The local structure of conjugated
polymers governs key
optoelectronic
properties, such as charge conduction and photogeneration at donor–acceptor
interfaces. Because conjugated polymers are large, stiff, and relax
slowly, all-atom molecular dynamics simulations are computationally
expensive. Here, we describe a coarse-graining method that exploits
the stiffness of constituent aromatic moieties by representing each
moiety as rigidly bonded clusters of atoms wherein virtual sites replace
several atoms. This approach significantly reduces the degrees of
freedom while faithfully representing the shape and interactions of
the moieties, resulting in 10 times faster simulations than all-atom
simulations. Simulation of a donor polymer (P3HT) and a non-fullerene
acceptor (O-IDTBR) validates the coarse-graining method by comparing
structural properties from experiments, such as the density and persistence
length. The fast simulation produces equilibrated systems with realistic
morphologies. The simulation results of an equimolar mixture of P3HT,
with a molecular weight of 1332 g mol–1, and an
O-IDTBR mixture suggest that the interface width must be larger than
7 nm. Also, we investigate the effect of slow cooling on morphologies,
particularly the number of close contacts that facilitates carrier
transport. Slow cooling increases close contacts, and the effect is
more pronounced in crystal-forming P3HT than in O-IDTBR, where bulky
side-groups hinder crystal formation.
The excess free energy of mixing $\Delta G_{ex}$ governs the phase behavior of mixtures and controls material properties. It is challenging, however, to measure $\Delta G_{ex}$ in simulations. Previously, we...
Dutta, S.; Nimbalkar, V.; Pande, P.; Dhumal, S.
AbstractProcess modeling of conveyer dryer for cellulosic fibre drying demands many fundamental insights. Present study highlights detailed cellulosic fibre drying aspects like mass transfer correlation relating mass transfer rate with process conditions, normalized drying curve and critical moisture content. Cellulosic fibre drying follows falling rate period, where rate of mass transfer decreases with moisture content. Conveyer dryer process model for commercial cellulosic fibre drying was developed and validated successfully. Moderate drying strategy derived based on developed process model and drying fundamentals was deployed at commercial scale which helped in reducing the moisture variability.
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