| 1. |
- Aristov, Maria, et al.
(författare)
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Separation of chiral colloidal particles in a helical flow field
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 9:8, s. 2525-2530
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Tidskriftsartikel (refereegranskat)abstract
- Stereoisomeric molecules with opposite chirality, so-called enantiomers, often vary regarding their sensory, pharmacological and toxicological properties. Such enantiomer specific effects play a central role in the development, testing and evaluation of drugs, pesticides and food related products. Accordingly, efficient techniques for separation of chiral mixtures into enantiopure compounds are of enormous practical relevance. Most current enantiomer separation methods are based on enantioselective interactions with an auxiliary substance which has to be developed and optimized for different chiral molecules in an elaborate and costly process. Here, we experimentally demonstrate the separation of micron-sized chiral particles in a helical fluid flow which is created inside a microfluidic device patterned with slanted grooves. We observe that the retention time of particles in a helical flow field strongly depends on their chirality which leads to an effective chiral separation within the channel. Our experimental results are confirmed by numerical calculations which demonstrate how the coupling of rotational and translational degrees of freedom leads to differences in the trajectories of particles with opposite chirality. Since our separation mechanism does not rely on material specific interactions, this offers considerable advantages over existing methods. We expect that our approach can be also applied at nanometre length scales by using channels with smaller diameters and with an optimized geometry.
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| 2. |
- Bechinger, Clemens, et al.
(författare)
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Active particles in complex and crowded environments
- 2016
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Ingår i: Reviews of Modern Physics. - 0034-6861. ; 88
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Forskningsöversikt (refereegranskat)abstract
- Differently from passive Brownian particles, active particles, also known as self-propelled Brownian particles or microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. Because of this constant flow of energy, their behavior can be explained and understood only within the framework of nonequilibrium physics. In the biological realm, many cells perform directed motion, for example, as a way to browse for nutrients or to avoid toxins. Inspired by these motile microorganisms, researchers have been developing artificial particles that feature similar swimming behaviors based on different mechanisms. These man-made micromachines and nanomachines hold a great potential as autonomous agents for health care, sustainability, and security applications. With a focus on the basic physical features of the interactions of self-propelled Brownian particles with a crowded and complex environment, this comprehensive review will provide a guided tour through its basic principles, the development of artificial self-propelling microparticles and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.
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| 3. |
- Helden, Laurent, et al.
(författare)
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Direct measurement of thermophoretic forces
- 2015
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 11:12, s. 2379-2386
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Tidskriftsartikel (refereegranskat)abstract
- We study the thermophoretic motion of a micron sized single colloidal particle in front of a flat wall by evanescent light scattering. To quantify thermophoretic effects we analyse the nonequilibrium steady state (NESS) of the particle in a constant temperature gradient perpendicular to the confining walls. We propose to determine thermophoretic forces from a "generalized potential" associated with the probability distribution of the particle position in the NESS. Experimentally we demonstrate, how this spatial probability distribution is measured and how thermophoretic forces can be extracted with 10 fN resolution. By varying temperature gradient and ambient temperature, the temperature dependence of Soret coefficient ST(T) is determined for r = 2.5 mm polystyrene and r = 1.35 mm melamine particles. The functional form of ST(T) is in good agreement with findings for smaller colloids. In addition, we measure and discuss hydrodynamic effects in the confined geometry. The theoretical and experimental technique proposed here extends thermophoresis measurements to so far inaccessible particle sizes and particle solvent combinations.
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| 4. |
- Kümmel, Felix, et al.
(författare)
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Circular Motion of Asymmetric Self-Propelling Particles
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:19, s. 198302-
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Tidskriftsartikel (refereegranskat)abstract
- Micron-sized self-propelled (active) particles can be considered as model systems for characterizing more complex biological organisms like swimming bacteria or motile cells. We produce asymmetric microswimmers by soft lithography and study their circular motion on a substrate and near channel boundaries. Our experimental observations are in full agreement with a theory of Brownian dynamics for asymmetric self-propelled particles, which couples their translational and orientational motion.
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| 5. |
- Volpe, Giorgio, et al.
(författare)
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Active matter in space
- 2022
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Ingår i: npj Microgravity. - : Springer Science and Business Media LLC. - 2373-8065. ; 8:1
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Recension (övrigt vetenskapligt/konstnärligt)abstract
- In the last 20 years, active matter has been a highly dynamic field of research, bridging fundamental aspects of non-equilibrium thermodynamics with applications to biology, robotics, and nano-medicine. Active matter systems are composed of units that can harvest and harness energy and information from their environment to generate complex collective behaviours and forms of self-organisation. On Earth, gravity-driven phenomena (such as sedimentation and convection) often dominate or conceal the emergence of these dynamics, especially for soft active matter systems where typical interactions are of the order of the thermal energy. In this review, we explore the ongoing and future efforts to study active matter in space, where low-gravity and microgravity conditions can lift some of these limitations. We envision that these studies will help unify our understanding of active matter systems and, more generally, of far-from-equilibrium physics both on Earth and in space. Furthermore, they will also provide guidance on how to use, process and manufacture active materials for space exploration and colonisation.
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