Final Report Summary - FREEFLUID (Channelfree liquid crystal microfluidics)
SCIENCE: The FREEFLUID supported research led to multiple research results that can be broadly encompassed into three main research themes: (i) fluidics of complex fluids, (ii) light-generated and affected complex fluids for flow generation, (iii) complex topological and hierarchical structures in nematic colloids. Below we present selected results that reflect the scientific core of FREEFLUID.
(i) Laser driven channelfree micropumping: We explored the generation of flow, as generated by external stimuli, including external electric fields and optical fields. The broken symmetry of the nematic field emerges as the central necessary condition to achieve net directional flows. In optical fields, the time-variable intensity and polarization structure are shown to drive complex flow patterns, and the off-central incidence of the beams is founds as possible route for generating net material flow.
(ii) Tuneable fnd shapable flows: We demonstrate the flow of a nematic liquid crystal in microfluidic channels with a rectangular cross section through experiments and numerical modeling. The flow profile and the liquid crystal orientational profile show three distinct regimes of weak, medium, and strong flow as the driving pressure is varied. These are identified by comparing polarizing optical microscopy experiments and numerical solutions of the nematofluidic equations of motion. The relative stability of the regimes is related to the de Gennes characteristic shear-flow lengths e1 and e2, together with the channelʼs aspect ratio. Also, we show that the liquid crystalline microfluidic flow can be fully steered from left to right of a simple micro-channel by applying transverse temperature gradients.
(iii) Dynamic modelling of light-controlled topological charge: By using full dynamic modelling we contribute to the demonstration of full control over the creation, manipulation and analysis of topological charges that are pinned to a microfibre in a nematic liquid crystal. Oppositely charged pairs are created through the Kibble–Zurek mechanism by applying a laser-induced local temperature quench in the presence of symmetry-breaking boundaries.
(iv)Topological structures in nematic colloidal fluids: Self-assembly and organization of various structures was demonstrated in systems of nematic liquid crystal colloids where the internal orientational order of the nematic fluid –especially the topological defects- was shown to play the central role. We have shown stablisation of 3D nematic colloidal crystals, Penrose tilings, templated blue phases and particle-field knots.
The work covered and acknowledged with FREEFLUID was published in 16 scientific papers, including 1x Nature Materials, 1x Nature Physics, 2x PNAS, 1x Nature Communications and 1x PRL, and was presented at >30 invited talks by the researcher (for complete list of results and bibliography please see http://miha.ravnik.si).
CAREER & INTEGRATION: The research was constantly complemented by successful integration activities of the researcher, who was in 2013 habilitated as (effectively, tenure-track) Assistant Professor at the Faculty of Mathematics and Physics at the University of Ljubljana. From October 2015, he has now a tenured permanent lecturer position. In October 2015, he was also awarded an additional affiliation with Jozef Stefan Institute (largest research institute in Slovenia). The researcher is now engaged in various teaching and managing activities, all clear evidences of integration. Furthermore, the researcher is now serving as advisor and group leader for several own PhD and undergraduate students; as of May 2016, 4 PhD students and 5 MSc students work under his supervision.
SOCIO-ECONOMIC IMPACT & OUTREACH: The general work on complex fluids encompassed within FREEFLUID supported the establishment of contacts of the researcher with the company Lek d.d. member of Sandoz. Various research project activities are now foregoing on theory and modelling of biopharmaceuticals aggregation. FREEFLUID was also regularly involved into various outreach activities, including presentations to high-school students, broadly available essay (seminar) works and mentoring topics of FREEFLUID to multiple MSc students (>20).