Crystal Properties

Supersaturation and Crystallization

What it shows:

A supersaturated solution is unstable, and by seeding it you can trigger rapid crystallization.

How it works:

Sodium acetate can dissolve in water in great quantities at high temperature, and if you let the solution cool carefully to around room temperature, you have a clear supersaturated solution. Disturbing this unstable equilibrium by dropping a small crystal of sodium acetate into the solution makes the whole thing solidify; the sodium acetate crystals growing radially outwards from the impact point of the...

Read more about Supersaturation and Crystallization
Liquid Crystal Sheets

What it shows:

The selective reflection of a specific wavelength of light through a chiral nematic liquid crystal is temperature dependent and forms the basis for LCD thermograms and thermometers.

How it works:

Liquid crystals are an intermediate state of matter or mesophase between (crystalline) solid and liquid. Substances that have a mesophase have a non-flexible rod-like molecular structure. Although in a liquid phase, the shape of the molecule and intermolecular forces means that the molecules retain a common preferred...

Read more about Liquid Crystal Sheets
Dilatancy of Deformation

What it shows:

When sand in a balloon, just as atoms in a lattice, are close packed, they occupy the least possible volume. Any deformation, even compression, deforms this close-packed arrangement causing an increase in volume.

How it works:

The balloon is filled with sand, and black ink added allowed to percolate down and fill the air gaps. A capillary tube sticking out of the balloon indicates the ink level. When the balloon is squeezed the sand, which had settled down to a closely packed arrangement, is dislocated. Larger gaps...

Read more about Dilatancy of Deformation
Crystal Growth & Recession

What it shows:

By providing a cold boundary, you can get water to crystalize as advancing needles of ice.

How it works:

This cold boundary can be provided by a petri dish of alcohol. Adding dry ice to this produces an endothermic reaction that lowers the temperature below 0°C. By placing a smaller petri dish containing distilled water within the alcohol dish (figure 1), the water freezes from the outer edge inwards. In front of a "thick" wall of ice shoots a monolayer of needles. The advance or recession can be...

Read more about Crystal Growth & Recession
Giant Vibrating Crystal

What it shows:

A simplified model crystal with non-rigid inter-atomic bonds. You can show that solids really do vibrate, distort and expand.

How it works:

A cubic lattice of 3×3×3 15cm diameter Styrofoam™ spheres linked by 3cm steel springs. The springs are epoxied to corks embedded in the Styrofoam.


Read more about Giant Vibrating Crystal
OHP Kinetic Theory Model

Simulation of molecular motion (Brownian, diffusion, etc.) with ball bearings on shaking table.

What it shows:

Two dimensional simulations of molecular dynamics and crystal structure using ball bearings. It can be used to show qualitatively the dynamics of liquids and gases, and illustrate crystalline forms and dislocations.

How it works:

The molecular dynamics simulator is more commonly known as a shaking table. It consists primarily of a circular shallow walled glass table that is oscillated vertically so as to vibrate and...

Read more about OHP Kinetic Theory Model

The microcystaline structure of a steel wire changes from body-centered-cubic to face-centered-cubic as it is heated to red-hot.

What it shows:

Iron atoms are arranged in a body-centered cubic pattern (BCC) up to 1180 K. Above this temperature it makes a phase transition to a face-centered cubic lattice (FCC). The transition from BCC to FCC results in an 8 to 9% increase in density, causing the iron sample to shrink in size as it is heated above the transition temperature.

How it works:

A three meter length of iron...

Read more about BCC to FCC
Solid, Liquid, Gaseous CO2

Observation of phase changes with corresponding pressure changes.

A two ml. plastic microcentrifuge vial and a small shop vise are used together to melt dry ice.

Wear safety glasses for this demo. The vial can explode, or shoot out of the vice, from the pressure of liquid carbon dioxide. Set up a camera with a close shot of an empty vial before putting in a loaded vial.

Crush a pellet of dry ice to make pieces that fit into the vial. Place a couple of pieces in the vial, and snap the lid closed.

Immediately place the vial horizontally in the jaws of the vice,...

Read more about Solid, Liquid, Gaseous CO2
Change of Volume with State

CO2 and He balloons in liquid nitrogen.

What it shows:

Cooling a gas causes a proportional decrease in volume with the drop in absolute temperature. A gas such as helium, which remains close to ideal at low temperatures, shows a four-fold decrease in volume when taken from room temperature 330K to liquid nitrogen temperature, 77K. Carbon dioxide however, sublimes at 194.5K, so is solid at 77K. Oxygen liquefies at 90K (S.T.P.). A qualitative demonstration of these effects can be shown with gas filled balloons.

How it works:...

Read more about Change of Volume with State
Periodic Potential

What it shows:

Ball bearings simulate atoms in a lattice sitting at local potential minimums. Giving them energy excites the atoms and they oscillate about their equilibrium positions in these wells; only with large amounts of energy can they be truly dislocated.

How it works:

A piece of wood 100 × 25 × 2cm acts as the ‘potential’ structure of the lattice. The atoms, 3cm diameter ball bearings sit at the bottom of a cosine varying potential cut to about 10cm depth in the wood by a jig saw.The balls are held in the 2-dimensional...

Read more about Periodic Potential
Molecular Size

Also known as the Ben Franklin pond experiment, after a story in B.F's autobiography.

Olive oil with a known volume is dropped onto water. The water has been dusted with lycopodium powder, which floats on the surface. The oil drop expands, pushing the powder aside to form a clear circle, until the oil forms a monolayer. Measuring the area of the monolayer, dividing the volume of the drop by that area, gives the thickness of the monolayer, which is the height of the oil molecule on water.

From our demonstration movie, we found these values. The size of the patch was 62 cm...

Read more about Molecular Size