Surface free energy measurement data

Change in surface free energy by UV ozone cleaning surface modification

Irradiating metals, glass, plastics, and other solids with short-wavelength UV light removes organic surface contaminants and generates functional groups such as OH, CHO, and COOH on the surface, thereby improving the wettability of the solid surface. For example, it is known that UV irradiation of a glass surface for 2 to 3 minutes lowers the contact angle of water to an angle as it nears single digits, and we measured the surface free energy using a contact angle meter to see how the energy state of the actual material surface changes. 

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Measurement conditions and equipment used

Measurement conditions	Room temperature	26.5℃
	Humidity	25.0％
Equipment used	UV surface modification cleaning equipment	ASM1101N
	Contact Angle Meter	B100
Surface modification treatment	UV irradiation lamp	110W 1-lamp type Low-pressure mercury vapor lamp
	Irradiation distance	30mm
Contact angle measurement conditions	Liquid drop volume	1.0μL
	Waiting time for stabilization after liquid drop	2 seconds
	Measurement point	5 points
	Computational theory	Owens and Wendt
	Probe solution	Water, Diiodomethane (Methylene iodide)

Probe solution

	Dispersion force（ｄ）	Hydrogen bond strength（ｈ）	Surface free energy（mJ/m2）
Water	21.8	51.0	72.8
Diiodomethane	49.5	1.3	50.8

Measurement Results

Acrylic

Irradiation time（sec）		0	30	60	90	120	150	180	210	240	270	300
Contact angle（°）	Water	64.26	62.93	55.20	55.23	51.91	49.21	39.26	32.34	28.91	26.48	29.76
	Diiodomethane	35.59	34.89	35.57	36.75	35.48	35.30	36.38	34.90	35.75	35.72	35.61
Component	Dispersion force（ｄ）	35.96	36.07	34.47	33.90	34.02	33.71	31.92	31.87	31.16	30.98	31.30
	Hydrogen bond strength（ｈ）	11.49	12.18	17.37	17.61	19.61	21.44	28.62	32.63	34.92	36.25	34.38
Surface free energy（mJ/m2）		47.45	48.25	51.84	51.51	53.63	55.15	60.54	64.50	66.08	67.23	65.68

Polycarbonade

Irradiation time（sec）		0	30	60	90	120	150	180	210	240	270	300
Contact angle（°）	Water	90.59	79.75	57.39	41.87	30.88	25.26	23.38	23.29	21.18	20.76	20.75
	Diiodomethane	24.23	33.94	32.04	30.92	29.54	29.11	29.61	28.83	29.23	28.64	28.30
Component	Dispersion force（ｄ）	46.32	39.69	36.58	34.70	34.04	33.72	33.37	33.68	33.37	33.57	33.70
	Hydrogen bond strength（ｈ）	0.35	3.55	14.99	25.42	32.00	34.93	35.98	35.82	36.88	36.90	36.82
Surface free energy（mJ/m2）		46.67	43.24	51.57	60.12	66.04	68.65	69.35	69.50	70.25	70.47	70.52

ABS

Irradiation time（sec）		0	30	60	90	120	150	180	210	240	270	300
Contact angle（°）	Water	85.39	62.35	47.14	41.06	33.53	28.36	23.25	20.45	20.27	19.67	18.48
	Diiodomethane	36.55	39.62	34.13	31.62	29.99	29.99	27.60	25.81	27.26	27.52	26.49
Component	Dispersion force（ｄ）	39.49	33.59	33.97	34.29	34.12	33.62	34.15	34.62	34.07	33.93	34.25
	Hydrogen bond strength（ｈ）	1.96	13.49	22.60	26.13	30.55	33.54	35.52	36.31	36.75	37.06	37.27
Surface free energy（mJ/m2）		41.45	47.08	56.57	60.42	64.67	67.16	69.67	70.93	70.82	70.99	71.52

SUS304

Irradiation time（sec）		0	30	60	90	120	150	180	210	240	270	300
Contact angle（°）	Water	70.67	59.60	54.91	36.49	29.23	23.07	24.67	23.83	31.07	20.93	23.14
	Diiodomethane	45.90	42.67	33.57	35.28	33.76	37.05	33.69	35.08	34.64	36.89	35.21
Component	Dispersion force（ｄ）	31.57	31.54	35.37	32.12	32.09	30.11	31.75	31.06	31.87	30.04	30.96
	Hydrogen bond strength（ｈ）	9.68	16.04	17.13	30.13	34.12	38.43	36.54	37.40	33.32	39.37	37.78
Surface free energy（mJ/m2）		41.25	47.58	52.50	62.25	66.21	68.54	68.29	68.46	65.19	69.41	68.74

It can be seen that UV irradiation tends to lower the contact angle of water for both resins and metals. The graph below summarizes the change in surface free energy over the irradiation time.

The hydrogen bonding strength of all materials tends to increase with time, suggesting that the functional groups have increased due to the surface modification effect of UV irradiation.

The results of the surface free energy calculation using Owen's theory show that the hydrogen bonding force of the surface free energy of both metals and resins increased dramatically due to the modification effect of the UV ozone cleaning modification, thereby the surface free energy of the solid approached the surface tension of water (72.8 mJ/m2 at 20°C), resulting in more better with water and improved wettability with water.