Effect of Solvent Affinity on Crystallization-driven Fibril Growth Kinetics in Diblock Copolymer Solutions

Junfan Chen and Wenbing Hu

State Key Lab of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, 210023 Nanjing, China

Crystallization-driven fibril growth of one block under nano-confinement of another non-crystalline block in diblock copolymer solutions has raised the interests in two important fields. One is the self-assembly of nano-particles for hierarchical construction [1, 2]. Another is the neuro-fibrillary tangles in Alzheimer’s disease [3]. The selective affinity of solvent in two blocks may influence the kinetics of the fibril growth, on processing the nano-particle assembly or hindering the disease development. We have recently performed dynamic Monte Carlo simulations of diblock copolymers in athermal solutions, with fibril crystallization of one block induced by a crystalline template but under the confinement of another amorphous block [4]. Continue reading Effect of Solvent Affinity on Crystallization-driven Fibril Growth Kinetics in Diblock Copolymer Solutions

Thermal Behavior of Silk Protein

P. Cebe1, D. Thomas1, J. Merfeld1, B. P. Parlow2, D. L. Kaplan2, R. Alamo3, A. Wurm4, E. Zhuravlev4, and C. Schick4

1Physics and Astronomy Dept., Tufts University, Medford, MA 02155 USA
2Biomedical Engineering Dept., Tufts University, Medford, MA 02155 USA
3Chemical and Biomedical Engineering Dept., Florida State University-FAMU, Tallahassee, FL 32310 USA
4 Institute for Physics and Competence Center Calorimetry of Interdisciplinary Faculty, University of Rostock, Rostock, Germany

Silk is a naturally occurring biopolymer which has been used in textiles for over 5000 years. Silk stands as an exemplar of the class of fibrous proteins. The properties of silk protein are related to its semicrystalline nature, imparted by the secondary structures, such as the non-crystalline helices and random coils, and the crystalline beta pleated sheets. Using techniques of condensed matter polymer physics, we investigate the structure and thermal behavior of silk fibroin [1-3]. Continue reading Thermal Behavior of Silk Protein

Oriented Recrystallization of Carbon-Coated Pre-oriented Ultrathin Polymer Films

Shouke Yan, and Le Ma

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China

The recrystallization behavior of carbon-coated preoriented polymer thin films was studied by means of transmission electron microscopy combined with electron diffraction and spectroscopy. It was found that vacuum evaporated carbon layer can keep the molecular chain orientation of pre-oriented polymer thin films. This demonstrates the existence of strong fixing effect of vacuum evaporated carbon layers on the surface layer of the polymer films, which prevents the relaxation of surface extended macromolecular stems in the crystals or at least from a complete relaxing during high-temperature melting. Continue reading Oriented Recrystallization of Carbon-Coated Pre-oriented Ultrathin Polymer Films

Amyloids from the origin to the end of life

Roland Riek1, Marielle Wälti1, Cedric Eichmann, and Jason Greenwald1

1Vladimir Prelog Weg 2, ETH, ETH Hönggerberg, CH-8093 Zurich

Protein aggregation is observed in many diseases including Alzheimer’s disease. These protein aggregates are termed amyloids. Amyloids are composed of pairs of tightly interacting, many-stranded, repetitive, inter-molecular beta-sheets termed the cross-beta-sheet structure. Because of this structure, amyloids can grow by recruitment of the same protein while their repeat can transform a weak activity into a potent one through cooperativity and avidity. Continue reading Amyloids from the origin to the end of life

Avoidance of Density Anomalies as a Structural Principle for Semicrystalline Polymers

Klaus Schmidt-Rohr

Chemistry Department, Brandeis University, Waltham, Massachusetts, USA

For a detailed analysis of the crystallization process, a realistic view of the chain trajectories in the lamellar semicrystalline morphology is of interest. We have come to the conclusion that the textbook models of melt-crystallized semicrystalline polymers unintentionally but inevitably contain layers with a higher density than in the crystallites.[1] Such density anomalies can be avoided by chain ends at the crystal surface and/or chain tilt in the crystallites. NMR shows that most CH3 end groups of polyethylenes (PEs) are indeed in all-trans chains near the crystal surface. As a consequence, many chain folds cannot be tight, also in agreement with NMR data. Continue reading Avoidance of Density Anomalies as a Structural Principle for Semicrystalline Polymers

Isothermal Crystallization of Triple Crystalline Biodegradable PEO-b-PCL-b-PLLA Triblock Terpolymers

J. K. Palacios1, A. Tercjaks2, J. Zhao3, N. Hadjichristidis3, A. J. Müller*1,4

1POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU, Donostia-San Sebastián, Spain
2Chemical and Environmental Engineering Department, Polytechnic School, University of the Basque Country UPV/EHU, Donostia-San Sebastián, Spain
3King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, KAUST Catalysis Center, Thuwal, Saudi Arabia
4IKERBASQUE, Basque Foundation for Science, Bilbao, Spain

 PEO-b-PCL-b-PLLA triblock terpolymers are fascinating materials, as they can develop three different crystalline phases1. Adjusting the block composition and crystallization conditions, each block is able to crystallize sequentially and separately from a homogeneous melt. Thus, crystallization drives superstructure formation into mixed spherulites that include lamellae of PLLA, PCL and PEO. The PLLA block crystallizes first at higher temperatures upon cooling from the melt (and templates the morphology), then the PCL block, and finally the PEO block2. In this work, a three-stage crystallization protocol was applied to study the isothermal crystallization kinetics of each block. The crystallization was studied by WAXS, SAXS, DSC and AFM. At the PLLA crystallization temperatures, both PCL and PEO molten chains caused a strong diluent effect on PLLA crystallization. Continue reading Isothermal Crystallization of Triple Crystalline Biodegradable PEO-b-PCL-b-PLLA Triblock Terpolymers

Surface Nucleation and the Design of Nucleating Agents by Molecular Simulation

Alexander J. Bourque1, C. Rebecca Locker2, and Gregory C. Rutledge1

1Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge MA, USA
2ExxonMobil Research and Engineering Company, Annandale, NJ, USA

In most cases of practical interest, nucleation of polymer crystallites is believed to occur heterogeneously, through the action of additives or impurities that serve as nucleation agents, significantly reducing the activation barrier to formation of a new phase [1]. The number and activity of these nucleating agents can alter the resulting morphology of the semicrystalline polymer, for example through polymorph selection, the number and size of spherulites or the orientation of individual lamellae; the properties of the polymer can also be controlled as a consequence. The classical theories of polymer crystal growth are similarly predicated on a surface nucleation mechanism, which may proceed through one or more precursor states. We report the results of molecular simulations that examine the phenomenon of 2-dimensional nucleation on both familiar and foreign surfaces. Continue reading Surface Nucleation and the Design of Nucleating Agents by Molecular Simulation