Colloidal spheres in suspension

Details Colloidal spheres in suspension Colloidal spheres in suspension

1990-12-18

1992-08-18

Kunemund, Robert

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

156600, 156622, 156DIG93, 156DIG100, 422245, C30B 700

Patent

active

051396114

DESCRIPTION:

BRIEF SUMMARY
This invention relates to colloidal spheres in suspension, more particularly to a method of growing oriented colloidal crystals and devices produced thereby.
Colloidal spheres are uniformly sized and perfectly round particles, and are usually made out of materials such as polymers or ceramics. They can be made as hard or soft, solid or porous spheres. Colloidal spheres can be manufactured using methods such as emulsion polymerisation or that of using small seed particles made to grow uniformly. The spheres can pack to form a spatial array, termed a colloidal crystal, although this spatial array does not have long term order. A colloidal crystal can exist in free air or with the inter-sphere space filled with liquid such as that which is used as a suspension liquid.
Suspensions of monosized sphereical colloidal particles in a liquid show a range of phase behaviour as the particle concentration is increased (P N Pusey and W van Megen Nature 320 no. 6060 p340 1986). If spheres whose interaction is steep and repulsive i.e. essentially hard sphere, are considered, then concentration of these spheres is expressed as volume fraction 0, the fraction of the total volume of the suspension which is occupied by the particles.
For .phi..ltoreq.0.49 the equilibrium state of the particles in suspension is fluid-like:- the particles are able to diffuse, in Brownian motion, throughout the suspension. For .phi..gtoreq.0.55 the equilibrium state is crystalline:- the particles are located at sites in an ordered spatial array. For 0.49.ltoreq..phi..ltoreq.0.55 co-existing fluid-like and crystalline phases are found. For .phi..gtoreq.0.58-0.60 the equilibrium state is still expected to be crystalline, the high viscosity of the suspension appears to hinder particle diffusion to the point where crystallisation is essentially suppressed and a glassy amorphous solid-like phase is formed.
Two crystallisation mechanisms have been found. The samples are mixed thoroughly and left to sit undisturbed. For 0.49.ltoreq..phi..ltoreq.0.58 crystallisation is nucleated homogeneously at sites randomly-distributed throughout the sample and small compact crystallites grow with random orientations. For .phi..ltoreq.0.58 (i.e. near the glass transition) crystallisation can be nucleated heterogeneously at the walls of the sample cell and larger irregularly shaped crystallites grow inwards.
Three features of these crystals, formed spontaneously by both mechanisms, make them unsuitable for materials applications: is effectively a random mixture of face centred cubic (f.c.c.) and hexagonal close packed (h.c.p.). occupy a significant fraction of the sample.
According to this invention, the above problems are solved by shearing a well mixed suspension of monosized colloidal spheres within a relatively narrow gap between two effectively parallel surfaces. This invention provides a method of growing oriented, essentially perfect, colloidal crystals, and devices produced by this method.
According to this invention a method of growing an oriented, essentially perfect, colloidal crystal comprises the sequential steps of: radii in the range of 0.1 microns to 1.0 microns having a volume fraction, .phi., greater than 0.49 in a suitable carrier liquid, two effectively parallel surfaces, and their surfaces, the relative motion having a frequency greater than that of the Brownian motion of the colloidal spheres and an amplitude approximately equal to that of the gap between the two surfaces.
Typical as supplied monosized colloidal sphere size distributions which are suitable for the invention method are those which are less than 5%.
The preferred minimum volume fraction of colloidal spheres is 0.55.
The relative motion of the plates is preferrably linear.
The two surfaces may be planar or concentrically cylindrical.
Selection of a suitable carrier liquid for suspension may be characterised by the need for a liquid with a refractive index close to, but not exactly equal to that of the particles.
After oscillations sufficient to establish a substantially single cryst

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