Poly(dimethyl siloxane) anti-corrosion coating with wide pH-responsive and self-healing performance based on core-shell nanofiber containers

doi:10.1016/j.jmst.2021.06.014

Abstract

Abstract:

In this research, core-shell electrospun fibers loaded with the shell of cellulose acetate and the core of oleic acid and alkyd varnish resin were synthesized and used within poly(dimethyl siloxane) (PDMS) to prepare self-healing and pH-responsive coatings for a steel substrate. The morphology of the electrospun fibers was characterized by scanning electron microscopy, transmission electron microscopy and confocal fluorescence microscopy. Thermo gravimetric analysis and Fourier transform infrared spectroscopy revealed that the self-healing agents were loaded successfully with a loading rate of 2.9%. The properties of the fiber-PDMS composite coating were characterized by water contact angle measurements, mechanical tests, electrochemical impedance spectroscopy, and scanning Kelvin probe. Results show that the maximum self-healing efficiencies of the fiber-PDMS coating in alkaline and acidic solution are 95.96% and 97.04%, respectively. The composition of the self-healing agents at the damaged part of the coating was verified by an infrared mapping test and using an energy dispersive spectrometer. In addition, the sandpaper abrasion test shows the hydrophobic effect of fiber-PDMS coating remains above 88.2% and decreases slightly through the addition of abrasion cycles. This research can pave the way for the industrial applications of pH-responsive self-healing coatings.

Key words: Core-shell fibers, Self-healing coating, Oleic acid, Hydrophobic effect

Xiaohong Ji, Wei Wang, Xia Zhao, Lifei Wang, Fubin Ma, Yanli Wang, DuanJi zhou, Baorong Hou. Poly(dimethyl siloxane) anti-corrosion coating with wide pH-responsive and self-healing performance based on core-shell nanofiber containers[J]. J. Mater. Sci. Technol., 2022, 101: 128-145.

Figures/Tables 23

Fig. 1. (a) Optical images of the Q235 carbon steel and (b) electrospinning fiber film coated on Q235 carbon steel.

Fig. 2. Schematic of process used for preparing self-healing coatings: (a) synthesis of CA@(OA+AVR) core-shell electrospun fibers, (b) preparation of hydrophobic solution, (c) preparation of hydrophobic fiber materials, and (d) applying the fiber composite coating on the surface of Q235 steel.

Fig. 3. (a) SEM image, (b) the diameter distribution, (c) SEM image of the poor-synthesized electrospun fibers, (d) TEM image, and (e, f) confocal fluorescence microscopy images of the well-synthesized electrospun fibers.

Fig. 4. FT-IR spectra of (a) OA (b) CA@(OA+AVR) fibers (c) AVR (d) CA.

Fig. 5. TG curves of CA@(OA+AVR) electrospun fibers in comparison to CA, OA, and AVR.

Fig. 6. SEM images (a, b, c) and EDS mapping (d, e, f) of hydrophobic fibers in Fig. 5(b).

Fig. 7. Load-extension curves derived from tensile tests based on the adhesion of the samples to tin foil paper: (a) fibers (b) PDMS coating, and (c) Fibers-PDMS coating.

Table 1 Mechanical parameters calculated based on tensile tests.

sample	Load (N)	Extension (mm)	Tensile strength (MPa)	Elongation (%)	Thickness (µm)
Fibers	8.92	1.45	0.59	0.240	100
PDMS coating	18.08	1.69	1.25	0.186	100
Fibers-PDMS coating	35.61	1.51	2.37	0.125	217

Fig. 8. (a) Schematic of hydrophobic structure; (b) the variation of water contact angle on the fiber-PDMS composite coating during sandpaper abrasion test; The water contact angle of (c) core-shell fibers coating and (d) PDMS coating.

Fig. 9. EIS results of blank PDMS and fiber-PDMS composite coatings tested by wet/dry cyclic corrosion tests (pH=11.8): (a, and d) Nyquist plots; (b-f) Bode and phase plots; (g) the values of |Z|0.01Hz; (h) The electrical equivalent circuit used for fitting EIS results. The points and lines represent the original experimental data and their corresponding fitting, respectively.

Table 2 Electrochemical parameters for blank coating and fibers coating with scratch derived from wet/dry cyclic corrosion tests (pH=11.8).

Coating	Time (days)	CPE_dl		R_f (kΩ·cm²)	CPE_f		R_ct (kΩ cm²)	\|Z\| (kΩ cm²)	ηe_R%
Coating	Time (days)	Y_{0, dl} (s·secⁿ)	n_dl	R_f (kΩ·cm²)	Y_{0, f} (s·secⁿ)	n_f	R_ct (kΩ cm²)	\|Z\| (kΩ cm²)	ηe_R%
Blank coating	1	4.35 × 10^-4	0.76	6.03	2.46 × 10^-4	0.65	0.29	4.76	-
	3	7.00 × 10^-4	0.73	6.11	3.61 × 10^-4	0.64	0.18	3.90	-
	5	9.50 × 10^-4	0.68	6.36	6.95 × 10^-4	0.61	0.12	2.71	-
	10	9.30 × 10^-4	0.69	6.00	8.92 × 10^-4	0.57	0.13	2.64	-
	12	1.00 × 10^-3	0. 67	0.11	7.00 × 10^-4	0.61	6.11	2.40	-
	15	9.40 × 10^-4	0.69	6.45	9.37 × 10^-4	0.57	0.14	2.38	-
Composite Coating	1	2.63 × 10^-6	0.65	0.537	1.10 × 10^-5	0.40	52.90	45.72	87.99
	3	2.61 × 10^-5	0.38	18.00	1.10 × 10^-9	0.77	51.34	54.07	90.93
	5	3.10 × 10^-5	0.28	29.72	7.80 × 10^-10	0.79	66.13	63.86	93.24
	10	2.79 × 10^-5	0.15	24.23	2.40 × 10^-10	0.87	32.40	86.40	89.18
	12	1.58 × 10^-5	0.21	30.85	2.60 × 10^-10	0.88	123.10	89.67	95.96
	15	3.43 × 10^-5	0.14	23.08	1.90 × 10^-10	0.89	137.00	65.80	95.88

Fig. 10. EIS results of blank PDMS and fiber-PDMS composite coatings tested by wet/dry cyclic corrosion tests (pH=4.0): (a, and d) Nyquist plots; (b-f) Bode and phase plots; (g) the values of |Z|0.01Hz; (h) The electrical equivalent circuit used for fitting EIS results. The points and lines represent the original experimental data and their corresponding fitting, respectively.

Table 3 The electrochemical parameters for the blank coating and fiber-PDMS composite coating with scratch derived from wet/dry cyclic corrosion tests (pH=4.0).

Coating	Time (days)	CPE_dl		R_f (kΩ·cm²)	CPE_f		R_ct (kΩ cm²)	\|Z\| (kΩ cm²)	ηe_R%
Coating	Time (days)	Y_{0, dl} (s·secⁿ)	n_dl	R_f (kΩ·cm²)	Y_{0, f} (s·secⁿ)	n_f	R_ct (kΩ cm²)	\|Z\| (kΩ cm²)	ηe_R%
Blank coating	1	8.70 × 10^-6	0.73	2.43	4.02 × 10^-5	0.73	0.094	2.97	-
	3	5.95 × 10^-6	0.78	2.15	1.46 × 10^-4	0.67	0.098	2.57	-
	5	7.96 × 10^-6	0.72	2.12	4.10 × 10^-4	0.61	0.11	2.41	-
	8	8.56 × 10^-6	0.71	2.09	4.10 × 10^-4	0.65	0.11	2.35	-
	10	6.21 × 10^-6	0.71	2.11	5.30 × 10^-3	0.69	0.089	2.37	-
	15	7.37 × 10^-4	0.69	0.06	1.48 × 10^-5	0.60	1.96	2.13	-
Composite Coating	1	3.80 × 10^-5	0.70	3.66	5.1 × 10^-9	0.68	8.17	11.60	78.66
	3	4.35 × 10^-11	1.00	23.40	3.9 × 10^-5	0.51	3.74	23.90	91.72
	5	4.04 × 10^-11	1.00	65.10	7.1 × 10^-6	0.50	10.20	69.50	97.04
	8	6.38 × 10^-6	0.55	6.70	2.2 × 10^-9	0.72	55.30	57.20	96.45
	10	1.96 × 10^-10	0.90	48.10	6.7 × 10^-6	0.52	8.50	52.90	96.11
	15	7.00 × 10^-6	0.52	8.78	2.7 × 10^-10	0.86	47.00	51.50	96.38

Fig. 11. (a, and b) SEM images and (c, and d) EDS analysis of the scratched fiber-PDMS composite coating (a, and c) after 0 day (b, and d) 15 days of wet/dry cyclic corrosion tests (pH = 11.8).

Fig. 12. SKP maps for the fiber-PDMS composite coating after different immersion times in wet/dry cyclic corrosion tests (pH = 11.8): (a) 1 day, and (b) 15 days.

Fig. 13. Digital photographs of blank coating ((a) 0, (b) 5, and (c) 15 days) and fiber-PDMS composite coating ((d) 0, (e) 5, and (f) 15 days) during wet/dry cyclic corrosion tests (pH=11.8) (scale bar = 1 cm).

Fig. 14. (a, and b) SEM images and (c, and d) EDS analysis of the scratched fiber-PDMS composite coating (a, and c) after 0 day (b, and d) 5 days of wet/dry cyclic corrosion tests (pH = 4.0).

Fig. 15. SKP maps for the fiber-PDMS coating after different immersion times in wet/dry cyclic corrosion tests (pH = 4.0): (a) 1 day, and (b) 5 days.

Fig. 16. Digital photographs of blank coating ((a) 0, (b) 5, and (c) 15 days) and fiber-PDMS composite coating ((d) 0, (e) 5, and (f) 15 days) during wet/dry cyclic corrosion tests (pH=4.0) (scale bar = 1 cm).

Fig. 17. (a) Diffusion models of different nanofibers in the coatings (M1, M2, M3), (b, d) the diffusion rate of (Cl-) concentration in different positions from the top of the coating at monitoring point (M4: A-1 µm, B-5 µm, C-11 µm and D-19 µm) and (c) simulation of diffusion kinetics of water in nanofiber coatings at different time points.

Fig. 18. (a) Optical images of the scratched fiber-PDMS composite coating after 12 days of wet/dry cyclic corrosion tests (pH = 11.8), (b) the FT-IR spectra of OA+AVR coating, (c-e) FT-IR mapping test by the FT-IR microscope.

Fig. 20. Schematic of self-healing and wear-resistance performance for fiber-PDMS composite coating: (a) before immersion and (b) after immersion in the corrosive media, (c) in alkaline NaCl solution and (d) in acidic NaCl solution.

Fig. 19. (a) Optical images of the scratched fiber-PDMS composite coating after 5 days of wet/dry cyclic corrosion tests (pH=4.0), (b) the FT-IR spectra of OA+AVR coating, (c-e) FT-IR mapping test by the FT-IR microscope.

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