Capillary surface treatments

Many industrial yams have specific surface function requirements. For technical yams the market share for composites or coated fabrics is almost 70%. Furthermore, textile applications also can benefit from a special surface treatment in order to improve the water repellency. Capillary membranes for dialysis, however, have totally different requirements enhanced biocompatibility of the membranes is needed.4-6... 

Polypropylene compositions containing magnesium hydroxide, with and without magnesium stearate surface treatment, were characterised at low and high shear rates using dynamic and capillary measurement techniques [36]. A significant reduction in viscosity was observed when surface treatment was present, particularly at low shear rates. In addition, with this system, the yield stress for the onset of flow was markedly reduced (Compare magnesium hydroxide variants A and E in Fig. 9). 

The use of an expression such as (70) indicates that drying occurs by removal of water from the exposed areas on the external surface of the particle and in its capillaries. The treatment may not be applied for temperatures of the solids above the boiling point of water, when intense vapor streams completely alter the heat- and mass-transfer mechanism. The psychrometric ratios have little meaning if the temperatme of the air is much above 250°F. 

In order to prevent water from entering masonry or brickwork by capillary action, surface treatment is essential. This can be achieved by a number of methods ... 

Chemical modification of surface silanol groups on the glass surface affects both the spreading of liquid films [97] and the residual adsorptive properties of glass capillary columns. Thus, the surface wettability problems can largely be solved through different individual surface treatment techniques, or their combination. Most of the recent developments in this area have been reviewed [100]. 

It was necessary to use a new cell each time, as removal of the metals with acid, or with alkaline detergent, even though followed by surface treatment, did not return the cell to the same condition as a new one, as evidenced by different capillary rises. 

Another device has been reported, the electrophoretron that used two capillaries with different polarity surface treatments. The capillaries were connected in a loop and a single power supply was used to apply a fixed potential across the two capillaries. The different polarity surface treatments cause the EOF to flow in a continuous loop around the capillaries. Injected analytes would continuously travel around the loop under the influence of the EOF. Such a device may prove useful for CEC separations of neutral analytes. However, any separation of charged species in one capillary will be almost negated in the second capillary due to the change in the polarity of the electric field. ... 

Finally, if heavy beads such as silica (SG = 2.1) are used, they can be assembled into a regular matrix by sedimentation [20]. One particular advantage of silica beads is that, after assembling them in a glass cell, sucrose can be added to the electrophoresis buffer to closely match the index of refraction of silica. This leads to a transparent material that is ideal for optical detection (at the expense of separation time, since sucrose increases the medium s viscosity, and thus reduces electrophoretic mobility). A second advantage is that some of the well-documented surface treatment strategies against electroosmosis developed for capillary electrophoresis can be directly transposed. 

The surfaces of devices often exhibit different wettability characteristics, depending on the manufacturing approach adopted. Surface modification techniques can be used to alter the wettability behavior of microfluidic devices. This difference in wettability can be used to control the flow rate in devices. There are many other benefits of hydrophilic surface treatments, including the ability to increase adhesion and capillary effects [2]. Irrespective of the material used in the device, the primary requirement that a material needs to fulfill is biocompatibifity in various applications. Therefore, it is also necessary to use surface modification techniques to render materials biocompatible. It is believed that future devices of increasing sophistication will often require programmable surface properties, including control of the spatial distribution of charge and polarity [3]. 

The surface tension of a liquid that wets glass is measured by determining the vertical distance, A/i, between levels of the two menisci in a U-tube having a small bore ri on one side and a larger bore vi on the other. The following data are known A/i = 1.90 cm, = 0.1 cm, T2 = 1.00 cm, and pl = 0.95 g cm Calculate the surface tension of the liquid using the simple capillary rise treatment. 

A distinct advantage of the coaxial capillary approach is in the surface treatment of the device both W/O/W and O/W/0 emulsions can be formed without any surface modification ofthe capillaries, because neither the middle nor the inner fluid touches the capillary wall surface. This is clearly different from the other techniques mentioned above in this section. An additional advantage is the flexibility of the system. For example, the structure ofthe device can be easily modified to make higher order multiple emulsions, such as triple emulsions [100, 101]. 

This technique, developed and commercialized in Japan, currently leads the superabsorbent polymers world market. On the other hand, companies in Western countries adopted polymers without surface treatment. As the trend for reducing thickness continued in the 1990s, use of a cotton-like pulp was reduced and the amount of superabsorbent polymers increased. Under such conditions, it became apparent that surface treatment was necessary to achieve superabsorbency. As the polymer concentration increases, diffusion of urine throughout the diaper via the capillary effect of the pulp cannot be relied upon and uneven swelling results. It has become important to prevent this so as to achieve effective use of the entire diaper. Under the pressure of body weight, this phenomenon may be even fiirther magnified. Due to such needs. Western companies also developed surface treatment technologies [29-31] and today most superabsorbent polymers for diaper application have surface-treated polymers. 

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