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This thesis investigates what is known as fluidity -- or more precisely the interfacial rheology -- of phospholipid bilayers and monolayers. Bilayers are of interest because they constitute the cell membrane and their fluidity is important in many biological processes for the physiology of the cell, e.g. cell homeostasis, cell signaling, and the formation of the metastatic cancer cells. Phospholipid monolayers have a relevance in itself, e.g. in lung surfactant functioning, and are used in this thesis as model material fora bilayer's leaflet. First, operating windows for interfacial rheometry are developed. They enable the measurement of these materials with clean kinematics. In a second step, the interfacial rheology of these monolayers is evaluated at conditions to be relevant in biological applications and to be comparable to phospholipid bilayers., In dieser Arbeit wird die Fluidität -- oder Grenzflächenrheologie -- von Phospholipid-Doppelschichten untersucht. Dieses Material ist von Interesse, weil es die Zellmembran bildet und seine Fluidität für viele biologische Prozesse wichtig ist, z.B. Zellhomöostase, Zellsignalisierung und die Bildung von metastatischen Krebszellen. Phospholipid-Mono-schichten werden als Modellmaterial für eine Seite der Doppelschicht verwendet. Zunächst werden Betriebsfenster entwickelt, die es ermöglichen, diese Materialien mit sauberer Kinematik zu messen. In einem zweiten Schritt wird die Grenzflächenrheologie dieser Monoschichten unter relevanten Bedingungen gemessen, um mit Phospholipid-Doppel-schichten zu vergleichen.

Colloidal particles equipped with platinum patches can establish chemical gradients in H O -enrichedsolutionsandundergoself-propulsionduetolocaldiffusiophoreticmigration.Inbulk 2 2 (3D), this class of active particles swim in the direction of the surface heterogeneities introduced by the patches and consequently reorient with the characteristic rotational diffusion time of the colloids. In this article, we present experimental and numerical evidence that planar 2D confinements defy this simple picture. Instead, the motion of active particles both on solid substrates and at flat liquid–liquid interfaces is captured by a 2D active Brownian motion model, in which rotational and translational motion are constrained in the xy-plane. This leads to an active motion that does not follow the direction of the surface heterogeneities and to timescales of reorientation that do not match the free rotational diffusion times. Furthermore, 2D-confinement at fluid–fluid interfaces gives rise to a unique distribution of swimming velocities: the patchy colloids uptake two main orientations leading to two particle populations with velocities that differ up to one order of magnitude. Our results shed new light on the behavior of active colloids in 2D, which is of interest for modeling and applications where confinements are present., New Journal of Physics, 19 (6), ISSN:1367-2630