Lateral force rate method

Lateral Force Rate Method, The sample is scanned at low load and the lateral force is measured as function of the scan rate at a fixed tenq>erature. Below Tg the lateral force is expected to be independent of the scan velocity. Tg is defined as the tenq>erature at which the onset of rate dependence is observed (16,17,20). 

After the formulation of defect thermodynamics, it is necessary to understand the nature of rate constants and transport coefficients in order to make practical use of irreversible thermodynamics in solid state kinetics. Even the individual jump of a vacancy is a complicated many-body problem involving, in principle, the lattice dynamics of the whole crystal and the coupling with the motion of all other atomic structure elements. Predictions can be made by simulations, but the relevant methods (e.g., molecular dynamics, MD, calculations) can still be applied only in very simple situations. What are the limits of linear transport theory and under what conditions do the (local) rate constants and transport coefficients cease to be functions of state When do they begin to depend not only on local thermodynamic parameters, but on driving forces (potential gradients) as well Various relaxation processes give the answer to these questions and are treated in depth later. 

The creation of 2D crystals of both micron sized and nanometre sized particles remains a somewhat empirical process due to the ill-defined role of the substrate or surface on which nucleation takes place. Perrin first observed diffusion and ordering of micron sized gamboge 2D crystals in 1909 under an optical microscope [32]. Several techniques have been proposed for the formation of 2D arrays at either solid-liquid surfaces or at the air-water interface. Pieranski [33], Murray and van Winkle [34] and later Micheletto et al. [14] have simply evaporated latex dispersions. Dimitrov and coworkers used a dip-coating procedure, which can produce continuous 2D arrays [35,36]. The method involves the adsorption of particles from the bulk solution at the tricontact phase line. Evaporation of the thin water film leads to an attractive surface capillary force which aids condensation into an ordered structure. By withdrawing the film at the same rate as deposition is occurring, a continuous film of monolayered particles is created. Since the rate of deposition is measured with a CCD camera, it is not possible to use nanometer sized particles with this method, unless a nonoptical monitor for the deposition process can be found. 

The principle behind SFM is that the lateral or shear force between an oscillating probe tip and the sample increases as the distance decreases. The probe is usually mounted in a support such that several millimeters of the aperture end of the optical fiber extends beyond the clamping point. The probe thus forms a cantilever having one fixed and one free end. It is driven transversely at a so-called tip resonance , which indicates that the resonance is due to the cantilever rather than the support structure of the microscope, with an amphtude 5nm. Shear forces between the probe tip and sample surface damp the oscillation. The amplitude is measured and fed back to the sample height position so as to maintain constant oscillation amplitude and presumably constant tip-sample distance. The amplitude was measured, originally, with optical deflection methods. Recently, a number of electrical measurement schemes have been demonstrated that may prove to have a number of advantages in speed, sensitivity or ease-of-use [12]. In near-field single molecule experiments the bandwidth of the feedback is not an issue as scan rate is limited by... 

Dynamic Process Study. More than two hundred coatings have been tested with this method. More than fifteen percent showed self-healing to different extents, mainly depending on their glass transition temperature, Tg. This is attributed to viscoelastic creep. Viscoelastic creep is different from elastic recovery it results in partial or complete recovery of a marred surface within a time frame from several minutes to several hours (J3, 14), while the elastic recovery occurs immediately after the marring tip moves over the surface. To study the creep in detail, we imaged the marred surface continuously, immediately after the scratching, at a time interval of 10 minutes up to several hours when the recovery was almost complete, and stored the data in a computer. Later we plotted the dimension of mar versus time, and studied the recovery rate, recoverable part, and unrecoverable part for the mars made under different normal forces. 

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