The chain length dependence of the self-diffusion coefficients of PDMS and PEO has been measured with pulsed field gradient NMR (PFG NMR). With PDMS the maximum molar mass region attainable with PFG NMR could be investigated. For molar masses larger than about lOM, the proportionality D -M-2 according to the strict reptation picture was observed; at small M Rouse-like diffueion is observed separated from the reptation part by a D(M) dependence characterized by a strong slowing down of the self-diffusion coefficient. The monomeric friction coefficients for PDMS derived from diffusion with the Doi-Edwards theory agree satisfactorily with those obtained from viscosity and also neutron scattering. Quantitatively, a discrepancy remains between the high molar mass part of D(M) where the monomeric friction coefficient is by a factor of about 0.5-0.6 smaller than that determined from the Rouse part of D(M) at low molar masses. Within experimental accuracy, for PDMS the activation energy of diffusion is equal to the activation energy of viscosity. For PEO the activation energy decreases from 24 to 18 kJ/mol at a molar mass of about 20 OOO g mol-'.

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The compositionJand concentration, 4, dependence of the self-diffusion coefficients of diblock copolymers in solutions in a common good solvent have been investigated by pulsed-field-gradient nuclear magnetic resonance and photon correlation spectroscopy. The difference in the entanglement characteristics of the parent homopolymers was found to be very important in determining the diffusion coefficients. The investigation on toluene solutions for a series of poly(styrene-bisoprene) diblocks, possessing almost similar molecular weights and compositions ranging from 0.18 to 0.74, showed that the dependence of the diffusivity on diblock compositionfconforms with the progressive transition from the Rouse to the entanglement regime at different concentrations due to the different critical molecular weights for entanglement of the parent homopolymers. The same idea can account for the diblock composition dependence of the self-diffusivity for poly-(styrene-b-butadiene) diblocks. Moreover, the self-diffusivities for three poly(styrene-b-methyl methacrylate) diblocks in toluene are insensitive to copolymer composition (0.35 to 0.69) in accord with the very similar entanglement characteristics of the two blocks.

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Many properties of complex porous media such as reservoir rocks are strongly affected by heterogeneity at different scales. Complex depositional and diagenetic processes have a strong control on the pore structures, leading to systems with a wide range of pore sizes covering many orders of magnitude in length scales. This poses a significant challenge for digital rock analysis since a single resolution image and associated simulation model cannot capture all the relevant length scales in sufficient detail due to limitations in computer memory and speed. The scale-transgressive effects of heterogeneity must therefore be accounted for through a multiscale digital rock workflow. We introduce a generalized multiscale imaging and pore-scale modelling workflow to derive transport properties of complex rocks having broad pore size distributions. A dry/wet micro-CT imaging sequence is used to spatially map the porosity and the connectivity of resolved and unresolved porous regions. The unresolved porosity regions are classified into different porosity classes or rock types. The resulting 3D rock-type map and the porosity map are combined and transformed into a multiscale pore network model. Resolved pores are treated in a conventional pore network manner while unresolved network elements are treated as a continuum Darcy-type porous medium. Similar to conventional continuum models, each Darcy pore is populated with single and multiphase flow properties. These properties are derived from high-resolution rock-type models constructed from backscatter SEM images and/or high-resolution micro-CT images of sub-samples. The multiscale digital rock workflow is applied to two heterogeneous rock samples: a mixed wet thinly laminated reservoir sandstone and an oil wet reservoir carbonate. Experimentally measured mercury-air primary drainage and oil-water imbibition capillary pressure curves (after ageing to restore wettability) are used to anchor the multiscale pore network model. Waterflood relative permeability is calculated in a blind test and compared with high-quality experimental data. A very encouraging agreement between computed and measured properties is found.