Photocleavable SAM

The virtual wall created can also be employed to carry out gas-liquid reactions. For instance, acetic acid vapor was allowed to react with a pH indicator solution at the virtual wall, allowing kinetic studies to be carried out (see Figure 3.21) [433], Moreover, using photocleavable SAM (with the 2-nitrobenzyl photosensitive group), the SAM can be patterned through a UV photomask, giving rise to complex flow patterns [433,434],... 

Figure 18 UV photopatterning method. The molecular structure of a photocleavable SAM formed on glass surfaces. UV irradiation through masks placed on top of SAM-modified microchannels leads to the production of hydrophilic carboxylate groups in the irradiated regions (Zhao et al, 2001).

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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