Spectroscopic Study of Water Adsorption and Desorption on/from Oligo(ethylene glycol)-Substituted Alkanethiolate Self-Assembled Monolayers

Abstract

Adsorption and temperature-driven desorption of water (D2O) on/from the surface of oligo­(ethylene glycol) (OEG)-substituted alkanethiolate self-assembled monolayers (SAMs) with a variable length of the OEG segment and variable termination (−OH or −OMe) were studied by synchrotron-based X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The characteristic spectroscopic features of D2O were monitored, with a predominant signature of amorphous ice upon adsorption at 105–125 K and subsequent heating up to desorption temperature. The adsorption occurred exclusively onto the SAM surface, with a strong distortion of the spectral pattern for the first layer (for OH-terminated surfaces) and without any indication for the penetration of the D2O molecules into the hydrogel-like OEG part of the SAMs. The thickness of the ice films increased linearly with the D2O dose with the same rate for all OH-terminated SAMs and a slightly lower rate for the CH3-terminated films. The desorption of D2O in the given quasi-static temperature increase regime occurred at ∼150–155 K for all SAMs studied. Specific features of the NEXAFS spectra could be tentatively interpreted as a signature of a hydration phase, formed by the temperature-driven diffusion of the adsorbed D2O molecules into the hydrogel-like OEG part of the SAMs.

Interaction of water with oligo(ethylene glycol) terminated monolayers: wetting versus hydration

“…Significantly, the packing density of the EGn-OH SAMs is mainly determined by their AT part and is, therefore, nearly independent of the length of the OEG segment, which has been verified by us. 27 Also, the wetting properties of these films are almost independent of n, 5,7 which have been verified as well. 27 However, their inertness to protein adsorption and biofouling varies significantly over the series: whereas these films are not biorepulsive at small n, they become protein-repelling if their OEG part consists of more than two or three EG units, 7,9,10 which has been verified by us using fibrinogen as a test protein.…”

“…27 Also, the wetting properties of these films are almost independent of n, 5,7 which have been verified as well. 27 However, their inertness to protein adsorption and biofouling varies significantly over the series: whereas these films are not biorepulsive at small n, they become protein-repelling if their OEG part consists of more than two or three EG units, 7,9,10 which has been verified by us using fibrinogen as a test protein. 27 Thus, the EGn-OH SAMs represent an ideal model system with variable proteinrepelling properties at an almost constant packing density and hydrophilicity, which both are similar to those of the reference EG0-OH film.…”

“…27 However, their inertness to protein adsorption and biofouling varies significantly over the series: whereas these films are not biorepulsive at small n, they become protein-repelling if their OEG part consists of more than two or three EG units, 7,9,10 which has been verified by us using fibrinogen as a test protein. 27 Thus, the EGn-OH SAMs represent an ideal model system with variable proteinrepelling properties at an almost constant packing density and hydrophilicity, which both are similar to those of the reference EG0-OH film. In contrast, the EG6-OMe SAM, exhibiting the same biorepulsivity as the EG6-OH monolayer, 5 is more hydrophobic, in view of the terminal methyl group.…”

The Effect of Ultraviolet Light on Biorepulsive Hydrogel Poly(ethylene glycol) Films

“…Representative XP spectra of the moderately thick (∼71 nm) PEG film, in the pristine state and exposed to UV light, are shown in Figure 3 (see also Figure S4 in the Supporting Information). The C 1s and O 1s spectra of the pristine film in Figure 3a,b, respectively, exhibit the characteristic peaks of PEG/OEG at 286.7 (C 1s) and 532.8 eV (O 1s), 43,44 which are the only perceptible features. The chemical identity of the PEG films and the lack of any contamination are thus verified.…”

Tuning the Properties of Poly(ethylene glycol) Films and Membranes by the Molecular Weight of the Precursors

“…Representative C 1s, O 1s, and N 1s spectra of the films prepared at a concentration of the precursors in the primary solutions of 20 mg/mL are shown in Figure 3; the analogous data for 10 and 30 mg/mL can be found in the Supporting Information (Figures S1 and S2). The C 1s and O 1s spectra in Figure 3a,b, respectively, exhibit exclusively the characteristic peaks of PEG at 286.7 eV (C 1s) and 532.8 eV (O 1s), 29,30 which are the only perceptible features. The chemical identity of the PEG films and the lack of any contamination are thus verified.…”