Claude Picot

Light and neutron scattering studies of excess low-angle scattering in moderately concentrated polystyrene solutions

Abstract The light scattering (LS) and small-angle neutron scattering (SANS) behaviour of semi-dilute solutions of polystyrene has been determined in both ‘good’ and ‘theta’ solvents. Above a critical concentration related to chain overlap, an excess small-angle scattering component is in evidence for scattering vectors, q, such that qRg

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Abstract Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (Tcrystallization = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 105 to 7 × 105 has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (Mw = 4 × 105) leads to results which do not agree with Florys model. In this case, measurements on radius of gyration Rg show on the one hand an important increase of this parameter (∼40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (Mw = 1.75 × 106), and the same tagged chains previously considered, a very weak variation of Rg with increasing crystallinity is observed. This leads to consider in this case Florys conformation which is corroborated by data obtained in the intermediate range.

Hydrogenated polystyrene-poly(methyl methacrylate) diblock copolymer micelles in selective solvent: 2. Binary solvent-precipitant mixtures — effect of mixture composition and temperature

Abstract The association of a polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymer in l-chloro-n-hexane/dioxane mixture has been studied by light scattering. A parallel is made between the effect of the addition of precipitant for one block and the decrease of the temperature. As the volume fraction ∅ of precipitant for the PMMA block increases, or at constant ∅ as the temperature T decreases, multimolecular aggregation occurs. Contrary to the degree of association of the molecules, which varies, the dimensions of the micelles are independent of ∅ or T so that the compactness of those micelles increases when ∅ increases or T decreases. At intermediate T or ∅ values, large structures seem to be present in dilute solution.

Hydrogenated polystyrene—poly(methyl methacrylate) diblock copolymer micelles in selective solvent: 1. Single solvent system — effect of temperature

Abstract The association of two block copolymers, hydrogenated polystyrene-poly(methyl methacrylate) (PSH-PMMA) in 1-chloro-n-hexane (a selective solvent for PSH) and deuterated polystyrene-poly(methyl methacrylate) (PSD-PMMA) in dimethyl sulphoxide (a selective solvent for PMMA), has been studied by light and neutron scattering. Unusual large particles are formed in the temperature range corresponding to the theta point of one block of the copolymer whereas small compact micelles are observed at room temperature. At low temperature the results show good agreement with the model of closed association where unassociated molecules are in equilibrium with monodisperse micelles.

A direct comparison of spinodal decomposition analysis by time and q resolved light scattering and n.m.r.

Abstract Time and q resolved light scattering and nuclear magnetic resonance spin-lattice relaxation time have been performed on polystyrene/poly(vinyl methyl ether) blends during the early stage of the spinodal decomposition. The two techniques are used to determine the apparent diffusion coefficient at two different temperatures. A satisfying agreement is found between the results of T 1 n.m.r. measurements and those from light scattering. Otherwise, it has been shown that n.m.r. spin-lattice relaxation measurements, during the decomposition time, permits discrimination between spinodal decomposition and nucleation and growth. T 1ρ experiments indicate that the homogeneous phase as well as the phase-separated quenched blend contain short scale inhomogeneities but it is not clear whether they compete with the larger scale spinodal decomposition process.

Morphology development during the polymerization of styrene within a polyurethane network: Investigations by small‐angle X‐ray and light scattering

Phase separation that takes place during the formation of semi-interpenetrating polymer networks based on crosslinked polyurethane and linear polystyrene was studied by small-angle X-ray scattering and light scattering. The kinetics of the chemical reactions was followed by Fourier transform infrared spectroscopy. The occurrence of broad peaks in the X-ray scattering curves was interpreted in terms of distances between the urethane crosslinks. Small modulations on these curves were assigned to sphere-like structures with a diameter of around 5 nm which might be related to the urethane crosslink regions. Small modulations on the light-scattering curves at the beginning of styrene polymerization were assigned to spheres with diameters of around 4.5 μm, which can be related to the polystyrene-rich phase. These modulations disappear with time, which might indicate an increasing polydispersity of the domain sizes. The final morphology was found to depend on the time at which polymerization of styrene is initiated with respect to the time of gelation of polyurethane.

Chain conformation of semicrystalline isotactic polystyrene by small-angle neutron scattering

The results obtained from SANS (small-angle neutron scattering) measurements on isotactic polystyrene in the bulk-crystallized state are discussed. For tagged chain molecular weights ranging from 2.5 × 105 to 7 × 105, variations of the radius of gyration both as a function of crystallinity, x, and the molecular weight of deuterated species for IPS hydrogenated matrices of, respectively, Mw= 4 × 105 and Mw= 1.7 × 106 are examined. In the case of the matrix of lower molecular weight, there is found at x= 0.3 for the law Rg≈Mν an exponent ν close to 0.78 with an appreciable increase in the dimensions on increasing crystallinity. Calculations performed on schematic models lead to the adoption in such a case of a conformation possessing a long crystallized sequence [along the (330) plane] with two linked amorphous wings. Experiments performed with the matrix of higher molecular weight reveal almost no variation in the radius of gyration even at the highest crystallinity. Accordingly, Florys conformation seems to be a good model in such a situation. These results are corroborated by the dependences on q–2 and the intensity levels measured in the intermediate range. Comparisons with amorphous samples confirm the proposed models. An attempt to explain these conformations is made by comparing the crystalline growth rates and the long relaxation times.

Static screening length behaviour in polystyrene solutions

Abstract The concentration dependence of screening lengths in polystyrene solutions is determined by light and neutron scattering measurements. The data support the existence of a marginal regime in the temperature-concentration diagram, inside which mean field behaviour is observed. In addition, it is found that polymer solutions conforming to either semidilute good or marginal behaviour can be described universally in terms of two common variables: a reduced correlation length, and a reduced concentration. Experimentally determined concentrations for crossovers between various regimes of solution behaviour are reported, and compared with quantitative predictions from a recent theory of Schaefer.

Calculation of Elastic Small-Angle Neutron Scattering from Labeled Gels

Crosslinked network polymers which have been labeled around the crosslinks are essentially triblock copolymers connected in groups of three or four at the ends. Although such networks are infinite in extent, it has been possible to calculate elastic small-angle neutron scattering (SANS) patterns for them after making reasonable assumptions about correlations in the networks. It is shown that the SANS from such crosslinked labeled networks is indistinguishable from the SANS of long-branched polymers made up of the same triblock copolymers. In fact, little difference is calculated between the SANS of the networks and the SANS of the constituent triblock copolymers. The calculated SANS of three different-long branched polymers are compared with the SANS of the triblock copolymer. It is shown that SANS of gels in which all of the crosslinks are labeled depends only on the extent of labeling and on the radius of gyration of the constituent block copolymer.