ABSTRACT
The interaction between a nanoprobe and a liquid surface is studied. The surface deformation depends on physical and geometric parameters, which are depicted by employing three dimensionless parameters: Bond number B_{o}, modified Hamaker number H_{a}, and dimensionless separation distance D. The evolution of the deformation is described by a strongly nonlinear partial differential equation, which is solved by means of numerical methods. The dynamic analysis of the liquid profile points out the existence of a critical distance D_{min}, below which the irreversible wetting process of the nanoprobe happens. For D ≥ D_{min}, the numerical results show the existence of two deformation profiles, one stable and another unstable from the energetic point of view. Different deformation length-scales, characterizing the stable liquid equilibrium interface, define the near- and the far-field deformation zones, where self-similar profiles are found. Finally, our results allow us to provide simple relationships between the parameters, which leads to determine the optimal conditions when performing atomic force microscope measurements over liquids.
Subject(s)
Membranes, Artificial , Models, Chemical , Models, Molecular , Nanostructures/chemistry , Nanostructures/ultrastructure , Computer Simulation , Elastic Modulus , Hardness , Molecular Probe Techniques , Molecular Probes , Surface PropertiesABSTRACT
Dielectric relaxation (DR) has shown to be a very useful technique to study dielectric materials like polymers and other glass formers, giving valuable information about the molecular dynamics of the system at different length and time scales. However, the standard DR techniques have a fundamental limitation: they have no spatial resolution. This is of course not a problem when homogeneous and non-structured systems are analyzed but it becomes an important limitation for studying the local properties of heterogeneous and/or nano-structured materials. To overcome this constrain we have developed a novel approach that allows quantitatively measuring the local dielectric permittivity of thin films at the nanoscale by means of Electrostatic Force Microscopy. The proposed experimental method is based on the detection of the local electric force gradient at different values of the tip-sample distance. The value of the dielectric permittivity is then calculated by fitting the experimental points using the Equivalent Charge Method. Even more interesting, we show how this approach can be extended in order to obtain quantitative dielectric images of insulating thin films with an excellent lateral resolution.
ABSTRACT
PSA films are obtained by coalescence of latices synthesized by free-radical emulsion polymerization of methyl methacrylate (MMA) and 2-ethylhexyl acrylate (EHA). For the same overall 50/50 molar composition, the polymer particles have well-defined structures when the feed composition and the feed mode (using batch or semicontinuous processes) are adjusted. The characterizations of the film structures by surface (tapping mode AFM) and bulk (DSC, rheology) analyses argue for the conservation of the initial particle structure when coalescence occurs. The influence of the chemical heterogeneity on the tack properties of the films is investigated to extend the study of these original acrylic PSA films up to relevant structure-property correlations.
