The history of monolayer research and Langmuir Trough development can be summarised by considering the roles of a few key figures.
Benjamin Franklin
Perhaps the first reported scientific observation of a monolayer was made by Benjamin Franklin in 1783. During his many years spent traveling on ships, it is very likely that he was made aware of the effect of the calming of waves using oil. This phenomenon was apparently well known to many sailors. During one journey, in a convoy of ships, Franklin observed that the water behind his ship was smoother than behind the other ships. Upon questioning the observation, a sailor explained to Franklin that the greasy water from the kitchen must have just been discarded.
Months later, back in London, during a visit to the pond at Clapham Common, Franklin set about performing his own experiment. He spread one teaspoonful of oil on to the surface of the pond and observed the way that it spread. He saw that the oil spread itself with surprising swiftness, making around half an acre of the surface as smooth as a looking glass. He reported these findings to the Royal Society in 1774.
By simple calculation it can be shown that the thickness of the observed film was only 2nm, corresponding to a layer only one molecule thick. Molecular dimensions were not known at the time and Franklin made no further investigation into monolayers. In the history of the development of the Langmuir Trough, it might be fair to say that the first Langmuir Trough used to observe monolayers was in fact a large pond in London. Needless to say, this equipment is very expensive and does not offer any sort of manipulation of the confined monolayer.
Agnes Pockels
The first person to make worthwhile, reproducible measurements on monolayers was Agnes Pockels who lived in Braunschweig, Germany. Agnes Pockels was the original housewife superstar. She performed her first experiments on monolayers in her kitchen in her home, starting in about 1882. She used a tin tray as the water container and a small disk suspended from a balance with a slide weight to measure the surface tension of the water.
By contaminating the water surfaces with different materials, Pockels created monolayers and observed their properties when confining the water surfaces to various areas using waxed tin strips. Pockels observed that the surface tension of a water surface varies with its size and depends on the type of contamination.
She sent an account of her work to Lord Rayleigh, who recommended its publication in the journal Nature. Lord Rayleigh had a similar interest in the science of interfaces and was inspired by Pockels to make his own experiments, from which he concluded that these layers were just a single molecule thick.
Irving Langmuir
Irving Langmuir was an industrial research scientist early in the 20th century. He was employed by the US General Electric Company in Schenectady in northern New York state. In spite of the earlier investigations of amphiphilic monolayers not only by Pockels and Rayleigh but also by many other physicists in France and England, these systems are now named after him because he was the first to give the modern understanding of their structure at the molecular level, in particular the fact that the molecules show a preferential orientation.
Langmuir was also the first to show that monolayers can be transferred from the air-water interface to solid substrates for further study. Together with his assistant, Katherine Blodgett, he showed that it was possible to go further and to deposit many monolayers onto the same substrate, thus building up a multilayer film of any required thickness. Deposited monolayers of any thickness are now known as Langmuir-Blodgett (LB) films.
Langmuir made further developments to the Langmuir trough, allowing the precision apparatus to yield more accurate values than the equipment used by Pockels. It was still manually operated and the idea of a computer controlled surface pressure-area isotherm was a distant dream.
In 1932 he was awarded the Nobel prize for his work on surface chemistry.
Katherine Blodgett
Katherine Blodgett was an assistant working with Irving Langmuir at General Electric. She observed his monolayer deposition technique and pushed it further by discovering that multilayer films of custom thickness can be built up by repeating the deposition process many times.
Blodgett found that films from one molecule thickness up to thicknesses of many wavelengths of light could have a physical application. In 1938 she published a paper on the use of LB films to cause deconstructive interference of light reflected from coated glass surfaces.
George Gaines
After the work of Langmuir and Blodgett there was a relatively quiet period in the research area of LB films. George Gaines, also a research chemist at General Electric, started publishing work on insoluble monolayers at liquid-gas interfaces in the 1960s. In a sense, he revived general interest in LB films and even published a book on the history of LB film research.
Kuhn & Möbius
It was perhaps the work of George Gaines that led to the LB film research performed by Kuhn and Möbius in the 1970s. They discovered the importance of molecular orientation and multilayer structure on the fluorescing and quenching of films of dye molecules. This made clear the point that it is possible to engineer films on the nanoscale that can be fabricated to suit our purpose, by controlling the molecular orientation and film structure.
This work opened up many new possibilities and has prompted monolayer research groups worldwide to investigate the fascinating properties of LB films of a constantly growing number of Langmuir materials.
NIMA Technology
During the time that Frank Grunfeld was completing his PhD in monolayer research, Langmuir troughs had become motor controlled with control systems to hold films at a constant surface pressure. The majority of troughs available at the time, however, were bulky, difficult to clean, unreliable and expensive. Frank decided that he could make better troughs than these himself. So in 1983 he set up his own company called Nima Technology. The Langmuir troughs he designed were made from single pieces of PTFE for easy cleaning and reliability. Barrier movement, surface pressure measurement and deposition mechanism control were all programmable using the Nima developed software.
Since then, Nima has continued to develop many Langmuir and LB Deposition Troughs, for various applications.
