Force curve measurement

Elegant force measurements have been made between adsorbed monolayers of die protein cytochrome-c, and insulin on mica, immersed in water [26]. Hydration forces here play no role. If the full armoury of theoretical predictions is invoked, the complicated force curves measured all seem to fall into place. It is possible, indeed probable that with real biological membranes that contain up to 50% proteins, the hydration forces that prevent fusion of pure phospholipid membranes do not always operate. 

The forces measured at higher surfactant concentration, up to 2 cmc (1.7 X 10 2 M), also display oscillations with a periodicity of 40 A. One example of such a force curve, measured at an SDS concentration of 1 cmc, is illustrated in Figure 17. We note that the periodicity of the oscillations remains unchanged when the SDS concentration is increased, but the number of oscillations and their magnitude differs. This is more clearly shown in Figure... 

The shapes of the force curves further indicate that two distinctly different behaviors in pull-off are apparent. For example, force curves measured for less compatible asphalts of lower molecular weight, such as asphalt AAD-1 (Fig, 6d), fail abruptly as the tensile stress of the material increases nearly linearly up to a point of sudden failure with applied pull-off force. The contact area between the tip and the surface is assumed to remain constant up to the point of... 

Figure 5.21. Force curve measured on PA films. The pull-off force is 125 nm. (Reprinted with permission from ref 27)...

The model systems studied have allowed us to express the mechanical and chemical surface contributions in a force curve measurement and to establish a relationship at the nanoscale which is quite similar to the relationship of Gent and Schultz [11]. Then a new relationship has been proposed to determine the thermodynamic surface properties of viscoelastic materials on the basis of AFM experiments. 

Fig. 6 (a) Typical B-S force curve of dsDNA. (b) Force curves of dsDNA obtained in a pow solvent, DEB. (c) Comparison of forces curve measured on dsDNA and ssDNA in poor solvent and fitting curve to the QM-FRC model. Figure reproduced with pennission from [32]... 

Figure 5.12 Force curves measured which is not accounted for in the standard...

Sensor (Machines), Fig. 6 Force curve measured by embedded sensor... 

In the present author s group, the electric double layer of Au(l 11)-BM1PF6 interface and its dependence on potential has been investigated systematically using in-situ AFM force curve measurements [22]. Figure 9.4 shows a high-quality AFM force curve measured at... 

AFM can provide a vast degree of localized mechanical information [73] by utilising probe-sample interactions to obtain a force curve, measured by noting the deflections of the cantilevers, that theoretically has femtonewton sensitivity [16]. However, ambient noise limits the level of detection. The deflection in the cantilever 8c (measured by the laser on the photodiode) is determined and is used to generate a force-distance curve based on the principles of Hookes Law (shown in Eq. 2). 

Figure 4.20 shows the force curves measured during thermal expansion and shrinkage for two different polypropylene libers (Foreman et al., TA Instruments Application Note 208 reference). A strain is imposed on the fiber and held constant. As the fiber is heated, the force is measured. The force decreases when the fiber expands and increases when the fiber shrinks.The fibers depicted... 

Force-Curves Measurements In force curve measurements, a vertical displacement of the sample, z, is imposed and the subsequent tip displacement, d, is measured. The tip-sample interaction force, F, is deduced by means of the Hooke s relation, F = -kcd, where is the cantilever stiffness. Force curves arc generally divided into different regions (7). If the part where the electrostatic repulsion forces are dominant is only considered, with silicon tips much stiffer than polymers, tips penetrate the sample surface and an indentation depth, 5, equal to Z d, can be measured. The lower the sample elastic modulus, the greater will be the indentation depth. By using the Hertz mechanical model adapted to the geometry of the tip-sample system (8,9) surface elastic modulus could be deduced from the following equations corresponding respectively to a spherical, a paraboloid and a conical tip ... 

The conversion factor of the voltage measured on the photodetectors into tip displacement was calibrated by performing a force-curve measurement on a rigid sample (silicon) and by assuming that, in this case, the tip displacement is equal to the sample displacement. This calibration procedure was repeated each time the cantilever was changed or the laser beam refocussed on the cantilever. 

Force curves measured between (A) silica (a) and polystyrene (b) substrates coated with C3M-PEO204/PAA139 and a silica probe at 10 mM NaCl, pH 7 (B) silica (a) and polysulfone (b) substrates coated with C3M-PVA445/P2MVPI228, and a silica probe at 10 mM NaCl, pH 7. Closed symbols correspond to approach and open to retraction. C3M corresponds to complex coacer-vate core micelles. (Reproduced from Brzozowska, A. M., et al.. Journal of Colloid and Interface Science, 353,380-91,2011. With permission from Elsevier.)... 

As shown in Ref. 43 the deposited volume can be deduced from the force curves measured during the deposition process. In the case of femtoliter droplets (diameter in the 1 p.m range], a sharp increase of droplet size is observed for short times (t < 2 s typically), followed by a saturation regime where prolonged contact time has no obvious impact on the liquid flow. This dynamics indicates a nondiffusive process for the liquid transfer in striking a contrast to molecule transfer in DPN and confirms the fundamental difference... 

The force curves measured during the retraction of the NADIS tip is the only information available during the deposition. It corresponds to the capillary force exerted by the liquid meniscus bridging the tip and the surface. These curves strongly differ from the ones obtained with a standard dry atomic force microscope tip on a surface. Examples of curves obtained using various NADIS tips are reported in Fig. 12.12. 

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