Chemistry directed assembly of multilayered polymer thin films and colloidal particles

Abstract

In this thesis, multilayered polymer thin films have been directed to different regions of a surface based on both electrostatic and secondary interactions between the polymer and the surface. This concept of adsorption directed by surface chemistry is universal, in that the same sets of rules derived for polymeric systems can also be applied to molecule and meso-scale systems, including dye molecules, colloidal particles, proteins and cells. An approach of "surface sorting" was proposed to direct two or more objects with varying functionalities to deposit on predetermined regions of a surface based on specific surface interactions. Specifically, on the surface patterned with alternating charged carboxylic acid (COOH) surface groups and neutral oligoethylene glycol (EG) surface groups, linear polyethyleneimine (LPEI) based multilayers predominately adsorb on the COOH surface, with maximal selectivity at the moderate pH level of 4.8; in contrast, polyallylamine hydrochloride (PAH) based multilayers are attracted to the EG surface under certain pH conditions, with maximal selectivity on EG also at a pH of 4.8. Chemical force microscopy was used to directly examine the intermolecular interactions between polyamines and functional surfaces. The driving forces were identified to be primarily an electrostatic interaction for LPEI adsorption on the COOH surface, and primarily a hydrophobic interaction for PAH adsorption on the EG surface, respectively. By combining the results of force measurements and systematic adsorption studies, a set of rules were established that define the conditions required for selective deposition on specific surface regions for polyelectrolyte adsorption.

(cont.) By understanding these principles, a micro-array containing two luminescent dyes side by side was achieved. These principles were successfully expanded to micron and sub-micron colloidal particle systems. The interplay of electrostatic interactions, hydrogen bonding, and hydrophobic interactions between colloid-colloid and colloid-surface has been finely tuned with pH, ionic strength and the addition of surfactants. Thus, the selectivity and packing density of colloid adsorption onto patterned polyelectrolyte multilayer templates could be controlled. The resultant 2D colloid structures have a range of potential applications such as photonic band gap materials, surface templates and lithography masks. The second developed tool in this thesis research is "polymer-on-polymer stamping", a new approach to create chemically patterned surfaces utilizing polymers and copolymers. In this approach, chemical patterns are achieved by the direct stamping of functional polymers onto a surface containing complementary functional groups. Polyelectrolyte multilayers are used to create functional surfaces which act as platforms for polymer stamping, as multilayers may be adsorbed on a number of different surfaces. The resulting pattern is then used as a template for the further deposition of materials on the surface. This method has led to a means of patterning common substrates such as glass and plastic without extensive surface treatments. It can be applied to various polymer systems and thin film deposition techniques. An oligoethylene oxide - maleic anhydride graft copolymer (EO-MAL) was printed on polyamine surface to direct selective layer-by-layer...