Unsymmetrical Spiroalkanedithiols Having Mixed Fluorinated and Alkyl Tailgroups of Varying Length: Film Structure and Interfacial Properties

Abstract

A custom-designed series of unsymmetrical spiroalkanedithiols having tailgroups comprised of a terminally fluorinated chain and a hydrocarbon chain of varying lengths were synthesized and used to prepare self-assembled monolayers (SAMs) on gold substrates. The specific structure of the adsorbates was of the form [CH3(CH2)n][CF3(CF2)7(CH2)8]C[CH2SH]2, where n = 7, 9, and 15 (designated as F8H10-C10, F8H10-C12, and F8H10-C18, respectively). The influence of the length of the hydrocarbon chain in the bidentate dithiol on the structure and interfacial properties of the monolayer was explored. A structurally analogous partially fluorinated monodentate alkanethiol and the corresponding normal alkanethiols were used to generate appropriate SAMs as reference systems. Measurements of ellipsometric thickness showed an unexpectedly low film thickness for the SAMs derived from the bidentate adsorbates, possibly due to disruptions in interchain packing caused by the fluorocarbon chains (i.e., phase-incompatible fluorocarbon-hydrocarbon interactions), ultimately giving rise to loosely packed and disordered films. Analysis by X-ray photoelectron spectroscopy (XPS) were also consistent with a model in which the films were loosely packed; additionally, the XPS spectra confirmed the attachment of the sulfur headgroups of the bidentate adsorbates onto the gold substrates. Studies of the SAMs by polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) suggested that as the length of the hydrocarbon chain in the adsorbates was extended, a more ordered surface was achieved by reducing the tilt of the fluorocarbon segment. The wettability data indicated that the adsorbates with longer alkyl chains were less wettable than those with shorter alkyl chains, likely due to an increase in interchain van der Waals forces in the former.

Patterning solar cell metal grids on transparent conductive oxides using self-assembled phosphonic acid monolayers

“…Fluorocarbon chains are known to cause disruption in inter-chain packing [14]. While hydrocarbon chains present a linear structure, perfluorinated chains form helical structure and therefore self-assemble in less compact and more disordered layers [15].…”

“…We also present preliminary results of the application of SAM layers as a patterned resist to plate thin lines of nickel, nickel here being meant to become an adhesion layer prior to copper plating. 12,12,13,13,14,14,15,15,15,15-nonafluoropentadecylphosphonic acid (fC15-PA), 12,12,13,13,14,14,15,15,16,16,17,17-tridecafluoroseptadecylphosphonic acid (fC17-PA), 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-Heptadecafluorononadecylphosphonic acid(fC19-PA), and 10,11-Bis (2,2,3,3,4,4,5,5,6,6,7,7,8,8,…”

Antifouling Coatings Generated from Unsymmetrical Partially Fluorinated Spiroalkanedithiols

“… 41 − 44 Only recently, Chinwangso and co-workers demonstrated the ability to generate films with controlled interfacial heterogeneity by linking two chemically dissimilar chains—a hydrocarbon chain with a partially fluorinated chain or an oligo(ethylene glycol) chain—on a bidentate spiroalkanedithiol (SADT) head group, as illustrated in Figure 1 . 30 , 38 − 40 , 45 …”

Antifouling Studies of Unsymmetrical Oligo(ethylene glycol) Spiroalkanedithiol Self-Assembled Monolayers

“…The enhanced stability of bidentate thiol-based SAMs on gold arises from the entropydriven "chelate effect" [31]. Another advantage of bidentate adsorbates is the ability to incorporate two different terminal groups into the same molecule, which offers flexibility in film composition, allowing the generation of unique nanoscale interfaces composed of phase-incompatible chemical entities [34,35]; these "conflicted" interfaces are comprised of chemically disparate species held in close proximity [34,35,[38][39][40][41]. Recently, we reported that "conflicted" SAM-based interfaces generated from bidentate spiroalkanedithiols possessing mixed hydrocarbon and fluorocarbon tailgroups exhibit enhanced protein resistance when compared to SAMs generated from their single-component monodentate counterparts [41].…”

“…Recently, we reported that "conflicted" SAM-based interfaces generated from bidentate spiroalkanedithiols possessing mixed hydrocarbon and fluorocarbon tailgroups exhibit enhanced protein resistance when compared to SAMs generated from their single-component monodentate counterparts [41]. Moreover, the generation of SAMs from dithiol-based adsorbates permits studies of the behavior and properties of interfaces consisting of homogeneously mixed disparate chemical species [38][39][40][41] that would typically phase-separate to form surfaces having patches of single-component domains [42][43][44][45][46].…”