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Nanolatex based nanocomposites: control of the filler structure and reinforcement. A. Banc 1 *, A-C. Genix 1, C. Dupas, M. Chirat 1, S.Caillol 2, and J.Oberdisse 1 1 Laboratoire Charles Coulomb, Université Montpellier 2, Montpellier, France 2 Institut Charles Gerhardt, Montpellier, France

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Mechanical reinforcement in nanocomposites ? M ICROSTRUCTURE σ λ Filler network Diluted regime Filler Percolation threshold Composite properties ≠ Filler properties + Matrix properties M ECHANICAL PROPERTIES Jouault et al. F ILLER - FILLER INTERACTIONS F ILLER - MATRIX INTERACTIONS

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Model nanocomposites with tunable filler structure Øsi≈30 nm Colloïdal silica + Drying Annealing Water evaporation Particles deformation Polymer diffusion Nanocomposite TUNABLE nanostructure: f( Si, Ø Si / Ø PEMA, M w ) PolyEthylMethacrylate (PEMA) Tg>Tamb Nanolatex Ø PEMA ≈30 nm OR 200nm Mw ≈ 20, 50 or 160 kg/mol

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E FFECT OF R latex / R si

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Small Angle Scattering kiki ksks Wave vector q= - ksks kiki I(q)= f( , , P(q), S(q)) = Volume fraction = Scattering objects - matrix = Scattering lengh density P(q) = Form factor S(Q)= Structure factor q(Å -1 ) P(q) S(q) I(q) Silica nanoparticles P(q) =14 nm =0,11 q max d P(q)*S(q) q -df df= fractal dimension

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● 0% ● 1% ● 3% ● 5% ● 10% Structure R silica ~R latex ~14 nm Q -2,4 Colloidal solutions R silica <

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5µm 500nm 5µm 500nm R silica ~R latex ~14 nmR silica <

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Rheological properties G’ G’’ G’ G’’ G’ Matrix 10% nanocomposite Silica structure little impacts G’ at low frequency (long times) N O IMPORTANT EFFECT OF THE SILICA STRUCTURE ON RHEOLOGICAL PROPERTIES (Low strain: 0,2%) x4

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E FFECT OF THE MATRIX M W

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Structure: SAXS Mw= 160 000g/mol 50 000g/mol 20 000g/mol 10% 5% 3% 1% Matrix Well dispersed filler Fractal aggregates d f =2,4 d f =2,3 Bigger fractal aggregates R silica ~R latex ~14 nm

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PEMA50 PEMA160 PEMA20 1%3%10% 500 nm Structure: TEM

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Structure: Monte Carlo simulation Image analysis 1% nanocomposites: No inter-aggregate structure factor 160 000g/mol 20 000g/mol Monte Carlo simulation Kappa=12.5% Kappa>20% Correlation direct space and reciprocal space via simulation =3 =51

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Structure: 10% nanocomposites d* d*=2 /q* Model cubic network Silica networks whose the characteristic size decreases with Mw => decrease of the wall thickness 20 000g/mol 50 000g/mol 160 000g/mol

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PEMA50 PEMA160 PEMA20 1%3%10% 500 nm Structure: overview d* =12% >20% df=2,4 df=2,3

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Rheological properties: matrices PEMA160 PEMA50 PEMA20 G’ G’’ G’ G’’ GNGN Master curve at annealing temperature (180°C): Filler mobility: PEMA20 > PEMA50 > PEMA160

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Rheological properties: nanocomposites Two filler volume fraction regimes: - < threshold viscoelastic material - > threshold elastic material Filler effect: -G’ at low frequency threshold <10%

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At < threshold G’~φ 1/(3-df) G’~φ 1,7 Aggregate fractal dimension: df=2,4 (SAXS) Reaction Limited Aggregation -Slow aggregation In the weak-link regime: Shih et al, 1990 Rheology of fractal objets

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d* At > threshold Fractal aggregates reinforce much more than the well dispersed filler. Power law ?

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Conclusions - Prospects => Dynamical approaches of the mechanical reinforcement Model nanocomposites Various nanoparticle dispersions: well dispersed / fractal aggregates / porous network => Novel structures with mixtures of latex bead sizes Mechanical reinforcement Mostly at low frequency – aggregated filler reinforce better than the well dispersed one Quantitative description of the filler structure : D IRECT SPACE R ECIPROCAL SPACE TEM SAXS Image analysis + Simulation => Behavior at large strains? …

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