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. 2020 Apr 29;6(7):1179–1188. doi: 10.1021/acscentsci.0c00068

Figure 2.

Figure 2

Higher temperature enhances polydopamine deposition and hair darkening. (A, B) Photographs of hair samples before (1) and after dyeing with polydopamine using 3% NH4OH (2), 0.05 N NaOH (3), 10 mM CuSO4/15 mM H2O2 (4), Tris buffer pH 8.5 (5), as well as color of the resulting polydopamine solutions. Dopamine polymerizations were carried out for 2 h at (A) room temperature and (B) 37–40 °C. (C) Optical microscopy images of the hair samples dyed at 37–40 °C are also reported. (D) UV–Vis spectra of solutions obtained after 2 h dopamine polymerization using 3% NH4OH and 0.05 N NaOH at either room temperature or at 37–40 °C. In every case, hair samples were washed five times with water and three times with a 10% shampoo solution prior to imaging/analysis (see Methods for protocols and for hair sample descriptions from alternative vendors).