Laser-induced anisotropic wettability on azopolymeric micro-structures

Abstract

The light-induced deformation of a micro-textured photo-sensitive polymeric material is exploited for modifying the surface hydrophobicity along deterministic directions. Arrays of azopolymeric micro-pillars are fabricated over large area and irradiated with a green laser. Upon laser irradiation, the micro-pillars deform reversibly along a direction parallel to the laser polarization, resulting in elongated shapes with controllable eccentricity. Such a locally anisotropic topography induces a directional yet reversible change of hydrophobicity, as measured by contact angles varying within a range of 30°.

Reversible Shaping of Microwells by Polarized Light Irradiation

“…In agreement with our previous experimental findings [19] and results from literature [20,21], we observe a directional mass migration of the polymer along the polarization direction. For a quantitative analysis, the mean roundness parameter is evaluated for each frame as the ratio between the minor ( ) and the major axis ( ) averaged over 20 microwells within a single field-of view of the microscope.…”

“…The image analysis reveals that an average roundness of about 1 is achieved after further 200 seconds of irradiation. Such reversible modification is advantageously promoted by an improved stiffness of the polymeric mixture due to the presence of a stabilizing PMMA component, as suggested elsewhere in other copolymer matrices containing azobenzenes [19][20][21][22]. We underline here that the role of PMMA seems to be crucial for reversibility, since with pure PAZO structures we were not able to restore the pristine shape.…”

“…Alternatively, the microwells can be reduced in size without changing the roundness till an almost complete closing is reached. Tuning the morphology of surface microstructures might provide a smart engineered platform where surface properties can be engineered on demand after fabrication [19,20]. The light-induced contraction and expansion based reshaping of polymeric microstructures shows exciting potential for several applications including microfluidics and lithography and, in the last years, is showing its potential application in biology, where cells behavior can be regulated in response to material manipulation.…”

“…The SEM image in Figure 1 Optical Setup. The optical setup employed in this work is described in detail in [19]. Briefly, we employ a pulsed laser (laser temporal width ≈ 10 ps, wavelength 490 nm, and average intensity ≈ 50 mW) circularly polarized.…”

External‐Field‐Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface

“…Pirani et al reported photoinduced anisotropic wettability on azopolymeric micropillars structures. [56] Upon laser irradiation, the micropillars reversibly deformed along a direction parallel to the laser polarization, resulting in a locally anisotropic topography that induced a directional reversible change of the hydrophobicity. Photoresponsive surface wettability owing to the shape-memory behavior of an azo-containing liquid-crystalline network was reported by Wu et al, which offers the possibility of precisely controlling droplet motion on microstructured surfaces.…”