Macromol. Theory Simul. 3/2016

Abstract

Front Cover: The glass transition behaviors and mechanical properties of the π‐conjugated polymers, polyacetylene (PA) and poly(para‐phenylene vinylene) (PPV), are predicted using atomistic simulations and compared with experimental measurements. The cover shows a molecular dynamics simulation box consisting of PPV molecules. The box, each side of which is about 7.4 nm, is filled with 60 polymer chains that are 40 monomer units long. The stresses generated upon subjecting the simulation box to small deformations are calculated employing force field parameters, and then used to determine the Young's modulus and the Poisson's ratio of the polymer. Also shown are representative data from nanoindentation measurements of PA and PPV at room temperature. Further details, including the temperature variations of the specific volumes, the cohesive energy densities, the torsion angle distributions, and the characteristic ratios of the two polymers, can be found in the article by Ramaswamy I. Venkatanarayanan, Sitaraman Krishnan,* Arvind Sreeram, Philip A. Yuya, Nimitt G. Patel, Adama Tandia, and John B. McLaughlin on page 238.

Dynamic Crosslinking of Polyethylene by Hydrogen Bonding Grafted Motifs: A Molecular Dynamics Simulation Study

“…Ramaswamy et al. [ 56 ] showed that the resulting volumetric thermal expansion coefficient, α, from molecular dynamics simulation, defined by Equation , was quite consistent with the experimental observations of Boyer and Spencer [ 57 ] for several common polymers. Using the resulted Tg value, the product α 2 Tg ≅ 0.1, which is consistent with experimental prediction.…”

“…[51] Also, as the glass transition of polymers exhibits a free volume dependency relationship, the temperature-free volume relationship was used to examine the glass transition temperatures for all samples. [52] The free volume and occupied volume of PE and ODIN-PEHEMAs boxes were calculated using the Connolly task in the Biovia Materials Studio software. The simulated fractional free volumes (FFV) of the polymers are dependent on the chosen Connolly radius since these were used as the probe particles.…”

“…The MSD of atoms at time t is given as follows: $$$$\begin{equation}{\mathrm{MSD\;}} = \frac{1}{N}\;\mathop \sum \limits_{i\; = \;0}^{N - 1} {\left| {\overrightarrow {{R_{\mathrm{i}}}} \left( t \right) - \overrightarrow {{R_{\mathrm{i}}}} \left( 0 \right)} \right|^2}\end{equation}$$$$where $$\overrightarrow {{R_i}} $$(t)denotes the current position of the i th atom at time t , and N is the total number of atoms of a given type. [ 52 ]…”

Stretchable Polymer Semiconductors for Plastic Electronics

“…However, this technique is nonideal for thin films below 1 µm thick, as the substrate could interfere with the measured modulus . It was shown that the modulus obtained from nanoindentation of 3 µm thick conjugated polymer films have good agreement to values from molecular dynamics simulations . For sub‐100 nm films however, atomic force microscopy (AFM) nanomechanical mapping may be more appropriate.…”

“…Nanoindentation is another standard technique often used to characterize the tensile modulus of thin films and had been used for conjugated polymers . However, this technique is nonideal for thin films below 1 µm thick, as the substrate could interfere with the measured modulus .…”