“Surface chemistry is the branch of chemistry that measures and analyzes
the factors and forces that act at the surface of solids, liquids, and gases,
or at the interfaces between two phases; such as the study of surface tension
— Pliny the Elder, Benjamin Franklin, and countless ships’ cooks?
People have been studying the effect of surface chemistry as a "natural science" for longer than you might think. When Benjamin Franklin wrote in his journal about his first observation of the effect of oil on water, he recalled the writings of Pliny the Elder (AD 23-79), on the same subject ó thus starting a trend of honorable men giving others credit for discoveries in the advancement of surface chemistry.
Aboard one of 96 ships traveling together from America to Europe in 1757, Franklin noticed that ships in back seemed to have smoother sailing than ships in the front. The captain explained with disdain that "The cooks have, I suppose, been just emptying their greasy water through the scuppers, which has greased the sides of those ships a little."
Thus the study of biofilms began.
Once in London, Franklin dropped a teaspoon of oil in Clapham Common Pond on a windy day and noted that it spread over half an acre, making it as smooth as glass.
A good scientist, he repeated his experiment. "After this,” he wrote, “I contrived to take with me, whenever I went into the country, a little oil in the upper hollow joint of my bamboo cane, with which I might repeat the experiment and I found it constantly to succeed.”
We don't know what kind of oil Franklin used, or if he always used the same kind, but we have learned why it worked.
About a century after Franklin's experiments, an English baron, Lord Rayleigh (John William Strutt), and a German hausfrau, Agnes Pockels, were researching the properties of water surfaces.
Lord Rayleigh, who received the Nobel Prize in Physics in 1904 "for his investigations of the densities of the most important gases and for his discovery of argon," was the first to write about light being scattered particles, and to explain what gave the sunset its color. According to the Nobel Foundation biography, his work also "ranged over almost the whole field of physics, covering sound, wave theory, colour vision, electrodynamics, electromagnetism, light scattering, flow of liquids, hydrodynamics, density of gases, viscosity, capillarity, elasticity, and photography."
But Pockels was the first to measure the surface tension properties of water. We know of her work thanks to Rayleigh.
Pockels did not attend college. When she first considered it in the mid 1800s, women were not admitted. Not much later, when women were being accepted, Pockels' aging parents asked her not to go. So, unmarried and devoting her life to the care of her invalid parents, the 19-year-old occupied her mind by reading material provided by her brother, Fritz, a student at the University of Heidelburg. And she conducted experiments in the kitchen sink. Using kitchen bowls, string, and buttons, she developed the first surface film balance.
As she explained:
"A rectangular tin trough, 70 cm. long, 5 cm. wide, 2 cm. high, is filled with water to the brim, and a strip of tin about 1 1/2 cm. laid across it perpendicular to its length, so that the underside of the strip is in contact with the surface of the water, and divides it into two halves. By shifting this partition to the right or the left, the surface on either side can be lengthened or shortened in any proportion, and the amount of the displacement may be read off on a scale held along the front of the trough."
Because of her lack of credentials, Pockels had no outlet to publish. So, having read Lord Rayleigh's work on properties of water surfaces, she shared her results with him. He sent the work to Nature magazine on March 2, with the following note:
"I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behaviour of contaminated water surfaces. The earlier part of Miss Pockels' letter covers nearly the same ground as some of my own recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels' experiments." Nature published Pockels' letter on March 12, 1891.
The physics department at the University of Heidelburg subsequently invited Pockels to work in their lab, which she did for 40 years. In her lifetime, she saw the science of surface films advance tremendously. For example, scientists learned that a little oil was able to cover so much water because it spreads until it is one molecule thick ó forming a monolayer.
Irving Langmuir, an industrial research scientist with General Electric in Schenectady, N.Y., studied the work of Rayleigh and Pockels, among others, and learned lessons in surface chemistry and fair play. Langmuir discovered that molecules in a monolayer assume a common orientation. On water, for instance, hydrophobic ends will be away from the water and hydrophilic ends will be toward the water.
He received the Nobel Prize in Chemistry in 1932 for his discovery. After the presentation, the Nobel committee decided to start a tradition of filming scientists in their labs talking about their work. It turns out that Langmuir was the only laureate ever filmed. He gave half of the film time to his assistant, Katherine Blodgett. Their joint research had demonstrated that the preferential orientation of monolayers could be used to stack monolayers of selected molecules to whatever thickness desired, a product now known as Langmuir-Blodgett films.
Our understanding of the amazing properties of monolayers has resulted in the ability to deliver medicines across cell membranes, to control mosquitos by spreading a monolayer of any substance on pools to prevent the larvae from getting air, to extinguish fires with just a little material that will spread and deny air to the fire, and the ability to store data on stacked monolayers. This last application is at the heart of a new technology called nanotechnology.
- Written by James Wightman, Honorary Alumni Distinguished Professor and Professor Emeritus of Chemistry (who credits the history research of the late Charles H. Giles, professor of chemistry at the University of Strathclyde)