Surface-modification techniques

Capillary electrophoretic separations are performed in small diameter tubes, made of Teflon, polyethylene, and other materials. The most frequently used material is fused silica. Fused silica capillaries are relatively inexpensive and are available in different internal and external diameters. An important advantage of a fused silica capillary is that the inner surface can be modified easily by either chemical or physical means. The chemistry of the silica surface is well established due to the popularity of silica surfaces in gas chromatography (GC) and liquid chromatography (LC). In capillary electrophoresis, the silica surface is responsible for the EOF. Using surface modification techniques, the zeta potential and correspondingly the EOF can be varied or eliminated. Column fabrication has been done on microchips.13... 

The relatively large surface area within micro-fluidic structures can be exploited in a proactive way to add chemical and or biological functionalisation to a process. A range of surface modification techniques have been developed and some of the more widely used techniques are outlined below. 

For example a polymer s interfacial characteristics determine chemical and physical properties such as permeability, wettability, adhesion, friction, wear and biocompatibility. " However polymers frequently lack the optimum surface properties for these applications. Consequently surface modification techniques have become increasingly desirable in technological applications of polymers. - ... 

The dry impact blending method has recently been used in the investigation of surface modification techniques of particles in the field of powder technology. In... 

We are concerned with both homogeneous gas-phase chemistry and heterogeneous surface chemistry. Certainly in combustion, gas-phase chemistry is usually dominant. However, there may be good reason to be concerned with heterogeneous chemistry, for example, on the relatively cool walls of a combustion chamber. Moreover there are emerging materials-synthesis and surface-modification techniques that depend on flame-surface interactions. 

As mentioned earlier, there are a large variety of surface-modification techniques for achieving a desired surface architecture. Due to lack of sophisticated instrumental facilities, the researchers in the past had to compromise with techniques that were less surface-specific and offered little control over the process. However, with system automation, it is possible to develop surfaces with well-defined properties and morphologies, avoiding tedious processes. 

In this section, only the surface modification techniques will be discussed, and not the impregnation, sol-gel or co-precipitation techniques. Furthermore, it is not our aim to fully cover all chemical modifications on the silica surface. We merely want to present in introduction to and an insight in the fast expanding field of silica modifications, in order to create new catalysts, sensors and immobilizators. 

Nitridated silica surfaces are very important in the semi-conductor and microelectronic industries. However, direct ammoniation of silica is -so far- a very uncontrollable procedure the required reaction temperatures are very high (> 1500 K), a lot of side products are formed (typically Si2N20, silicon-oxynitride) and the nitride diffuses into the silica matrix. Direct nitridation of silica should therefore be considered as a bulk synthesis, and not as a surface modification technique. 

Similar to static contact angles from the sessile droplet method, Wilhelmy dynamic contact angles are an excellent indication of the change in surface characteristics due to surface modification techniques such as plasma polymerization coating. The cosine of dynamic advancing contact angles from the first immersion, cos 0D,a,i of untreated, TMS-treated, and (TMS-I-02)-treated conventional... 

Recently one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxide.s. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named "chemical filing". Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT). ... 

The silicon surface can be stabilized using surface modification techniques which are divided into three categories (1) attachment of redox mediator which consumes the holes on the surface (2) attachment of electronically conducting polymer and (3) coating with thin metal or semiconducting films to create a buried semiconductor interface. Combinations of these approaches can also be used to stabilize the sihcon surface. ... 

Austenitic stainless steels like 31 OS, 316, or 316L are typically used for the construction of cathode and anode current collectors and bipolar separator plates. Corrosion of these steel components is a major lifetime-limiting factor in MCFC. The corrosion behavior of stainless steel components in molten carbonate conditions has been studied extensively during the past decade. Research is being aimed at increasing the corrosion resistance of these components by altering the alloy composition or by surface modification techniques. ... 

Another surface modification technique involves the free radical reaction of a primary alkene (e.g., Ci6H33CH=CH2, 1-octadecene) with hydrogen terminated silicon. Fig. 4 shows the structure of 1-octadecene while Fig. 7 displays a simplified diagram... 

As already mentioned, a dye monolayer can also be deposited on a semiconductor by means of a surface modification technique. In particular, semiconductor oxides can... 

Chemical surface modification techniques provide effective routes to mesoporous solid catalysts which are active in various liquid phase organic reactions including selective oxidations, nucleophilic substitutions, and oevenagel reactions. 

Adhesion is due to van der Waals interaction with the surface, and, while polyparylene films exhibit excellent chemical stability, poor adhesion continues to be a major technological problem and limitation. Surface modification techniques, which result in covalent interaction between the polymer film and the surface, might greatly improve adhesion and hence render polyparylene films more protective. 

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