Alkyl phosphonic acid monolayers

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer stmctures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer stmcture with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is - 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

A mixture of benzene and methanol (19 to 1) was used for spreading the alkyl phosphonates. To minimize the influence of benzene on the film properties, the concentrations of the spreading solutions were > 1.5 X 10 3 gram per ml., and the experiments were performed at tt > 4 dynes per cm. (25). Moreover, higher proportions of methanol in the spreading solution did not alter the film properties under study for selected monolayers. For the sulfates, a mixed solvent containing water-benzene-2-propanol (1 10 10) was used because with the benzene-methanol solutions the properties of the films depended on the age of solution from which the films were prepared. Stearic and palmitic acids were spread from either hexane or the benzene-methanol solvent used for the phosphonates. Identical desorption results were obtained with the two solvents. 

Many examples of surface-surfactant interactions which promote self-assembly are known. Apart from gold-thiol monolayers which are formed because of the creation of the strong S—Au bond, other commonly studied monolayers include alkyltrichlorosilane layers on hydroxylated surfaces (such as SiC>2)6, fatty acids on metal oxide surfaces7 8 and alkyl phosphonate salts on zirconium9. 

This chapter describes chemical modification of various n-type TCO electrode surfaces with various organic molecules in which one end is a binding group (X—), the other end is a terminal group with a different functionality (e.g. permanent dipole moment) (—Y), and these two ends are linked by groups of alkyl chain and 7T-system as shown schematically in Fig. 2. Studies for formation of various organic monolayers with carboxylic and phosphonic acids as well as organosilanes... 

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