Polymer Diffusion in the Interphase Between Surface and Solution.

Total internal reflection fluorescence correlation spectroscopy (TIR-FCS) is applied to study the self-diffusion of poly(ethylene glycol) solutions in the presence of weakly attractive interfaces. Glass coverslips modified with aminopropyl- and propyl-terminated silanes are used to study the influence of solid surfaces on polymer diffusion. A model of three phases of polymer diffusion allows to describe the experimental fluorescence autocorrelation functions. Besides the two-dimensional diffusion of adsorbed polymer on the substrate and three-dimensional free diffusion in bulk solution, a third diffusion time scale is observed with intermediate diffusion times. This retarded three-dimensional diffusion in the solution is assigned to the long-range effects of solid surfaces on diffusional dynamics of polymers. The respective diffusion constants show Rouse scaling ( D ∼ N-1), indicating a screening of hydrodynamic interactions by the presence of the surface. Hence, the presented TIR-FCS method proves to be a valuable tool to investigate the effect of surfaces on polymer diffusion beyond the first adsorbed polymer layer on the 100 nm length scale.

Manipulation of Liquid Crystalline Properties by Dynamic Covalent Chemistry─En Route to Adaptive Materials.

Dynamic covalent bonds bear great potential for the development of adaptive and self-healing materials. Herein, we introduce a versatile concept not only for the design of low-molecular-weight liquid crystals but also for their in situ postsynthetic modification by using the dynamic covalent nature of imine bonds. The methodology allows systematic investigations of structure-property relationships as well as the manipulation of the materials' behavior (liquid crystallinity) and the introduction of additional properties (here, fluorescence) by a solvent-free method. For the first time, the transamination reaction is followed by variable-temperature 19F solid-state NMR in the mesophase, providing insights into the reaction dynamics in a liquid crystalline material. Finally, the application potential for the design of liquid crystalline materials with adaptive properties is demonstrated by a sequential combination of these reactions.

Investigation of Roughness Correlation in Polymer Brushes via X-ray Scattering.

Thin polymer films and coatings are used to tailor the properties of surfaces in various applications such as protection against corrosion, biochemical functionalities or electronic resistors. Polymer brushes are a certain kind of thin polymer films, where polymer chains are covalently grafted to a substrate and straighten up to form a brush structure. Here we report on differences and similarities between polymer brushes and spin-coated polymer films from polystyrene and polymethyl methacrylate with special emphasis on surface roughness and roughness correlation. The phenomenon of roughness correlation or conformality describes the replication of the roughness profile from the substrate surface to the polymer surface. It is of high interest for polymer physics of brush layers as well as applications, in which a homogeneous polymer layer thickness is required. We demonstrate that spin-coated films as well as polymer brushes show roughness correlation, but in contrast to spin-coated films, the correlation in brushes is stable to solvent vapor annealing. Roughness correlation is therefore an intrinsic property of polymer brushes.

Hydrogel Functionalized Polyester Fabrics by UV-Induced Photopolymerization.

We address a strategy to graft hydrogels onto polyethylene terephthalate (PET) fabrics using different acrylate-based monomers. The hydrogel-modified fabrics were prepared by a two-step modification. To this end, double functional groups were firstly introduced onto the PET surface via an aminolysis reaction involving allylamine. The final grafted polymer networks were then obtained after UV-induced radical photopolymerization by varying acrylate monomer types in the presence of a cross-linker. After characterization, the resulting hydrogels showed different morphologies and abrasion resistance performances depending on their chemical nature. UV-photopolymerization is a fast and low-cost method to achieve technical fabrics with specific desired properties.

Confinement Assembly of ABC Triblock Terpolymers for the High-Yield Synthesis of Janus Nanorings.

Block copolymers are versatile building blocks for the self-assembly of functional nanostructures in bulk and solution. While spheres, cylinders, and bilayer sheets are thermodynamically preferred shapes and frequently observed, ring-shaped nanoparticles are more challenging to realize due to energetic penalties that originate from their anisotropic curvature. Today, a handful of concepts exist that produce core-shell nanorings, while more complex ( e. g., patchy) nanorings are currently out of reach and have only been predicted theoretically. Here, we demonstrate that confinement assembly of properly designed ABC triblock terpolymers is a general route to synthesize Janus nanorings in high purity. The triblock terpolymer self-assembles in the spherical confinement of nanoemulsion droplets into prolate ellipsoidal microparticles with an axially stacked lamellar-ring ( lr)-morphology. We clarified and visualized this complex, yet well-ordered, morphology with transmission electron tomography. Blocks A and C formed stacks of lamellae with the B microdomain sandwiched in-between as nanorings. Cross-linking of the B-rings allowed disassembly of the microparticles into Janus nanorings carrying two strictly separated polymer brushes of A and C on the top and bottom. Decreasing the B volume leads to Janus spheres and rods, while an increase of B results in perforated and filled Janus disks. The confinement assembly of ABC triblock terpolymers is a general process that can be extended to other block chemistries and will allow to synthesize a large variety of complex micro- and nanoparticles that inspire studies in self-assembly, interfacial stabilization, colloidal packing, and nanomedicine.

Electrical conductivity of silver nanoparticle doped carbon nanofibres measured by CS-AFM.

In this work, a pioneering study on the electrical properties of composite carbon nanofibres (CNFs) using current-sensitive atomic force microscopy (CS-AFM) has been demonstrated. CNFs are highly interesting materials which are usable in a wide array of applications e.g. electrode materials for biosensors, lithium ion batteries, fuel cells and supercapacitors. CNFs offer a high specific surface area and thus have a high contact area for charge transfer. CNFs can be produced using spinnable polyacrylonitrile (PAN) as a precursor for carbonisation. For the purpose of developing efficient CNFs with high conductivity and power density, silver nanoparticle (AgNPs)-containing PAN solutions were electrospun to form composite nanofibres which was followed by heat treatment. The applied voltage of the spinning setup and the content of both PAN and the silver nanoparticles in the spinning solution were varied in order to study their influence on the morphology and the electrical properties of the nanofibres. The resultant morphologies and fibre diameters were determined by scanning electron microscopy (SEM). The formation of silver nanoparticles was characterised in solution by UV-visible absorption spectroscopy and dynamic light scattering (DLS), while energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) were carried out to investigate the presence as well as the average diameter of the AgNPs. The electrical properties of the CNFs were investigated using CS-AFM. This technique gives us the possibility to explore the electrical properties of single fibers and hence derive relationships between the structural features and the electrical properties. Our results show that the composite CNFs have a higher electrical conductivity than the neat CNFs and both the average diameter of the fibers and the electrical conductivity increase with an increasing AgNP content.