Evaporation of Sessile Droplet on Grooved PDMS Substrate and Resultant Cassie-Wenzel Transition†

doi:10.7503/cjcu20141035

Abstract

Abstract:

The evaporation of sessile droplets(water) on grooved polydimethylsiloxane(PDMS) substrate was investigated in detail. The contact angles and diameters of the droplet show clear difference between vertical (V) and parallel (P) directions, indicating the anisotropy of the droplet. Upon evaporation, three stages including constant diameter mode(CDM), constant contact-angle mode(CCM) and combination mode of them have been tracked as well as the results on the flat PDMS. The transition from Cassie to Wenzel state, leading to the simultaneous quick increase of the contact diameter and the sudden decrease of the height and contact angle, was observed in the first stage(CDM). The transition time depends crucially on the area fraction of the protrusion. Furthermore, the anisotropy of the droplet disappears, resulting in the equal diameters in P and V directions in the second stage ( CCM). The results are significant for the control of superhydrophobicity surface.

Key words: Wenzel state, Cassie state, Evaporation, Transition, Polydimethylsiloxane substrate, Sessile droplet(water)

CLC Number:

O631

TrendMD:

ZENG Mengmeng, ZHU Yu, YOU Jichun, LI Yongjin. Evaporation of Sessile Droplet on Grooved PDMS Substrate and Resultant Cassie-Wenzel Transition^†[J]. Chem. J. Chinese Universities, 2015, 36(7): 1441.

Figures/Tables 8

Scheme 1 Schematic representation of Wenzel(A), Cassie(B) states and grooved PDMS substrate(C)

Table 1 Structure parameters of the adopted grooved PDMS substrate

Sample	w/μm	d/μm	h/μm	Φ_s(%)	View
16-4	16	4	2	20	P/V
12-8	12	8	2	40	P/V
8-12	8	12	2	60	P/V
4-16	4	16	2	80	P/V
Flat				100

Fig.1 Evolution of contact angle(A) and contact diameter(B) of water droplet on flat PDMS during evaporation

Fig.2 Optical microscopy of patterned PDMS substrate(A), the water droplet image taken by DSA from P direction(B) and V direction(C)

Fig.3 Water droplet images(V direction) during evaporation for 0 s(A), 160 s(B), 220 s(C),260 s(D), 1100 s(E), 2800 s(F), 4000 s(G), 4560 s(H) on 8-12 PDMS substrate

Fig.4 Evolution of contact angle(A, A'), contact diameter(B, B') and droplet height(C, C') during evaporation on 8-12 PDMS substrate^(A'—C') Enlarged parteners of 0—600 s.

Fig.5 Area fraction of the protrusion dependence of Cassie-Wenzel transition time

Fig.6 Evolution of contact diameter(A) and contact shape anisotropy(B) on 8-12 PDMS substrate

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