Self-Assembly of Organic Molecules on a Smectic Clay Surface
Self-assembly of molecules to form complex systems have enormous potential in a variety of areas. A point where computer processors cannot be further miniaturized due to physical and economic constraints is rapidly approaching. Solid-state silicon circuitry and silicon-based semiconductor technology will have to seek new methods to keep up with demands. Silicon-based semiconductor manufacture utilizing lithography is currently unable to obtain feature sizes below 0.1 micrometers. Utilizing current methods, the lower limit is forecast to be 30 nanometers. The solution to this problem may be in the investigation of single molecule switches and nanoscale memory systems. Construction of these nanoscale systems of circuits and memory devices requires self-assembly. Some methods currently used to fabricate such systems are chemical self-assembly, physical self-assembly, and colloidal self-assembly; however, these methods have not, as yet, achieved a system of ordered arrangement. The research proposed here explores a novel approach to creating a self-assembled nanoscale system of molecules via ion-dipole interaction with cationic counter ions on smectic clay surfaces. Molecular modeling of the candidates was conducted to assess the viability of self-assembly prior to experimental determinations. A study of ion-dipole bonding to the exchangeable cation on the smectic clay surface was conducted. Candidates were intercalated in montmorillonite clay and basal d-spacing was determined with X-ray diffraction. This suggests the extent of self-assembly in the system. Thermal analysis was conducted to assess the retention of organic molecules on the clay surface. Additional reinforcement of the self-assembled structure is believed to be possible with the addition of π- electron interaction. in the tail. An attempt to synthesize and characterize mesogenic species, to examine π- electron interaction, was conducted. Inadequate time and investment resulted in the inability to synthesize sufficient quantities of these compounds to form and investigate organoclay systems. It was found that the ion-dipole interaction is controlled by a polar head group, and Van der Waals interaction in the alkyl chain. The identity of the head group and the length of the alkyl tail group both contributed to self assembly of the system. Furthermore, it was discovered that the organoclay systems will reorder themselves over time. These studies are a prelude to the synthesis of liquid crystalline mesogenic candidates, the self-assembly of these molecules in the smectic system, and experimentation of self-assembly on a vermiculite surface. Additionally, the synthesis of electro-active molecules such as those in the oligo(phenylene ethynylene) class combined with a head group favorable to self-assembling structures can be accomplished followed by the eventual testing of organoclays made with these compounds or the dispersal of these organoclays in a polymer matrix.
self-assembly, molecules, x-rays, clay, diffraction
Goss, M. (2005). Self-assembly of organic molecules on a smectic clay surface (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.