Study on the Interfacial Properties of Surfactants and Their Interactions with Dna

Bearing a hydrophilic part and a hydrophobic part, surfactants can adsorb onto interfaces and lower the tension (γ) of the interfaces, thereby enhancing the interfacial properties and leading to the applications of surfactants in cleaning, surface functionalization, foaming and emulsification. To understand how they work in these applications it is important to know the time-scales of the surfactant adsorption and desorption. This means that it is necessary to investigate the adsorption and desorption kinetics of surfactants, which have already been widely studied. However, traditional studies tend to make many assumptions, for example, extending the applicability of the equilibrium relations to the non-equilibrium cases. In this dissertation, using a bubble compression method, we first measured the equation of state γ(Γ), followed the time-dependent surface concentration Γ(t) and clarified the adsorption/desorption process without using many assumptions. Cationic surfactants are receiving much interest for biological applications. The DNA/cationic surfactant system is of use in DNA extraction, DNA purification and gene delivery. Although the interaction between cationic surfactant and anionic polyelectrolyte has been extensively studied, there still remains need to further understand the complex system, especially to rationalize the choice of surfactants to reach controllable DNA binding ability and low toxicity to the organism. In this dissertation, we introduced the systematic investigation on the micellization processes of two novel cationic surfactants (gemini surfactants and ionic liquid surfactant) and their interactions with DNA. Chapter 1 and Chapter 2 include a general introduction to surfactants, their micellization, interfacial properties, and interactions with DNA. One of the key themes is the complex interplay of surfactant molecules between the interface and the bulk. The adsorption and desorption kinetics of surfactants are included in the interfacial properties of surfactants, consisting the first important component of the thesis. The interaction between cationic surfactant and DNA will be discussed in detail, as it is the second essential part of this thesis. Chapter 3 describes the experimental and numerical methods utilized in this te l-0 08 52 18 6, v er si on 1 20 A ug 2 01 3