Doris Pospiech

Facile preparation of superhydrophobic coatings by sol–gel processes

Different organic/inorganic compositions and deposition methods were used to prepare superhydrophobic surfaces using metal alkoxides and the sol-gel process. Both surface roughness and composition had to be adjusted in order to obtain very high contact angles and low contact angle hysteresis as a necessary requirement for superhydrophobicity. Multilayer samples with a fluorinated organic-inorganic top layer showed water contact angles of about 157 degrees with low hysteresis (2 degrees ). Water drops rolled easily off their surface at a tilt angle as low as 4 degrees .

Surface structure of fluorinated polymers and block copolymers

SummariesThe self-organisation of semifluorinated segments was used to create polymers and block copolymers with ultra-low surface free energy. The aromatic polyester poly(p-phenylene oxydecyl-perfluorodecyl-isophthalate) showed an extremely low value ofγsv of 9mN/m. It was proven that this low value was caused by an ordered surface structure. Introduction of these semifluorinated polyester segments into block copolymers with a basic structure (A–B)n resulted in a combination of good film-forming properties of polysulfone with the low surface free energy of the semifluorinated polyester. Thus, materials were obtained having both good mechanical performance as well as anti-adhesion properties. The block copolymers can be used to prepare blends with the respective homopolymers with different degrees of phase separation.The polymers and block copolymers can form a self-cleaning surface when coated on roughened aluminium substrates. It was shown that the adsorption of proteins, such as human serum albumin and fibrinogen from buffer solutions, significantly decreased on such polymer surfaces.RésuméL’autoorganisation des segments semi-fluorés a été utilisée pour créer des polymères et des bloc copolymères avec une énergie surfacique libre ultrabasse. Le polyester poly(p-phenylène oxydécylperfluorodécyl-isophthalate) aromatique a montré une très basse valeur deγsv de 9mN/m. Il a été prouvé que cette basse valeur était causée par une structure surfacique ordonnée. L’introduction de ces segments de polyester semi-fluorés dans des bloc copolymères ayant une structure fondamentale (A–B)n a ajouté les bonnes qualités du polysulphone vis à vis de la formation du feuil à la basse énergie surfacique libre du polyester semi-fluoré. Donc on a obtenu des matériaux qui démontraient une bonne performance mécanique aussi bien que des propriétés d’anti-adhésion. Les bloc polymères peuvent être utilisés avec les homopolymères respectifs pour préparer des mélanges ayant de différents degrés de séparation de phase.Les polymères et les bloc polymères peuvent former une surface autonettoyante quand ils revêtissent un substrat d’aluminium rendu rugeux. On a montré que l’adsorption des protéines telles que le sérum humain, albumine et le fibrinogène des solutions tampon diminue sur de telles surfaces polymériques.ZusammenfassungDie Selbstausrichtung von semifluorinierten Segmenten wurde verwendet, um Polymere und Block-Copolymere mit extrem niedriger freier Oberflächenenergie herzustellen. Das aromatische Polyester Poly(p-phenylen oxydecyl-perfluorodecyl-isophthalat) zeigte einen extrem niedrigen gsv-Wert von 9mN/m. Es wurde gezeigt, daß dieser niedrige Wert auf eine gut geordnete Oberflächenstruktur zurückgeführt werden konnte.Die Hinzufügung von semifluorinierten Polyestersegmenten zu Block-Copolymeren mit einer Struktur von (A–B)n ergab eine Kombination von den guten filmbildenden Eigenschaften von Polysulfon mit der niedrigen freien Oberflächenenergie von semifluoriniertem Polyester — in anderen Worten, ein Material das gute mechanische Eigenschaften mit einer niederen Adhäsionskraft vereinbarte. Durch die Verwendung von Block-Copolymeren lassen sich Mischungen mit den respektiven Homopolymeren mit verschiedenen Graded der Phasentrennung herstellen.Die Polymere und Block-Copolymere können auf aufgerauhte Aluminiumoberflächen aufgetragen werden, wo sie eine selbstreinigende Oberfläche bilden. Es wurde ausserdem gezeigt, daß die Adsorption von Proteinen wie Serum Albumin oder Fibrinogen von Pufferlösungen auf so beschichteten Oberflächen deutlich zurückging.

Synthesis and Phase Separation Behaviour of High Performance Multiblock Copolymers

The phase separation behaviour of block copolymers of the type (A–B) n (segmented block copolymers, multiblock copolymers) containing segments with different degrees of flexibility was investigated using a stepwise variation of the incorporated blocks A and B. Amorphous/rigid blocks (polysulfone segments) were systematically combined with amorphous/flexible blocks (poly(tetramethylene glycol), semiflexible/nematic blocks (different kinds of aromatic polyesters and poly(ester imides) as well as semicrystalline fluorinated polyester blocks). All multiblock copolymers were synthesized using a conventional transesterification polycondensation in the melt and the polycondensation results are discussed. The phase separation in the synthesized block copolymers was investigated both experimentally and theoretically. Flory–Huggins interaction parameters of the block copolymers were calculated and used together with mean field calculations in order to understand the phase separation behaviour of all block copolymers correlated to their chemical structure. On the other hand, the onset of phase separation in a series of block copolymers with a systematic variation of block molecular weights was examined experimentally, mainly by DSC and SAXS. Finally, the question is discussed whether or not the degree of phase separation in the investigated systems determines the properties of the polymers or not. This is for example outlined for the mechanical properties and, in particular, the surface properties of fluorinated block copolymers.

Modelling of the phase separation behaviour of semiflexible diblock copolymers

For a realistic theoretical description of the structure factor and the phase behaviour of melts of block copolymers, the partial stiffness of the chains has to be taken into account, particularly for diblocks consisting of blocks of very different chain stiffness. In this paper, a simple theoretical description for the structure factor of semiflexible microdisperse diblock copolymers is presented. It is derived by introducing the persistence length in addition to the monomer length and is based on the random phase approximation (RPA) in combination with a cumulant expansion for the semiflexible form factor. The persistence lengths of the two blocks are in general different and arbitrary, encompassing all experimentally important cases of Gaussian-Gaussian, semiflexible-semiflexible, rod-rod, Gaussian-semiflexible, Gaussian-rod and semiflexible-rod diblocks. It is shown that the formalism is capable of predicting reasonable structure factors and spinodals for semiflexible diblock copolymers. In particular, the experimentally observed unsymmetry of the spinodals for copolymers with blocks of different stiffness is reflected in the theory, as presented in this investigation.

LC multiblock copolymers containing polysulfone segments. I. Synthesis and morphology

Multiblock copolymers offer the possibility to combine the properties of different polymers. Thus, new materials with tailor-made unique properties are available by coupling of different suitable polymeric segments. The goal of the work discussed in this paper was to combine advantageous properties of liquid-crystalline polymers (LCP) with those of polysulfone (PSU). Therefore, liquid crystalline poly(ethylene terephthalate-co-1,4-oxybenzoates) were connected with PSU oligomers. Chemically homogeneous multiblock copolymers with high molecular weight were obtained by a melt transesterification procedure. It was demonstrated by wide angle x-ray scattering (WAXS), polarizing microscopy, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) that the properties of the multiblock copolymers (solid phase structure, phase behavior, morphology, glass transition, and melting behavior) can be balanced by the segment length of the incorporated blocks. The investigations clearly reveal the existence of a two-phase structure. However, a change of properties compared to the corresponding homopolymers refers to certain interactions between the phase due to the chemical connection of the LCP and PSU segments.

Self-assembly and viscoelastic properties of semifluorinated polyesters

The structure and dynamics of polyesters composed from a rigid aromatic backbone and oxyalkylperfluoroalkyl side chains have been studied using differential scanning calorimetry, small- and wide-angle X-ray scattering, pressure-volume-temperature measurements and rheology. The system was found to undergo three phase transitions. Starting from lower temperatures they reflect the melting of the fluorinated side chains, the unfreezing of the backbone mobility and the melting of the smectic layered structure. In addition, rheology has shown that these compounds are thermorheologically complex at all temperatures investigated and exhibit non-Newtonian low-frequency response.

Effect of multiblock copolymers in polymer blends

The use of multiblock copolymers for the compatibilization of immiscible polymer blends is controversially discussed in the literature. Investigations have been carried out to estimate the effect of multiblock copolymers containing segments of a liquid crystalline polyester (LCP) and polysulfone (PSU) segments in blends of the based homopolymers. One goal was to determine whether multiblock copolymers provide an opportunity for compatibilizing PSU/LCP blends. By using PSU/LCP multiblock copolymers with different molecular weights of the blocks in the appropriate binary, solution-casted blends, it was shown that the interpenetration of the polysulfone phase of the block copolymer and the PSU matrix leads to an improved miscibility of the blend. This effect is retained in ternary blends of PSU, LCP, and the multiblock copolymer, assuming a certain critical molecular weight of the multiblock copolymer segments. In addition, some mechanical characteristics of PSU/LCP melt blends such as the E-modulus and fracture strength are improved by adding long-segmented multiblock copolymers.

Hydrophilic modification of polysulfone via incorporation of poly(oxy-1,4-butanediyl) segments

Polysulfone was modified by incorporation of hydrophilic poly(oxy-1,4-butanediyl) [synonyms: poly(tetramethylene ether glycol), PTMG, poly(tetrahydrofuran), poly(THF), poly(tetramethylene oxide)] units into the polysulfone chain resulting in the formation of segmented block copolymers. These block copolymers were prepared by a melt transesterification procedure. The influence of the molecular weights of both, polysulfone and PTMG segments on the solid phase structure, the thermal behavior, the wetting behavior as well as the surface composition of the products was studied. It was shown that the incorporation of hydrophilic PTMG segments leads to a significant hydrophilization of polysulfone that partially results in an enhanced swelling ability.

W.a.x.s. and force field constrained RIETVELD modelling of meta-linked fully aromatic copolyesters: 1. Poly(p-phenylene isophthalate)

Abstract Fully aromatic copolyester with regular chain structure containing kinked monomer units were investigated by powder diffraction experiments combined with structure modelling. Temperature dependent X-ray measurements show the existence of low and high temperature solid state modifications of poly( p -phenylene isophthalate), (IPA-HQ) n . From the X-ray scattering data, d -spacings were determined taking some experimental corrections into account. Lattice parameters as well as atom coordinates of lt -(IPA-HQ) n were calculated and optimised by means of modelling procedures based on force field constrained RIETVELD algorithms. From this, a monoclinic unit cell of lt -(IPA-HQ) n with a = 0.775 nm, b = 0.567 nm, c = 2.410 nm, β = 91.8° was found considering the chemical structure as well as interactions between the particles. The (IPA-HQ) n polyester is a typical representative of this kind of polymer with kinked monomeric, and hence is useful for further structural investigations.

In situ Synthesis of Poly(ethylene terephthalate)/layered Silicate Nanocomposites by Polycondensation

The goal of the work presented here was to develop nanocomposites consisting of layered silicates and poly(ethylene terephthalate) (PET). Two nanocomposite preparation methods were compared: first, the usual melt compounding technique, and second, in-situ synthesis of PET in presence of different types of layered silicates. Montmorillonite (MMT) without and with organophilic modification was employed as layered silicate. In most cases, PETs with acceptable properties (molecular weight and discoloration) were synthesized in presence of different MMTs although the molecular weights of the in-situ PETs were lower than the control sample. These materials were used as masterbatch for PET nanocom-posites with 5 wt.% inorganic content. The exfoliation in both types of nanocomposites was not complete, but they showed a good distribution of clay within the polymer matrix.