Hyper-Aging Dynamics of Nanoclay Suspension

Shahin, A.; Joshi, Yogesh M.

doi:10.1021/la205153b

Cited by 43 publications

(64 citation statements)

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“…These values greatly exceed the values found here, all less than unity. Shift rates above unity have also been reported by others in shear-melting experiments on a laponite colloidal system using DWS and rheology [37,40]. The reason for the large difference in shift rates, by macrorheology and microrheology, in the current study is currently unclear and warrants further investigation.…”

supporting

confidence: 72%

“…The shift rate μ = d log 10 a tw /d log 10 t w can be obtained from the slopes in Fig. 3(c) when in the power-law regime [4,37,38]. We remark that the shift factors are scaled relaxation times, usually scaled to a reference state in the physical aging of molecular glasses, the curve of shift factor versus aging time is not linear in the entire domain and should be a sigmoidal shape, and the double logarithm shift rates were always obtained from the powerlaw regime.…”

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confidence: 99%

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Comparison of the physical aging behavior of a colloidal glass after shear melting and concentration jumps

Peng

McKenna

2014

Phys. Rev. E

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Colloidal systems are considered good models of molecular glasses and we further explore the range of validity of this paradigm using a thermosensitive core-shell particle dispersion to study the aging response of a colloidal glass subsequent to both shear-melting and temperature (concentration)-jump perturbations in the vicinity of the glass transition concentration or temperature. Sequential creep experiments were used to probe the different aging responses of the system. The colloidal glass displays aging behavior after both types of perturbation and our results indicate that this colloidal glass is similar to a molecular glass, in that shift rates are found to be below unity and to decrease towards zero as the glass temperature (or concentration) is approached as temperature increases. However, the kinetics of the aging in the two cases are different indicating that the structural changes induced by the mechanical perturbation are different from those induced by the temperature or concentration jump-similar to findings on mechanical rejuvenation of molecular glasses. We also find differences between the colloidal glass and molecular glasses: In the case of the colloidal glass the structural recovery or equilibration times do not diverge, while the mechanical relaxation times do. On the other hand, for the molecular glass, both times change very rapidly with decreasing temperature, apparently towards a distant point of divergence.

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confidence: 72%

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confidence: 99%

Comparison of the physical aging behavior of a colloidal glass after shear melting and concentration jumps

Peng

McKenna

2014

Phys. Rev. E

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“…where A is a constant, m t is the characteristic relaxation time associated with the aging process and m is the power law coefficient. Interestingly the power law dependence given by equation (9) has been observed for a variety of non-ergodic systems such as polymeric glasses, 8,9 colloidal glasses, 56,69 soft glassy materials, 55,57,67,70 spin glasses, 71 etc. Incorporation of the equation (9) into (6) and assigning 0 m t t = leads to:…”

Section: Resultsmentioning

confidence: 93%

Signatures of physical aging and thixotropy in aqueous dispersion of Carbopol

Agarwal

Joshi

2019

Physics of Fluids

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In this work, we investigate signatures of physical aging in an aqueous dispersion of Carbopol that shows yield stress and weak enhancement in elastic modulus as a function of time. We observe that the creep curves, as well as strain recovery, show a significant dependence on waiting time elapsed since shear melting.The corrected strain, which is the strain in excess of the recovered strain, has been observed to show time -waiting time superposition in the effective time domain, wherein time is normalized by time dependent relaxation time that shows a powerlaw dependence. The corresponding power law exponent, which is close to unity in a limit of small stresses, decreases with stress and tends to zero as stress approaches the yield stress. For a range of stresses, the material shows time -stress superposition suggesting the shape of the evolving relaxation time spectrum to be independent of the time as well as the stress. This work, therefore, suggests the presence of physical aging in an aqueous dispersion of Carbopol even though the elastic modulus shows only a weak enhancement. We also discuss Andrade type of creep behavior in aqueous Carbopol dispersion.

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“…In order to address these limitations Shahin and Joshi (Shahin and Joshi 2011) proposed an effective time domain approach based on the theoretical developments by Hopkins (Hopkins 1958), Struik (Struik 1978) and Fielding and coworkers (Fielding et al 2000) and successfully applied the same to various soft glassy materials. This approach allows time -aging time superposition to consider any duration of process data (Shahin and Joshi 2012). Gupta and coworkers (Gupta et al 2012) included the effect of temperature, and for the first time proposed a systematic treatment of time -temperature superposition for aging time dependent soft materials.…”

Section: Introductionmentioning

confidence: 99%

Long time response of aging glassy polymers

Joshi

2014

Rheol Acta

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Abstract:Aging amorphous polymeric materials undergo free volume relaxation, which causes slowing down of the relaxation dynamics as a function of time.The resulting time dependency poses difficulties in predicting their long time physical behavior. In this work, we apply effective time domain approach to the experimental data on aging amorphous polymers and demonstrate that it enables prediction of long time behavior over the extraordinary time scales. We demonstrate that, unlike the conventional methods, the proposed effective time domain approach can account for physical aging that occurs over the duration of the experiments. Furthermore, this procedure successfully describes timetemperature superposition and time -stress superposition. It can also allow incorporation of varying dependences of relaxation time on aging time as well as complicated but known deformation history in the same experiments. This work strongly suggests that the effective time domain approach can act as an important tool to analyze the long time physical behavior of aging amorphous polymeric materials. | P a g e I Introduction:Glassy materials such as amorphous polymers (Hodge 1995), colloidal glasses and gels (Fielding et al. 2000), spin glasses (Rodriguez et al. 2003) are usually time dependent materials owing to thermodynamically out of equilibrium state they are arrested in. Typically specific volume (and specific entropy/enthalpy) associated with an amorphous polymer is in excess compared to its equilibrium value (Donth 2001, Larson 1999, Struik 1978.Inherent tendency of any material to achieve equilibrium initiates structural rearrangement in the amorphous polymeric compounds so as to cause relaxation of specific volume (accompanied by decrease in specific entropy/enthalpy) as a function of time (Callen 1985, Struik 1978. This phenomenon is addressed in the literature as physical aging (Hodge 1995). In polymeric glasses, while taking the material closer to the equilibrium state, physical aging manifests itself by causing enhancement in relaxation time and stiffness as a function of time (Struik 1978). This time dependency continuously changes the material response to the external stimuli such as application of deformation field (stress field or strain field), electric field, etc.Consequently, a priory prediction of the long time behavior of the response function becomes a challenging task. In this work we employ the so called effective time domain approach, which allows direct prediction of long time material response of amorphous polymers by carrying out tests over the practical timescales. | P a g eThe amorphous polymeric materials when quenched rapidly from the molten state undergo glass transition (McKenna 1994). Physical aging initiates in the material subsequent thermal quench (Hodge 1995). The time elapsed since thermal quench is typically known as the aging time or the waiting time.If the material is deformed during this annealing period, response functions (such as creep compliance and relaxation modulus, depending upon ...

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Hyper-Aging Dynamics of Nanoclay Suspension

Cited by 43 publications

References 55 publications

Comparison of the physical aging behavior of a colloidal glass after shear melting and concentration jumps

Comparison of the physical aging behavior of a colloidal glass after shear melting and concentration jumps

Signatures of physical aging and thixotropy in aqueous dispersion of Carbopol

Long time response of aging glassy polymers

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