Local mobility and microstructure in periodically sheared soft particle           glasses and their connection to macroscopic rheology

Mohan, Lavanya; Pellet, Charlotte; Cloître, Michel; Bonnecaze, Roger T.

doi:10.1122/1.4802631

Cited by 65 publications

(54 citation statements)

References 44 publications

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“…Oscillatory strain experiments [28][29][30] and simulations [31][32][33] typically involve deforming a glass through large numbers of strain cycles toward a steadystate oscillation, also usually at strain rates that are orders of magnitude higher than in our experiments. Our experiments focus on the initial deformation of a glass at very low strain rates, and we reverse the strain in order to probe the reversibility of the local deformations.…”

Section: Methodsmentioning

confidence: 86%

Local shear transformations in deformed and quiescent hard-sphere colloidal glasses

2014

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We performed a series of deformation experiments on a monodisperse, hard-sphere colloidal glass while simultaneously following the 3D trajectories of roughly 50,000 individual particles with a confocal microscope. In each experiment, we deformed the glass in pure shear at a constant strain rate (1 − 5 × 10 −5 s −1 ) to maximum macroscopic strains (5 − 10%), then reversed the deformation at the same rate to return to zero macroscopic strain. We also measured 3D particle trajectories in an identically-prepared quiescent glass in which the macroscopic strain was always zero. We find that shear transformation zones exist and are active in both sheared and quiescent colloidal glasses, revealed by a distinctive four-fold signature in spatial autocorrelations of the local shear strain.With increasing shear, the population of local shear transformations develops more quickly than in a quiescent glass, and many of these transformations are irreversible. When the macroscopic strain is reversed, we observe partial elastic recovery, followed by plastic deformation of the opposite sign, required to compensate for the irreversibly transformed regions. The average diameter of the shear transformation zones at maximum strain is 2.3 particle diameters.

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Section: Methodsmentioning

confidence: 86%

Local shear transformations in deformed and quiescent hard-sphere colloidal glasses

2014

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“…The peak in G" has been widely reported for suspensions of both hard and soft particles and is known as the weak strain overshoot (Hyun et al, 2011). For particle suspensions with repulsive interactions, the overshoot occurs due to localized particle motions that lead to increased dissipation (Mohan et al, 2013). Unfortunately this information alone is not enough to describe the suspension microstructure.…”

Section: Influence Of Slip During Large Amplitude Oscillatory Shearmentioning

confidence: 95%

“…During LAOS the material response is out-of-equilibrium as the material is periodically returned to the same state of deformation without necessarily having time to relax (Mohan et al, 2013). LAOS can give information about suspension microstructure, elastic relaxation times and by varying strain and frequency independently can allow access to a wide range of measurement conditions (Hyun et al, 2011).…”

Section: Slip During Oscillatory Shearmentioning

confidence: 99%

“…Unlike steady shear the material is periodically returned to the same state of deformation without necessarily having time to relax (Mohan et al, 2013). It has been suggested that due to the out-of equilibrium response, LAOS gives more information about the suspension microstructure than equilibrium shear rheology or small amplitude oscillatory shear (SAOS).…”

Section: Introductionmentioning

confidence: 99%

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Rheology of soft particle suspensions

Shewan¹

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The purpose of this work is to investigate the effect of particle elasticity on suspension rheology and flow. Non-colloidal (~ 10 µm) spherical agarose microgels suspended in water are used as a model system. The advantage of these microgels is that they are manufactured to a specific elastic modulus, ranging from 8 to 300 kPa, determined from the modulus of an agarose gel disk. This is in contrast to routinely studied colloidal microgels where the particle modulus cannot be established. Colloidal microgel modulus and specific volume are variable as they are responsive to suspension conditions (such as, pH, temperature and osmotic pressure). Using experimental rheology, an investigation was carried out into the liquid and solid-like behaviour of agarose microgel suspensions. Suspension concentration regimes from dilute to densely packed were investigated to show explicitly the effect of particle modulus on rheology, which becomes increasingly more significant with increasing phase volume. In addition, particle modulus is shown to influence two shear flow characteristics -slip and shear thickening.To interpret suspension viscosity as a function of phase volume the model, developed by Maron and Pierce (1956) and popularised by Quemada (1977) (MPQ model), is applied. This model is based on a scaling relation of the pair distribution function and predicts the critical phase volume at which the viscosity tends to infinity, corresponding to when spherical particles are randomly close packed (φ rcp ).Commonly, it is used empirically by free fitting of experimental data to obtain the critical phase volume. In this work, a method has been developed to use the MPQ model in accordance with its theoretical basis by independently predicting φ rcp from the particle size distribution. It is shown that this theoretical form of the MPQ model, with no adjustable parameters, results in an accurate prediction (within experimental uncertainty, ± 5 %) of the viscosity-phase volume relationship for hard spheres. In addition, alterations in suspension microstructure (for example, through particle aggregation) or rheological artefacts (such as, particle migration) are readily identified by plotting the MPQ model in a linear form.In contrast to hard spheres, the phase volume of agarose microgels is difficult to define accurately. The approach typically used in literature, and used here, is to iii define the specific volume from dilute suspension viscosity. This approach can be corroborated using the theoretical viscosity-phase volume model validated with hard sphere suspensions. The specific volume of agarose microgels is easily defined at φ rcp using the particle size distribution. From this approach it is discovered that, in the viscous regime, below φ rcp , particle elasticity does not explicitly affect suspension viscosity. However, it is shown that particle elasticity has an indirect effect on viscosity at phase volumes between ~ 0.4 and φ rcp due to limited re-swelling during microgel preparation procedures.When microgels c...

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“…On the other hand, a soft interaction potential may enhance structural distortions, as observed for soft glasses. [32][33][34] Clearly, the underlying dynamics of the particles also plays an important role and therefore, a pronounced coupling between rheology, microstructure and particle dynamics is to be expected. Connecting transient rheological behavior with the dynamically changing structure remains challenging even for this conceptually simple model system, despite its importance to many applications, and fundamental understanding of liquid flow.…”

Section: Introductionmentioning

confidence: 99%

Connecting structure, dynamics and viscosity in sheared soft colloidal liquids: a medley of anisotropic fluctuations

et al. 2016

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Structural distortion and relaxation are central to any liquid flow. Their full understanding requires simultaneous probing of the mechanical as well as structural and dynamical response. We provide the first full dynamical measurement of the transient structure using combined coherent X-ray scattering and rheology on electrostatically interacting colloidal fluids. We find a stress overshoot during the start-up of shear which is due to the strong anisotropic overstretching and compression of nearest-neighbor distances. The rheological response is reflected in uncorrelated entropy-driven intensity fluctuations.While the structural distortion under steady shear is well described by Smoluchowski theory, we find an increase of the particle dynamics beyond the trivial contribution of flow. After the cessation of shear, the full fluid microstructure and dynamics are restored, both on the structural relaxation timescale. We thus find unique structure-dynamics relations in liquid flow, responsible for the macroscopic rheological behavior of the system.

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Local mobility and microstructure in periodically sheared soft particle glasses and their connection to macroscopic rheology

Cited by 65 publications

References 44 publications

Local shear transformations in deformed and quiescent hard-sphere colloidal glasses

Local shear transformations in deformed and quiescent hard-sphere colloidal glasses

Rheology of soft particle suspensions

Connecting structure, dynamics and viscosity in sheared soft colloidal liquids: a medley of anisotropic fluctuations

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