2006 International Conference on Nanotechnology, April 26-28, 2006 Atlanta, GA Polysaccharide Self- assembly on Cellulose A Surface Plasmon Resonance Study

Presented by:

Abdulaziz Kaya Virginia Tech Outline • Background • Experimental Techniques and Results – Model Cellulose Surface – Surface Plasmon Resonance (SPR) Spectroscopy – Elemental Composition of Model Cellulose Surface – Adsorption Studies of Pullulan and Pullulan Abietate by SPR • Conclusions and Future Work Motivation

¾Growing interest in renewable raw materials which mimick natural composites ¾Weak cellulose-polymer interfaces for cellulose based biocomposites ¾Surface modification of cellulose fibers may create a good interface Mohanty, A.K., M. Misra, and L.T. Drzal, Composite Interfaces, 2001. 8(5): p. 313-343. Chemical Composition of Wood

OH

O ¾Cellulose is composed HO

HO of anhydro-D- O HO O OH HO

glucopyranose units OH O O HO

HO ¾Hemicelloses are non- O n crystalline COOH heteropolysaccharides1 ¾Lignin is a biopolymer consisting of Pullulan (PA) and Pullulan 2 phenylpropane units abietate (PAAb) (D.S. =0.03) 1. Thomas, R. J. Wood structure and chemical composition, ACS Symposium Series vol. 43, 1977. 2. Serimaa, R. et. al Langmuir 2004, 20, 9736-9744. Objectives

¾Mimicking the self-assembly of wood’s three major components by investigating pullulan modified by hydrophobic abietic acid

¾Adsorption studies of pullulan and pullulan abietate onto bare gold, self-assembled monolayer (SAM), and model cellulose surfaces by surface plasmon resonance (SPR) Model Cellulose Surface

• Self-assembled monolayer (SAM) Si

attached to the gold surface O O O O

O • Trimethylsilylcellulose (TMSC) Si transferred onto SAM using the Si Langmuir-Blodgett technique n • TMSC is desilylated by exposing Cellulose

the surface to the vapor of 10 % SAM HCl solution Gold OR OH

HCl, H O(g) (H3C)3Si Chromium O 2 O O O OR O + RT HO Glass OR (H3C)3Si (g) n OH R=H, Si(CH3)3 n

Schaub, M.; Wenz, G.; Wegner, G.; Stein, A.; Klemm, D. Adv. Mater. 1993, 5, 919. Surface Plasmon Resonance

Glass prism

kx y ky θsp Metal film x Sample π ksp θ θ ′ ε sp sp ε π = 2λ m s 2 ksp ε kx = np sinθsp m + εs λ

When kx = ksp ; 2π 2 2 = nmns ksp 1 2 2 2 + 2 nmns λ nm ns sinθsp = 2 + 2 n nm ns Earp,R.L.; Dessy, R. E. Chemical Analysis, 1998, 148, p. 109-111. p Surface Plasmon Resonance

Buffer Adsorbate Buffer Reversible adsorption and bulk effect

° Δθsp ( ) Δθ a Irreversible adsorption

Time (1) From instrument calibration: (3) After SPR experiments: dθ dθ / dn = 61.6° Δθ = Δθ − Δc • sp sp s a sp dc (2) From differential refractometer measurements: (4) After theoretical Fresnel calculations: dθ dθ Δθ (n − n ) sp = sp • dns Γ = a f s dθ/dL dn / dc dc dns dc s Sigal, G. B.; Mrksich, M.; Whitesides, G. M. Langmuir, 1997, 13, 2749-2755. de Feijter Equation − Δθ − Γ = L (nf ns ) = a (nf ns ) θ (dns / dc) d /dL (dns/dc) Γ : adsorbed molecules per unit area (mol/cm2) L : thickness of the adsorbed film nf : refractive index of the adsorbed film ns : refractive index of the solution (without the adsorbent) dns/dc : refractive index increment of the solution

Δθa : change in angle corrected for bulk refractive index changes dθ/dL : dependence of the SPR angle on the thickness of adsorbed film de Feijter, J. A.; Benjamins, J.; Veer, F. A. Biopolymers 1978, 17, 1759. Surface Tension of PAAb Solutions

70

65

-1 60 -1 CAC ~ 50 mg•L 55 /mN•m

γ 50

45

40 0 2000 4000 6000 8000 10000 -1 Concentration/mg•L ¾Wilhelmy plate technique is used for surface tension measurements. ¾PA showed no surface activity at the air-water interface. ¾The critical aggregation concentration (CAC) for PAAb signifies the onset of aggregate formation. Gradwell, S. Master’s thesis, Virginia Polytechnic Institute and State University, 2004. Elemental Composition of Cellulose Surfaces

Au 4f (mol %) C 1s (mol %) O 1s (mol %) Si 2p (mol %)

Spin-coated Exp. 0.26 % 65.08 % 22.28 % 12.64 % TMSC surface Theo. 0 % 62.82 % 25.65 % 11.53 % Vapor Exp. desilylated 0.16 % 60.11 % 39.72 % 0 %

Theo. 0 % 54.54 % 45.45 % 0 %

1.0 X-ray photoelectron spectroscopy (XPS) is

0.8 O 1s

C KLL performed using a Mg anode at 250 W with 89.45 eV pass energy. 0.6 O KVV

C 1s Absence of Si 2s and Si 2p peaks in the 0.4 survey spectrum demonstrates complete

Normalized Intensity 0.2 Si 2p

TMSC surface Si 2s desilylation of TMSC. Cellulose surface Au 4f Au

1000 800 600 400 200 0 Binding Energy / eV SPR of PA and PAAb onto Bare Gold

485 mg/L 738 mg/L 0.14 242 mg/L 606 mg/L 0.07 590 mg/L 364 mg/L 291 mg/L 443 mg/L 170 mg/L 207 mg/L 148 mg/L 0.12 121 mg/L 0.06 89 mg/L 73 mg/L 30 mg/L 12 mg/L 0.10 48 mg/L 0.05 6 mg/L 24 mg/L 4 mg/L 0.08 0.04 1 mg/L 12 mg/L

/ degrees / degrees / 0.06

sp 0.03 sp

Δθ T = 20°C Δθ 0.02 0.04 T = 20°C Flow Rate = 0.35 mL/min Flow Rate = 0.35 mL/min 0.01 0.02

0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 Time /minutes Time /minutes PA PAAb PAAb adsorbs onto gold more than PA because water is a better solvent for PA than it is for PAAb SPR of PA and PAAb onto 40 Cellulose Layers

786 mg/L 0.008 610 mg/L T = 20°C T = 20°C 0.30 629 mg/L Flow Rate = 0.35 mL/min Flow Rate = 0.35 mL/min 458 mg/L 472 mg/L 0.006 0.25 CAC 314 mg/L 305 mg/L 0.20 220 mg/L 0.004 214 mg/L

153 mg/L / degrees / degrees 0.15 157 mg/L

61 mg/L sp sp Δθ Δθ 94 mg/L 0.002 0.10 31 mg/L 13 mg/L 0.05 6 mg/L PAAb 0 4 mg/L PA 1 mg/L PA 0 0 50 100 150 0 100 200 300 400 500 Time /minutes Time /minutes No significant adsorption of PA onto 40 cellulose layers. Above the CAC, PAAb starts to adsorb in larger amounts than it adsorbs below the CAC. SPR of PA onto Hydrophilic SAM

0.012 738 mg/L SH T = 20°C 590 mg/L HO 0.010 Flow Rate = 0.35 mL/min 443 mg/L

0.008 295 mg/L Ethanolic solutions of 1- 207 mg/L 0.006 148 mg/L

/g mercapto-1-undecanol 89 mg/L

sp 30 mg/L 12 mg/L 0.004 6 mg/L are used to prepare 4 mg/L 0.002 1 mg/L hydrophilic SAMs.

0 0 50 100 150 200 250 Time /minutes No significant adsorption of pullulan onto hydrophilic SAMs. Thickness Dependence of SPR Angle

Layer Thickness n, refractive κ, absorption (Å) index coefficient 53.5 40 LB cellulose layer Sapphire 0.5 mm 1.760741 0 53.4 Prism degrees / sp Chromium 10 Å 4.11062 4.34922 θ 53.3 Gold 500 Å 0.1422 4.75712 53.2

3 3 53.1 Cellulose 328 Å 1.44 0 Theoretical

PA or PAAb vary 1.45 0 0 20 40 60 80 100 Water 500 Å 1.328234 0 Thickness/Å A Mathlab program based on Fresnel’s equations For adsorption onto cellulose: θ is used to calculate theoretical dθ/dL values for d sp − = 4.40×10 3 deg• Å-1 each surface dL The refractive indices of PA and PAAb are For adsorption onto bare gold and SAM: dθ assumed to be 1.45 sp = 4.01×10−3 deg• Å-1 1. Malitson, I. H., J. Opt. Soc. Am., 1962, 52, 1377-1379. dL 2. Palik, E. D., Handbook of Optical . Academic Press: Orlando, 1985. 3. Holmberg, M. et al. J. Colloid Interface Sci.1997,186, 369-381. 4. Harvey, A. H. et al. Journal of PhysicalConstants and of Solids 1998, 27, 761-774.

Chemical Reference Data Quantification of Surface Excess

Adsorption of PAAb to Bare Gold Surface 0.10 Δθ 0.12 max Δθ irr 0.08 24 mg/L 0.10 Δθ max Δθ 0.06 irr 0.08 12 mg/L / degrees /

/ degrees / 0.06

0.04 sp sp Δθ

Δθ max Δθ 0.04 Δθ 0.02 a Δθ 0.02 irr 0 0.00 0 20 40 60 0 100 200 300 400 500 600 -1 Time /minutes Concentration /mg•L

dθ Δ = Δ − Δ • sp θa θsp c θ = ° dc d sp / dn 61.6 θ θ d d dn dn − sp = sp • s s = 0.149 ± 0.007 mL• g 1 dc dns dc dc Quantification of Surface Excess

1.4 2.5

1.2 2.0 1.0 -2 -2

0.8 PA onto Bare Gold Surface 1.5 PAAb onto Bare Gold Surface

/mg•m 0.6 /mg•m

Γ 1.0 Γ 0.4 Maximum adsorption 0.5 Maximum adsorption 0.2 Irreversible adsorption Irreversible adsorption 0 0 100 200 300 400 500 600 700 -1 0 100 200 300 400 500 600 -1 Concentration /mg•L Concentration /mg•L θ L (n − n ) Δθ (n − n ) d sp −3 -1 Γ = f s = a f s = 4.01×10 deg• Å θ dns / dc d /dL dns / dc dL

From differential refractometer at 20˚C:

dn − dn −1 s = 0.133± 0.003 mL• g 1 s = 0.149 ± 0.007 mL• g dc dc Adsorption Isotherms of PA

1.4 For bare gold surfaces, adsorption can

1.2 be fit with a Freundlich-type isotherm

1.0 -2 Γ = K • (C)1/ nF 0.8 F

/mg•m 0.6 Γ KF 1/nF 0.4 Bare Gold SAM 0.95±0.03 0.06±0.01 0.2 LB Cellulose

0 0 100 200 300 400 500 600 700 -1 Concentration /mg•L For SAM surfaces, the adsorption can be fit with a Langmuir-type isotherm. Γ K •C = ± • -1 θ = = L K L 0.308 0.021 L mg Γ + • max 1 (K L C)

KL : Langmuir constant; θ : surface coverage Adsorption Isotherms of PAAb

6 A Freundlich-type isotherm describes 5 adsorption onto LB cellulose surfaces. 4 -2 1/ n 3 Γ = • F K F (C) /mg•m

Γ 2 K 1/n 1 Bare Gold SAM F F LB Cellulose 0.14±0.02 0.56±0.02 0 0 100 200 300 400 500 600 700 800 -1 Concentration /mg•L KF : Adsorption capacity; 1/nF : Adsorption affinity constant For bare gold and SAM surfaces, adsorption can be described by a Langmuir-type isotherm.

Γ K •C K (Gold) (L/mg-1) K (SAM) (L/mg-1) θ = = L L L Γ + • max 1 (K L C) 0.075±0.003 0.136±0.016

Kaggwa, G.B. et al. Langmuir 2005, 21, 4695-4704. Mechanism of PAAb Adsorption onto Cellulose

Below CAC Above CAC PAAb adsorption onto Do PAAb onto cellulose surfaces aggregates adsorb is hydrophobically more strongly onto driven. cellulose surfaces? Conclusions

¾ Adsorption of PAAb onto hydrophilic cellulose surfaces is hydrophobically driven and specific interactions do not appear to be important for adsorption. ¾ Reversible adsorption is higher for PAAb than it is for PA. ¾ XPS results indicate the model cellulose surfaces are of high quality. ¾ Adsorption of PA onto SAM and bare gold is less than PA, because water is a better solvent for PA which favors PA remaining in solution. ¾ Adsorption isotherms of PA and PAAb onto different types of surfaces can be fit to Langmuir-type or Freundlich-type isotherms. ¾ Self-assembly of polysaccharides onto cellulose surfaces, can be enhanced by adding hydrophobic lignin-like species. Future Work

¾Synthesis of pullulan cinnamate derivatives and the investigation of self-assembly onto cellulose surfaces.

¾Real-time investigations of adsorption of PAAb onto cellulose surface by in-situ Atomic Force Microscopy. Thank You

PRESENTED BY Abdulaziz Kaya Graduate Student Virginia Tech [email protected]