Hydrophobic SAMs

Figure 4c shows that the amount of adsorbed proteins is rapidly saturated within several minutes of exposing serum-containing medium to a surface. Albumin, the most abundant serum protein, was expected to preferentially adsorb onto the surfaces during early time points. Then, adsorbed albumin was expected to be displaced by cell adhesion proteins. To investigate the effect of preadsorbed albumin displacement on cell adhesion, SAMs were first exposed to albumin then, HUVECs suspended in a serum-supplemented medium were added [21, 42]. Very few cells adhered to hydrophobic SAMs that had been pretreated with albumin, due to the large interfacial tension between water and the hydrophobic surfactant-like surface. Albumin was infrequently displaced by the cell adhesive proteins Fn and Vn. One the other hand, HUVECs adhered well to hydrophilic SAM surfaces that had been preadsorbed with albumin. In that case, the preadsorbed albumin was readily displaced by cell adhesive proteins. 

Fig. 5 Illustration of NIST Gradient UV-Ozone device for generating surface energy libraries on substrates functionalized with hydrophobic SAM species. The sample stage accelerates the specimen blue) beneath a slit-source of UV light. (Reproduced with permission from [12])...

Figure 6.1 illustrates such an example (Abbott et al. 1992). Here, a gold surface is first coated with a hydrophilic SAM of alkanethiolate. The desired geometric pattern is then formed on the surface through micromachining (in this case, using a surgical scalpel), and the resulting features are covered with a hydrophobic SAM (of dialkyl disulfide) (see Fig. 6.1a). This procedure can be used to construct micrometer-scale hydrophobic lines on the surface so that the resulting shapes and distribution of liquid drops can be controlled (see Fig. 6.1b).

The third question in 3D MESA - the dimension of the smallest pieces that can self-assemble - motivated experiments with metallic, polyhedral, 10- xm-sized plates [ref. 63]. The fabrication of 10- xm-sized polyhedra is difficult, so these experiments examined the self-assembly of flat plates, which were easily obtained at this scale. Photolithography, electrodeposition, and electron beam evaporation provided a convenient way to form plates having surfaces whose properties could be modified selectively. The surfaces of these plates consisted of either gold or chromium. Treatment with a long-chained alkanethiol formed a hydrophobic SAM on the gold with a phosphonic acid-terminated thiol, a hydrophilic one. Similarly, a phosphonic acid-terminated thiol formed a hydro-phobic SAM on chromium (through coordination of the acid with surface Cr... 

Figure 11A shows an optical micrograph of water drops preferentially condensed on hydrophilic SAMs terminated by carboxylic (COOH) groups no water condensed on the hydrophobic SAMs terminated by methyl (CH3) groups [98]. This process shows how the functionality of a SAM influences the eondensation of water vapor on a SAM-derivatized surface. It uses self-assembly at two scales the formation of SAMs at the molecular scale and the directed condensation of water vapor at the macroscopic scale. The organization of liquids into patterned arrays illustrates one of the uses of self-assembly in microfabrication [99]. 

On the other hand, long-chain oligo(ethylene oxides) in hydrophobic SAMS reject biopolymers, e.g. proteins. Stabilization of colloids by solvophilic polymers can be explained by a concept called steric repulsion which means disfavourable compression and resulting loss of chain mobilities in colliding polymers. 

In recent years, self-assembly was successfully applied in micrometer-scale structures. Self-assembled monolayer (SAM) [11] is the representative example of self-assembly microfabrication, in which stufaces consist of a single layer of molecules on a substrate. SAMs can be prepared simply by adding a solution of the desired molecule onto the substrate surface and washing off the excess. The technique was utilized on the metal substrates with PDMS stamps to form the combined system for controlling of crystal nucleation [12]. Another example involves a fluidic technique based on patterned hydrophobic SAMs and capillary forces to self-assemble micro-fabricated sihcon blocks onto silicon and quartz substrates [13]. 

Jeon et al. reported a selective deposition of Ta205 aswellas LiNbOs and (Pb,La)TiOs thin films on patterned SAMs (Jeon et al., 1995). The surface of the substrates was selectively functionalized with hydrophobic SAMs of octadecyltrichlorosilane by /iCP. 

Figure 7. Electron micrographs of cadmium sulfide films deposited on a hydrophilic silicon substrate and on a hydrophobic SAM substrate at various times after initiation of film deposition.

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