Abstract
In homodisperse and crystallographically defined AgBr-gelatin systems of known surface areas, reversible adsorption of organic cations increased with length of their alkyl chain. In neutral or alkaline 0.001 M KBr, the silver halide surface could be saturated by singly charged alkyl pyridinium or quinolinium cations at equilibrium concentrations below about 10 −3 M, provided the alkyl chains contained at least 12 methylene groups. Longer alkyl chains enhanced adsorbability without influencing the saturation coverage. Doubly charged α,ω-alkyl quaternaries gave similar adsorption characteristics but, compared with their singly charged long-chain analogs, the amounts adsorbed at saturation coverage were low. At equilibrium concentrations between 10 −4 and 10 −3 M, adsorption of both types of cations fitted the Langmuir equation for which adsorption coefficients were evaluated; these yielded free energies of adsorption ranging between 6 and 11 kcal./mole, depending on structure and substrate variables. The highest apparent free-energy values were obtained with a cationic cyanine dye in an iodide-containing substrate. It was demonstrated that the limiting area occupied by this dye or other quaternary salts was the same for cubic and octahedral substrates.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have