Detachment time

At low flow velocity of the dispersed phase, the interfacial tension does not influence the droplet diameter but it affects the time-scale parameters for droplet formation [35-37] the detachment time becomes shorter at high interfacial tension (low surfactant concentration) [38]. 

Usually, the syringe simply needs to be lowered until the tip is submerged in the primary fluid. Note that in some drop volume tensiometers, the final resting position of the holder may need to be adjusted manually. The drop formed at the tip of the syringe must be located just above the LED detector so that the detachment time cart be determined accurately. 

Initially, a drop with a specific volume is very rapidly formed at the tip of the syringe. The drop volume is slightly smaller than the critical volume that corresponds to the equilibrium interfacial tension at which the drop would ordinarily detach. The drop will therefore remain attached to the tip surface. As surface-active material adsorbs at the liquid interface, the interfacial tension decreases and the drop will eventually detach. The time required between drop formation and drop detachment is the so-called drop detachment time. If the time required to form the drop is small compared to the drop detachment time, then the drop detachment time can be set equal to the effective age of the interface. Gradually, reducing the drop volume will increase the time required for the drop to detach. The drop detachment time and thus the age of the interface can be varied between 10 sec and 30 min. 

The most conunon variations involved solutions containing the proteolytic enzyme trypsin (0.05-0.25%) or the chelating agent ethylenediaminetetrsiacetate (0.5-5 mM EDTA). Detachment times... 

For collecting cells for the co-culture after 2 weeks of ACM collection, the cells are washed with PBS 2 times and passage with 5 ml 0.25% trypsin (shake, tap, and scrape until most of the cells detach, time 15min), pooled into 150 ml DMEM + S to stop the trypsinization, and the cell suspension centrifnged for 5 min at 1,000 rpm (180g). 

Decreasing rate of bubble release The mean bubble detachment frequency Af6-1 directly controls the onset of the gas film. For large enough bubbles, such as the infinite cluster, the bubble detachment time Atb becomes so large that the gas film can be formed. Atb is affected by other parameters such as the wetting of the electrode, viscosity and density of the electrolyte, or the local hydrodynamical fluxes. 

For terminal voltages around U 1.5 (which are, as will be seen in Part 2 of this book, typical for micromachining applications), the gas film formation time is similar to the mean detachment time of the gas bubbles. 

From the data presented (Miller et al. 1994a) it can be concluded that the drop detachment time t is the characteristic parameter for the observed hydrodynamic effects at small drop times and... 

A video camera with a silicon intensifier target (SIT) tube was used to prepare video tapes which were analyzed one frame at a time (the time between frames is 33 ms). The location and arrival and detachment time of each cell were recorded. Notations were made of the movements of cells to new positions on the surface and a record was made of unoccupied grid spaces which had previously contained cells. The surfaces examined were albumin-, fibronectin- and collagen-precoated glass. Exposure times to flow were kept short, 1-4 min, in order to minimize the effects of protein desorption and exchange. 

The interface transition time is ri h /D, where h 5 x 10 m. The attachment time ti, at the worst, is reduced to the time required for searching the appropriate place (grain boundary dislocation, etc.) given by (cf/Ds), d being equal to several atomic distances. The detachment time, obviously, is dose to T2 by the order of magnitude. The characteristic time of transfer through the layer is Ax Ax Ax ... 

The time dependent surface tension decay was measured according to the drop-volume technique as outlined by Tornberg [18,19]. The automatization procedure according to Arnebrant and Nylander [20] was employed. In this method surface tension reduction by macromolecules during adsorption at the air-water interface is measured by formation of drops of certain volumes. Time for detachment of the droplets is recorded. Surface tension calculated [19, 20] was plotted against detachment time and the value attained after 2000 seconds was set as the equilibrium value. The surface tension of the solutions is still decreasing after this period of time, but the rate of decrease is small, less than 0.05 mNm" per 100 seconds. The maximum error in surface tension values is 1.5%. 

Since the drop volume method involves creation of surface, it is frequently used as a dynamic technique to study adsorption processes occurring over intervals of seconds to minutes. A commercial instrument delivers computer-controlled drops over intervals from 0.5 sec to several hours [38, 39]. Accurate determination of the surface tension is limited to drop times of a second or greater due to hydrodynamic instabilities on the liquid bridge between the detaching and residing drops [40],... 

Place 20 g. of dry powdered benzoic acid in C, add 15 ml. (25 g., i.e., a 30% excess) of thionyl chloride and some fragments of porcelain, and then clamp the apparatus on a boiling water-bath as shown so that no liquid can collect in the side-arm of C. Heat for one hour (with occasional gentle shaking), by which time the evolution of gas will be complete. Cool the flask C, detach the condenser and fit it to the side-arm for distillation, using a 360° thermometer for the neck of C. To the lower end of the condenser fit a small conical flask G (Fig. 67(B)) by a cork carrying also a calcium chloride tube. 

Upon emerging from the quadrupole, the ions are accelerated through about 40 V and focused into the time-of-flight (TOF) analyzer. A pusher electrode is sited alongside this focused ion beam. Application of a pulse of high electric potential (about 1 kV) to the pusher electrode over a period of about 3 ps causes a short section of the ion beam to be detached and accelerated into the TOF analyzer. A positive potential is used to accelerate positively charged ions and vice versa. 

Surface Tension. Interfacial surface tension between fluid and filter media is considered to play a role in the adhesion of blood cells to synthetic fibers. Interfacial tension is a result of the interaction between the surface tension of the fluid and the filter media. Direct experimental evidence has shown that varying this interfacial tension influences the adhesion of blood cells to biomaterials. The viscosity of the blood product is important in the shear forces of the fluid to the attached cells viscosity of a red cell concentrate is at least 500 times that of a platelet concentrate. This has a considerable effect on the shear and flow rates through the filter. The surface stickiness plays a role in the critical shear force for detachment of adhered blood cells. 

SoUd Diffusion In the case of pore diffusion discussed above, transport occurs within the fluid phase contained inside the particle here the solute concentration is generally similar in magnitude to the external fluid concentration. A solute molecule transported by pore diffusion may attach to the sorbent and detach many times along its... 

As previously discussed, many, if not most, cases of particles adhering to substrates involve at least one of the contacting materials deforming plastically, rather than elastically. Under such circumstances, it would be expected that the extent of the contact should increase with time and, with it, the force needed to detach a particle from a substrate. Moreover, material flow can occur, resulting in the engulfment or encapsulation of the particles. 

The relationship between the increase in contact radius due to plastic deformation and the corresponding increase in the force required to detach submicrometer polystyrene latex particles from a silicon substrate was determined by Krishnan et al. [108]. In that study, Krishnan measured the increase in the contact area of the partieles over a period of time (Fig. 7a) and the corresponding decrease in the percentage of particles that could be removed using a force that was sufficient to remove virtually all the particles initially (Fig. 7b). 

Fig. 7. The increase in contact area (a) and corresponding decrease in detachment efficiency (b) as a function of time (from ref. [108]).

A similar analysis can be done for the curved surface of an essentially spherical particle that contains asperities. Let us assume that all the asperities are the same size. Initially, no more than three asperities on the particle can contact the presumably smooth surface. As the asperities compress under the applied load, more asperities, that are situated further away from the substrate due to the curvature of the particle s surface, come into contact. These are the first to separate from the substrate upon application of a detachment force. In essence, detachment occurs by breaking the contacts between the asperities and the contacting surface, one at a time. 

This test measures the ability of a tape to resist creep under applied load. The test is covered in ASTM D-3654 and PSTC-7. A specified area (typically 12.7 mmx 12.7 mm) of conditioned tape is rolled down with a specified pressure on the substrate of choice, such as polished 302 stainless steel. The panel is fixed in the vertical position or up to 2° tilted back so that there is no element of low angle peel in the test (Fig. lb). A weight (often 1000 g) is fixed to the end of the tape and the time to failure, i.e. complete detachment from the plate, is measured. Infrequently, the time required for the tape to creep a given distance is measured and reported. 

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