Interfacial Properties of Specifically Fluorinated Self-Assembled Monolayer Films

Colorado, Ramon; Graupe, Michael; Kim, Hyun I.; Takenaga, Mitsuru; Oloba, Olugbenga; Lee, Seung Hwan; Perry, Scott S.; Lee, T. Randall

doi:10.1021/bk-2001-0781.ch004

Cited by 10 publications

(22 citation statements)

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“…Regarding the second trend, the enhanced stability afforded predominantly by the perfluorocarbon segment can be rationalized on the basis of stronger solid-state fluorocarbon–fluorocarbon interactions than hydrocarbon–hydrocarbon interactions . Given that the terminally fluorinated SAMs and the hydrocarbon SAMs reported here are all crystalline in nature, ,,− their solid-state thermal stability can be evaluated with respect to the melting points of n -perfluoroalkanes, semifluorinated n -alkanes (F(CF 2 ) x (CH 2 ) y H), and n -alkanes. ,− It is known that n -perfluoroalkanes melt at higher temperatures than the corresponding semifluorinated n -alkanes, F(CF 2 ) x (CH 2 ) y H, which melt at higher temperatures than the corresponding n -alkanes . Given these data and assuming that the initial steps of the thermal degradation of SAMs can be viewed as a “melting” of the crystalline chains to form liquidlike films, SAMs with a longer perfluorocarbon moiety would be expected to “melt” or disorder at a higher temperature than SAMs with a shorter perfluorocarbon moiety.…”

Section: Resultsmentioning

confidence: 93%

Solution-Phase Desorption of Self-Assembled Monolayers on Gold Derived From Terminally Perfluorinated Alkanethiols

et al. 2011

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The solution-phase thermal desorption of three series of self-assembled monolayers (SAMs) on gold generated from terminally perfluorinated alkanethiols was examined. Series 1 SAMs, F(CF2) x (CH2)11SH, where x = 1–10, consisted of a constant hydrocarbon segment length with an increasing fluorocarbon segment length. Series 2 SAMs, F(CF2)10(CH2) y SH, where y = 2–6, 11, consisted of a constant fluorocarbon segment length with an increasing hydrocarbon segment length. Series 3 SAMs, F(CF2) x (CH2) y SH, where x = 1–10 and y = 16 – x, consisted of both hydrocarbon and fluorocarbon segments in which the segment lengths were varied while holding the total chain length constant at 16 carbon atoms. SAMs from these three series were prepared and characterized using both ellipsometry and contact-angle measurements. The resultant SAMs were shown to be highly hydrophobic and oleophobic. The SAMs were heated in decalin (DC) and perfluorodecalin (PFD) at 80 °C for various periods of time to monitor their thermal stability when exposed to hydrocarbon versus fluorocarbon solvents. In general, SAMs derived from n-alkanethiols and terminally perfluorinated alkanethiols exhibited diminished thermal stabilities upon heating in a hydrocarbon solvent (DC) versus heating in a perfluorocarbon solvent (PFD). The thermal stability of the SAMs increased with increasing lengths of the CF2 or CH2 segments. We also examined the kinetics of thermal desorption of these SAMs. From these studies, SAMs composed of higher degrees of terminal perfluorination exhibited smaller rate constants for the initial stage (fast regime) of desorption. When compared with analogous alkanethiol SAMs, the terminally perfluorinated SAMs exhibited greater thermal stabilities in both DC and PFD. In addition, values of the rate constants for desorption of the alkanethiol SAMs were approximately double those of the terminally perfluorinated SAMs having similar chain lengths.

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Section: Resultsmentioning

confidence: 93%

Solution-Phase Desorption of Self-Assembled Monolayers on Gold Derived From Terminally Perfluorinated Alkanethiols

et al. 2011

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“…The effect of surface dipoles on wettability with polar liquids has previously been shown to follow a similar trend; that is, an increase in surface dipoles leads to an increase in θ s . 22,24,31 This paper highlights two key points relating to hydrophobicity that can be translated to wetting and other technologies relying on liquid contact with a SAM: (i) Experimental realization of the odd−even effect in wetting, here, hydrophobicity, depends upon the quality of the surface. (ii) Surface dipoles has a more dominant effect than the packing density in SAM hydrophobicity and may account for the high θ s , relative to hydrocarbon polymers.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Previous studies on hydrophobicity of n -alkanethiolate SAMs, as captured in the contact angle formed between the SAM and a water droplet (θ adv ) on either Ag or Au, are not conclusive with regard to the presence or absence of an odd–even effect (Figure a). ,,,,− Two of the initial studies by Laibinis et al (Whitesides’ group) and Walczak et al (Porter’s group) are in disagreement: the former observing an odd–even oscillation in the values of the advancing contact angle, θ s adv , while the former did not. Other studies that followed did not support the presence of an odd–even effect in the hydrophobicity of n -alkanethiolate SAMs. − ,− ,− The odd–even effect was, however, observed with liquids that wet the SAM (θ s < 90) or when the thiol had a different terminal moiety besides −CH 2 CH 3 , for example, a terminal −CH 2 CF 3 . These CF 3 -terminated n -alkanethiols have a larger dipole moment and interact more strongly with a relatively weak dipole, such as that in water, and this is enough to overcome surface roughness effects, giving rise to a measurable odd–even effect .…”

Section: Hydrophobicity Of N-alkanethiolate Samsmentioning

confidence: 98%

Odd–Even Effect in the Hydrophobicity of n-Alkanethiolate Self-Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

et al. 2014

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The origin of the odd-even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (θs) made by water droplets on n-alkanethiolate SAMs with an odd (SAM(O)) or even (SAM(E)) number of carbons (average θs range of 105.8-112.1°). When SAMs were fabricated on smooth "template-stripped" metal (M(TS)) surfaces [root-mean-square (rms) roughness = 0.36 ± 0.01 nm for Au(TS) and 0.60 ± 0.04 nm for Ag(TS)], the odd-even effect, characterized by a zigzag oscillation in values of θs, was observed. We, however, did not observe the same effect with rougher "as-deposited" (M(AD)) surfaces (rms roughness = 2.27 ± 0.16 nm for Au(AD) and 5.13 ± 0.22 nm for Ag(AD)). The odd-even effect in hydrophobicity inverts when the substrate changes from Au(TS) (higher θs for SAM(E) than SAM(O), with average Δθs |n - (n + 1)| ≈ 3°) to Ag(TS) (higher θs for SAM(O) than SAM(E), with average Δθs |n - (n + 1)| ≈ 2°). A comparison of hydrophobicity across Ag(TS) and Au(TS) showed a statistically significant difference (Student's t test) between SAM(E) (Δθs |Ag evens - Au evens| ≈ 5°; p < 0.01) but failed to show statistically significant differences on SAM(O) (Δθs |Ag odds - Au odds| ≈ 1°; p > 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M(AD) versus M(TS)) and orientation of the terminal -CH2CH3 (by comparing SAM(E) and SAM(O) on Au(TS) versus Ag(TS)) play major roles in the hydrophobicity and, by extension, general wetting properties of n-alkanethiolate SAMs.

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“…Variation solely at the terminus can preserve the structural characteristics of HSAMs, such as packing density, lattice spacing, and the ordering of the lm. [38][39][40][41] Paum et al evaluated the differences in structure for CF 3 -terminated versus CH 3 -terminated monolayers using scanning tunneling microscopy (STM), surface-grazing incidence X-ray diffraction (GIXD), and helium scattering. 16 Their STM results, which concentrated predominantly on decanethiol and u,u,u-triuorodecanethiol, showed that in the close-packed phase (standing-up phase), the interchain distance of CF 3terminated SAMs is equal to that found in an HSAM ($5 Å).…”

Section: Introductionmentioning

confidence: 99%

“…16 However, increasing the number of methylenes in the alkyl spacer, which increases the vdW interactions between the alkyl chains, lessens the impact of charge repulsions, as has been shown in several other studies on the molecular packing of CF 3 -terminated SAMs. [38][39][40][41] In addition, Kim and co-workers have shown that the size of the terminal group also affects the frictional properties of the lm. 38,41 Specically, CF 3 -terminated SAMs exhibit a higher frictional response than their CH 3 -terminated analogs.…”

Section: Introductionmentioning

confidence: 99%

The impact of fluorination on the structure and properties of self-assembled monolayer films

2013

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The adsorption of partially fluorinated amphiphiles on metal/metal oxide surfaces allows for the generation of specifically fluorinated thin-film interfaces. Such surfaces are often compared to polytetrafluoroethylene (PTFE), which exhibits a low surface energy, accompanied by biological and chemical inertness, making perfluorinated interfaces applicable to a wide range of technologies. In thinfilm research, self-assembled monolayers derived from fluorinated alkanethiols (FSAMs) serve as welldefined systems that can be used to evaluate the physical and chemical properties of interfaces produced with varying degrees of fluorination. The characteristics of these surfaces have been attributed to both the chemical composition of the individual molecular adsorbates and the consequent structural features associated with monolayers formed from these unique partially fluorinated adsorbates. Specifically, this review seeks to correlate the structural and interfacial properties of FSAMs on gold with the structure/composition of the fluorinated moiety present in the adsorbed molecules and to highlight how the degree of fluorination influences the interfacial ordering of the individual alkanethiolate chains and the vacuum energy levels of the modified metal substrate. Additionally, the thermal stability of these organic thin films is analyzed as a function of adsorbate structure. Included are highlights of some of the studies in which FSAMs, formed from a variety of new types of surfactants, were used to modify colloidal systems, to generate anti-adhesive materials, and to enhance the stability of fluorinated thin films toward low-energy electron degradation.

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Interfacial Properties of Specifically Fluorinated Self-Assembled Monolayer Films

Cited by 10 publications

References 1 publication

Solution-Phase Desorption of Self-Assembled Monolayers on Gold Derived From Terminally Perfluorinated Alkanethiols

Solution-Phase Desorption of Self-Assembled Monolayers on Gold Derived From Terminally Perfluorinated Alkanethiols

Odd–Even Effect in the Hydrophobicity of n-Alkanethiolate Self-Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

The impact of fluorination on the structure and properties of self-assembled monolayer films

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