Liquid crystalline and gelling properties of cellulose nanocrystal suspensions Liquid crystalline and gelling properties of cellulose nanocrystal suspensions Derek Gray Department of Chemistry McGill University Montreal, Canada International Liquid Crystal Elastomer Conference, Lisbon, September 7, 2011
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Liquid crystalline and gelling propertiesof cellulose nanocrystal suspensions
Liquid crystalline and gelling propertiesof cellulose nanocrystal suspensions
Derek GrayDepartment of Chemistry
McGill UniversityMontreal, Canada
International Liquid Crystal Elastomer Conference, Lisbon, September 7, 2011
Cellulose
• Homopolymer of glucose.• Insoluble, but hydrophilic surface.• Present as long, crystalline microfibrils.• Oxidizing chemicals may convert some hydroxyl groups to
carboxylic acids.
OCH2OH
H H
OHH
H
HO
H
H
O
HH
CH2OH
OH
O
OHO
H
OCH2OH
H H
OH
H
HO
H
O
CHEMISTRYMcGill University
Elastic modulus of crystalline cellulose, >110 Gpa.
Cellulose properties
Like most polymers, cellulose is not completely crystalline, but containsdisordered regions. A variety of models seek to explain the dual nature ofcellulose. In the fringed micelle model, the cellulose chains pass throughboth crystalline regions and amorphous (disordered) regions.
Other models attribute the disorder to imperfections, chain ends and surfaceregions of the microfibril.
CHEMISTRYMcGill University
Cellulose derivatives, esters and ethers were the first widelyused polymeric materials. An accidental discovery...
• Hydroxypropylcellulose dissolves in water at roomtemperature.
• It shows an upper consolute solution temperature ataround 40C.
• This led to the observation of an unusual liquidcrystalline phase (Werbowyj and Gray, 1976).
base
Propylene oxide
OCH2CH(OH)CH3
O
O
O
OCH2CHCH3
HO
OCH2CH(OH)CH3
OH
HO
OH
O
O
O
One of the first polymeric liquid crystal phases...
• Hydroxypropylcellulose (MS ~4, DS ~2.5) in water atroom temperature forms fluid mesophase at <~40% w/wconcentration.
• The solutions shows the iridescent colours characteristic ofa chiral nematic (cholesteric) liquid crystal.
• Soon, many other cellulose derivatives were found to formliquid crystalline phases.
• Recently, cross-linked HPC derivatives have been shownto form elastomeric thin films (Godinho et al., 2009-)
Meanwhile, biologists had found chiral nematic order in naturalmaterials
• The groups of Bouligand, Neville and Rolland foundstructures with chiral nematic order in a wide range ofanimal and plant tissues.
• However, the ordered structural elements were notmolecular, but consisted of microfibrils of cellulose,chitin, collagen…
• The next step was to try and replicate these materials invitro. "Cellulose crystallites, cellulose nanocrystals, …"
Reviews:
Nanocelluloses:Klemm et al., Angew. Chemie Int.Ed., 2011, 50, 5438-5466.
Nanocrystalline cellulose:Habibi et al., Chem. Rev. 2010, 110,3479–3500.
Cellulosic nanomaterials:Moon et al., Chem. Soc. Rev., 2011,40, 3941–3994.
We consider only the relatively short nanocrystals preparedfrom Cellulose I by acid hydrolysis:-
•Preparation of cellulose nanocrystals.
•Chiral nematic (cholesteric) suspensions of nanocrystals inwater.
•Chiral nematic films cast from nanocrystal suspensions.
• Gelation and liquid crystal order in cellulose nanocrystalsuspensions.
CHEMISTRYMcGill University
Fifty years ago, the production of colloidal suspensions ofcellulose by the sulphuric acid hydrolysis of cellulose fibreswas first reported by Rånby.
The hydrolysis produced rod-like particle of cellulose, withdimensions in the 0.5-100 nm range, which formed aqueouscolloidal suspensions stabilized by sulphate groups.
Nanocrystals from cotton(Mukherjee et al., 1952)
CHEMISTRYMcGill University
1. Start withcellullose
2. Removecellulose
3. Product:cellulose
Tight control of starting material history and reactionconditions are necessary!
Image of part of a solid film cast from cellulosenanocrystal suspension
optical microscope, between crossed polars
The aim of the workwas to determine whatstructure could givethis pattern !
It looks like patternsshown by layer-likesmectic or some chiralnematic (cholesteric)liquid crystals.
CHEMISTRYMcGill University
Roman and Gray, Langmuir, 21(12), 5555-5561 (2005)
-20 -10 10 20y
-20
-15
-10
-5
z
-20 -10 10 20x
-20
-15
-10
-5
z
-20 -10 10 20y
-10
-5
5
10z
-20 -10 10 20x
-10
-5
5
10z
Selected layers in a parabolic focal conic
CHEMISTRYMcGill University
Roman and Gray, Langmuir, 21(12), 5555-5561 (2005)
Model of parabolic focal conic near centre xy plane showing layerorientation (left), and polarizing light microscope image of film
assembled from cellulose nanocrystals in same orientation (right)
Cellulose nanocrystals spontaneously self-assemble in complex, regular pattern!
Roman and Gray, Langmuir, 21(12), 5555-5561 (2005) CHEMISTRYMcGill University
Possible uses for Chiral Cellulose Films:• Anti-counterfeiting components in security papers.• As iridescent components in decorative laminates.• Optically variable non-toxic pigments.
CHEMISTRYMcGill University
Possible uses for Cellulose Nanocrystals (NCC):• As reinforcing agent in composite materials.• As rheology modifier in cosmetics and foods.• As carrier or scaffold in biomedical applications.
Availability of NCC):• Research quantities from FPInnovations.• CelluForce pilot plant nearing completion.
Cellulose nanocrystal surfaces are hydrophilic:• For some applications, surface modification required.• Hydrophobicization required for compatibility with
most polymers.
CHEMISTRYMcGill University
Gels containing NCC:• Magnetically oriented ordered gels for protein NMR.• NCC reinforcement of poly(vinyl alcohol) gels.
Cellulose nanocrystal surfaces are anionic:• A method of making cationic cellulose nanocrystals is
described. These formed thixotropic aqueous gels.
Cationic Surface Functionalization of CelluloseNanocrystals
While the functionalized nanocrystals looked the same and thecharge density was similar
(with reversed charge)
there was one significant difference…
Cationic Surface Functionalization of Cellulose Nanocrystals
CHEMISTRYMcGill University
• HPTMAC-CNC gelled at low concentrations (3.5%).• No chiral nematic liquid crystal phase separation was observed.• Shear birefringence was seen when suspensions were shaken.• Thixotropy and shear thinning were also evident.
Cationic Surface Functionalization of Cellulose Nanocrystals
Cellulose nanocrystal surfaces are hydrophilic:• For some applications, surface modification required.• Hydrophobicization required for compatibility with
most polymers.
CHEMISTRYMcGill University
Gels containing NCC:• Magnetically oriented ordered gels for protein NMR.• NCC reinforcement of poly(vinyl alcohol) gels.
Cellulose nanocrystal surfaces are anionic:• A method of making cationic cellulose nanocrystals is
described. These formed thixotropic aqueous gels.
The nanocellulose suspensions respond to a magnetic field
CHEMISTRYMcGill University
Individual cellulose nanocrystals have anegative diamagnetic anisotropy which alignstheir long axes orthogonal relative to an appliedmagnetic field. So chiral nematic axis orientsalong field.
Residual dipolar couplings (RDCs) provide long-range information onthe orientation of inter-nuclear vectors within a molecular frame ofreference and are thus valuable in structural and dynamicalinvestigations of macromolecules.•RDCs result from anisotropic averaging of the orientation-dependentdipolar coupling interaction when molecules are dissolved in an orderedmedium, such as a liquid crystal.•We have worked out a detailed protocol for preparing oriented samplesusing liquid crystalline suspensions of cellulose nanocrystals, andoffer guidelines for when this medium can be employed in biomolecularNMR. The cellulose systems requires gelation of the ordering mediumin the magnetic field.
• Fleming, Gray, Prasannan and Matthews, J. Am. Chem. Soc., 122, 5224-5225 (2000)
• Denisov, Kloser, Gray, Mittermaier, J. Biomolecular NMR, 47, 195–204 (2010).CHEMISTRYMcGill University
Cellulose nanocrystal suspensions can be used as protein orientationsystem for NMR residual dipolar coupling measurements 1,21,2
Abitbol, Johnstone, Quinn and GraySoft Matter, 7(6), 2373-2379 (2011)
• The addition of CNCs into PVA hydrogels resulted in gels which were lesscrystalline and swelled to a greater extent, but had improved elasticproperties.
• The cellulose nanocrystals also induce order in the PVA hydrogels formedby freeze-thaw processing.
Abitbol, Johnstone, Quinn and Gray Soft Matter, 7(6), 2373-2379 (2011)
PVA, no cellulosenanocrystals
PVA with 1.5 wt%cellulose nanocrystals
53 freeze-thaw cycles
1
CHEMISTRYMcGill University
Abitbol, Johnstone, Quinn and GraySoft Matter, 7(6), 2373-2379 (2011)
Conclusions
•Cellulose derivatives form lyotropic and thermotropic chiralnematics. Left and right-handed phases are observed.
• Cellulose nanocrystals also form chiral nematic colloidcrystals. To date only left-handed phases have beenobserved.
•Solid cellulose films with chiral nematic structure readilyform on evaporation of water.
•Cellulose nanocrystals can also form gels, and can reinforceaqueous polymer gels.
CHEMISTRYMcGill University
Acknowledgements
• Revitalizing liquid crystalline cellulosics: M.-H. Godinho et al.• Preparation and EM of cellulose nanocrystals: J.-F. Revol.• Phase separation of suspensions: Xue-Min Dong• Structure of cellulose nanocrystal films: Dr. Maren Roman• Cationic nanocrystals: Merima Hasani and Emily Cranston• Protein NMR: Steve Matthews group, Imperial College London• PvOH gels: Tiffany Abitbol
CHEMISTRYMcGill University
Support from NSERC, FPInnovations/Paprican*, FQRNT