For the absorption of a mixture of two alkanethiols, the mole fraction of each thiol in solution reflects, but is not equal to the mole fraction of it as an absorbate in the SAM. Experimental conditions influence the ratio of absorbates in the SAM formed on the substrate surface. Again, the length of the alkyl chain is significant, with a bias towards the longer alkanethiol which increases over time. The choice of solvent can also be a factor if the SAM is formed from a mixture of polar and non-polar molecules. Asymmetric disulfides (RSSR') pose an alternative for forming mixed SAMs, though they have lower solubility. Their S-S bond cleaves to form a bond between the metal and the sulphur molecule (M-S), as with thiols. A similar trend is seen when using asymmetric disulfides to create a mixed SAM as with using two different alkanethiols, where there is not a 1:1 ratio of absorbates present in the SAM.