The relationship between structure, PEO mobility, and ionic conductivity is investigated for the solid polymer electrolyte, PEO/LiClO 4 . Amorphous and semicrystalline samples with ether-oxygen-to-lithium ratios ranging from 4:1 to 100:1 are measured. Previous X-ray diffraction results show that three crystalline phases can form in this system depending on the LiClO 4 concentration: (PEO) 3 :LiClO 4 , pure PEO, and (PEO) 6 : LiClO 4 . We use SANS to determine that the (PEO) 3 :LiClO 4 phase forms cylinders with a radius of 125 Å and a length of 700 Å. We also measure the amount and size of pure PEO lamellae by exploiting the neutron scattering length density contrast that arises because of crystallization. The samples are thermally treated such that the (PEO) 6 :LiClO 4 phase does not form. QENS is used to measure PEO mobility directly in amorphous and semicrystalline samples, and it reveals two processes. The first process at short times is attributed to the segmental mobility of PEO, and the second process at longer times is attributed to the restricted rotation of protons around the Li + ions. The type of motion and the radius of rotation are consistent with a cylindrical structure observed by diffraction: two PEO chains wrapping around Li + ions in an ether-oxygen-to-lithium ratio of 6:1. By directly comparing structure, mobility, and conductivity of the same samples, we determine that at 50 °C, a semicrystalline sample (concentration of 14:1) has the highest conductivity despite being less mobile, partially crystalline, and having less charge carriers than amorphous samples at the same temperature. The results suggest a decoupling of ionic conductivity and polymer mobility.

We report all-atom molecular dynamics simulations following adsorption of gold-binding and non-gold-binding peptides on gold surfaces modeled with dispersive interactions. We examine the dependence of adsorption on both identity of the amino acids and mobility of the peptides. Within the limitations of the approach, results indicate that when the peptides are solvated, adsorption requires both configurational changes and local flexibility of individual amino acids. This is achieved when peptides consist mostly of random coils or when their secondary structural motifs (helices, sheets) are short and connected by flexible hinges. In the absence of solvent, only affinity for the surface is required: mobility is not important. In combination, these results suggest the barrier to adsorption presented by displacement of water molecules requires conformational sampling enabled through mobility.

The mechanism for improved ionic conductivity in nanoparticle-filled solid polymer electrolytes containing polyethylene oxide [PEO], LiClO4, and Al2O3 is investigated using differential scanning calorimetry [DSC], dielectric spectroscopy, small-angle neutron scattering [SANS], and quasi-elastic neutron scattering [QENS]. We measure samples with ether oxygen to lithium ratios ranging from 14:1 to 8:1 and Al2O3 nanoparticle concentrations ranging from 5 to 25 wt %. The T g and pure PEO crystal fraction are unaffected by nanoparticle addition, and SANS reveals nanoparticle aggregation, with the extent of aggregation similar in all samples regardless of LiClO4 or Al2O3 concentration. Despite the similarity between samples, nanoparticles improve conductivity at all temperatures, but only at the eutectic concentration (ether oxygen to lithium ratio of 10:1). Our QENS results indicate that a rotation is present in both filled and unfilled samples at all concentrations and is consistent with the rotation of (PEO)6:LiClO4, a channel-like structure that is more conductive than the amorphous equivalent. The rotation becomes more restricted in the presence of nanoparticles.

A high-flux backscattering spectrometer and a time-of-flight disk chopper spectrometer are used to probe the molecular mobility of model freeze-dried phospholipid liposomes at a range of temperatures surrounding the main melting transition. Using specific deuteration, quasielastic neutron scattering provides evidence that, in contrast to the hydrocarbon chains, the headgroups of the phospholipid molecules do not exhibit a sharp melting transition. The onset of motion in the tails is located at temperatures far below the calorimetric transition. Long-range motion is achieved through the onset of whole-lipid translation at the melting temperature. Atomistic simulations are performed on a multibilayer model at conditions corresponding to the scattering experiments. The model provides a good description of the dynamics of the system, with predictions of the scattering functions that agree with experimental results. The analysis of both experimental data and results of simulations supports a picture of a gradual melting of the heterogeneous hydrophobic domain, with part of the chains spanning increasingly larger volumes and part of them remaining effectively immobile until the thermodynamic phase transition occurs.

Coarse-grained models that preserve atomistic detail display faster dynamics than atomistic systems alone. We show that this " indirect speed up" is robust: coarse-grained dynamic observables computed with time scaled by a constant factor are in excellent agreement with their underlying atomistic counterparts. Borrowing from accelerated dynamics methods used in the field of rare events, we predict the scaling factor within 7%, based on reduced intermolecular attraction yielding faster neighbor cage escapes.