JSM-Seminar: Simple models for a comple phase behavior: the case of Laponite suspension
Emanuela Zaccarelli, Sapienza Università di Roma, Italy
- 17 Jan 2013 11:00
- Lecture Hall, PGI/ICS, on Thursday
Laponite is a synthetic smectite clay resembling the natural clay mineral hectorite. In water, it forms a colloidal dispersion of nanometer-sized discotic platelets with positive charges on the plates and negative ones on the rims. The anisotropy in the shape and in the interactions, in addition to the nontrivial and very slow aging dynamics, makes it the prototype of a complex colloid. To explain recent experimental findings, which have provided evidence of different non-ergodic states with varying clay concentration, we use of a combination of modeling and numerical simulations.
At extremely low clay concentration, a phase separation is observed between colloid-poor and colloid-rich phases, the latter arresting into a so-called equilibrium gel state. We explain these findings in terms of a primitive patchy model. At larger, but still very low clay concentration, a different type of structure (with different aging dyamics) is observed. We argue that this arrested state is a disconnected Wigner glass, stabilized by the screened Coulomb repulsion, due to a combination of SAXS measurements, dilution experiments and modeling. The finding of a percolating network structure at low clay concentration and a disconnected one at larger (but still very low) concentration is attributed to the different timescales controlling respectively the competing attractive and repulsive interactions.
We will also illustrate our view on some of the many (still) open questions regarding Laponite and on how the different physical ingredients could be taken into account to design a more realistic model for such a complex system.
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