Hydroxy-terminated self-assembled

The advancing contact angles of 110 -112° for the methyl-terminated self-assembled monolayer and of 55° for the hydroxy-terminated surfaces support the model of an organized layer with the -CH3 and -OH end groups of the amphiphilic molecules being exposed to the ambient environment (vacuum, air, or water) and with the phosphate groups being oriented toward the substrate. 

The present paper describes two novel approaches to modifying metal oxide surfaces the use of aqueous solutions of alkane phosphates in the self-assembly process and the tailoring of surface wettability based on mixed alkane phosphate/hydroxy-terminated alkane phosphate SAMs. 

It is also possible to produce more hydrophilic SAMs using aqueous solutions ofthe ammonium salt of hydroxy-terminated dodecyl phosphate. Furthermore, the wettability (water contact angle) imposed onto a metal oxide siuface can be varied in a controlled, predictable way by the formation of mixed methyl-Thydroxy-terminated dodecyl phosphate SAMs, self-assembled from aqueous solutions containing both molecules in an appropriate ratio. Investigations of the relationship between adsorbate composition and solution amphiphile concentration ratio for mixed SAM systems (by XPS and ToF-SIMS) as well as amphiphile orientation and order in the different SAMs (by NEXAFS and AFM) are currently under way. 

The molecular ion (M — H) intensity of the methyl-terminated phosphate is 1 order of magnitude greater than that of the hydroxy-terminated phosphate. It has been reported that the detection of molecular mass ions M - H is correlated with the degree of order in self-assembled monolayers, resulting from energy transfer and stability effects. We assume that the higher count rate... 

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