Langmuir-Blodgett films: Ultra thin monolayers of 'fat' are strange but brilliant
Figure 1 Pic from nanoscience.com featuring the topographical image of a Langmuir-Blodgett film. The top arrow points to regions that have been more or less destroyed relative to that associated with the shorter arrow at the bottom.
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"...the oil, though not more than a teaspoonful, produced an instant calm over a space several yards square, which spread amazingly, and extended itself gradually till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a looking glass." |
Benjamin Franklin analyzing his experiment at the pond within Clapham Common
It was Irvine Langmuir in 1918 who discovered that the constituents of an amphipile monolayer substance can be transferred to a substrate and subsequently placed distinctively on a solid surface (Figure 2); a monolayer that lies above a major liquid influences its surface tension ( 72 mN/m for water, almost zero with a monolayer on top). Langmuir's assistant, Katherine Blodgett discovered 16 years later that the process could be repeated so as to result in a multi-monolayer stack of any desired thickness essentially making up what is now deemed as the Langmuir-Blodgett film (Figure 1).
Figure 2 Solid polar substrate is immersed (or emmersed) into the solution to collect the organic monolayer. More about the details of this phenomena can be found at http://www.ksvltd.com/content/index/keylbfilm .
Applied technology, BAM http://www.nima.co.uk/basics/basindex.htm
"A monolayer is extremely thin, approximately ½% of the wavelength of visible light. The relative effect it has on the electric field reflected from a water surface is therefore very small and the monolayer is under normal conditions quite invisible. However if the water surface is illuminated with p-polarized light at the Brewster angle, there is no reflection from the water surface. The background is then completely dark and it is possible to make out the tiny effect of the monolayer. This is the principle of the Brewster angle microscope or BAM.
The BAM was invented independently and almost simultaneously by two groups, that of Jacques Meunier in Paris, France and that of Dietmar Möbius in Göttingen, Germany. For the first time it was possible to see exactly what a monolayer looked like, and to provide definitive answers to questions which had remained open for 50 years. For example the picture on the left shows the pattern of condensed domains surrounded by a matrix of expanded phase at the main phase transition of a lipid, proving unequivocally that it is a first order transition (Figure 3)."
Figure 3 BAM picture of liquid condensed phase in matrix of liquid expanded phase. DMPE - dimyristoyl phosphatidyl ethanol amine.
"Modern technological interest in Langmuir-Blodgett (LB) films began with the work of Kuhn, based initially in Marburg, Germany in the late 1960's[5] and later in Göttingen (where his group gave birth to Nima's partner company NFT). Over a decade, Kuhn and his colleagues showed that LB films could be fabricated with all the characteristics required for an information-processing technology in which individual molecules perform distinct functions. They showed not only that the films could be made with molecular-scale patterning, but that previously deposited 'sub-assemblies' could be manipulated to build up more complicated systems[6]. They showed that the built-up films could remain stable for long periods, and that their defect levels were acceptably low[7]. Kuhn's exciting results and his effective communication of them not only around Europe but also around the world inspired many groups to carry on his research. "
From http://www.nima.co.uk/basics/basics1.htm
More relevance of these monolayers and technological applications (e.g. molecular electronics).......
http://www.nima.co.uk/basics/basics4.htm
