Bo Nyström

Molecular Transport in Semidilute Macromolecular Solutions

Abstract Studies of static and dynamic properties of semidilute (or moderately concentrated) macromolecular solutions have generated a considerable interest in recent years. The newly awakened interest can mainly be ascribed to the successful application of new theoretical tools, e.g. the renormalization-group technique and scaling laws to semidilute polymer solutions [1–5], and to recent advances in small-angle neutron-scattering (SANS) experiments [3, 6, 7]. The SANS technique was found to be of outstanding importance to yield information about static properties, e.g., conformation properties of polymer chains [7].

Fractional coefficient of macromolecules in concentrated solution and in the vicinity of the critical solution temperature. Diffusion and sedimentation studies of polystyrene in toluene and trans-decalin

Abstract The concentration dependence of the frictional coefficient ( f ) in concentrated solutions of well-defined polystyrene fractions has been studied both in a good solvent (toluene) and in a solvent where θ conditions and condition in the vicinity of phase separation can be realized ( trans -decalin). f and the self-diffusion coefficient ( D + ) have been calculated from a combination of measured translational diffusion coefficients ( D ) and osmotic pressure data for the systems; polystyrene (M = 390 000) trans- decalin up to 90 kg/m 3 at 20° (θ-conditions), 30° and 40°C; polystyrene (M = 110 000) toluene up to 120 kg/m 3 at 25°C. Sedimentation measurements are also reported. The main results are: (a) over a concentration interval 0–100 kg/m 3 , f shows more than a ten-fold and almost linear increase; (b) in trans -decalin when the temperature is raised from 20° (θ-conditions) to 40°C (good solvent conditions), keeping the concentration constant, f increases only slightly, the increase being somewhat more pronounced at higher concentrations; (c) the concentration dependence of the ratio D D + is considerable under good solvent conditions but becomes gradually less pronounced when θ-conditions are approached; (d) diffusion/osmosis and velocity sedimentation give identical values of f over the entire concentration interval.

Sedimentation in concentrated polystyrene solutions and the observation of an “anomaly” in a good solvent

Abstract Sedimentation coefficients are reported for three polystyrene fractions (molecular weights 1.1 × 10 5 , 3.9 × 10 5 and 1.8 × 10 6 ) in toluene and trans -decalin (θ-conditions) up to high concentrations. The difference between the sedimentation behaviour in good and poor solvents is discussed; an “anomalous” effect was observed in toluene in a concentration region where incipient entanglement is likely.

Test of ‘scaling laws’ describing the concentration dependence of osmotic pressure, diffusion and sedimentation in semidilute macromolecular solutions

Abstract Data of osmotic pressure, diffusion and sedimentation in semidilute macromolecular solutions are systematized with regard to scaling laws. The observed main features are: (a) the concentration dependence of the osmotic pressure both at good and theta solvent conditions is in excellent agreement with that predicted by the scaling laws. (b) The concentration dependence of the mutual diffusion coefficient D m could not uniquely be described by a simple scaling law. A difference in concentration dependence between D m and the cooperative diffusion coefficient was observed for polystyrene under good solvent conditions. (c) The concentration dependence of the permeability coefficient (related to sedimentation) and the sedimentation coefficient were for most of the systems in close agreement with that predicted by the scaling laws.

Velocity sedimentation transport properties in dilute and concentrated solutions of hydroxypropyl cellulose in water at different temperatures up to phase separation

Abstract Velocity sedimentation measurements have been performed for the system hydroxypropyl cellulose in water in both dilute and concentrated solutions (0–100 kg m −3 ) and at temperatures remote from as well as close to θ-conditions (25–40°). In dilute solutions, the experimentally determined concentration dependence of the sedimentation coefficient was compared with that calculated from the theory of Yamakawa; fairly good agreement was obtained. The difference between the sedimentation behaviour under good and poor solvent conditions is also discussed. Furthermore, the frictional properties are discussed and compared with those deduced from diffusion measurements.

Transition between dilute and concentrated solution behaviour as revealed by excimer fluorescence

Abstract Excimer fluorescence measurements at 25° on polystyrene, with molecular weights 111,000, 392,000 and 900,000, in 1,2-dichloroethane over an extended concentration region are reported. The curve representing the normalized ratio of excimer to monomer fluorescence intensities shows an upward curvature at c [ η ] ≈ 1 for all the molecular weights. This observation is attributed to enhanced intermolecular excimer formation. Some theoretical aspects on this phenomenon are also considered.

Sedimentation velocity measurements close to the upper critical solution temperature and at θ-conditions: polystyrene in cyclopentane over a large concentration interval

Abstract Sedimentation velocity measurements on polystyrene (M = 110 000) in cyclopentane over an extended concentration region and from 5°C (close to the upper critical solution temperature) to 40°C are reported. The concentration dependence parameter (ks)w increases from 2 to 5°C to 27 at 40°C. For all temperatures except 5°C, s 0 s vs. w[η]w shows an upward curvature at w[η]w ≈ 1; at 5°C, on the other hand, s 0 s is independent of concentration over the region considered. Furthermore, measurements have also been performed at 20°C (θ-conditions) over a large concentration interval for the molecular weights M = 20 400, 390 000 and 950 000. The parameters s0 and (ks)w were both found to be proportional to M 1/2 w . In the ‘hydrodynamically normalized’ plot s 0 s vs. w[η]w the sedimentation behaviour can approximately be represented by a single curve for all the molecular weights.

Dilute and concentrated solutions of polystyrene in trans-decalin close to and far from the θ-temperature—II. Osmotic pressure measurements

Abstract Osmotic pressure measurements on polystyrene ( M n = 396. 000 ) in trans -decalin for concentrations up to 140 kg m −3 and from 20 to 40 are reported. The θ-temperature is 20.8 . The ratio ∂( π c ) ∂c c=0 ∂( π c ) ∂c c=c + where c + is the concentration at which a homogeneous segment distribution is assumed to prevail, increases with temperature up to the plateau value of 0.7. From the temperature dependence of the osmotic pressure, the partial molar enthalpy. Δh 1 , and entropy, Δs 1 . of mixing are found to be positive. The solvent-solute interaction parameter increases linearly with concentration at all temperatures.

Solvent self-diffusion in semidilute polystyrene solutions. Pulsed-gradient spin-echo measurements on a standard Fourier transform n.m.r. spectrometer

Measurements of solvent self-diffusion coefficients in the systems polystyrene/dichloromethane and polystyrene/cyclopentane recorded on a standard Fourier transform n.m.r. spectrometer are reported. The ratio DsDs,0 was found to decrease linearly with increasing volume fraction of polystyrene, over the interval studied (oPS<0.27), for both systems. For PS/cyclopentane an increase in temperature from 12.5°C (close to UCST) to 40°C was not found to alter the concentration dependence of the ratio DsDs,0 significantly.

Dilute and concentrated solutions of polystyrene in trans-decalin close to and far from the θ-temperature—1. Velocity sedimentation measurements

Abstract Velocity sedimentation measurements on polystyrene in trans-decalin up to 100 kg m−3 and from 20 to 40°C are reported. ks increases from 0.036 m3 kg−1 at θ-conditions (20.8°C) to 0.096 m3 kg−1. Values calculated from the Pyun-Fixman theory agree within 10%. The Yamakawa theory gives the temperature dependence correctly but underestimates ks. At θ-conditions, so/s vs c[η] shows an upward curvature at c[η] ≈ 1.3; at 40°C the plot is linear over the entire region. Sedimentation in concentrated solutions is discussed in terms of permeability.