Structural models and barrier properties of amine-terminated trialkoxysilane monolayers incubated in nonpolar vs. polar protic solvents

• DOI: 10.1016/j.matchemphys.2021.125113
• Publication Date: 2021-08-11T06:26:05Z
• Authors: Giin-Shan Chen; Wen-Hong Chang; Chin-Chia Chang; Yi-Hsin Chien; Jau-Shiung Fang; Yi-Lung Cheng
• Keywords: Silanization

Abstract The effect of solvent chemistry and polarity on molecular structure and barrier capacity of a resulting trialkoxysilane self-assembled monolayer (SAM) has not yet been well explored. Here, comparative studies of synthesizing (3-aminopropyl)trimethoxysilane (APTMS) SAMs in nonpolar and polar protic solvents, toluene and ethanol, respectively, are made under strictly controlled silanization protocols favoring the growth of orderly SAMs. Atomic force, transmission and scanning electron microscopies suggest that (a) silanization for the two solvents proceeds concurrently from molecule adsorption, admolecule orientation adjustment to the formation of a stably assembled monolayer and (b) both SAMs effectively adsorb 2-nm-sized catalytic particles for electroless Cu deposits to evolve identically in terms of surface coverage. However, bonding structural analysis by angle-resolved X-ray photoelectron spectroscopy suggests that SAM (toluene) has a much higher ordering and closer packing than SAM (ethanol), and is the only qualified barrier for Cu. The effect of solvent's chemistry and polarity on molecular structure and barrier properties of the two SAMs is elucidated by molecular incubation models determined by the relative weighting of bimolecular nucleophilic substitution (SN2) reaction theoretically and uncontrolled molecular oligomerization found experimentally from dynamic light scattering.