Annette Thierry

Low Tc growth transitions in isotactic polypropylene: β to α and α to smectic phases

SummaryTwo growth transitions are observed by optical microscopy in the low Tc range (105–80°C) of isotactic polypropylene (iPP): β to α and α to (probably) smectic phases. These transitions (notably β to α) may be the cause of the complicated annealing and recrystallization behaviour of β iPP, which is known to depend on the initial crystallization and post-crystallization thermal history.

Epitaxy of isotactic poly(1-butene): new substrates, impact and attempt at recognition of helix orientation in form I′ by AFM

Abstract Epitaxial crystallization of isotactic poly(1-butene) (iPBu) is performed on different substrates, which help expand the range of interactive substrates used in a previous study. All three crystal forms of iPBu1, which rest on different helix and unit-cell geometries and symmetries, have been produced by epitaxial crystallization. The different epitaxial interactions are discussed. Epitaxial crystallization of form I′ yields an exposed (110) contact plane. The films have true single crystal structure; they display electron diffraction patterns with sharp peaks, but also characteristic streaks due to the co-existence of up and down helices in the crystal structure (anticline helices). The streaks are modelled with a ‘Diffraction faulted’ program. Further, this same (110) contact face of Form I′ provides the potential to observe in direct space (i.e. by AFM) the up or down orientation of helices. Such a possibility would require differentiation by AFM of a methyl group from an ethyl group of the side chains. The AFM resolution reached in our investigation falls short of doing so, but the problematics could be adapted to other, more suitable polymers.

Structural characterisation of single crystals and thin films of α,ω-dihexylquaterthiophene

Single crystals and thin films of the p-type organic semiconductor α,ω-dihexylquaterthiophene have been studied using X-ray diffraction and TEM, respectively. The single crystal analysis reveals the presence of monomolecular layers of quaterthiophene cores with terminally bound hexyl chains. A herringbone molecular packing akin to that exhibited by the parent quaterthiophene molecule is observed. Electron diffraction of thin films on silica clearly shows the crystalline polymorph of the solution-grown crystals and the crystallites deposited by organic molecular beam deposition are identical. However, thin film crystallites are severely affected by multiple twinning.

Crystal structure of polycrystalline films of quaterthiophene grown by organic molecular beam deposition

Abstract The growth of thin films of oligothiophenes by organic molecular beam deposition (OMBD) can produce highly ordered polycrystalline samples. Recently, quaterthiophene (4T) thin films were grown on different substrates (silica, graphite, potassium acid phthalate, silicon). In some cases, their optical behavior was found to resemble that of 4T single crystals, with a macroscopic anisotropy close to that of the bulk crystal. A careful structural characterization of these films was undertaken. A morphological and optical characterization was performed by atomic force microscopy (AFM) and optical absorption. Electron microscopic examination in both bright field and diffraction was carried out on 4T thin films deposited on two selected substrates: silica and single crystals of potassium phthalate acid salt. The crystal polymorph, contact plane, and coherent orientation obtained on these 4T micro-crystalline films fully agree with the optical behavior of the samples.

Key role of solvent type in organogelation

In this paper we again assess the role played by the solvent type in the organogelation process of photo/electroactive oligo (para-phenylene vinylene) (OPV) molecules . In this aim we have investigated gelation in benzyl alcohol, a polar solvent, and trans-decahydronaphthalene, an apolar solvent. Several techniques have been used: DSC, SEM, AFM, TEM, X-ray diffraction, UV-vis, and fluorometry. We have observed that the gel thermodynamics (T–C phase diagram), morphologies, molecular order, and optical properties differ considerably with the solvent type. The results are discussed by considering the interaction of the solvent with the different moieties of the OPV molecule. The reason why fibrils are obtained instead of 3-D crystals is also considered on the basis of micro-diffraction experiments performed by electron microscopy on finite aggregates.

Epitaxial crystallization of isotactic poly(4-methyl-pentene-1)

The crystallization of isotactic poly(4-methylpentene-1) in its stable tetragonal crystal modification based on the 72 helix conformation was achieved on three different low molecular weight organic substrates and on polytetrafluoroethylene. The contact face was always the (100) face, although the details of the epitaxial relationships generated one, two, or even three chain axis orientations in the polymer epitaxial overgrowth.

UNUSUAL CRYSTALLIZATION AND MELTING PROCESSES OF AN OPTICALLY ACTIVE POLYOLEFIN: ISOTACTIC POLY((S)-4-METHYL-HEXENE-1)

Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization.

Mixing of a self-assembled supramolecular polymer and a covalent polymer in organic solutions☆

We report on a neutron scattering study of the molecular structure of a self-assembled supramolecular polymer composed of a bicopper complex within a solution of a covalent polymer (atactic polystyrene/trans-decalin). The study is achieved by putting two binary phases in contact and allowing for diffusion of both components in either phase. It is shown that the one-dimensional bicopper filaments are compatible to a high extent with the atactic polymer. These results are discussed in the light of a recently devised encapsulation process of the bicopper filaments within the fibrils of a physical network of isotactic polystyrene.

Recent developments in synthetic polymer crystal growth

Abstract Under the usual crystallization conditions, polymer crystal growth is dominated by the strong tendency of polymer chains to fold and form microscopic folded-chain lamellae. As described first, an original growth method called “self-seeding” has been devised to to master or improve the growth of such folded-chain lamellae or even of more complex crystalline entities like spherulites. Introduction of order at a much larger scale or formation of macroscopic polymer single crystals necessitates, however, completely different growth procedures, such as epitaxial crystallization, epipolymerization of virgin polymer processing briefly discussed herein. The aim of such procedures is to reach extended chain macroconformations either by avoiding the chain folding process or by orienting the polymer chains. Some of the techniques described can be applied as such, or with proper adjustments, to fibrous biological macromolecules.

Origine moléculaire de l'enroulement des lamelles cristallines du poly(fluorure de vinylidène), phase γ

Resume Les lamelles cristallines formant les spherolites de la phase γ du poly(fluorure de vinylidene) (γPVDF) ont une forme originale : elles sont enroulees en spirale et forment un rouleau (de type parchemin) dont le grand axe est parallele au rayon du spherolite. Cette geometrie est expliquee dans la presente note par une difference de composition chimique des plis dans les faces de repliement opposees des lamelles cristallines. La difference de structure traduit la « polaritede la structure cristalline de la phase γ, et les contraintes geometriques imposees aux repliements.