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Biomedical subjects

R Blossey

Publications and source records attributed to R Blossey.

18 recordsLinked to original sources
PubMed2006

Fluidics of a nanogap.

We have determined the filling properties of nanogaps with chemically heterogeneous walls. The quantitative criteria we present allow the prediction of the liquid loading of the nanostructure. They can easily be applied in combination with contact-angle measurements on planar substrates of the nanogap materials. We present an application of the theory to a recently developed nanogap biosensor. Chemical force microscopy (CFM) is employed to characterize the initial silanol properties of the gap. The functionality of the complex surface chemistry of the biosensor is demonstrated by the observation of functionalized nanoparticles in the gap with its resulting characteristic current-voltage relationship.

Humans↗
PubMed2006

Slip vs. viscoelasticity in dewetting thin films.

Ultrathin polymer films on non-wettable substrates display dynamic features which have been attributed to either viscoelastic or slip effects. Here we show that in the weak- and strong-slip regime, effects of viscoelastic relaxation are either absent or essentially indistinguishable from slip effects. Strong slip modifies the fastest unstable mode in a rupturing thin film, which questions the standard approach to reconstruct the effective interface potential from dewetting experiments.

Journal Article↗
PubMed2006

Regulating chromatin: on code and dynamic models.

In this short comment on the contributions by Arndt Benecke, Francois Fuks and Helmut Schiessel I refer to some recent experimental work which sheds light on the histone code hypothesis. Further, I make some remarks on the role theoretical approaches can play in decoding chromatin regulation.

Genetic Code↗
PubMed2005

A thin-film equation for viscoelastic liquids of Jeffreys type.

We derive a novel thin-film equation for linear viscoelastic media describable by generalized Maxwell or Jeffreys models. As a first application of this equation we discuss the shape of a liquid rim near a dewetting front. Although the dynamics of the liquid is equivalent to that of a phenomenological model recently proposed by Herminghaus et al. (S. Herminghaus, R. Seemann, K. Jacobs, Phys. Rev. Lett. 89, 056101 (2002)), the liquid rim profile in our model always shows oscillatory behaviour, contrary to that obtained in the former. This difference in behaviour is attributed to a different treatment of slip in both models.

Journal Article↗
PubMed2005

Chains, dimers, and sandwiches: melting behavior of DNA nanoassemblies.

We have studied, in experiment and theory, the melting behavior of DNA nanoassemblies of perylenediimide-bis-oligonucleotides (PON), in which two short oligonucleotide chains (16- or 24-mers) are attached to the extremities of a spacer molecule. By varying both the sequence orientation (exchange of 3' and 5' ends neighboring the spacer) and the oligomer composition of the solutions, nanoassemblies of different complexity can be generated. Our results show a subtle dependence of the melting behavior on the supramolecular arrangement of the DNA-based assemblies.

Computer Simulation↗
PubMed2004

Novel formulation of nonlocal electrostatics.

The accurate modeling of the dielectric properties of water is crucial for many applications in physics, computational chemistry, and molecular biology. This becomes possible in the framework of nonlocal electrostatics, for which we propose a novel formulation allowing for numerical solutions for the nontrivial molecular geometries arising in the applications mentioned before. Our approach is based on the introduction of a secondary field psi, which acts as the potential for the rotation free part of the dielectric displacement field D. For many relevant models, the dielectric function of the medium can be expressed as the Green's function of a local differential operator. In this case, the resulting coupled Poisson (-Boltzmann) equations for psi and the electrostatic potential phi reduce to a system of coupled partial differential equations. The approach is illustrated by its application to simple geometries.

Biopolymers↗
PubMed2004

Blobs, channels and "cigars": morphologies of liquids at a step.

We have studied the equilibria of liquid droplets wetting a step edge with an opening angle 0 < alpha < pi by a combination of analytical and numerical methods. Depending on the wetting properties of the substrate walls and on the liquid volume, different locally or globally stable liquid morphologies are found. Complete spreading of the liquid along the bottom edge of the step is observed at equilibrium contact angles theta satisfying theta < theta(s) = pi/2 - alpha/2. If the contact angle theta exceeds a threshold value theta(b) the liquid exists in a blob-like configuration. Surprisingly, we find an intermediate regime at a sufficiently high liquid volume and in a range of contact angles theta(s) < theta < theta(b), in which "cigar"-shaped configurations arise in addition to the blob. We close the paper by a detailed discussion of the stability of this novel liquid morphology.

Journal Article↗
PubMed2000

Heterogeneous hole nucleation in electron-charged 4He wetting films

4He wetting layers on Cs exhibit an unusually long-lived metastable state upon undercooling to temperatures well below the wetting temperature T(w) approximately 1.9 K. The decay of this state by homogeneous thermal nucleation of holes is disfavored by the incipient divergence of the free energy barrier separating the metastable thick film from the stable thin-film state. We propose that interface deformations ("dimples") created by electrons bound at the 4He liquid-vapor interface can be used as nuclei for the heterogeneous nucleation of holes. The size and excess free energy of the dimple can be tuned by an applied electric field E which allows the lifetime of the metastable film to be controlled.

Journal Article↗
PubMed2000

Dynamics of wetting layer formation

We study the formation and growth of wetting layers in the binary liquid mixture cyclohexane-methanol. By progressively deuterating the methanol we can tune the equilibrium wetting layer thickness. Hysteresis of the transition is observed for large thicknesses and is absent for thinner ones. This can be understood by calculating the activation energy for wetting layer nucleation as a function of the film thickness. We also show that the late-stage growth of the wetting layer after the nucleation process follows a power law in time, in agreement with a diffusion-limited growth mechanism proposed theoretically.

Journal Article↗
PubMed2000

Capillary-wave effects at critical wetting in type-I superconductors

We discuss the effect of fluctuations of the superconductor-normal (SC/N) interface on the (short-range) critical wetting transition in type-I superconductors. Functional renormalization of a standard effective interface Hamiltonian shows that the fluctuation regimes found for short-range critical wetting in conventional fluid systems appear in superconductors with slight modifications. Because the fluctuation parameter omega approximately 1/(1-sqrt[2]kappa) depends on the Ginzburg-Landau parameter kappa, strong fluctuation effects would be expected in the limit kappa-->1/sqrt[2]. However, the capillary-wave spectrum of the SC/N interface has an unusual form due to a relevant magnetic field contribution which suppresses long wavelength fluctuations, invalidating conclusions drawn from the standard effective interface Hamiltonian, and validating the results of mean-field theory.

Journal Article↗
PubMed1999

First-Order Wetting Transitions under Gravity.

We discuss the effect of a gravitational field on the first-order wetting transition of a liquid layer on a horizontal surface. Gravity limits the thickness of the wetting layer and leads to a smooth first-order transition line Deltaµw(T, g) in the wetting phase diagram of chemical potential difference from bulk coexistence, Deltaµ identical with µ - µc, temperature T, and gravitational acceleration g. Consequences for the interpretation of wetting experiments are pointed out. Copyright 1999 Academic Press.

Journal Article↗