Evaluating the quality of information in ultrasonic inspection: Krug, G.A., Defectoscopy (English Translation), No 5 (September–October 1967) pp 383–387 (1300)

Abstract

A self-assembled monolayer of alkanethiols having functional groups (HS-(CH2) 10−X; X = −H, −COOH, −CONH2) was immobilized on Au electrodes of a quartz-crystal microbalance (QCM), and the adsorption behavior of gaseous organic molecules, such as aliphatic acids, amines, alcohols, and alkanes, was observed from frequency decreases (mass increases) of the QCM plate in gas-phase. We used a super-sensitive, seventh overtone frequency of a 9 MHz AT-cut QCM (63 MHz) in order to detect a monolayer adsorption of small organic molecules. Association constant (Ka), adsorption (K1), and desorption rate constants (K−1) could be obtained from curve fitting of time courses of frequency changes (mass changes). All organic molecules hardly adsorbed onto the alkane (X = −H) membrane. To the -CONH2 membrane, only acetic acid can be selectively adsorbed compared with the -H membrane, but not caproic and nonanoic acids, which explains that hydrogen-bond interactions are important but hydrophobic interactions are not. To the -COOH membrane, both acetic acid and ethyle-nediamine can largely adsorb compared with the -H membrane, but not monoamines. The adsorption of ethylenediamine can be explained by acid-base interactions.