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  • 1
    Digitale Medien
    Digitale Medien
    Collective and self diffusion of PS microgels in solution as observed by thermal diffusion forced Rayleigh scattering (1997)
    Springer
    Colloid & polymer science 104 (1997), S. 132-134 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Microgels ; thermal diffusion ; self diffusion ; forced Rayleigh scattering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Thermal diffusion in solutions of polystyrene micro-network spheres (microgels) in toluene has been studied by the holographic scattering technique of thermal diffusion forced Rayleigh scattering (TDFRS) and by photon correlation spectroscopy (PCS). Size distributions of microgels of different crosslink ratios are obtained from TDFRS measurements on dilute solutions at very lowq-values around 4000cm−1. At low concentrations a single diffusive mode is observed and the diffusion coefficient increases with concentration. It is attributed to the collective diffusion of the microgels and the solvent. At high concentrations an additional slow mode appears whose diffusion coefficient decreases with increasing concentration. Both diffusive modes are observed with PCS and TDFRS. Contrary to PCS, heterodyne TDFRS-measurements reveal a negative amplitude of the slow mode. We attribute the slow mode to self-diffusion of the microgels, made visible by the polydispersity of their size distribution. It is discussed in terms of a fast coupled thermal diffusion with subsequent decoupling of the individual microgels and relaxation into a new Soret equilibrium by self-diffusion of the microgels.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182429
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Stochastic Thermal-Diffusion Forced Rayleigh Scattering (1999)
    Springer
    International journal of thermophysics 20 (1999), S. 1-18 
    Details
    ISSN: 1572-9567
    Schlagwort(e): diffusion ; forced Rayleigh scattering ; Fourier transform ; Ludwig–Soret effect ; polymer solutions ; stochastic excitation ; thermal diffusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The holographic grating technique of thermal-diffusion forced Rayleigh scattering (TDFRS) utilizes the Ludwig–Soret effect to induce a concentration modulation within a binary liquid. The signal generation is described in terms of a linear response formalism, and the memory function for the concentration mode g(t) and its Fourier transform, the diffusion susceptibility, are measured by means of pseudostochastic random binary sequences with flat power spectra in combination with fast Fourier transform and correlation techniques. For polydisperse polymer solutions the individual modes contribute proportional to their concentration to g(t), contrary to photon-correlation spectroscopy, where the correlation function is dominated by the high molar mass components. Other advantages of stochastic TDFRS are time-scale delocalization of dust spikes and frequency multiplexing. Measurements are reported on monodisperse and bimodal polystyrene in toluene.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021461726559
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Holographic grating study of mass and thermal diffusion of polystyrene/toluene solutions (1995)
    Springer
    International journal of thermophysics 16 (1995), S. 11-21 
    Details
    ISSN: 1572-9567
    Schlagwort(e): diffusion ; forced Rayleigh scattering ; holography ; polymer solution ; thermal diffusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The transient grating technique of thermal diffusion forced Rayleigh scattering (TDFRS) has been employed to study translational and thermal diffusion of polystyrene in toluene. Different molar masses and concentrations below or slightly above (lie overlap concentrationc * have been investigated. The translational diffusion coefficients agree well with results obtained from photon correlation spectroscopy. Small remaining diferences can be attributed to sample polydispersity. The molar mass independence of the thermal diffusion coefficient is confirmed, and thermal diffusion and Soret coefficients are compared with data obtained from thermal field flow fractionation and diffusion cell experiments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01438953
    Standort Signatur Erwartet Verfügbarkeit
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