Complex liquids are liquids that are structured at different length scales and thus have various internal degrees of freedom, e.g. dispersions, polymer melts or solutions, surfactant solutions, emulsions, foams, or other liquids that show a non-Newtonian behavior. Complex surfaces include solid or soft substrates showing ordered or random topological patterns, chemical heterogeneities, porosity with typical length scales in the micro- or nanometer range, or adaptable or switchable coatings. Also soluble or viscoelastic surfaces are of significance for various applications.
Why this research field is so important and attractive? Our understanding of how complex liquids spread over micro-structured or smart surfaces is still to be developed. Knowledge of complex wetting opens the gate to the field of micro-flows governed by capillary and intermolecular forces: the phenomena at the nano- and micro- scales near the contact region significantly influence the macro-flows. Modelling of complex wetting precedes technological advances in chemical, pharmaceutical, environmental and food industry and ensures the leadership of European companies in these wide areas. It is essential in many conventional and emerging technologies involving micro- and nanofluidics, functional printing and coating, regeneration medicine and the development of new methods of treating live threatening diseases, in which complex liquids and patterned substrates are used to manipulate the flow and deposition of material, to control, optimize and intensify novel technological processes.
Why this study is so challenging and difficult? The main issue is that spreading processes take place at molecular and sub-microscopic length scales, while most observations are macroscopic. This gap needs to be bridged and it forms one of the core aims of CoWet. Wetting and spreading are a result of the interplay between short ranged intermolecular forces both at equilibrium and dynamic wetting processes at the microscopic scale as well as hydrodynamic forces at the macroscopic scale. All this makes the study of static and dynamic wetting a multiscale problem that needs to be addressed from various perspectives.
The CoWet network will focus its activities on interfaces at which liquids interact with the surrounding media, solid, vapour, other liquids via corresponding interfaces. Such interfaces and the associated interfacial phenomena are ubiquitous in our daily lives and represent key technologies in many established and emerging fields. We recognize five fundamental factors influencing interactions at a liquid-solid, liquid-vapour and vapour-liquid interfaces which shape the research goals of the Consortium.
The goals of this network are: (i) to create an international, interdisciplinary and intersectorial training pool in the field of spreading of complex liquid over complex substrates; (ii) to improve the career prospects and employability of researchers involved and (iii) to develop innovative experimental and theoretical tools and computational methods to investigate such complex processes, which will be made available to the wider European community focusing on existing and potential industrial applications. The mobility and interdisciplinarity of a strong group of early-stage and experienced researchers will be fostered through a set of well-defined objectives and effective networking between different institutions and industries.
The major research goals of the CoWet network encompass the understanding, design, development, and application of complex liquids and complex surfaces, in particular in the natural and engineering sciences:
- Improve our understanding of influence of fundamental factors on spreading of complex fluids over complex substrates, and develop new models for describing these processes
- Generate creative approaches for control of the physico-chemical factors during the stages of production/manufacturing of new complex surfaces and/or liquids, as well as during operation of complex wetting processes in practice
- Develop overall control strategies that embody the factors, and lead to improved performance of complex wetting processes
- As an outlook we plan to formulate novel combinations of factors, which will have high potential for innovation in engineering applications, particularly for time-dependent complex wetting phenomena
Efficient and reliable methods to analyze equilibrium and dynamic contact angle phenomena at various time and length scales, and a theoretical understanding of the fundamental physico-chemical processes are key elements in most proposed work packages (WP) of the CoWet network, which is composed of a well-balanced European consortium of participants from all the relevant disciplines. Due to the importance of complex wetting/spreading in industrial processes, the industrial partners have played a significant role in defining the specific project goals that are the framework within which the theoretical and computer goals will be developed.