Search results for "Chemical physics"

Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities

2017

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (…

Minimizing geminate recombination losses in small-molecule-based organic solar cells

2019

Small-molecule-based organic solar cells (OSCs) are a recurrent alternative to polymer-based OSCs. Due to the higher purity and definition of small molecules compared to polymers, the morphological requirements can be more relaxed. Here, we present a series of novel rhodanine-based small-molecule electron donors and blend them with the standard acceptor PC70BM. By performing a target analysis on femtosecond spectroscopy data, we quantify the rates of geminate charge recombination. We are able to reproduce these rates by applying the Marcus–Levich–Jortner equation, using results from quantum chemical calculations. This shows that in a series of differently substituted compounds, one can corr…

Simulations of Polymers in Confined Geometries

1991

The properties of flexible polymers moving inside porous structures are believed to be relevant to practical problems such as filtration, gel permeation chromatography, heterogeneous catalysis, oil recuperation, etc.1. Similarly the adsorption of macromolecules on interfaces plays an important role for problems such as adhesion, flocculation and stabilisation of colloid particles, biological membrane function, artificial organs in medicine, etc. 2. Aside from this eventual practical application, the configurational statistics of polymers in such confined geometries is a challenging problem of theoretical physics. The present brief review will be concerned with the study of a single long fle…

Diffusion of spherical micronetworks in polymer diluent systems and melts studied by dynamic light scattering techniques

1994

Spherical polystyrene (PS) micronetworks can be prepared in microemulsion with bulk radii of 5–60 nm and different cross-linking densities. The diffusion of these PS spheres has been studied in polymer diluent systems ranging from dilute solutions to plasticized melts by using forced Rayleigh scattering and photon correlation spectroscopy. On increasing the PS concentration, a colloid glass transition is observed at a volume fraction ΦC ≈ 0.64 of the swollen spheres. At higher concentration inside the “colloid glass” state the sphere diffusion is slowed down and becomes very complex but can be observed up to the limit of a melt of collapsed spheres.

Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels

2016

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and fo…

Hybrid Lattice Boltzmann/Dynamic Self-Consistent Field Simulations of Microphase Separation and Vesicle Formation in Block Copolymer Systems

2011

We present a hybrid numerical method to introduce hydrodynamics in dynamic self-consistent field (SCF) studies of inhomogeneous polymer systems. It solves a set of coupled dynamical equations: The ...

Dynamics of entangled supramolecular polymer networks in presence of high-order associations of strong hydrogen bonding groups

2017

Dynamics of entangled polymer chains in the melt state are deliberately excluded in most of the studies on supramolecular polymer networks by utilizing nonentangled precursor chains. Relaxation of the system mainly depends on the dissociation of the associative groups in latter case and nonentangled chains deliver nothing to resist afterward. Conversely, in an entangled system, relaxation of polymer chains and dissociation of associative groups can occurred parallel. Supramolecular networks based on an entangled precursor polymer with different levels of strong associating ureidopyrimidinone (UPy) groups are synthesized to screen the corresponding effects on the dynamics of the system. Bina…

2018

Star-shaped polymers show a continuous change of properties from flexible linear chains to soft colloids, as the number of arms is increased. To investigate the effect of macromolecular architecture on the flow properties, we employ computer simulations of single chain and star polymers as well as of their mixtures under Poiseuille flow. Hydrodynamic interactions are incorporated through the multi-particle collision dynamics (MPCD) technique, while a bead-spring model is used to describe the polymers. For the ultradilute systems at rest, the polymers are distributed uniformly in the slit channel, with a weak dependence on their number of arms. Once flow is applied, however, we find that the…

Entropic Unmixing in Nematic Blends of Semiflexible Polymers.

2020

Binary mixtures of semiflexible polymers with the same chain length, but different persistence lengths, separate into two coexisting different nematic phases when the osmotic pressure of the lyotropic solution is varied. Molecular Dynamics simulations and Density Functional Theory predict phase diagrams either with a triple point, where the isotropic phase coexists with two nematic phases or a critical point of unmixing within the nematic mixture. The difference in locally preferred bond angles between the constituents drives this unmixing without any attractive interactions between monomers.

Role of Solvent Compatibility in the Phase Behavior of Binary Solutions of Weakly Associating Multivalent Polymers

2021

AbstractCondensate formation of biopolymer solutions, prominently those of various intrinsically disordered proteins (IDPs), is determined by “sticky” interactions between associating residues, multivalently present along the polymer backbone. Using a ternary mean field “stickers-and-spacers” model, we demonstrate that if sticker association is of the order of a few times the thermal energy, a delicate balance between specific binding and non-specific polymer-solvent interactions gives rise to a particularly rich ternary phase behavior under physiological circumstances. For a generic system represented by a solution comprising multi-associative scaffold and client polymers, the difference i…