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.

Despite many merits, biobased and biodegradable poly(lactic acid) (PLA) suffers from inherently high flammability, significantly impeding its practical applications in the areas of packaging, fibers, electric and electronics, etc. Phosphoramidesbased flame retardants have demonstrated exceptional flame retardancy in PLA only at very low loading levels. Unfortunately, exiting synthetic processes of phosphoramides often involve the use of a huge amount of organic solvents, presenting a potential threat to the ecosystem and human beings, in addition to high production costs. Herein, we report a one-pot, solvent-and catalyst-free, and green approach for the synthesis of a polyphosphoramide (DM-H) via two-step polycondensation between dimethyl methylphosphonate (DMMP) and 1,6-hexanediamine (HDA). As-synthesized DM-H exhibits exceptional flame-retardant efficiency in the PLA while preserving the mechanical properties of the PLA. The addition of only 2 wt % DM-H enables the PLA to achieve a desirable V-0 rating during vertical burning tests and a high limited oxygen index (LOI) value of 29.7%, because the DM-H can act both in the gas and condensed phases. Moreover, the tensile strength is of 59.7 MPa comparable to 62.1 MPa of the bulk PLA. This work offers an innovative and green approach for the synthesis of polyphosphoramides to create high-performance sustainable PLA materials with balanced flame retardancy and mechanical performances.

No abstract