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Coefficient de diffusion translationnel de polystyrene marque avec des derives de l'azobenzene, dans des matrices du meme polymere dans le toluene

The binary interaction parameter χ eff has been obtained for deuterated polystyrene/poly(vinyl methyl ether) blends as a function of temperature, composition and molecular weight from small-angle neutron scattering experiments. The consistency of the correlation length ξ, the zero-wavenumber scattering intensity S (0) and the χ eff parameter with the mean-field prediction has been demonstrated by the q dependence of the static structure factor S ( q ) and the 1/T dependence of ξ −2 , S (0) −1 and χ eff . The effective interaction parameter χ eff can be related to the Flory-Huggins interaction parameter χ eff can be related to the Flory-Huggins interaction parameter χ F . The free-energy function as well as the spinodal curve and cloud-point curve have been constructed.

A new photochromic probe, bis(9-anthryl methyl) ether (BAME) derivative, was synthesized and introduced as an effective probe for forced Rayleigh scattering (FRS) measurement. It is shown that BAME and polystyrene labelled with BAME exhibit a large change in refractive index under irradiation of u.v. light (363.8 nm). The self-diffusion of BAME and polystyrene labelled with BAME (PSA) were measured in various solvents. Results of PSA in good, marginal and poor solvents are consistent with those obtained from quasi-elastic light scattering (QELS). Since the photodimerization reaction of anthracene has been extensively studied in solution and crystal as well as in polymer matrix, unfavourable multistep photochemical reactions can be avoided. One such unfavourable case, which involves a fluorescence quenching solvent CCl4, is demonstrated. A temperature dependence study of polystyrene in semi-dilute theta solution by FRS has suggested that the non-exponential intensity decay is due to large concentration fluctuations in the solution. The well known photochemistry, large refractive index change and temperature stability have made BAME a very promising probe for FRS measurements.

Les mesures de diffusion Rayleigh forcee dans un champ electrique avec des molecules chargees, qui sont soit photochromes par elles-memes soit marquees avec des colorants photochromes, permettent de determiner les mobilites electrophoretiques, ainsi que les coefficients de diffusion, de ces molecules. Exemples dans le cas des molecules du colorant azophenolique

A new type of photochromic compound, a bis-(9-anthrylmethyl) ether ((BAME), is introduced as a potential probe for the forced Rayleigh scattering (FRS) technique. Upon irradiation with ultra-violet (u.v.) light (∼360 nm), BAME undergoes intramolecular dimerization which involves a large refractive index change in the visible region. The dimerization process is known to be essentially irreversible in the absence of short u.v. light (∼250 nm) at room and moderately high temperatures. A derivative of BAME is synthesized and chemically attached to polystyrene chains. Some photochemical properties of the BAME-labelled polystyrene are reported together with the results of a preliminary diffusion measurement of polystyrene by the FRS technique.

Heterodyne detection of light scattered from capillary waves is used to study the surface properties of the air–liquid interface. A diffraction grating is employed to select a precise ripplon wave vector k and to provide a stable local oscillator field. The optics are designed to form a real image of the grating on the surface, thus allowing the measurements to be reproducible within 5%. The power spectrum detected in frequency domain is well fitted by a Lorentzian profile for the range of ripplon wave vectors 260≤k≤390 cm−1. The shape of the scattered spectra at each wave vector is corrected for the incident beam profile by effecting a convolution of the Lorentzian and Gaussian functional forms. The surface tensions and the kinematic viscosities of water, anisole, and ethanol are deduced from the ripplon dispersion relation corrected to the first order in damping, and found to be within 5% of the literature values. Thus we confirm the validity of approximations made for the instrumental function and the dispersion relation.

A novel modification of the forced Rayleigh scattering method for determining the translational diffusion coefficient and lifetime of photochromic moieties is effected through imposition of a non-sinusoidal transient optical grating (TOG) to a condensed medium sample. A multiple-order diffraction pattern is observed and subsequent analysis of the exponential decays of higher-order diffraction spots reveals that they originate from the higher-order spacial Fourier components of TOG.

Steady-state shear viscosity (γ˙) of unconcatenated ring polymer melts as a function of the shear rate γ˙ is studied by a combination of experiments, simulations, and theory. Experiments using polystyrenes with Z ≈ 5 and Z ≈ 11 entanglements indicate weaker shear thinning for rings compared to linear polymers exhibiting power law scaling of shear viscosity ∼γ˙-0.56 ± 0.02, independent of chain length, for Weissenberg numbers up to about 102. Nonequilibrium molecular dynamics simulations using the bead-spring model reveal a similar behavior with ∼γ˙-0.57 ± 0.08 for 4 ≤ Z ≤ 57. Viscosity decreases with chain length for high γ˙. In our experiments, we see the onset of this regime, and in simulations, which we extended to Wi ∼104, the nonuniversality is fully developed. In addition to a naive scaling theory yielding for the universal regime ∼γ˙-0.57, we developed a novel shear slit model explaining many details of observed conformations and dynamics as well as the chain length-dependent behavior of viscosity at large γ˙. The signature feature of the model is the presence of two distinct length scales: the size of tension blobs and much larger thickness of a shear slit in which rings are self-consistently confined in the velocity gradient direction and which is dictated by the size of a chain section with relaxation time 1/γ˙. These two length scales control the two normal stress differences. In this model, the chain length-dependent onset of nonuniversal behavior is set by tension blobs becoming as small as about one Kuhn segment. This model explains the approximate applicability of the Cox-Merz rule for ring polymers.

Solution semidiluee de polystyrene dans le toluene, comme matrice et un polystyrene de longueur de chaine plus courte comme diffusant

The rotational relaxation times of rabbit myosin and myosin rod have been determined by electric birefringence measurement. The relaxation time of myosin measured in 10 mM pyrophosphate buffers in a pH range of 7.6–9.5 was found to have substantial concentration and pH dependences. The infinite-dilution limit of the relaxation time, τ°, was determined as 38 ± 2 μs, and it was found to be independent of pH. For myosin rod, a possible thermally induced conformational change was investigated in a temperature range of 1–43°C. The rotational relaxation time of myosin rod shows no clear indication of conformational change in this temperature range, and the radius of gyration measurement by light scattering was shown to be consistent with this observation. The steady-state birefringence, however, decreases substantially above around 40°C. This, the myosin rod appears to be only slightly flexible even at physiological temperature, but the possibility of a “melting” or “hinging” of the myosin rod cannot completely be ruled out on the basis of these experiments.

Small angle neutron scattering (SANS) measurements were performed on poly(isoprene) networks at different uniaxial strains, i.e., 1.0 ≤ λ (extension ratio) ≤ 2.1. The networks were prepared from anionically polymerized, α,ω,-dihydroxy-poly(isoprene) precursors (H-chains) and the corresponding poly(isoprene-d8) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrofuran solutions by trifunctional crosslinkers, tri-isocyanates. The two components of the radius of gyration of elastic strands, parallel and perpendicular to the strain axis, were determined from the SANS data of the networks with 8% and 15% D-chains. Two molecular weights of D-chains, 26,000 and 64,000, crosslinked with approximately the same molecular weight H-chains (29,000 and 68,000 respectively) were examined for the deformation behaviors. From the observed changes in the parallel and perpendicular components of the radius of gyration relative to macroscopic extension ratio, after appropriate correction for the dangling chain contributions, the chain extensive deformation is found to follow a behavior intermediate between the junction affine model and the phantom network model which allows unrestricted fluctuations of network junctions. On the other hand, the chain contractive deformation follows closely the chain affine model, indicating an asymmetry between extensive and contractive chain deformation. In either case, the deformation behavior is found to be the same for the two molecular weights.

The osmotic response of bovine red blood cell ghosts to a series of sugars is studied by light scattering. The sealed and right-side-out ghosts are prepared by the procedure of Steck and Kant (Steck, T.L. and Kant, J.A. (1974) Methods Enzymol. 31, 172–180), swollen in a hypotonic phosphate-buffered saline solution and their size and shape determined by elastic and quasielastic light scattering. Different carbohydrates are then added to the suspending medium in order to examine the osmotic responses, and the osmotic deformation of ghosts is shown to be spherically symmetric. Having thus established the deformation behavior, we then rank the osmotic activity of a carbohydrate relative to a standard, i.e., raffinose. It is found that the osmotic response of the ghosts to sucrose is about the same as that to raffinose, and the response to the smaller carbohydrates simply follows the number of carbons in various sugars; glucose and fractose are about 1.7 times less effective than raffinose, and pentaerythritol and meso -erythritol are 2.3 times less effective. Glyceraldehyde, which is 3.6 times less effective than raffinose, is the least effective sugar analog among those that we have tested.

Ring polymers have attracted a great deal of scientific interest due to the lack of free ends which has dramatic consequences on their rheology. Previous studies show that the zero shear viscosity of pure rings is much lower than that of their linear counterparts with the same molecular weight.1 However, it has been shown that when linear polystyrene is mixed with rings in certain ratios, the zero shear viscosity of the blend is even higher than that of the linear. Uniaxial extensional rheology measurements of the blend show that the maximum stress was enhanced and followed by an unexpected stress overshoot at large Hencky strains. The strain hardening up until the maximum could be relevant e.g. for fiber spinning since strain hardening leads to increased molecular orientation and stretching that again leads to increased fiber strength. Ring linear blends may thus lead to stronger fibers in the future. In order to study the structural origin of the observed strain hardening, Very Small Angle Neutron Scattering (VSANS) is used in this study.In the present work, to explore how the rings affect the linear molecules, a blend of 30 % ring and 70 % linear polystyrene molecules (both of molecular weight 185 k and with 10 wt% deuterated linear chains) and a reference sample of pure linear polystyrene (also of molecular weight 185 k and 10 wt % deuterated chains) are used. The samples were prepared by using a filament stretching rheometer at 130oC with a constant Hencky strain rate of 0.003 s-1, and quenched at different times. One sample was quenched before the maximum stress where the segments start to be oriented. A second sample corresponds to maximum stress for the blend where the linear chains in the blend are stretched the most with respect to their counterparts in the pure linear. In this way, the level of molecular stretching of the linear component in the blend is quantified and compared with the linear material. Thus, we shine light on the origin of the strain hardening in the linear ring blend.

1,1,12,12-Tetramethyl[1.1]silaferrocenophane ( 1 ) and poly(ferrocenylsilane) ( 2 ) were formed as the major products in the reaction of FeCl 2 with the dilithium salt of (C 5 H 5 ) 2 SiMe 2 , and the X-ray crystallography for 1 revealed its molecular structure of an anti conformation.