Wetting and evaporation of drops has become a central problem in many technological, biological and industrial processes. Over the last few decades, there has been an increasing interest in the topic of wetting and evaporation of drops. This is driven by the need to understand fundamental processes underlying applications such as ink-jet printing, spray cooling, food industries, biomedical and environmental processes and many others. The ever-increasing research into these fundamental processes has led to an exponential growth in studies investigating the evaporation of liquid drops. These have covered various aspects such as evaporation rates, wetting behaviour, contact line dynamics and internal flows. Some other aspects have remained untreated until very recently such as non-symmetrical drops, three-dimensional approaches instead of 2D, multiple drops instead of single ones, etc.
As far as textbooks and monographs on this important topic are concerned, very little has been published in comparison to the wealth of research publications in open literature. The need for textbooks on this subject is driven by the very large community of graduate students and early career researchers who are starting work on these problems and would benefit from a textbook written in a pedagogical fashion.
There has been, in recent decades, an important textbook on the topic of wetting of drops and capillary phenomenon.1 This was an outstanding contribution, which has been used by scientists and researchers around the world. The authors of the book however chose not to include the phase change aspect, i.e. evaporation and condensation. Another contribution came later to focus on drop evaporation. A more recent monograph2 focused on drop evaporation, and was a first attempt to cover this growing topic. This monograph, however, was limited to simple and pure systems.
The more progress researchers make on this topic the more they realise the need to adapt the approach to reflect real applications. Indeed, real applications tend to involve complex fluids, as opposed to pure fluids, and involve multiple drops. Complex fluids range from biological fluids to mixtures to suspensions or any fluid which is composed of other than a pure single component. Although the early approaches in the research on drop evaporation dealt with pure and simple fluids, which helped reveal the basic behaviour of these drops as they evaporate, there is a need to expand the research on complex fluid drops as more applications emerge. The technologies making use of the evaporation of complex fluids drops are growing and require a further understanding of these processes.
This monograph bridges a gap in the field of research that is increasingly important to many emerging technologies and applications. It aims to give an overview of some selected topics on the evaporation of complex fluid drops. It recalls some fundamental aspects of the evaporation of drops then presents a series of topics such as surfactant drops, ternary drops, nano-suspension drops, biomedical drops, etc. The broad range of complex fluid drops presented in this monograph highlights the need for more research on these systems.
We hope that through a combination of these selected topics, some important themes of importance to the evaporation of complex fluid drops are covered. The selected topics are by no means exhaustive, as a host of other fluids would fall under the definition of complex fluids. Nonetheless, it is a good start for graduate students and researchers who may be interested in this field.
We would like to extend our thanks to the contributing authors as well as to the Royal Society of Chemistry for making this possible.
K. Sefiane, University of Edinburgh, UK
D. Brutin, Aix-Marseille University, France