Rheology of aging suspensions

E.H Purnomo

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

Soft glassy materials are widely used in our daily life. Macroscopically, soft glassy materials behave like a solid but they have an amorphous structure just like a liquid. Due to their metastability and arrested structure, this class of materials often exhibits aging i.e. their mechanical properties evolve continuously with time. We study this glassy behavior using model systems which contain colloidal thermosensitive soft particles. The unique property of the model system is that we can control its volume fraction (¢) via the temperature (T ). We use rheology and particle tracking to study aging, the glass transition, relaxation processes, and dynamical heterogeneity of the model systems.
Aging in soft glassy materials inherently affects their rheological prop- erties and also affects the displacements of probe particles embedded in the systems. We measure the elastic modulus Gt(w, t), the loss modulus Gtt(w, t), the creep compliance J(t tw, tw), and the mean squared displacement .6.r2(t tw, tw) of the glassy suspensions at different ages and found that they depend strongly on their age. We use the soft glassy rheology (SGR) model to quantitatively describe the rheological moduli.
The glass transition is studied by measuring Gt(w, t), Gtt (w, t), and 2 (.6.r (t - tw, tw)) as function of temperature (T ) and mass concentration (c).
We find that this soft colloidal system can be tuned reversibly between the glass at low temperatures and the liquid state at high temperatures. The volume fraction at which the glass transition occurs, ¢trans, approaches the one of hard sphere particles (¢trans = 0.58) as the particles get harder (i.e. more elastic). We also find an indication that aging stops after a certain time if we approach the hard sphere limit with our particle softness.
From the evolution of the Gt(w, t), Gtt(w, t), and the .6.r2(t tw, tw) measured at different ages we find that the average relaxation time T increases linearly with the age. More over we observe that the dynamics of glassy systems at short times (t tw < T ) are inhomogeneous as indi- cated by the mobile and immobile parts in the non Gaussian displacement distribution.




Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Mugele, Frieder G., Supervisor
  • Mellema, J., Supervisor
  • van den Ende, Dirk, Advisor
Award date3 Jul 2008
Place of PublicationEnschede
Publisher
Print ISBNs9789036526944
Publication statusPublished - 3 Jul 2008

Keywords

  • METIS-248709

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