Chemically modified silicon dioxide surfaces. Wetting properties of compact n‐alkyl‐dimethylsiloxy layers, and their mixed surface crystals. The Question of Wetting of Molecularly Rough and of Swollen Surfaces

Abstract

SummaryBy means of contact angle measurements, it has been shown that compact alkyl-dimethyl-doxy layers can be obtained on the surface of acid leached glass using the method previously developed for fume silica. Subsequently, a series of densest possible alkyl-dimethylsiloxy layers were prepared having non-branched alkyl substituents, CZH2z+1, (with z = 1, 2, 3, 6 , 10, 14, 18 and 22) and wetting angles were measured as a function of the temperature. On surfaces coated with longer alkyl substituents the formation of mixed crystals, consisting of the sparse chemically bonded alkyl layer and a n-alkane acting as a wetting agent, has been observed at low temperatures. At higher temperatures such surfaces appeared to be 'molten', and at the same time swollen by the wetting agent. Equations have been derived to deduce the free surface energies and to account for the wetting properties of rough and swollen surfaces. Application of the results to the data presented in this paper revealed that glass surfaces covered with short alkyl chains (methyl, ethyl and propyl) are rough and those covered with long chains (tetradecyl, octadecyl and docosyl) are swollen. Surfaces formed by hexyl-and decyl-dimethylsiloxy substituents exhibit intermediate properties.

Linearity of homologous series retention plots in reversed-phase liquid chromatography

“…If the solute alkyl chain is sorbed along a bristle, then a discontinuity in the plot Ed vs. nc should be expected when nc becomes larger than the critical value depending on the length of the bonded moieties. Although such a solute ligand association is entropically unfavorable, Kovats and co-workers have shown that it does exist (19). This is also in agreement with the concept of the critical chain length introduced by Berendsen et al (12).…”

“…The magnitudes of the steps are obtained by extrapolating the two lines corresponding to the plateau regions and by drawing a vertical line at the inflection point of the step. They are approximately [15][16][17][18][19][20] cal/mol with a precision of 20-30%. The observation of Figures 3D and 4 also reveals that there is no step with the C4 and the polymeric C18 phases.…”

Trialkylsilane Monolayers Covalently Attached to Silicon Surfaces: Wettability Studies Indicating that Molecular Topography Contributes to Contact Angle Hysteresis

“…The longer chain alkylsilane derivatives are less rigid, more liquidlike, and thus smoother surfaces at the molecular level. The effect of molecular roughness on contact angle (not hysteresis) has been discussed in the literature but has not been demonstrated.

2 Contact angle hysteresis as a function of chain length of grafted n -alkyldimethylsilane: CH 2 I 2 (·); C 16 H 34 (▴); (a) toluene, room temperature; (b) toluene, 60−70 °C; (c) vapor phase, 60−70 °C.

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Density and surface tension of 83 organic liquids

“…We have previously reported the synthesis of a series of 2,5and 5,6-dihalonicotinic acids of potential medicinal interest (1)(2)(3)(4)(5). As an extension of that work, we now wish to report the preparation and characterization of the methyl esters (I-VIII) of eight of the aforementioned acids.…”