Date: 2008/11/7 Complex Fluids & Molecular Rheology Laboratory, Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan, R.O.C. Speaker: C. C. Hua ( 華繼中 ) Single-Chain and Aggregation Properties in Semiconducting Conjugated Polymer Solutions Rheo-Optical Measurements and Multiscale Simulation 成大化工演講

Introduction & motivation Spin- coating Cast films Ink-jet printing Conducting conjugated polymer precursor solution Real process Flexible PLED display PLED displayPolymer solar celle-Paper Cambridge Display Technology (CDT) LG.Philips LCD Co. Ltd. Cambridge Display Technology (CDT) Seiko Epson Corporation Konarka Technologies, Inc. Scientific American Feb. 2004

Viscometric Properties of MEH-PPV Solutions Hua et al, J Rheol 49, 641 (2005) Poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) [M w : 70,000-10,000 g/mol, PDI: 2.5] MEH-PPV PSA. Effect of aging B. Effect of thermal annealing

Dynamic Light Scattering (DLS)/Photoluminescence (PL): Effects of solvent quality and concentration M/T: 1 mg/mlM/T: 3 mg/ml, no filtrationM/C: 3 mg/ml, no filtration M/T M/C Hua et al., Appl. Phys. Lett. 93, (2008)

In situ viscometirc/flow turbidity measuring apparatus Mechanical measuring system Temperature control system Optical measuring system

Specific turbidity measuring theory Derived specific turbidity representation equation Kerker, M., THE SCATTERIG OF LIGHT AND OTHER ELECTROMAGNETIC RADIATION (Academic Press, San Diego, 1969). van de Hulst, H. C., Light Scattering by Small Particles (Dover Publications, New York, 1981).

Specific turbidity measuring theory Heller, W., and W. J. Pangonis, “Theoretical Investigations on the Light Scattering of Colloidal Spheres. I. The Specific Turbidity,” J. Chem. Phys. 26, (1957). Liberatore, M. W., and A. J. McHugh, “Dynamics of shear-induced structure formation in high molecular weight aqueous solutions,” J. Non- Newton. Fluid 132, (2005). Plot figure of specific turbidity vs. Mie radius So, quantity of Mie radius can get from equation of fitting curve.

Experiment design and procedure DLS In-situ viscometirc/flow turbidity measurement Use DLS to measure hydrodynamic radius. Compared the value with the Mie radius from turbidity measurement. Shear flow: 10 min Shear rate: 60 [s -1 ] Flow rested 15 min Shear flow: 10 min Shear rate: 151~2,800 [s -1 ] Flow rested 15 min Altered shear rate Shear flow: 10 min Shear rate: 60 [s-1] Flow rested 15 min Shear flow: 10 min Shear rate: 151~2,800 [s -1 ] Flow rested 15 min Run2 Run1 Altered shear rate MEH-PPV/DOP Sample The main idea is to change polymer conc. and aging time to observe their effects on aggregation properties. Conc. [mg/ml] Aging time W/o aging2-days aging Experiment factors setting Run1 is to observe the effect of flow shearing and cessation. Run2 is to further study the effect of preshearing.

Specific turbidity signal (w/o aging) 0.02 mg/ml0.3 mg/ml1.0 mg/ml3.0 mg/ml Page 07 Before shear

1.0 mg/ml1.0 mg/ml (2-days aging)3.0 mg/ml1.0 mg/ml (w/o aging)0.3 mg/ml0.3 mg/ml (2-days aging)0.02 mg/ml0.3 mg/ml (w/o aging) Specific turbidity signal (2-days aging) Before shear

Turbidity measurement vs. viscosity measurement Mie radius w/o aging Close correlation was generally noted between these two measurements The Mie radius and reduced viscosity decreases with increased polymer concentration. Preshearing effect was quite obvious at lower concentrations Reduced viscosity

Turbidity measurement vs. DLS measurement Aging effectConc. Mie radiusHydrodynamic radius Before shearing W/o aging 0.02 mg/ml mg/ml mg/ml mg/ml Aged 2 days 0.02 mg/ml mg/ml mg/ml mg/ml Except for the case with the lowest concentration, good agreement was found between the two measurements for the estimated aggregate size.

Ongoing work on rheo-optical measuring systems Lenstra, T. A. J., Colloids near phase transition lines under shear, Doctoral thesis, Utrecht University, Flow/turbidity Dicroism & birefringence SALS & multi-angle LSWide range of rheo-optical measurement Kume et al., Macromolecules 30, (1997). Anton Paar SALSMulti-angle LS Ongoing work by Liu, Wen, and Kuo. Ongoing work by Chen. Page 15

Multi-Angle Dynamic/Static Light Scattering Sample cell Photomultiplier tube Temperature Controller 10~70 o C θ = 30~150 o Polarizer 1 Polarizer 2 Circulating water Detection arm

Small Angle Light Scattering (SALS) CCD Photodiode 1 Photodiode 2 θ = 0.5~10 o Sample cell

CCD Laser Spatial filterMini rod mirror 2 mm Objective lens Pinhole Lens Iris Beamsplitter Photodiode 1 Sample cell Lens set 1Lens set 2 Photodiode 2 Iris DAQ Schematic Diagram of SALS Setup Onset Edmund Ray tracing

Rheo-Turbidity Optical cell Thermal bath Photodiode Photodiode 1 Photodiode 2 Rheometer Temperature Controller Optical flow cell

Couette flow cell Polarizer 2 at 135 o Polarizer 1 at 45 o Photodiode 2 Photodiode 1 Rheometer Flow Birefringence (Crossed Polarizers) He-Ne laser

Flow Light Scattering (FLS) Lens A Laser Pinhole A Iris Lens B Pinhole B Detector Index matching vat Rotor Data analysis Rotary detection arm (top view)

Optical flow cell for FLS

主要量測系統 : (1) 即時光學 — 流變系統 I. Particle Interactions II. Microstructures III. Molecular Anisotropy

主要量測系統 : (2) 光學旋轉塗佈成膜系統 Video Microscopy Laser Doppler, DLS I. Ellipsometry (film thickness & reflective index) II. Aggregation Microstructure/Anisotropy & Hydrodynamics under controlled (a)Solution Properties (solvent quality, volume fraction, viscosity & volatility) (b) Spin Rate (c) Baking (d) Interfacial Properties

Fundamental Particle (Polymer segment) Interactions Small Aggregates Self-assembly/ Phase separation Microscopic/Mesoscopic Structure & Anisotropy Particle size, shape, Surface modifications, (grafting & charge) Solution properties (solvent quality, concentration, viscosity, volatility) Interfacial properties (wetting & brushing) Operating Conditions (spin rate,evaporation viscoelasticity) Optoelectronic/ Mechanical Properties X-ray Scattering Dynamic Light scattering Molecular Rheology Static light scattering & Birefringence/ Dichroism Video Microscopy Spectroscopy (EL & PL etc), TEM, AFM etc. Non-Equilibrium & Memory Effects

Parameter-Free Multiscale Coarse-Grained (CG) Simulations

System No. of chains/ in monomer unit No. of solvent particles Density （ g/cm 3 ） Concentration （ wt % ） (a) (b) (c) MEH-PPV (n=100) × 11 PS (n=100) × 11 Chloroform × 8000 Toluene × 8000 Cyclohexane × (c) Aggregates versus Entanglements Temperature ＝ 55 ˚C, Pressure ＝ 1 atm, Time ＝ 1 ns, Time step = 10 fs Y-Z plane Y-X planeX-Z plane Y-Z plane Y-X planeX-Z plane (a)(b) Hua et al, J Rheol 49, 641 (2005)

Automatic mappings and Langevin Dynamics Simulations: Bond anglePlanar angle Force-Fields Construction for the CG-model Lee, C. K.; Hua, C. C.; Chen, S. A. J. Phys. Chem. B 112, (2008). Bond length Toluene vs Toluene Chloroform vs Chloroform Monomer vs Monomer Intramolecular Intermolecular

Parameter-Free, Self-consistent Langevin Dynamics of the CG-Model: M / T 6 ns M / C 6 ns from the MD simulation of single-particle diffusivities CGMD : Parallel computation system (IBM-P690 with 4 CPUs) with 36 hrs CGLD : Single-CPU personal with 10 min Which yields the exact (generally poor) solvent qualities for MEH-PPV solutions: Toluene: 0.32 Chloroform: MEH-PPV monomers per Kuhn length

M / T 0.5 ns Nucleation of two small aggregates Nucleation of two small aggregates Collapsing of ten MEH-PPV chains Collapsing of ten MEH-PPV chains into an aggregate cluster into an aggregate cluster M / C 0.38 ns M / T 7.5 ns M / T 0.38 ns M / T 0.38 ns M / T 0.38 ns M / C 7.5 ns M / C 7.5 ns M/T 0.8 ns M/T 8 ns M/C 0.8 ns M/C 8 ns M/T 0.8 ns M/T 8 ns M/C 0.8 ns M/C 8 ns

Brownian Dynamics of Chain Models Solvent Molecular weight (Da) Number of monomers, N m Size of monomer, b m (nm) a end-to-end, (nm 2 ) a,b Solvent quality,  a,c Chloroform Toluene Basic information of MEH-PPV Chains in solvents at 298K : a Estimated from atomic molecular dynamics simulations. b The mean-square end-to-end distance. c Based on end-to-end = K(N m -1) 2 , where K is a certain constant independent of the polymer molecular weight. L Kuhn (=17.5 nm): the Kuhn length h* (= 0.25): hydrodynamic interactions parameter f  : total volume fraction of monomer as polymer chain in a  solvent R g, : radius of gyration of a FJC (or FRC) under the -condition (=L Kuhn 2 /(12k B T)): relaxation time of the Kuhn segment, where , k B and T are the drag coefficient, the Boltzmann constant and absolute temperature The values chosen for H  and H  produce a end-to-end of FRC/FJC in agreement with the predicted ideal chain behavior. FRC (freely rotating chain) FJC (freely jointed chain) The value of  for a given polymer solution can in princinple be determined from the polymer collapsed transition shown above.

Aggregation in MEH-PPV Solutions: Freely Jointed Chain Model Case I Case II

Scattering of Single Collapsed Chains/interchain aggregates predicted by Freely Rotating Chain Model SANS profiles of MEH-PPV in (a) chloroform and (b) toluene at 25 °C. Mn = 216,000 g/mol and PDI = 2.0. (Ou-Yang et al., Phys. Rev. E 72, (2005)) (b) (a) local rod-like feature of MEH-PPV molecules qL Kuhn > 5, rod-like 1<qL Kuhn <5, fractal structure To retrieve pure MEH-PPV contributions from the SANS data, the scattering intensity is normalized as I(q)/() 2, where  is the difference of scattering length density between the MEH-PPV monomer and the solvent molecule. Effects of single-chain polydispersity and interchain aggregation S. C. Shie, C. C. Hua, and S. A. Chen, “Simulation of large-scale material properties of semiflexible chains in poor solvents” to be submitted.

Parameter determinations for even more coarse-grained, rigid dumbbell models: From Freely joined chains to dumbbells The right figure shows that the interchain potential as a function of the separation in the mass centers can be well mimicked by some linear functions Solvent  /R s  /(kT) r cut / [ end-to-end ] 1/2 MEH-PPV Chloroform Toluene PS  -solvent Parameter evaluations for the dumbbell: Shie et al. Macroml. Theory. & Simul. 16, 117 (2007)

Mapping and Reverse Mapping Atom model (AMD) Monomer model (CGLD) Ellipsoid model (CGMC) tetrahedral defects Centipede model (CGMD) Mapping Reverse Mapping