Elasticity electrostatic force

RosaZeiser, A., Weilandt, E., Hild, S. and Marti, O., The simultaneous measurement of elastic, electrostatic and adhesive properties by scanning force microscopy pulsed-force mode operation. Measur. Sci. Techno ., 8(11), 1333-1338 (1997). 

Several types of interaction can be probed with AFM (i) Van der Waals forces and ionic repulsion, (ii) magnetic and electrostatic forces, (iii) adhesion and frictional forces and (iv) the elastic and plastic properties of the surface. In terms of the interactions relevant to electrochemistry, only those interactions typified in (i) will be considered. 

It is easy to understand that these solutions must exhibit viscoelastic properties. Under shear flow the vesicles have to pass each other and, hence, they have to be deformed. On deformation, the distance of the lamellae is changed against the electrostatic forces between them and the lamellae leave their natural curvature. The macroscopic consequence is an elastic restoring force. If a small shear stress below the yield stress ery is applied, the vesicles cannot pass each other at all. The solution is only deformed elastically and behaves like Bingham s solid. This rheological behaviour is shown in Figure 3.35. which clearly reveals the yield stress value, beyond which the sample shows a quite low viscosity. 

From this discussion, the mechanism of dependence of pH on relaxation properties is as follows. Introduced side chains are ionized with an increase in pH, so that wood swells increasingly because of electrostatic repulsion of main chains of wood components. The swelling pressure increases until the balancing by elastic repulsive force due to the ultrastructure of wood is reached... 

Another AFM-based technique is chemical force microscopy (CFM) (Friedsam et al. 2004 Noy et al. 2003 Ortiz and Hadziioaimou 1999), where the AFM tip is functionalized with specific chemicals of interest, such as proteins or other food biopolymers, and can be used to probe the intermolecular interactions between food components. CFM combines chemical discrimination with the high spatial resolution of AFM by exploiting the forces between chemically derivatized AFM tips and the surface. The key interactions involved in food components include fundamental interactions such as van der Waals force, hydrogen bonding, electrostatic force, and elastic force arising from conformation entropy, and so on. (Dther interactions such as chemical bonding, depletion potential, capillary force, hydration force, hydrophobic/ hydrophobic force and osmotic pressure will also participate to affect the physical properties and phase behaviors of multicomponent food systems. Direct measurements of these inter- and intramolecular forces are of great interest because such forces dominate the behavior of different food systems. 

The electrostatic forces which combine to form the internal field F are balanced by the elastic forces of the last term in equation (2). If the displacement s is equal to the elastic force must... 

If chemical bonding is considered to be too short range to account for possible interactions between CS planes we must look for other interactions which persist over longer distances in the solid. The two which come to mind are electrical interactions, such as electrostatic forces, and physical interactions, such as elastic strain. Both of these are amenable to theoretical analysis, and in the last two years a number of papers concerning these analyses has appeared in the literature. We will summarize the results so far obtained in the Sections below. 

The cluster is not infinitely stable. At some temperature the cluster decomposes, and at that temperature the elastic forces and the electrostatic forces just balance each other. Since the elastic force was calculated per chain and the electrostatic force per ion pair, Wch can be set equal to W at thus... 

The swelling and bending behaviour of hydrogels results from the equilibrium of different forces osmotic pressure forces, electrostatic forces, visco-elastic restoring forces, etc. To describe the different phenomena occurring in the gels and between the gel and solution phase adequately, the modelling can be performed on different scales (Fig. 3) ... 

Let us now consider again picture a in Fig. 12. If is increased to values ranging from 2-3 V/pm, we observe that the quadrupoles come into contact and can coalesce despite the elastic repulsion evidenced above. Indeed, for these field values, the attractive electrostatic force completely overwhelms the elastic repulsion force which eventually leads to a one-dimensional coalescence of the drops as shown in Fig. 14. Thus, the system is again unstable in the presence of high electric fields. Depending on the field intensity, we can then control the droplet coalescence and thereby their size. 

The lag period before back diffusion starts is just like the whole diffusion time course it is practically identical for all the prepulse amplitudes. The lag period is also independent of the viscosity of the aqueous solution. It is possible that the photosystems aggregate when compressed under the influence of the electrical field, in which case the lag time could be identified with disaggregation time. Because contact between particles is a necessary condition for aggregation, elastic as well as electrostatic forces are probably invoked to stop electrophoretic motion. 

Chemical potential and water content, X, can be related through an uptake isotherm. Uptake isotherms of k as a function of water-vapor activity or relative humidity, such as that given in Figure 5.1, are prevalent in the literature [4, 6, 42, 43]. They have been used in almost every model that deals with vapor-equilibrated membranes and treats the membrane as a single phase [1]. As discussed in the proposed physical model, the water uptake is described by the hydration of the sulfonic acid sites in the membrane clusters and a balance between osmotic, elastic, and electrostatic forces. The approach taken here is to calculate the isotherms using the chemical model of Meyers and Newman [5] with some modifications [39]. 

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