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Séminaire de Manish Kaushal

"Rheology of structurally arrested soft materials"

Abstract :

Soft materials such as concentrated suspensions and emulsions, colloidal
gels, foams, clay suspensions, pastes, etc., undergo structural arrest
either due to crowding of constituents or due to physical gelation of
the same. In any case materials do not attain the thermodynamic
equilibrium state owing to kinetic constraints, and therefore are also
referred to as soft glassy materials (SGMs). As a result SGMs undergo
slow structural evolution to attain those states that have progressively
low free energy. Consequently SGMs show time dependent physical
properties and therefore do not obey fundamental principles of linear
viscoelasticity. By carrying out experiments on variety of SGMs we show
that they indeed validate fundamental principles of linear
viscoelasticity such as Boltzmann superposition principle and
convolution relation by transforming the material behavior from the real
time to the effective time domain. Such validity is subject to condition
that shape of spectrum of relaxation times SGMs is invariant of time.
The effective time domain is obtained by normalizing the real time
domain by time dependent relaxation time. We extend this concept also to
chemically crosslinking systems. In a subsequent work we show that shape
of the spectrum of relaxation times can be altered by applying
controlled deformation field. We show theoretical validation of this
concept by linear viscoelasticity and soft glassy rheology model. We
also study rheological behavior of the suspensions of electrically
polarizable particles in nonpolar solvents that undergo structural
arrest upon application of electric field, and show striking similarity
with that of the soft glassy materials.


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