Thermal Stability of Perfluoroalkyl Silane Self-Assembled on a Polycrystalline Aluminum Surface

Abstract

Thermal stability behavior of 1H, 1H,2H,2H-perfluorooctyl trichlorosilane self-assembled on aluminum substrates is characterized using a grazing-angle Fourier transform infrared spectrometer, Fourier transform-Raman spectroscopy, and contact angle measurements. The self-assembled monolayer (SAM) is heated quasi-statically from room temperature to above 633 K with a heating rate of 1 K/s. Variations in peak frequencies, integrated areas of intensities of symmetric and antisymmetric CF2 stretches, and the relative tilt angle of the SAM are reported. We find that the conformational order in the SAM is not disrupted because of thermal cycling when the peak temperature is below 423 K. When the peak temperature is between 423 and 603 K, the cycling results in only a partial retention of the original order. When the peak temperature is above 603 K, the process is completely irreversible. Surface-enhanced Raman spectroscopy and contact angle measurements support these observations. We confirm these trends for a longer chain (1H,1H,2H,2H-perfluordecyl trichlorosilane) molecule of the same family using the same techniques. We discuss the possible reasons for the changes in light of the tilting-untilting and uncoiling-coiling of the helical silane monolayer.

Use of Eyring Equation to Explore the Frictional Responses of a –CF3 and a –CH3 Terminated Monolayers Self-Assembled on Silicon Substrate

“…The significantly higher stiffness of the fluorocarbon molecules than that of the hydrogenated molecules have been demonstrated by a number of authors [49][50][51]. In a previous paper [20] we have attributed the high stiffness of fluroalkyls to its helical structure. Shear coordination does not necessary mean an overall decrease in friction as we observe by comparing the structural energy factor (-s/ ?…”

“…To check the polymerization of the FOTS SAM, we had [20] compared the IR spectra with those obtained for the molecules assembled from the gas phase. Close identity of the two spectra indicates that the FOTS monolayer assembled here is well packed with minimal lateral polymerization.…”

“…4.3) when a molecular structure is made more disordered. FOTS and ODTS in their self-assembled state are however well ordered [15,20] and have similar packing densities [48]. So why does ODTS respond with greater shear coordination to sliding traction and a corresponding smaller change in local volume than what is done by the FOTS?…”

Engineering Silicon Oxide Surfaces Using Self‐Assembled Monolayers

“…SAMs of OTS are stable in air up to about 150 8C, [17,[77][78][79][80] after which irreversible changes occur in the monolayer structure. Perfluorinated SAMs appear to be even more resistant towards thermal decomposition: [78,81] Srinivasan et al reported that 1H,1H,2H,2H-perfluorodecyltrichlorosilane coatings remain intact even up to 400 8C. [78] The stability toward various chemicals is also remarkable: OTS SAMs can be washed with organic solvents, hot (tap) water, or detergent solutions without detectable damage to the layer.…”

Gestaltung der Siliciumoxidoberfläche durch selbstorganisierte Monoschichten

“…An der Luft sind SAMs von OTS bis zu einer Temperatur von 150 8C stabil, [17,[77][78][79][80] und erst bei Temperaturen darüber verändert sich die Struktur der Monoschicht irreversibel. Perfluorierte SAMs scheinen sogar noch beständiger gegen thermische Zersetzung zu sein: [78,81] Srinivasan et al berichteten von 1H,1H,2H,2H-Perfluordecyltrichlorsilan-Beschichtungen, die sogar bis 400 8C intakt bleiben. [78] Auch die Stabilität gegen verschiedene Chemikalien ist beachtlich -so können OTS-SAMs mit organischen Lösungsmitteln, heißem (Leitungs-)Wasser oder Reinigungslösungen gewaschen werden, ohne dass die Schicht dabei beschädigt wird.…”