Scanning Calorimetry Measurements of Liquid Crystal / Graphite Suspensions
EMSL Project ID
2089
Abstract
We would like to perform exploratory measurements using scanning calorimetry to determine phase transition temperatures and enthalpy changes in two liquid crystal (LC) / graphite suspensions. Both suspensions consist of graphite powder dispersed in a liquid crystal fluid. One suspension also contains a small quantity of the alkane C40H82 (n-tetracontane). In both systems molecules adsorbed on the surface of graphite flakes form a crystalline monolayer at room temperature. We seek to determine 1) the temperature at which this crystalline monolayer melts, 2) the phase transition temperatures of the bulk LC fluid. From variable temperature scanning tunneling microscopy measurements, we estimate the monolayers melt at 35 55 deg. C. We estimate the bulk fluid will undergo phase transitions at the following temperatures: Smectic ? nematic 35 deg. C; nematic ? isotropic 40 deg. C. We also wish to know the enthalpy change per gram of solution for both systems at each phase transition. We estimate the enthalpy change occurring during monolayer melting to be approximately 0.1 J / g of solution. The enthalpy change accompanying bulk LC fluid phase transitions is unknown. All relevant phase behavior for both systems can be determined over the temperature range 25 100 deg. C. From discussions with Dr. Chuck Peden at PNNL, it seems that the TGA-IR instrument in the Interfacial Chemistry and Engineering group should work well for this application. We can provide the samples in sealed glass vials. The fluids should be mixed (by vigorous shaking) immediately prior to analysis. There are no special hazards associated with these materials. They can be treated similar to any other organic solvent. The compounds are stable in air and up to temperatures of at least 125 deg. C.
Project Details
Project type
Exploratory Research
Start Date
2001-03-01
End Date
2001-09-01
Status
Closed
Released Data Link
Team
Principal Investigator