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In this study, polyetheretherketone composites were compounded using a two-screw extruder followed by injection moulding. The effects of multi-fillers on the mechanical properties and crystallization performances were investigated. Differential scanning calorimetry results indicate that the addition of fillers slightly increases the crystallization temperature and crystallinity. Compared to neat polyetheretherketone, the incorporation of inorganic filler leads to a significant improvement in matrix hardness, matrix stiffness and a slight increase in tensile strength. However, the material ductility, the impact strength and the fracture toughness of polyetheretherketone composites decrease. Fractography analyses show that the addition of fillers restraints the ductile deformation of polymers, which is responsible for the reduction of material ductility, impact strength as well as fracture toughness of polyetheretherketone composites.

The tribological properties of Poly-ether-ether-ketone (PEEK) were studied systematically by multiple scratch tests in both unidirection and bidirection mode on the micro- and nano-length scale. The tip geometry has a strong influence on the scratch friction behavior, in particular on the scratch initiation and on the resulting damage patterns. Plowing contributions to friction are significant for nano-scale tips during the initial scratch cycles. Shear contributions dominate for both nano- and micro-scale once a groove has been established by multiple scratches. While the damaging mechanisms are the same for both micro- and nano-scratch tests, the resulting damaging patterns differ depending on the scratching mode (unidirection or bidirection) and the normal load. Patchy layers of material formed by scratching are torn into fracture by nano-scale tips, while they are stretched to flakes by the micro-scratch indenter.

Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be studied in detail by means of friction force microscopy. Atomic-scale variations of the lateral force allow investigation of microscopic mechanisms of sliding. Friction force microscopy even reveals surface reconstruction of the gold surface as a modulation of the lateral force signal. Experiments indicate that the mobility of surface atoms at room temperature and plastic deformation mechanisms give rise to neck formation between gold and microscopic asperities in sliding contact. The frictional properties of gold surfaces change dramatically at temperatures below 150 K, where the surface diffusion is greatly reduced. Insight into the lubrication properties of self-assembled monolayers is provided by molecular-scale modulations of frictional forces. Molecular-scale maps of the friction force also allow identification of the relevant surface structure in experiments on electrochemically modified gold surfaces. Variation of the electrochemical potential is a means to reversibly switch between low and high friction states on gold surfaces.

The friction of microstructured polydimethylsiloxane samples against a glass surface is studied through force measurements and simultaneous optical microscopy. Both average friction forces and the amplitude of stick-slip oscillations are greatly reduced by the structuring. Optical microscopy reveals waves propagating through the contact in connection which stick-slip events. The experimental observations are interpreted with the help of simulations of a spring-block model for which parameters are directly derived from the experiment. Stress gradients across the contact area are found to play an important role for the frictional behavior.

In comparison of a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with a Pt(111) single crystal we find that wearless friction is determined by chemistry through bond formation alloying, while wear is determined by structure through plasticity mechanisms. In the wearless regime, friction is affected by the chemical composition of the counter body and involves the formation of a liquid-like neck and interfacial alloying. The wear behavior of Pt-based metallic surfaces is determined by their structural properties and corresponding mechanisms for plastic deformation. In the case of Pt(111) wear occurs by dislocation-mediated homogeneous plastic deformation. In contrast the wear of Pt57.5Cu14.7Ni5.3P22.5 metallic glass occurs through localized plastic deformation in shear bands that merge together in a single shear zone above a critical load and corresponds to the shear softening of metallic glasses. These results open a new route in the control of friction and wear of metals and are relevant for the development of self-lubricated and wear-resistant mechanical devices.

We present an algorithm for reconstructing a sample surface potential from its Kelvin probe force microscopy (KPFM) image. The measured KPFM image is a weighted average of the surface potential underneath the tip apex due to the long-range electrostatic forces. We model the KPFM measurement by a linear shift-invariant system where the impulse response is the point spread function (PSF). By calculating the PSF of the KPFM probe (tip+cantilever) and using the measured noise statistics, we deconvolve the measured KPFM image to obtain the surface potential of the sample.The reconstruction algorithm is applied to measurements of CdS-PbS nanorods measured in amplitude modulation KPFM (AM-KPFM) and to graphene layers measured in frequency modulation KPFM (FM-KPFM). We show that in the AM-KPFM measurements the averaging effect is substantial, whereas in the FM-KPFM measurements the averaging effect is negligible.

Friction on Au(100) surfaces has been studied by atomic force microscopy under electrochemical control. Atomic-scale stick-slip pattern in the lateral force signal reveal changes in the surface structure upon changing electrochemical potential, in particular between the hexagonal reconstruction and the Au(100)-(1 × 1) structure. Friction on Au(100) is higher on its (1 × 1) structure than on its hexagonal reconstruction. The frictional response after switching between the two structures is delayed due to the necessary surface reorganization. Atomic periodicity in the stick-slip pattern indicates that the increased friction on Au(100)-(1 × 1) is not caused by an ordered anion adlayer, but by the open structure of the (100) surface. Friction is highest on the oxidized surface, and can be switched reversibly between high and low values on the oxidized and the reduced surface.

Single asperity measurements on Si wafers with variable SiO2 layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO2 layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO2 layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model.

α-Cyclodextrin (αCD) was threaded onto 10 kDa poly(ethylene glycol) (PEG), which was then stoppered with bulky end groups (4-methoxynaphthyl or 9-anthracenylmethyl) to give polyrotaxanes containing about 38 αCD rings threaded onto a PEG backbone. The polyrotaxanes were converted into soluble macroinitiators for atom transfer radical polymerization (ATRP) by esterifying the hydroxyl groups of the threaded αCDs with 2-bromoisobutyryl bromide to a degree of substitution (DS) of 8 per αCD. Living ATRP of methyl methacrylate (MMA) from these polyrotaxane macroinitiators led to polymer brushes with molecular weights of up to 1.7 MDa. Polymer brushes were observed by atomic force microscopy. Surprisingly, large amounts of unthreaded αCD star polymer were observed by GPC. The appearance of these unthreaded αCD star polymers was attributed to the shear-induced rupture of the PEG backbone during passage of the brush through the GPC column. Backbone rupture also occurred upon heating the brushes to elevated temperatures. Proof of the bottle-brush structure was further provided without backbone rupture using diffusion ordered NMR spectroscopy.

Sliding friction experiments on graphene grown on SiC(0001) have been performed using a combination of a microtribometer with an atomic force microscope (AFM) allowing for the investigation of atomic-scale wear. The graphene layer delaminates within 10 sliding cycles starting from substrate step edges. After run in, friction is dominated by the interaction between a changing configuration of asperities at the probe sphere and a graphitic interface layer terminating the SiC substrate. Friction varies unpredictably due to changes in the contact configuration. However, the linear relation between friction and contact area can be confirmed and a shear strength as low as a few MPa is found for the contact between ruby and the graphitic layer on SiC, which remains intact under continuous sliding.