The surface roughness of polymer gels was investigated by tapping mode atomic force microscopy (AFM). The spongelike domains on N-isopropylacrylamide (NIPA) gels were directly observed in water. It was found that the surface domain structure was strongly affected not only by the degree of the homogeneities of polymer networks but also by the bulk phase transition in response to the change in the external temperature. The domain size of homogeneous gels prepared at the ice temperature was found to be much smaller than that of the inhomogeneous gels prepared at a temperature above the cloud point of NIPA polymers. The surface structure was reproducibly observed at exactly the same position below and above the volume phase transition temperature, and its change was found to be reversible with temperature. The surface roughness due to the spongelike domains was discussed in terms of the autocorrelation function, the root-mean-square roughness, and the power spectral density, which were calculated from the AFM images.

We report here, for the first time, the direct observation of the submicron structure of gel surfaces in water by using an atomic force microscope ͑AFM͒. We present also its change in response to external stimuli; we investigated, among the variables that affect the topography of the gel surface, the effect of the network density of poly͑acrylamide͒ gels and the effect of the temperature change of poly N-isopropylacrylamide gels. Gels were prepared with disklike shape of thickness ranging from 10 to 50 m, and one of the gel surfaces was chemically adhered onto a glass plate. Spongelike domains of submicrometer scale were found here on the gel surfaces, which was strongly affected by the cross-linking density ͑nature of the gel network͒ as well as the osmotic pressure ͑environmental condition͒, and also thickness ͑condition of constraint͒. The qualitative properties of the surface microscopic structure of gels are discussed in relation to a hypothetical model of two-dimensional gels based on the Flory-Huggins theory. These results disclose that the surface microstructures of polymer gels in solvent as well as the nanometer scale structural changes are associated with the gel phase transition. Moreover, they indicate that the potential for a new technology to control the domain size of the gel surface as well as its function by external stimuli could emerge, which would find a variety of applications in many fields, such as engineering, medicine, and biology.

Icing on an aircraft is the cause of numerous adverse effects on aerodynamic performance. Although the issue was recognized in the 1920s, the icing problem is still an area of ongoing research due to the complexity of the icing phenomena. This review article aims to summarize current research on aircraft icing in two fundamental topics: icing physics and icing mitigation techniques. The icing physics focuses on fixed wings, rotors, and engines severely impacted by icing. The study of engine icing has recently become focused on ice-crystal icing. Icing mitigation techniques reviewed are based on active, passive, and hybrid methods. The active mitigation techniques include those based on thermal and mechanical methods, which are currently in use on aircraft. The passive mitigation techniques discussed are based on current ongoing studies in chemical coatings. The hybrid mitigation technique is reviewed as a combination of the thermal method (active) and chemical coating (passive) to lower energy consumption.

Ice accretion is detrimental to numerous industries, including infrastructure, power generation, and aviation applications. Currently, some of the leading de-icing technologies utilize a heating source coupled with a superhydrophobic surface. This superhydrophobic surface reduces the power consumption by the heating element. Further power consumption reduction in these systems can be achieved through an increase in passive heat generation through absorption of solar radiation. In this work, a superhydrophobic surface with increased solar radiation absorption is proposed and characterized. An existing icephobic surface based on a polytetrafluoroethylene (PTFE) microstructure was modified through the addition of graphite microparticles. The proposed surface maintains hydrophobic performance nearly identical to the original superhydrophobic coating as demonstrated by contact and roll-off angles within 2.5% of the original. The proposed graphite coating also has an absorptivity coefficient under exposure to solar radiation 35% greater than typical PTFE-based coatings. The proposed coating was subsequently tested in an icing wind tunnel, and showed an 8.5% and 50% decrease in melting time for rime and glaze ice conditions, respectively.

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