Local mechanical property

Among the many microscopy-based techniques for the study of biomolecular interactions on surfaces, scanning probe microscopies, and especially the atomic force microscopies (AFM), are the most used because of their molecular and sub-molecular level resolution and in situ imaging capability. Apart from the high resolution mapping of siuface nanotopographies, AFM can be used for the quantification and visualisation of the distribution of chemistry, hydrophobicity and local mechanical properties on surfaces, and for the fabrication of nanostructmes on surfaces. 

Fig. 16 Schematic representation of an interface-induced segregation scenario. As long as the viscosity of the crosslinking system is low enough, segregation of epoxy resin and curing agent may occur, driven by the polar surface of the Cu component. Conservation of mass requires a depletion zone close to the zone of enrichment. Via the network structure the concentration profile is reflected by the local mechanical properties of the cured epoxy system...

AFM can also be used to probe local mechanical properties of thin films of food biopolymers, which are difficult to measure using traditional rheological methods. Several mechanical models have been developed to analyze the Young s modulus of food systems. One of the simplest models, the Hertz model, assumes that only the elastic deformation exists in a surface with spherical contacts, and the adhesion force can be neglected (Hugel and Seitz 2001). Equation (8.2) describes the relationship between the loading force, F and the penetration depth, d, where a is the radius of contact area, R the curvature of the tip radius, Vi and the Poisson s ratios of the two contact materials that have Young s modulus, Ei and E2. ... 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

It will be shown that the level of uniaxial orientation and the variation of local mechanical properties generated by controlling the injection temperature can be conveniently characterized by microhardness measurement in combination with the measurement of optical birefringence An and DSC. In Section 2.7 we saw that microhardness is a very useful mechanical property, which can provide direct information about the anisotropy developed within highly oriented polymers. 

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. 

This is the reason why the AFM appears as an interesting, versatile tool, for investigating local mechanical properties. Beyond a pure topographical approach, the analysis of change in the surface properties becorines a way of characterising a surface at the siibmicrometer scale. Obviously, for soft samples... 

In order to determine the local mechanical properties such as the hardness and modulus of non-flat samples or heterogeneous multiphase materials, a DSI system was integrated in a scanning device. This system combines SFM-like topography imaging with the ability of DSI tests to be performed at selected areas of interest by using a well-defined diamond tip. 

Boundaries between a reactive polymer system, e.g. an epoxy, and solid substrates modify the mechanical properties of the polymer in the interface-near region. The so created interphases are of unexpected width up to several hundred pm. The recently developed Brillouin microscopy grants nondestructive access to the local mechanical properties within these interphases. It turns out that these mechanical interphases depend strongly on the kind of polymer system, the substrate material and the preparation conditions. 

Note that in addition to the standard Dirichlet boundary data for the displacements, Dirichlet boundary data for the microstructural parameter also have to be prescribed. Experimentally [24, 37] the local mechanical properties in the interphase depend on both the polymer and the substrate. The possibility of prescribing additional boundary conditions for k is utilized to describe the variations of the mechanical properties in the interphase depending on the substrate. If on the one hand ic = ko is chosen as Dirichlet data for the structural parameter, no interphase is predicted by the model. If on the other hand, ic > Kq or K < Ko is chosen, an interphase is predicted which is either stiffer or weaker than the bulk material, respectively. The thickness of the interphase is mainly governed by the material parameters a and yS. 

At this point, it is worth noting that there is limited data regarding the actual local mechanical properties of native and diseased tissues. Rather, our knowledge of tissue mechanical properties is largely based on macroscopic mechanical measurements. The lack of mechanical property characterization at the microscale... 

Sato, M., Nagayama, K., Kataoka, N. et al.. Local mechanical properties measured by atomic force microscopy for cultured bovine endothelial cells exposed to shear stress, J. Biomech., 33, 127,... 

Camposeo, A., Greenfeld, 1., Tantussi, E, Pagliara, S., Moffa, M., Fuso, E, Allegrini, M., Zussman, E., Pisignano, D., 2013. Local mechanical properties of electrospun fibers correlate to their internal nanostructure. Nano lett. 13,5056-5062. 

AFM can be used not only for imaging the topography of surfaces but also for measuring local mechanical properties, as it will be described in Section 4.4.5. 

A scanning force instrument also allows for the acquisition of force-distance curves to characterize the local mechanical properties of the sample. Well-defined indentation experiments on soft surfaces like swollen hydrogels in aqueous media are possible with the colloidal probe technique. Raw data are assessed, for example, according to the Hertz model, with the assumption... 

Mosaliganti, K.R., Noche, R.R., Xiong, F., Swinburne, LA., Megason, S.G. ACME automated cell morphology extractor for comprehensive reconstruction of cell membranes. Biol, PLoS Compu. (2012). doi 10.1371/joumal.pcbi.l002780 Neuman, K.C., Block, S.M. Optical trapping. Rev. Sci. Instrumen. 75, 2787-2809 (2004) Ohashi, T., Ishii, Y., Ishikawa, Y., Matsumoto, T., Sato, M. Experimental and nnmerical analyses of local mechanical properties measured by atomic force microscopy for sheared endothelial cells. Biomed. Mater. Eng. 12, 319-327 (2002)... 

Nanostructural and Local Mechanical Properties in the Sureace Region... 

PHASE MORPHOLOGY AND LOCAL MECHANICAL PROPERTIES IN BLOCK COPOLYMER SYSTEMS... 

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