Fluorescence correlation spectroscopy in thin films at reflecting substrates as a means to study nanoscale structure and dynamics at soft-matter interfaces

Abstract

Structure and dynamics at soft-matter interfaces play an important role in nature and technical applications. Optical single-molecule investigations are noninvasive and capable to reveal heterogeneities at the nanoscale. In this work we develop an autocorrelation function (ACF) approach to retrieve tracer diffusion parameters obtained from fluorescence correlation spectroscopy (FCS) experiments in thin liquid films at reflecting substrates. This approach then is used to investigate structure and dynamics in 100-nm-thick 8CB liquid crystal films on silicon wafers with five different oxide thicknesses. We find a different extension of the structural reorientation of 8CB at the solid-liquid interface for thin and for thick oxide. For the thin oxides, the perylenediimide tracer diffusion dynamics in general agrees with the hydrodynamic modeling using no-slip boundary conditions with only a small deviation close to the substrate, while a considerably stronger decrease of the interfacial tracer diffusion is found for the thick oxides.

Macroscopic Domains within an Oriented TQ1 Film Visualized Using 2D Polarization Imaging

“…Theoretical considerations and a recent investigation of protein adsorption from a solution show an influence of long-range van der Waals interactions at the interfaces on the dynamics of liquids and solutes. Because of the importance of the geometrical shape of the molecules and electrostatic interactions for the self-arrangement of liquid-crystalline materials in a liquid-crystal phase, liquid-crystalline materials are, in particular, sensitive to long-range interactions of the material with interfaces in confined geometries. − The actual orientation of the liquid-crystal molecules at the interface is determined by the short-range interactions of the molecules with the interface. However, the extension of the interfacial alignment into the bulk liquid-crystal (the so-called anchoring strength) is influenced by the long-range interactions .…”

Nanoscale Chain Alignment and Morphology in All-Polymer Blends Visualized Using 2D Polarization Fluorescence Imaging: Correlation to Power Conversion Efficiencies in Solar Cells

“…The preparation by spincasting from polymer solution in chloroform does not provide sufficient time for the polymer chains to reach thermal equilibrium before the solvent has evaporated, resulting in unfavorable chain conformations . Moreover, TQ1 has thermotropic liquid-crystalline properties, and annealing it above its T g (≈ 100 °C), therefore, is likely to induce structural changes which due to long-range interactions with the substrate − and confinement in the thin film geometry lead to enhancement of the local order parameter in respect to the as-prepared films. The decrease of ε thus points to an increased parallelization of TQ1 chains, in accordance with the observed redshift in the spectra (Figure ) and the planarization of TQ1 chains suggested from X-ray investigations .…”

A Comprehensive Review of Fluorescence Correlation Spectroscopy

“…Being a powerful tool for detecting molecular concentration, hydrodynamic radius, diffusional dynamics, and the interaction of different biomolecules, FCS has been widely applied to different fields. Except for the applications in biology, FCS also has been applied in other fields [129][130][131]. For instance, FCS has been applied in physics for the study of dynamics/structure of liquid crystal molecules on silicon wafers [131], as well as anomalous diffusion inside soft colloidal suspensions [130].…”

“…Except for the applications in biology, FCS also has been applied in other fields [129][130][131]. For instance, FCS has been applied in physics for the study of dynamics/structure of liquid crystal molecules on silicon wafers [131], as well as anomalous diffusion inside soft colloidal suspensions [130]. We believe that, with further developments of lasers and sensors, FCS will become a more and more powerful tool for the study of molecular dynamics in different fields.…”