NMR Matrix Technique for Detecting Self Diffusion in Polymers

A technique is discussed where monodisperse small spheres or cylindrical fibers of a polymer are embedded in a matrix of the corresponding fully deuterated polymer. On annealing the sample at a temperature above the glass transition the protonated macromolecules diffuse into the deuterated matrix and vice versa. Since the NMR spectrum depends upon the intermolecular proton proton dipolar coupling, the decrease of this coupling can be used to monitor the diffusion process. For particle diameters d ∼ 10−4 cm and annealing times t ∼ 105 s, extremely small diffusion constants D < d2/t are attainable. The NMR analysis of prospective diffusion experiments with polystyrene is discussed in some det…

Dynamics of Colloidal Hard Spheres in Thin Aqueous Suspension Layers—Particle Tracking by Digital Image Processing and Brownian Dynamics Computer Simulations

Abstract A new experimentally simple technique is introduced for studying dynamical properties of hard sphere colloids in thin aqueous suspension layers by light-microscopy observation supported by computer-aided digital image processing. The thickness of the layers of the colloidal samples confined between two smooth glass plates is accurately adjusted by monodisperse "spacer" spheres which are larger than the diffusing spheres. Tracking of single particles in concentrated phases is accomplished using fluorescence light microscopy where a few dyed particles are mixed with the undyed colloidal spheres of the same size. First results are presented for the self-diffusion coefficient—(i) in ve…

Tracer diffusion in polymer and organic liquids close to the glass transition studied by forced rayleigh scattering

Translational diffusion coefficients D of photochronic dye molecules have been measured by forced Rayleigh scattering in polymer diluent systems at compositions from pure polymer to pure diluent. D could be measured down to below the glass transition temperature T g. In the pure diluent, D(T g) was found typically about two decades below that in the pure polymer but still far above the Stokes-Einstein prediction extrapolated from high temperatures. Some experimental results are in contrast with predictions from free-volume theory.

Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation.

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.

RELAXATION METHODS FOR STUDYING MACROMOLECULAR MOTION IN THE BULK

Abstract Macromolecular motion in amorphous and partially crystalline polymers is discussed in the light of recent relaxation experiments with particular emphasis on NMR methods. Polystyrene and polyethylene serve as pertinent examples where a considerable amount of new experimental data provides a bysis for better understanding molecular processes below and above the glass transition, and in the melt.

Pseudo-solid echoes of proton and deuteron NMR in polyethvlene melts

The solid echo technique is applied to determining residual dipolar and quadrupolar couplings in molten polyethylene (PE) and deuterated PE, respectively. The residual coupling defined by the square root of the second moment is about 1% of the corresponding quantity in the solid. It increases with molecular weight, and decreases with rising temperature. A theoretical treatment of time dependent residual couplings yields a decay time that is found experimentally to be about 0.1 ms in molten PE, and independent of molecular weight and temperature within our limits of accuracy. The residual coupling is discussed in relation with chain entanglement in PE. Measurements of the spin-lattice and sp…

Brownian dynamics simulations of colloidal hard spheres. Effects of sample dimensionality on self-diffusion

The self-diffusion coefficients of colloidal hard spheres were determined by Brownian dynamics (BD) computer simulations using a new efficient algorithm for treatment of the hard-sphere interactions. Calculations were done on an Apple PC type MacIIcx and on a Micro VAX 3000, considering samples in two and three dimensions at varying particle concentrations. Our results in three dimensions are compared with experimental results from our own group which were obtained by forced Rayleigh scattering (FRS), and with numerical results from a dynamical Monte Carlo simulation by Cichocki and Hinsen. Good agreement with the latter was found for particle volume fractions up to 0.40. Differences in the…

Brownian dynamics of polydisperse colloidal hard spheres: Equilibrium structures and random close packings

Recently we presented a new technique for numerical simulations of colloidal hard-sphere systems and showed its high efficiency. Here, we extend our calculations to the treatment of both 2- and 3-dimensional monodisperse and 3-dimensional polydisperse systems (with sampled finite Gaussian size distribution of particle radii), focusing on equilibrium pair distribution functions and structure factors as well as volume fractions of random close packing (RCP). The latter were determined using in principle the same technique as Woodcock or Stillinger had used. Results for the monodisperse 3-dimensional system show very good agreement compared to both pair distribution and structure factor predic…

1H-NMR relaxation in polyethylene melts as studied by the deuteron dilution technique

Anisotropic diffusion in etched particle tracks studied by field gradient NMR

Etched particle tracks produced after heavy ion irradiation of polymer foils are used as model systems to test the performance of NMR in a newly developed ultrahigh magnetic field gradient system. The stimulated NMR echo decay of molecules diffusing in the channels, formulated in terms of the self part of the intermediate scattering function, is anisotropic and yields the form factor of the channels.