Colloidal Crystallization: Nucleation and Growth Dave Weitz Harvard •Colloids as model systems – soft materials •Nucleation and growth of colloidal crystals •Defect growth in crystals •Binary Alloy Colloidal Crystals EMU 6/7//04 NSF, NASA http://www.deas.harvard.edu/projects/weitzlab Urs Gasser Konstanz Rebecca Christianson Harvard Peter Schall Harvard Eric Weeks Emory Andy Schofield Edinburgh Peter Pusey Edinburgh Frans Spaepen Harvard John Crocker UPenn
51
Embed
Colloidal Crystallization: Nucleation and Growth Crystallization: Nucleation and Growth Dave Weitz Harvard ... it is a crystal-like particle. Colloidal Crystallization. Determination
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Colloidal Crystallization: Nucleation and Growth
Dave Weitz Harvard
•Colloids as model systems – soft materials•Nucleation and growth of colloidal crystals•Defect growth in crystals•Binary Alloy Colloidal Crystals
•Follow 3000-5000 particles, in 3D•200-1000 time steps = hours to days•≈ 4 GB of images per experiment
Confocalmicroscopy:
Particletracking:
First direct 3D observation of dynamics
Brownian Motion in Real Time
1 cm
25 µmBragg scattering of visible lightHexagonal close-packed layers (FCC/HCP)
Colloidal Crystals
Nucleation and Growth of Colloidal Crystals
2.3 µm diameter PMMA spheres
Questions:•How do crystals nucleate?•What is structure of pre- and post-critical nuclei?•How does structure evolve with time?•What is free energy barrier?
Crystallization
( ) ( )2 3434γ π µ π∆ = − ∆r rG
Chemical potentialSurface energy
r
∆G
How to Identify Crystals
2.3 µm diameter PMMA spheres
Must identify incipient crystal nuclei
defines nearest neighbor particles
Voronoi polyhedra --Delaunay triangulation
(“Wigner-Seitz cell”)
Local Crystallization Order Parameter
P. R. ten Wolde, M. J. Ruiz-Montero,D. Frenkel: J. Chem. Phys. 104, 9932 (1996)
•Find nearest neighbor connections rij
•Resolve connections in spherical harmonics:
qlm(i)=⟨Ylm(rij)⟩j
•Examine l=6•Define Order Parameter: q6m(i) · q6m(j)•If q6m(i) · q6m(j) > 0.5, then bond (ij) is “crystal-like”•if particle has ≥ 8 “crystal-like” bonds, it is a crystal-like particle