Article
Materials Science, Multidisciplinary
Panpan Zhu, Ji Lin, Rui Xiao, Haofei Zhou
Summary: This work investigates the stress responses of pre-deformed glassy polymers using coarse-grained molecular dynamics simulations. The competition between intra-chain deformation and inter-chain friction is found to govern yielding and strain hardening. A mean-field shear transformation zone model is developed based on the physical mechanisms revealed by the simulations, which successfully captures the observed mechanical responses.
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
(2022)
Article
Chemistry, Multidisciplinary
Sandrine Lteif, Khalil Akkaoui, Samir Abou Shaheen, Maya Chaaban, Steven Weigand, Joseph B. Schlenoff
Summary: This study reports two key advances in preparing and using aqueous colloidal dispersions of polydimethylsiloxane (PDMS), demonstrating the production of PDMS nanoparticles via flash nanoprecipitation and the significant enhancement in bulk modulus in nanocomposites. The hierarchical nanostructuring within the composite, with 4 nm PDMS micelles as the smallest unit, presents a new paradigm for stabilizing liquidlike building blocks for nanomaterials.
Article
Polymer Science
Chia-Cheng Chu, Pai-Yi Hsiao
Summary: This article proposes a two-stage model to explain the phenomena of chain expansion released from a confining cavity. In the first stage, the chain is assumed to expand as a sphere, while in the second stage it expands like a coil. The kinetic equations for the variation of chain size are derived in the two stages by balancing the rate of the free energy change with the rate of energy dissipation. Langevin dynamics simulations are performed to examine the theory. The simulation results support the theory and reveal that the expansion process is dominated by the second stage, confirming the predicted curve for coil expansion.
Article
Chemistry, Physical
Matthew Mears, Zhenyu J. Zhang, Ryan C. D. Jackson, Yuchen Si, Tigerlily J. B. Bradford, John M. Torkelson, Mark Geoghegan
Summary: Fluorescence correlation spectroscopy was used to study the temperature-dependent diffusion coefficient of PEO on various surfaces, showing an increase in diffusion below T-gs for certain surfaces, accompanied by an unexpected increase in friction at the same temperature.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Chemistry, Multidisciplinary
Biao Zuo, Cheng Li, Quanyin Xu, Katelyn Randazzo, Naisheng Jiang, Xinping Wang, Rodney D. Priestley
Summary: This study demonstrates that polymer brushes with ultrahigh grafting density exhibit significantly improved thermal stability, overcoming confinement and interfacial effects to control thin-film material properties. The dense packing and molecular ordering in the amorphous state of ultradense brushes prepared by surface-initiated atom transfer radical polymerization in combination with a self-assembled monolayer of initiators play a crucial role in enhancing the thermal stability of polymer films.
Article
Polymer Science
Sanwardhini Pantawane, Stephan Gekle
Summary: In this study, atomistic and coarse-grained molecular dynamics simulations were used to investigate the conformation of a single poly(3-hexylthiopene) chain at different temperatures. It was found that bundle and toroid structures were predominantly present, with bundles becoming more abundant at lower temperatures. A comparison of atomistic and Martini-based coarse-grained models showed excellent agreement. Furthermore, the temperature dependence of P3HT was linked to that of simple Lennard-Jones model polymers in a vacuum. The addition of solvent (THF) resulted in a prominent swelling of the molecular size at around 220 K, which correlated well with experimental observations of increased frequency of bundle structures.
Article
Polymer Science
Emmanuel N. Skountzos, Katerina S. Karadima, Vlasis G. Mavrantzas
Summary: The study investigates the impact of adsorbed domains and nanoparticle bridging chains on the properties of attractive polymer nanocomposite melts through MD simulations. The presence of adsorbed polymer significantly affects the dynamic and conformational properties of the nanocomposite, especially under conditions favoring higher surface-to-volume ratios. Moreover, the bridging chains drive the formation of a nanoparticle network which becomes denser and stronger with increasing concentration of the polymer matrix in nanoparticles.
Article
Polymer Science
Tianren Zhang, Ning Wang, Robert A. Riggleman
Summary: This study investigates the mechanical properties of glassy block copolymer thin films using molecular dynamic simulations. The results show that films with fingerprint morphologies have higher toughness compared to homopolymers and oriented lamellar films, due to the increase in randomness of domain orientations and entanglements.
Article
Polymer Science
Fan Jin, Shichen Yuan, Shijun Wang, Yi Zhang, Ying Zheng, You-lee Hong, Toshikazu Miyoshi
Summary: This study investigates the crystallization mechanism of polymer chains by tracking the local chain trajectory. The results reveal that folding occurs prior to crystallization and that melt and cold crystallization proceed through rearrangements of polymer chains without inducing additional folding.
Article
Polymer Science
Weizhao Ren, Yanlong Li, Yuling Tang, Jianquan Xu, Cuiyun Zhang, Ophelia K. C. Tsui, Xinping Wang
Summary: In this study, the desorption of adsorbed chains in a bilayer system was investigated using fluorine-labeled polystyrene (PS). The results showed that the exchange of PS-flattened chains with top-free chains was slower compared to PS-loose chains, and it was highly dependent on molecular weight (MW). Interestingly, in the presence of loosely adsorbed chains, the desorption of flattened chains was greatly accelerated and had weaker MW dependence. The MW-dependent desorption was attributed to the average number of contact sites between polymer adsorbed chains and the substrate, which increased rapidly with increasing MW. Additionally, the desorption of loosely adsorbed chains provided extra conformational energy to accelerate the desorption of flattened chains.
Article
Engineering, Chemical
Andreas Schoenhals, Paulina Szymoniak, Mohamed A. Kolmangadi, Martin Boehning, Michaela Zamponi, Bernhard Frick, Markus Appel, Gerrit Guenther, Margarita Russina, Dmitry A. Alentiev, Maxim Bermeshev, Reiner Zorn
Summary: The study found that poly(tricyclononenes) with Si-substituted bulky side groups have high microporosity, making them potential candidates for active separation layers for gas separation membranes. The low temperature relaxation process involving methyl group rotation suggests that some methyl groups may be immobilized in their rotation due to steric hindrance.
JOURNAL OF MEMBRANE SCIENCE
(2022)
Article
Biochemistry & Molecular Biology
Aleksandra Wypych-Puszkarz, Onur Cetinkaya, Jiajun Yan, Ruslana Udovytska, Jaroslaw Jung, Jacek Jenczyk, Grzegorz Nowaczyk, Stefan Jurga, Jacek Ulanski, Krzysztof Matyjaszewski, Joanna Pietrasik, Marcin Kozanecki
Summary: Core-shell nanocomposites consisting of barium titanate nanocrystals grafted onto poly(methyl methacrylate) chains were prepared. The nanocomposites exhibited enhanced dielectric permittivity and improved thermal stability. The presence of ceramic nanoparticles affected the molecular dynamics and structure of the polymer chains.
Article
Chemistry, Physical
Jiaxin Wu, Zhiyong Yang, Xiaoou Cai, Linxi Zhang
Summary: The dynamics of polymer chains confined to a periodic cylinder were studied using molecular dynamics simulation and theoretical analysis. It was found that the diffusion coefficient of a confined polymer chain decreases with increasing periodicities and strongly depends on the chain monomer density. The diffusion coefficient also showed oscillation relationship with the ratio of the mean end-to-end distance to the periodicity. The results were in good agreement with theoretical analysis and can help understand the dynamics of particles in periodic media.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Polymer Science
James H. Merrill, Ruoyu Li, Connie B. Roth
Summary: The local glass transition temperature (Tg) of pyrenelabeled polystyrene (PS) chains mixed with end-tethered PS chains on a neutral silica substrate was measured. The results showed that the end-grafted chains significantly increased the local Tg of the matrix chains by approximately 45 K compared to the bulk Tg, regardless of the molecular weight and chemical end-group of the grafted chains, as well as the grafting density in the mushroom-to-brush transition regime. The immobilization of chain ends through covalent bonding in this athermal system suggests a mechanism that increases the local activation energy required for cooperative rearrangements.
Article
Chemistry, Physical
H. A. Vinutha, Fabiola Doraly Diaz Ruiz, Xiaoming Mao, Bulbul Chakraborty, Emanuela Del Gado
Summary: We investigated the spatial correlations of microscopic stresses in soft particulate gels through 2D and 3D numerical simulations. By using a newly developed theoretical framework, we predicted the analytical form of stress-stress correlations in amorphous assemblies of athermal grains that acquire rigidity under an external load. These correlations exhibit a pinch-point singularity in Fourier space, resulting in long-range correlations and strong anisotropy in real space. Our analysis of model particulate gels showed that stress-stress correlations have similar characteristics to granular solids and can be used to identify force chains. We demonstrated that these correlations can distinguish between floppy and rigid gel networks and reflect changes in shear moduli and network topology during solidification.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Polymer Science
Nils Neubauer, Martin Tress, Rene Winkler, Emmanuel Urandu Mapesa, Wycliffe Kiprop Kipnusu, Petra Uhlmann, Friedrich Kremer
Article
Chemistry, Physical
Magdalena Tarnacka, Wycliffe K. Kipnusu, Ewa Kaminska, Sebastian Pawlus, Kamil Kaminski, Marian Paluch
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2016)
Article
Chemistry, Physical
Wycliffe K. Kipnusu, Mohamed Elsayed, Reinhard Krause-Rehberg, Friedrich Kremer
JOURNAL OF CHEMICAL PHYSICS
(2017)
Article
Polymer Science
Wilhelm Kossack, Anne Seidlitz, Thomas Thurn-Albrecht, Friedrich Kremert
Article
Chemistry, Physical
Wilhelm Kossack, Martha Schulz, Thomas Thurn-Albrecht, Jorg Reinmuth, Viktor Skokow, Friedrich Kremer
Article
Chemistry, Physical
Malgorzata Jasiurkowska-Delaporte, Wilhelm Kossack, Wycliffe K. Kipnusu, Joshua R. Sangoro, Ciprian Iacob, Friedrich Kremer
JOURNAL OF CHEMICAL PHYSICS
(2018)
Article
Polymer Science
Wycliffe K. Kipnusu, Mandy M. Elmandy, Mohamed Elsayed, Reinhard Krause-Rehberg, Friedrich Kremer
Article
Chemistry, Physical
Arthur Markus Anton, Evgeny Zhuravlev, Wilhelm Kossack, Ruslan Andrianov, Christoph Schick, Friedrich Kremer
COLLOID AND POLYMER SCIENCE
(2020)
Article
Chemistry, Physical
Wycliffe Kiprop Kipnusu, Carlos Donate-Buendia, Mercedes Fernandez-Alonso, Jesus Lancis, Gladys Minguez-Vega
PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION
(2020)
Article
Chemistry, Physical
Jan Philipp Gabriel, Martin Tress, Wilhelm Kossack, Ludwig Popp, Friedrich Kremer
Summary: Density plays a crucial role in theories related to the glass transition of supercooled liquids and melts, while the interplay between intra- and intermolecular interactions in creating density remains underexplored. Using Fourier-Transform InfraRed spectroscopy on a homologous series of polyalcohols, it was found that intramolecular interactions exhibit minor changes in expansion, while intermolecular interactions show a much stronger response with distinct kinks at the glass transition temperature. The study highlights the importance of distinguishing between strong and weak intermolecular hydrogen bonds and demonstrates the necessity of atomistic simulations to understand heterogeneities in liquids and glassy systems.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Chemistry, Physical
Wycliffe Kiprop Kipnusu, Evgeny Zhuravlev, Christoph Schick, Friedrich Kremer
Summary: Nanocalorimetry and Fourier transform infrared (FTIR) spectroscopy are combined to measure the calorimetric properties and molecular spectra of PA66. The study reveals the initial steps of homogeneous nucleation on a molecular scale by determining IR difference absorption spectra. It shows that the increase in H-bonding network in amorphous domains leads to an increase in the number of H-bonded chemical moieties. However, as the sample transitions to the ordered crystalline structure, the number of H-bonded chemical moieties decreases.
COLLOID AND POLYMER SCIENCE
(2022)
Article
Polymer Science
Wycliffe Kiprop Kipnusu, Evgeny Zhuravlev, Christoph Schick, Friedrich Kremer
Summary: Fast scanning calorimetry (FSC) and Fourier transform infrared (FTIR) spectroscopy are combined to trace the evolution of the calorimetric properties and molecular interactions in a strongly crystallizing polymer, PET. The results demonstrate the high molecular specificity of homogeneous nucleation and crystallization when compared to polyamide 66.
MACROMOLECULAR CHEMISTRY AND PHYSICS
(2023)
Article
Biochemistry & Molecular Biology
Friedrich Kremer, Wycliffe Kiprop Kipnusu, Martin Fraenzl
Summary: The limitations of the Debye approximation in the theory of orientation polarization and dielectric relaxation are discussed, and specific parameters of molecular absorption are measured using infrared spectroscopy, interpreting the observed effects as caused by orientation polarization of the OH and CH2 moieties.
INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES
(2022)
Article
Chemistry, Physical
Wycliffe K. Kipnusu, Mohamed Elsayed, Ciprian Iacob, Sebastian Pawlus, Reinhard Krause-Rehberg, Marian Paluch
