Spatial Orientation and Order of Molecular Subunits in Films of Organic Semiconductors

A. M. Anton and F. Kremer

Peter Debye Institute for Soft Matter Physics, Leipzig University, Linnéstr. 5, 04013 Leipzig

Conjugated donor/acceptor copolymers have obtained significant attention due to their soft matter properties combined with semiconducting characteristics, which allows for their operation in organic field effect transistors or solar cells, for instance [1]. Because the devices’ macroscopic properties arise from the materials’ molecular organization, a detailed understanding of the microscopic structure is essential for targeted developments. In order to shed light on the spatial orientation and order in thin films of P(NDI2OD-T2) the technique of Infrared Transition Moment Orientational Analysis (IR-TMOA) is employed. Therefore, the absorbance of structure-specific bands depending on the inclination of the sample and on the polarization of the IR light is evaluated [2,3]. This enables to determine the tensor of absorption separately for the respective molecular moieties as well as to deduce the orientation of atomistic planes defined through the polymer subunits, relative to the substrate and hence relative to each other. We found that the solvent used for spin coating (chlorobenzene or a chloronaphthalene:xylene mixture) determines the alignment of the T2 part (either face on or edge on), whereas the NDI unit is not affected. On the other hand, the inclination of the NDI plane is well retained for diverse sample thicknesses in between nano- and micrometers.

[1] A. C. Arias, J. D. MacKenzie, I. McCulloch, J. Rivnay, A. Salleo, Chem. Rev. 110, 3 (2010). (link)
[2] A. M. Anton, R. Steyrleuthner, W. Kossack, D. Neher, F. Kremer, JACS 137, 6034 (2008). (link)
[3] A. M. Anton, R. Steyrleuthner, W. Kossack, D. Neher, F. Kremer, Macromolecules 49, 1798 (2016). (link)

Crystallization of Supramolecular Polymers Linked by Multiple Hydrogen Bonds

Pengju Pan, Jianna Bao, Xiaohua Chang, Ruoxing Chang, Guorong Shan, Yongzhong Bao

State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, P. R. China.

Supramolecular polymers (SMPs) have different crystallization behavior from conventional polymers. Crystallization of SMPs occurs in a “confined” and “dynamic” manner. Because of the reversible and stimuli-responsive natures of non-covalent bonds in SMPs, crystalline structure and crystallization kinetics of SMPs depend strongly on crystallization conditions (e.g., crystallization temperature, Tc). This offers a feasible way to tune the physical properties and functions of SMPs in processing. We first selected the 2-ureido-4[1H]-pyrimidione (UPy)-bonded poly(L-lactic acid) (PLLA) as a model SMP and investigated the crystallization kinetics, polymorphic crystalline structure, and phase transition of supramolecular PLLAs (SM-PLLAs). Crystallization rate and crystallinity of SM-PLLAs were strongly depressed as compared to the non-functionalized PLLA precursors. Crystalline structure of SM-PLLAs was sensitive to Tc. A low Tc (80~100 °C) facilitated the formation of metastable β crystals of PLLA in SM-PLLAs. The β crystals formed in SM-PLLAs transformed into the more stable α crystals in the following heating process. We further studied the stereocomplex crystallization between UPy-functionalized PLLA and poly(D-lactic acid) (PDLA). It was found that the stereocomplexation ability of PLLA and PDLA was highly improved after UPy end functionalization; this was ascribed to the enhanced interchain interaction.

[1] Chang, R. X., Pan, P. J., et al. Macromolecules 2015, 48, 7872. (link)
[2] Bao, J. N., Pan, P. J., et al. Polym. Chem. 2016, 7, 4891. (link)
[3] Bao, J. N.; Pan, P. J., et al. Cryst. Growth Des. 2016, 16, 1502. (link)

Structure and Morphology Orientation of Comb-like Polymers with Rigid Backbones

V. Danke1,2, G. Gupta1,2, and M. Beiner1,2

1Fraunhofer-Institut für Mikrostruktur von Werkstoffen und Systemen IMWS, Walter-Hülse-Straße 1, 06120, Halle, Germany
2Institut für Chemie, Martin Luther Universität Halle-Wittenberg, 06120, Halle, Germany

Comb-like polymers with rigid backbones and flexible side chains are an important class of functional materials with applications in various fields like organic semiconductors and light weight components in high performance composite materials. A common feature of such polymers is the formation of layered structures with typical spacing in the 1-3 nm range wherein the side chains (long methylene sequences) aggregate to form alkyl nanodomains [1]. Crystallographic analysis in poly (1,4-phenylene-2,5-n-didecyloxy terephthalate) (PPDOT) and poly (2,5-didecyloxy-1,4-phenylene vinylene) (DOPPV) each having 10 alkyl carbons per side chain shows that PPDOT exhibits an orthorhombic unit cell, whereas the DOPPV is characterized by a monoclinic unit cell. The interplay between backbone and side chain packing within the alkyl nanodomain leading to different crystallographic states is discussed. Investigations on molecular orientation in extruded fibers of poly (1,4-phenylene-2,5-n-dialkyloxy terephthalate)s (PPAOT) and poly (2,5-dialkyloxy-1,4-phenylene vinylene)s (AOPPV) show that the backbones in case of PPAOT align along the shear direction whereas in AOPPV they align preferentially perpendicular to the shear direction [2]. Potential reasons for the differences in the preferred orientations for PPAOT and AOPPV are considered.

[1] About different packing states of alkyl groups in comb-like polymers with rigid backbones. T. Babur, G. Gupta and M. Beiner, Soft Matter, 2016, 12, 8093-8097 (link)
[2] Interrelations Between Side Chain and Main Chain Packing in Different Crystal Modifications of Alkoxylated Polyesters. G. Gupta, V. Danke, T. Babur, and M. Beiner. J. Phys. Chem. B, 2017, 121, 4583-45. (link)

Influence of Propylene-based Elastomer on Stress-whitening for Impact copolymer

Ying Lu2, Yingying Sun1, Lan Li1 and Yongfeng Men2

1ExxonMobil Asia Pacific Research & Development Co., Ltd, 1099 Zixing Road, Minhang District, 200241 Shanghai, P.R. China
2State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Renmin Street 5625, 130022 Changchun, P.R. China

Two pure impact copolymer polypropylenes (ICP), one pure homo-polypropylene (HPP) and their compounds with different type and fraction of VistamaxxTM propylene-based elastomer (“Vistamaxx”) were used to investigate the stress whitening activated in the impact processes via ultra-small angle X-ray scattering technique. A characteristic macroscopic whitening of deformed materials was showed due to the formation of voids or cavities with a typical size up to the wavelength of visible light, that is, some hundreds of nanometers. The stress whitening presented in ICP is confirmed to be caused by the interfaces existed between ethylene-propylene (EP) rubber and polypropylene (PP) matrix, such kind stress whitening is apparently unlike the one initiated in the crystal phase of HPP. In this study, Vistamaxx with high crystallinity can adjust the compatibility of EP rubber and PP matrix which results in a reduction of interfaces, thus, a phenomenon of reduced stress whitening can be observed in blends of ICP with Vistamaxx. However, the enhancement of stress whitening can be found in blends of ICP with Vistamaxx which occupied low crystallinity. Such behaviors can be assigned to the poor compatibility between Vistamaxx and PP matrix.

Early oligomers and the process of oligomerization of the amyloid peptides Aβ40 and Aβ42

Jana Rüdel, Maria Ott

Institute of Physics, Martin-Luther-University Halle-Wittenberg

Similar to synthetic polymers like polyamides, amyloidogenic proteins as well as short peptide sequences display the inherent ability to form long and very stable fibers called fibrils. Along the pathway from a single peptide to the mature fibrils, various transient and long-lived intermediate states are formed spanning the whole range between small and mostly unstructured oligomers to well-ordered, β-sheet rich protofibrils. As early oligomeric states were found to be neurotoxic, they are a presumptive key to understand the development of neurodegenerative diseases [1].
In order to reveal the leading mechanisms of amyloid aggregation, we studied the appearance and development of early oligomeric states of the Aβ40- and the Aβ42-peptides using a combined approach of single-molecule fluorescence spectroscopy and imaging techniques, such as TEM and AFM. Additionally, thermodynamic stabilities of the detected amyloid aggregates were studied by the use of ultrafast-scanning calorimetry.
We could reveal and characterize soluble oligomers of the Aβ40- and the Aβ42-peptide and found distinct differences in terms of size distribution as well as the process of oligomerization. While the fibrillation of Aβ42-peptides includes small and large oligomers, the assembly of Aβ40-peptide display only small oligomers and an overall slower kinetic of fibril formation. We will discuss our results by the use of thermodynamic models of self-assembly.

[1] F. Bemporad and F. Chiti, Protein misfolded oligomers: Experimental approaches, mechanism of formation, and structure-toxicity relationships, Chem. Biol. 19 (2012), 315 (link)

Large area three-dimensional polarization control in P(VDF-TrFE) polymer films on graphite

R. Roth1, M. Koch2, J. Schaab2, M. Lilienblum2, T. Thurn-Albrecht1, and K. Dörr1

1Institute of Physics, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
2Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 1-5/10,
8093 Zürich, Switzerland

Ferroelectric polymers are attractive candidates for functional layers in electronic devices like non-volatile memories, piezo- and magnetoelectric sensors, and capacitor-based high speed energy storage devices. Unfortunately, such thin films often reveal low di- and piezoelectric responses due to reduced crystalline and electrical dipole order, leading to compensation effects and low effective electric performance. One of the best characterized and often applied ferroelectric polymers is poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). We will present results on micron-sized domains with three dimensional ferroelectric polarization alignment in P(VDF-TrFE) films on graphite. The ferroelectric domains have been achieved by a combined procedure of electrical poling and mechanical annealing with an atomic force microscopy tip. They show strongly increased lateral and vertical piezoresponse compared to the as-prepared film and can be deliberately written and switched.

Effects of Hofmeister Ion Series on Stability of a Salt Bridge

S. Pylaeva, H. Elgabarty, and D. Sebastiani

Theoretical Chemistry, Institute of Chemistry, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120, Halle, Germany

Salt bridges are important components of protein structure stability. They can be defined as an interaction of two aminoacid side chains of opposite charge [1]. Such Coulomb attraction interaction is sensitive to presence of other charged species in the vicinity. Concentration of charged species – free ions can be significant in a crowded environment of a living cell. Additionally Hofmeister ion series have been shown to have a significant impact on structure and dynamics of water and solvated proteins [2, 3].

We have investigated effects of Hofmeister ion series on an arginine – aspartic acid salt bridge by means of computer simulations [4]. Changes in thermodynamic properties of a salt bridge and dynamic properties of their solvation shells will be discussed in a poster.

[1] J.E. Donald, D.W. Kulp, W.F. DeGrado, Proteins, 79(3), 898 (2011). (link)
[2] C. Allolio, N. Salas-Illanes, Y.S. Desmukh, M.R. Hansen, D. Sebastiani, JPCB 117(34), 9939 (2013) (link)
[3] M.D. Smith, L. Cruz, JPCB 117, 6614 (2013) (link)
[4] M. Fyta, R. Netz, JCP 136, 124103 (2012). (link)

Amyloid peptide aggregation near interfaces

T. John1,2,3, L.L. Martin3, H.J. Risselada1,4, and B. Abel1,2

1Leibniz Institute of Surface Modification, Leipzig (Germany)
2Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, Leipzig University, Leipzig (Germany)
3School of Chemistry, Monash University, Clayton (Australia)
4Department of Theoretical Physics, Georg-August-University Göttingen, Göttingen (Germany)

Amyloid peptides aggregate into characteristic fibrils with cross-β-sheet structure, also known as amyloid plaque. They are associated with several diseases such as Alzheimer’s disease or type II diabetes. However, there is evidence that indicates the soluble transient oligomers, instead of mature fibrils, as the toxic species. Amyloid-forming peptides are natively soluble and only aggregate under certain circumstances. Comprehensive knowledge on the aggregation mechanism and a detailed characterisation of the transient species is essential to understand the physiological role of these peptides [1].

Interfaces, such as nanoparticles, can act to accelerate or inhibit peptide aggregation. Experimental studies and molecular dynamics simulations (MD) presented an accelerated fibril formation in the presence of citrate-stabilised gold nanoparticles [2,3]. The role of gold surfaces in oligomer formation and peptide aggregation is discussed in this study. Moreover, possible mechanisms for the observed acceleration of the peptide aggregation by a reduction of the conformational space that is sampled are presented.

[1] F. Chiti, and C.M. Dobson, Annu. Rev. Biochem., 75, 333 (2006). (link)
[2] A. Gladytz, B. Abel, and H.J. Risselada, Angew. Chem., Int. Ed., 55, 11242 
(2016). (link)
[3] A. Gladytz, M. Wagner, T. Häupl, C. Elsner, and B. Abel, Part. Part. Syst. 
Charact., 32, 573 (2015). (link)

Crystallization-Driven Reversible Actuation in Cross-Linked Poly(ε-caprolactone)

O. Dolynchuk1, I. Kolesov2, D. Jehnichen3, U. Reuter3, H.-J. Radusch4, and J.-U. Sommer3

1Institute of Physics, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle, Germany
2Interdisciplinary Center for Transfer-oriented Research, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
3Leibniz-Institut für Polymerforschung Dresden e.V., 01069 Dresden, Germany
4Center of Engineering Sciences, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany

Crystallization of the pre-deformed polymer network under constant load can result in a non-trivial macroscopic elongation accompanied by network stiffening, which is reversible upon melting. Such actuation, known as the reversible shape-memory effect (rSME), is in focus due to fundamental interest of underlying molecular mechanisms and numerous potential applications. The rSME was studied in cross-linked linear poly(ε-caprolactone) (PCL) under various constant loads [1]. A striking rSME under stress-free conditions was found in PCL with the highest obtained cross-link density. The viscoelastic and thermal properties of the material as well as size and orientation of the crystals formed in PCL networks under and without load were investigated. As concluded, the directed growth of crystals is the origin of the reversible actuation in both loaded and free-standing PCL. The mean field approach was employed to calculate the free energy change during non-isothermal crystallization of PCL networks under load, whereby the possible morphology and orientation of crystals were analyzed. The analytical results on the nanocrystalline structure along with fitting curves of the temperature dependent strain, which were obtained by modeling the SME in PCL under load, are in good accordance with experimental findings.

[1] O. Dolynchuk, I. Kolesov, D. Jehnichen, U. Reuter, H.-J. Radusch, J.-U. Sommer, Macromolecules 50, 3841 (2017). (link)

Transition from Ring- to Chain-Dominated Phases in Supramolecular Polymer Networks

E. Lee, T. Shakirov, and W. Paul

Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06099 Halle (Saale), Germany

Rheological properties of supramolecular polymers depend on their structures including the size, the number, and the topology of aggregates. A linear polymer with hydrogen bonding units at both ends is one of widely used precursors to build the supramolecular polymer networks. Due to complex interplay between chain stiffness, hydrogen bonding interaction, and polymer conformational entropy it is difficult to theoretically predict the structure of the supramolecular polymer. In this work, we investigate structures of supramolecular polyethylene glycol and polybutylene glycols whose ends are capable of the hydrogen bond using a coarse-grained (CG) model via stochastic approximation Monte Carlo simulation (SAMC) method. Our CG force field is constructed by Boltzmann inversion of the probability distributions of all-atom polymer conformations. SAMC provides all the thermodynamic information of the system, which allows one to investigate supramolecular structures in a wide temperature range. This work especially focuses on the transition from ring- to chain-dominated phases since the contaminant of rings in a melt is known to significantly influence its rheology. In a limit of dilute concentration, the transition temperature (T*) shows non-monotonous behavior as molecular weight of the precursor increases due to competition between chain stiffness and hydrogen bonding. We also investigate the polymer concentration (c) dependence on T* to construct a c-T phase diagram.