Surface stiffness

Leather finishes penetrate to a greater or lesser extent and have a profound effect on the grain or wrinkle characteristics of the leather. Penetration of the resia into the leather tightens the grain but may produce a surface stiffness and a tendency toward grain cracking upon flexing. The development of leather finish resins and the appHcation of these finishes is done by specialty houses. 

At r > Tr, the relaxation of a non-equilibrium surface morphology by surface diffusion can be described by Eq. 1 the thermodynamic driving force for smoothing smoothing is the surface stiffness E and the kinetics of the smoothing is determined by the concentration and mobility of the surface point defects that provide the mass transport, e.g. adatoms. At r < Tr, on the other hand, me must consider a more microscopic description of the dynamics that is based on the thermodynamics of the interactions between steps, and the kinetics of step motion [17]. 

Besides spectroscopic techniques such as infrared-reflection-absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS), SFM-based stiffness imaging was applied in order to detect radiation-induced variations of surface stiffness [180]. For that purpose, when exposing the PE-film to the VUV-radiation, the film was covered with a Ni mesh. Thus, the PE-film was partially masked and exposed to the VUV radiation only within the square-shaped holes of the mesh. After having finished that treatment and having removed the mesh, the sample surface was scanned in force modula-... 

Force modulation imaging is the dynamic contact mode that identifies and maps differences in surface stiffness or elasticity. These techniques use a variety of surface properties to differentiate among materials where topographical differences are small or not measurable. 

Here we consider only high-symmetry orientations, such as [001] and [111]. In this case, the forbidden orientation implies that the surface-stiffness tensor [24, 8],... 

Typical dispersion curves defined by (39) are qualitatively the same as shown in Fig.2b. Note that the critical wavenumber at the threshold does not depend on the wetting potential and is determined only by the surface stiffness and the energy of edges and corners. For the parameter values typical of semiconductors like Si or Ge, with the surface energy 7 2.0 Jm , surface stiffness a 0.2 Jm , the lattice spacing ao 0.5 nm and the regularization parameter u Oq 5.0 X 10 J, the wavelength of the structure at the onset of instability is 14.0 nm. 

The film wets the substrate if F < or fs/ffo > e + 1. In this case, the nonlinear anisotropy coefficient a in eq.(32) is always positive. The faceting instability requires a negative surface stiffness that can be achieved only if... 

In the contact mode, there are static modes (de-modes), and dynamic modes (ac-modes). In the former, a cantilever-type spring bends in response to the force which acts on the probing tip until a static equilibrium is established [1]. In the dynamic mode, the lever oscillates close to its resonance frequency. A distance-dependence force shifts the resonance curve. Another technique is to modulate the position of the sample at a frequency below the cantilever resonance but above the feedback-response frequency and send the response signal to a lock-in amplifier to measure the signal s amplitude and phase [4]. The lock-in output is connected to the auxiliary data acquisition channels to form an image - this approach is popularly known as force modulation (FM-mode). FM-mode imaging or force cmve is an AFM technique that identifies and maps differences in surface stiffness or elasticity. 

Here the sum of y and its second derivative with respect to orientation is called the surface stiffness. For the special case of a 2-dimensional monatomic island on a single crystal surface, the surface energy is replaced by the step energy, and the eqttation for the chemical potential of the island edge, eqtrivalent to Eq. (17), is... 

The surface stiffness modulus is calculated using the following general equation (Highways Agency 2009b) ... 

In some countries, the satisfactory compaction is judged by running the plate bearing test twice, with two different numbers of passes. The surface stiffness modulus is determined in both cases (Ej and 2) from the k value obtained. If the 2/ i ratio is less than 2, the compaction is considered satisfactory. 

It is noted that EME2 is recommended to be laid over a foundation class 3 or 4 or foundation class 2 that has a surface stiffness modulus of at least 120 MPa at the time of construction. 

Figure 8 Height mode topographical (A) and force modulation (B) images of colloidal hydrogel nanoparticles immobilized on a silica substrate. Scan domain is 12 pm x 12 pm. Note that in the topographical image darker areas represent lower regions, whereas in the force modulation image the darker areas represent greater surface stiffness.

Graham, R.M., Joseph, P.F., Dooley, R.L. and LaBerge, M. (1995) Effect of lubricant viscosity and bearing surface stiffness on the lubrication mechanism of a point contact as a total hip arthroplasty model. Transactions of the Society For Biomaterials, 23, 124. 

Both mammalian cell—material interactions and bacterial adhesion are affected by various chemical and physical factors on the material surface. These factors include the surface biochemistry, surface charge, surface hydrophobicity, surface roughness/ topography, surface porosity, surface crystaUinity and surface stiffness. All of these will be discussed as follows. 

The surface stiffness-dependent behaviour of bacteria has been less explored compared with that of mammalian cells. Using polyelectrolyte multilayer thin films composed of poly(allylamine hydrochloride) and poly(acrylic acid) as model materials, Lichter et al. found that the adhesion of Staphylococcus epidermidis is positively correlated with the stiffness of this material with a varied Young s modulus from 0.8 to 80 MPa, independent of surface roughness and charge density. Other photo-cross-linkable polyelectrolyte films made from poly(L-lysine) (PLL) and hya-luronan derivative modified with photo-reactive vinylbenzyl groups (HAVE) have also been examined. The adhesion and growth of two model bacteria, E. coli and Lactococcus lactis, were examined on the softer (non-cross-linked) and stiffer... 

Consider the chemical potential expression (8.137) for the special case when the surface energy density Us depends on orientation 9 but not on surface strain e. Verify that the chemical potential expression reduces to x = f/ — n Us 4- Dg), where the prime denotes differentiation with respect to 6. The quantity in parentheses is sometimes called surface stiffness its existence presumes the function Us 9) is indeed twice differentiable. 

Equation 2 gives the penetration depth, equation 3 gives the surface stiffness and equation 4 is the calculated effective modulus based on bulk modulus, E, and Poisson s ratio, v. We have applied this analysis to our materials to calculate the surface penetration and surface stiffness using the measured radius of our tip and the known bulk mechanical constants of the materials at an applied load of 50 nN (Table II). 

Table IL Calculated surface stiffness and tip penetration depths for several materials using a silicon nitride cantilever (ks0.58N/m, tip radiuss40 nm) and...

Variable temperature Scanning Force Microscopy of mixed polystyrene (2000 - 100000 g/mol) and poly (methylmethacrylate) (100000 g/mol) thin films was used to probe mechanical properties such as surface stiffness and pull-off forces. Adhesion data can be explained by the molecular properties of the constituents. The adhesion of Polystyrene samples was measured by force distance curves and using the Pulsed Force Mode. It can be shown that surface tension is not the dominant part of the tip-surface interaction, but the mechani cal properties of the material will influence the measured adhesive force. Wetting of the tip by polymer molecules at higher temperatures due to increasing mobility is one possible model. 

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