For a Newton black film made from the aqueous solution of sodium dodecyl sulphate and 0.5 mol/dm3 NaCl, one dodecyl sulphate ion occupies 36 1020 m2 at 298 K. Determine the thickness of the aqueous core, if the equivalent thickness of the film is 4.4 nm. Also given: The mol. Wt. of the hydrocarbon tail is 0.169 kg/mol. Let us take the refractive index and density of liquid dodecane as a reasonable approximation. Therefore, = 750 kg/m3 , n1 = 1.411, refractive index of water n2 = 1.333