Design of surfactant molecules for active and passive control of surface and bulk properties of aqueous solutions

The research described in this thesis leads to the development of a molecular thermodynamic model that provides insight into the molecular origins of the surface properties of redox active ferrocenyl surfactants. This understanding is used in this thesis to design and synthesize new generations of redox active surfactants. This thesis is founded on recent experimental observations which have established that electrochemical transformations of redox-active ferrocene-based surfactants (Fc(CH₂)₁₁N+(CH₃) ₃, where Fc is ferrocene) can lead to large and reversible changes in the surface tensions of aqueous solutions. While these past studies have revealed that large and reversible changes in surface tension can be driven by using Fc(CH₂)₁₁N+(CH₃)₃ in combination with electrochemical methods, many questions regarding the molecular origins of these phenomena have remained unanswered.; This thesis describes four phases of investigation; (i) development of a molecular thermodynamic model; (ii) use of this model to design a new generation of redox active surfactants; (iii) synthesis of a new redox-active surfactant and measurement of its equilibrium and dynamics properties; (iv) refinement of the model based on experimental observations of the surface behavior of the new redox active surfactant.; This thesis has led to an understanding of the molecular-level contributions to the surface properties of Fc(CH₂)₁₁N+(CH ₃)₃ by using a combination of modeling and experiment. Moreover, the model has been used to propose a surfactant structure (HO(CH₂) ₁₁N+(CH₃)₃) for passive control of surface tension. This surfactant possesses properties that differ from classical ionic surfactants. For example, the surface tensions of aqueous solutions of this surfactant are less sensitive to changes in electrolyte concentration than is the case with classical ionic surfactants.; Our modeling also led to the design of a new redox active ferrocenyl surfactant (Fc(CH₂)₁₁SO₃−). This surfactant has properties that differ from redox active surfactants studied in the past. At high concentration, for example, changes in surface tension that are controlled by changes in the oxidation state of the molecule are independent of the concentration of the surfactant. Moreover, in the bulk solution, it is possible to affect a reversible transformation from micellar aggregates to vesicles by the redox transformation. This molecule permits the spontaneous formation of vesicles by using a single component surfactant system.