A Virginia Tech – Air Force research team lead by chemistry professor Alan R. Esker has studied very thin films of hybrid organic/inorganic molecules (polyhedral oligomeric silsequioxanes — or POSS — derivatives) that can be converted to a heat and fire resistant coating.
The organic part of the molecule is burnt off to leave behind an inorganic polymer less than two nanometers thick.
‘The composites are used in engines,’ Esker said. ‘The Air Force is testing them as a coating for the cone where the exhaust comes out of rockets. The aim is to reduce weight, which improves fuel efficiency and allows for a bigger pay load in space.’
Wherever possible, aeroplanes and rockets are assembled with adhesives rather than bolts and screws for weight reduction.
The researchers have been looking at different organic groups to control the compatibility of the POSS molecule with the polymers used as adhesives, and to control other attributes of the molecule.
‘Whether or not you get something that is homogeneous depends on the organic groups,’ said Esker. The organic component affects how you process the materials and the final properties, such as transparency for optical coatings or conductivity for microelectronic coatings.
The Virginia Tech researchers are taking a unique approach to studying the morphology or distribution of POSS blended with polymers.
They are the first group to study the compounds as ‘soaps.’ The organic/inorganic molecule looks like a cube.
‘We take a cube, which is hydrophobic, and break it to get something that is partially hydrophobic and partially hydrophilic,’ Esker explained. ‘It’s a surfactant, like soap, so it will assemble on the air-water interface as a monolayer one to two nanometers thick.’
The researchers will report on the differences in the morphology resulting from various POSS-polymer blends due to differences in surface chemistry of both the POSS and the polymer at the 222nd national meeting of the American Chemical Society.