Effects of Fluorination on Self-Assembled Monolayer Formation from Alkanephosphonic Acids on Aluminum:  Kinetics and Structure

Abstract

We have used infrared spectroscopy, ellipsometry, and contact angle measurements to study self-assembled monolayer (SAM) formation on aluminum native oxide from three alkanephosphonic acids: CF3(CF2)7(CH2)11PO3H2 (F8H11PA), and CH3(CH2) n PO3H2 (n = 15 (H16PA); n = 21 (H22PA)). These compounds show significant differences in film structure and film formation kinetics. Strikingly, the methylene segment of the semifluorinated F8H11PA SAM never reaches an ordered state even at long assembly times. This contrasts with the ordered chains in equilibrium films from H16PA and H22PA. We attribute this behavior to steric effects of the fluorocarbon segment and the phosphonic acid headgroup. F8H11PA represents an amphiphile in which bulky head and tail groups prevent an interposed hydrocarbon segment from ordering. For all three phosphonic acids, negative peaks attributed to loss of Al−OH groups in the infrared spectra of the monolayers are consistent with a condensation reaction between the acids and surface hydroxyls to form bound aluminophosphonate salts. With respect to kinetics, our results indicate that F8H11PA approaches its equilibrium film structure considerably faster than the hydrocarbon phosphonic acids. We interpret the structural dependence of film formation kinetics in terms of the T c formalism advanced by Rondelez and co-workers (Langmuir 1994, 10, 4367−4373). We also suggest that the accelerated film formation exhibited by F8H11PA may be due to chain entanglement and solubility effects, to the extent that this species may self-assemble as islands of approximately vertically oriented chains which fill in as coverage increases. H22PA may also deposit as islands, but in contrast, film formation for H16PA probably involves initially disordered chains with higher tilt angles that order and reorient as film assembly proceeds.

Development and characterization of polymer-grafted ceramic membranes for solvent nanofiltration

“…Different studies with octadecylphosphonic acid (OPDA) [176][177][178] on metal oxide supports showed the formation of well-ordered monolayers with high grafting densities of about 4 groups/nm -2 . Self-assembly monolayers, comprising the molecules of three phosphonic acids, namely CF 3 (CF 2 ) 7 (CH 2 ) 11 PO 3 H 2 , n-C 16 H 33 PO 3 H 2 and n-C 22 H 45 PO 3 H 2 , on the surface of aluminium metal covered with a native oxide film were studied [179]. These authors demonstrated that in all cases a monolayer is formed, however, in the case of the fluorinate acids more time is needed.…”

Organic corrosion inhibitors: where are we now? A review. Part IV. Passivation and the role of mono- and diphosphonates

“…An important role in the interest to SAMs on Al and its alloys belongs to the results obtained in [42]. Its authors used IRS, ellipsometry, and measurements of the  angle to study SAM on natural Al oxide formed by three APhs: CF 3 (CF 2 ) 7 (CH 2 ) 11 PO 3 H 2 (APhC 19 F 17 ); APhC 16 and APhC 22 .…”

Self-Assembly and Charge Transport of a Conjugated Polymer on ITO Substrates

“…Assembly of organic species on conducting substrates in the form of molecular wires and molecular assemblies have been widely studied, and within recent years, research have increased in polymer assemblies on varies conducting substrate [3,4,12]. Conjugated polymers end-functionalized with phosphonic acid anchoring groups have been grafted onto oxide substrates such as indium tin oxide (ITO) [5,[13][14][15][16], zinc oxide [17], silicon dioxide (SiO 2 ) [18], titanium dioxide (TiO 2 ) [19,20], and aluminium oxide (Al 2 O 3 ) [21]. Through a dehydration (condensation) reaction, the phosphonic acid group binds to each substrate covalently and possibly electrostatically (via hydrogen bonds), producing several binding modes [15].…”