Biomedical subjects

G J Vancso

Publications and source records attributed to G J Vancso.

4 recordsLinked to original sources

PubMed2005

Fluorescence lifetime fluctuations of single molecules probe local density fluctuations in disordered media: a bulk approach.

We investigated the nanometer scale mobility of polymers in the glassy state by monitoring the dynamics of embedded single fluorophores. Recently we reported on fluorescence lifetime fluctuations which reflect the segmental rearrangement dynamics of the polymer in the surroundings of the single molecule probe. Here we focus on the nature of these fluorescence lifetime fluctuations. First the potential role of quenching and molecular conformational changes is discussed. Next we concentrate on the influence of the radiative density of states on the spontaneous emission of individual dye molecules embedded in a polymer. To this end we present a theory connecting the effective-medium theory to a cell-hole model, originating from the Simha-Somcynsky free-volume theory. The relation between the derived distributions of free volume and fluorescence lifetime allows one to determine the number of segments involved in the local rearrangement directly from experimental data. Results for two different polymers as a function of temperature are presented.

Journal Article↗

PubMed2003

Single molecule lifetime fluctuations reveal segmental dynamics in polymers.

We present a single molecule fluorescence study that allows one to probe the nanoscale segmental dynamics in amorphous polymer matrices. By recording single molecular lifetime trajectories of embedded fluorophores, peculiar excursions towards longer lifetimes are observed. The asymmetric response is shown to reflect variations in the photonic mode density as a result of the local density fluctuations of the surrounding polymer. We determine the number of polymer segments involved in a local segmental rearrangement volume around the probe. A common decrease of the number of segments with temperature is found for both investigated polymers, poly(styrene) and poly(isobutylmethacrylate). Our novel approach will prove powerful for the understanding of the nanoscale rearrangements in functional polymers.

Journal Article↗

PubMed2002

Surface energy characteristics of toner particles by automated inverse gas chromatography.

Inverse gas chromatography (IGC) was applied to the surface energy study of surfaces of toner particles. The dispersive component of the surface energy was determined for three toner materials by infinite dilution IGC. The values obtained were comparable to the values obtained from contact angle experiments. Previous adhesion experiments by atomic force microscopy suggested that the toner is a hydrophilic material with multiple adsorption energy sites. Both aspects were at least qualitatively confirmed by finite concentration IGC. Several indications for surface heterogeneity were found: (i) the difference between the dispersive component of the surface energy determined by IGC and the unexpectedly low total surface energy as determined by droplet analysis, (ii) the strong tailing behavior of the peaks of the injected polar probes, (iii) the decrease of the net retention volume with increasing n-pentane concentration, and finally (iv) the broad energy site distribution function with a dominant site at 28 kJ/mol, as determined by finite concentration IGC for n-pentane as molecular probe.

Adsorption↗

PubMed2001

Chemistry on surface-confined molecules: an approach to anchor isolated functional units to surfaces.

The synthesis of surface-confined, nanometer-sized dendrimers and Au nanoparticles was performed starting from single Pd(II) pincer adsorbate molecules (10) embedded as isolated species into 11-mercapto-1-undecanol and decanethiol self-assembled monolayers (SAMs) on gold. The coordination of monolayer-protected Au nanoclusters (MPCs) bearing phosphine moieties at the periphery (13), or dendritic wedges (8) having a phosphine group at the focal point, to SAMs containing individual Pd(II) pincer molecules was monitored by tapping mode atomic force microscopy (TM AFM). The individual Pd(II) pincer molecules embedded in the decanethiol SAM were visualized by their coordination to phosphine MPCs 13; isolated objects with a height of 3.5 +/- 0.7 nm were observed by TM AFM. Reaction of these embedded Pd(II) pincer molecules with the dendritic wedge 8 yielded individual molecules with a height of 4.3 +/- 0.2 nm.

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