An Introduction to Polyelectrolyte Multilayers Layer-by-Layer Adsorption (LbL): An Enabling Technology for the Nano- construction of Multifunctional Films on Solvent Accessible Surfaces. G. Decher / Institut Charles Sadron Institut Charles Sadron 1 Differences between chemistry in bulk and at interfaces Some trivia: • Surface functional groups accessible only from the solution side. ( SN1 might be favored over SN2 ; reactivities different from bulk) • Typical monolayer thicknesses of 0.5 nm to 5 nm. • Typical surface areas of 0.20 nm2 per molecule, 5 1014 molecules per cm2. • At a mass of 400 g/mol, 1 cm2 of a densely packed monolayer corresponds to 0.33 µg of material. • 5g (semi-preparative scale), would cover an area of 1500 m2. • Monomolecular layers of polymer may be thinner and less dense and typically consist of 0.1 to 1.5 mg of material per 1 m2. • Less than 0.02 mg for chemical analysis and physical characterization Advantage: We only need tiny amounts from colleagues doing synthesis Institut Charles Sadron 4 Build-to-Order Assembled Films Build-to-Order (BTO) is the capability to quickly build standard or mass-customized products upon receipt of spontaneous orders without forecasts. Layer-by-Layer assembly allows to design functional surfaces and surface-based nano-devices in a "build-to-order" fashion. It exceeds simple self-organization under equilibrium conditions by making it possible to arrange many different materials at will with nanoscale precision. Institut Charles Sadron 5 The multilayer films that can do everything . Pierre Schaaf, Gero Decher, Jean-Claude Voegel La Recherche, No. 389, SEPT. 2005, 56-58 Institut Charles Sadron 6 A Disruptive Nano-Coating Technology Layer-by-layer deposition can provide solutions in two areas: • Surface modification (engineering the interaction of a given object with its environment) • Fabrication of thin film devices (permitting multimaterial assemblies including proteins and colloids) Applications: anticorrosion, antireflective coatings, biocompatibilisation, biosensors, implants, optical waveguides, electroluminescent devices, microreactors, and many more … The ease by which even multimaterial coatings can be put together using an environmentally friendly low cost technique has kindled widespread interest, not only in academia. The first commercial products have already been introduced to the market in 2001, 2002 and 2004. Institut Charles Sadron 7 Schematic of the Layer-by-Layer Deposition Process Simplified “molecular” picture of the first two adsorption steps depicting film deposition as starting with a positively charged substrate. Counterions are omitted for clarity. Polyion conformation is highly idealized and layer interpenetration is not shown in order to better represent the surface charge reversal with each adsorption step. G. Decher, Science 277, 1232-1237 (1997) > 1750 ISI-Citations (as of January 2006) Institut Charles Sadron 8 LbL is (analogous to) a chemical reaction ! Classic Synthesis LbL - Deposition Reagent(s) Surface (atoms, synthons) (template) series of series of reaction deposi- steps tion steps Product(s) Multilayer Film (typically single species) (defined layer sequence) Molecular scale Nano (meso) scale Multilayer Thin Films: Sequential Assembly of Nanocomposite Materials; Decher, G. and Schlenoff, J. B., eds., Wiley-VCH: Weinheim, 2003; 524 pages. Institut Charles Sadron 9 An Unprecedented Number of “Reagents“ for LbL-Deposition linear tacticity branched degree of polymerization Reagents: polymers (starshaped) composition copolymers monomer sequence size polymeric polydispersity colloids metallic oxidic composition surface functionality proteins biomacromolecules polynucleotides bioaggregates small molecules . small & complex ions . Multilayer Thin Films: Sequential Assembly of Nanocomposite Materials; Decher, G. and Schlenoff, J. B., eds., Wiley-VCH: Weinheim, 2003; 524 pages. Institut Charles Sadron 10 An Example of the integration of nanoparticles into the films Schmitt, J.; Decher, G.; Dressik, W. J.; Brandow, S. L.; Geer, R. E.; Shashidhar, R.; Calvert, J. M. Metal Nanoparticle/Polymer Superlattice Films: Fabrication and Control of Layer Structure. Adv. Mater. 1997, 9, 61-65. Institut Charles Sadron 11 LbL Deposition (Programmed Assembly) Advantages: deposition on surfaces of almost any kind and any shape broad processing window many control parameters: concentration adsorption time ionic strength solvent composition temperature . Multilayer Thin Films: Sequential Assembly of Nanocomposite Materials; Decher, G. and Schlenoff, J. B., eds., Wiley-VCH: Weinheim, 2003; 524 pages. Institut Charles Sadron 12 A bit of History (1): It all started with “Bola”-Amphiphiles 0.60 0.50 Substrate Adsorption Adsorption 0.40 Bola-dianion Bola-dication 0.30 0.20 Absorbance @ 262 nm 0.10 Abs. biphenyl @ 262 nm 0.00 0 5 10 15 20 25 30 35 40 Number of Layers G. Decher, J.-D. Hong, Makromol. Chem., Macromol. Symp. 46, 321-327 (1991) 420 ISI-Citations (as of January 2006) Institut Charles Sadron 13 A bit of History (2): the next step were mixed bola/polyelectrolyte films 0.10 0.08 Adsorption Adsorption 0.06 Polyanion Bola-dication Absorbance 0.04 0.02 Abs. phenyl @ 225 nm Abs. biphenyl @ 262 nm 0.00 0 1 2 3 4 5 6 7 8 Number of Layers G. Decher, J.-D. Hong, Ber. Bunsenges. Phys. Chem. 95, 1430-1434 (1991) 409 ISI-Citations (as of January 2006) Institut Charles Sadron 14 A bit of History (3): and finally polyanion/polycation multilayers 0.15 225 nm Adsorption Adsorption 0.10 Polyanion Polycation 0.05 Absorbance @ Abs. phenyl @ 225 nm 0.00 0 5 10 15 20 25 30 35 40 Number of Layers G. Decher, J.-D. Hong, J. Schmitt, Thin Solid Films 210/211, 831-835 (1992) 729 ISI-Citations (as of January 2006) Institut Charles Sadron 15 A Small List of Polyions Already Used for Multilayer Fabrication SO - 3 O- Na+ - + N OSO3 Na NH NH+ • SO2 O O NH S SO - Na+ 3 HO3S HO3S HN N N - CO2 OH Na+ NaPSS PVS PAZO PAPSASPAN PTAA PAMPSA H + + NH2 S N Cl - N NH + Cl- + 3 N N H N + 2 Cl - R HN N + N I - N S+ Cl - HN NH2 PSMDEMA PAH Pre-PPV PDDA PMPyA R-PHPyV PEI Institut Charles Sadron 16 Fine-tuning the film thickness by ionic strength (X-ray reflectometry) (Addition of salt yields thicker layers; polyanion from salt, polycation from pure water) 1011 600 109 50 alt. layers 500 107 42 alt. layers 5 10 400 30 alt. layers 103 20 alt. layers 300 1 10 Film Thickness [Å] 16 alt. layers 1.0 m NaCl 10-1 200 (17.7 Å / layer pair) Reflected X-ray Intensity [a.u.] 1.5 m NaCl 12 alt. layers (19.4 Å / layer pair) -3 2.0 m NaCl 10 (22.6 Å / layer pair) 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5 1015202530 Scattering Angle 2 [deg.] Number of PSS-Layers G. Decher and J. Schmitt, Progr. Colloid Polym. Sci. 89, 160-164 (1992) 193 ISI-Citations (as of January 2006) Institut Charles Sadron 17 Inversion of surface charge with deposition of each layer Adsorption of polycations 40 PEI poly(ethylene imine) (PEI) and PAH PAH poly(allyl amine) (PAH) renders the PAH PAH PAH poly(allyl amine) (PAH) renders the surface positively charged. The 20 deposition of poly(styrene sulfonate) (PSS) yields a negative surface charge. Similar measurements were also 0 obtained from other groups. For a theory of surface charge -20 inversion see M. Castelnovo and J. F. Zeta Potential [mV] Joanny, Langmuir 16(19), 7524-7532 PSS PSS PSS PSS PSS (2000) and for a mechanism of -40 multilayer formation see J. B. bare SiO surface 2 Schlenoff and S. T. Dubas, Macromolecules 34(3), 592-598 0 5 10 15 20 25 30 35 40 (2001). Number of Measurement G. Ladam, P. Schaad, J. C. Voegel, P. Schaaf, G. Decher, and F. Cuisinier, Langmuir 16(3), 1249-1255 (2000). Institut Charles Sadron 18 QCM-D (Q-Sense D300), Q-Sense AB, Gothenburg, Sweden, unpublished data Institut Charles Sadron 19 Automatic Layer Deposition Using a “Dipping” Robot Automated deposition device, R&K Ultrathin Organic Film Technology, Berlin, Germany Institut Charles Sadron 20 Deposition conditions are (in general) not really crucial PEI/(PSS/PAH) on quartz from x M NaCl PEI/(PSS/PAH) on quartz from x M NaCl 5 5 manual dipping; dried after every layer automated device; no intermediate drying 0.15 300 0.15 300 0.14 280 0.14 280 260 260 0.13 0.13 D [Å] 240 D [Å] 240 0.12 0.12 220 220 0.11 200 0.11 200 A @ 226 nm A @ 226 nm 0.10 180 0.10 180 160 0.09 160 0.09 140 140 0.08 0.08 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.4 0.6 0.8 1.0 1.2 1.4 1.6 c c NaCl NaCl A @ 226 nm D [Å] A @ 226 nm D [Å] y = m1 + m2*m0 y = m1 + m2*m0 y = m1+m2*m0 y = m1+m2*m0 Value Error Value Error Value Error Value Error m1 0.054 0.002 m1 67 15 m1 0.059 0.006 m1 74 1 m2 0.061 0.003 m2 146 15 m2 0.063 0.006 m2 150 1 Chisq 6.8405e-06 NA Chisq 243.12 NA Chisq 4.3167e-05 NA Chisq 1.151 NA R 0.99822 NA R 0.98912 NA R 0.98951 NA R 0.99995 NA However, dependence on ionic strength is stronger than in one of the previous cases since both polyions are deposited from saline solutions Institut Charles Sadron 21 From Neutron Reflectivity Curves: Number of Deuterated Layers, Layer Positions and Layer Profiles 107 8.0 10-6 -6 105 7.0 10 ] -2 6.0 10-6 [Å 3 n 10 5.0 10-6 101 4.0 10-6 3.0 10-6 10-1 2.0 10-6 Reflected Intensity (Neutron) -3 10 Scattering Length Density 1.0 10-6 10-5 0.0 100 0 0.02 0.04 0.06 0.08 0.1 0 500 1000 1500 2000 2500 Q [Å-1 ] z Z [Å] M.