pH-dependent stability of self-assembled monolayers on gold

Abstract

Part I reports the effect of pH on the stability of self-assembled monolayers (SAMs) of various alkanethiols with different terminal groups on gold. The SAMs of 1-hexadecanethiol $(HS-(CH_2)_{15}-CH_3)$, 16-mercaptohexadecanol $(HS-(CH_2)_{16}-OH)$, 16-mercaptohexadecanoic acid $(HS-(CH_2)_{15}-COOH)$ and 16-amino-1-hexadecanethiol $(HS-(CH_2)_{16}-NH_2)$ were prepared, and their stability was investigated at pH values from 1 to 14 for one week. The ellipsometric measurements showed that these SAMs were unstable under highly basic conditions. For example, the thickness of all the four SAMs decreased rapidly within one day at pH 14. At the pH values of 13 and 13.5, the SAMs of $(HS-(CH_2)_{16}-NH_2)$ were found to be stable, while the thickness of the three other SAMs decreased gradually. The SAMs remained stable at pH 12 and below, and no thickness decrease was observed even at pH 1 and 2. Part II describes the studies of polymer-grafted surfaces and their chemical and biological applications. To generate the surfaces with special functionality, stimuli-responsive polymers and highly protein/cell resistent polymers were used to form surface-tethered polymer brushes. Various polymerization methods such as ring-opening metatheis polymerization and atom transfer radical polymeriation were adopted to form the polymer brushes on numerous substrates, including gold, silicon oxide, and glass. Polymer-grafted surfaces with the special functionality were then applied for selective morphological switching of the surface, effective cell culture surface, and powerful protein/cell-resistent surface maintaining the original form of cell micropatterns. In Chapter 1, we reported the formation of diblock copolymer brushes on a gold surface by surface-initiated, ring-opening metathesis polymerization (SI-ROMP) with the newly developed ruthenium catalyst, $[(H_2IMes)(3-Br-py)_2(Cl)_2Ru=CHPh]$. Taking advantage of the highly improved activity of the ruthenium catalyst and the...