Determination of shape parameter of nanocrystalline cellulose rods

Transcription

1 Determination of shape parameter of nanocrystalline cellulose rods Yaman Boluk and Liyan Zhao Cellulose and Hemicellulose Program Forest Products Alberta Research Council June 25, International Conference on Nanotechnology for the Forest Products Industry Edmonton, Alberta Canada

2 Outline Introduction Dilute dispersions Materials and experiments Intrinsic viscosity and shape factor Semi-dilute dispersions Testing theories for semi-dilute solutions Concluding remarks Boluk and Zhao 2

3 Particulate Dispersions Composites, pharmaceuticals, foodstuffs, paints, ceramics Potential applications for nanocrystalline cellulose (NCC) Flow behavior is vital for the commercial success Boluk and Zhao 3

4 Nano Rodlike Suspensions Nanocrystalline cellulose (NCC) Rod shaped particles with L= nm; d=4-10 nm In suspensions NCC particles exhibit Complex translational and rotational motions Measurement of flow properties To characterize rods-shaped NCC particles To predict and understand macroscopic behavior of NCC in solution and bulk In addition such systems provide testing ground for theories of dynamics of complex fluids Boluk and Zhao 4

5 Concentration Regimes of Rod Shaped NCC Dilute V<1/L 3 L = 200 nm; d=10 nm V=1.25x10 20 #/m 3 Ф = m= Semi - dilute Concentrated isotropic 1/L 3 <V<1/dL 2 V>1/dL 2 V=2.50x10 21 #/m 3 Ф = 0.04 m= 0.06 Concentrated Nematic current work where L= length; d=diameter; V=number density; Ф =volume fraction; m=weight concentration Boluk and Zhao 5

6 Shear Viscosity of Dilute Dispersions Physical assumptions The suspended NCC rods are large w.r.t. to the molecules of the suspending liquid but small to the characteristics length of experimental apparatus The undisturbed flow of dispersion is sufficiently slow so that inertial effects are neglected The suspending liquid adheres to NCC rod surfaces without slipping The concentration of the dispersion is dilute Boluk and Zhao 6

7 Viscosity Dilute Range ηd 2 3 ηr = = 1+ [ η] φ + C2φ + θ ( φ ) η For sphere dispersions: 0 [ η] = 2.5 Einstein (1906) +... C 2= 6.2 Batchelor (1977) for Brownian hard spheres In low shear rates, anisotropic particle shapes increase magnitude of both parameters. We will consider the effect of a rod-shaped NCC particle on low shear viscosity of dispersion. Boluk and Zhao 7

8 In a simple shear flow particle motions will be determined by Shear forces Brownian motion Ratio of shear forces/brownian motion Péclet Number Dynamics of NCC rods Pe rot = γ * D r γ * D where : shear rate; : rotational diffusion constant r Boluk and Zhao 8

9 Experimental NCC Dispersions L=350 nm d=8 nm r=44 D r0 =270 s -1 γ * = 1 s-1 Pe r = << 1 AFM of NCC from MCC Boluk and Zhao 9

10 Intrinsic viscosity calculations for prolate spheroids [ η ] = lim c 0 η sp c η sp = ( η η ) / η0 = ηr 0 1 Onsager (1923) [ η] = 4 15 r ln 2 r for r>>1 and Pe rot <<1 Kuhn and Kuhn (1945) [ η] = 2 r 5 1 ( 3(ln 2r 1.5) + 1 (ln 2r ) 0.5) for r>15 and Pe rot <1 Simha (1940) 2 r [ η] = 15(ln 2r 1.5) + 2 r 5(ln 2r 0.5) for r>15 and Brownian contribution neglected where r=l/d Boluk and Zhao 10

11 High and low shear rate intrinsic viscosities of spheroidal particles Low shear Intrinsic viscosity Einstein: 2.5 High shear r ln r Aspect ratio L/d From Hinch and Leal, J. Fluid Mech., 62, 4, (1972) Boluk and Zhao 11

12 Low shear rate intrinsic viscosities of spheroidal particles Intrinsic Viscosity Onsager Kuhn and Kuhn Simha Aspect Ratio Boluk and Zhao 12

13 Nanocrystalline Cellulose Materials 1. WP Whatman Paper 2. CT Cotton 3. MC Microcrystalline cellulose 4. DP Dissolving softwood pulp Method of preparation from: Bondeson, Mathew and Oksman, Cellulose,13, (2006) Boluk and Zhao 13

14 Rheological Measurements TA Instruments Rheometer AR 2 Geometry: Cone and Plate Aluminum cone Angle:1:58:20 deg:min:sec Diameter: 60 mm Approximate sample volume: 2 ml Torque limit: 0.01 micro N.m Boluk and Zhao 14

15 Viscosity vs. Shear Rate Data Viscosity (Pa.s) g/dl 0.75 g/dl 0.50 g/dl 0.25 g/dl Shear Rate (1/s) Boluk and Zhao 15

16 Fedors Equation The equation is applicable for relative viscosities from 1 to about 100 2( η = + 1/ 2 1) [ η] c [ η] c r m Boluk and Zhao 16

17 Intrinsic Viscosity Calculation from Fedors Plot 5.00 y = 1.195x R 2 = /c Boluk and Zhao 17

18 Intrinsic Viscosity and Shape Parameter Intrinsic Viscosity from Fedors Plot: [η]= 0.84 dl/g =127 v/v Shape factor from Simha Equation: r=l/d = 45 Shape Factor from Microscopy L=350 nm d= 8 nm r=l/d =44±10 Boluk and Zhao 18

19 Single-Point Intrinsic Viscosity Procedure [ η ] = [2( η r 1 c ln η r 1/ )] 2 Solomon-Ciuta equation Efficient alternative to multi-point concentrations for macromolecules We propose test the validity of assumptions of Solomon-Ciuta equation for NCC dispersions Boluk and Zhao 19

20 Validity of Solomon-Ciuta Method Needs a weak concentration dependence of equation Depends on NCC/solvent systems Overestimation by 10% for * [η].c 1.0 k H =0.6 * Pamies, Cifre, Martines and de la Torre, Colloid Polym. Sci., 286, (2008) Boluk and Zhao 20

21 Intrinsic Viscosities Data Material [η] (dl/g) Multi point plot [η] (dl/g) Single point Deviation Current Bleached % softwood g/dl) Araki * Bleached % softwood (@0.52 g/dl) Bercea ** Tunic sea % animals (@0.40 g/dl) * Araki, Wada, Kuga and Okano, Colloids and Surface A, 142, (1998) ** Bercea and Navard, Macromolecules, 33, (2000) Boluk and Zhao 21

22 Shape Parameters from Single Point Intrinsic Viscosities Sample [η] (dl/g) R (L/d) Cotton MCC Whatman Dissolving Pulp Boluk and Zhao 22

23 η η Semi-Dilute Dispersions Doi and Edwards, The Theory of Polymer Dynamics, Oxford 1988 νkt 30D vkt 10 ro D r D ro 3kt = (ln r 3 πη L 0 δ ) Where D ro at infinite dilution and δ is a correction factor which is a function of r (L/d) Boluk and Zhao 23

24 Entanglement of the surrounding rods Tube model Rotational diffusion of a tagged rod may be interpreted as a tube. Rotational diffusion is only possible by series of longitudinal steps Boluk and Zhao 24

25 Tube Model and Doi-Edwards Reptation D r = βd ro 1 ( ν L 2 3 ) π η = 1 + νl + ( ν r 90ln r 30β ln r L 3 π 3 ) 3 Doi and Edwards, J. Chem. Soc. Faraday Trans.. 2, 74, 560 (1978) Boluk and Zhao 25

26 Log jamming- Sato and Teramato D r 1 2 = βdr 0( ) ( ε ( νdl 3 νl 2 ) 3/ 2 ε where indicating the degree of log jamming ) η r = π 90ln r π 30ln r νl νl + [1 + ] ν L 2 β (1 ενdl ) Sato and Teramoto, Macromolecules, 24, 193 (1991) Boluk and Zhao 26

27 Relative viscosity of NCC dispersions as function of number density concentration Doi-Edwards Sato Experiment Relative Viscosity Number Density*L^3 Boluk and Zhao 27

28 Fit parameters of the low shear viscosity data System L (nm) R (L/d) β DE ε ST β ST NCC Schizophyllan 1 Silica rods 2 Xanthan Gum Enomoto, Einaga and Teramoto, Macromolecules, 18, 2695 (1985) 2 Wierenga and Philipse, J. Colloid Interface Sci., 180, 30 (1996) 3 Yakada, Sato and Teramoto, Macromolecules, 24, 6215 (1991) Boluk and Zhao 28

29 Concluding Remarks In dilute dispersions, the low-shear viscosity is largely determined by dimensions of rods and theory predicts the low-shear viscosity of NCC dispersions fairly well. Intrinsic viscosity is an excellent method to characterize shape parameters of NCC particles Intrinsic viscosity can be one of NCC specification Single point method can be adapted to measure intrinsic viscosity of NCC dispersions A standard test method can be established Theories are less than perfect in semi-dilute regime, nevertheless NCC dispersions are excellent experimental systems to test theories for rodlike dispersions. Hydrodynamic interactions, electroviscous effects etc. Boluk and Zhao 29

30 Acknowledgement Funding Alberta Forestry Research Institute NCC preparations Frank Tosto Rheological measurements Heather Lorenz Boluk and Zhao 30