On the interactions between poly(ethylene oxide) and graphite oxide: A comparative study by different computational methods

Structural, energetic and dynamic investigation of poly(ethylene oxide) in imidazolium-based ionic liquids with different cationic structures

In this work, two imidazolium-based ionic liquids (ILs) with different cations including dications (DIL) and monocations (MIL) were blended with poly(ethylene oxide) (PEO). The influence of ILs' structure on the structural and dynamic properties of a PEO/IL system was investigated by molecular dynamics (MD) simulation and density functional theory (DFT) methods. The simulation results show that DIL exhibits weaker interaction with PEO than MIL due to a stronger IL aggregation effect. The intermolecular interaction also makes the PEO chain tend to organize around the imidazolium ring of ILs, which causes the conformational entropy loss. Compared with PEO/MIL, this phenomenon is more significant in PEO/DIL because of the double positive centers of the dication and a longer hydrogen bond lifetime. MD simulation also demonstrates that DIL could act as a "crosslinker" to promote the formation of a physical crosslinking network which has strong dependence on the concentration of IL. The competition between physical crosslinking and plasticizing effects induces non-monotonic variations of relaxation time in PEO/DIL, which is consistent with its unusual change of the glass transition temperature (Tg). Despite stronger hydrogen bonding interactions between PEO and MIL demonstrated by atom-in-molecules (AIM) and reduced density gradient (RDG) analysis, the segmental mobility is slower in PEO/DIL according to the MSD curve. These differences in multiple structural or energetic factors finally lead to different conductive mechanisms and hence obtain different ionic conductivities.

Adaptive insertion of a hydrophobic anchor into a poly(ethylene glycol) host for programmable surface functionalization

Covalent and non-covalent molecular binding are two strategies to tailor surface properties and functions. However, the lack of responsiveness and requirement for specific binding groups makes spatiotemporal control challenging. Here, we report the adaptive insertion of a hydrophobic anchor into a poly(ethylene glycol) (PEG) host as a non-covalent binding strategy for surface functionalization. By using polycyclic aromatic hydrocarbons as the hydrophobic anchor, hydrophilic charged and non-charged functional modules were spontaneously loaded onto PEG corona in 2 min without the assistance of any catalysts and binding groups. The thermodynamically favourable insertion of the hydrophobic anchor can be reversed by pulling the functional module, enabling programmable surface functionalization. We anticipate that the adaptive molecular recognition between the hydrophobic anchor and the PEG host will challenge the hydrophilic understanding of PEG and enhance the progress in nanomedicine, advanced materials and nanotechnology.

Unraveling the Polymer Chain-Adsorbed Constrained Interfacial Region on an Atomistically Thin Carbon Sheet

Confinement of graphene and its functional derivatives in synthetic and biomacromolecules has been widely demonstrated recently to manifest in several multiscale phenomena in their mixtures. However, the intricate adsorbed interfacial region formed between polymer chains and a single layer of atomistically thin carbon sheet hitherto evaded an understanding of its nature and characteristics. Here, we reveal the structure of this constrained region and estimate the thickness of the adsorbed polymer layer on a single layer of an atomistically thin graphene oxide sheet using both direct experiments and molecular dynamics simulations. We use small-angle neutron scattering on a model multicomponent mixture formed by an adsorbing polymer, graphene oxide, and solvent for revealing the structure of the constrained interfacial region. We quantify the intricate adsorbed polymer layer thickness on a single layer of atomistically thin graphene oxide sheet by Euclidean approximation of the experimentally observed self-similar interfacial structure. The state of polymer chain random walk and influence of unadsorbed chains under experimental conditions are investigated and juxtaposed against the accuracy of this quantification. For long-chain polymers, the adsorbed layer thickness increases with increasing polymer molecular weight and shows a scaling relationship δ ∼ R_g^0.22 with the polymer radius of gyration. For short-chain polymers, the thickness is nearly independent of molecular weight and shows a scaling relationship δ ∼ 0.6 R_g^0.22. Coarse-grained molecular dynamics simulations performed on a model system similar to experiments qualitatively ratify the experimentally observed molecular weight-thickness relationship. Simulations show no discernible scaling relationship between radius of gyration and adsorbed layer thickness for low-molecular-weight polymers but show a consistent scaling δ ∼ R_g for high-molecular-weight polymers. A comparison between results from experiments and simulations indicates a discerning pathway in deciphering interface-governed multiscale phenomena in mixtures of adsorbing macromolecules with graphene and its functional derivatives.

Toward highly compressible graphene aerogels of enhanced mechanical performance with polymer

The highly compressive durable graphene aerogels with enhanced strength was prepared by combining the freeze-casting process with the binding effect of polymer.