Fourier-Transform Rheology

Wilhelm, Manfred

doi:10.1002/1439-2054(20020201)287:2<83::aid-mame83>3.0.co;2-b

Cited by 430 publications

(192 citation statements)

References 43 publications

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“…However, if more accuracy were required in examining the nonlinear viscoelastic properties, further experiments to study this could include strain-dependent relaxation modulus measurements as conducted by Xu et al in studies of the rheology of F-actin networks 45 or Fourier transform rheology. 46 An apparent yield stress has been observed in other mucus systems as well. Pedal mucus from terrestrial gastropods (snails and slugs) is known to have a yield stress, and the yield stress has been identified as the primary attribute which allows these creatures to crawl up inclined surfaces such as vertical walls.…”

Section: Figure 2 Creep Compliance J(t) ) γ(T)/σ0 Versus Time Formentioning

confidence: 91%

Rheology of Gastric Mucin Exhibits a pH-Dependent Sol−Gel Transition

et al. 2007

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Gastric mucin, a high molecular weight glycoprotein, is responsible for providing the gel-forming properties and protective function of the gastric mucus layer. Bulk rheology measurements in the linear viscoelastic regime show that gastric mucin undergoes a pH-dependent sol-gel transition from a viscoelastic solution at neutral pH to a soft viscoelastic gel in acidic conditions, with the transition occurring near pH 4. In addition to pH-dependent gelation behavior in this system, further rheological studies under nonlinear deformations reveal shear thinning and an apparent yield stress in this material which are also highly influenced by pH.

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Section: Figure 2 Creep Compliance J(t) ) γ(T)/σ0 Versus Time Formentioning

confidence: 91%

Rheology of Gastric Mucin Exhibits a pH-Dependent Sol−Gel Transition

et al. 2007

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“…Application of the Fourier transform methodology to rheological problems (FTR) is several decades old (36,37), but it gained prominence more recently as a tool for the analysis of nonlinear viscoelastic response in polymeric systems subjected to large amplitude oscillatory shear (38). FTR was applied to analyze the nonlinear viscoelastic behavior of the PNC series with the most viscous matrix, namely with PS1220.…”

Section: Fourier-transform Rheology (Ftr)mentioning

confidence: 99%

“…Consequently, better dispersion of clay platelets is expected in the solution-intercalated sample than that in the melt-compounded one. response in polymeric systems (38). The FTR is capable of measuring the higher harmonics that in the past were qualitatively characterized by, e.g., the Lissajou stress-strain loops.…”

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confidence: 99%

Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

Tanoue

Utracki

García‐Rejón

et al. 2004

Polymer Engineering & Sci

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Polystyrene‐based nanocomposites (PNC) were prepared using three grades of polystyrene (different molecular weights). The resin was melt‐compounded with 0 to 10 wt% of commercial organoclay in a co‐rotating twin‐screw extruder. Owing to thermo‐oxidative degradation the degree of dispersion was poor. The rheological properties of PNC were determined under dynamic and steady state shear as well as under extensional flow conditions. At the higher clay content, dynamic strain sweep demonstrated that the storage and loss moduli decrease continuously with an increase of strain. To characterize this nonlinear viscoelastic behavior, the Fourier‐transform rheology was applied. The low strain frequency sweep showed that the storage and loss moduli increase with organoclay content. The extracted zero‐shear viscosity data were used to calculate the intrinsic viscosity and then the aspect ratio of dispersions. In spite of nonlinear viscoelastic behavior, the time‐temperature superposition was observed in the full range of concentration. The horizontal and vertical shift factors were found to be almost independent of organoclay content and molecular weight of PS. For comparison, PNC was also prepared by the solution method. A high degree of dispersion was obtained, reflected in the aspect ratio: p = 269, to be compared with p = 16 calculated for the melt‐compounded PNC. Polym. Eng. Sci. 44:1061–1076, 2004. © 2004 Society of Plastics Engineers.

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“…FT-rheology FT-rheology can be used as a tool to quantify the nonlinear response to large-amplitude oscillatory shear (LAOS), by analysis of higher harmonics in the stress response [17,19]. For an oscillatory shear measurement with applied frequency x 1 , in the non-linear regime the formation of mechanical odd harmonics at 3x 1 , 5x 1 , 7x 1 , and so forth appear in the torque response.…”

Section: Methodsmentioning

confidence: 99%

“…We measured birefringence, Dn¢, and dichroism, Dn¢¢, as a function of strain. To quantify the non-linearity of the stress deformation response of the fibrillar ovalbumin solutions, we made use of FTrheology, allowing us to measure the intensity of higher harmonics in the stress response as a function of strain [17,18,19].…”

mentioning

confidence: 99%

Shear-induced aggregation and break up of fibril clusters close to the percolation concentration

et al. 2004

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IntroductionStructural changes of complex fluids under steady shear flow were investigated for different type of materials, such as suspensions, associating polymers and polymer solutions [1,2,3,4,5,6]. Under specific conditions, depending on the material, a shear-thickening regime is observed followed by shear-thinning behaviour [3,4,6]. Shear-thickening is often the result of shear-induced formation of intermolecular structures (clusters), leading to an increase in the effective volume fraction [1,2,3,5,7]. Clusters convected by shear flow may aggregate upon contact, due to attractive interactions of particles on the periphery of the clusters. Cluster-cluster collisions that occur along the streamlines of shear flow lead to the formation of larger clusters [7]. In polymer solutions, the size of these clusters depends upon the concentration [4]. Shear-induced stretching of the structures can also contribute to a shear-thickening effect [4,8,9]. Increasing the shear rate increases the stress on these structures, and once a critical stress is exceeded, they break up, giving rise to shear-thinning behaviour [3,4,6]. Abstract To probe the behaviour of fibrillar assemblies of ovalbumin under oscillatory shear, close to the percolation concentration, c p (7.5%), rheo-optical measurements and Fourier transform rheology were performed. Different results were found close to c p (7.3%), compared to slightly further away from c p (6.9 and 7.1%). For 6.9 and 7.1%, a decrease in complex viscosity, and a linear increase in birefringence, Dn¢, with increasing strain was observed, indicating deformation and orientation of the fibril clusters. For 7.3%, a decrease in complex viscosity was followed by an increase in complex viscosity with increasing strain, which coincided with a strong increase in Dn¢, dichroism, Dn¢¢, and the intensity of the normalized third harmonic (I 3 / I 1 ). This regime was followed by a second decrease in complex viscosity, where Dn¢,Dn¢¢ and I 3 /I 1 decreased. In the first regime where the viscosity was decreasing with increasing strain, deformation and orientation of existing clusters takes place. At higher oscillatory shear, a larger deformation occurs and larger structures are formed, which is most likely aggregation of the clusters. Finally, at even higher strains, the clusters break up again. An increase in complex viscosity, Dn¢, Dn¢¢ and I 3 /I 1 was observed when a second strain sweep was performed 30 min after the first. This indicates that the shear-induced cluster formation and break up are not completely reversible, and the initial cluster size distribution is not recovered after cessation of flow.

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Fourier-Transform Rheology

Cited by 430 publications

References 43 publications

Rheology of Gastric Mucin Exhibits a pH-Dependent Sol−Gel Transition

Rheology of Gastric Mucin Exhibits a pH-Dependent Sol−Gel Transition

Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

Shear-induced aggregation and break up of fibril clusters close to the percolation concentration

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