Mechanism of Hydrophobic Over-recovery on Polyethylene Surface Modified by Oxygen Plasma†

doi:10.7503/cjcu20140253

Abstract

Abstract:

Low density polyethylene(LDPE) surface was modified by oxygen capacitively coupled plasma(CCP) under a radio frequency(RF) power of 200 W for an exposure time of 1 min. The aging process of the plasma-modified LDPE was studied at aging temperatures of 60 and 90 ℃ for an aging time of 24 h. The morphology with the nanonodules was obtained on the as-modified LDPE surface under 200 W for 1 min and was stable on the post-aged LDPE surface at 60 and 90 ℃ after 24 h. The plasma modification under 200 W for 1 min introduced lots of polar oxygen-containing groups on the as-modified LDPE surface. The aging process at 60 ℃ after 24 h aroused the decrease of the polar oxygen-containing groups on the post-aged LDPE surface and lower oxygen-containing group content appeared on the post-aged surface at 90 ℃. The as-modified hydrophi-lic surface with the contact angle of 42.3° underwent the hydrophobic recovery into hydrophobicity on the post-aged surface with the contact angle of 95.9° at 60 ℃ after 24 h similar to the original LDPE surface with 97.2°, and further hydrophobic over-recovery into higher hydrophobicity of the post-aged surface with the contact angle of 104.2° at 90 ℃ after 24 h than the original surface. Based on the time-dependent contact angle model for the aging of the rough surface containing different wetting patches, the surface restructuring on the plasma-modified LDPE surface experiencing the hydrophobic over-recovery during aging process was quantitatively analysized.

Key words: Low density polyethylene(LDPE), Oxygen capacitively coupled radio frequency plasma, Aging, Surface restructuring, Hydrophobic over-recovery

CLC Number:

O631

TrendMD:

LI Yupeng, ZHANG Zhichao, LI Shengyao, SHI Wei, LEI Mingkai. Mechanism of Hydrophobic Over-recovery on Polyethylene Surface Modified by Oxygen Plasma^†[J]. Chem. J. Chinese Universities, 2014, 35(8): 1816.

Figures/Tables 6

Fig.1 SEM images of original LDPE surface(A), as-modified surface under oxygen CCP of 200 W for an exposure time of 1 min(B), and post-aged surface at an aging temperature of 60 ℃(C) and 90 ℃(D) after an aging time of 24 h

Fig.2 Deconvolution of XPS C1s spectra of original LDPE surface(A), as-modified surface under oxygen CCP of 200 W for 1 min(B), and the post-aged surface at 60 ℃(C) and 90 ℃(D) after 24 h

Table 1 Component percentage in the C1s spectra and atomic concentration of C and O measured by XPS for original LDPE surface, as-modified surface under oxygen CCP of 200 W for 1 min and the post-aged surface at 60 and 90 ℃ after 24 h

Sample	Bonding contribution(%)				Elemental composition(%)
Sample	C—C(285.0 eV)	C—O(286.5 eV)	C O(288.0 eV)	O—C O(289.0 eV)	C	O
Original	93.1	3.3	2.9	0.7	95.6	4.4
As-modified	76.9	16.4	2.2	4.5	82.9	17.1
Post-aged at 60 ℃	83.0	13.1	1.9	2.0	84.5	15.5
Post-aged at 90 ℃	84.1	10.1	3.1	2.7	85.4	14.6

Fig.3 Contact angle on post-aged LDPE surface at 60 ℃(a) and 90 ℃(b) during 24 h for oxygen CCP modified sample under 200 W for 1 min

Fig.4 Fitting curve of the time-dependent contact angle θw(t) on the post-aged LDPE surface dependent on the aging time t at 60 ℃(a) and 90 ℃(b) during 24 h for the oxygen CCP modified sample under 200 W for 1 min

Table 2 Surface restructuring parameters of the post-aged LDPE surface during aging estimated by using Eq.(1) from the experimental data in Fig.4

Sample	$f im p$ (%)	f $m p$ (%)	f^p(t=0 h) (%)	f^np(t=0) (%)	f^p(t=24 h) (%)	f^np(t=24 h) (%)	f^p(t=∞) (%)	f^np(t=∞) (%)	τ/h
Post-aged at 60 ℃	26.7	34.0	60.7	39.3	26.7	73.3	26.7	73.3	0.81
Post-aged at 90 ℃	13.5	48.2	61.7	38.3	13.5	86.5	13.5	86.5	0.41

Table 2 Surface restructuring parameters of the post-aged LDPE surface during aging estimated by using Eq.(1) from the experimental data in Fig.4

Sample	$f im p$ (%)	f $m p$ (%)	f^p(t=0 h) (%)	f^np(t=0) (%)	f^p(t=24 h) (%)	f^np(t=24 h) (%)	f^p(t=∞) (%)	f^np(t=∞) (%)	τ/h
Post-aged at 60 ℃	26.7	34.0	60.7	39.3	26.7	73.3	26.7	73.3	0.81
Post-aged at 90 ℃	13.5	48.2	61.7	38.3	13.5	86.5	13.5	86.5	0.41

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