a two-step fracture pattern. Between the fracture steps, strain hardening behaviour was observed. Confocal laser scanning microscopy was used to identify structural differences between the gels. Greater inhomogeneity was found in gels produced under large amplitude compared to small amplitude strain. It is suggested that localised redistribution of aggregates due to shear during gelation increases the average pore size and possibly creates two distinct types of aggregate structure with differing moduli. The combined effect of heating rate and oscillatory strain was also investigated. We postulate that the mechanism underlying our observations is generic to many gel systems.

Filter cake compaction by oscillatory shear

ABSTRACTIn cake filtration, low values of residual moisture are desirable. This can be achieved by filter cake compaction. The present work proposes a new method for filter cake compaction by applying oscillatory shear superimposed with normal pressure. An experimental setup for the application of oscillatory shear is presented and the influence of oscillation frequency and displacement as well as the number of cycles and the magnitude of superimposed normal pressure on the compaction behavior is investigated. It was found that the reduction of residual moisture with number of cycles follows an exponential decay law. The variation of displacement implies that displacement and oscillation frequency are not independent parameters, but the resulting mean shear rate determines the degree of compaction that can be reached. The compaction behavior with frequency or shear rate, respectively, was strongly influenced by the superimposed normal pressure. The effect of oscillatory shear on the compaction of the filter cake was compared to the compaction obtained by applying solely mechanical pressure. By applying oscillatory shear, a significant reduction of compaction pressure needed to obtain a certain value of residual moisture could be obtained.

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

In this study, effects of oscillatory shear with different frequencies (0–2.5 Hz) and amplitudes (0–20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene (LLDPE) were investigated. It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude (0.2 Hz/4 mm) oscillatory shear. The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear. The Young’s modulus and tensile strength of LLDPE are improved by 27% and 20%, respectively, when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young’s modulus and tensile strength are improved by 49% and 47%, respectively, when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz. The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry, wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.

Effect of Processing Parameters and Vibrating Field on Poly(Vinyl Chloride) Microcellular Foam Morphology

The effects of processing parameters such as processing pressure, temperature, mixing time and rotor speed on polyvinyl chloride foams were investigated by using a novel microcellular foaming setup. The experimental results show that a proper temperature and a high pressure can promote CO2 dissolving in polymer, which makes cell density increase and cell size decrease. Increasing mixing time and rotor speed also promote CO2 dissolving in PVC and speed up forming single-phase polymer/CO2 solution. The effects of oscillatory shear on polyvinyl chloride cell morphology were also studied. The combined shear improves the mixing, and thus shortens the time needed for homogeneous polymer/supercritical CO2 solution formation. Foamed samples with the cell density of 1.0 × 107–3.5 × 108 cells/cm3, average cell size of 15–60 µm and bulk density of 0.6–0.87 g/cm3 had been produced.

Effect of Oscillatory Shear on Polystyrene Cell Morphology

In the present study, a novel microcellular processing experimental setup is developed. With this setup, an oscillatory shear flow is superimposed perpendicular to a steady shear flow during microcellular processing. The effects of processing conditions such as processing pressure, shear rate, and vibration frequency on polystyrene (PS) cell morphology are investigated. The cell morphology is analyzed with a scanning electron microscope (SEM). The results show that the cell density increases and cell size decreases with the increase of processing pressure, shear rate, and vibration frequency. The effects of steady and oscillatory shear on PS cell morphology are further studied with lower melt flow index PS processed with a larger gap thickness. The results show that the final cell structure processed under simple steady shear flow shows an elongated oval shape, while those processed under combined shear flow show nearly spherical cell shape.

Effect of oscillatory shear on polymer solutions.

We consider the effects of oscillatory shear flow on small concentration fluctuations in polymer solutions, which we model as highly asymmetric entangled polymer blends. A simple model that enables us to predict the scattering patterns in the flow-vorticity plane is presented. It is shown that peaks in the patterns occur in the flow direction at a finite wave vector, their position strongly depends on the angular frequency of oscillatory shear flow, whereas the intensity of these peaks is rather controlled by the amplitude of the flow. The model reproduces characteristic double-winged anisotropic scattering patterns called "butterfly," which are stable and thus represent concentration fluctuations rather than phase separation.

Effect of oscillatory shear on the fluid–solid phase transition of supercooled water

The present study aims at the methodological improvement of the electrofreezing of supercooled water by applying oscillatory shear along with a homogeneous electric field in non-equilibrium molecular dynamics simulations of simple water models (such as TIP4P and SPC/E). The application of a planar Couette flow field accounts for a moderate speedup in the phase transition. Since the system goes through a nonergodic glassy state in the course of the process, it is not surprising that a macroscopic manifestation of the Lyapunov instability inherent in the equations of motion is observed. The formation of a conjectured high-density ice polymorph (ice XII) has been studied in terms of the applied electric and oscillatory flow fields. The threshold value of the electric field for the crystallization has been determined. The method of applying the oscillatory flow field was also investigated in detail.