Step towards nanotechnology
Content
Thousands of years ago, people wondered what the surrounding bodies are made of. The answers varied. In ancient Greece, scientists expressed the opinion that all bodies are made up of small indivisible elements, which they called atoms. How little, they could not specify. For several centuries, the views of the Greeks remained only hypotheses. They were returned to them in the XNUMXth century, when experiments were carried out to estimate the size of molecules and atoms.
One of the historically significant experiments, which made it possible to calculate particle sizes, was carried out English scientist Lord Rayleigh. Since it is simple to perform and at the same time very convincing, let's try to repeat it at home. Then we turn to two other experiments that will allow us to learn some of the properties of molecules.
What are the particle sizes?
Rice. 1. A method of preparing a syringe for placing a solution of oil in extracted gasoline into it; p - poxylin,
c - syringe
Let's try to answer this question by conducting the following experiment. From a 2 cm syringe3 remove the plunger and seal its outlet with Poxiline so that it completely fills the outlet tube intended for insertion of the needle (Fig. 1). We wait a few minutes until Poxilina hardens. When this happens, pour into the syringe about 0,2 cm3 edible oil and record this value. This is the amount of oil used.o. Fill the remaining volume of the syringe with gasoline. Mix both liquids with a wire until a homogeneous solution is obtained and fix the syringe vertically in any holder.
Then pour warm water into the basin so that its depth is 0,5-1 cm. Use warm water, but not hot, so that the rising steam cannot be seen. We drag a paper strip along the surface of the water several times tangentially to it to clean the surface of random pollen.
We collect a little mixture of oil and gasoline into the dropper and drive the dropper through the center of the vessel with water. Gently pressing on the eraser, we drop as small a drop as possible onto the surface of the water. A drop of a mixture of oil and gasoline will spread widely in all directions over the surface of the water and form a very thin layer with a thickness equal to one particle diameter under the most favorable conditions - the so-called monomolecular layer. After some time, usually a few minutes, the gasoline will evaporate (which is accelerated by the rise in water temperature), leaving a monomolecular oil layer on the surface (Fig. 2). The resulting layer most often has the shape of a circle with a diameter of several centimeters or more.
Rice. 2. Monomolecular layer of oil on the water surface
m – pelvis, c – water, o – oil, D – formation diameter, d – formation thickness
(oil particle size)
We illuminate the water surface by directing a beam of light from a flashlight diagonally onto it. Due to this, the boundaries of the layer are more visible. We can easily determine its approximate diameter D from a ruler held just above the surface of the water. Knowing this diameter, we can calculate the area of the layer S using the formula for the area of a circle:
If we knew what is the volume of oil V1 contained in the dropped drop, then the diameter of the oil molecule d could be easily calculated, assuming that the oil melted and formed a layer with a surface S, i.e.:
After comparing formulas (1) and (2) and a simple transformation, we obtain a formula that allows us to calculate the size of an oil particle:
The easiest, but not the most accurate way to determine the volume V1 is to check how many drops can be obtained from the total volume of the mixture contained in the syringe and divide the volume of oil Vo used by this number. To do this, we collect the mixture in a pipette and create droplets, trying to make them the same size as when they are dropped onto the surface of the water. We do this until the entire mixture is exhausted.
A more accurate, but more time-consuming method is to repeatedly drop a drop of oil on the surface of the water, obtain a monomolecular layer of oil and measure its diameter. Of course, before each layer is made, the previously used water and oil must be poured out of the basin and poured clean. From the measurements obtained, the arithmetic mean is calculated.
Substituting the obtained values into formula (3), do not forget to convert the units and express the expression in meters (m) and V1 in cubic meters (m3). Get the particle size in meters. This size will depend on the type of oil used. The result may be erroneous due to the simplifying assumptions made, in particular because the layer was not monomolecular and that the droplet sizes were not always the same. It is easy to see that the absence of a monomolecular layer leads to an overestimation of the value of d. The usual sizes of oil particles are in the range of 10-8-10-9 m. Block 10-9 m is called nanometer and is often used in the booming field known as Nanotechnology.
"Disappearing" volume of liquid
Rice. 3. The design of the liquid shrinkage test vessel;
g - transparent, plastic tube, p - poxylin, l - ruler,
t - transparent tape
The following two experiments will allow us to conclude that the molecules of different bodies have different shapes and sizes. To do the first, cut two pieces of transparent plastic tube, both 1-2 cm in internal diameter and 30 cm long. Each piece of tube is glued with several pieces of adhesive tape to the edge of a separate ruler opposite the scale (Fig. 3). Close the lower ends of the hoses with poxylin plugs. Fix both rulers with glued hoses in a vertical position. Pour enough water into one of the hoses to make a column about half the length of the hose, say 14 cm. Pour the same amount of ethyl alcohol into the second test tube.
Now we ask, what will be the height of the column of the mixture of both liquids? Let's try to get an answer to them experimentally. Pour alcohol into the water hose and immediately measure the top level of the liquid. We mark this level with a waterproof marker on the hose. Then mix both liquids with a wire and check the level again. What do we notice? It turns out that this level has decreased, i.e. the volume of the mixture is less than the sum of the volumes of the ingredients used to produce it. This phenomenon is called fluid volume contraction. The reduction in volume is usually a few percent.
Model explanation
To explain the compression effect, we will conduct a model experiment. Alcohol molecules in this experiment will be represented by pea grains, and water molecules will be poppy seeds. Pour large-grained peas about 0,4 m high into the first, narrow, transparent dish, for example, a tall jar. Pour poppy seeds into the second same vessel of the same height (photo 1a). Then we pour poppy seeds into a vessel with peas and use a ruler to measure the height to which the top level of grains reaches. We mark this level with a marker or a pharmaceutical rubber band on the vessel (photo 1b). Close the container and shake it several times. We put them vertically and check to what height the upper level of the grain mixture now reaches. It turns out that it is lower than before mixing (photo 1c).
The experiment showed that after mixing, small poppy seeds filled the free spaces between the peas, as a result of which the total volume occupied by the mixture decreased. A similar situation occurs when mixing water with alcohol and some other liquids. Their molecules come in all sizes and shapes. As a result, smaller particles fill the gaps between larger particles and the volume of the liquid is reduced.
Photo 1. The following stages of the study of the compression model:
a) beans and poppy seeds in separate vessels,
b) grains after shedding, c) reduction in the volume of grains after mixing
Modern implications
Today it is well known that all the bodies around us are made up of molecules, and those, in turn, are made up of atoms. Both molecules and atoms are in constant random motion, the speed of which depends on temperature. Thanks to modern microscopes, especially the scanning tunneling microscope (STM), individual atoms can be observed. There are also known methods that use an atomic force microscope (AFM-), which allows you to accurately move individual atoms and combine them into systems called nanostructures. The compression effect also has practical implications. We must take this into account when selecting the amount of certain liquids necessary to obtain a mixture of the required volume. You must take it into account, incl. in the production of vodkas, which, as you know, are mixtures of mainly ethyl alcohol (alcohol) and water, since the volume of the resulting drink will be less than the sum of the volumes of the ingredients.
