Effect of temperature on aging and time–temperature superposition in nonergodic laponite suspensions

Awasthi, Varun; Joshi, Yogesh M.

doi:10.1039/b915105b

Cited by 40 publications

(48 citation statements)

References 27 publications

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“…10,35,37 It should be noted that procedure for estimation of  using effective time theory is different from the conventional procedure. 28,[44][45][46] In the conventional technique, which is due to Struik, 28…”

Section: Resultsmentioning

confidence: 99%

Hyper-Aging Dynamics of Nanoclay Suspension

Shahin

Joshi

2012

Langmuir

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Aqueous suspension of nanoclay Laponite undergoes structural evolution as a function of time, which enhances its elasticity and relaxation time. In this work, we employ an effective time approach to investigate long-term relaxation dynamics by carrying out creep experiments. Typically, we observe that the monotonic evolution of elastic modulus shifts to lower aging times, while maxima in viscous moduli get progressively broader for experiments carried out on a later date after preparation (idle time) of the nanoclay suspension. Application of effective time theory produces a superposition of all the creep curves irrespective of their initial state. The resulting dependence of the relaxation time on aging time shows very strong hyper-aging dynamics at short idle times, which progressively weakens to demonstrate a linear dependence in the limit of very long idle times. Remarkably, this behavior of nanoclay suspensions is akin to that observed for polymeric glasses. Consideration of aging as a first-order process suggests that continued hyper-aging dynamics causes cessation of aging. The dependence of relaxation time on aging time, therefore, must attenuate eventually producing linear or weaker dependence on time in order to approach a progressively low-energy state in the limit of very long times as observed experimentally. We also develop a simple scaling model based on a concept of aging of an energy well, which qualitatively captures various experimental observations very well, leading to profound insight into the hyper-aging dynamics of nanoclay suspensions.

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Section: Resultsmentioning

confidence: 99%

Hyper-Aging Dynamics of Nanoclay Suspension

Shahin

Joshi

2012

Langmuir

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“…We believe that this apparent contradiction is due to the way in which the distribution of particles in various energy wells determines the modulus of the system and the average relaxation time. If b is the characteristic length-scale associated with the microstructure of the suspension and if E i is the depth of the energy well of the particle, the local modulus scale can be represented as: [29,30]. Correspondingly, the cage diffusion timescale associated with that…”

Section: Resultsmentioning

confidence: 99%

Stress relaxation in aging soft colloidal glasses

2010

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1We investigate the stress relaxation behavior on the application of step strains to aging aqueous suspensions of the synthetic clay Laponite. The stress exhibits a two-step decay, from which the slow relaxation modes are extracted as functions of the sample ages and applied step strain deformations. Interestingly, the slow time scales that we estimate show a dramatic enhancement with increasing strain amplitudes. We argue that the system ends up exploring the deeper sections of its energy landscape following the application of the step strain.

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“…Interestingly time-temperature and time -stress superposition were also found to be valid for soft glassy materials (Awasthi and Joshi 2009, Shaukat et al 2010. These momentary superpositions aid the prediction of long time behavior even further.…”

Section: Introductionmentioning

confidence: 90%

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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Effect of temperature on aging and time–temperature superposition in nonergodic laponite suspensions

Cited by 40 publications

References 27 publications

Hyper-Aging Dynamics of Nanoclay Suspension

Hyper-Aging Dynamics of Nanoclay Suspension

Stress relaxation in aging soft colloidal glasses

Long time response of aging glassy polymers

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