Whitesides et al. Science 295, 2418 (2002); Self assembly at all scales?
What drives self assembly? Static assembly (thermodynamic free energy minimum) -- once formed it is stable Dynamic assembly (kinetically formed, not necessarily thermodynamic minimum) -- not necessarily stable Forces of chemical bonding (4) covalent, ionic, van derWaals, hydrogen Other forces (magnetic, electrostatic, fluidic,...) Polar/Nonpolar (hydrophobicity) Shape (configurational) Templates (guided self assembly) Kinetic conditions (e.g., diffusion limited)
Excerpt from Letter of Benjamin Franklin to William Brownrigg (Nov. 7, 1773)...At length being at Clapham, where there is, on the Common, a large Pond... I fetched out a Cruet of Oil, and dropt a little of it on the Water. I saw it spread itself with surprising Swiftness upon the Surface... the Oil tho' not more than a Tea Spoonful... which spread amazingly, and extended itself gradually till it reached the Lee Side, making all that Quarter of the Pond, perhaps half an Acre, as smooth as a Looking Glass.... A nanofilm!
Langmuir Film pressure e.g., steric acid monolayer film water hydrophilic end hydrophobic end of an amphiphilic molecule
Langmuir-Blodgett Film Must control movable barrier to keep constant pressure multiple dips - multiple layers solid liquid
SAM: Self Assembled Monolayer Review article: J.C. Love, et al., Chem. Rev. 2005, 105, 1103 (G. Whitesides group, Chem Dept, Harvard) HS(CH 2 ) n X alkanethiol on gold (Au) where X is the end group of the chain –CH 3, –OH, or –COOH Longer alkanethiol molecules have greater thermodynamic stability
SAM: Self Assembled Monolayer Chemisorbed molecules Stabilized by intermolecular van der Waals interaction solid molecules from solution
SAMs on Nanoparticles J.C. Love, et al., Chem. Rev. 2005, 105, 1103 gold NP There are now many configurations and uses of SAMs imperfect packing
SAMs via Microcontact Printing J.C. Love, et al., Chem. Rev. 2005, 105, 1103 A type of stamping! (silicon rubber)
SELF ASSEMBLY with DIBLOCK COPOLYMERS Block A Block B 10% A 30% A 50% A 70% A 90% A ~10 nm Ordered Phases PMMA PS Scale set by molecular size
CORE CONCEPT FOR NANOFABRICATION Deposition Template Etching Mask Nanoporous Membrane Remove polymer block within cylinders (expose and develop) Versatile, self-assembling, nanoscale lithographic system (physical or electrochemical)
nanoporous template Nanomagnets in a Self-Assembled Polymer Mask 1x10 12 magnets/in 2 Data Storage......and More
Metal Nanorings Ferromagnetic cobalt rings as small as 15 nm OD
Mohan Srinivasarao, et al. Science 292, 79 (2001). Kinetic Self-Assembly - by Breath Figures Polystyrene Film
More Fabrication by Breath Figures UMass: Alexander Böker, Yao Lin, Kristen Chiapperini, Reina Horowitz, Mike Thompson, Vincent Carreon, Ting Xu, Clarissa Abetz, Habib Skaff, A. D. Dinsmore, Todd Emrick and Thomas P. Russell, Nature Materials 3, 302 - 306 (2004) a, Breath-figure pattern obtained with pure polystyrene. b, Optical and c, confocal fluorescence microscope images of different areas of a sample obtained from solvent-casting a polystyrene film from chloroform with CdSe nanoparticles. Scale bars: 16 mum. The inset in c shows a fluorescence intensity scan along the line indicated.