Assessment of Surface Accessibility of Nanocellulosic Structures Using Surface Sensitive Methods

Transcription

1 Assessment of Surface Accessibility of Nanocellulosic Structures Using Surface Sensitive Methods Tekla Tammelin VTT Technical Research Centre of Finland Ltd Designing Cellulose for the Future II May 19, 2016

2 2 Objectives To obtain deeper understanding on the surface behavior of cellulosic nanofibrils with respect to reactivity and surface accessibility, and formation of functional structures using surface sensitive methods Surface chemical composition by X-Ray photoelectron spectroscopy (XPS) Indirect information on surface reactivity by following the relative abundance of C-C bonds, following the success of surface modifications Atomic force microscopy (AFM) Changes in fibrillar fine structure Contact angle - Direct information on wetting behaviour which can be linked to available -OH groups Strategies to overcome challenges related to nanocellulose chemical modifications in order construct efficient, renewable and bioinspired material solutions

3 3 Surface modification of individual cellulose nanofibrils

4 4 Solvent impact on CNF surface chemistry and fine structure in DMA in toluene The effect of solvent on media driven aggregation tendency H 2 O MeOH DMA H 2 O MeOH Toluene Changes in fine structure by AFM Surface chemical composition by XPS indirect information on surface reactivity and medium dependent conformation Water contact angle direct information on the surface adaptation, accessibility and surface passivation Johansson, L.-S., Tammelin, T., Campbell, J. M., Setälä, H., Österberg, M.Soft Matter 2011, 7,

5 5 Understanding the nature of CNF surface by XPS How to maximize the available surface for derivatizations Determination of different carbon bonds Relative abundance of C-C bonds CNF surface is extremely reactive!! Free accessible OH groups generate high surface free energy Minimizing the surface free energy when exposed to hydrophobic media by accumulating air-borne contaminants passivated surfaces

6 6 Changes in CNF wetting behavior Water contact angle direct information on the surface adaptation, accessibility and surface passivation Orientation of the hydrophilic and hydrophobic planes of the cellulose molecules Behavior demonstrated by several researchers hydrophilic plane hydrophobic plane Holmberg et al. J. Colloid Interface Sci., 1997, 186, 369; Yamane et al. Polym. J., 2006, 38, 819; Tammelin et al. Cellulose, 2006, 13,519, Suchy et al. Biomacromolecules, 2010, 11,515.

7 7 Silylation on individual cellulose nanofibrils 500 nm The effect of solvent H 2 O MeOH DMA H 2 O MeOH Toluene Degree of surface substitution by XPS Changes in fine structure by AFM Andresen et al., Cellulose, 2006, 13, 665.

8 8 Nanofibrillar structure retained in cellulose compatible solvent Nanocellulose reactivity XPS indicates Increase in silica content Increase in the relative abundance of C-C and C-Si bonds Degree of surface substitution can be calculated AFM results confirm the successful surface modification the maintained nanofibrillar structure The same derivatisation procedure: DMA-exchanged CNF DS=1.0 ± 0.2 Toluene-exchanged CNF DS = 0.02 ± 0.01 Surface chemistry of fibers and CNF: Relative abundance of C-C bonds indicates that CNF surface is extremely reactive and is easily passivated in hydrophobic media. In CNF compatible solvent the reaction efficiency is higher and the nanoscale structure is retained

9 9 AFM height image AFM phase image Unmodified CNF AFM images suggest the maintained nanofibrillar structure evenly distributed chemical modification on the fibril surface Silylated CNF 5 5 μm images

10 10 Surface modification of already assembled CNF films

11 11 Clean and reactive CNF film surfaces UV/O 3 treatment XPS indicates Decrease in the relative abundance of C-C after UV/O 3 treatment (11% -> 4%) Removal of non-cellulosic carbonaeous contamination layer Contact angle results show Increased hydrophilicity Expected to facilitate more efficient CNF film surface functionalization. Österberg, M., Peresin, M. S., Johansson, L.-S. and Tammelin, T., Clean and reactive nanostructured cellulose surface. Cellulose, 2013, 20,

12 12 The effect of UV/O 3 treatment on CNF film surface activation Direct chemical modification via surface silylation XPS indicates Clear increase in silica content Increase in the relative abundance of C-C and C-Si bonds Degree of surface substitution can be calculated C-C C-C + C-Si C-C + C-Si The same derivatisation procedure: unactivated CNF film: DSs = 0.07 UV/O3 activated CNF film: DSs = 0.26 UV/O 3 activated + silylated unactivated + silylated unactivated CNF film

13 13 Attachment of polymeric group on CNF film surface Direct chemical modification: pnipam on TEMPO CNF Element (at%) Sample C 1s O 1s N 1s S 2p TCNF-PVA TCNF-PVA esterified TCNF-PVA pnipam XPS indicates successful pnipam attachment on CNF film surface Nanoscaled surface structure retained Hakalahti, M.; Mautner, A.; Johansson, L.-S.; Hänninen, T.; Setälä, H.; Kontturi, E.; Bismarck, A.; Tammelin, T.; (2016) ACS Applied Materials & Interfaces, 8,

14 14 Thermoresponsive membrane template Water permeability as a function of temperature

15 15 Conclusions Information gained by surface sensitive methods can effectively link the material behaviour at interfaces to the macroscale physical properties Changes in surface chemistry on the outermost surface of nanocellulosic materials due to medium driven surface adaptation and passivation are experimentally evidenced When the CNF surfaces remain clean and the fibrils are not aggregated, the hydroxyl and carboxyl groups on the fibril surface are better accessible for further chemical reactions Controlling the reactivity and accesibility of CNF surface Significant improvement on properties of surface modified CNF films after activation Full performance of CNF when considering the formation of 2D and 3D structures

16 16 Acknowledgements Prof Monika Österberg, Dr Leena-Sisko Johansson, Dr Maria Soledad Peresin, MSc Minna Hakalahti, Dr Harri Setälä, MSc Jaakko Pere, MSc Pia Qvintus, Prof Eero Kontturi, Dr Andreas Mautner, Prof Alexander Bismarck European Community s Seventh Framework Programme (FP7-NMP-2011-SMALL-5) Nº Nanoselect ( WoodWisdom-Net Research Programme TunableFilms

17 17 Thank You for Listening