When Microrheology, Bulk Rheology, and Microfluidics Meet: Broadband Rheology of Hydroxyethyl Cellulose Water Solutions
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In this work, we present new insights related to a debate on the morphological structure of hydroxyethyl cellulose (HEC) molecules when dissolved in water, i.e., whether HEC adopts a linear-flexible or a rod-like fibrillar configuration. We have employed "seven" rheological techniques to explore the viscoelastic properties of HEC solutions at different time and length scales. This work demonstrates an excellent convergence between various rheological techniques over a broad range of frequencies and concentrations, allowing us to derive microstructural information for aqueous HEC solutions without the use of complex optical imaging techniques. We find that when dissolved in water unmodified HEC behaves like a linear uncharged polymer, with an entangled mass concentration of ce = 0.3 wt%. Moreover, for the first time we provide the concentration scaling laws (across ce) for the longest relaxation time λ of HEC solutions, obtained from direct readings and not inferred from fitting procedures of fluids shear flow curves.Keywords:
Microrheology
Hydroxyethyl cellulose
We observed the diffusive motion of a micron-sized bead in an entangled-DNA solution to investigate the effect of the viscoelasticity on the bead motion. In the absence of external stress (passive microrheology), subdiffusion appears in the timescale of 0.1–10 s, and the normal diffusion recovers in longer timescales. We evaluated the apparent viscosity and elasticity, which yields a simple relaxation time for the viscoelastic medium. We found that the absence of DNA-length dependence for the time-dependent diffusion is explained by the simple relaxation of the viscoelastic media rather than the reptation dynamics, including the disentanglement. On the other hand, in the presence of a small external stress in active microrheology, the bead motion showed clear length dependence owing to the viscoelasticity. These results suggest that the viscoelasticity of the entangled DNA is highly sensitive to the external stress, even in the linear response regime.
Microrheology
Reptation
Stress relaxation
Elasticity
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In this work, we present new insights related to a debate on the morphological structure of hydroxyethyl cellulose (HEC) molecules when dissolved in water, i.e., whether HEC adopts a linear-flexible or a rod-like fibrillar configuration. We have employed "seven" rheological techniques to explore the viscoelastic properties of HEC solutions at different time and length scales. This work demonstrates an excellent convergence between various rheological techniques over a broad range of frequencies and concentrations, allowing us to derive microstructural information for aqueous HEC solutions without the use of complex optical imaging techniques. We find that when dissolved in water unmodified HEC behaves like a linear uncharged polymer, with an entangled mass concentration of ce = 0.3 wt%. Moreover, for the first time we provide the concentration scaling laws (across ce) for the longest relaxation time λ of HEC solutions, obtained from direct readings and not inferred from fitting procedures of fluids shear flow curves.
Microrheology
Hydroxyethyl cellulose
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The rheological dynamics for the formation of clear fracturing fiuids of viscoelastic micelles were investigated. The rheological dynamics model and equations were established firstly, and was applied to simulate the formation of clear viscoelastic micelles fracturing fluids. The results show that, the rheological dynamics equation can be applied to describe the formation of viscoelastic micelle system correctly, the calculated data are in good agreement with the experimental data, and the meanings of the model parameters are clear and reasonable.
Dynamics
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ABSTRACT Three different flours were examined to study the influence of moisture content on the dynamic viscoelastic behavior of wheat flour dough. Doughs with moisture contents varying from 43 to 58% were submitted to dynamic testing using a mechanical spectrometer operating in frequency sweep mode, obtaining information about rheological response in the linear viscoelastic range. To characterize the influence of moisture content on the dynamic viscoelastic behavior of wheat flour dough, some hypotheses regarding the functional role of the water molecules were verified by applying reduction procedures of the rheological curves. By shifting the rheological curves along the vertical axis, it was possible to verify that varying the moisture content of the doughs not only changed dynamic properties but also modified viscoelastic response. By applying a reduction procedure similar to that used to estimate the constants of the Williams, Landel, and Ferry equation, we demonstrated that not only did the viscoelastic response of doughs vary, but that water molecules interfere with the dynamic by which relaxation phenomena take place. Finally, we proved that the rheological behavior of flour dough is similar to that of concentrated polymer solutions, and that it can be characterized by using a double reduction procedure, shifting the rheological curves along the vertical and horizontal axes, and obtaining a master curve that can be considered inherently characteristic of viscoelastic behavior.
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Microrheology provides a technique to probe the local viscoelastic properties and dynamics of soft materials at the microscopic level by observing the motion of tracer particles embedded within them. It is divided into passive and active microrheology according to the force exerted on the embedded particles. Particles are driven by thermal fluctuations in passive microrheology, and the linear viscoelasticity of samples can be obtained on the basis of the generalized Stokes-Einstein equation. In active microrheology, tracer particles are controlled by external forces, and measurements can be extended to the nonlinear regime. Microrheology techniques have many advantages such as the need for only small sample amounts and a wider measurable frequency range. In particular, microrheology is able to examine the spatial heterogeneity of samples at the microlevel, which is not possible using traditional rheology. Therefore, microrheology has considerable potential for studying the local mechanical properties and dynamics of soft matter, particularly complex fluids, including solutions, dispersions, and other colloidal systems. Food products such as emulsions, foams, or gels are complex fluids with multiple ingredients and phases. Their macroscopic properties, such as stability and texture, are closely related to the structure and mechanical properties at the microlevel. In this article, the basic principles and methods of microrheology are reviewed, and the latest developments and achievements of microrheology in the field of food science are presented.
Microrheology
Soft matter
Complex fluid
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The features of thermo-tropic polymer are that viscosity will be increased with rising temperature,which is different with traditional gel and viscoelasticity.So it is necessary to study on rheological behavior of this gel,which can provide a theoretical basis its application.In this paper,we studied the relationship between strain and time of thermo-tropic gel.According to the basic rheological model of viscoelasticity the basic rheological model of viscoelasticity was established by experimental data and fitted the constants of different conditions.We analysis the rule of viscosity,elasticity,as well as the rate of reaching another equilibrium.
Elasticity
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Microrheology
Rheometry
Particle (ecology)
Mean squared displacement
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The viscoelastic behavior of polymer solutions is commonly measured using oscillating shear rheometry, however, the accuracy of such methods is limited by the oscillating frequency of the equipment and since the relaxation time of the dilute polymer solutions is short, this requires measurement at very high frequencies. Microrheology has been proposed to overcome this technical challenge. Yet the equipment for resolving the statistics of particle displacements in microrheology is expensive. In this work, we measured the viscoelastic behavior of Methocel solutions at various concentrations using a conventional epi-fluorescence microscope coupled to a high-speed intensified camera. Statistical Particle Tracking is used in analyzing the mean-squared displacement of the dispersive particles. Relaxation times ranging from 0.76 - 9.00 ms and viscoelastic moduli, G' between 11.34 and 3.39 are reported for Methocel solutions of concentrations between 0.063 - 0.5%
Microrheology
Rheometry
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Mean squared displacement
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To screen and design hydrogels for specific applications, the ability to characterize and tailor their rheological properties is essential. During the processing and application of hydrogels, rheology plays a threefold role to determine the processability (= injectability or printability) of the materials, to determine their macroscopic mechanical performance in the end-use application together with the evolution from the liquid-like state under processing conditions toward the more solid-like state in the end-use application and finally to act as an indirect structure probing technique. In the present chapter, an overview is given of the different rheological characterization techniques and the material properties resulting from these characterizations. The material properties are subdivided into linear viscoelastic properties, which are characteristic for the small deformation behavior, and non-linear viscoelastic properties that characterize the response to large deformations. In the latter category, both non-linear deformations experienced during use as well as the flow behavior relevant for processing are considered. In addition, a critical overview is given of the main experimental challenges that complicate the rheological characterization of hydrogels. Finally, a brief introduction is given to microrheology, which provides the possibility for non-contact, high-throughput, local characterization of the rheological properties on minute sample quantities.
Microrheology
Characterization
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