Preface

Wormlike micelles (WLMs)—also called thread-like or giant micelles—are elongated, flexible aggregates made by the spontaneous self-organization of amphiphilic molecules in solution. This particular morphology is dependent on the nature of the surfactant (mostly its geometry and hydrophilic–hydrophobic balance) and can be tuned by the association with other compounds as well as by controlling physico-chemical parameters, such as temperature, pH, or salinity. Similarly to polymer chains, WLMs entangle into a transient network above a threshold concentration, imparting remarkable viscoelastic or ‘gel-like’ properties. There is, however, a fundamental difference from polymer solutions because these structures are dynamic: WLMs continuously rupture and reassociate, with surfactant molecules constantly joining and leaving the ‘worms’. Their self-assembled nature thus gives WLMs the capacity to break and reform on a very short time-scale, but also to change their morphology (from worms to spheres or to vesicles), and thus their rheology, in response to environmental changes or composition. As a result, WLMs have been exploited in many industrial and technological fields, particularly in the oil industry.

This book covers a range of topics relating to WLMs, providing an authoritative guide to this vast area, with profuse references, both classic and recent. The emphasis of the book is on surfactant-based WLMs, but polymeric WLMs are also mentioned in several sections. For better clarity, the book is divided into three areas: the first focuses on systems, the second on characterization, and the third on applications. Each chapter has been written by academics and industrialists with extensive experience in their area, and provides a summary of research from the last decade to some of the latest developments and trends; each stands alone and can be read individually. To start with, the introductory Chapter 1 provides an overview of the field, equipping the reader with the basic tools and lexicon of WLMs, as well as making specific references to the chapters that follow.

The first part (Chapters 2–6) offers a molecular focus, and reports on building blocks that depart from the traditional WLM-forming surfactants originally reported (mostly cationic surfactants with electrolytes). Chapter 2 describes the unusual case of WLMs that exhibit gel-like properties (infinite relaxation time and zero-shear viscosity) and the common characteristics of the surfactants that make them. Chapter 3 discusses reverse WLMs and the use of pulsed field magnetic gradient (PFG)-NMR to explore their structure and dynamics. Chapter 4 reports on an assortment of unusual surfactants that have been reported to form WLMs, such as biological amphiphiles, or surfactants with original architectures. Chapter 5 explores the novel properties that are obtained by the association of WLMs with nanoparticles. Chapter 6 reviews and summarizes the booming area of ‘smart’ WLMs, which respond to a variety of stimuli.

Part 2 (Chapters 7–11) changes the emphasis from the chemistry to cutting-edge techniques that have led to advances in the understanding of WLM structure and dynamics. Chapter 7 highlights the key contributions made by direct imaging techniques in unravelling the structure, kinetics and dynamics of WLMs. Chapter 8 describes advances in rheo-SANS, the combination of rheology with small-angle neutron scattering techniques, which now enables a robust characterization of flow-induced structures in WLMs. Chapter 9 describes the use of microfluidic devices as a versatile platform to assess the effect of complex flow fields and spatial confinement on WLMs microstructure. Chapter 10 reviews recent findings in the emerging field of multiscale simulations applied to WLMs. Chapter 11 returns to a molecular view of WLMs, but gives a thermodynamic outlook from recent isothermal titration calorimetry measurements, as well as discussing recent findings in WLMs formation kinetics from time-resolved small-angle X-ray scattering.

Part 3 (Chapters 12–14) adopts a more engineering perspective and showcases commercial applications of WLMs. Chapter 12 reviews the main use of WLMs in oil and gas well stimulation and also discusses research into novel systems. Chapter 13 focuses on the drag-reduction capability of WLMs and their applications in the oil industry, as well as heating and cooling systems. Chapter 14 discusses recent efforts to measure and improve the predictability of process flows of WLMs in complex geometries relevant to industry.

We would like to acknowledge all the authors and co-authors who have invested a lot of time, attention, and enthusiasm into composing these original chapters and thus made this book possible. We would also like to thank the Royal Society of Chemistry team who has supported us at various stages of the process, in particular Cara Sutton, Lindsay McGregor, Catriona Clarke and Sylvia Pegg.

We hope that this book will prove to be both a useful reference and a stimulating read for academics, industrialists or simply the science-curious, and help inspire a new generation of research on WLMs.

Cécile A. Dreiss, London, UK

Yujun Feng, Chengdu, China