Measurement of slides

For the characterization of wetting properties we employed dynamic contact angle measurements as well as measurements of sliding/roll-off angles using a Data-Physics OCA20 measurement system. 

The measurement of sliding angles and roll-off angles at a defined drop volume of 35 pi was performed by motorized rotation of the contact angle measurement system along its horizontal axis. 

Furthermore, the measurements of sliding angles show that although the modified samples are superhydrophobic, a small water droplet (5 pi) on their surface cannot roll off when the samples are tilted to any angle, even upside down, i.e., it is firmly pinned on such surface. Generally, the three-phase (air-liquid-solid) contact line plays an important role in sliding behavior of water droplets [37-39], and a... 

A. S. Najafi, Z. Xu, and J. Masliyah, Measurement of sliding velocity and induction time of a single micro-bubble under an inchned collector surface. Can. J. Chem. Eng., 86,1001-1010 (2008). 

For the measurement of sliding friction during the course of deformation of the polymeric billet in the extrusion process, a direct extrusion set up (Fig. 1) with a movable die-head was designed... 

The film pressure is defined as the difference between the surface tension of the pure fluid and that of the film-covered surface. While any method of surface tension measurement can be used, most of the methods of capillarity are, for one reason or another, ill-suited for work with film-covered surfaces with the principal exceptions of the Wilhelmy slide method (Section II-6) and the pendant drop experiment (Section II-7). Both approaches work very well with fluid films and are capable of measuring low values of pressure with similar precision of 0.01 dyn/cm. In addition, the film balance, considerably updated since Langmuir s design (see Section III-7) is a popular approach to measurement of V. 

In practice, measurements are made with the use of an accelerometer. This device is connected to a sound level meter and may make measurements of acceleration in terms of decibels (or by changing scales or use of a device similar to a slide mle, in direct terms). An integrator can be connected between the accelerometer and the meter to express the results in terms of velocity or displacement. 

Oils may act in two ways they provide a measure of boundary lubrication and they may exclude oxygen from the rubbing zone. However, their effectiveness is not as great as with unidirectional sliding, since there is usually sufficient oxygen present in most cases to allow oxide debris to be generated, and this tends to displace any lubricant film that was initially present between the surfaces. 

The friction coefficient at PVA gel/OTS modified quartz is 0.300 while that at PVA gel/unmodrfied quartz is 0.076. Frictions were measured by using a rheometer (ARES, TA instruments) as a function of sliding velocity in water and these values were calculated from the experimental resultsoflowestsbdingvelodty,7.5 x 10 m/s. 

The present authors have had experience using rotary samplers for field studies involving relatively small droplets for vector control applications and for the measurement of droplet size at far-field distances. When using magnesium oxide slides, the spread factor for droplets varies from 0.75 for crater diameters up to 15 jam, to 0.8 for 15-20 p.m and 0.86 for crater diameters above 20 am. 

The viscosity of a fluid is an important property in the analysis of liquid behavior and fluid motion near solid boundaries. Viscosity is the fluid resistance to shear or flow and is a measure of the adhesive/cohesive or frictional fluid property. The resistance is caused by intermolecular friction exerted when layers of fluids attempt to slide by one another. 

Friction is the resistive force that we experience when we try to slide one object over the surface of another. The coefficient of friction is the ratio of the lateral force required to slide the surfaces past one another relative to the force holding them in contact. Polymers exhibit two coefficients of friction the static coefficient of friction is a measure of the force required to initiate movement, the dynamic coefficient of friction is a measure of the force required to sustain movement at a constant rate. In general, the force required to initiate sliding is somewhat greater than that required to maintain a constant rate of movement. 

The fraction of slide surface to be covered by collected droplets is an important factor influencing overall measurement accuracy and time. If the slide is covered by too many droplets, the measurement error and time will increase due to droplet overlap and tedious counting. If too few droplets are collected, the sample may not be large enough to generate statistically representative data. For the measurement accuracy and ease, a coverage of 0.2% has been found to be sufficient and satisfactory with an upper limit of 1.0%. 1 ... 

Figure 4.15 Representation of the disposable slide for the measurement of potassium by the Vitros Chemistry System. The difference in potential between the two half-cells, one receiving the sample and the other a reference solution of known potassium ion concentration, is mathematically converted to give the concentration of potassium ions in the sample.

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