Surface properties mechanical

The friction force vs. load plots provide access to the friction coefficient of the particular tip—polymer sample combination. As illustrated in Fig. 4.18 (right), the friction coefficients increase with increasing degree of surface oxidation. 

Apart from repulsive and attractive forces between a given polymer sample surface and an AFM tip, surface mechanical properties can be measured in contact mode AFM. This requires the acquisition of force-displacement curves and their conversion into force—indentation curves. The subsequent analysis is based on theoretical models and provides access to surface elastic moduli, among others. Since the AFM tip is typically very sharp, moduli can be obtained with high spatial resolution. 

Indentation force measurements utilize the indentation part of a force-displacement curve (Fig. 4.19). In the case of a non-compliant sample surface, the SFM tip does not indent the sample and hence the deflection vs. piezo position curve in the contact region has a slope of 1.0. For compliant samples, the slope is 1.0 and can be used to obtain the elastic modulus of the sample by fitting the measured 

4 Polymer Surface and Interface Properties and (Dynamic) Processes 

Van Landigham et al. reviewed nanoindentation of polymers, [40, 41] including a summary of the most common analyses of load-indentation data. Chief among these methods is an analysis of indentation load-penetration curves according to the Oliver-Pharr method. [42] This method is based on relationships developed by Sneddon for the penetration of a flat elastic half space by different probes with particular axisymmetric shapes (e.g., aflat-ended cylindrical punch, a paraboloid of revolution, or a cone) [43], More recently, Withers and Aston discussed indentation in the context of plasticity and viscoelasticity [44]. 

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Asif, S.A.S., Colton, R.J. and Wahl, K.J., Nanoscale surface mechanical property measurements Force modulation techniques applied to nanoindentation. In Ovemey, R.M. and Frommer, J.E. (Eds.), Interfacial Properties on the Submicron Scale. ACS/Oxford Press, Oxford, 2001. 

Figures 4 and 5 give a broad indication of the relevant biomechanical properties of a number of flow sensitive biomaterials. In the case of the data shown in Fig. 5, the surface mechanical properties are lumped into a single measure of the surface integrity. Admittedly, in view of what has been said in the introduction about the viscoelastic nature of the wall material, the information given in Figs. 4 and 5 are oversimplistic. The data in Fig. 5 are based on reported critical minimum stresses (often expressed in terms of the mean bulk fluid stresses) at which physical damage is first observed. Figure 6 gives an indication of the...

Surface mechanical properties (nanoindentation). Nanoindentation technique has an important role in the characterisation of mechanical properties of materials... 

The development of multipurpose nanoindentation instruments that also perform scratch testing, profiling, and measurements of scratch hardness, film stress, friction, and other surface-mechanical properties. 

To explore the behaviour of ion-implanted polymers microfriction studies were conducted on 1 MeV Ar" " implanted PEEK, and PS implanted to fluences of 5, 10 and 50 x 10 ions m (Rao et al, 1995). The results were compared with macrofriction values obtained using standard pin-on-disc-type tests. The polymers were also characterized for surface mechanical properties using the nanoindentation technique. The most striking aspect of the microfriction tests on the ion-implanted polymers is a marked stick-slip behaviour, which was not observed for the non-irradiated polymers. 

In addition to its capability of imaging the topography of polymer surfaces with virtually eliminated shear forces, intermittent contact (tapping) mode AFM, can also be useful to probe various surface properties, such as adhesive or surface mechanical properties. Thereby AFM can help to identify and quantify the abundance and distribution of the phases present in multicomponent systems. As shown already... 

Compositional contrast, as well as modulus, can also be assessed by laterally resolved imaging of normal or lateral forces in the contact mode AFM. In the corresponding mapping [121] (see also Chap. 4), force-displacement curves are recorded for each pixel. Subsequently, the pull-off forces, as a measure for adhesion, and the indentation part of the loading curves, to extract/fit the elastic modulus, are evaluated for each pixel. In particular for adhesion mapping, the use of chemically functionalized AFM probe tips [122], has been shown to be a suitable approach to map chemical composition and functional group distributions down to the sub-50 nm scale [123]. The mapping of adhesion, friction, and surface mechanical properties will be treated in more detail in Chap. 4. 

In a recent study, the interphases for different fiber/polymer matrix systems were investigated. By using phase imaging the differences in local mechanical property variation in the interphase of glass fiber reinforced epoxy resin (EP) and glass fiber reinforced polypropylene matrix (PP) composites could be unraveled. As shown in Fig. 3.68, the glass fiber, the interphase and the PP matrix can be differentiated based on their surface mechanical properties as assessed qualitatively by TM phase imaging. 

H.-J. GLASEL, F. BAUER, E. HARTMANN, R. MEHNERT, H. MOBUS, V. PTATSCHEK, Radiation-cured polymeric nanocomposites of enhanced surface-mechanical properties , NIM-B, (2003)... 

The oldest relaxation teehniques, developed to measure dilational elasticities and exchange of matter, are the methods of wave damping. If a wave is generated by mechanical or other means, it propagates along the surface and is damped by hydrodynamic and surface mechanical properties (Goodrich 1962). 

Surfaces - an introduction/Structure of surfaces/Thermodynamics of surfaces/ Dynamics at surfaces/Electronic properties of surfaces/The surface chemical bond/ Catalysis by surfaces/Mechanical properties of surfaces... 

The resistance to deformation at the surface can be quantified at the micrometer and nanometer scale. At the micrometer scale, traditional hardness measurements are conducted on a polymer system using a handheld durometer, whereby the penetration tip is varied to properly quantify the Shore hardness. At the nanometer scale, measurements of modulus and depth of penetration are quantified using quasi-static nanoindentation. Increases in stiffiiess at the surface of an American football helmet outer shell material exposed to accelerated weathering (Krzeminski et al., 2014c) and repetitive linear impacts (Krzeminski et al., 2014b) have been quantified using quasi-static nanoindentation. However, Shore A hardness measurements were reported to be overly forceful to quantify shifts in surface mechanical properties of injection-molded American football helmet outer shell materials (Krzeminski et al., 2014b,c). 

Wol] studied the influence of microalloying with Ti on the plastic deformation of Fe-40Cr alloys. A study of surface mechanical properties of Ti implanted Cr-Fe alloys has been performed by [1988Sas]. 

Sas] Surface hardness, friction coefficient Surface mechanical properties of TY-implanted Cr-Fe alloys... 

Sas] Sasaki, J., Iwaki, M., Surface Mechanical Properties and Micro-Characteristics of tC-Implanted Fe-Cr Alloys Depending on Cr Concentration in Fundamentals of Beam-Solid Interactions and Transient Thermal Processing , Symposium. Mater. Res. Soc., 185-190, (1988) (Phase Relations, Meehan. Prop., Experimental, 8)... 

Tavares AC, Guknine JV, Lepienski CM, Lepienski A. The effect of accelerated aging on the surface mechanical properties of polyethylene. Polym Degrad Stab 2003 81 (2) 367-373. 

Hu Y, Zhou S, Wu L (2009) Surface mechanical properties of transparent poly(methyl methacrylate)/zirconia nanocomposites prepared by in situ bulk polymerization. Polymer 50(15) 3609-3616... 

A lot of work has been done regarding how surface mechanical properties regulate the activities of mammalian cells. The mechanical property discussed in the litera-... 

IntGrmittGnt Contact ModG SFM. Intermittent contact mode SFM, also called tapping mode SFM, has been developed to reduce shear forces (36), which can cause sample deformation or even destruction of soft samples in contact mode SFM (for a recent review see Ref 19). In addition, this mode can be useful to probe adhesive or surface mechanical properties, and thus achieve contrast between different materials. Intermittent contact mode SFM uses an oscillating cantilever/tip assembly to minimize contact time and contact forces, and to especially eliminate shear forces between tip and sample surface. This mode relies on a similar setup as contact mode SFM. However, in intermittent contact mode (in air) a stiffer cantilever is used ik = 20-80 N/m). This cantilever is excited to vibrate near its resonance frequency by an excitation piezo. Close to a sample surface, the vibration is damped as a result of tip sample interactions. The original amplitude Aq is hence reduced to A, depending sharply on the distance to the surface (Fig. 2c). The... 

Normal Forcos. In the treatment of normal forces, a differentiation into the measurement of adhesive forces, related to, eg, surface chemistry, quantification of entropic and enthalpic forces, dealing with single polymer chain properties, and finally indentation measurements, yielding surface mechanical properties, has been made. 

Further examples for real-time studies, which are becoming increasingly more important, target (surface) glass-transition temperatures (225-228), and thermotropic transitions in liquid crystalline polymers both at high and low temperatures (299-301). The analysis of temperature-dependent dynamical-mechanical surface properties has already been mentioned in the section under Surface Mechanical Properties (229-231,270-273). 

Also, the surface softness increases due to hydrolysis-formed pores. On the other hand, Saiz-Arroyo et al. [47] showed that the surface mechanical properties of PLLA, such as the creep constant and microhardness, decreased with NHD. 

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