Self-Assembly of Highly Immiscible Polymers Using Balanced Surfactants

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

SELF-ASSEMBLY OF HIGHLY IMMISCIBLE POLYMERS USING BALANCED SURFACTANTS The PI's objective is to create a library of surfactants for controlling the nano-scale self-assembly in mixtures of highly immiscible polymers. This will enable the creation of new nano-structured polymer materials. It may also enable reusing commingled polymeric waste. The proposed approach represents a risky departure from the large body of previous experimental and theoretical work in this field which relied of the surfactancy of A-B copolymers for organizing mixtures of A and B homopolymers. It is now recognized that these types of copolymers can only organize interfaces if the homopolymers are weakly immiscible. The surfactant that will be uses in the study is a balanced A-C block copolymer. The notion of balance is adapted from the rich literature on surfactancy in aqueous systems. Nonionic surfactants with balanced hydrophobic and hydrophilic character have been successful in creating nano-scale organization in oil/water mixtures in spite of their high degree of incompatibility. The goal is to apply this principle to polymers. The proposed experiments will be conducted on mixtures of highly immiscible polyolefins, polybutene (PB) and polyisobutylene (PIB). The PI will use a polybutene-block-head-to-head polypropylene (PB-PP) copolymer as a surfactant. The objective is to demonstrate that PB/PIB/PB-PP blends exhibit the rich self-assembly characteristics found in aqueous systems. The PI chose this system because the magnitude and sign of the temperature dependence of the PB/PP and PIB/PP Flory-Huggins interaction parameters are (approximately) equal and opposite, respectively. Model polymers required for this study will be synthesized by anionic and cationic polymerization. Self-assembly will be studied by small angle neutron scattering, light scattering, and electron microscopy. IMPACT STATEMENT This proposed research on balanced surfactants holds the potential of introducing radically new technology for controlling the morphology of polymer blends. It will enable the creation of new blended materials from industrially important polymers such as polyisobutylene (a polymer of considerable current importance because of its use in the manufacture protective garments for working in chemically and biologically contaminated areas). Industrial production of nanostructured blends of electrically conducting and non-conducting polymers may also be enabled by the proposed research. The approach of using balanced surfactants is inspired by the efficacy of synthetic and natural surfactants in aqueous systems. However, the scientific challenge of applying principles learned in aqueous systems to hydrocarbon polymers is considerable because of the difference in fundamental intermolecular interactions. Interactions with water molecules are dominated by their permanent dipole and specific interactions such as hydrogen bonding. The SGER proposal seeks to explore the possibility of designing balanced surfactants in the absence of these interactions.