Towards local tracking of solvated metal ions at solid-liquid interfaces

The dynamics of individual solvated ions near solid surfaces is the driving force behind numerous interfacial processes, from electrochemical reactions to charge storage, mineral growth, biosignalling and bioenergetics. The precise system behaviour is delicately dependent on the atomistic and molecular details of the interface and remains difficult to capture with generalisable, analytical models. Reported dynamics can vary by orders of magnitude depending on microscopic details of the solvent, ions and/or surface chemistry. Experimentally, tracking single solvated ions as they move at or along interfaces remains highly challenging. This is, to some extent, offset by simulations that can provide precise atomistic insights, but usually over limited timescales. The aim of this review is to provide an overview of this highly interdisciplinary field, its achievements and remaining challenges, reviewing both experimental and computational results. Starting from the well accepted continuum description of dissolved ions at solid-liquid interfaces, we outline the challenges of deriving local information, illustrating the discussion with a range of selected studies. We explore the challenges associated with simultaneously achieving the spatial and temporal resolution needed to gain meaningful, yet contextual insights of single ions’ dynamics. Based on the current studies, we anticipate the future developments in the field, outlining remaining challenges and opportunities

Non-equilibrium dynamics of actively-driven viscoelastic networks

To maintain internal organization, living systems need to dissipate energy at the molecular level, thus operating far from thermodynamic equilibrium. At the larger scales, non-equilibrium behavior can be manifest through circulation in the phase space of mesoscopic coordinates and various techniques and measures have been developed to detect and quantify this circulation. It is however still not clear what these measures teach us about the physical properties of the system and how they can be employed to make useful predictions. In the following thesis, we will first review recent progress in detecting and quantifying mesoscopic currents in soft living systems; we will then employ minimal models of actively driven viscoelastic networks to understand how the non-equilibrium dynamics are affected by the internal mechanical structure. Finally, we will introduce a method of assessing non-equilibrium fluctuations in a tracking-free fashion via time-lapse microscopy imaging.Um ihre innere Organisation aufrechtzuerhalten, müssen lebende Systeme Energie auf molekularer Ebene dissipieren. Somit arbeiten sie weit entfernt vom thermodynamischen Gleichgewicht. Auf größeren Skalen kann sich Nichtgleichgewichtsverhalten in zirkulärer Bewegung im Phasenraum der mesoskopischen Koordinaten niederschlagen. Um diese Zirkulation zu erkennen und zu quantifizieren, wurden verschiedene Techniken und Methoden entwickelt. Es ist jedoch immer noch nicht klar, was diese Methoden über die physikalischen Eigenschaften des Systems aussagen und wie sie für nützliche Vorhersagen eingesetzt werden können. In dieser Arbeit werden wir zunächst die jüngsten Fortschritte bei der Erkennung und Quantifizierung mesoskopischer Ströme in Systemen aus weicher lebendender Materie untersuchen. Anschließend werden wir minimale Modelle aktiv getriebener viskoelastischer Netzwerke verwenden, um zu verstehen, wie die Nichtgleichgewichtsdynamik durch deren interne mechanische Struktur beeinflusst wird. Schließlich werden wir eine Methode zur Messung von Nichtgleichgewichtsfluktuationen aus Zeitraffermikroskopieaufnahmen, ohne tracking auskommt, einführen

Non-equilibrium dynamics of actively-driven viscoelastic networks

To maintain internal organization, living systems need to dissipate energy at the molecular level, thus operating far from thermodynamic equilibrium. At the larger scales, non-equilibrium behavior can be manifest through circulation in the phase space of mesoscopic coordinates and various techniques and measures have been developed to detect and quantify this circulation. It is however still not clear what these measures teach us about the physical properties of the system and how they can be employed to make useful predictions. In the following thesis, we will first review recent progress in detecting and quantifying mesoscopic currents in soft living systems; we will then employ minimal models of actively driven viscoelastic networks to understand how the non-equilibrium dynamics are affected by the internal mechanical structure. Finally, we will introduce a method of assessing non-equilibrium fluctuations in a tracking-free fashion via time-lapse microscopy imaging.Um ihre innere Organisation aufrechtzuerhalten, müssen lebende Systeme Energie auf molekularer Ebene dissipieren. Somit arbeiten sie weit entfernt vom thermodynamischen Gleichgewicht. Auf größeren Skalen kann sich Nichtgleichgewichtsverhalten in zirkulärer Bewegung im Phasenraum der mesoskopischen Koordinaten niederschlagen. Um diese Zirkulation zu erkennen und zu quantifizieren, wurden verschiedene Techniken und Methoden entwickelt. Es ist jedoch immer noch nicht klar, was diese Methoden über die physikalischen Eigenschaften des Systems aussagen und wie sie für nützliche Vorhersagen eingesetzt werden können. In dieser Arbeit werden wir zunächst die jüngsten Fortschritte bei der Erkennung und Quantifizierung mesoskopischer Ströme in Systemen aus weicher lebendender Materie untersuchen. Anschließend werden wir minimale Modelle aktiv getriebener viskoelastischer Netzwerke verwenden, um zu verstehen, wie die Nichtgleichgewichtsdynamik durch deren interne mechanische Struktur beeinflusst wird. Schließlich werden wir eine Methode zur Messung von Nichtgleichgewichtsfluktuationen aus Zeitraffermikroskopieaufnahmen, ohne tracking auskommt, einführen

Droplet motion on miniaturized ratchets

The main objective of this study is to evaluate the feasibility of using miniaturized asymmetric structures to move liquid droplets and understand the driving mechanism. We developed the fabrication process for large area topological ratchets with the period ranging from millimeter down to sub-micrometer using micromachining techniques. Non-wetting superhydrophobic surfaces were successfully fabricated using soft UV or thermal nanoimprint lithography, reactive ion etching by oxygen plasma, and chemical surface modification by fluorinated silane vapor deposition. An accurate and reproducible experimental setup equipped with high speed camera and automatic injection system was established. Image processing tools allowed us to obtain various critical information related droplet motion and behavior along the ratchets surface. Various influences on the motion such as the surface temperature, ratchets dimension, surface wettability, droplet volume, kind of liquid, initial impact speed of droplet, polymer additive, and surface slope were systematically investigated for miniaturized non-wetting asymmetric ratchets. It is observed that the droplet motion on the ratchets is strongly dependent on the ratchets dimensions as well as the surface temperature. Extremely fast water droplet motion was achieved from the sub-micrometer ratchets near the Leidenfrost temperature. Even though the Leidenfrost-miniaturized ratchets system can be considered as an efficient pumping and cooling component, further intensive study to reduce the operating temperature and drive the liquid motion within microchannel is required for the broad range of applications

Flowing matter

This open access book, published in the Soft and Biological Matter series, presents an introduction to selected research topics in the broad field of flowing matter, including the dynamics of fluids with a complex internal structure -from nematic fluids to soft glasses- as well as active matter and turbulent phenomena.Flowing matter is a subject at the crossroads between physics, mathematics, chemistry, engineering, biology and earth sciences, and relies on a multidisciplinary approach to describe the emergence of the macroscopic behaviours in a system from the coordinated dynamics of its microscopic constituents.Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. Phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strongly enough. This volume presents several research topics that address these phenomena encompassing the traditional micro-, meso-, and macro-scales descriptions, and contributes to our understanding of the fundamentals of flowing matter.This book is the legacy of the COST Action MP1305 “Flowing Matter”

Dynamics and statics of polymer nanocomposite self-assembly via molecular dynamics

DNA linker mediated self-assembly of nanoparticles- grafting complementary sequences of single stranded DNA to nanoparticles to program their self-assembly, is a flexible strategy for designing novel polymer nanocomposites. In this dissertation, a scale-accurate coarse grained model of nanoparticles grafted with DNA is developed. Using Molecular Dynamics simulations, the dynamics of self-assembly and equilibrium phases are investigated for systems where nanoparticles are spherical or anisotropic

Mathematics of microrheology with applications to pulmonary liquids

This thesis results from the Virtual Lung Project at the University of North Carolina at Chapel Hill, whose target is to understand the mechanism of this disease and provide guidance for effective therapeutic strategies. Instead of taking the problem as a whole, the focus here is to develop new methods to characterize rheological properties of low volume biological samples, such as mucus, sputum and their simulants, as well as to work out fluid dynamical behaviors that are associated with experiments using micro-scale beads in biological materials. Classical rheological experiments (creep, relaxation and dynamical) are mostly designed for the averaging steady state properties of milliliter size samples. The difficulties lie in the fact that these biological samples are low-volume (on the order of microliters), highly heterogeneous, sensitive to the surrounding environment and subject to change over time, even during the same course of a constant stress load. The term thixotropy is then used to describe the property of time-dependent change in viscosity. Therefore, in this very first problem, we follow Baravian et al. to exploit inertia in the creep device, which is always present until transients pass, to gain rheological information beyond the typical creep data analysis. A MATLAB graphical user interface (GUI) is developed to allow users to fit different mechanical models to the data by least square fits. In our studies of biological samples, we show that the time average is a poor reflection of data, instead, allowing time-dependence in the material parameters during a constant loading is the correct methodology of studying thixotrophy. We also address the difference of using rheometers of different length scales: cone-and-plate on milliliters and parallel-plate on microliters and associate this difference with the size of macromolecular structures of the materials. As a proof, we show that the CP and PP yield similar rheological properties (same order of magnitudes) for hyaluronic acid but quite different ones (at least one order difference in the magnitudes) for agarose gels. For our second problem, our goal is to develop new methods for characterizing viscoelastic properties of biological liquids by the driven bead experiments done by our collaborators at UNC Physics department. The standard method relies on a force balance argument with an ad hoc geometry factor and fitting with 1D mechanical models. Instead of following this method, we solve the 3D unsteady Stokes equations with specified driving force. These results extend classical solutions of the Stokes equations, called Stokes singularities, from a viscous to a linear viscoelastic medium. With the viscoelastic version of Stokes singularities, we are able to give exact solutions for points, spherical and planar forces, as illustrated in Chapter 3. The difference between a point and a spherical source is also addressed in this chapter

Magnetic Hybrid-Materials

Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials