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Force curve experiments

Figure 7 Force curve experiments on PS films normalized variation of the vertical displacement AZu needed to unstick the tip from the sample with time for three samples 1890 - 23000 - 284000. The variation with time is obtained by the number of cycles multiplied by the duration of one cycle. Whereas for the 284000 sample AZu is quite constant, its changes for the smaller PS its normalized variation can be fitted by an exponential law, enabling to extract a characteristic time for the smaller samples. Figure 7 Force curve experiments on PS films normalized variation of the vertical displacement AZu needed to unstick the tip from the sample with time for three samples 1890 - 23000 - 284000. The variation with time is obtained by the number of cycles multiplied by the duration of one cycle. Whereas for the 284000 sample AZu is quite constant, its changes for the smaller PS its normalized variation can be fitted by an exponential law, enabling to extract a characteristic time for the smaller samples.
Vertical displacement needed to unstick the tip from the sample in a force curve experiment... [Pg.150]

To illustrate the relationship between the microscopic structure and experimentally accessible information, we compute pseudo-experimental solvation-force curves F h)/R [see Eq. (22)] as they would be determined in SEA experiments from computer-simulation data for T z [see Eqs. (93), (94), (97)]. Numerical values indicated by an asterisk are given in the customary dimensionless (i.e., reduced) units (see [33,75,78] for definitions in various model systems). Results are correlated with the microscopic structure of a thin film confined between plane parallel substrates separated by a distance = h. Here the focus is specifically on a simple fluid in which the interaction between a pair of film molecules is governed by the Lennard-Jones (12,6) potential [33,58,59,77,79-84]. A confined simple fluid serves as a suitable model for approximately spherical OMCTS molecules confined... [Pg.31]

The mechanical instability, jump-in and pull-off phenomenon, can also be observed in a macroscopic system, and both the trajectory and force curves exhibit similar patterns to those in Fig. 6. As a comparison, Fig. 9 shows a force curve obtained from SFA experiments of mica surface separation in diy air [8]. The pattern of the force variation, the... [Pg.170]

Fig. 19—Force curve in a AFM experiment as the probe travels along the surface of NaCI crystal (from Ref. [14]). Fig. 19—Force curve in a AFM experiment as the probe travels along the surface of NaCI crystal (from Ref. [14]).
Figure 9.14 shows a typical approach force curve along with schematic drawings of the relative positions of the SPM tip and the sample surface, as related to the force curve. At the start of the experiment, i.e., position A on the right-hand side of the figure, the tip is above the surface of the sample. As it approaches the surface the Z value decreases until at position B the tip contacts the surface. With further downward movement of the piezo the cantilever starts to be deflected by the force imposed on it by the surface. If the surface is much stiffer than the cantilever, we get a straight line with a slope of — 1, i.e., for every 1 nm of Z travel we get 1 nm of deflection (Une BC in Figure 9.14). If the surface has stiffness similar to that of the cantilever, the tip wUl penetrate the surface and we get a nonlinear curve with a decreased slope (line BD in Figure 9.14). The horizontal distance between the curve BD and the line BC is equal to the penetration at any given cantilever deflection or force. The piezo continues downward until a preset cantilever deflection is reached, the so-called trigger. The piezo is then retracted a predetermined distance, beyond the point at which the tip separates from the sample. Figure 9.14 shows a typical approach force curve along with schematic drawings of the relative positions of the SPM tip and the sample surface, as related to the force curve. At the start of the experiment, i.e., position A on the right-hand side of the figure, the tip is above the surface of the sample. As it approaches the surface the Z value decreases until at position B the tip contacts the surface. With further downward movement of the piezo the cantilever starts to be deflected by the force imposed on it by the surface. If the surface is much stiffer than the cantilever, we get a straight line with a slope of — 1, i.e., for every 1 nm of Z travel we get 1 nm of deflection (Une BC in Figure 9.14). If the surface has stiffness similar to that of the cantilever, the tip wUl penetrate the surface and we get a nonlinear curve with a decreased slope (line BD in Figure 9.14). The horizontal distance between the curve BD and the line BC is equal to the penetration at any given cantilever deflection or force. The piezo continues downward until a preset cantilever deflection is reached, the so-called trigger. The piezo is then retracted a predetermined distance, beyond the point at which the tip separates from the sample.
Fig. 8. (a) Schematic of the AFM pulling experiments and expected unraveling of an individual nucleosome as a result of pulling on the DNA. (b) Example force-extension curves on isolated chicken erythrocyte chromatin fibers redrawn from Ref [69]. (c) Idealized schematic of a typical force-extension curve obtained on pulling single titin moleeules, as in the experiments of Rief et al. [71]. (d) Explanation of the titin force curve by successive unfolding of individual protein domains (see text). [Pg.387]

Earlier attempts to use the AFM for mechanically stretching chromatin fibers have run into a rather unexpected artifact. Long native chromatin fibers isolated from chicken erythrocytes, or fibers assembled in vitro from purified histones and relatively short, tandemly repeated DNA sequences were deposited on mica or glass surfaces and pulled with the AFM tip [69,70]. In such stretching experiments the scanning of the sample in the x- and y-direction used for imaging was disabled, and the cantilever-mounted tip was allowed to move only in the z-direction, i.e., upwards and downwards, away and towards the surface. When the AFM tip is pushed into the sample, it may attach to the sample by non-specific adsorption upon retraction it stretches the sample and force-extension curves are recorded (see Fig. lb for an explanation of a typical force curve). [Pg.387]

In contrast, the Morse force is not monotonic. For a force setpoint of e.g. —InN, two solutions are possible z 2 A and z 4 A. The slope of the force curve is different for the two solutions. Assume that we wish to operate the AFM at a distance of 4 A and a corresponding force of —InN. We would have to wire up the feedback such that it approaches if the actual force is greater than —1 nN, and withdraws if the actual force is smaller than — 1 nN. However, if the tip would encounter an upward atomic step of Az = 2 A, the actual force would be +10nN. Because this value is greater than the setpoint, the feedback would inevitably drive the tip into the sample, leading to a premature and unintended end of the experiment. [Pg.76]

To illustrate the relation between microscopic structure and experimentally accessible information, we focus on the computation of pseudo-experimental solvation-force curv es F h) /R [see Eqs. (5.57), (5.59), (5.63), and (E.46)] as they would be determined in SEA experiments. However, here these curves are computed from computer simulation data for and where P, is... [Pg.203]

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. [Pg.47]

When preparing the calibration curve experiments in a method characterization or validation experiment, there are some key things to remember. It is important to first examine and plot the detector response to analyte in pure or defined solvent (calibration function) and also at various concentrations in the matrix (i.e., in the presence of interferants, or analytical function). Remember that more standard solutions and more calibration points are required when a non-linear response is observed. Extrapolation above or below the analytical range may be used to approximate behavior at zero if a blank is not included in the calibration standards, but the curve should not be forced through the origin. Typically, a curve prepared by... [Pg.276]

This model was subjected to a wide range of loading conditions. A single set of model parameters is sufficient to describe the main features of isometric, isotonic, and quick release and stretch experiments. The model is sensitive to mechanical disturbances, consistent with experimental evidence from muscle force curves [34], aequorin measurements of free calcium ion [35], and high-speed x-ray diffraction studies [36]. The model is also consistent with sarcomere length feedback studies [29] where reduced internal motion delays relaxation. [Pg.141]

An advantage of SMFS is that the polymer sample can be measured in different environments. Such measurements suggest that the double-stranded DNA is thermodynamically unstable in at least some non-aqueous media. To screen the effects of water on the structure of DNA, Cui et al. performed the SMFS experiments on dsDNA in diethylbenzene (DEB, a poor solvent for DNA) [64]. The force curves obtained in DEB were very different from those obtained in water in that they... [Pg.108]

Fig. 18 Schematic of the SMFS experiment and typical force curve obtained in a hexadecane. Figure reproduced with permission from [134]... Fig. 18 Schematic of the SMFS experiment and typical force curve obtained in a hexadecane. Figure reproduced with permission from [134]...

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See also in sourсe #XX -- [ Pg.134 , Pg.136 ]




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Force curve

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