Cellulose nanocrystals (CNC) can be studied on a single crystal level when deposited as a submonolayer. This allows observation of effects caused by for instance exposures to different environments or crystal lattice manipulation. Submonolayers were produced by using either spin-coat or adsorption method to deposit CNCs on a cationized silica. This surface pretreatment prevents the anionic CNCs from aggregating and (3-aminopropyl)trimethoxysilane (APTS) was chosen as the cation due to its superb adsorption of CNCs according to our previous tests. The allomorph can be changed from cellulose I to cellulose III in a number of different ways, however the use of an ethylenediamine (EDA) treatment was chosen. Surfaces were prepared by using one of the two following methods: 1) depositing cellulose III nanocrystals, or 2) performing the allomorph change treatment on already deposited cellulose I nanocrystals. The allomorph change was determined for samples produced for Method 1 with CP-MAS <sup>13</sup>C-NMR, whereas for Method 2 Raman spectroscopy was utilized.The surfaces were analyzed with both AFM and TEM, and compared to non-treated cellulose I CNC and its submonolayer. The cellulose III submonolayer produced with Method 1 yielded the same dimensions for the crystals as the reference CNC submonolayers. In contrast, the submonolayers produced via Method 2 showed distinct changes to the CNCs with the notable difference being the formation of aggregates (Figure 1). Moreover, it was observed that the CNCs - both in the aggregates and individually - were thinner. In fact, the crystal thickness was decreased by over 50% from around 5 nm to 2 nm. Since the allomorph transition treatment used in this work involves the breaking and re-structuring of inter- and intramolecular hydrogen bonding, it is feasible that the detected reduction in crystal size results from the peeling off of the outermost layers of the crystals.

Allomorph transformation in cellulose nanocrystals from cellulose I to cellulose III on a 2D-surface submonolayer

251st National Meeting (2016)

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