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Controlling the formation of ice on surfaces
(Nanowerk Spotlight) In recent years, researchers working on de-icing and anti-icing strategies have been inspired by biology and nanotechnology to develop nanocoatings and other nanostructured surfaces.
Researchers now have demonstrated the ability to spatially control frost nucleation (ice formation from water vapor) and to manipulate ice crystal growth kinetics.
"The spatial control of icing in the condensation-freezing process and through the coating of hydrophilic materials has been demonstrated before," Ming-Chang Lu, Associate Professor in the Department of Mechanical Engineering at National Chiao Tung University, tells Nanowerk. "However, the ice nucleation control and the confinement of ice crystal growth direction through manipulating the roughness scale have not been reported in the literature."
Control of ice growth kinetics
Control of ice growth kinetics. (A) Hexagonal ice composed by two basal facets (c-axis) and six prism facets (a-axis). (B) Random and aligned orientations of c-axes were found on trapezoid-shaped microgrooves (TMG) and V-shaped microgrooves (VMG) surfaces, respectively. (C) Ice embryos appear on the side walls, the edges, and the valleys of groove on TMG surfaces, resulting in different orientations of ice crystals. On the other hand, an ice embryo forms only at the valley of grooves on the VMG surface, leading to the confined ice orientation. Scale bars are 15 µm. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
In previous work, Lu and his team demonstrated that heterogeneous nucleation of condensation could be spatially controlled by manipulating surface roughness (Advanced Functional Materials, "Spatial Control of Heterogeneous Nucleation on the Superhydrophobic Nanowire Array"). This motivated them to further explore whether the same control could be achieved in the icing process.
Indeed, as they recently have reported in ACS Nano ("Control of Ice Formation"), they found that a surface's anti-icing (preventing ice formation) and deicing performances could be promoted through the control of nucleation and the confinement of the ice crystal growth direction.
The scientists achieved control of nucleation and the confinement of the crystal growth kinetics by manipulating the local free energy barrier for nucleation.
Moreover, the growth kinetics of ice can also be altered by adjusting the shape of microgrooves on the surface: Ice stacked along the direction of V-shaped microgrooves, whereas it grew in random directions on trapezoid-shaped microgrooves.
As the researchers demonstrate in their paper, the spatial control of frost formation and the confinement of ice-growing kinetics improved the anti-icing and deicing performances.
"We have shown that ice formation and ice crystal growth could be manipulated by tailoring surface roughness," notes Lu. "We believe that our results could be potentially applied to alleviate the icing issues in many industrial systems such as power transmission systems, telecommunication systems, heat exchangers, aircraft, etc."
In this work, the team systematically investigated – under an environmental scanning electron microscope (ESEM) – frosting and deicing processes on a plain silicon surface, a silicon nanowire (SiNW) array-coated surface, and V-shaped and trapezoid-shaped microgroove patterned surfaces.
Nucleation is the first step of the phase transition during freezing. The team's goal is to gain complete control of the ice formation process including nucleation, crystal growth, and ice spreading.
"The results we demonstrated were on a silicon surface and on a laboratory chip; in my opinion, the future directions for this research are to explore whether the phenomena could be realized on other materials and on a larger scale," concludes Lu. "The ultimate goal is to have full controls of icing and deicing processes."
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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