Viscoelasticity

Malkin, A. Ya.; Isayev, A. I.

doi:10.1016/b978-1-895198-49-2.50007-4

Cited by 8 publications

(4 citation statements)

References 130 publications

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“…The analysis provides readings of the storage modulus on shear ( G ′), which is the elastic component of the network, loss modulus ( G′′ ; viscous component), and dynamic viscosity (η*). Variations with time and temperature can further be assessed as a measure of the “phase lag” δ (tan δ = G′′ / G ′) of the relative liquidlike and solidlike structure of the material .…”

Section: Methodsmentioning

confidence: 99%

Combined Use of Thermomechanics and UV Spectroscopy To Rationalize the Kinetics of Bioactive Compound (Caffeine) Mobility in a High Solids Matrix

Kasapis

Shrinivas

2010

J. Agric. Food Chem.

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An investigation of the diffusional mobility of a bioactive compound (caffeine) within a carbohydrate matrix (glucose syrup) at a glassy consistency is reported. The experimental temperature range was from 30 to - 70 degrees C, and the techniques of modulated differential scanning calorimetry, small-deformation dynamic oscillation on shear, and UV spectrometry were employed. It is not a straightforward matter to identify the relaxation dynamics of such a glassy matrix. This makes suggestions of the relationship between the structural properties of the matrix and the diffusional mobility of bioactive compounds reported earlier in the literature rather tenuous. To address this issue, we recorded mechanical spectra over the aforementioned temperature range and utilized the combined framework of the Williams, Landel, and Ferry (WLF) equation with the time-temperature superposition principle to rationalize results. The protocol produced a fundamental definition of the glass transition temperature and free volume parameters of the glucose syrup sample within the glass transition region. Results were related to the kinetic rates of caffeine diffusion derived by UV spectroscopy leading to the conclusion that the diffusional mobility of the chemical substance is independent of the carbohydrate matrix. This conclusion was further supported by the high level of fractional free volume of caffeine, which is congruent with the predictions of the reaction rate theory (modified Arrhenius equation), as compared to the collapsing levels of free volume in the glucose-syrup matrix that make appropriate WLF considerations.

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Section: Methodsmentioning

confidence: 99%

Combined Use of Thermomechanics and UV Spectroscopy To Rationalize the Kinetics of Bioactive Compound (Caffeine) Mobility in a High Solids Matrix

Kasapis

Shrinivas

2010

J. Agric. Food Chem.

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“…The storage modulus of the suspensions is weakly dependent on the oscillation frequency in the region of the frequencies applied and, thus, can be considered a plateau. Comparison of the measured storage moduli ( G ′) enables us to compare between the colloidal structures of the dispersions, as the plateau value is reciprocally proportional to mesh size of the transient network formed in a suspension . As the lowest value is measured in CNCs suspensions, and the highest in CNCs–CB dispersions, one may conclude that mesh size formed in the native concentrated gel-like CNCs suspensions is decreased in CB dispersions.…”

Section: Resultsmentioning

confidence: 99%

Exclusion and Trapping of Carbon Nanostructures in Nonisotropic Suspensions of Cellulose Nanostructures

Mendelson¹,

Chu

Ziv³

et al. 2019

J. Phys. Chem. B

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Incorporation of carbon nanotubes (CNTs) into liquid crystalline phases of cellulose nanocrystals (CNCs) may be used for preparation of hybrids with novel optical, electrical, and mechanical properties. Here, we investigated the effect of nanoparticle diameter, geometry, aspect ratio, and flexibility on the exclusion of dispersed carbon nanostructures (CNs) from the chiral nematic phase (N*) of the CNCs. Although the CNs are nicely dispersed in isotropic suspensions of CNCs, we observe that fullerenes, carbon black, and CNTs are depleted from the N* phase. This observation is surprising as theoretical predictions and previous observations of nanoparticles indicate that nanometric inclusions would be incorporated within the N* phase. Cryogenic transmission electron microscopy imaging reveals that the dispersed CNs induce misorientation of the CNCs, irrespective of their geometry and size. Rheological measurements suggest that about 10% of the CNCs are affected by the CNs. The multiparticle nature of the interaction may be the origin of the nonsize selective exclusion of the CNs. Re-entrant behavior is observed at high CNC concentrations (about 13 wt %), where a (nematic) gel-like phase kinetically traps the CNs. These phases exhibit non-Newtonian flow behavior and birefringence, offering a pathway for preparation of nonisotropic CNCs−CNT composites and thin films via liquid processing.

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“…Burger's model consisted of the Maxwell element and the Kelvin−Voigt element connected in a series that can be used to characterize the behavior of viscoelastic soft-solids during the creeping stage. 40 In this case, the time-dependent shear compliance, J(t) = γ(t)/τ, reflecting the deformability of a material, can be presented as a sum of three terms. The first two of them represent the instantaneous purely elastic and purely viscous responses of the Maxwell element, while the third one corresponds to the viscoelastic (including purely elastic and purely viscous contributions) retarded response of the Kelvin− Voigt element.…”

Section: Mechanical Properties Of the Hydrogels Under Shearmentioning

confidence: 99%

Thermoregulation of Hydrogel Spatiotemporal Mechanics by Exploiting the Folding–Unfolding Characteristics of Globular Proteins

2023

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The incorporation of proteins into hydrogel networks has the potential to enhance bioactivity and biocompatibility. In this work, we report on the fabrication of a polymer–protein hydrogel consisting of polymethacrylamide (PMAAm) and bovine serum albumin (BSA). The hydrogel was prepared by in situ polymerization of methacrylamide in the presence of BSA at elevated temperatures. Due to its specific interactions between corresponding functional groups, BSA acts as a cross-linker of polymer chains. Hydrogel with optimized composition and preparation conditions (BSA/methacrylamide ratio and synthesis temperature) demonstrated excellent mechanical properties. Due to the presence of side amide groups in PMAAm, the energy barrier required for heat-induced transformation of globular BSA structures into unfolded linear structures decreased, causing a significant shift in the transition temperature. This transition led to a steep and substantial strengthening of the two-component hydrogel. After compressive and shear deformation, the hydrogel restored damaged structure and demonstrated superior fatigue resistance. Compared to BSA that is globular, it was found that BSA in its unfolded state has a much greater impact on the mechanical properties of the hydrogel.

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Viscoelasticity

Cited by 8 publications

References 130 publications

Combined Use of Thermomechanics and UV Spectroscopy To Rationalize the Kinetics of Bioactive Compound (Caffeine) Mobility in a High Solids Matrix

Combined Use of Thermomechanics and UV Spectroscopy To Rationalize the Kinetics of Bioactive Compound (Caffeine) Mobility in a High Solids Matrix

Exclusion and Trapping of Carbon Nanostructures in Nonisotropic Suspensions of Cellulose Nanostructures

Thermoregulation of Hydrogel Spatiotemporal Mechanics by Exploiting the Folding–Unfolding Characteristics of Globular Proteins

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