Concept: If particles are added to a system of two immiscible liquids, they tend to locate at the interface between the two liquids and decrease of the interfacial tension between the immiscible liquids. These characteristics are reminiscent of surfactants i.e. particles can behave like surfactants even though they are not amphiphilic. The hypothesis of this proposal is that such interfacially active particles can be employed to control the morphology of two-phase polymer blends.
Motivation: Immiscible polymers are commonly blended together in the melt state to achieve materials with properties not feasible with single homopolymers. Many of the desired properties require the blend to have a specific microstructure e.g. a conductive blend may be realized by blending a small amount of conductive homopolymer into an insulating one provided the conductive homopolymer is the continuous phase. An ability to control the morphology resulting from two-phase blending operations is therefore critical. Success of this project will provide an entirely new method to control two-phase morphologies.
Research Proposal: In past research on particles at interfaces, particles were deposited directly at the interface in a spreading solvent. This procedure of depositing particles directly at the interface is unsuitable for polymer blend applications. The first goal of this project therefore is to devise a mechanical blending procedure that will deliver particles to the interface and allow them to adsorb there.
The second goal is to quantify the concentration of particles at the interface at any location in the two-phase structure, the corresponding interfacial tension, and the contact angle of the particles at the interface. The final goal is to demonstrate that the dynamics of two-phase flows, and the morphology resulting from them, can indeed by modified using particles. The overall objective is to establish proof-of-principle of the hypothesis above, and lay the ground for more detailed research on two-phase structure control with particles.
Merits: While particles are commonly used to modify the bulk properties of homopolymers, this proposal attempts to exploit particles specifically as surface-active agents. It offers a radically new approach to controlling the morphology of polymer blends. At present, the only common surface-active agents for polymers are block copolymers. These are generally system-specific; a given block copolymer is surface-active for only a few homopolymer pairs. A significant advantage of particles is that they are non-specific and may be used in a wider range of blends. This research will complement other research on multiphase flow in the PI's lab. It will train one graduate and one undergraduate student on experimental research in polymers. The research on capillary instabilities to be conducted as a part of this project is relevant to a variety of applications such as dispersive mixing, inkjet printing, etc. and thus important in its own right.
The PI has extensive knowledge and experimental skills in the research topics covered here. All the necessary experimental resources are either available, or will be procured or fabricated during this research.
