Properties of Block-Copolymer Interfaces

• Main Author: Rozairo, Damith P.
• Format: Others
• Published: North Dakota State University 2016
• Online Access: http://hdl.handle.net/10365/25529

There is considerable interest in the fabrication and mechanism of soft spheres and capsules because of their use in a large number of applications ranging from targeted drug delivery systems to cosmetically active agents. The performance of these soft spheres depends on the enhancement of the mechanical properties of these materials. This dissertation is focused on studying the fundamental physics of these soft spheres. First, we study a simple fluid-fluid system covered by a diblock copolymer. Specifically, we use laser confocal microscopy to adapt a sessile drop geometry to a measurement of the static properties of an ensemble of polystyrene-b-poly(ethylene oxide) (PS-PEO) stabilized oil droplets. We present a simple model derived from Bashforth-Adams model for sessile drops. This method can be used to measure the surface tension of any fluid-fluid interface using a simple optical microscope without looking at the full geometry of a deformed droplet. We then synthesize a polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS) elastic-shell-coated emulsion drop that shows an identical deformation to the fluid-like PS-PEO droplets. Both systems, in sessile geometry, can be related to their basic material properties through appropriate modeling. We find that the elastic shell is dominated by its surface tension, easily enabling it to match the static response of a purely fluid drop. Motivated by the sessile drop geometry, we study how these idealized cargo carrying spheres interact with a hard wall. As a polymer covered droplet approaches a flat wall, it buckles in and traps an amount of the outer fluid. This fluid is slowly drained out through a narrow channel covered with a polymer brush. A simple scaling model predicts the drainage rate of the fluid through the polymer brush. Finally, we look at how a long diblock copolymer (PS-PEO) molecule is packed at an oil-water interface and how it affects the surface tension. We find that as the polymer to oil concentration is reduced, it goes from the critical concentration at which no more chains can be fitted to the bare oil interface quickly. Furthermore, we find that the outer brush thickness (PEO) increases as the PS-PEO concentration is increased. === American Chemical Society: Petroleum Research Fund (52062-DNI7)