Complex Tracer Diffusion Dynamics in Polymer Solutions (original) (raw)
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The diffusion of macromolecules in cells and in complex fluids is often found to deviate from simple Fickian diffusion. One explanation offered for this behavior is that molecular crowding renders diffusion anomalous, where the mean-squared displacement of the particles scales as 〈r(2)〉 ∝ t(α) with α < 1. Unfortunately, methods such as fluorescence correlation spectroscopy (FCS) or fluorescence recovery after photobleaching (FRAP) probe diffusion only over a narrow range of lengthscales and cannot directly test the dependence of the mean-squared displacement (MSD) on time. Here we show that variable-lengthscale FCS (VLS-FCS), where the volume of observation is varied over several orders of magnitude, combined with a numerical inversion procedure of the correlation data, allows retrieving the MSD for up to five decades in time, bridging the gap between diffusion experiments performed at different lengthscales. In addition, we show that VLS-FCS provides a way to assess whether the ...
Fluorescence Correlation Spectroscopy Study of Molecular Probe Diffusion in Polymer Melts
Fluorescence correlation spectroscopy (FCS) was employed to study the diffusion of molecular tracers in different polymer melts (polydimethysiloxane (PDMS), 1,4-cis-polyisoprene (PI), poly-(vinylethylene) (PVE), and a symmetric PI/PVE blend) as a function of molecular weight (M w ) and temperature (T). The single molecule sensitivity of the FCS technique precludes any modification of the matrix polymer properties. In all studied systems, the small tracer diffusion coefficient D(M w ,T) senses local segmental dynamics depending on the glass transition temperature T g (M w ) of the polymer matrix and not its macroscopic viscosity. From the good representation of the D(T) data by the common non-Arrhenius (VFT) function, we found that the activation energy (B D ) increases with tracer size (R) and for a given tracer the value of B D in PI is almost 2 times bigger than in PDMS. The possibility to establish a direct relation between D(T) and the segmental relaxation time τ(T) of the polymer matrix was critically addressed based on experimental data in dynamically homogeneous (homopolymers) and heterogeneous (miscible blend) systems and discussed in view of recent computer simulations of polymer/penetrant mixtures.
Matrix effects on the diffusion of long polymer chains
Macromolecules, 1986
Macromolecules purification. All NMR spectra were obtained on a Varian XL-400 spectrometer operating a t 399.93 MHz for 'H and 100.56 MHz for 13C a t a probe temperature of 18 & 1 "C. Unless otherwise indicated, spectra were obtained for 0.4 M solutions of hydrocarbon in the appropriate solvent. Heteronuclear shift-correlated spectra were obtained with a version of this experiment that provides 'H-'H decoupling.21 Typical spectra were obtained with a 240-Hz spectral width in the fl ('H) domain and 2000-Hz spectral width for fz (13C). Forty time increments were used with zero-filling in 256 in fi while 2048 data points were collected in fz with zero-filling to 4096. Sixty-four transients were collected for each time increment and, with a relaxation delay of 1.0 s between increments, total measuring time was 1.1 h. Pseudoecho processingz2 was applied in both domains to ensure maximum resolution. Repeat measurements indicated that 'H chemical shifts could usually be determined with a precision of 0.005 ppm, Le., 2 Hz. Acknowledgment. Financial support from the Natural Sciences and Engineering Research Council of Canada in the form of a strategic grant (W.
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We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly-(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a singlemolecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.
Molecular dynamics in polymeric systems
e-Polymers, 2004
It is well known that the properties of polymeric materials depend strongly upon their chemical structure. Other more specific factors that may be related to the chemical structure also determine the macroscopic behaviour of such materials, namely the relative position of the different segments of the polymeric chain, the molecular architecture (molecular weight distribution, branching, copolymer organisation, cross-linking extent, etc.), the crystalline environment and the pressure/temperature conditions. All these factors have a common impact in the material: they are strongly correlated to the mobility on the molecular level. That is why a huge amount of work has been devoted to the study of translational/rotational mobility that occurs within the polymeric chains. This review is intended to provide a brief survey on such kinds of mobilities, how they can be studied and what are their main characteristics. Examples on systems studied in our groups will be provided, obtained by di...
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Progress in Polymer Science, 1990
I. Introduction 337 2. Luminescence phenomena 338 3. The excimer formation process 338 3.1. General considerations 338 3.2. Evaluation of the mobility of the intramolecular excimer-forming probe 340 4. Relation between excimer formation and polymer dynamics in bulk 342 5. Samples 343 6. Temperature effects 344 6.1. Investigation of polymer mobility via intramolecular excimer tk)rmation of ,ne.so-2,4-di(N-carbazolyl) pentane (meso-l)NCzPe) 344 6.2. Influence of the excited lifetime of the chromophore group 350 6.3. Influence of the size of the chromophore group 351 6.4. Probe effects 352 7. Pressure effects 353 8. Conclusions 356 9. Appendix Basic considerations on the free volume theory 356 9.1. Temperature dependence of the relaxation times 356 9.2. Pressure dependence of the relaxation times 358 Ack no'~ledgement 359 References 359