We report novel molecular-to-macroscopic ordering mechanisms to direct growth, shape change, and induce spontaneous symmetry breaking that address fundamental questions in materials science, chemistry and physics. By coupling molecular phase transitions in liquid droplets[1], without any external applied fields, are able to generate a number of regular geometric shapes, including octahedra, hexagons, rhomboids, triangles and fibers. This rich behaviour is the result of an oil plastic crystal phase with a special curvature forming at the oil/water interface, which counteracts surface tension, but at the same time is modulated by the surface tension. The competition of forces of similar magnitudes gives rise to such rich shape behaviour even from a single phase transition. We have described over 60 systems of oils and surfactants exhibiting this shape change (including triglyceride oils), making this a general phenomenon with good thermodynamic underpinnings.[2] We explain this general behaviour, the transitions between these shapes, and methods to control them in both the liquid and solid state. We have since classified a number of functional classes of oils that can be shaped in this manner, and produced a theoretical model which explains the sequence of multiple symmetry shapes as a competition between the frustrated formation of a plastic crystal phase at the surface of the droplets opposed by increasing interfacial energy.[3] Most recently we have also discovered we can drive an emulsion system to smaller and smaller droplet sizes (and higher and higher energies) by harnessed thermal fluctuations in the environment.[4] Thus it is possible to grow scalable amounts of complex macroscopic particles, in a bottom-up fashion with controlled size and shape, which could lead to novel methods for sustainable manufacturing with high energy and material efficiency. They could enable applications not possible with current planar lithographic processing and its relatively low throughput and expensive infrastructure. I will outline a number of implications for further fundamental discoveries and for potential applied explorations we are pursuing in symmetry breaking, manufacturing and nanoscience.
Refs:
[1] Denkov N,Tcholakova S,Lesov I,Cholakova D,Smoukov SK*,Self-Shaping of Droplets via Formation of Intermediate Rotator Phases on Cooling, NATURE 528, 392–395 (2015)
[2] Cholakova D, Denkov N, Tcholakova S, Lesov I, Smoukov SK*,Control of drop shape transformations in cooled emulsions, Adv. Colloid & Interface Sci (2016)
[3] Haas PA, Goldstein RE*, Smoukov SK*, Cholakova D, Denkov N, A Theory of Shape-Shifting Droplets, PRL 118 088001 (2017)
[4] Tcholakova S, Valkova Zh, Cholakova D, Vinarov Z, Lesov I, Denkov N, Smoukov SK, Efficient self-emulsification via cooling-heating cycles, Nature Comm., accepted, (2017)
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BIO:
Stoyan Smoukov is the Head of the Active and Intelligent Materials group since 2012 in the Department of Materials Science and Metallurgy at the University of Cambridge. He has published more than 60 journal papers, cited over 1700 times, with H-index of 18, co-founded a startup company for producing nanofibers, and is leading the work on a number of European projects and industrial collaborations. His current research interests are focused on the fundamentals of confinement, multi-responsive materials, as well as geometry and processing technologies for achieving responsiveness. The longer term goal is to create autonomous material robotics, where the materials themselves are the robots.
