Showing papers by "Christoph Weder published in 2013"

Light-Healable Supramolecular Nanocomposites Based on Modified Cellulose Nanocrystals

Abstract: Polymers that can be repaired after being damaged are attractive, because this feature can improve the reliability, functionality, and lifetime of these materials. We report here light-healable nanocomposites based on a telechelic poly(ethylene-co-butylene) that was functionalized with hydrogen-bonding ureidopyrimidone (UPy) and cellulose nanocrystals (CNCs) decorated with the same binding motif. These nanocomposites show significantly improved mechanical properties when compared to the supramolecular polymer alone. When these materials are exposed to ultraviolet radiation, the UPy motifs are excited and the absorbed energy is converted into heat. This causes temporary disengagement of the hydrogen-bonding motifs, concomitant with a reversible decrease of the supramolecular polymers’ molecular weight and viscosity. As a result, deliberately introduced defects can be healed quickly and efficiently, even at a filler content of 20% w/w, that is, in compositions that exhibit high strength and stiffness.

Optically healable polymers

Abstract: Polymers that can easily be repaired after being damaged are attractive as this characteristic can improve the reliability, functionality, and lifetime of many products. In the last decade, researchers have thus developed new approaches to create stimuli-responsive polymer systems, which have the ability to autonomously heal or can be repaired upon exposure to an external stimulus. This review summarizes the current knowledge of optically healable or photo-healable polymers. The use of light as a stimulus for healing offers several attractive features, including the ability to deliver the stimulus locally, which opens up the possibility of healing the material under load, as well as the ability to tailor the wavelength of light to selectively address a specific component of the material, e.g. only the damaged parts. So far, two main classes of optically healable polymers have been explored, which are structurally dynamic polymers and mechanically activated reactive systems.

Physiologically Responsive, Mechanically Adaptive Bio-Nanocomposites for Biomedical Applications

Abstract: We report mechanically adaptive bionanocomposites based on poly(vinyl alcohol) (PVOH) and cellulose nanocrystals (CNCs), whose mechanical properties change significantly upon exposure to simulated physiological conditions. These nanocomposites were made using CNCs derived from tunicates (t-CNCs) and cotton (c-CNCs) to explore how aspect ratio, surface charge density, and filler content influence the mechanical properties. Dynamic mechanical analysis data reveal a significant enhancement of the tensile storage modulus (E′) upon introduction of CNCs, which scaled with the CNC type and content. For example, in the dry, glassy state at 25 °C, E′ increased up to 23% (for c-CNCs) and 88% (for t-CNCs) compared to the neat polymer. Exposing the materials to simulated physiological conditions caused a drastic softening of the materials, from 9.0 GPa to 1 MPa for c-CNCs and from 13.7 GPa to 160 MPa for t-CNCs. The data show that the swelling characteristics of the nanocomposites and the extent of mechanical switchi...

Melt-processed polymer glasses for low-power upconversion via sensitized triplet–triplet annihilation

Abstract: The process of low-power light upconversion by triplet–triplet annihilation is well established in solutions of appropriate sensitizer–emitter pairs, but has only recently been reduced to practice in polymeric materials. Here, the fabrication of upconverting glasses based on poly(methyl methacrylate) (PMMA), palladium octaethylporphyrin (PdOEP, sensitizer, 0.005–0.5% w/w relative to the polymer) and large amounts of diphenylanthracene (DPA, emitter, 25% w/w relative to the polymer) is reported. These materials were produced by compression-molding pre-mixed blends and subsequently quenching the samples in a molecularly mixed state. The resulting films upconvert green incident light (543 nm) of low incident power density (34 mW cm−2) into blue light (440 nm). The dependence of the upconversion intensity on the sensitizer concentration was studied and the results suggest that an optimal composition range exists, where the upconversion efficiency is maximal.

Risk assessment of released cellulose nanocrystals - mimicking inhalatory exposure

Abstract: Cellulose nanocrystals (CNCs) exhibit advantageous chemical and mechanical properties that render them attractive for a wide range of applications. During the life-cycle of CNC containing materials the nanocrystals could be released and become airborne, posing a potential inhalatory exposure risk towards humans. Absent reliable and dose-controlled models that mimic this exposure in situ is a central issue in gaining an insight into the CNC-lung interaction. Here, an Air Liquid Interface Cell Exposure system (ALICE), previously designed for studies of spherical nanoparticles, was used for the first time to establish a realistic physiological exposure test method for inhaled fiber shaped nano-objects; in this case, CNCs isolated from cotton. Applying a microscopy based approach the spatially homogenous deposition of CNCs was demonstrated as a prerequisite of the functioning of the ALICE. Furthermore, reliability and controllability of the system to nebulise high aspect ratio nanomaterials (HARN, e.g. CNCs) was shown. This opens the potential to thoroughly investigate the inhalatory risk of CNCs in vitro using a realistic exposure system.

Polymer nanocomposite having switchable mechanical properties

Abstract: A polymer nanocomposite (1) having switchable mechanical properties comprises a matrix polymer (2) and a nanoparticle network, wherein the nanoparticle network is formed by a formation of a substantially three-dimensional network of nanoparticles (3) which are incorporated in the matrix polymer (2) and interact with each other and/or with the matrix polymer (2). The polymer nanocomposite (1) in a first switching state comprises a first stiffness characterized by a first tensile storage modulus (E') greater than 6 GPa, in a second switching state comprises a second stiffness characterized by a second tensile storage modulus (E') of less than 1 GPa and is switchable between the first switching state and the second switching state by exposing the polymer nanocomposite (1) to a stimulus that influences interactions among the nanoparticles (3) and/or between the nanoparticles (3) and the matrix polymer (2). In this way a polymer nanocomposite is provided which in a beneficial way may be employed within medical applications

Medical injection device

Abstract: A medical injection device (4) having switchable mechanical properties comprises a hollow tube section (40) having an inner bore (400), wherein the hollow tube section (40) at least partially is made of a material exhibiting switchable mechanical properties such that the material in a first switching state comprises a first stiffness characterized by a first tensile storage modulus (E'), in a second switching state comprises a second stiffness characterized by a second tensile storage modulus (E') smaller than the first tensile storage modulus and is switchable from the first switching state to the second switching state by exposing the material to a stimulus.