Influence of specific intermolecular interactions on the self-assembly and phase behavior of oligo(ethylene glycol)-terminated alkanethiolates on gold
2001 (English)In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 105, no 23, 5459-5469 p.Article in journal (Refereed) Published
A comparative study of the self-assembly and phase behavior of seven different oligo(ethylene glycol) (OEG)-terminated alkanethiols on polycrystalline gold surfaces is presented. The general structure of the compounds is HS(CH2)m-X-EGn, where m = 11, 15, n = 2, 4, 6, and the linkages X are amide (-CONH-), ester (-COO-), or ether (-O-) groups. The amide and ester groups give rise to the intermolecular hydrogen bonding and dipole-dipole interactions, respectively, whereas the ether lacks specific interactions. The results from contact angle goniometry, null ellipsometry, and infrared reflection-absorption spectroscopy (IRAS) indicate that the intermolecular interactions can be partly used to control the conformation and order of the OEG portion of the self-assembled monolayers (SAMs). It is shown that the lateral hydrogen bonding stabilizes the all-trans conformation of the EG4 tails in the SAMs. Further on, the mechanism behind the thermal phase behavior of the OEG SAMs is investigated using temperature-programmed IRAS in ultrahigh vacuum. In the present study we show that the earlier reported helix-to-all-trans conformational transition at 60°C in the SAM of HS(CH2)15CONH-EG6 (Valiokas, R., Östblom, M., Svedhem, S., Svensson, S. C. T., Liedberg, B. J. Phys. Chem. 2000, 104, 7565-7569.) is a result of the particular molecular design of the SAMs through the specifically built-in lateral hydrogen bonds. A shortening of the alkyl chain to 11 methylenes has no effect on the amide-EG6 phase behavior. Contrary, the ester- and ether- containing SAMs undergo a melting type of transitions at 52 and 68°C, respectively, similar to that observed for poly(ethylene glycol).
Place, publisher, year, edition, pages
2001. Vol. 105, no 23, 5459-5469 p.
National CategoryEngineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-47353DOI: 10.1021/jp004441gOAI: oai:DiVA.org:liu-47353DiVA: diva2:268249