Smart responsive surfaces switching reversibly between super-hydrophobicity and super-hydrophilicity

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Smart responsive surfaces switching reversibly between super-hydrophobicity and super-hydrophilicity

Authors: Fan Xia, Ying Zhu, Lin Feng and Lei Jiang

Soft Matter, 2009, 5, 275–281

Soft matter keywords

superhydrophobicity, photowetting, electrowetting, thermowetting, pH-response, mechanowetting, multiresponsive surfaces

By Alex Epstein


Abstract from the original paper

Super-hydrophilicity and super-hydrophobicity are fundamentally opposite properties of special wettability, which are governed by surface chemical composition and surface roughness. Smart responsive surfaces switching reversibly between super-hydrophobicity and super-hydrophilicity can be effectively fabricated by modification of stimuli-responsive materials on rough surfaces. The externally applied stimuli include light irradiation, electrical potential, temperature, pH or selected solvents, and mechanical forces. Such surfaces with controllable wettability are of great importance to both fundamental research and practical applications.

Soft matters

The authors, who have written a considerable body of papers on controllable wettability, review five principal systems of surface wetting control. There is clearly a good deal of progress to date in reversibly switching between superhydophobic and philic surface states.

Photo-response

Fig. 1 (a) Water-drop profiles for the nano-structured V2O5. (b) SEM of a rose-garden-like nanostructure V2O5 substrate. (c) XPS of the O 1s level before and after UV irradiation. (d) Reversible wettability transitions through UV exposure and dark storage, respectively.

[[Image:smart2.png|thumb|right|400px|Fig. 2 (a) SEM image of the nanograss substrate. (b) Demonstration of electrically induced reversible transitions between different wetting states on a nanostructured substrate. (1) With no voltage applied. (2) With the application of about 35 V. (3) With a short pulse of electrical current.

Fig. 3 (a) SEM image of the nanostructures on rough substrate modified with PNIPAAm. (b) Water drop profile for responsive surface at 25 C and 40 C. (c) Diagram of reversible formation of intermolecular hydrogen bonding between PNIPAAm chains and water molecules (left) and intramolecular hydrogen bonding between C]O and N–H groups in PNIPAAm chains (right) below and above the LCST, which is considered to be the molecular mechanism of the thermally responsive wettability of a PNIPAAm thin film. (d) CAs in at two different temperatures 20 C and 40 C for PNIPAAm-modified rough substrate.
File:Smart4.png
Fig. 4 SEM images of deposited gold structures: (a) micro-scale gold structures, (b) magnified image of the gold clusters. Photographs of (c) acid and (d) base droplet applied on the surface. The CA of the acid droplet is 154 deg and the basic droplet will spread out on the surface gradually.
Fig. 5 Reversibly change in structure and wettability of the triangular polyamide film during extension and unloading.