This paper reviews some characteristic results obtained by scattering techniques in two sorts of swollen covalently crosslinked networks : neutral networks swollen by a good solvent and weakly ionized gels. For neutral networks swollen at saturation, the local conformation of the chains was found to be the same as in semi-dilute solutions, whereas some concentration inhomogeneities are observed at larger scale. Ionized gels are characterized by a peak of the structure factor and the absence of long range stationary concentration fluctuations at the concentration of preparation of the gels.

We consider the curvature elastic properties of a layer of block copolymer at the interface between two incompatible homopolymers. We focus on the relation between the relative lengths of the blocks and the elastic properties of the interfacial layer which determines the phase behavior. The curvature elastic moduli K and K, as well as the spontaneous curvature, c0, are obtained. The curvature free energy is used to predict the relative stability of spherical, cylindrical, lamellar, and ordered bicontinuous saddle-shaped structures as functions of concentration and polymer properties.

The orientational order generated in a polymer network by an uniaxial stress is probed with NMR. The experiments are performed on an end-linked polydimethylsiloxane network. When a uniaxial force is applied a detailed analysis of the spectrum shows that the segmental motions become uniaxial around constraint direction. This experimental fact is explained by shortrange orientational interactions between chain segments.

We have carried out x-ray scattering studies in melts of a series of linear polyisoprenes with highly polar sulfo-zwitterion groups at one end. The zwitterion end groups cause aggregation in good solvents for polyisoprene. The aggregation number depends strongly on the molecular weight of the polyisoprene tails and on the polarity of the solvent. Molecular mechanics simulations of the interactions between the zwitterion head groups suggest tubelike or diskline structures for the aggregates. Spherical structures are not energetically favorable. High resolution synchrotron x-ray scattering studies were carried out for six different (chain) molecular weights between 2000 and 23,000. For low molecular weights (between 2000 and 4000) a tubular structure is found with the tubes organized on a well-defined, two-dimensional triangular lattice with very large domain sizes >2000Å. A structural phase transition to a cubic (bcc) phase with long range order is observed to occur for molecular weights >10,000. The lattice spacing increase over the molecular range was between 95Å (for MW-2000) and 206Å (for MW-23,000). For the high molecular weight melts, annealing transforms the structure from (bcc) (with long range order) to an (fcc) disordered structure with short range order.

Curing reactions of linear vinyl terminated poly(dimethylsiloxane) with a four functional hydride silane crosslinker at various stoichiometric ratios, were studied by wave propagation at ultrasonic frequencies. Longitudinal wave velocity was found to be sensitive to the covalent endlinking, and gel point in these systems.

The observed changes in longitudinal wave velocity during the reaction are governed by changes in the bulk modulus of the system.

We report a theoretical study of the equilibrium statistical mechanics of polymer chains end-grafted in the dense liquid state to a surface. We consider the special features which arise when two immiscible polymer species are present. In constrast to ungrafted polymer blends, this system has two distinct scaling regimes of strong immiscibility: endsegregated and fully segregated. We discuss the mixing energy and bistability properties in each regime using approximations valid for large chain elongation.

Recently, many works have been devoted to the study of the critical properties of the sol-gel transition. Only a few of them have dealt with the description of the properties observed on the whole range of the values of the gelation control parameter. In the present paper, we discuss the steady-state rheological properties observed near and far from the gelation threshold and we show that the effective medium theory in conjunction with the percolation model allows to understand entirely the variations of the viscosity and of the elastic modulus.

In the first part, we present the gelling polymer system under study and the experimental methods with the help of which we measured the variations of the rheological quantities versus the concentration in crosslink points. In the second part, we discuss the critical behaviors observed near the gelation threshold. Finally, in the third part, we propose an effective medium theory applied to the description of the gelling polymer and we compare the variation of the viscosity measured outside of the critical domain to the results of these effective medium calculations.

The ability to produce block copolymers has led to new materials with unique properties. The chemical connectivity of incompatible blocks forces segregation to occur at distances of the order of the block sizes. In block copolymer melts, the segregated domains form periodic ordered structures called microphases. Most block copolymers are strongly incompatible. In such cases, in order to ensure equilibrium microphase separated samples, the microphases are prepared from solution. Microphase separation in semidilute solutions of block copolymers in nonselective good solvent is analyzed. The solvent effects on the thermodynamics in the weak segregation limit are discussed. The concentration of block copolymer at the transition in good solvents, scales as φt N−.62 and in ϑ solvents as N−.5. The transitions between microphase morphologies as a function of block copolymer concentration are studied.

The influence of the gravity on fluids and mixtures near critical points or on heterogeneous materials are well known. In the present paper, we show that gravity also affects gelling systems. We report unexpected results on weakly concentrated gels which find their origin in the deformation under its own weight of the polymer network.

A reversible diffusion-limited aggregation model for self-assembling polymers has been developed with the aid of computer simulations. The calculations have been performed in three dimensions and apply to linear chains bearing an associating site at each terminus. The results reveal that the associating sites form finite-sized clusters that, in turn, lead to the assemblage of a supermolecular network. The average cluster size is found to vary with the degree of reversibility of site binding.

Measurements of the collective diffusion coefficient, for polyelectrolyte solutions at high ionic strength and in the dilute regime, are reported. The data are discussed within the framework of a persistent chain with electrostatic contribution to account for the Coulomb interactions.

We describe how molecular dynamics simulations for a relatively simple coarse grained model can be very useful for investigating the static and dynamic properties of polymers and other macromolecular liquids. We show that it is important to use a simplified coarse grained model instead of a detailed microscopic model if one is interested in studying on modern supercomputers large systems which also relax slowly. As examples we present results for isolated star polymers with f-arms and diluted gelation/percolation clusters. We find in agreement with recent neutron scattering experiments that diluted percolation clusters swell and that their fractal dimension is reduced from 2.5 to 2. We also discuss our results for a dense melt of entangled linear polymers to show that the method is effective at high density. Our results for the entangled melt cover the crossover from Rouse to reptation and strongly support the concept of reptation.

Surfactants in solution may associate into two dimensional aggregates (membranes) which self-organize either in liquid crystalline phases or in liquid isotropic phases made of connected bilayers. When specially designed surfactants or mixture of surfactants are used the elastic modulus of these membranes may be of the order kBT. In this case, thermal fluctuations are important and lead to interesting predictions among which the existence of undulation forces and logarithm corrections to thermodynamical properties, characteristic of fluctuations in two dimensional systems, have been observed experimentally.

Recently there has been a large effort to understand the statistical and phase behavior of collections of surfaces and membranes. Experimental activity has focused on the behavior of stacked films in lamellar phases of microemulsions. Here I briefly sumnmarize the role of fluctuations and undulations in four classes of films: fluid, hexatic, solid, and charged.

We study the acoustic properties of AOT micelles and microemulsions by measuring the velocity of sound as a function of droplet volume fraction and of frequency, using Brillouin scattering and ultrasonic techniques. These weakly attractive interparticle interactions lead to the formation of short–lived networks of droplets, which can support shear and result in a pronounced increase in the speed of sound at high frequencies. These networks do not persist for sufficiently long times to affect the sound velocity at lower frequencies. The increased rigidity due to the networks exhibits a percolation behavior with volume fraction, while the frequency dependence of the interactions depends on hydrocarbon chain length of the solvent. Increasing the water concentration results in an increase in interaction energy, but a decrease in the intrinsic droplet rigidity, which affects the magnitude and frequency dependence of the contribution of the microemulsion networks to the elastic constant of the suspension. A consistent picture of the viscoelastic behavior of these suspensions is obtained.

Self-diffusion coefficients from pulsed-gradient spin-echo NMR are reported for four components of the tetradecylpyridinium bromide - 85% heptane/15% pentanol - water pseudoternary system. Measurements were taken throughout the inverted microemulsion region and also in a small isotropic region beyond the domain of lamellar liquid crystals. Observations of the self-diffusion coefficients for water relative to those of the surfactant, oil and alchohol show several distinct structural transitions within the water-in-oil region of the phase diagram. The smaller isotropic region exhibits a complete inversion of phase relative to the water-in-oil region. Conductivity measurements were used to further clarify the NMR data. Subsequent small angle neutron scattering (SANS) measurements on the same system show the transition from the single particle (heavy water + Stern layer droplet) scattering regime at low water concentration to the mixed single/interdroplet scattering regime when the intermicellar distance becomes comparable to the size of the micelles.

We present results for the pressure dependence of the critical temperature (dTc/dP) for several microemulsions of n-dodecane, water, n-pentanol and sodium dodecylsulfate with critical points along a criticial line ending at a critical end point (CEP). The variation of dTc/dP as a function of the water to surfactant ratio X shows a nonlinear behavior, with large changes near the CEP, and similar to the X dependence previously observed for the correlation length amplitude ξo. From the negative sign of dTc/dP we also conclude that a possible anomaly in the density must be opposite to the anomaly recently reported for the refractive index.

In this paper we present a conceptual overview of our recently developed molecular-thermodynamic approach to predict micellization, thermodynamic properties, and phase separation of micellar solutions. A detailed exposition may be found in Ref..

Aqueous solutions of amphiphilic molecules which reversibly assemble into well defined polydisperse rod-like aggregates display a characteristic sequence of lyotropic mesophases including translational as well as orientational ordering. We have developed a model for such systems which incorporates a phenomenological description of aggregate assembly with a scaled particle calculation of the configurational entropy in the fluid dimensions and a cell theory description of the configurational entropy in the translationally ordered dimensions. The model reproduces many of the features seen in the experimental phase diagrams, including regions of isotropic, nematic, columnar and crystalline stability. In addition to the calculated phase diagram, related aggregate size distributions are reported.

Measurements of the breaking time of cylindrical micelles of cetyltrimethylammonium bromide in aqueous solutions have been performed by means of T-Jump experiments with light scattering detection. The results provide an unambiguous test of a recent theoretical model for stress relaxation.