Soft Matter Lab

Viridiana Carmosa Sosa visits the Soft Matter Lab. Welcome!

Viridiana Carmosa Sosa studied her bachelor and master degree in Physics in the National Autonomous University of Mexico. In those years, she was working with optical tweezers, structured laser beams, and cavitation bubbles. Nowadays, she is a PhD student at Sapienza University of Rome under the supervision of Roberto Di Leonardo, where she uses two-photon polymerization to fabricate microstructures that allow her to study the dynamics of active and non-active matter at the micron scale.

She will spend a week at the Soft Matter Lab to work together with Alessandro Magazzù on a joint project.

Francesco Patti visits the Soft Matter Lab. Welcome!

Francesco Patti is a PhD student in Physics at the University of Messina (started in October 2017). His master’s degree thesis was about “Theoretical study of the interaction between E.M. radiation and chiral nanomaterials” (July 2017) and now he is a visiting student at the Soft Matter Lab where he will work on modeling of optical forces in liquids and vacuum as well as modelling of passive and active stochastic systems“ (June-July 2018).

Frida Brogren, Kirill Danilov, Klas Holmgren, Oskar Leinonen, Benjamin Midtvedt & Arian Rohani defended their Bachelor Thesis. Congrats!

Frida Brogren, Kirill Danilov, Klas Holmgren, Oskar Leinonen, Benjamin Midtvedt & Arian Rohani defended their Bachelor Thesis at Chambers University of Technology on 25 May 2018.

Title: Experimentell studie av kritiska fenomen med optiska pincetter

Abstract: I samband med nanoteknologins framfart ses ett växande intresse för kolloida sy- stem för att överkomma många svårigheter med konstruktionen av nanostrukturer. På grund av kritikalitetens skalinvarianta egenskaper kan kolloider användas som analo- ger för nanopartiklar i studier av kritiska fenomen. Detta arbete ämnar att undersöka och utvidga förståelsen av kritiska fluktuationer och kritiska Casimirkrafter, som kan användas för att binda och styra kolloider. En optisk pincett byggdes för att undersö- ka kritisk motorisering och kolloida aggregationer, medan en färdigbyggd holografisk pincett användes för att mäta kritiska Casimirkrafter. De motoriserade kolloiderna uppvisade mer kaotisk rörelse för högre lasereffekter, och de kritiska Casimirkrafterna visades växa skarpt i närheten av den kritiska temperaturen.

Supervisors: Alessandro Magazzù & Giovanni Volpe, Department of Physics, University of Gothenburg
Examiner: Lena Falk, Department of Physics, University of Gothenburg
Opponent: Markus Fällman, Gabriella Grenander, Oskar Holmstedt, Viktor Olsson, Maria Söderberg & Wilhelm Tranheden
Place: FL62
Time: 25 May, 2018, 11:05-11:50

Markus Fällman, Gabriella Grenander, Oskar Holmstedt, Viktor Olsson, Maria Söderberg & Wilhelm Tranheden defended their Bachelor Thesis. Congrats!

Markus Fällman, Gabriella Grenander, Oskar Holmstedt, Viktor Olsson, Maria Söderberg & Wilhelm Tranheden defended their Bachelor Thesis at Chambers University of Technology on 25 May 2018.

Title: Sökstrategier i komplexa miljöer – Påverkan av kiralitet på aktiva agenters sökförmåga i komplexa miljöer

Abstract: I en framtid där autonoma agenter sannolikt kommer spela en betydande roll är utveck- lingen av enkla sökstrategier relevant. Ett specialfall av sådana är sökning utan återkopp- ling från miljön, något som kan vara viktigt för enkla agenter med begränsad datorkraft. Kiralitet är ett fenomen som i applikationer ofta ses som en olägenhet hos sådana agen- ter. Det är en asymmetri hos agenten som leder till att dess rörelse roterar åt ett visst håll. Detta beteende är vanligt inom robotik, men har även observerats inom kemi och biologi, till exempel hos olika mikroorganismer. Influensen av kiralitet på prestationen hos sökstrategier är i hög grad okänd. Studier saknas på huruvida kiralitet kan förbättra prestationen för agenter utan miljöåterkoppling och, om så är fallet, i vilken sorts miljöer som denna positiva effekt uppstår.
Genom datorsimuleringar och robotexperiment har vi funnit att kiralitet kan ha en positiv effekt på aktiva agenters sökförmåga i både regelbundna och stokastiska miljöer och med olika grad av stokastiskt brus som påverkar agenternas rörelse. Vi visar också att det finns en positiv relation mellan existensen av hörn i miljön och den relativa prestationen av kiral rörelse.
Våra resultat är relevanta för den som är intresserad av att manipulera eller förstå rörelsen hos kirala agenter i komplexa miljöer. Resultaten är också relevanta för vidare forskning riktad mot potentiella implementationer inom till exempel robotik och mikroteknik.

Supervisor: Giovanni Volpe, Department of Physics, University of Gothenburg
Examiner: Lena Falk, Department of Physics, University of Gothenburg
Opponent: Frida Brogren, Kirill Danilov, Klas Holmgren, Oskar Leinonen, Benjamin Midtvedt & Arian Rohani
Place: FL62
Time: 25 May, 2018, 10:15-11:00

Antonio A. R. Neves visits the Soft Matter Lab. Welcome!

Antonio Alvaro Ranha Neves is a Visiting Professor from the Federal University of ABC in Brazil. His visiting position is financed through a FAPESP-ERC grant. He will visit us for 4 months from May 12, 2018, to September 12, 2018.

He works mainly with optical tweezers studying optical forces with both experimental and theoretical tools.

He obtained his Ph.D. in physics in 2006, at the State University of Campinas (Brazil). From 2006 to 2012, he worked as a postdoctoral researcher at the National Nanotechnology Laboratories of the Nanoscience Institute in Lecce (Italy), within the Soft-matter division. Since 2012, he is a professor at the Federal University of ABC (Brazil), accredited in the graduate program of Nanoscience and Advanced Materials.

His main research interest is in the field of light-matter interaction, with a special focus on the applications of optical tweezers as well as linear and multi-photon spectroscopy as well. His current line of research is the study of bull sperm motility with optical tweezers, and starting the characterization of thermal properties of metallic nanoparticles in optical traps.

Seminar by G. Volpe at TU Dresden, 3 May 2018

Emergent Complex Behaviors in Active Matter
Giovanni Volpe
TU Dresden, Dresden, Germany
3 May 2018

After a brief introduction of active particles, I’ll present some recent advances on the study of active particles in complex and crowded environments.
First, I’ll show that active particles can work as microswimmers and microengines powered by critical fluctuations and controlled by light.
Then, I’ll discuss some examples of behavior of active particles in crowded environments: a few active particles alter the overall dynamics of a system; active particles create metastable clusters and channels; active matter leads to non-Boltzmann distributions and alternative non-equilibrium relations; and active colloidal molecules can be created and controlled by light.
Finally, I’ll present some examples of the behavior of active particles in complex environments: active particles often perform 2D active Brownian motion; active particles at liquid-liquid interfaces behave as active interstitials or as active atoms; and the environment alters the optimal search strategy for active particles in complex topologies.

Mite Mijalkov defended his PhD Thesis. Congrats!

Mite Mijalkov defended his PhD Thesis on 24 April 2018 in the Physics Department seminar room (SA240).

Assoc. Prof. Hande Toffoli (Middle-East Technical University), Prof. Tayfun Ozcelik (Bilkent University), Assoc. Prof. Alpan Bek (Middle-East Technical University), Assist. Prof. Seymur Cahangirov (Bilkent Unievrsity) and Assist. Prof. Giovanni Volpe (Bilkent University) will be the thesis committee members.

Thesis title: Graph Theory Study of Complex Networks in the Brain

Thesis abstract: The brain is a large-scale, intricate web of neurons, known as the connectome. By representing the brain as a network i.e. a set of nodes connected by edges, one can study its organization by using concepts from graph theory to evaluate various measures. We have developed BRAPH – BRain Analysis using graPHtheory, a MatLab, object-oriented freeware that facilitates the connectivity analysis of brain networks. BRAPH provides user-friendly interfaces that guide the user through the various steps of the connectivity analysis, such as, calculating adjacency matrices, evaluating global and local measures, performing group comparisons by non-parametric permutations and assessing the communities in a network. Furthermore, using graph theory, we showed that structural MRI undirected networks of stable MCI (sMCI) subjects, late MCI converters (lMCIc), early MCI converters (eMCIc), and AD patients show abnormal organization. This is indicated, at global level, by decreases in clustering and transitivity accompanied by increases in path length and modularity and, at nodal level, by changes in nodal clustering and closeness centrality in patient groups when compared to controls. In samples that do not exhibit differences in the undirected analysis, we propose the usage of directed networks to assess any topological changes due to a neurodegenerative disease. We demonstrate that such changes can be identified in Alzheimer’s and Parkinson’s patients by using directed networks built by delayed correlation coefficients. Finally, we put forward a method that improves the reconstruction of the brain connectome by utilizing the delays in the dynamic behavior of the neurons. We show that this delayed correlationmethod correctly identifies 70% to 80% of the real connections in simulated networks and performs well in the identification of their global and nodal properties.

Name of the PhD programme: Material Science and Nanotechnology Graduate Program
Thesis Advisor Giovanni Volpe, Department of Physics, Bilkent University

Place: Physics Department seminar room (SA240), Bilkent University
Time: 24 April, 2018, 11:00

Talk by A. Argun at IONS Scandinavia 2018, Copenhagen, 5-9 Jun 2018

Experimental realization of a minimal microscopic heat engine
Aykut Argun, Jalpa Soni, Lennart Dabelow, Stefano Bo, Giuseppe Pesce,
Ralf Eichborn & Giovanni Volpe
IONS Scandinavia 2018, Copenhagen, Denmark
5-9 June 2018

Abstract: Microscopic heat engines are microscale systems that convert energy flows between heat reservoirs into work or systematic motion. We have experimentally realized a minimal microscopic heat engine. It consists of a colloidal Brownian particle optically trapped in an elliptical potential well and simultaneously coupled to two heat baths at different temperatures acting along perpendicular directions. For a generic arrangement of the principal directions of the baths and the potential, the symmetry of the system is broken, such that the heat flow drives a systematic gyrating motion of the particle around the potential minimum. Using the experimentally measured trajectories, we quantify the gyrating motion of the particle, the resulting torque that it exerts on the potential, and the associated heat flow between the heat baths. We find excellent agreement between the experimental results and the theoretical predictions.

Reference: Argun et al. Experimental realization of a minimal microscopic heat engine. Physical Review E 96(5), 052106 (2017)

Invited talk by G. Volpe at the 9th Nordic Workshop on Statistical Physics, Stockholm, 21-23 Mar 2018

Recent Progress on the Experimental Study of Active Matter
Giovanni Volpe
The 9th Nordic Workshop on Statistical Physics: Biological, Complex and Non-equilibrium Systems, NORDITA, Stockholm, Sweden
21-23 March 2018

Seminar on photophoretic forces by Ayan Banerjee from IISER-Kolkata, Nexus, 20 Mar 2018

Photophoretic forces: A new enabler for robust single fiber-based optical traps in air
Seminar by Ayan Banerjee from the Indian Institute of Science Education and Research (IISER), Kolkata, India

Abstract: Photophoretic forces, which are derived from the momentum exchange of absorbing particles with surrounding fluid molecules, are especially useful for trapping particles in air, where their very large magnitude (about five orders more than optically induced dipole forces) successfully balances gravity. Thus, particles levitate in the direction of gravity, while in the transverse direction, they are trapped by a restoring force emanating from the rotation of the particles around the trapping beam axis. Photophoretic forces thus enable the use of single optical fibers for stable three dimensional traps. In this talk, I shall describe our efforts to develop such single fiber based traps, where we find that a single mode fiber is not necessarily the most efficacious in terms of trapping. Robust trapping is achieved when the off-axis intensity of the trapping beam is high, so that rather unexpectedly, we observe that a single multi-mode fiber allows much stronger trapping in general, and especially in the radial direction compared to a single mode finer. We are able to trap particles at extremely low laser powers (around 5 mW) in air, and can manipulate printer toner particles of diameter less than 20 microns at translation velocities of 5 mm/s in our multi-mode fiber trap. Particles can be manipulated by merely changing the power in the trapping beam, which accentuates the power and promise of this technique as a possible candidate for single fiber-based hand held tweezers for confining and even spectroscopically analysing aerosols or pathogens present in the air.

Bio: Ayan Banerjee has been working in the field of optics and spectroscopy for the last 22 years. He obtained his Ph.D in physics from the Indian Institute of Science, Bangalore, following which he was a research scientist at General Electric Global Research, Bangalore, India. Since 2009, he has been an associate professor of physics at the Indian Institute of Science Education and Research (IISER), Kolkata. His research interests span a wide range of subjects in optics and spectroscopy. At IISER, he has set up an optical tweezers lab to study diverse problems in a truly interdisciplinary mode of research.

Place: Nexus, meeting room, Fysik Origo, Fysik
Time: 20 March, 2018, 14:00