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  • 1.
    Claesson, Per M.
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap. RISE.
    Dobryden, Illia
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    He, Yunjuan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Li, Gen
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Surface Nanomechanics of Coatings and Hydrogels2019Inngår i: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing , 2019, nr 1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Due to the increasing use of nanostructured materials and thin coatings as barrier materials, it has become of high importance to measure and understand material properties on the nm to 100 nm length scales. In this article we demonstrate and discuss how atomic force microscopy techniques can be used to this end. It is demonstrated that the classical analysis based on the assumption of a purely elastic material response is a fair approximation for relatively stiff coatings (elastic modulus order of GPa), whereas viscous responses must be considered for soft materials (apparent modulus order of MPa) such as hydrogels.

  • 2.
    He, Yunjuan
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Li, Gen
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Hwang, Ki-Hwan
    Claesson, Per Martin
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Nano-scale mechanical and wear properties of a corrosion protective coating reinforced by cellulose nanocrystals: initiation of coatingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Organic coatings are commonly used for protection of substrate surfaces like metals and wood. In most cases they fulfil their purpose by acting as a barrier against unwanted substances such as oxygen, water or corrosive ions. However, with time coatings fail due to degradation caused by chemical reactions or wear by wind, water, impact of solid particles or sliding motions against other solid objects. In this work we focus on a nanocomposite coating having a hydroxyacrylate-melamine matrix and being reinforced by a small amount (0.5 wt.%) of cellulose nanocrystals. This nanocomposite is of interest as it has shown favourable corrosion protection properties on carbon steel. Here we investigate the nanomechanical and nanowear properties of the coating in air and in water, and we also explore how these properties are affected by exposure to a corrosive 0.1 M NaCl solution. Our data show that the nanomechanical properties of the coating surface is strongly affected by the environment (air or water), and that exposure to the corrosive solution affects the coating surface well before any deterioration of the corrosion protective properties are found. We suggest that our experimental methodology constitutes a powerful way to investigate and understand the initiation of coating degradation.

  • 3.
    Li, Gen
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Dobryden, Illia
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Salazar-Sandoval, Eric Johansson
    RISE Res Inst Sweden, Div Biosci & Mat, Box 5607, SE-11486 Stockholm, Sweden..
    Johansson, Mats
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Claesson, Per M.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap. RISE Res Inst Sweden, Div Biosci & Mat, Box 5607, SE-11486 Stockholm, Sweden..
    Load-dependent surface nanomechanical properties of poly-HEMA hydrogels in aqueous medium2019Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, nr 38, s. 7704-7714Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical properties of hydrogels are of importance in many applications, including scaffolds and drug delivery vehicles where the release of drugs is controlled by water transport. While the macroscopic mechanical properties of hydrogels have been reported frequently, there are less studies devoted to the equally important nanomechanical response to local load and shear. Scanning probe methods offer the possibility to gain insight on surface nanomechanical properties with high spatial resolution, and thereby provide fundamental insights on local material property variations. In this work, we investigate the local response to load and shear of poly(2-hydroxyethyl methacrylate) hydrogels with two different cross-linking densities submerged in aqueous solution. The response of the hydrogels to purely normal loads, as well as the combined action of load and shear, was found to be complex due to viscoelastic effects. Our results show that the surface stiffness of the hydrogel samples increased with increasing load, while the tip-hydrogel adhesion was strongly affected by the load only when the cross-linking density was low. The combined action of load and shear results in the formation of a temporary sub-micrometer hill in front of the laterally moving tip. As the tip pushes against such hills, a pronounced stick-slip effect is observed for the hydrogel with low cross-linking density. No plastic deformation or permanent wear scar was found under our experimental conditions.

  • 4. Peng, T.
    et al.
    Yan, Q.
    Li, Gen
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Zhang, X.
    The Influence of Cu/Fe Ratio on the Tribological Behavior of Brake Friction Materials2018Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, nr 1, artikkel-id 18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Copper and iron are the major ingredients in friction materials, among which Fe often been served as friction reinforcement in the past. But in our recent study, the coefficients of friction (COF) decreased with increasing iron content in composites. In order to study the influence of Cu/Fe ratio on the tribological behavior of the composite under simulative braking conditions, a subscale testing apparatus with the pad-on-disk configuration under various initial braking speeds (IBS) was applied. The changes in mean COFs, wear rates, morphologies and chemical constitutions of friction surface for different composites were investigated. Results showed that the composite containing more Fe content always showed lower mean COF and wear rate, which different from the previous studies. This is because, under severe braking conditions, the tribological behavior of composite mainly depends on the evolution of tribo-oxide film on the surface, not just on the substrate themselves. Higher Fe content accelerated the formation of tribo-oxide film and in turn inhibited the destruction of tribo-oxide film on the surface, which leading to lower mean COF and wear rate, as well as a higher critical IBS for the transition of mean COF and wear rate. This work also provides a way to characterize the fracture strength of tribo-film by carried out a peeling test.

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