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

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

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.

States of Matter

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.

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

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

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

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!

Hard Sphere Colloids PMMA colloid with PHSA coating

‘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 = 0.605 0.618 0.633 absence of glass transition

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 2009. No spherical ‘seeds’ added. Just the sub-micron sized PMMA in refractive index matching fluid. These samples differ in their size polydispersity.

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)

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, 6.4 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

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.

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

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

Complexity of Phase Dynamics Polymer concentration PCS F. Renth, W.C.K. Poon and R.M.L. Evans, PRE 64, 031492 (2001) Colloid volume fraction BCAT-5 Compete

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

BCAT C1 SFU Samples Polymer concentration PCS Colloid volume fraction

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