Cooperative Dynamics of Highly Entangled Linear Polymers within the Entanglement Tube.

We present a quantitative comparison of the dynamic structure factors from unentangled and strongly entangled poly(butylene oxide) (PBO) melts. As expected, the low molecular weight PBO displays Rouse dynamics, however, with very significant subdiffusive center-of-mass diffusion. The spectra from high molecular weight entangled PBO can be very well described by the dynamic structure factor based on the concept of local reptation, including the Rouse dynamics within the tube and allowing for non-Gaussian corrections.

Interchain Hydrodynamic Interaction and Internal Friction of Polyelectrolytes.

Polyelectrolytes (PE) are polymeric macromolecules in aqueous solutions characterized by their chain topology and intrinsic charge in a neutralizing fluid. Structure and dynamics are related to several characteristic screening length scales determined by electrostatic, excluded volume, and hydrodynamic interactions. We examine PE dynamics in dilute to semidilute conditions using dynamic light scattering, neutron spinecho spectroscopy, and pulse field gradient NMR spectroscopy.

Dynamic structure factors of polymer melts as observed by neutron spin echo: Direct comparison and reevaluation.

In this work, we compare the single chain dynamic structure factors for five different polymers: polyolefins (PE and PEP), poly-dienes (PB and PI), and a polyether (PEO). For this purpose, we have extended the De Gennes approximation for the dynamic structure factor. We describe the single chain dynamic structure factor in multiplying the coherent scattering functions for local reptation and Rouse motion within the Rouse blob.

Chain Confinement and Anomalous Diffusion in the Cross over Regime between Rouse and Reptation.

By neutron spin echo (NSE) and pulsed field gradient (PFG) NMR, we study the dynamics of a polyethylene-oxide melt (PEO) with a molecular weight in the transition regime between Rouse and reptation dynamics. We analyze the data with a Rouse mode analysis allowing for reduced long wavelength Rouse modes amplitudes. For short times, subdiffusive center-of-mass mean square displacement ⟨()⟩ was allowed.

Passive Macromolecular Translocation Mechanism through Lipid Membranes.

The translocation of biologically active macromolecules through cell membranes is of vital importance for cells and is a key process for drug delivery. Proteins exploit specific conformational changes in their secondary structure to facilitate membrane translocation. For the large class of biological and synthetic macromolecules, where such conformational adaptions are not possible, guidelines to tailor the structure of monomers and macromolecules to aid membrane translocation and cross-membrane drug delivery would be highly desirable.

Quasielastic neutron scattering reveals the temperature dependent rotational dynamics of densely grafted oleic acid.

We study the dynamics of pure oleic acid and grafted oleic acid synthesized by decomposing iron oleate into oleic acid grafted iron oxide nanoparticles. Our quasielastic neutron scattering study shows that oleic acid dominantly performs translational diffusion at room temperature. On the other hand, in nanocomposites, constraints imposed by grafting and crowding of neighboring chains restrict the grafted oleic acid to uniaxial rotation.

Understanding the Drying Behavior of Regenerated Cellulose Gel Beads: The Effects of Concentration and Nonsolvents.

The drying behavior of regenerated cellulose gel beads swollen with different nonsolvents (., water, ethanol, water/ethanol mixtures) is studied on the macroscopic scale with an optical microscope as well as on nanoscale using small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques. Depending on the cellulose concentration, the structural evolution of beads during drying follows one of three distinct regimes.

Evidence of supercoolable nanoscale water clusters in an amorphous ionic liquid matrix.

Nanoscale water clusters in an ionic liquid matrix, also called "water pockets," were previously found in some mixtures of water with ionic liquids containing hydrophilic anions. However, in these systems, at least partial crystallization occurs upon supercooling. In this work, we show for mixtures of 1-butyl-3-methylimidazolium dicyanamide with water that none of the components crystallizes up to a water content of 72 mol.

Strain- and field-induced anisotropy in hybrid elastomers with elongated filler nanoparticles.

The implementation of anisotropy to functional materials is a key step towards future smart materials. In this work, we evaluate the influence of preorientation and sample architecture on the strain-induced anisotropy in hybrid elastomers containing covalently attached elongated magnetic filler particles. Accordingly, silica coated spindle-type hematite nanoparticles are incorporated into poly(dimethylsiloxane)-based elastomers, and two types of composite architectures are compared: on the one hand a conventional architecture of filled, covalently crosslinked elastomers, and on the other hybrid elastomers that are crosslinked exclusively by covalent attachment of the polymer chains to the particle surface.

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers.

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively.

Cooperative Chain Dynamics of Tracer Chains in Highly Entangled Polyethylene Melts.

By neutron spin echo spectroscopy, we have studied the center of mass motion of short tracer chains on the molecular length scale within a highly entangled polymer matrix. The center of mass mean square displacements of the tracers independent of their molecular weight is subdiffusive at short times until it has reached the size of the tube d; then, a crossover to Fickian diffusion takes place. This observation cannot be understood within the tube model of reptation, but is rationalized as a result of important interchain couplings that lead to cooperative chain motion within the entanglement volume ∼d^{3}.

Self-Similar Dynamics of Large Polymer Rings: A Neutron Spin Echo Study.

This work clarifies the self-similar dynamics of large polymer rings using pulsed-field gradient nuclear magnetic resonance and neutron spin echo spectroscopy. We find center of mass diffusion taking place in three dynamic regimes starting (i) with a strongly subdiffusive domain ⟨r^{2}(t)⟩_{com}∼t^{α} (0.4≤α≤0.

Small Groups, Big Impact: Eliminating Li Traps in Single-Ion Conducting Polymer Electrolytes.

Single-ion conducting polymer electrolytes exhibit great potential for next-generation high-energy-density Li metal batteries, although the lack of sufficient molecular-scale insights into lithium transport mechanisms and reliable understanding of key correlations often limit the scope of modification and design of new materials. Moreover, the sensitivity to small variations of polymer chemical structures (e.g.

Macro- and Microstructural Evolution during Drying of Regenerated Cellulose Beads.

The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process.

Self-Similar Polymer Ring Conformations Based on Elementary Loops: A Direct Observation by SANS.

We report small angle neutron scattering (SANS) results on very large polyethylene-oxide (PEO) rings in the melt. Major findings are (i) the observation of a cross over in the SANS pattern from a strong -dependence at intermediate to a dependence at higher that is independent of the ring size. Summing up scattering amplitudes in a minimal model that contains the ring closure and a cross over from Gaussian statistics at short distances to more compact structures at larger distances, we identify the cross over to occur at a distance along the ring of = 45 ± 2.

Supramolecular Dimerization in a Polymer Melt from Small-Angle X-Ray Scattering and Rheology: A Miscible Model System.

We present a structural and dynamic study on the simplest supramolecular hetero-association, recently investigated by the authors to prepare architectural homogeneous structures in the melt state, based on the bio-inspired hydrogen-bonding of thymine/diaminotriazine (thy-DAT) base-pairs. In the combination with an amorphous low T poly(butylene oxide) (PBO), no micellar structures are formed, which is expected for nonpolar polymers because of noncompatibility with the highly polar supramolecular groups. Instead, a clear polymer-like transient architecture is retrieved.

A practical method to account for random phase approximation effects on the dynamic scattering of multi-component polymer systems.

Investigations of polymer systems that rely on the interpretation of dynamical scattering results as, e.g., the structure factor S(Q, t) of single chains or chain sections may require the inclusion of effects, as described within the framework of the random phase approximation (RPA) for polymers.

Direct Observation of Dynamic Tube Dilation in Entangled Polymer Blends: A Combination of Neutron Scattering and Dielectric Techniques.

We report a microscopic observation of the time-dependent dynamic tube dilation process on isofrictional bidisperse melts. By applying neutron spin echo (NSE) and dielectric techniques on blends of long polyisoprene (PI) chains with short PI additives with different topology, we access the dynamics of the tube dilation process on a molecular scale. The time-dependent tube dilation is directly revealed by NSE as an additional time dependence of the dynamic structure factor in the local reptation regime.

Polymer dynamics under confinement.

We review recent neutron scattering work and related results from simulation and complementary techniques focusing on the microscopic dynamics of polymers under confinement. Confinement is either realized in model porous materials or in polymer nanocomposites (PNC). The dynamics of such confined polymers is affected on the local segmental level, the level of entanglements as well as on global levels: (i) at the segmental level the interaction with the surface is of key importance.

Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach.

The preparation of poly(N-isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e., from core-shell-like to a more homogeneous one.

Creating a synthetic platform for the encapsulation of nanocrystals with covalently bound polymer shells.

We present a platform for the encapsulation of superparamagnetic iron oxide nanocrystals (SPIONs) with a highly stable diblock copolymer shell allowing a homogeneous dispersion of the nanocrystals into a polymer matrix in the resulting nanocomposites. High polymer shell stability was achieved by crosslinking the inner polydiene shell for example in a persulfate based redox process. The advantage of this crosslinking reaction is the avoidance of heat and UV light for the initiation, making it suitable for heat or UV sensitive systems.

Confinement Facilitated Protein Stabilization As Investigated by Small-Angle Neutron Scattering.

While mesoporous silicas have been shown to be a compelling candidate for drug delivery and the implementation of biotechnological applications requiring protein confinement and immobilization, the understanding of protein behavior upon physical adsorption into silica pores is limited. Many indirect methods are available to assess general adsorbed protein stability, such as Fourier-transform infrared spectroscopy and activity assays. However, the limitation of these methods is that spatial protein arrangement within the pores cannot be assessed.