204 JOURNAL OF COSMETIC SCIENCE
Natural gray hair was treated in 20% ethanolamine solution at pH 9–10 for 1 hour, followed
by removal of excess liquid using absorbent paper and allowing it to dry naturally. In this
study, the single-factor test was conducted to access the dyeing time of GA-Fe(II)-stained
natural white hair, the pH of GA-Fe(II) solution, and the molar ratio of GA-Fe(II) to Fe(II).
The optimal dyeing conditions for GA-Fe(II)-stained natural white hair were determined
by measuring the color difference value of stained white hair.
ETHANOLAMINE EMULSION FOR UNFOLDING NATURAL WHITE HAIR SCALES
First, 2 mL of ethanolamine was added to 8 mL of water and mixed, and the pH was adjusted
to 9.2–9.4. Then, 0.8 mL of glycerol, 0.4 mL of Tween-80, 0.2 g of sodium dodecyl sulfate,
0.1 g of sodium sulfite, 0.2 g of sodium benzoate, 2 mL of propylene glycol, and 2.3 mL of
water were added to the ethanolamine solution and mixed at 65°C for 15 minutes to obtain
the aqueous phase solution. Additionally, 2 mL of isopropanol and 2 mL of oleic acid were
heated and stirred at 65°C for 15 minutes to create the oil phase solution. The oil phase
was added to the aqueous phase solution while heating and stirring at 65°C for 10 minutes,
resulting in the formation of the oil-in-water ethanolamine emulsion. The emulsion was
allowed to cool to room temperature, and 0.2 g of natural white hair was immersed in the
emulsion for 1 hour. Subsequently, the emulsion was removed, and the residual solution on
the white hair was wiped off with absorbent paper to be set aside.
GA-FE(II)+DA HAIR DYE FOR DYEING NATURAL WHITE HAIR
0.035 g GA was dissolved in 30 mm of 5 mL Tris solution to obtain GA solution. Next,
0.2088 g of ferrous chloride tetrahydrate was dissolved in 3 mL of water to create the Fe(II)
solution (with a molar ratio of GA to Fe(II) at 1:5). The two solutions were mixed by vortex
vibration for 10 seconds. Then, 0.035 g of DA was dissolved in the mixture, and the pH
was adjusted to 5.0–5.2. Afterward, it was centrifuged (2,000 g for 5 minutes) to remove
the precipitate, resulting in the preparation of the GA-Fe(II)+DA solution.
To prepare the aqueous phase solution, 2 mL of propylene glycol, 0.4 mL of Tween-80,
0.2 g of sodium dodecyl sulfate, 0.1 g of sodium thiosulfate, 0.1 g of sodium sulfite, 0.1 g
of ascorbic acid, 0.2 g of sodium benzoate, 0.8 mL of glycerol, and 3.8 mL of water at 65°C
with heating and stirring for 15 minutes. The GA-Fe(II)+DA solution was then added
under the same conditions and further heated and stirred for 10 minutes.
The oil phase solution was prepared by mixing 2 mL of isopropanol and 2 mL of oleic acid
at 65°C with heating and stirring for 15 minutes. The oil phase was added in a fine stream
to the aqueous phase solution while heating and stirring at 65°C, and the mixture was
stirred for an additional for 10 minutes to obtain the oil-in-water emulsion. The emulsion
was cooled to room temperature to yield GA-Fe(II)+DA hair dye. The natural white hair,
unfolded by ethanolamine, was dipped into the hair dye for 2 hours. Then the residual
solution was washed off with water and dried with a hair dryer.
MEASUREMENTS OF COLOR PARAMETERS
Color parameters, including L* (luminance), a* (red/green coordinates), and b* (yellow/blue
coordinates), were obtained using a colorimeter (HP-2136, Shanghai HanPat Optoelectronics

205 Polyphenol-metal Complex With Dopamine
Technology Company Limited, Shanghai, China). The measurements were repeated three
times in different areas of the hair sample. The averages of the measured parameters (L*,
a*, b*) represent the averages of three repeated measurements in different areas. Color
difference (ΔE) is calculated by the formula: ΔE =[(100– L*)2 +(a*)2 +(b*)2]1/2.
COLOR DURABILITY TEST
The dyed hair samples were completely immersed in 50 mL of shampoo solution, soaked,
and rubbed for 1 minute, then dried with a hair dryer for one wash. The washing procedure
was repeated to determine the color parameters for 1, 10, 20, and 40 washes, allowing the
determination of the color durability of the dyed hair samples.
HAIR DYE UV-VIS, FT-IR ANALYSIS, AND SEM CHARACTERIZATION OF HAIR SAMPLES
The UV-visible absorption spectra of GA, DA, GA-Fe(II)+DA were determined using a
UV-visible spectrophotometer (Shanghai Metash Instruments Co., Ltd., UV-5500PC). The
infrared spectra of dopamine hydrochloride, GA, ferrous chloride tetrahydrate, GA-Fe(II)
solution, and GA-Fe(II)+DA solution were determined by FT-IR infrared spectrophotometer
(PerkinElmer, Spectrum Two). The hair morphology was observed using a field emission
SEM Zeiss, Sigma 500).
HAIR STRETCHING TEST
Hair’s tensile strength was measured using an electronic universal material testing
machine (Shimadzu, AGS-X50N AGS-10KN) with a 200 mm scale and a stretching speed
of 20 mm/min.
RESULTS AND DISCUSSION
POLYPHENOL STAINING EFFECT AND CHELATION RATE
Phenolic compounds contain many dihydroxyphenyl or trihydroxyphenyl groups with
high π electron content and aromatics, which provide an effective negative binding site for
cation formation cation-π interactions. These interactions, which dominate non-covalent
cation-π interactions in the presence of other competing motifs, form stable polyphenol-
metal structures. During staining, polyphenol-Fe(II) first comes into contact with the
outer layer of hair scales and then develops color by adsorption, diffusion to the cortex,
and accumulation in its interior to form a polyphenol-Fe(II) network structure. Different
polyphenols react with ferrous ions to form structures that result in different colors and
varying dyeing effects on white hair. We selected eight polyphenol materials, dopamine,
and polydopamine to stain commercial gray hair and measured the color difference value
(Figure 2A). In addition, we used ultraviolet spectrophotometry to establish a standard
curve (Figure 2B), measured the absorbance value (A) of each polyphenol material chelated
to Fe(II) at 510 nm, and calculated the chelation rate according to the standard curve and
equation (1)(2)(3)(4)(5) to further screen for the best polyphenol materials.