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Chemical vapor deposition of a thin titanium dioxide (TiO 2 ) fi lm on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between water-superabsorbent and water-repellent states. Cellulose nanofi brils (diameters in the range of 5-20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here fi rst formed by freeze-drying from the corresponding aqueous gels. Well-defi ned, nearly conformal TiO 2 coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO 2 -coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140 ° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofi brils spontaneously aggregate into porous sheets of different length scales during freeze-drying is relevant: in the water-repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water-spreading into the aerogel cavities by capillary effects. The TiO 2 -coated nanocellulose aerogels also show photooxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purifi cation. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications.

The walls of microfludic “smart channels” are coated by responsive mixed polymer brushes with a gradient of chemical composition. The concept of the smart channels is based on switching/adaptive behavior of the mixed polymer brushes where wetting and nonwetting can be tuned upon interaction with liquids. This design of microfluidic channels brings new opportunities for manipulating the passage of liquids in the channels. The developed approach allows us to fabricate three microfluidic elements for separation, sensing, selection, and dosing microvolumes of liquids.

We report on a thin polyelectrolyte film (mixed polyelectrolyte brush) with a gradual change of the composition (ratio between two different oppositely charged surface-grafted weak polyelectrolytes) across the sample. The gradient of surface composition creates a gradient in surface charge density and, consequently, a gradient of the wetting behavior. The gradient film is sensitive to a pH signal and can be reversibly switched via pH change.