The Cellulose Nanocrystal Electro-optic optic Effect

Transcription

1 The Cellulose Nanocrystal Electro-optic optic Effect Chad Teters,, Wei Kong, Melissa Taylor, John Simonsen, Mike Lerner, Tom Plant, Glenn Evans Oregon State University Corvallis, Oregon

2 Presentation Overview Cellulose nanocrystals (CNXLs) Production Properties TEB Alignment Optical effects Multi-order rotation Device fabrication issues

3 Cellulose

4 Cellulose Nanocrystal Production Native cellulose - Semi crystalline Polymer (~70% crystalline). Crystalline portion Amorphous portion CONTROLLED ACID HYDROLYSIS

5 TEM image of cellulose nanocrystals

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8 ~ 7 nm

9 ~150 nm

10 Sources of nanocrystalline cellulose

11 Wood

12 Sugar Beets

13 Cotton

14 Barnacles (tunicin)

15 Bacterial Cellulose

16 CELLULOSE BIOSYNTHESIS R.M. Brown, J. Mat. Sci. Pure Appl. Chem. A33(10):

17 Slide from Wankei Wan, U. W. Ontario, London, ON, Canada

18 Cellulose source Tunicate Algal (Valonia) Bacterial Cellulose nanocrystals Length 100 nm microns Cross section Aspect ratio 10-0 nm 5 to > 100 (high) > 1000 nm 10 to 0 nm 50 to > 10 nm (high) 100 nm microns Cotton nm 5 nm 5-10 x nm Wood nm 3 5 nm Beck-Candanedo, et. al. Biomacromol. (005) 6: to > 100 (medium) 0 to 70 (low) 0 to 50 (low)

19 Surface Area m /g E-glass fibers * ~1 Paper fibers 4 Graphite Fumed silica Fully exfoliated clay ~ 500 Cellulose nanocrystals 50 Carbon nanotubes*** ~ 100 -? * ** Winter, W. presentation at ACS meeting, San Diego, March 005 ***

20 Material Mechanical Properties tensile strength GPa modulus GPa cellulose crystal Glass fiber Steel wire Graphite whisker Carbon nanotubes 3 1. Marks, Cell wall mechanics of tracheids Sturcova, et al. (005) Biomacromol. 6, Yu, et al Science (000) 87, 637

21 Optics

22 Transient Electric Birefringence, aka the Kerr Effect Crossed polarizers typically emit no light Unless an optically active substance rotates the light Electric field can cause substances to become optically active in this way Kerr cells, Pokels cells used in fiber optics, lasers, confocal microscopy, etc.

23 Original Kerr Cell 1875 Optically active medium = glass from Kelvin's Instruments and the Kelvin Museum by G. Green and J. T. Lloyd

24 Kerr Cell

25 Setup HeNe laser 1) Half-wave plate ) Prism polarizer 3) Kerr cell 4) Pinhole 5) Quarter-wave plate 6) Prism polarizer 7) Line-pass filter 8) Diffuser 1 PMT

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29 Basic Detection Theory E ll E HeNe = 1 ε o ( i(kẑ ωt+ k d)ŷ i(kẑ ωt+ k d)ŷ ) e + e E y E x E E = 1 ε e ik o d E ll = 1 ε oe iδ e ik d δ = ( πd / λ) Δn E x δ sin ( ) I = I o sin π dδn λ Δn = sin 1 I I π d λ o 1/

30 Alignment Theory (static field) θ - U 1 U = U + U total μ α μ = μe cos θ U α = Δα Δ α = α E α cos θ Torque du dθ [ ] E cos θ μe sin θ = Δα

31 Alignment Theory (static field) U = U + U total μ α U μ = μe cos θ U α = Δα Δ α = α E α cos θ Torque du dθ [ ] E cos θ μe sin θ = Δα

32 Alignment Theory (static field) Orientation function f ( θ) = π e 0 e U / kt U / kt sin θ dθ Alignment parameter P ( θ ) π = 0 f ( θ ) 3 cos θ 1 sin θ dθ Birefringence π Δn = φv Δg P ( θ) P n s ( θ)

33 Alignment Theory (t-dependent field) Growth: D 3k BT L = ln πηl d r 3 λ = σ σ = 1 3 β Δα E a = 6 σ 5 Differential equation d τ P (t) = a λ Dr P (t) No initial alignment P (t) a D t Decay: P (t) = P (max) exp( 6D r (t t off ))

34 Empirical fit Δn P 1 P ( θ ) Δn = Δ n PMT, V rise ( exp( a t) ) A1 1 1 B1 exp( b1t ) + B exp( bt) time (ms) decay

35 Alignment Theory (fitting parameters) PMT, V B1 exp( b1t ) fast 0. 0 ( exp( )) A a 1 1 1t B exp( bt) slow time (ms)

36 CNXL Results (E field dependence) P(ave) kV/cm 3.33kV/cm 4.00kV/cm 4.66kV/cm 1 / ms b1, fast time (ms) E^ [(kv/cm)^] 15 a1, rise b, slow 1 / ms E^ [(kv/cm)^] 1 / ms E^ [(kv/cm)^]

37 CNXL Results (conc. dependence) P(ave) %wt.063 %wt..031 %wt..016 %wt. 1 / ms b1, fast time (ms) %wt. 1 / ms a1, rise A1, rise %wt. 1 / ms b, slow %wt.

38 Kerr Cell comparison 6 nitroben, E = 400V/cm PMT Response (mv) cellulose, E = 0V/cm time (ms) delta n (10-7 ) nitrobenzene CNXL Sample Kerr(m /V ) nitrobenzene 8.3 x n (ms) - n (ms) Max 5330 V/cm E (V/mm) Liq. Crystal 1.40 x CNXL.63 x V/cm

39 CNXL Results (multi-order rotation) kv/cm time (ms)

40 CNXL Results (multi-order rotation) kv/cm 1.5 kv/cm time (ms)

41 CNXL Results (multi-order rotation) kv/cm 1.5 kv/cm 1.7 kv/cm time (ms)

42 CNXL Results (multi-order rotation) kv/cm 1.5 kv/cm 1.7 kv/cm 1.8 kv/cm time (ms)

43 CNXL Results (multi-order rotation) kv/cm time (ms)

44 Wave plate optics Γ = πδnl λ Γ = phase shift n = refractive index L = pathlength λ = wavelength Δn = KλE Kerr equation n = refractive index K = Kerr constant λ = wavelength E = electric field strength K = f(concentration) = K C Linearity is an assumption Γ = π K' C L E

45 Applications Display devices Privacy glass Electrically variable waveplate for microscopy, general optics???

46 Schematic of liquid crystal display Exit polarizer Color filter Liquid crystal Thin film transistor Entry polarizer Backlight

47 %Transmittance of CNXL dispersion 0.16% carboxylate CNXLs, E=3.88kV/cm 0.1 ms pulse % T time (ms)

48 CNXL vs LCD LCD CNXL Field 15-0 kv/cm 1-55 kv/cm, L dependence Fabrication Rubbing process $$ Liquid dispersion $$ Rise time ms 0-50 μs Brightness 40% T 90% T

49 CNXL challenges Colloid stability Conductivity, Joule heating Scattering Field direction