UV-visible spectra of samples as formed by PLA and further aged in water. (a) UV-visible spectra and color change (inset) of the colloidal solutions as formed by PLA in water and those with further dwelling in water for days numbered. Note the color change from black to light yellow and finally limpid due to sedimentation of significantly coarsened/assembled particles as indicated by the shaken bottle denoted as 20S to the further right of the panel for the solution dwelled in water for 20 days. The magnified spectrum of the as-formed sample in (b) shows broad absorbance in the visible region to exhibit a dark color. The samples further dwelled in water for (c) 1 and (d) 2 days have absorbance corresponding to a minimum bandgap of 2.75 and 2.68 eV based on their intersection with the base line at 451.1 and 464.9 nm, respectively.
Lin et al. Nanoscale Research Letters 2012 7:272 doi:10.1186/1556-276X-7-272