TY  - JOUR
A1  - Everaers, Ralf
A1  - Karimi-Varzaneh, Hossein Ali
A1  - Fleck, Franz
A1  - Hojdis, Nils
A1  - Svaneborg, Carsten
T1  - Kremer–Grest Models for Commodity Polymer Melts: Linking Theory, Experiment, and Simulation at the Kuhn Scale
JF  - Macromolecules
N2  - The Kremer–Grest (KG) polymer model is a standard model for studying generic polymer properties in molecular dynamics simulations. It owes its popularity to its simplicity and computational efficiency, rather than its ability to represent specific polymers species and conditions. Here we show that by tuning the chain stiffness it is possible to adapt the KG model to model melts of real polymers. In particular, we provide mapping relations from KG to SI units for a wide range of commodity polymers. The connection between the experimental and the KG melts is made at the Kuhn scale, i.e., at the crossover from the chemistry-specific small scale to the universal large scale behavior. We expect Kuhn scale-mapped KG models to faithfully represent universal properties dominated by the large scale conformational statistics and dynamics of flexible polymers. In particular, we observe very good agreement between entanglement moduli of our KG models and the experimental moduli of the target polymers.
Y1  - 2020
U6  - http://dx.doi.org/10.1021/acs.macromol.9b02428
SN  - 1520-5835
VL  - 53
IS  - 6
SP  - 1901
EP  - 1916
PB  - ACS Publications
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Eckert, Alexander
A1  - Abbasi, Mozhdeh
A1  - Mang, Thomas
A1  - Saalwächter, Kay
A1  - Walther, Andreas
T1  - Structure, Mechanical Properties, and Dynamics of Polyethylenoxide/Nanoclay Nacre-Mimetic Nanocomposites
JF  - Macromolecules
N2  - Nacre-mimetic nanocomposites based on high fractions of synthetic high-aspect-ratio nanoclays in combination with polymers are continuously pushing boundaries for advanced material properties, such as high barrier against oxygen, extraordinary mechanical behavior, fire shielding, and glass-like transparency. Additionally, they provide interesting model systems to study polymers under nanoconfinement due to the well-defined layered nanocomposite arrangement. Although the general behavior in terms of forming such layered nanocomposite materials using evaporative self-assembly and controlling the nanoclay gallery spacing by the nanoclay/polymer ratio is understood, some combinations of polymer matrices and nanoclay reinforcement do not comply with the established models. Here, we demonstrate a thorough characterization and analysis of such an unusual polymer/nanoclay pair that falls outside of the general behavior. Poly(ethylene oxide) (PEO) and sodium fluorohectorite form nacre-mimetic, lamellar nanocomposites that are completely transparent and show high mechanical stiffness and high gas barrier, but there is only limited expansion of the nanoclay gallery spacing when adding increasing amounts of polymer. This behavior is maintained for molecular weights of PEO varied over four orders of magnitude and can be traced back to depletion forces. By careful investigation via X-ray diffraction and proton low-resolution solid-state NMR, we are able to quantify the amount of mobile and immobilized polymer species in between the nanoclay galleries and around proposed tactoid stacks embedded in a PEO matrix. We further elucidate the unusual confined polymer dynamics, indicating a relevant role of specific surface interactions.
Y1  - 2020
U6  - http://dx.doi.org/10.1021/acs.macromol.9b01931
SN  - 1520-5835
VL  - 53
IS  - 5
SP  - 1716
EP  - 1725
PB  - ACS Publications
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Mennicken, Max
A1  - Peter, Sophia K.
A1  - Kaulen, Corinna
A1  - Simon, Ulrich
A1  - Karthäuser, Silvia
T1  - Transport through Redox-Active Ru-Terpyridine Complexes Integrated in Single Nanoparticle Devices
JF  - The Journal of Physical Chemistry C
N2  - Transition metal complexes are electrofunctional molecules due to their high conductivity and their intrinsic switching ability involving a metal-to-ligand charge transfer. Here, a method is presented to contact reliably a few to single redox-active Ru-terpyridine complexes in a CMOS compatible nanodevice and preserve their electrical functionality. Using hybrid materials from 14 nm gold nanoparticles (AuNP) and bis-{4′-[4-(mercaptophenyl)-2,2′:6′,2″-terpyridine]}-ruthenium(II) complexes a device size of 30² nm² inclusive nanoelectrodes is achieved. Moreover, this method bears the opportunity for further downscaling. The Ru-complex AuNP devices show symmetric and asymmetric current versus voltage curves with a hysteretic characteristic in two well separated conductance ranges. By theoretical approximations based on the single-channel Landauer model, the charge transport through the formed double-barrier tunnel junction is thoroughly analyzed and its sensibility to the molecule/metal contact is revealed. It can be verified that tunneling transport through the HOMO is the main transport mechanism while decoherent hopping transport is present to a minor extent.
Y1  - 2020
U6  - http://dx.doi.org/10.1021/acs.jpcc.9b11716
SN  - 1932-7455
VL  - 124
IS  - 8
SP  - 4881
EP  - 4889
PB  - ACS Publications
CY  - Washington, DC
ER  -