We use molecular dynamics simulations to investigate the control of electroosmotic flow by grafting polymers onto two parallel channel walls. The effects of the grafting density and the electric field strength on electroosmotic flow velocity, counterion distribution and conformational characteristics of grafted chains have been studied in detail for athermal, good, and poor solvent cases. The simulation results indicate that in the range of grafting densities investigated, increasing the grafting density induces a different change tendency of electroosmotic flow velocity for three different solvent qualities. These tendencies are demonstrated to be related to counterion distribution, polymer coverage, and interactions between monomers and solvent particles. It is found that counterions tend to move toward the interface between polymer layer and solvent as the grafting density increases. Especially in the poor solvent case, most of the counterions gather near the interface at high grafting densities. A similar behavior is also observed when enhancing the electric field strength at a fixed grafting density.

Functional branched group design of a ligand to improve the stability of CsPbBr3 quantum dots for phosphor-converted applications

Using coarse-grained molecular dynamics simulations, we study the behavior of a DNA-nanosphere complex in the absence and presence of an external stretching force exerted on two ends of DNA chain. In this work, we use an accurate coarse-grained model for double-stranded DNA chain recently developed by Savelyev and Papoian [Biophys. J. 96, 4044 (2009)]. Charged particles are uniformly distributed on the surface of the sphere. Without a stretching force, an ordered or disordered complex is formed depending on the surface charge density and the salt concentration. It is found that DNA wraps randomly around the sphere only at an intermediate salt concentration and high surface charge density. Additionally, the DNA folding around the sphere induces a reduced distance between DNA monomers close to the spherical surface. When an external force is applied, the force-extension relation reveals a discontinuous transition of DNA stretching during the unwrapping process. Moreover, the discrete change becomes more obvious for a higher salt concentration.

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