Force versus distance curves

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

FIG. 9 Curve of sample motion versus lever motion. The experimental starting point for generating a force versus distance curve. 

Fig. 19 Representative force-versus-distance curves (approach trace) measured on NI-PAAm graft-polymerized surfaces. Solid curves 25 °C, dashed curves 40 °C...

Fig. 34 Peel force versus distance curves for polysulfide/nanoclay adhesive systems...

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

Fig. 37 Peel force versus distance curves of and BCLNA16...

Comparison of the frost crystals observed via SEM at humidity of 30% (Fig.3a and 3b) prepared with those observed via AFM under similar conditions (Fig.2a, 2b, 2c and 2d) shows very little similarities. The temperature difference between the laser heated tip " and the ice surface has a large impact on the AFM imaging process. When the tip touches the surface covered with frost, melting of frost crystals immediately takes place, so that the tip loses contact with frost/ice (established via force-versus-distance curves). In this case the tip was approached further to the surface. The small size of the crystallites obtained at humidity... 

From the general shape of the E r) curve, one can easily sketch the shape of a typical force versus distance curve, as shown in Fig. 4.6. The following salient features are noteworthy ... 

The accurate and absolute measurement of the distance, D, between the surfaces is central to the SFA technique. In atypical experiment, the SFA controls the base position, Z3, of the spring and simultaneously measures D, while the spring constant, k, is a known quantity. Ideally, the simple relationship A F D) = M (D-z ) applies. Since surface forces are of limited range, one can set F(D = qo) = 0 to obtain an absolute scale for the force. Furthermore, 5F(Z) = qo)/5Z) 0 so that one can readily obtain a calibration of the distance control at large distances relying on an accurate measurement of D. Therefore, D and F are obtained at high accuracy to yield F D), the so-called force versus distance curve. 

Fig. 3 Schematic deflection-versus-piezo translator position curve (Az versus Azc). At large separation, no force acts between tip and sample (a). The cantilever is not deflected. When approaching the surface, it was assumed that a repulsive force is acting (b) and the cantilever is bent upwards. At a certain point, the tip often jumps onto the sample. This happens when the gradient of attractive forces, for example, the van der Waals forces, exceeds the spring constant of the cantilever. After the jump-in, the tip is in contact with the sample surface (c). When retracting the tip, often an adhesion force is observed (d) and the tip has to be pulled off the surface. The deflection-versus-piezo translator position curve has to be transformed as described in the text to obtain a force-versus-distance curve (F versus D).

Fig. 10 Normalized force-versus-distance curve measured with a hydrophilic silica particle in aqueous electrolyte with no added DTAB, 0.1 mM DTAB, 5.4 mM DTAB, and 13.2 mM DTAB (from Ref [143]). The electrolyte contained 0.3 mM KCl, the pH was around 5.5. The insert at 5.4 mM shows the electrostatic repulsion before the jump-in. The particle radius Rwas 2.5 pm.

In the more dilute KCl solution, the force versus distance curve extended beyond a 30-nm separation whilst in the 1 X 10 mol dm KCl solution, the force interaction decayed within the first 8 nm (see Fig. 8). This behavior was... 

The nanotribological properties of the SAM films generated from CnOH, CnCHs, and CsCH3 SAM films were characterized through the measurement of frictional forces with a plasma-cleaned silicon nitride tip as a function of load under distilled water. Representative friction-versus-load plots obtained by AFM are presented in Fig. 4a. The force-versus-distance curves obtained from the same three SAM films are shown in Fig. 4b. In order to ensure a statistically valid comparison, the measurements were repeated several times in varying order using the same tip/... 

Measurements with oxygen-plasma-treated probes were performed in air, deionized water, and the same PBS buffer as used in the protein-adsorption experiments. Force-versus-distance curves in air with an oxygen-plasma-treated probe (k = 0.03 N/m) revealed no significant differences between the EG3-OMe SAMs on gold and silver. A large adhesion hysteresis primarily due to capillary forces was found for both surfaces. Pull-off... 

Figure 5.9 (a) Force versus distance curves for alumina at different pH values calculated from Equations (5.8) and (5.11) with parameters as detailed in Franks et al. (2000). At pH 9 the van der Waals attraction dominates. As pH is decreased the range and magnitude of the EDL repulsion increases as zeta potential increases (see Figure 5.8). At very small separation distances the van der Waals attraction always dominates the EDL repulsion, (b) Force versus distance curves for silica particles interacting with an adsorbed polymer (Zhou et al, 2008). Upon approach, the adsorbed polymer provides a weak steric repulsion. Upon separation (retraction) the polymer creates a strong long range attraction because chains are adsorbed on both surfaces. The van der Waals only interaction is shown for comparison...

First, we note that a force versus distance curve may be obtained in two fundamentally different ways. The force can be controlled and the resulting separation measured. This is the principle used in the thin film balance. Alternatively, the distance can be controlled and the resulting force determined, and this is the method utilized in the SFA, AFM and MASIF approaches. The methodology used in these latter techniques does, however, differ in several important respects. Perhaps the most fundamental difference is how the force and the surface separation are determined. 

Scanning Force Microscopy. All measurements were performed under a constant humidity of 45 %. For recording the Force Curves, silicon cantilevers with a spring constant of 1.2 N/m were used. Curves were taken with frequency of 1 Hz. To get Force versus Distance Curves (FDC) s from the measured Force versus Piezo Displacement Curves, these curves were transformed by a standard calibration procedure. Reduced cantilever stiffhess is taken into account when calaculating the FDCs of the thin polymer films at different temperatures. Pull-off forces estimated from 10 curves have a standard deviation of about 3 nN. 

Force versus Distance Curves. Figure 3 shows representative curves for different polymer films at room temperature (27 C) and at 67 °C. Changes in penetration depth and in the slope of the retraction segment of these curves are summarized in Table 2. The slope of the curves reflect the elastic properties of the film, where a larger slope is correlated to a higher local stiffness. As expected, the local stiffness... 

Probe tests to measure the tack adhesion are accomplished by bringing a probe into contact with the surface of the polymer material being tested under a given force for a specified period of time. The probe is then raised at a constant velocity while measuring the force required to do so. The resulting force versus distance curve provides valuable information on the adhesion properties of the material. The measured adhesion depends on the probe... 

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