Jean-Claude Wittmann

Structure of colloidal particles in water oil mixtures stabilized by polymeric emulsifiers: 1. Phase diagrams and electron microscope studies

Abstract The phase diagrams of toluene/water mixtures, stabilized by amphiphilic graft copolymers in the presence of an alcohol, show two domains in which these systems are optically clear. The composition of the continuous phase of the polymeric microemulsions was determined by dialysis experiments. The results indicate a preferential solvation of the copolymer sequences by the ternary solvent mixture. The micellar particles were observed by electron microscopy on carbon replicas of freeze-fractured samples. Depending on the copolymer composition and the location of the system in the phase diagram, the micrographs reveal either individual particles ( 50 A radius A ), well-dispersed in the continuous medium, or inter-particle clusters.

Eutectic solidification and oriented growth in mixtures of polyethylene and 1,3,5-tribromobenzene

Abstract The melting and crystallization behaviour of mixtures of linear polyethylene and 1,3,5-tribromobenzene has been investigated by differential scanning calorimetry, optical and electron microscopy. The phase diagram reveals the existence of a pseudo-binary eutectic (polymer volume fraction of about 58%; T m =116°C). The experimental observations are compared with the predictions of the Flory-Huggins theory of melting point depression. The polyethylene component of the eutectic assumes a habit in which lamellae are highly oriented with the chains in the [110] contact plane parallel to the tribromobenzene needle axes. This well defined orientation is most probably based on an epitaxial relation between polymer and substrate.

Structural properties and topological defects of swollen polymeric mesophases: Low angle X-ray diffraction and optical microscopic studies

Abstract Homogeneous mesophases encountered in water-toluene mixtures stabilized by polystyrene-poly(ethylene oxide) graft copolymers in the presence of 2-propanol are investigated. In these four-component systems, mesomorphic phases are produced for fairly high values of the copolymer/2-propanol ratio close to the transition region between cloudy and transparent systems. Low angle Xray diffraction studies show evidence of lamellar and reversed hexagonal structures, according to the composition of the systems. By addition of 2-propanol, the birefringent phases undergo a transition to isotropic systems which have either a cubic structure or consist of reversed water-swollen micelles. The existence of mesomorphic phases was further confirmed by optical microscopic investigation. These dilute polymeric mesophases exhibit a great variety of textures similar to those encountered in low molecular-weight lyotropic systems (soaps). For lamellar structures, typical textures such as classical focal conics, oily streaks, or batonnets are described and discussed. In addition, well-resolved polygonal arrays, interpreted recently in terms of a parabolic focal conic structure by Rosenblatt et al. , are also observed. The textures most commonly found for hexagonal structures include fan-shaped and striated ones. These observations have been complemented by flow birefringence measurements.

Quantitative analysis of electron diffraction data from epitaxially grown crystals

Abstract Epitaxial growth produces oriented crystal projections where a long unit cell axis is parallel to the major crystal face rather than perpendicular to it and thus provides a favorable condition for electron diffraction data collection which minimizes perturbations due to elastic crystal bending. Even though the crystals are not so perfect as those produced by solution growth, the intensity data from them have been useful for the quantitative crystal structure analysis of several molecular organic compounds and linear polymers as discussed in this review.

Solubilization of Immiscible Liquids Into Mesophases Formed from Amphiphilic Block Copolymers

Abstract Optical microscopy and X-ray diffraction studies reveal the presence of highly swollen mesophases in four-component systems containing amphiphilic triblock copolymers. According to the composition of the system, lamellar phases or hexagonal structures are produced. The polymeric mesophases exhibit textures very similar to those encountered in low molecular weight liquid crystalline phases.