Single-molecule Distributions Research Articles

Distribution of single molecules in polymer thin films

Distribution of fluorescent dye molecules in polymer thin (∼100nm) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide distribution, varying in the number of fluorescent spots composed of one, two, three or group of molecules. The number of the molecules present in the fluorescent spots was also ascertained by fluorescence photobleaching experiments. Photocounts associated with maxima of the histograms were found to be independent of the concentrations; however, the number of occurrences associated with more than one molecule decreased with decreasing concentration. By reducing concentration as well as by mixing dye molecules into a polymer solution, fluorescent spots grouping more than one molecule were separated considerably into fluorescent spots including a single-molecule.

Single molecule lines and spectral hole burning of terrylene in different matrices

We observe fluorescence excitation lines of single terrylene molecules in three new polymer matrices (polyvinylbutyral, polymethylmethacrylate, and polystyrene) and in two crystals, n-hexadecane (polycrystalline Shpol’skii matrix) and anthracene single crystal. We also burn persistent spectral holes in bulk samples of these solutions for comparison to single molecule lines. In all matrices where hole burning is efficient enough, we find good agreement between the average width determined from the distribution of single molecules’ linewidths and the homogeneous width deduced from spectral holes, which demonstrates the consistency and complementarity of the two techniques.

Bead‐spring macromolecules: The kinetic contribution to the total stress

AbstractUsing complete phase space distributions, this analysis predicts an isotropic kinetic contribution to the total stress for both the solvent and polymer. The solvent's contribution depends on the polymer's intramolecular potential energy, as well as the intermolecular potential between the solvent and polymer. The analysis questions whether single molecule distributions are capable of investigating the possibility of anisotropic kinetic distributions. The analysis uses the peculiar velocity fields in lieu of modeling molecular collisions.