The Surface Area Effect
by Robin Hegg
As you’ve probably already learned by now, large-scale particles and nanoparticles can exhibit very different properties. And changes made on the nanoscale can create materials that exhibit different properties as well. The development of nanomaterials have led to the development of stain resistant cloth, bicycle frames that are both stronger and lighter, and the possibility of being able to deliver medicines just to the cells that need them.
One of the main reasons nanoparticles behave differently is that they have much higher surface area than larger particles. Surface area is the measure of how much exposed area an object has. Since chemical reactions take place at the surface level, a larger surface area allows more available space for reactions. This can change a material’s mechanical, electrical, thermal, and chemical properties.
Surface area is expressed in square units and for objects with flat faces, it can be calculated by adding together the areas of its faces. All objects (even those with round surfaces) have surface area. As particles are broken down, more surface area becomes exposed, so one large object has less surface area than many smaller objects.
Sugar Sweet Nano
Bakers use two common types of sugar when cooking: granulated sugar (regular table sugar) and confectioner’s sugar (powdered or icing sugar). The difference between these two types of sugar is surface area. Powdered sugar (also called icing sugar) is made up of smaller particles, and as such, the same volume of powdered sugar has more surface area than granulated sugar. Granulated sugar normally has grains about .5mm across and powdered sugar normally has grains about .06mm across.
In the same way that scientists grow carbon nanotubes and graphene from differently formed carbon molecules, sugar crystals can be grown from sugar solutions made from different-sized sugar particles.
In this activity, you will grow crystals from sugar solutions made from sugar with two different surface areas. How do you think the difference in surface area will affect the behavior of the sugar particles and the resulting crystals?
To grow and compare your sugar crystals, you’ll need:
– Two clean glass cups or measuring cups
– 2 pieces of thin cotton string (with length at least 1.5 times the cup’s height)
– 2 pencils or sticks
– A washer or screw to weigh down the string
– 3 cups of granulated sugar
– 3 cups of powdered confectioners’ sugar (icing sugar)
– 2 cups very hot water (poured by an adult)
Step One: Label each cup with the type of sugar it will hold. Have an adult pour one cup of very hot water into each of the two cups.
Step Two: Add 3 cups of each type of sugar into their respective cups and stir to dissolve (the water will look perfectly clear when the sugar is dissolved).
Step Four: Tie one end of the string to a pencil. Add a weight (a washer or screw) to the other end of the string.
Step Five: Place the appropriate string into the water with the weighted end down, allowing the pencil to sit across the top of the cup, holding the string in place.
Step Six: Observe the cups each day for 4-7 days. If possible, examine a sample of each of the resulting crystals under a microscope.
1. Which type of sugar dissolved more quickly? What effect do you think the difference in surface area had on the results?
2. How are the crystals grown from the granulated sugar and those grown from the powdered sugar different? How did your results differ from your hypothesis?
3. What does the difference in the two types of crystals show you about nanotechnology and nanostructures?