A low electrode-electrolyte impedance interface is critical in the design of electrodes for biomedical applications. To design low-impedance interfaces a complete understanding of the physical processes contributing to the impedance is required. In this work a model describing these physical processes is validated and extended to quantify the effect of organic coatings and incubation time. Electrochemical impedance spectroscopy has been used to electrically characterize the interface for various electrode materials: platinum, platinum black, and titanium nitride; and varying electrode sizes: 1 cm2, and 900 microm2. An equivalent circuit model comprising an interface capacitance, shunted by a charge transfer resistance, in series with the solution resistance has been fitted to the experimental results. Theoretical equations have been used to calculate the interface capacitance impedance and the solution resistance, yielding results that correspond well with the fitted parameter values, thereby confirming the validity of the equations. The effect of incubation time, and two organic cell-adhesion promoting coatings, poly-L-lysine and laminin, on the interface impedance has been quantified using the model. This demonstrates the benefits of using this model in developing better understanding of the physical processes occurring at the interface in more complex, biomedically relevant situations.

The microstructure of coagulated colloidal particles, for which the interparticle potential is described by the Derjaguin-Landau-Verweg-Overbeek theory, is strongly influenced by the particles' surface potential. Depending on its value, the resulting microstructures are either more "homogeneous" or more "heterogeneous," at equal volume fractions. An adequate quantification of a structure's degree of heterogeneity (DOH), however, does not yet exist. In this work, methods to quantify and thus classify the DOH of microstructures are investigated and compared. Three methods are evaluated using particle packings generated by Brownian dynamics simulations: (1) the pore size distribution, (2) the density-fluctuation method, and (3) the Voronoi volume distribution. Each method provides a scalar measure, either via a parameter in a fit function or an integral, which correlates with the heterogeneity of the microstructure and which thus allows to quantitatively capture the DOH of a granular material. An analysis of the differences in the density fluctuations between two structures additionally allows for a detailed determination of the length scale on which differences in heterogeneity are most pronounced.

The macroscopic mechanical properties of densely packed coagulated colloidal particle gels strongly depend on the local arrangement of the powder particles on length scales of a few particle diameters. Heterogeneous microstructures exhibit up to one order of magnitude higher elastic properties and yield strengths than their homogeneous counterparts. The microstructures of these gels are analyzed by the straight path method quantifying quasi-linear particle arrangements of particles. They show similar characteristics than force chains bearing the mechanical load in granular material. Applying this concept to gels revealed that heterogeneous colloidal microstructures show a significantly higher straight paths density and exhibit longer straight paths than their homogeneous counterparts.

Since the pioneering work of Turing on the formation principles of animal coat patterns [Turing AM (1952) Phil Trans R Soc Lond B 237(641):37-72], such as the stripes of a tiger, great effort has been made to understand and explain various phenomena of selfassembly and pattern formation. Prominent examples are the spontaneous demixing in emulsions, such as mixtures of water and oil [Herzig EM, et al. (2007) Nat Mater 6:966-971]; the distribution of matter in the universe [Kibble TWB (1976 A zobenzenes, which belong to photochromic materials, are switchable two-state systems with distinct optical, electronic, magnetic, and/or electrochemical properties that can be reversibly converted by irradiation. Since the discovery of the unique photochemical properties of azobenzene in 1937 (1), azobenzenes have been mainly used in the chemical industry. Only recently, after studies of the molecular physics of the photoisomerization of azo dyes have revealed that the photoisomerization reaction occurs on the timescale of a few picoseconds (2, 3), azobenzenes came back into focus as potential photoswitchable materials (4, 5). Azobenzenes have been investigated in terms of ultrafast spectroscopy (4, 6, 7), mechanoisomerization (8), the effect of slow photons (9), two-photon absorption (10) and laser-induced periodic surface structuring (11-17). The latter describes the phenomenon of Turing pattern formation on the surface of an azopolymer film upon exposure to UV or visible light. The outstanding feature of this photoactivated pattern formation is its dependence on both the light's intensity and polarization, which allows for the formation of a large variety of Turing patterns, such as hexagonal cells, parallel stripes, or turbulent structures. Several attempts have been made to understand the underlying physics that controls these various forms of pattern formation (18-23), but a sound picture is still lacking.In this paper, we demonstrate that the photoactivated pattern formation on azopolymer films can be entirely explained by the physical concept of phase separation of two coexistent immiscible phases in the polymer. A phase separation can be briefly characterized as follows: A (meta)stable configuration subjected to an external perturbation (temperature, light) becomes unstable. The unstable system tends to equilibrate by the formation of two immiscible phases. These two phases tend to separate leading to a spatial reorganization of the system.In the case of azopolymers, the instability is caused by the random optical excitation of the isomers in the polymer film. Excited by a photon of suitable energy (λ = 200-550 nm), the azobenzene isomer undergoes a structural transition by inversion or rotation (3), called photoisomerization, and relaxes either in the trans or cis ground state. The symmetry of the system is broken. The principle of the photoisomerization reaction for one azobenzene isomer is illustrated in Fig. 1A. The ground-state energy is characterized by an asymmetric double-well potential (Fig. 1A), containing...

During the growth of metal thin films on dielectric substrates at a given deposition temperature T d , the film's morphology is conditioned by the magnitude and asymmetry of up-and downhill diffusion. Any severe change of this mechanism leads to a growth instability, which induces an alteration of the thin film morphology. In order to study this mechanism, ultra-thin Pt films were deposited via pulsed laser deposition (PLD) onto yttria-stabilized-zirconia single crystals at different deposition temperatures. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and standard image analysis techniques. The experimentally obtained morphologies are compared to simulated thin film structures resulting from a two-dimensional kinetic Monte Carlo (KMC) approach. Two main observations have been made: i) thin Pt films deposited onto ZrO 2 undergo a growth transition from two-dimensional to three-dimensional growth at T d > 573 K. The growth transition and related morphological changes are a function of the deposition temperature. ii) A critical cluster size of i * = 4 in combination with an asymmetric Ehrlich-Schwoebel (ES) barrier favoring the uphill diffusion of atoms allows for a computational reproduction of the experimentally obtained film morphologies.PACS numbers: 68.55. 81.15.Fg, 87.10.Rt