Microscopic wettability of ester- and acetate-terminated self-assembled monolayers
1997 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, no 15, 4003-4012 p.Article in journal (Refereed) Published
Four different carbonyl-containing self-assembled monolayers (SAMs) of alkanethiolates on gold were studied to assess the impact of the functional group Linked to the carbonyl upon its hydrogen bond accepting capability. These SAMs (HS(CH2)(16)O(C=O)-X,X = CH3, CF3, or C6H5, and HS(CH2)(15)(C=O)OCH3) were thoroughly characterized with contact angle measurements, single wavelength ellipsometry, and infrared reflection-absorption spectroscopy (IRAS) prior to the studies of interaction with D2O. The first three monolayer compounds were introduced by reacting hydroxyl-terminated SAMs (HS(CH2)(16)OH) with either acetyl chloride, trifluoroacetic anhydride, or benzoyl chloride. The behavior of D2O ice on the SAMs was investigated at 100 K with IRAS and temperature programmed desorption (TPD). On all monolayers the D2O molecules were shown to interact with the carbonyl oxygen. The degree of interaction depended upon the termination of the thiol, where the size, structure, and electronegativity of the terminating groups in the molecules comprising the monolayer were found to be important factors. Indications of interaction with the C-O-C oxygen were seen for all compounds, as well as weak interaction between water molecules and the CF3 group of one of the investigated SAMs. Common behavior for all four monolayers with an adsorbed D2O overlayer was a decrease in the number of hydrogen bonds to the substrate when the overlayer was annealed from amorphous ice at 100 K to polycrystalline-like ice at 140 K. The spectral changes accompanying the structural transition were consistent with a change from a mainly flat overlayer to condensed three-dimensional clusters. The bulk-to-surface molecular ratio of adsorbed ice clusters could be assessed by IRAS and correlated to macroscopic wetting properties. Our results infer that microscopic ice clusters on these SAMs qualitatively mimic the shape of macroscopic water drops on the same SAMs. Results of TPD measurements are also consistent with this view.
Place, publisher, year, edition, pages
American Chemical Society , 1997. Vol. 13, no 15, 4003-4012 p.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-76336DOI: 10.1021/la9608526ISI: A1997XM64200017OAI: oai:DiVA.org:liu-76336DiVA: diva2:513890