Correlation of mass fractal dimension and asymmetry

Resolving Segmental Polymer Dynamics in Nanocomposites by Incoherent Neutron Spin-Echo Spectroscopy

The segmental dynamics of styrene-butadiene nanocomposites with embedded silica nanoparticles (NPs, ca. 20 vol. %) has been studied by broadband dielectric (BDS) and neutron spin-echo spectroscopy (NSE). It is shown by BDS that overlapping contributions only allow us to conclude on a range of distributions of relaxation times in simplified industrial nanocomposites formed with highly polydisperse NPs. For comparison, structurally similar but less aggregated colloidal nanocomposites have a well-defined distribution of relaxation times due to the reduced influence of interfacial polarization processes. This distribution is widened with respect to the neat polymer, without change in the position of the maximum and at most a small slowing down visible in the average time. We then demonstrate that incoherent NSE can be used to resolve small modifications of segmental dynamics of the industrial samples. By carefully choosing the q-vector of the measurement, experiments with fully hydrogenated polymer give access to the self-dynamics of the polymer in the presence of silica on the scale of approximately 1 nm. Our high-resolution measurements show that the segmental motion is slightly but systematically slowed also by the presence of the industrial filler NPs.

Scalable Electrically Conductive Spray Coating Based on Block Copolymer Nanocomposites

Currently available conductive inks present a challenge to achieving electrical performance without compromising mechanical properties, scalability, and processability. Here, we have developed blends of carbon black and the commercially available triblock copolymer (BCP), poly(styrene-ethylene-butylene-styrene)-g-maleic anhydride (SEBS-g-MAH) (FG1924G, Kraton), that can be readily applied as a conductive coating via a spray-coating process, for a wide range of insulating materials (fabric, wood, glass, and plastic). Simple but effective mechanical and chemical modifications of the ingredients can increase the electrical conductivity (∼100 S/m) by an order of magnitude more than previously reported for carbon black composites; moreover, the coatings display excellent mechanical flexibility (tensile strain ε ∼ 5.00 mm/mm). To correlate electrical conductivity and nanoscale structural changes with mechanical deformation, small-angle X-ray scattering (SAXS) during in situ tensile testing was performed. We show that the nanocomposite can be produced using low-cost ingredients (∼$ 10/kg), ensuring scalability for fabrication of large-scale devices without specialized material synthesis. Equally important, the phase behavior of block copolymers can enable recovery from physical damage via thermal annealing, which is critical for product longevity.

Structural changes in precipitated silica induced by external forces

The morphology of pure precipitated silica, silica filled in polydimethylsiloxane rubber, and silica filled in styrene butadiene rubber was studied by means of small-angle X-ray scattering experiments. The silica at a length scale of a few nanometers consists of primary particles, which form aggregates, and clusters with aggregates as basic units. It is evidenced that the aggregate branching, represented by the mass fractal dimension, and the aggregate diameter are different if pure silica and silica in rubber are compared. Contrary, the size of the primary particles and their surface are not influenced. It is demonstrated that the change in the aggregate morphology is due to the external mechanical forces appearing during the mixing process. This is achieved by model experiments using a pistil and a mortar and a composite with different silica fractions. By that means, a systematic change in the morphology with grinding time is observed. Then, the experiments on the composite demonstrate that the major contributions to the mass fractal dimensions are due to the external mechanical forces. In order to test reproducibility and universal validity in the case of precipitated silicas, independent experiments on one silica and further silicas are performed. Several important conclusions are obtained from the study. First, it is shown that a comparison of different pure silica samples without knowing their history may be difficult or questionable. Second, it becomes evident that it is not sufficient to provide only a description of the materials, rather than the details of the sample treatment have to be reported. Therefore, solely the characterization of the morphology of the pure silica is not sufficient to be compared to the mechanical properties of the composites.

A novel model for the interpretation of small-angle scattering experiments of self-affine structures

A novel theory is presented which allows, for the first time, the analytical description of small-angle scattering experiments on anisotropic shaped clusters of nanoparticles. Experimentally, silica-filled rubber which is deformed is used as an example. The silica can be modelled by solid spheres which form clusters. The experiments demonstrate that the clusters become anisotropic as a result of the deformation whereas the spheres are not affected. A comparison of the newly derived model function and the experiments provides, for the first time, microscopic evidence of the inhomogeneous deformation of clusters in the rubbery matrix.