Superhydrophobicity of nanofibrillated cellulose materials through polysiloxane nanofilaments
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The wetting behavior of nanofibrillated cellulose (NFC) was drastically changed from hydrophilic to superhydrophobic, achieving limited contact angle hysteresis. Remarkably, superhydrophobicity was attained for a variety of morphologies, namely dense and porous films, foams and powders, thus exploiting a wide spectrum of cellulose manifestations. The superhydrophobic behavior resulted from the combined action of hydrophobic polysiloxane nanofilaments, formed by controlled reaction of methyltrichlorosilane with water at the surface of NFC fibrils, and the NFC substrates surface morphology, established by various drying methods of the nanofibrils. In particular, the optimal conditions for polysiloxane nanofilaments growth, with identification of various regimes of coating versus nanofilaments growth, were identified. Depending on the morphology, we demonstrated that modified NFC materials can act multiple roles, such as superhydrophobic liquid-infused lubricating surfaces, filters for dodecane drops capture from a nebulized dodecane/water mixture, hydrocarbon absorption from an aqueous phase, with absorbance capacity as high as 50 gdodecane/gfoam, and beds to separate hydrocarbon/water mixture. As such, the versatile combination of two materials with nanoscale features (nanocellulose and nanofilaments), which provide multi-tier topography and unprecedented wetting characteristics, can serve for all those applications, in which liquid mixture behavior (e.g. water/hydrocarbon) needs to be controlled.
KeywordsMicrofibrillated cellulose Superhydrophibicity Methyltrichlorosilane MTCS SLIPS LIS Oil absorber Foams
Dr. P. Tingaut and Dr. T. Geiger are kindly acknowledged for fruitful scientific discussions. We kindly acknowledge Empa colleagues B. Fischer for TGA measurements, E. Strub for SEM imaging, A. Huch for SEM/EDX imaging, and M. Koebel for providing access to the Karl-Fischer titration device and other laboratory facilities.
The manuscript was written through contributions of all authors. PO and CA designed and carried out the experimental work related to dense films, porous films and foams. PO and AS performed nanofiber chemical modification and characterization. CA performed contact angle measurements. WJM performed the solid-state NMR analysis and interpretation. WRC and TZ supervised the scientific activities throughout the entire work. All authors have given approval to the final version of the manuscript.
EMPA is kindly acknowledged for internal funding.
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