Electronic Supplementary Material

Cellulose Nanocrystals with CO2-Switchable Aggregation and Redispersion Properties

Hai-Dong Wang, Philip G. Jessop, Jean Bouchard, Pascale Champagne*, Michael F. Cunningham*

Corresponding author: M. F. Cunningham*

Department of Chemical Engineering, Queen’s University, 19 Division Street, Kingston, Ontario K7L 3N6, Canada

e-mail: ; tel: 613-533-2782; fax 613-533-6637

Co-Corresponding author: P. Champagne*

Department of Civil Engineering, Queen’s University, 58 University Avenue, Kingston, Ontario K7L 3N6, Canada

e-mail: ; tel: 613-533-3053; fax 613-533-2128

Fig. S1 DRIFT-IR spectra of native CNC and CNC-APIm

Table S1 Degree of protonation of HPIm calculated by different protons at different conditions measured by 1H NMR spectroscopy (see Fig.5for the assignment of different protons in HPIm). HPIm concentration is fixed at 15 mg/ml

Protons / Degree of protonation at different conditionsa
Original
(%) / CO2 Sparging (5 min)
(%) / CO2 + N2 Sparging (5+30 min)
(%)
1 / 7.0 / 77 / 16
2 / 25 / 108 / 35
3 / 19 / 97 / 28
Average / 17 / 94 / 26
aData were recorded on a Bruker Avance 400 NMR spectrometer at 25oC using 90% H2O + 10% D2O as solvent. The degree of protonation was calculated as: , where , , and denote a specific chemical shift and chemical shifts at 100% (1.0 M HCl) and 0% (1.0 M NaOH) degree of protonation, respectively. To check reproducibility, all NMR measurements were conducted at least in triplicate and differences for all repeated measurements were less than 5%. Only one set of data were used for the calculation in this table. The degree of protonation value is not exact.

Calculation of Surface Imidazole and SulfateDensities

The elemental analysis data (Table 1) show that: 1. the two CNC-APIm samples are consistent suggesting high reproducibility of the CNC-APIm preparation and purification procedures as described in this work and; 2. the S concentrations for native CNC and CNC-APIm are similar indicating that the sulfate groups are not significantly hydrolyzedafterthe CNC-APIm preparation and purification processes. According to the TEM images (Fig.6), native CNC and CNC-APIm show similar dimensions with lengths ranging from around 100 nm to 300 nm and diameters of ca. 10 nm. Treating CNC as a nanorod with a square cross-section, we made the following assumptions before conducting an approximate calculation of the APIm and sulfate density on the CNC surface:

  1. Both CNC and CNC-APIm are nanorods with a square cross-section of 7.1 nm × 7.1 nm (diagonal: 10 nm). The nanorods have non-reactive ends;
  2. Any cross-section of CNC and CNC-APIm, along the axial direction, is packed with cellulose Iβ unit cells in the same pattern. These cellulose unit cells, as determined by X-ray diffraction(Sugiyama et al. 1991), have cross-sectional dimensions of 0.61 nm × 0.54 nm in the directions parallel to the two sides of CNC square cross-section(Habibi et al. 2006);
  3. Anhydrous glucose units (AGUs) are evenly distributed on four sides of each cellulose unit cell with the two ends having no AGU;
  4. The sulfate groups remain intact after the APIm coupling reaction;
  5. The CNC-APIm has the same density as native CNC which is around 1.6×10-21 g/nm3(Habibi et al. 2010; Majoinen et al. 2011).

If we take 1 nm length (one unit volume) of CNC-APIm (side of cross-section is 7.1 nm as determined in the above assumption), then its volume and surface area are 50.4 nm3 and 28.4 nm2, respectively. In the elemental analysis results (Table 1), the average of the two CNC-APIm measurements is used for the calculation. So the imidazole and sulfate molarities in one unit volume are (50.4×1.6×10-21)×3.75%/42=7.20×10-23 mol and (50.4×1.6×10-21)×0.72%/32=1.81×10-23 mol, respectively. Assuming that all of these groups are at the surface, we have:

Surface imidazole density: 1.53 units/nm2

Surface sulfate density: 0.38 units/nm2.

In the same unit volume of CNC-APIm, there is (50.4×1.6×10-21)/162=4.98×10-22 mol of AGUs.The CNC-APIm surface cellulose units account for around 2×[(7.1/0.61+7.1/0.54)-2]/[7.1×7.1/(0.61×0.54)]=0.3 (30%) of the total mass. Then we have:

Surface AGU to imidazole molar ratio: 4.98×10-22×0.3/(7.20×10-23)=2.08;

Surface AGU to sulfate molar ratio: 4.98×10-22×0.3/(1.81×10-23)=8.25.

References

Habibi Y, Chanzy H, Vignon MR (2006) TEMPO-mediated surface oxidation of cellulose whiskers. Cellulose 13(6):679-687

Habibi Y, Lucia LA, Rojas OJ (2010) Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem Rev 110(6):3479-3500

Majoinen J, Walther A, McKee JR, Kontturi E, Aseyev V, Malho JM, Ruokolainen J, Ikkala O (2011) Polyelectrolyte brushes grafted from cellulose nanocrystals using Cu-mediated surface-initiated controlled radical polymerization. Biomacromolecules 12(8):2997-3006

Sugiyama J, Vuong R, Chanzy H (1991) Electron-Diffraction Study on the 2 Crystalline Phases Occurring in Native Cellulose from an Algal Cell-Wall. Macromolecules 24(14):4168-4175

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