1. BCAT-C1 Three-Phase Dynamics and Seeded Crystal Growth
Simon Fraser University
Scitech Instruments, Inc.
Barbara Frisken
Art Bailey
New York University
Andrew Hollingsworth, Paul Chaikin

2. BCAT Apparatus SFU – 7 samples NYU – 3 samples
The BCAT Slow Growth Sample Module is 12.7cm x 26.7cm x 3.2cm and contains 10 (2.3cc) sample cuvettes.
SFU – 7 samples
NYU – 3 samples

3. BCAT-C1 Science Objectives
Simple statements defining BCAT-C1 experiment
SFU
Study the kinetics of phase separation when gas, solid and liquid phases of a colloidal suspension coexist.
NYU
An experiment to explore the effects of seeding the growth of colloidal crystals.

4. States of Matter

5. Phase Transitions
Transition from one state to another
Boiling
Freezing
Sublimation
Demixing
Mixtures – vinaigrette, fuels
Alloys – Al 6061, SS 316
Polymer blends
What are the “mechanisms” of these phase transitions?
Tougher problems to study because non-equilibrium problems.

6. Phase Separation in 3-Phase Coexistence
2-phase Separation studied for more than 50 years.
3-phase Separation relatively unstudied
Crystals, Liquid and Gas all forming out of a homogenized mixture
Applications
Properties of polyolefin blended plastics
Mechanical properties determined by the separation / crystallization.
Polypropylene and Polyethylene
Fire retardants, packing materials
Protein Crystallization
Tetragonal Lyzozyme crystals
lysozyme.co.uk/crystallization.php

7. What’s a Colloid?
Colloids – Particles of size 1 nm – 10 microns. Larger than atomic/molecular size, smaller than ‘macroscopic’.

8. Why Colloids? Lots of technological examples
Colloids model atomic and molecular systems but are simpler to study

9. Why Colloids in Space Sedimentation
Particle a h
Ball bearing
1 mm
10-20 m
Air molecule
1 nm
103 m
PMMA spheres in water
2 mm
particle size, a
gravitational height, h
if h<a,gravity is important
Gravity causes colloids and colloid structures to fall to the bottom of the sample cell!

10. Hard Sphere Colloids
PMMA colloid with PHSA coating

11. ‘Phase diagram’ of colloidal hard spheres (CDOT-1 & CDOT-2: Space Shuttle Columbia STS 73; Discovery STS 95)
f =
Hard spheres are model atoms (but, big and slow). Temperature is the only driving force. Start with spheres in completely randomized positions. Maximum entropy is achieved at high concentrations, , when particles form a lattice to maximize their individual “freedom”. On Earth gravitational settling jams the particles, suppressing this natural tendency to form order out of disorder.
f =
absence of glass transition

12. BCAT – 4 absence of glass transition, f = 0.60
NYU samples 8 & 9
Colloidal ‘glass’, no seeds
absence of glass transition, f = 0.60
absence of glass transition , f = 0.60
Our first glassy samples since the CDOT-1 (1995) and 2 (1998) experiment. These pictures were taken in No spherical ‘seeds’ added. Just the sub-micron sized PMMA in refractive index matching fluid. These samples differ in their size polydispersity.

13. Adding spherical seeds (particular size relative to the primary particles) is expected to greatly increase the rate at which crystals nucleate. Rs s
Rs/s = 0
Rs/s = 5
10 kBT
Rs/s = 6
Energy barrier
Theorists (Frenkel et al.) have predicted that adding a small number of larger spheres to a supersaturated suspension should cause many different crystals for form at once; this is called heterogeneous nucleation. It turns out that the size of the spherical seed relative to that of the bulk particles is important and will have a direct influence on the crystal nucleation rate. Therefore, the selection of size of crystallization promoter is critical. Microgravity allows the possibility to study this mechanism without the complicating effects of particle sedimentation. We needed to figure out how to produce PMMA spheres with up to a 14:1 size ratio.
Rs/s = 7
Size of nucleus
Cacciuto, Auer, Frenkel, Nature (2004)

14. primary particles s ~ 420 nm
BCAT-C1
SEM image
seed ~5.4 mm
primary particles s ~ 420 nm
In this experiment, the samples are identical in terms of the primary particles (fixed size, volume fraction and polydispersity). Only the seed particle size is varied (0, 5.4 or 6.5 microns diameter), corresponding to a “Frenkel number” of Rs/s = 0, and 7.7. 8
Cuvette, Slow Growth Module *8
420 nm PMMA particles with PHS stabilization coating
45% decalin /55% tetralin by volume
60%
40% 1
2.65ml
NYU seeded growth 9
Cuvette, Slow Growth Module *9
5400 nm PMMA seeds with PHS stabilization coating
< 0.1% 10
Cuvette, Slow Growth Module
*10
6500 nm PMMA seeds with PHS stabilization coating

15. BCAT – 5 Rs/s = 5.8 absence of glass transition
NYU Sample 9, ‘SeededGrowth’
0.33 mm
3.8 mm
Rs/s = 5.8
absence of glass transition
Effect of spherical seeds on colloidal particle nucleation.
Preliminary results: this colloidal ‘glass’ reveals colorful Bragg reflections. The colloidal crystals were nucleated from micron-sized spherical seeds that were added to the dense suspension of smaller particles. These results will provide insight into the question of how small ‘foreign objects’ influence the rate of crystal nucleation. The first observation is that the crystallites appear much different in size and shape as compared with another NYU sample, a monodisperse glassy colloid in BCAT-4. That one also crystallized in microgravity, but without the seed particles.

16. Attractive Colloids – Depletion Interaction
Range of attraction:
Attraction strength:
__________
x =
Polymer radius Rg
Colloid radius a
Uo ~ Polymer concentration cp
Adding a non-absorbing polymer induces an attractive force between the particles resulting from polymer entropy
Asakura and Oosawa, 1954; Vrij, 1976 a Rg
colloid-polymer mixtures

17. Physics of Colloids in Space
Colloid Polymer Phase Separation
(EXPPCS)
Polymer concentration
Physics of Colloids in Space
Bailey, Weitz et al
Colloid volume fraction

18. Complexity of Phase Dynamics
Polymer concentration
PCS
F. Renth, W.C.K. Poon and R.M.L. Evans, PRE 64, (2001)
Colloid volume fraction
BCAT-5 Compete

19. Phase Separation + Crystal Growth
mg - imaging
1g - Scattering

20. BCAT C1 SFU Samples Polymer concentration PCS Colloid volume fraction

21. Conclusion
BCAT-C1 will result in exciting new colloid science that cannot be observed without microgravity.