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

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

T=0.15 T=0.10

No strong density dependence in peak position

Mean square displacement