Sorption of dimethyl methylphosphonate within Langmuir-Blodgett films of trisilanolphenyl polyhedral oligomeric silsesquioxane.

Trisilanolphenyl polyhedral oligomeric silsesquioxane (POSS) molecules are used to create well-ordered Langmuir-Blodgett films containing silanol groups that interact strongly with dimethyl methylphosphonate (DMMP), a commonly used simulant for the chemical warfare agent sarin. The interaction of DMMP within multilayer POSS films is studied by uptake coefficient and temperature-programmed desorption (TPD) measurements, as well as reflection-absorption infrared spectroscopy (RAIRS). Results indicate a low uptake probability; however, in a DMMP-saturated atmosphere, the organophosphonate molecules are capable of diffusing into and adsorbing within the films. TPD and RAIRS measurements reveal no evidence of DMMP decomposition within the film. Rather, DMMP is found to desorb molecularly with a desorption energy of 122 kJ/mol. RAIRS reveals that strong hydrogen-bonding interactions between the phosphoryl groups of the organophosphonate molecules and the silanol groups of the POSS molecules are responsible for the high sorption energy of the system.

Corner capping of silsesquioxane cages by chemical warfare agent simulants.

The room-temperature uptake and reactivity of gas-phase methyl dichlorophosphate (MDCP) and trichlorophosphate (TCP) within trisilanolphenyl-polyhedral oligomeric silsesquioxane (POSS) Langmuir-Blodgett films are investigated. The halogenated phosphate molecules are found to readily diffuse into and react with the hybrid inorganic-organic silicon-oxide films under ambient conditions. Reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and fast atom bombardment-mass spectrometry (FAB-MS) measurements suggest that the chlorophosphates undergo hydrolysis with the silanol groups of the POSS LB-film. Substitution and elimination reactions appear to cap the corner of the POSS molecules, leaving a surface-bound phosphoryl group and a resulting structure that is highly stable at elevated temperatures.

Well-ordered self-assembled monolayers created via vapor-phase reactions on a monolayer template.

The reaction of vapor-phase alkyl isocyanates (O=C=N-(CH2)n-1CH3) with OH-terminated alkanethiol template monolayers on Au produces well-organized self-assembled monolayers, containing intrachain carbamate linkages (Au/S(CH2)16O(C=O)NH(CH2)n-1CH3, where n = 1-8, 11, and 12). X-ray photoelectron spectroscopy, contact angle goniometry, and reflection absorption infrared spectroscopy suggest that the template surface completely reacts with the isocyanates yielding a monolayer that contains an interchain hydrogen-bonded carbamate network. Spectroscopic data indicates that the alkyl underlayer remains well ordered following reaction with the isocyanates. The order of the overlayer and the hydrogen-bonding interactions between adjacent chains increase as a function of the alkyl isocyanate chain length, n. The overlayer appears to be well ordered for n > or = 5.