Tunable mixed amorphous–crystalline cellulose substrates (MACS) for dynamic degradation studies by atomic force microscopy in liquid environments

Atomic force microscopy in liquid environments (L-AFM) became a state of the art technique in the field of enzymatic cellulose degradation due to its capability of in situ investigations on enzymatic relevant scales. Current investigations are however limited to few substrates like valonia cellulose, cotton linters and processed amorphous cellulose as only these show required flatness and purity. Structurally monophasic, these substrates confine conclusions regarding enzymatic degradation of mixed amorphous–crystalline substrates as commonly found in nature. To exploit the full potential of the technique, cellulose substrates with multiphase properties, flat topology and purity are therefore absolutely required. In this study we introduce a special preparation route based on highly crystalline Avicel PH101^® cellulose and the ionic liquid 1-butyl-3-methylimmidazolium chloride as dissolution reagent. As comprehensively shown by atomic force microscopy, wide angle X-ray scattering, Raman spectroscopy and electron microscopy, the developed material allows precise control of its polymorphic composition by means of cellulose types I and II embedded in an amorphous matrix. Together with the tunable composition and flat topology over large areas (>10 × 10 µm²) the material is highly suited for L-AFM studies.