Scientific publications

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Title	Year
Syndiotactic Polystyrene Films with Different Uniplanar Orientations: Additional Information on Crystal Phase Transitions 2013, Paola Rizzo, Alexandra R. Albunia, Gaetano Guerra. Syndiotactic Polystyrene Films with Different Uniplanar Orientations: Additional Information on Crystal Phase Transitions Macromolecular Chemistry and Physics, 214 (-), 2013, 41-45 Syndiotactic polystyrene δ form fi lms, exhibiting a // c // and a ⊥ c // uniplanar orientations and subjected to annealing procedures in the temperature range of 60–130 ° C, have been thoroughly characterized by X-ray diffraction. The reported results indicate that the gradual irreversible transformation from the nanoporous δ phase toward the dense γ phase occurs with a continuous transformation of the 010 and 210 reflections of the δ form into the 020 and 200 refl ections of the γ form, respectively. This analysis allows ruling out of the occurrence of a new refl ection typical of an intermediate phase, as suggested by X-ray diffraction measurements on unoriented or axially oriented samples. printme	2013
Control of guest transport in polymer films by structure and orientation of nanoporous-crystalline phases 2013, Alexandra R. Albunia, Paola Rizzo, Gaetano Guerra. Control of guest transport in polymer films by structure and orientation of nanoporous-crystalline phases Polymer, 54, 2013, 1671-1678 The possibility to control guest transport in polymer films, by selecting between available nanoporous-crystalline phases and their uniplanar orientations, is explored. The study is conducted on syndiotactic polystyrene films, presenting a nanoporous-crystalline phase (d or ε) or the dense g phase and exhibiting uniaxial orientation or each of the three known uniplanar orientations. In particular, the different films are compared as for the uptake of a relevant pollutant (1,2-dichloroethane) from dilute aqueous solutions. High guest solubility is observed only for films exhibiting the nanoporous-crystalline phases while the diffusivity is minimum for d form films with a//c// orientation and maximum for ε form films with ct uniplanar orientation. These results can be easily rationalized on the basis of crystal structure considerations. printme	2013
Linking Chemically Specific Structure Information to Physical Properties of Polymers 2013, Lavinia Utiu, Vipin Agarwal, Victor Litvinov, Markus Gahleitner, Arno P.M. Kentgens. Linking Chemically Specific Structure Information to Physical Properties of Polymers Dutch Polymer Days 2013, Lunteren, NL - 18.-19.03.2013 , - (-), 2013, - Among the polymeric materials, polyolefins play an important role in nowadays, becoming an indispensable part of our daily life. They are used in many applications such as transportation, packaging, medical, consumer products, electronics, cables, insulation, building and construction. Polyolefins may be homopolymers, copolymers or terpolymers, where the comonomer can be chosen to vary properties of the resulting elastomer. These properties include the crystallinity, melting point, strength, stiffness and impact behaviour. In addition, polyolefin homo-, co- and terpolymers are the foundation material for polyolefin blends. The largest amount of homopolymers produced yearly is polyethylene (PE) and polypropylene (PP). All PE and PP’s are semicrystalline, comprising crystalline and amorphous regions. It is known that the amount, length and position on the chain of branches in polyethylene strongly affect the crystallinity of the materials. An important question in the design of polyolefin (co)polymers is how the substituent sidechains are organized in the crystalline/amorphous regions and how this influences the physical properties of the polymer. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful technique to characterize materials and particularly polymers. It provides unique insight since it allows the characterization of the structure and dynamics both in the crystalline and amorphous regions. printme	2013
Polypropylene/Polyethylene Blends as Models for High-Impact Propylene–Ethylene Copolymers, Part 1: Interaction Between Rheology and Morphology 2013, Cornelia Kock, Markus Gahleitner, Alois Schausberger, Elisabeth Ingolic. Polypropylene/Polyethylene Blends as Models for High-Impact Propylene–Ethylene Copolymers, Part 1: Interaction Between Rheology and Morphology J.Appl.Polym.Sci., 128 (-), 2013, 1484–1496 In this work, composition effects on interfacial tension and morphology of binary polyolefin blends were studied using rheology and electron microscopy. The amount of dispersed phase (5–30 wt %) and its type [ethylene–octene copolymer, linear low density polyethylene (LLDPE), and high-density polyethylene] was varied, and the influence of different matrix materials was also studied by using a polypropylene homopolymer and a ethylene–propylene (EP) random copolymer. The particle size distribution of the blends was determined using micrographs from transmission electron microscopy (TEM). A clear matrix effect on the flow behaviour could be found from the viscosity curves of the blends. Analyzing the viscosity of the blends applying the logarithmic mixing rule indicated a partial miscibility of the EP random copolymer with low amounts of the LLDPE in the melt. Micrographs from TEM also showed a clear difference in morphology if the base polymer is changed, with PE lamellae growing out of the inclusions or being present directly embedded in the matrix. To verify these findings, the interfacial tension was determined. The applicability of Palierne’s emulsion model was found to be limited for such complex systems, whereas Gramespacher–Meissner analysis led to interfacial tensions comparable with those already reported in the literature. The improved compatibility when changing the matrix polymer from the homopolymer to the random copolymer allows the development of multiphase materials with finer phase structure, which will also result in improved mechanical and optical performance. printme	2013
Cooling rate effects on crystal modification development in beta-nucleated polypropylene 2013, Daniela Mileva, Markus Gahleitner, ayret Mollova, Rene Androsch. Cooling rate effects on crystal modification development in beta-nucleated polypropylene ASPM 2013 - 3rd Austrian-Slovenian Polymer Meeting, Bled / SI, 3.-5.4.2013, - (-), 2013, - The present work provides comprehensive information about the condition of formation and the stability of different polymorphs in isotactic polypropylene (iPP) containing a beta nucleating agent. Cooling the quiescent melt at rates lower than 50 K s–1 resulted in formation of betaa-crystals. Solidification at rates between 50 and 300 K s–1 let to replacement of the beta-phase by alpha-crystals. Faster cooling was connected with formation of mesophase. Fast scanning chip calorimetry revealed different mechanisms of nucleation at low and high supercooling, confirmed by the different crystal geometry demonstrated by atomic force microscopy analysis. printme	2013
Heterogeneous Ziegler-Natta, metallocene, and post-metallocene catalysis: Successes and challenges in industrial application 2013, Markus Gahleitner, Luigi Resconi, Petar Doshev. Heterogeneous Ziegler-Natta, metallocene, and post-metallocene catalysis: Successes and challenges in industrial application MRS bulletin, 38 (3), 2013, 229-233 The success of polyolefins is governed to a big extent by the development of robust and versatile catalysts offering excellent morphology control. This review highlights the major evolution steps made in the polyolefin catalyst systems in terms of productivity and possibilities to control the molecular architecture of both polypropylene [PP] and polyethylene [PE]. Starting from the initial TiCl3–types, the continuous improvement of the Ziegler-Natta (ZN) catalysts in terms of performance and cost is the major factor behind their wide market penetration. On the other hand, metallocene (MC) and the other “single-site” catalysts enabled an unprecedented fine-tuning of chain microstructure by ligand design. In this paper a special emphasis is put on the influence of catalyst type on polymer structure characteristics like molecular weight distribution, stereoregularity, comonomer distribution and ultimately on the end-use properties of polyolefins. It is the excellent balance among price, performance, and processability which will further strengthen the position of polyolefins as dominant class of materials in the polymer industry. printme	2013
Rheology/Morphology Interaction in Polyolefin Blends: Mechanical and Optical Consequences 2013, Markus Gahleitner, Cornelia Kock, Petar Doshev, Martina Sandholzer. Rheology/Morphology Interaction in Polyolefin Blends: Mechanical and Optical Consequences AERC 2013 Conference, Leuven / BE, 02.-05.04.2013, - (-), 2013, - The phase structure and related performance of blends of polypropylene (PP) with polyethylene (PE) and possibly an amorphous ethylene-propylene ‘rubber’ (EPR) are of interest in many areas. PP-based high-impact compositions are not just used in technical applications like the automotive area, but also for advanced packaging systems combining low-temperature toughness with transparency. Also in mixed recycling of polyolefins the question of retaining high impact strength with a certain variation of composition is a key success factor. In even another case, namely the production of peel-layers for easy opening of packaging, low toughness and controlled disintegration is the target. In all cases, the performance will be defined by a combination of modifier particle size, and the particle/matrix interface quality. Several examples of model studies showing the effects of viscosity ratio, phase compatibility and the presence of EPR as compatibilizer will be presented. In some cases the full concentration range from continuous PE to continuous PP phases was investigated, and a combination of rheology and electron microscopy was found suitable to study the systems. For the mechanical and optical performance, also the differences in modulus and refractive index between the phases need to be considered. printme	2013
Crystallization of isotactic polypropylene containing beta-phase nucleating agent at rapid cooling 2013, ayret Mollova, Rene Androsch, Daniela Mileva, Markus Gahleitner, Sergio S. Funari. Crystallization of isotactic polypropylene containing beta-phase nucleating agent at rapid cooling Eur.Polym.J., 49 (-), 2013, 1057-1065 The crystallization behavior of isotactic polypropylene containing a β-phase nucleating agent has been investigated, focusing on evaluation of the effects of cooling rate and/or supercooling of the melt on the generation of different polymorphs. It has been found that β-crystals only form on cooling the melt at rates lower than about 50 K s-1 while cooling at rates between 50 and 300 K s-1 leads to formation of α-crystals; even faster cooling is connected with mesophase formation or vitrification of the entire melt. Fast scanning chip calorimetry revealed different mechanisms of nucleation at low and high supercooling. In comparison to non-nucleated iPP the presence of the β-phase nucleating agent only affects the crystallization kinetics at low supercooling, supporting the idea that ordering at high supercooling is governed by homogeneous nucleation. β-crystals, formed initially on slow cooling, melt below about 420 K on slow heating, followed by formation of few α-crystals on continuation of heating. The mesophase initially formed on fast cooling and aging at ambient temperature, in contrast, re-crystallizes directly into α-structure. The results of the present work provide comprehensive information about the condition of formation and the stability of different polymorphs in isotactic polypropylene containing a β-phase nucleating agent. printme	2013
The trigonal form of i-PP in random C3/C5/C6 terpolymers 2013, Luca Boragno, P Stagnaro, Fabrizio Forlini, Fiorenza Azzurri, Giovanni Carlo Alfonso. The trigonal form of i-PP in random C3/C5/C6 terpolymers Polymer, 54 (-), 2013, 1656-1662 The formation of the trigonal structure of isotactic polypropylene (i-PP) in a series of random terpolymers of propylene (C3) with n-pentene-1 (C5) and n-hexene-1 (C6) by cooling from the molten state was investigated with the aim of assessing to what extent the intrinsic molecular disorder and the length of the side branch of the comonomers reflect on structuring kinetics and features of the crystal lattice. Experiments were performed on samples with an overall content of comonomers of ca. 25 mol% and show that, alike in the random copolymers of propylene with 1-pentene (C3/C5) or with 1-hexene (C3/C6), the trigonal modification of i-PP, delta form, develops upon cooling from the molten state also in the case of random terpolymers. At a constant molar fraction of propylene, the values of a and b axes of the unit cell linearly depend on the relative proportion of the two comonomers. Crystallinity and cell constant values as a function of terpolymer composition were provided by evaluation of data obtained from deconvoluted WAXD patterns. The development of crystallinity in isothermal conditions was followed at 0 and 20°C, both by WAXD and DSC. Results were compared with those of the correspondent C3/C5 andC3/C6 copolymers and used to confirm the kinetic model proposed in a previous paper. printme	2013
Organic field-effect transistor based sensors with sensitive gate dielectrics used for low-concentration ammonia detection 2013, Andreas Klug, Martin Denk, Martina Sandholzer, Ulrich Scherf, Christian Slugovc, Emil J.W. List. Organic field-effect transistor based sensors with sensitive gate dielectrics used for low-concentration ammonia detection Organic Electronics, 14 (-), 2013, 500-504 A novel organic field-effect transistor (OFET)-sensor concept is presented based on the application of an ion-conducting organic dielectric material, which is chemically adapted to change its electronic properties upon contact with an analyte, thereby generating an electrically detectable response. By employing pH-sensitive, ring-opening metathesis polymerized materials as gate dielectrics in bottom-contact OFETs with a meander-shaped topgate structure, the concept was successfully realized and evaluated with ammonia (NH3) as gaseous analyte, easily providing distinct sensor response at concentration levels as low as 100 ppm. In addition to current–voltage OFET-analysis, optical spectroscopy and capacitance measurements were used to rationalize the underlying sensor mechanism, which is mainly attributed to a deprotonation of the pH-sensitive groups of the active-sensing dielectrics by NH3 and a resulting generation of mobile ions, leading to an increase of the charge carrier density within the OFET channel. The proposed concept provides several advantages over existing OFET-sensor detection principles, including the separation of the sensing mechanism from the charge-transport functionality of the semiconductor, inherent protection of the latter against air exposure and increased selectivity by the application of specific dielectric materials. It therefore offers a great deal of promise in contributing to the development of cheap, integrated, smart and flexible (bio)sensor systems. printme	2013