Self-assembled monolayer hydrophobic

Derjaguin, B. V. (1934) Interaction forces between hydrophobic and hydrophilic self-assembled monolayers. KoUoid Zeits., 69, 155-164. 

Fig. 5.1 Scheme for patterned deposition of PbS. (a) Self-assembled monolayer (SAM) of long-chain mercapto-carboxylic acid. On exposure to UV radiation through a mask, the exposed thiol group is oxidized to a sulphonate group (b) that is weakly bound to the An substrate and can be easily rinsed away (c). Subsequent formation of a long-chain alkyl thiol SAM occurs only on the exposed Au (d). CD of PbS occurs only on hydrophilic car-boxylate endgroups and not on hydrophobic methyl groups (e). (See Ref. 41). 

FIG. 6.1 Control of wettability of surfaces through chemistry (a) schematic illustration of formation of hydrophobic lines on a hydrophilic surface with self-assembled monolayers (SAMs) and micromachining (b) top view of the shapes and confinement of water drops on an engineered surface. (Reproduced with permission of Abbott et al. 1992.)... 

While in the mentioned work on PABA on a charged silver electrode also the adsorption degree of the molecules was controlled by surface charge, Lahann et al. showed a concept in which molecules immobilized as a low-density self-assembled monolayer on a gold surface were electrically stimulated to undergo conformational transitions between a hydrophilic and a hydrophobic state (Lahann et al., 2003). Such a surface wetting switch may then be used to immobilize, for example, enzymes, as was discussed in the previous section. This is an example of switching both the orientation and the activity of adsorbed molecules. 

Similar methods to the formation of hydrophobic self-assembled monolayers (SAMs), as described in the previous section, were used with chemical modification to prepare surfaces with different functionality, such as alkenes or hydro-xylated surfaces. This approach was used by Thirtle et al. [67], where the adsorption of a series on nonionic surfactants from C12E5 to C16E6 onto surfaces... 

Biology and organic chemistry are replete with examples of self-assembly. Examples include lipid bilayers, the DNA duplex, proteins in their correctly folded forms, self-assembled monolayers, and crystals. In MESA, we extend ideas abstracted from molecular recognition - shape recognition, chirality, directional interactions, hierarchy of bonds, and hydrophobicity - to the mesoscale. 

A self-assembled monolayer of 4-cyano-4 -(10-thiodecoxy)stilbene on a Au-electrode was shown to have different hydrophobicities. In the trans-(18a) and cis- (18b) isomeric states (Figure 7.25). When the monolayer is in the CIS-State (18b), the polar cyano-groups are hidden in the monolayer and the hydrophobic spacers are exposed to the solution, thus providing the hydrophobic properties of the interface. After irradiation of the monolayer (X > 350 nm), the ds-stilbene units are photoisomerized to the fmws-state (18a), and the polar cyano-groups are mainly exposed to the solution. In this case, the interface becomes more hydrophilic, and the monolayer displays markedly different wetting properties. This difference allows the photo-patterning of the surface. ... 

Figure 13.24. Procedure for forming a self-assembled monolayer on a silver island film, followed by adsorption of a hydrophobic analyte (A) preceding SERS analysis. See References 53, 57 and 58.

Inorganic Hydrophobic coating of gold chemoresistor for rejection of polar interferents Polarity of analyte and interferents, design of self-assembled monolayers 42... 

Pt(IV) than Pd(n) [49], An interesting system, with asymmetric inorganic membranes, was used for selective metal ion separation. The membrane phase was a self-assembled monolayer of alkyl thiols as a hydrophobic phase for a trialkyl phosphate and phosphine oxide-based metal ion carrier. This organic mixture was attached on alumina porous supports with thin layers of gold. The thin membrane layer gave high fluxes and high selectivity, while metal ions transport was carrier limited [50]. 

It has been demonstrated that hydrophobic, fluorinated, hyperbranched poly(acrylic acid) films can passivate and block electrochemical reactions on metal surfaces thus preventing surface corrosion [57]. Hyperbranched films can be synthesized on self-assembling monolayers on the metal surface via sequential grafting reactions to obtain thick and homogeneous films. 

A study conducted by Zhao et al. created intricate patterns of hydrophilic and hydrophobic regions down the microchannel to improve extraction [205]. This was achieved by laying down photocleavable SAM (self-assembled monolayer) and exposing with UV light to create exposed hydrophilic regions. The unexposed regions remained hydrophobic. If pressure is controlled properly, once patterned, the aqueous phase will remain separated from the organic phase. 

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