Kinetics of octadecyltrichlorosilane self-assembly on silicon oxide surfaces: An experimental and numerical study.
Item
-
Title
-
Kinetics of octadecyltrichlorosilane self-assembly on silicon oxide surfaces: An experimental and numerical study.
-
Identifier
-
AAI9917668
-
identifier
-
9917668
-
Creator
-
Krishnan, Srinivasan.
-
Contributor
-
Adviser: Alexander Couzis
-
Date
-
1999
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Engineering, Chemical | Chemistry, Physical | Engineering, Materials Science
-
Abstract
-
In this work, we present and discuss the results of our in-situ study on the kinetics and mechanism of self-assembly of octadecyltrichlorosilane (OTS) onto a silicon oxide surface. FTIR-ATR is the technique used to monitor the self-assembly process. The surface coverage of the adsorbing OTS, Gammaads, is determined using the molar absorptivity of adsorbed OTS, epsilonads. The rate of adsorption and the final F.& increase with increasing concentration of OTS, and also with increasing flow rate of the OTS solution over the silicon ATR surface. The effects of water, both at the substrate surface and in the solvent are investigated. We present proof of the ordering occurring in the adsorbing layer. First, the position of the absorption peak, characteristic of the asymmetric -CH- stretch of the -CH2- moiety in the adsorbate shifts to lower wavenumber with increase in time. In addition, in-situ polarized FTIR-ATR data of OTS self-assembly offers evidence for the changes occurring in the conformation and ordering of the adsorbate molecules at the solid/liquid interface. The crystalline ordering occurring in the adsorbing layer, as evidenced by the shift in the peak position, is also supported by the crystalline split occurring in the -CH2- bending moment at 1460 cm-1 . By using a silicon wafer sandwiched to a germanium ATR crystal we extend the useful spectral range beyond 1600 cm-1.;Also for the first time, we have described the adsorption over the entire time scale of our experiment with a single mathematical model. This model accounts for an activation energy for adsorption, (EA)ads , that varies as a function of the surface coverage. The dependence of (EA)ads on Gammaads is due to the interactions between the hydrocarbon chains of the surfactant molecules on the solid surface. As a result every incoming surfactant molecule has to overcome an increasingly larger energy barrier in order to adsorb onto the substrate. This energy barrier, which is dependent on the surface coverage, assigns a probability for the adsorption of an incoming surfactant to the substrate surface, with the probability being the greatest at the beginning of the process and decreasing as the surface coverage increases.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
