摘要(英) |
The polymer-surfactant interaction in poor solvent is studied by dissipative particle dynamics (DPD) simulations. The polymer-surfactant interaction leads to the formation of polymer-surfactant complex. For flexible polymer in good solvent, the necklace morphology is well accepted. The purpose of this work is to examine whether the polymer-surfactant complex in poor solvent follows the necklace model or not. Both flexible and rigid polymers are considered. The motivation for studying the latter case is because most applications employing the unique electronic, thermal, optical, and mechanical properties of carbon nanotubes require the large-scale manipulation of stable suspensions in water at high weight fraction by surfactant addition. The stability of rigid polymer-surfactant complex therefore becomes an important issue.
This thesis involves two topics. In the first topics, the surfactant characteristics are explored. The influence of molecular structure on the surfactant property in terms of critical micelle concentration (CMC) is investigated at the same interaction parameters. The surfactant structures are changed by altering head group length, tail length, tail rigidity, and tail architecture. The qualitative behavior of CMC determined by DPD agrees with that of experimental results.
In the second topic, the adsorption behavior of surfactant onto polymer in poor solvent is investigated. Although a flexible polymer collapses into a globule in poor solvent, it is swollen and wrapped within a micelle upon addition of surfactant. The rigid-polymers tend to aggregate into a buddle in poor solvent. Nonetheless, upon addition of surfactant with short tail, which has specific interactions with polymer segment, the rigid-polymers disperse stably in the solvent due to the coverage of surfactant. A large micelle is formed to enclose the rigid-polymer and thus the necklace model is invalid in poor solvent.
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