Fabrication of complex shaped microparticles for self-assembly applications - Oluwatosin Omofoye
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Fabrication of complex shaped microparticles for self-assembly applications - Oluwatosin Omofoye
- 1. FABRICATION OF COMPLEX SHAPED MICROPARTICLES FOR SELF- ASSEMBLY APPLICATIONS Oluwatosin Omofoye, C. Wyatt Shields IV, Gabriel P. Lopez
- 2. MOTIVATION Assembly of colloids into distinct patterns is paving way of the future of materials science Various applications in Photonic band gap materials Bio sensing materials Opal is a natural photonic crystal http://opalux.com/ 1
- 4. FABRICATION OF SHAPED COLLOIDS Spin coat SU-8 2 2 1 Silicone wafer 3 Mask of Array 4 Expose UV light through Mask 5 Remove residual SU-8 6 Suspend in solution Photolithography
- 5. EXTRACTION METHODS Using rubber scraper or a blade Sacrificial Layer (Omnicoat) below SU-8 Nano PG Remover Solvent Silicone substrate Sacrificial Layer SU-8 Rubber PolicemanMaterial layers during fabrication 3
- 6. NANO PG REMOVER IMPROVEMENT10umCylinders5umsquares PG Remover 4 Dry Extraction
- 7. EXAMPLES OF TILE PARTICLES 5um wide 0.5um thick square 10um wide 2um thick hexagons 5
- 8. PARTICLE MODIFICATION Fluorescence and Metal Deposition Fluorescent Particles Gold/Cobalt Coated Particles 2 um thick hexagonal tiles 6
- 10. PREVIOUS ASSEMBLY TECHNIQUES Electric Assembly Magnetic Assembly C. Shields IV, S. Zhu, Ye Yang, B. Bharti, J. Liu, B. Yellen, O Velev, G. Lopez. Soft Matter, 2013. 7
- 11. EVAPORATION INDUCED CONFINED AREA ASSEMBLY 1 2 3 4 5 An evaporation based form of assembly G. Singh, S. Pillai, A. Arpanaei and P. Kingshott, Soft Matter, 2011, 7, 3290. 8
- 12. EVAPORATION INDUCED CONFINED AREA ASSEMBLY SEM Images of achieved patterns G. Singh, S. Pillai, A. Arpanaei and P. Kingshott, Soft Matter, 2011, 7, 3290. 9
- 13. INITIAL RESULTS WITH SHAPED COLLOIDS 5um wide 2um thick cylinders 10um Cubes and 2um diameter cylinders 10um wide 2um thick squares 10um wide hexagonal prisms and 2um Particles 10
- 14. PROPOSED SOLUTION Liquid – liquid interface method Assembly at interface of liquids with different densities 11
- 15. CONCLUSION Successfully created a broad range of shaped micro-particles Modified them to have metallic and fluorescent properties Created self-assembled and active assembled structures 12 Magnetic field assembly of Metal coated Particles Passive assembly of shaped particles
- 16. ACKNOWLEDGEMENTS LORD Foundation: Sponsor Dr. Gabriel Lopez: Lab Professor Wyatt Shields: Graduate Student Mentor SMiF (Shared Materials Instrumentation Facility) Peter Kingshott and University of Swinburne (Research collaborators) 13
- 17. QUESTIONS?
Editor's Notes
- Fabrication of colloids (basically microparticles) with unsual shapes and properties and arranging them into specific patterns is future of materials science Regular materials found in nature have basic building blocks such as atoms, molecules, polymers etc By fabricating these micro particles, we are basically creating new types of building blocks that allow us to create new materials with propoerties that cannot be found in nature One of these are photonic crystals, photonic bandgap materials Due to their optical properties and periodic structures, photonic crystals affect the motion of light in the same way that semiconductors affect electrons Opal is a natural photonic crystal Silica sphears that are 150-300nm in diameter and arranged in a tighly packed lattice Visible light cannot pass through tightly packed structure Light based computers, much higher processing power Invisible cloaks The ordered assembly of colloids is known as a most feasable method of creating the 2D and 3D crystal lattice structures needed to make these materials J. Zhang, Z. Sun and B. Yang, Curr. Opin. Colloid Interface Sci., 2009, 14, 103-114. Biomolecules are immobilized on surface of monolayer Sensitivity and specificity of molecules used for puposes such as measuring chemical concentrations in blood Performing research in protein molecule interactions Quarts crystal micro balance T. Wink, S. J. van Zuilen, A. Bult and W. P. van Bennekom, The Analyst, 1997, 122, 43R-50R.
- How we make these micro particles that we will later assemble into lattices
- Spin coat SU-8 on silicon substrate Expose under UV light through desired mask Development and extraction -Start with a silicon wafer, - pippet SU-8, epoxy based photoresist - depending on SU-8 type and spin speed, we get different particle thickness - get picture of thickness graph - prebake SU-8 is UV sensitive, when exposed to UV it hardens. Procedure is performed in the clean room under non-uv light Mask that has large array of desired shape is placed over wafer, and Light is shown through it. Hardens based on particular array Make picture of mask on google sketch Post-baked Development, put in solution that removes un-crosslinked SU-8 Particles are extracted off wafer and put in solution, covered in next slide
- Extraction is probabaly the most difficult step of our process Rubber Police man and blade only worked well with 2um thick particles Discovered that spinning water soluble scarificial layer called omnicoat and soaking wafer in water during extraction made it work Failed with 0.5 um thick particles Blade would actually destroy particle because they were so thin Discovered a solvent called Nano PG remover that simplified our whole extraction process should be present progress of our project? Pictures comparing initial method and current method with PG Remover Doesn’t damage particles, higher yields, and surprisingly also helps disperse particles in solution old method also had problems with clumping of particles
- 0.5 um thick squares, 2 um thick cylinders With PG remover. Drastic increase in the yield and quality of our extrations. PG remover actually helps prevent the particles from clumping up, keeps them dispersed in solution very well
- 2 mg Nile red / 1 mL SU-8 2002 We also successfully made these particles fluorescent Mixing a small concentration of nile red dye and 2-anilinonaphthalene-6-sulfonic acid (2, 6-ANS) a blue dye. 0.001g per mL of SU-8 resist In picture: 2 mg Nile red / 1 mL SU-8 2002 Particles will glow when used under a fluorescent microscope Used to better view particles, or differentiate them based on specific properties Metal deposition is another modification we perform on the particles Can deposit specific thicknesses onto sureface of the paricles Metal deposition machine, usually deposit about 250 nm of cobalt, or gold depending on desired use Fluorescence used to help determine orientation of metal coated colloids during assembly
- - Now that we have made the particles, we assemble them Previously our lab has performed dielectric and metallic assembly using metal coated particles Only works for large particles So we are going to rely on evaporation methods to assemble the smaller microparticles
- An evaporation based form of self-assembly Suspension of particles of a specified size are spread over a hydrophilic substrate encircled by a rubber ring During evaporation Receding meniscus of liquid generates forces that draw particles into regular two-dimensional patterns Picture from kingshot article, graph picture and process picture Changing the stoichiometric ratios of the particles as well as their sizes results in different types of crystal lattices Pictures of achieved pattern’s w/ spheres G. Singh, S. Pillai, A. Arpanaei and P. Kingshott, Soft Matter, 2011, 7, 3290.
- Types of patterns created with spheres Very efficient method, in that it creates these perfect arrays with little irregularities, Very simple Hexagonal and triangular based patterns inspired us to use this method to assemble shaped particles Cells will be able to fit in between spaces, can be used to research their interactions D scale bar: 3um Red blood cells are 6-8 microns
- We are attempting to perform the same methods with the shaped particles that we have developed Offers new possibilities for the type of patterns and arrays that can be created Initial results have not resulted in any good date Several reasons why it did not work as well Size of particles Original particles were able to roll to specific location because they were spherical, during the assembly process 5um wide 2um thick cylinders in 1%SDS in MQ 10um wide 2um thick squares in 25% ethanol, 25%heavy water in MQ
- Achievement with successful extraction of small tiles is encouraging Believe smaller size will allow forces to have a greater impact on the particles, and there will be improved pattern formation Idea of a liquid-liquid interface Two liquids of different densities, Also improves mobility Ability of spheres to roll after settlement allows formation of pattern We are still in the early stages of developing this idea, but we are optimistic and hopeful that it will work
- - Dielectrophoresis
- extration: - took 12 minutes Take out words on spin coat – type name: photolithography Eplicitly stated differenced btw/, omnicoat, sacrificial layer Make a table for slide 6 Slide 8: change DEP field assembly to specific metals being used Used bullet point for uses of these modification methods Slide 12: use figure slides Use a future applications for this Number slides: in green slides Know who each person is, fill out acronyms