Tailoring the functionality of self-assembled monolayers (SAMs) can be achieved either by depositing prefunctionalized molecules with the appropriate terminal groups or by chemical modification of an existing SAM in situ. The latter approach is particularly advantageous to allow for diversity of surface functionalization from a single SAM and if the incorporation of bulky groups is desired. In the present study an organocatalytic isothiourea-mediated Michael addition–lactonization process analogous to a previously reported study in solution is presented. An achiral isothiourea, 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole (DHPB), promotes the intermolecular Michael addition–lactonization of a trifluoromethylenone terminated SAM and a variety of arylacetic acids affording C(6)-trifluoromethyldihydropyranones tethered to the surface. X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, and ellipsometry analysis were conducted to confirm the presence of the substituted dihydropyranone. A model study of this approach was also performed in solution to probe the reaction diastereoselectivity as it cannot be measured directly on the surface.

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C–C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion.

Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for a tailoring of surface properties. A vapor phase deposition of such films would offer advantages in cases where the preparation from solution is not an option or not desired, for example in connection with silicon microstructures such as micro-electromechanical systems. We show that SAMs of 9-decenyltrichlorosilane (CH2CH(CH2)8SiCl3), 10-undecenyltrichlorosilane (CH2CH(CH2)9SiCl3), 14-pentadecenyltrichlorosilane (CH2CH(CH2)13SiCl3), decyltrichlorosilane (CH3(CH2)9SiCl3), and octadecanetrichlorosilane (CH3(CH2)17SiCl3) can be prepared both from solution and from the vapor phase. The resulting layers were compared by static contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy to determine their surface wettability, the film thickness, the smoothness and homogeneity of the respective films, and their chemical composition and each method gave films of comparable quality. Deposition of functionalized SAMs from the vapor phase is rare. Here we report the parameters for the preparation of well-ordered vinyl-terminated SAMs from the vapor phase.Highlights► Vinyl-terminated self-assembled monolayers (SAMs) were prepared on SiOx substrates. ► Films were comprehensively characterized with surface analytical techniques. ► High quality vinyl-terminated SAMs were obtained from the vapor phase. ► Vapor phase deposition can be applied in connection with microstructures.

Oligo(ethylene glycol) (OEG) containing self-assembled monolayers (SAMs) on gold are known for their protein resistant properties. The underlying molecular mechanisms and the contributions of the interactions involved, however, are still not completely understood. It is known that electrostatic, van der Waals, hydrophobic, and hydration forces all play a role in the interaction between proteins and surfaces, but it is difficult to study their influence separately and to quantify their contributions. In the present study we investigate five different OEG containing SAMs and the influence of the ionic strength and the electrostatic component on the amount of a negatively charged protein (fibrinogen) that adsorbs onto them. Atomic force microscopy (AFM) was employed to record force–distance curves with hydrophobic probes depending on the ion concentration, and the amount of the protein that adsorbs relative to a hydrophobic surface was quantified using ellipsometry. The findings suggest that electrostatic forces can create a very low energy barrier thus only slightly decreasing the number of negatively charged proteins in solution with sufficient energy to approach the surface closely, and have a rather small influence on the amount that adsorbs. The films we investigated were not protein resistant. This supports other studies, reporting that a strong short-range repulsion as for example caused by hydration forces is required to make these films resistant to the non-specific adsorption of proteins.

In atomic force microscopy (AFM) a sharp tip fixed close to the free end of a cantilever beam interacts with a surface. The interaction can be described by a point-mass model of an equivalent oscillator with a single spring located at the position of the tip. However, other spring constants have to be used to describe the oscillation behavior correctly if forces are acting on the cantilever over an extended lateral range. A point-mass model is then no longer valid. In the present study we derive expressions for the spring constants of cantilevers that can interact with any part of their plan view area along the beam and for all flexural modes. The equations describe the oscillation behavior in the corresponding mass model and are based on the eigenfrequencies and modal shapes of the free cantilever. The results are of high practical relevance, for example if an AFM is operated in a higher flexural mode, if the tip is not located at the free end of the cantilever beam, or if the external conservative forces affecting cantilever movement are not restricted to a single point. The limitations of the approach are discussed.

We have investigated the friction and adhesion properties of two structurally different phases of ω-(4′-methylbiphenyl-4-yl) butanethiol CH3(C6H4)2(CH2)4SH (BP4) self-assembled monolayers (SAMs) on gold under water with scanning force microscopy. While the identical chemistry of the two phases is reflected by very similar water contact angle values, lateral force measurements and force distance curves reveal the strong influence of the structure, that is, of the molecular and defect density on the mechanical properties of the SAM. A surprisingly high difference in the resistance of the films to shearing but a similar friction coefficient is found for the two phases indicating a crucial influence of the film structure on the energy dissipation in SAMs. The results highlight the importance of structural effects in the interpretation of surface properties.

We have synthesised novel oligo(ethylene glycol), CF3-terminated switching self-assembled monolayers, which allow the force experienced by a hydrophobic object to be controlled via the ionic strength of the environment.

We demonstrate that the thermal response of uncalibrated atomic force microscope cantilevers can be used to extract the density and the viscosity of viscous liquids with good accuracy. Temperature dependent thermal noise spectra were measured in water/poly(ethylene glycol) mixtures. Empirical parameters characteristic of the resonance behavior of the system were extracted from data recorded for one of the solutions at room temperature. These parameters were then employed to determine both viscosity and density values of the solutions simultaneously at different temperatures. In addition, activation energies for viscous flow were determined from the viscosity values obtained. The method presented is both fast and reliable and has the potential to be applied in connection with microfluidic systems, making macroscopic amounts of liquid and separate measurements with a viscometer and a densimeter redundant.

Dialkyldimethylammonium films on mica prepared via ion exchange from solution have been reported to be of high quality in terms of their density and molecular orientation. Different preparation procedures are described in the literature. The molecular order and the inclination of the alkyl chains, however, are often deduced from indirect experimental evidence such as the wettability and the film thickness. In the present study we employed near edge X-ray absorption fine structure spectroscopy (NEXAFS) to determine directly the order of the molecules adsorbed from different solvents (water, methanol, water/methanol 1:1, cyclohexanol, and chloroform). It was found that films prepared from different solvents are displaying large differences in the established surface coverage and orientation. In particular, NEXAFS disclosed that the orientation of the alkyl chains can differ significantly even when similar water contact angle values are observed.

Oligo(ethylene glycol) (OEG) containing self-assembled monolayers (SAMs) on gold are known for their protein resistant properties. The underlying molecular mechanisms and the contributions of the interactions involved, however, are still not completely understood. It is known that electrostatic, van der Waals, hydrophobic, and hydration forces all play a role in the interaction between proteins and surfaces, but it is difficult to study their influence separately and to quantify their contributions. In the present study we investigate five different OEG containing SAMs and the influence of the ionic strength and the electrostatic component on the amount of a negatively charged protein (fibrinogen) that adsorbs onto them. Atomic force microscopy (AFM) was employed to record force–distance curves with hydrophobic probes depending on the ion concentration, and the amount of the protein that adsorbs relative to a hydrophobic surface was quantified using ellipsometry. The findings suggest that electrostatic forces can create a very low energy barrier thus only slightly decreasing the number of negatively charged proteins in solution with sufficient energy to approach the surface closely, and have a rather small influence on the amount that adsorbs. The films we investigated were not protein resistant. This supports other studies, reporting that a strong short-range repulsion as for example caused by hydration forces is required to make these films resistant to the non-specific adsorption of proteins.

We have synthesised novel oligo(ethylene glycol), CF3-terminated switching self-assembled monolayers, which allow the force experienced by a hydrophobic object to be controlled via the ionic strength of the environment.