# Presentation: 871322

## Understanding Lubricants on the NanoscaleHaskall Taub, University of Missouri-Columbia, DMR 0705974 and DMR 0411748 

-      Alkane molecules are the principal constituents of commercial lubricants such as engine oils.  Our current research deals with what gives alkane films their good lubricating properties.  For example, how do the molecules orient themselves on a solid surface and do they form uniformly thick liquid films; i.e., wet the surface?

- Upon further heating, the monolayer patch spontaneously transforms into small three-dimensional liquid droplets rather than wetting the surface in a film of uniform thickness.

-      Our studies using Atomic Force Microscopy of alkane films have revealed unexpected features of the structure, morphology, and wetting of alkane films on the nanoscale.

- Upon heating an alkane film, we observe an unusual liquid phase only a single molecule thick in which the rod-shaped molecules are oriented perpendicular to a solid surface.

- Europhys. Lett. **79**, 26003 (2007)

- Proposed model of an alkane nano droplet

**Notes:**
	Alkanes (chemical formula CnH2n+2) are flexible chain-like molecules that are the principal constituents of commercial lubricants such as engine oils.  They also serve as models for other flexible-chain molecules used in lubricants.  Our current research is focused on trying to understand at the atomic level what makes a molecule a good lubricant. 
	How do molecular properties such as the alkane’s shape, orientation, and flexibility affect the wetting of the film to a solid surface, i.e., the formation of a fluid film of uniform thickness?  Nonwetting of films on the nanoscale may alter their lubricating properties in such devices as computer hard drives where droplets could be comparable in size to components requiring lubrication. 
	The images shown above have been recorded with an Atomic Force Microscope that can be used to investigate the structure of a liquid on a scale of nanometers (109 meters).  They show a film of an intermediate-length alkane molecule, dotriacontane (C32H66), adsorbed on top of thin silicon wafer used in fabricating electronic devices.  As we heated the film, we expected to see a solid particle melt and spread out to form a uniform coating as one might imagine a piece of candle wax doing on a smooth surface.  In the top image, we see a droplet spreading; but we were surprised in measuring its height to find that it was equal to the length of the rod-shaped molecules, indicating that the molecules were oriented perpendicular to the surface rather than lying flat on it.  On further heating, we were even more surprised to see holes develop in this molecular monolayer patch and then to watch it transform into small liquid droplets.  On the nanoscale, this model lubricant does not wet the surface!
	A report on this work has appeared in Europhysics Letters.

## Understanding Lubricants on the NanoscaleHaskell Taub, University of Missouri-Columbia,  DMR 0705974 and DMR 0411748 

- Two graduate students (Armand Diama and Haiding Mo), two undergraduates (Matthew Simpson and William Danchus), three postdoctoral fellows (Mengjun Bai, Siao-Kwan Wang, and Sven Trogisch), and a Visiting Professor (Klaus Knorr, Universität des Saarlandes, Germany) have been involved in our research.
- 	Drs. Bai and Wang are continuing our AFM studies of alkane films.  Dr. Diama received his Ph.D. in 2006 and returned to the Ivory Coast to join the faculty of the National University.  Simpson, a recipient of a Goldwater Scholarship, is attending medical school.  Dr. Mo is now a postdoctoral fellow at Brookhaven National Laboratory, and Dr. Trogisch has taken an industrial research position in Germany.

**Understanding Lubricants on the Nanoscale**Haskell Taub, University of Missouri-Columbia,  DMR 0705974 and DMR 0411748** **

**Societal Impact****:**
-      Alkane molecules are the principal constituents of commercial lubricants.  A microscopic understanding of the structure and dynamics of very thin alkane films could lead to the development of better and more durable lubricants in applications ranging from computer hard drives to automobile engines.

**Notes:**
	Our research program has contributed to education at the undergraduate, graduate, and postdoctoral levels.  Students have received training that has prepared them for careers ranging from teaching physics at the undergraduate level to the medical profession as well as conducting research in condensed matter physics at a national lab or in private industry.  Our research program utilizes the University of Missouri Research Reactor as well as facilities at national labs.  In this way, we are helping train scientists who can be employed at or be an external user of major national facilities such as the Spallation Neutron Source and the Advanced Photon Source.
	Our research program has significant international outreach.  Armand Diama was the first graduate student from Africa to receive a Ph.D. in our department, and he has returned to teach at the National University of the Ivory Coast.  During the present grant period, we have also had a graduate student and a postdoctoral fellow from China.  In addition to the visit of Professor Klaus Knorr from the Universität des Saarlandes in Germany, we have maintained long-standing collaborations with Professor Flemming Hansen at the Technical University Denmark (for 29 years) and with Professor Ulrich Volkmann at the Catholic University of Chile (for 10 years).  During the last year, we hosted two graduate students from Chile for a one-month visit to participate in experiments in Atomic Force Microscopy.