Cluster Phases, Gels and Yukawa Glasses in charged colloid-polymer mixtures. 6th Liquid Matter...
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Transcript of Cluster Phases, Gels and Yukawa Glasses in charged colloid-polymer mixtures. 6th Liquid Matter...
Cluster Phases, Gels and Yukawa Glasses in charged colloid-polymer mixtures.
6th Liquid Matter Conference
In collaboration with S. Mossa, P. Tartaglia, E. Zaccarelli
Francesco Sciortino
MRTN-CT-2003-504712
MotivationsInvestigate the competing effects of short range attraction and longer-range repulsion in colloidal systems
Focus: Dynamics close to arrested states of matter: Cluster Phases, Glasses and/or Gels
Cluster Ground State: Only Attraction
Cluster Ground State: Only Repulsion---> No clusters !
Cluster Ground State: Attraction and Repulsion (Yukawa)
Vanishing of the “surface tension” !
Short Range Attraction,--dominant in small clusters
Longer Range Repulsion
Competition Between Short Range Attraction and Longer Range Repulsion: Role in the clustering
Importance of the short-range attraction: Only nn interactions
A=8 =0.5
A=0.05=2
Typical Shapes in the ground state
Size dependence of the cluster shape
“Linear” Growth is an “attractor”
Role of T and :
On cooling (or on increasing attraction), monomers tend to cluster….
From isolated to interacting clusters
In the region of the phase diagram where the attractive potential would generate a phase separation….repulsion slows down (or stop) aggregation. The range of the attractive interactions plays a role.
How do clusters interact ?
How do “spherical” clusters interact ?
Yukawa Phase Diagram
Yukawa Phase Diagram
lowering T
Increasing packing fraction
Interacting Clusters - Linear caseThe Bernal Spiral
Campbell, Anderson, van Dujneveldt,
Bartlett PRL June (2005)
T=0.15
T=0.12
T=0.10
Pictures of the clusters at =0.08
T=0.07
T=0.15
T=0.12
T=0.10
Pictures of the aggregation
at =0.125
Cluster shape c=0.125 T=0.07
A gel !
n ~ ss
= 2.2(random
percolation)
Cluster size distribution
Fractal Dimension
size
T=0.1
Bond Correlation funtions
stretched exponential
~0.7
(a.u.)
power law fits
D~ (T-Tc )
~ 2.1-2.3
Diffusion Coefficient
Density fluctuations
Conclusions……Several morphologies can be generated by the competition of
short-range attraction (fixing the T-scale) and the strength and length of the interaction. A new route to gelation.
Continuous change from a Wigner-like glass to a gelWhile equilibrium would probably suggest a first order
transition to a lamellar phase, arrested metastable states appear to be kinetically favored
Possibility of exporting ideas developed in colloidal systems to protein systems (Schurtenberger, Chen) and, more in general to biological systems in which often one dimensional growth followed by gelation is observed.
Campbell, Anderson, van Dujneveldt, Bartlett PRL in press (2005)
increasing colloid density
Bartlet data
Groenewold
and Kegel
Upper Limit
Optimal Size
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T=0.15 T=0.10
No strong density dependence in peak position
Mean square displacement