Publikationen

The wear resistance of pure rubber materials is very limited in engineering applications, such as pneumatic or sealing elements. In order to improve their wear resistance, various fillers were incorporated into the rubber matrix. In this background, the present work deals with the investigations of the mechanical and tribological properties of SBR/NR rubber composites containing 1 part per hundred rubber (phr) graphene and cellulose nanocrystal (CNC), respectively. The sliding wear tests were performed on a block-on-ring tribometer against a 100Cr6 bearing steel ring under dry sliding conditions. The results revealed that the incorporation of graphene and CNC slightly increases the storage modulus and decreases the hysteresis loss. However, the glass transition temperature was not affected. In the studied range of load conditions, it was found that the friction and wear properties of the rubber composites strongly depend on the normal load and sliding velocity. The wear resistance was obviously improved, especially under low F·v-factors, when CNC were introduced into the rubber composite. Under F·v-condition of 12 N and 0.1 ms−1, the specific wear rate was reduced by approximate 70% after addition of CNC compared to that of the benchmark material. The optical analysis of the wear track on the steel counterface reveals that this low wear rate can be attribute to the formation of a thin tribofilm on the steel disc surface.

Polymeric materials filled with micro-sized short carbon fiber (SCF) and various internal lubricants, i.e. graphite and PTFE etc., have been proved as a beneficial tribomaterial formulation in contact with a steel counterbody. The SCFs carry the most load applied on the tribosystem, while the internal lubricants improve the friction behavior of the polymer matrix. In the present study, the roles of rigid particles on the friction and wear performance of SCF filled Polybutylenterephthalate (PBT) with and without graphite were investigated by using a pin-on-disc (PoD) tribometer under dry sliding condition. The experimental results show that the tribocomposite filled with nanoparticles without graphite particles presents outstanding friction and wear performance especially under moderate and severe load conditions in combination with superior mechanical properties compared with graphite-filled tribocomposite. The friction coefficient and wear rate under a pv-condition of 3 MPa and 2 m/s are 0.18 and 0.8*10−6 mm3/Nm, respectively. Based-on the optical analysis of the worn surfaces of the polymer samples and the transfer layers formed on the steel disc, the possible friction and wear mechanisms were discussed.

A fully coupled model for mass and heat transport, mechanics, and chemical reactions with trapping is proposed. It is rooted in non-equilibrium rational thermodynamics and assumes that displacements and strains are small. Balance laws for mass, linear and angular momentum, energy, and entropy are stated. Thermodynamic restrictions are identified, based on an additive strain decomposition and on the definition of the Helmholtz free energy. Constitutive theory and chemical kinetics are studied in order to finally write the governing equations for the multi-physics problem. The field equations are solved numerically with the finite element method, stemming from a three-fields variational formulation. Three case-studies on vacancies redistribution in metals, hydrogen embrittlement, and the charge–discharge of active particles in Li-ion batteries demonstrate the features and the potential of the proposed model.

Supramolecular chemistry has provided versatile and affordable solutions for the design of intelligent soft materials, but it cannot be applied in stiff materials. This paper describes a new concept for the design of high-performance supramolecular thermosets by using the noncovalent cation–π interaction as cross-linking. These supramolecular thermosets are a class of infusible and insoluble stiff polymers having excellent mechanical properties even at temperatures exceeding 300 °C. The cation–π interaction can be locally and reversibly installed and removed by aqueous treatments at high or low pH, respectively. Local manipulation of cross-linking confers these thermosets with multiple stimuli-responsive functions, such as recyclability, healability, adhesion, and nondestructive detection of cross-linking and mechanical properties.

Abstract Traditional dynamic adaptive materials rely on an atomic/molecular mechanism of phase transition to induce macroscopic switch of properties, but only a small number of these materials and a limited responsive repertoire are available. Here, liquid as the adaptive component is utilized to realize responsive functions. Paired with a porous matrix that can be put in motion by an actuated dielectric elastomer film, the uncontrolled global flow of liquid is broken down to well-defined reconfigurable localized flow within the pores and conforms to the network deformation. A detailed theoretical and experimental study of such a dynamically actuated liquid-infused poroelastic film is discussed. This system demonstrates its ability to generate tunable surface wettability that can precisely control droplet dynamics from complete pinning, to fast sliding, and even more complex motions such as droplet oscillation, jetting, and mixing. This system also allows for repeated and seamless switch among these different droplet manipulations. These are desired properties in many applications such as reflective display, lab-on-a-chip, optical device, dynamic measurements, energy harvesting, and others.

Abstract In this study a surfactant-free and shape controllable preparation of microgel beads using super-repellent surfaces is reported. The extreme hydrophobicity and the interfacial tension of the liquid force the droplet of a gel precursor solution into spherical shape on a superamphiphobic or hemisphere shape on slippery surface. During gelation on the surface, the shape is maintained. Living cells and molecules, which hardly interact with substrate, can be therefore encapsulated in situ. The encapsulation of MC3T3 mouse osteoblast is demonstrated as a proof of concept.

We demonstrate a hydrogel bowl capable of selectively and rapidly collecting spilled oil while floating on water. The bowl has macroscopic openings in its sidewall, and its surface is first coated with octadecyltrichlorosilane (OTS) and then with diffusion pump oil, which imparts exceptional hydrophobic, oleophilic, and high oil wettability properties. The use of a hydrogel makes it possible to obtain surface hydrophobicity and oleophilicity, while also being inexpensive, eco-friendly, and easy to fabricate. Using a prototype of the bowl and a small pump system, we demonstrate that oils with a broad range of viscosities (2.7–2000.0 cSt at 20–40 °C) are more rapidly and efficiently collected from the surface of both pure water and seawater than with any other reported technique. The hydrogel bowl can collect oil for more than one month without losing its efficiency and can be stored in oil for reuse. Therefore, such hydrogel bowls represent a new alternative to conventional oil spill remediation techniques.