Ellipsometry measurements were carried out with an α-SE instrument (J. A. Woollam) at an incidence angle of 70° over a 380-900 nm multi-wavelength spectral range. Psi and delta spectroscopic curves were extracted and fitted against simple native oxide/Cauchy models in CompleteEASE (J.A. Woollam). The dry thickness was determined in air, whereas for swollen thickness, substrates were placed in an in-house-built liquid cell fitted with quartz windows normal to the light beam path. All measurements were conducted in triplicate at room temperature.