M.Sc Thesis


M.Sc StudentBoris Haimov
SubjectOn the Formation of Hybrid Organic/Liquid Metal Interfaces
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor Professor Pokroy Boaz
Full Thesis textFull thesis text - English Version


Abstract

Surfaces tend to lower their free energy by adsorbing organic molecules and impurities. Such organic matter can play important functional roles by acting as diffusion barriers, decreasing the surface reactivity, changing the surface resistivity, and altering other physical properties. Such surface “impurities” usually lack binding specificity, chemical function, and reproducible physical or chemical properties. By contrast, self-assembled monolayers (SAMs) have the potential for precise control of the surface properties in a reproducible, flexible, and tailored fashion. Different types of SAMs organize themselves spontaneously from the gas or liquid phase on the surfaces of oxides, metals, and semiconductors into a flexible two-dimensional (2D) phase.

The development of SAMs on surfaces has proved enormously useful in many areas of science and technology. Among the most extensively studied and utilized SAMs are alkanethiols. These compounds bind strongly to coinage and noble metals. Nevertheless there has been very little research on the kinetics of SAM formation on liquid metals due to experimental difficulties that are not present for solid surfaces.   

Herein we have studied the interaction and kinetics of adsorption of alkanethiol SAMs on liquid metals from different points of view:

(i) The kinetics of adsorption of SAMs on liquid metal drops via the change in the drop’s surface tension. We calculate the latter from the axisymmetric drop shape. Further, we derive the surface coverage fraction from the surface tension. Utilizing this methodology allows us to optically detect very low concentrations of SAM molecules in solution, down to tenths of ppb.

(ii) The formation of large alkanethiol/mercury hybrid crystals via increasing the organic/metal interface area by intense sonication. We show that due to the strong bonding of the thiol groups to mercury (213 kJ/mol) and the van der Waals forces between long alkane backbones, fast formation of layered hybrid crystals are formed probably via a self assembly process.

The results of this work show that:

(1)    It is indeed possible to extract information regarding the kinetics of the SAM development on the sessile drop using a simple experimental setup.

(2)   The rate of the kinetic process is slower for shorter thiol-alkanes, with the exception of nonane-thiol (C9SH) and tetradecane-thiol (C14SH).

(3)   The rate of the kinetic process is slower for lower surfactant concentrations.

(4)   It is possible to synthesize mercury-thiolate crystals with an accelerated process and by spontaneous reactions.