The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on Their Tribological Properties at Elevated Temperatures

The chapter discusses the tribological properties of samples with multilayer composite nanostructured Ti-TiN-(Ti,Cr,Al,Si)N, Zr-ZrN-(Nb,Zr,Cr,Al)N, and Zr-ZrN-(Zr,Al,Si)N coatings, as well as Ti-TiN-(Ti,Al,Cr)N, with different values of the nanolayer period λ. The relationship between tribological parameters, a temperature varying within a range of 20–1000°C, and λ was investigated. The studies have found that the adhesion component of the coefficient of friction (COF) varies nonlinearly with a pronounced extremum depending on temperature. The value of λ has a noticeable influence on the tribological properties of the coatings, and the nature of the mentioned influence depends on temperature. The tests found that for the coatings with all studied values of λ, an increase in temperature first caused an increase and then a decrease in COF.

Mechanical Properties and Size Effects of Self-Organized Film

In our research, we have focused on the estimation of tribological and mechanical characteristics of self-organized copper film, formed through a friction of brass-steel pair in aqueous solutions of carbolic acid. We have found out that self-organized copper film formed through a friction interaction of pair brass-steel is nanostructural. The data obtained through the indentation of self-organized copper films indicated size effect. With an increasing load and contact area of interacting bodies, the coefficient of friction first drops sharply with an increasing normal load and then begins to grow. We have found out that the adhesion component of friction contributes to the friction coefficient at small loads. We have shown that the hardness of self-organized copper films formed at friction in aqueous solutions of acids increases upon shifting from acetic to caproic acid.

Requirement for and polarized localization of integrin proteins during Drosophila wound closure

Wound reepithelialization is an evolutionarily conserved process in which skin cells migrate as sheets to heal the breach and is critical to prevent infection but impaired in chronic wounds. Integrin heterodimers mediate attachment between epithelia and underlying extracellular matrix and also act in large signaling complexes. The complexity of the mammalian wound environment and evident redundancy among integrins has impeded determination of their specific contributions to reepithelialization. Taking advantage of the genetic tools and smaller number of integrins in Drosophila, we undertook a systematic in vivo analysis of integrin requirements in the reepithelialization of skin wounds in the larva. We identify αPS2-βPS and αPS3-βPS as the crucial integrin dimers and talin as the only integrin adhesion component required for reepithelialization. The integrins rapidly accumulate in a JNK-dependent manner in a few rows of cells surrounding a wound. Intriguingly, the integrins localize to the distal margin in these cells, instead of the frontal or lamellipodial distribution expected for proteins providing traction and recruit nonmuscle myosin II to the same location. These findings indicate that signaling roles of integrins may be important for epithelial polarization around wounds and lay the groundwork for using Drosophila to better understand integrin contributions to reepithelialization.

Towards development of a versatile and efficient strategy for fabrication of GO based polymer nanocomposites

Graphene oxide was facilely functionalized with synthetic polymers in aqueous solution using dopamine as the adhesion component.

THE FRICTION MECHANISM BETWEEN SURFACES WITH REGULAR MICRO GROOVES UNDER BOUNDARY LUBRICATION

The results of research related to the influence of partially regular microrelief parameters on the adhesion component of the friction factor under boundary lubrication are presented. It has been shown that micro grooves are effective under boundary friction on precision surfaces with low roughness when lack of film and probability of seizure appear. The deformation component of the friction force of surfaces with micro grooves has been studied. The time of micro running-in was the key factor while assessing the dependence of the deformation component on friction when taking into account the depth of micro grooves and their relative area. The research was conducted using a tribometer according to the friction model entitled “shaft & flexible steel tape”.

Interpretation of the human skin biotribological behaviour after tape stripping

The present study deals with the modification of the human skin biotribological behaviour after tape stripping. The tape-stripping procedure consists in the sequential application and removal of adhesive tapes on the skin surface in order to remove stratum corneum (SC) layers, which electrically charges the skin surface. The skin electric charges generated by tape stripping highly change the skin friction behaviour by increasing the adhesion component of the skin friction coefficient. It has been proposed to rewrite the friction adhesion component as the sum of two terms: the first classical adhesion term depending on the intrinsic shear strength, τ 0 , and the second term depending on the electric shear strength, τ elec . The experimental results allowed to estimate a numerical value of the electric shear strength τ elec . Moreover, a plan capacitor model with a dielectric material inside was used to modelize the experimental system. This physical model permitted to evaluate the friction electric force and the electric shear strength values to calculate the skin friction coefficient after the tape stripping. The comparison between the experimental and the theoretical value of the skin friction coefficient after the tape stripping has shown the importance of the electric charges on skin biotribological behaviour. The static electric charges produced by tape stripping on the skin surface are probably able to highly modify the interaction of formulations with the skin surface and their spreading properties. This phenomenon, generally overlooked, should be taken into consideration as it could be involved in alteration of drug absorption.

Osteoblast Sensitivity to Topographical and Chemical Features of Titanium

The titanium-osteoblast-interaction can be influenced both by surface roughness and by chemical modifications. We have ascertained that a positively charged titanium surface boosts osteoblast cells adhesion due to their negatively charged cellular hyaluronan coat. In current experiments, chemical surface modifications were combined with different topographies. Titanium disks of technical purity were modified (i) in their roughness by polishing (P), machining (M) and corundum blasting (CB), and (ii) by subsequently chemical functionalization by a thin film (d≤0.1 µm) of microwave plasma polymerized allylamine (PPAAm). In addition, collagen I was immobilized on PPAAm via the bifunctional linker polyethylene glycol diacid or glutar dialdehyde, respectively. The cell shape and material's contact of human osteoblasts was analyzed by FE-SEM and time dependent cell adhesion measured by flow cytometry. The cell dynamic of the adhesion component vinculin was observed in living cells. Amino-functionalization (PPAAm) considerably enhances the adhesion of osteoblasts in combination with topographical features, which was in contrast to collagen modified surfaces. PPAAm allows the cells to literally melt into the groove structure of the titanium. The bone cells lie over a large area and very close to the surface, so that the edges of the cells can hardly be distinguished from the structure of the surface. The combinatory effect of topography and plasma modification could improve bonding of the implant to the bone tissue.

Studies of Friction Mechanism in Silica and Carbon Black Filled SBR: (3) Friction of Carbon Black and Silica Filled SBR Blends

Tire tread compounds usually consist of polymer blends. In this paper the friction for immiscible SBR blends which consist of two different SBRs having different glass transition temperatures of −51 °C and −6 °C are investigated. The effects of the blend ratio of these two SBRs and the added fillers such as carbon black and silica on the friction are also investigated. The friction forces are measured when rubber specimens are rubbed against dry or wet metal gauze. The friction force-sliding speed curves for the SBR blends are related to their storage modulus E′, loss tangent tan δ, contact area A and shear strength s. The adhesion component of the friction for each SPR blend shows a peak at the sliding speed range examined. As the blend ratio of the SBR having higher Tg of −6 °C is raised, the peak value is lowered and the peak shifts to lower sliding speed. The adhesion component of the friction for silica-filled SBR blends is higher than that of carbon black-filled SBR blends. These trends are also shown when rubber specimens are rubbed against the wet metal gauze. On the other hand, the hysteresis component of friction is raised when the blend ratio of the SBRs having higher Tg is increased.