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We report an AC technique to measure both the sign and magnitude of (e 1 + e 3 ) using electrooptic measurements on a hybrid aligned nematic cell. A detailed numerical analysis of the optical signal allows us to obtain the temperature dependences of (e 1 + e 3 ), the rotational viscosity coefficient γ 1 as well as the anchoring strengths at the two surfaces. Our measurements on CCH-7 show the following interesting results. a) The extrapolation length L 1 at the homeotropic surface shows a small decrease as the temperature is increased to 66 °C beyond which it shows a sharp increase which we interpret as arising from a softening of the chains of the aligning ODSE layer. b) The slope of the temperature dependence of the extrapolation length L u at the homogeneous surface changes sign around 72 °C. c) (e 1 + e 3 )/S is a constant upto 72 °C and decreases rapidly beyond this temperature. The last two results are attributed to an increase in the conformational freedom between the rings of CCH-7 molecules beyond that temperature.

Penning ionization electron spectroscopy of the CO molecule by He*(2 1 S) metastable atoms is studied. Vibrational populations are reported for the three energetically accessible states of the CO + ion (X 2 Σ + , A 2 Π and B 2 Σ + ). An obvious discrepancy is observed between the excited vibrational levels of the X 2 Σ + state and the calculated Franck-Condon factors. This result is attributed to an excitation transfer process via Rydberg vibrational progression converging to the CO + (D 2 Π) ionic state in agreement with the recent observations by fluorescence of neutral dissociate states. The presence of electrons coming from the well-known σ shape resonance is not excluded.

The viscosity of a fluid can be measured by observing the motion of a probe sphere (or ball) in a centrifuge tube filled with this fluid. The hydrodynamic behavior of the probe ball moving in the centrifuge tube has been solved theoretically. We have got the universal relationship (for balls of a given material and size in a given tube) between the terminal ball velocity, the fluid viscosity and the centrifuge acceleration using the only adjustable parameter - the rotational friction coefficient between the ball and the tube. The rotation of the centrifuge tube in the horizontal plane induces an inertia force which is counterbalanced by the friction force acting on the ball. As a result, the ball moves along the tube with some characteristic speed, which is a measure of the viscosity of the fluid. This speed was calculated in the lubrication approximation. The gravitational acceleration causes the ball to move very close to the bottom of the centrifuge tube. In this situation, the gravity is balanced by a levitation force introduced and calculated in the present paper. The origin of this force is the formation of the bubble behind and below the moving ball. The theoretical development on the terminal velocity for the ball moving very near the bottom of the horizontal centrifuge tube is tested by using a specially designed centrifuge for two types of balls and a wide set of viscosity standards. Excellent agreement between theory and experiment suggests that we have developed a new approach to measure high viscosities of fluids at low shear rates which might be especially useful for the investigation of polymer melts.

Nous observons par diffusion de neutrons aux petits angles la structure de chaines de polystyrene en solution semi-diluee confinees dans un milieu poreux modele, le Vycor. La taille des chaines en solution a l'etat libre est toujours superieure au diametre des pores, 70 A. L'utilisation d'un melange adequat de solvants et de polymeres hydrogenes et deuteres nous permet de mesurer directement le facteur de forme d'une seule chaine au milieu des autres. La penetration des chaines dans le milieu poreux est presque totale pour la concentration (Φ = 20%) et la gamme de poids moleculaire (35 000 < M w < 800 000) utilisees. Le rayon de gyration des chaines confinees est toujours inferieur au rayon de gyration des chaines libres dans la solution equivalente. Nos mesures sont en accord avec les predictions theoriques etablies par Daoud et de Gennes pour des chaines confinees dans un pore cylindrique quand les chaines sont enchevetrees et comprimees transversalement mais restent ideales a grande echelle dans la direction du cylindre a cause de l'ecrantage du volume exclus (regime dit de cigares semi-dilues). Les valeurs des coefficients de partage des chaines entre le milieu poreux et la solution libre ainsi que le comportement asymptotique des facteurs de structure montrent que le polystyrene s'adsorbe sur la surface nue du Vycor. Nous montrons que la silanisation du Vycor supprime cette adsorption.

Recent Neutron Scattering experiments by Richter et al. [1] show that the presence of coil-crystalline block copolymer (PE-PEP) micelles in a mixed alkane bath suppresses the crystallization out of solution of the long alkane component at low temperatures. Motivated by these experiments, we study theoretically the thermodynamics and kinetics of lamellar coil-crystalline block copolymer micelles in a bimodal solvent to better understand the factors determining the anti-precipitation action of coil-crystalline block copolymers. We assume an Alexander-de Gennes brush model for the strongly stretched corona chains and explicitly account for the polydispersity of the solvent chains. For the thermodynamic distribution of solvent chains in the corona, we find a predominance of short solvent chains to long solvent chains in the corona phase compared to the solvent bath, both with and without nematic interactions in the corona phase. We also calculate the rate of crystallization of the long solvent chains onto the micellar crystal core and find that the rate is sensitive to both brush and core parameters. In particular, we predict that to maximize the rate, both E fold /kTN A and X n need to be made as small as possible, where E fold is the folding energy of the crystal core chains, N A the number of statistical segments of the solvated corona chains and X n parameterises the strength of nematic interactions in the micellar corona. This leads to the surprising result that for fixed E fold , the rate of crystallization is increased when we increase the molecular weight of the corona blocks.

The microstructure of a ternary system of a non-ionic surfactant (n–dodecyl pentaoxyethylene glycol ether, C12E5), water and a water-soluble random heteropolymer, poly (styrene-r-Na styrene sulfonate) with degrees of sulfonation ranging from 30% to 90% is investigated at room temperature. Using small angle X-ray scattering and freeze-fracture electron microscopy we focus on the lamellar phase region and study samples along four different paths of constant surfactant-to-water ratio with increasing polymer content. We demonstrate that for samples with low water content (S/W ratios 3.4 and 4.9), regardless of the sulfonation degree of the polymer, the lamellar phase persists up to several weight percent of polymer and the polymer molecules are confined inside the surfactant bilayers. With increasing quantity of polymer the lamellar phase Bragg peak shifts in a manner consistent with the increase of the lamellar period, which indicates increased bilayer thickness. For mixtures less concentrated in surfactant first order phase transitions are observed for all polymer charge contents when the amount of polymer is increased. For low charge contents of polymer (30% and 45%) the lamellar stack of the polymer-doped surfactant bilayers coexists with either cubic or another lamellar phase and microscopic phase separation is only observed. For large charge contents (65% and 90%) a surfactant-rich lamellar phase coexists with a polymer-rich water solution. It is suggested that the observed phase behaviour is governed by the concentration number of free water molecules.

We study the cubic phase made of the non-ionic surfactant C12(EO)6 in presence of water. The 3D periodic structure of this phase is characterized by the space group Ia3d. This structure corresponds to a centred cubic phase where the surfactant molecules build two identical 3D periodic interwoven labyrinths separated from each other by a continuous water medium. We present recent results obtained at I.L.L. on the Spin Echo spectrometer IN 11. Our experiments show for the first time, the dynamical character of the fluctuations observed in the investigated cubic phase. Therefore measurement have been performed on a single crystal (~ 0.1 cm3) . The time dependent diffusion function $S({\bf q},t)$ has been measured for different scattering vectors q. For q vectors which do not correspond to Bragg peaks, the neutrons are scattered according to a quasi-elastic process and the associated $S({\bf q},t)$ function decreases with a characteristic time of about 20 ns. The dynamical fluctuations are most probably related to collective deformation modes of the labyrinths.

We use the Landau-de Gennes theory of a nematic liquid crystal to investigate anew aspects of the properties of the interface between the isotropic and nematic liquid crystal phases of the same fluid. The equations of the static interface have been solved, both numerically and using asymptotic analysis, with an emphasis on the effect of inclusion of the order parameter biaxiality on the physical properties. We have compared the results of the exact solutions to the commonly used de Gennes ansatz, which assumes positive and uniform unixiality through the interface. Although the de Gennes ansatz in general gives good results, when bend and splay elastic constants dominate over the twist constants, it can lead to errors of up to 10% in the surface energy. The asymptotic analysis also shows that, by contrast with the de Gennes ansatz, the order parameter wings in the isotropic phase exhibit negative order parameter, with principal axis perpendicular to the surface. For moving interfaces, using an approximation which at this stage does not yet include hydrodynamic coupling, we have compared our results with the analogue of the de Gennes ansatz used by the present authors in an earlier paper. We find that including biaxiality leads to larger effects in the dynamic than in the static properties, and that whereas this is essentially a perturbation to the energy, the velocity of the moving interface can be significantly slowed down. The slowing down effects are strongly correlated with surface biaxiality, but both effects seem to be diminished when the isotropic phase is advancing.

The experimental results of Cladis et al. ill about the behaviour of smectic-C liquid crystal free-standing films subjected to a two-dimensional shear flow are reproduced via a Ginzburg-Landau model which is simulated numerically. The model takes into account effects that were first neglected in the theoretical analysis made by Cladis et al. particular emphasis is put on the influence of the elastic anisotropy and the nonrotational part of the flow.