Introductory Chapter: Surfactants – Bridging Fundamental Concepts with Emerging Perspectives

1. Introduction

Surfactants are amphiphilic molecules with hydrophilic head and hydrophobic tail groups (Figure 1). The amphiphilicity of these surfactant molecules drives their assembly into a wide range of structures including micelles, reverse micelles, liquid crystalline mesophases, and vesicles [1]. These surfactant assemblies have been exploited as templates for nanostructured-materials synthesis [2, 3]. Surfactants are applied in a wide range of applications including the formulation of detergents, medicines, vaccines, paints, cosmetics, oil spill dispersants, enhanced oil recovery agents, and agrochemicals products. This book provides an overview of the fundamentals, emerging perspectives, and applications of surfactants.

Figure 1.

Surfactant self-assembly and microstructures.

Typical considerations in the study and application of surfactant systems are built on their fundamental assembly and physicochemical properties (Figure 2). For effectiveness in technological applications, surfactant is typically applied as mixed systems including mixtures of multiple surfactants, particles, and polymers [1, 4, 5, 6, 7, 8, 9]. The novelty of research efforts on surfactant can include synergism with nanomaterials, process scalability and environmental impacts (Figure 2).

Figure 2.

General considerations in the study and application of surfactant systems.

The first two chapters of this book present a fundamental review of surfactant systems. These introductory chapters should be an excellent introduction to the fundamental phenomena of surfactants. Chapter 1 covers a broad scope of the structure and application of surfactants. However, concerns about the potential impacts of surfactant in our everyday lives has stimulated recent research efforts in the development and application of environmentally benign surfactant systems [10, 11, 12, 13, 14]. Thus, Chapter 2 provides a more-tailored perspective on the development and application of eco-benign surfactants.

Chapter 3 presents an interesting topic of combining surfactants with clay minerals. The combination of surfactant and clay minerals such as halloysite clay nanotubes has attracted significant attention in environmental remediation applications [15, 16]. The unique hollow geometry of the interfacially adherent particles allows for surfactant encapsulation and delivery to the oil-water interface. Surfactant release lowers the interfacial tension and facilitates oil dispersion [15]. In general, the synergistic combination of surfactant and clay minerals in organoclays can provide significant benefits in several practical applications beyond oil spill remediation. The characteristics of the organoclays formed from the clay-surfactant interactions are determined by the individual characteristics of the surfactant and clay mineral as well as the method of preparation. Thus, the chapter starts with a fundamental discussion on surfactants including their classification, physicochemical, and interfacial adsorption characteristics. This is followed by a section focused on clay minerals. The classification of clay minerals, chemical structure, and fundamental properties such as swelling capacity, cation exchange capacity, surface area, and charge are presented. The interaction of surfactant and clay minerals is then discussed with critical details on the preparation methods and prevailing physicochemical mechanisms. The chapter also provides insights into the structure of the resulting surfactant-modified clay minerals (organoclays) and their practical applications.

The use of Ionic Liquid-Based Surfactants in Chemical Enhanced Oil Recovery (CEOR) is presented in Chapter 4. Surfactants play a critical role in reducing the Interfacial tension (IFT) [15] and altering surface wettability [17]. However, the tunability and stability of ionic liquids in harsh environmental conditions make them attractive for CEOR [18, 19]. The fundamental characteristics of ionic-liquid-based surfactants and their relevance to Chemical Enhanced Oil Recovery (CEOR) mechanisms are first discussed in the chapter. The discussion includes the critical physical properties and chemical structure of Ionic Liquid-based surfactants. The chapter briefly introduces the various enhanced oil recovery methods including gas injection, thermal methods, chemical methods, and new emerging methods in the field. The next section in the chapter then provides a deep dive into the chemical methods spanning surfactant flooding, micellar flooding, and alteration of reservoir rock wettability from oil-wet to water-wet. The efficacy of surfactant systems in CEOR is strongly dependent on IFT reduction. The last section discusses the effectiveness of Ionic Liquid-Based Surfactants relative to conventional surfactants in CEOR. These are key considerations that are relevant in surfactant screening for CEOR applications [20].

Surfactants have found application in microheterogeneous catalysis with superior properties for catalytic reactions and process tunability relative to homogeneous reactions [21, 22]. This is especially relevant in reactions where all the reactants cannot be solubilized in a single solvent [21]. These reaction systems are complex with the presence of reactants; multiple to effectively understand the surfactant mechanisms in complex microheterogenous catalysis applications, combining experimental and modeling techniques is beneficial [23, 24]. The last chapter in this book provides a unique perspective on the models that have been developed to explain the surfactant effects on reaction rates. Overall, this book bridges the fundamental concepts and emerging applications of surfactant systems.