Spreading Dynamics of Polymer Nanodroplets

The spreading of polymer droplets is studied using molecular dynamics simulations. To study the dynamics of both the precursor foot and the bulk droplet, large drops of ~200,000 monomers are simulated using a bead-spring model for polymers of chain length 10, 20, and 40 monomers per chain. We compare spreading on flat and atomistic surfaces, chain length effects, and different applications of the Langevin and dissipative particle dynamics thermostats. We find diffusive behavior for the precursor foot and good agreement with the molecular kinetic model of droplet spreading using both flat and atomistic surfaces. Despite the large system size and long simulation time relative to previous simulations, we find no evidence of hydrodynamic behavior in the spreading droplet.Comment: Physical Review E 11 pages 10 figure

Experimental investigation of the link between static and dynamic wetting by forced wetting of nylon filament

Forced wetting experiments with various liquids were conducted to study the dynamic wetting properties of nylon filament. The molecular-kinetic theory of wetting (MKT) was used to interpret the dynamic contact angle data and evaluate the contact-line friction ζ0 at the microscopic scale. By taking account of the viscosity of the liquid, ζ0 could be related exponentially to the reversible work of adhesion. This clearly establishes an experimental link between the static and dynamic wetting properties of the material. Moreover, statistical analysis of the equilibrium molecular displacement frequency K⁰ and the length of the displacements λ reveals that these two fundamental parameters of the MKT are strongly correlated, not only in the linearized form of the theory (valid close to equilibrium) but also when the nonlinear form of the equations has to be considered at higher wetting speeds.status: publishe

Biochemical interaction analysis on ATR devices: a wet chemistry approach for surface functionalization.

A new generic device suitable for the investigation of ligand-receptor interactions is presented. In particular, the research focused on optical waveguides constituted by an attenuated total internal reflection (ATR) element, transparent in the infrared and whose surfaces were activated in view of covalently binding a receptor. Silicon and germanium ATR elements were considered. The original method is based on the grafting of bifunctional spacer molecules directly at the surface of the germanium crystal, avoiding the deposition of an intermediate metal layer. The grafting of these binding molecules (under their N-hydroxysuccinimidyl ester forms) was performed either by wet chemistry or by photochemistry. The functionalized surfaces, which allow the binding of molecules bearing peripherical NH2 groups, were successfully used, e.g. for the detection of proteins (streptavidin) or of small molecules (biotin). In the latter case, the biotin was readily detected for concentrations as low as 10(-12) M.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Superhydrophobic surfaces from various polypropylenes

Superhydrophobic surfaces were prepared from solutions of isotactic polypropylenes of various molecular weights using soft chemistry. Varying the conditions of the experiments (polymer concentration and initial amount of the coated solution) allowed us to optimize the superhydrophobic behavior of the polymer film. Results show that decreasing the concentration and/or film thicknesses decreases the probability to get superhydrophobicity for all polypropylenes tested. Measurement and analysis of advancing and receding contact angles as well as estimation of surface homogeneity were performed. Similar results were obtained with syndio- as well as atactic polypropylenes.status: publishe