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Combinatorial Chemistry

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  1. Combinatorial Chemistry High-Throughput Methods for Developing New Materials Group Members: Christopher Gold, Melissa Lackey, Chih-Fang Liu, Ryan Wu Advisors: Dr. Earl Ryba, Kevin Gallagher - PPG Industries

  2. Project Statement • Develop a high-throughput process that employs the principles of combinatorial chemistry to dramatically reduce the time and labor required to evaluate the durability of new resins and coatings, specifically abrasion resistant clear coatings on a polycarbonate substrate.

  3. Goals • Research combinatorial chemistry and high-throughput methods to present a means of drastically increasing productivity and efficiency

  4. Goals • Research combinatorial chemistry and high-throughput methods to present a means of drastically increasing productivity and efficiency • Reduce cost and increase profit through miniaturization of sample size and increased coating discovery rate

  5. Combinatorial Chemistry • Miniaturization and automation yield high-throughput experimentation • Decreased sample size • Processes almost completely automated

  6. Combinatorial Chemistry • Miniaturization and automation yield high-throughput experimentation • Decreased sample size • Processes almost completely automated • Quantitative analysis of data • All steps linked to central database • Self-updating processes • Easy to use • Reliable and versatile

  7. Automation of Production and Testing • Faster formulation of wide array of coatings • Fast, accurate, and quantitative testing

  8. Automation of Production and Testing • Faster formulation of wide array of coatings • Fast, accurate, and quantitative testing • Immediate data feedback to central database • Enables coatings to be produced and tested at rates > 100x conventional methods

  9. The Combinatorial Factory • Formulation of coatings • Creation of coating arrays • Preliminary screening • Optical, abrasion, and adhesion testing • Secondary screening • Weathering • Integrity evaluation • Larger scale testing to meet industry specifications

  10. Schematic of The Combinatorial Factory Capable of screening 100 to 200 coatings per day

  11. Formulation and Creation of Arrays

  12. Formulation and Creation of Arrays • Easily accomplished with robot mixing technology • Quickly create arrays with formulations of varying composition and thickness • Rates of > 1 array/2 hours • Coating and curing accomplished at rates > 1 array/hour

  13. The Array • Polycarbonate base film, 0.5-mm thick • 6x8 array of coatings • each sample is 2-5-μm thick and 10-mm in diameter • Flexible silicon rubber template to create wells

  14. Positive aspects Coating can be leveled after array creation Allows for very diverse library of coatings to be produced on substrate Spin Casting

  15. Positive aspects Coating can be leveled after array creation Allows for very diverse library of coatings to be produced on substrate Problems arise after array creation Meniscus Differential evaporation Coffee ring effect Spin Casting

  16. Spin Casting

  17. Leveling and Curing the Array • Coatings leveled via horizontal centrifuge at 2000-3000 rpms • Curing can take place separately by UV, thermal, as necessary

  18. Problems during leveling • Problems arise due to meniscus and air flow in centrifuge

  19. Problems during leveling • Problems arise due to meniscus and air flow in centrifuge • At 2000 rpms, air speeds reach up to 60 mph • Heavy air flow causes differential evaporation and coffee ring effect

  20. The Meniscus and Air Flow

  21. The Effect of Covered Wells • Cover well with permeable layer • Solvent can still evaporate • Air flow from above no longer affects samples

  22. Conquering Differential Evaporation • Hole in center of permeable layer allows solvent in center to evaporate at rate equal to that at well edges • Consistent evaporation eliminates liquid flow to well walls

  23. The Result

  24. High-Throughput Screening Primary Secondary

  25. Multilevel Performance Screening • 1st stage screening • Test optical clarity, abrasion resistance, and adhesion • Eliminates ~ 90% of samples • 2nd stage screening • Test weatherability, integrity, gloss, and surface smoothness • Rapidly identify coating samples with desired properties • Candidates for scale up • Test according to the customer’s specifications

  26. Multilevel Performance Screening • 1st stage • 100-200 samples per day • 2nd stage • ~10% of the samples • Rapidly identified materials • Candidates for scale up

  27. Conventional Methods

  28. High-Throughput Screening Primary: Optical Clarity

  29. Optical Clarity • Crucial property – clear coating on polycarbonate, needs to be able to replace glass • First screening of samples – immediately eliminate some • Corresponds to the absence of light scattering • Later screenings optimized for up to 30% haze

  30. High-Throughput Optical Clarity • Fiber optic probe – measures intensity of 360o back-scattered light

  31. High-Throughput Optical Clarity • Maximum intensity = optical clarity • Lower intensity  higher optical clarity • Relate percent haze to scattered light: • S2 = SK/(1 + 100/H) • S2 = scattered light • S = transmitted light + scattered light • K = constant, relates methods • H = percent haze

  32. High-Throughput Optical Clarity • Valid method? Yes! Correlation shown between scattered light intensity from the high-throughput method to percentage of haze of reference materials.

  33. High-Throughput Screening Primary: Abrasion Resistance

  34. Abrasion Resistance • Basic factor in durability • Caused by mechanical actions, such as rubbing, scraping, or erosion from wind and water • Related to other physical characteristics • Hardness • Cohesive and tensile strength • Elasticity • Toughness

  35. High-Throughput Abrasion Test • Samples: • 10 mm diameter • 2-5 μm thick • 8x6 arrays of 48 coatings on polycarbonate substrate • Abrasion methods; • Air blast test • Oscillating sand test

  36. High-Throughput Abrasion Test • Air Blast Abrasive Test: • 50 μm Al2O3 particles • Constant pressure and flow rate • Nozzle with 1 mm diameter opening • Sheet advanced automatically, 15 cm/min • Change distance of nozzle to coating from 2.5 to 10 cm, 1.25 cm increments

  37. High-Throughput Abrasion Test • Oscillating Sand Test • 1,000 ml sand on array in container • Oscillate container for set amount of time • Vary level of abrasion by changing time: 10 min, 20 min, 30 min

  38. High-Throughput Abrasion Test • Sample analysis: spectroscopic measurements of scattered light. • Less scattered light = better abrasion resistance.

  39. High-Throughput Abrasion Test • Spectroscopic system: • White light source • Monochromator • Selection of illumination wavelength • Light focused into fiber-optic probe

  40. High-Throughput Abrasion Test • Spectroscopic system: • White light source • Monochromator • Selection of illumination wavelength • Light focused into fiber-optic probe • Portable spectrometer • 600-grooves/mm grating blazed at 400 nm • Spectral range: 250-800 nm • Linear CCD-array detector

  41. High-Throughput Abrasion Test • Excitation wavelength set at 500 nm (0 order of monochromator) • Setup optimized for samples with up to 30% haze • Probe angle – highest change in detector response over range of measured haze • Distance from probe to coating – ideal spot size ~4-6 mm • Spectral acquisition conditions

  42. High-Throughput Abrasion Test • Minimal contributions from light directly reflected back from coating into probe • Just collect diffusively reflected portion of radiation interacting with coating surface

  43. High-Throughput Abrasion Test • Valid method? Yes! Correlation shown between the high-throughput method and the Taber abrasion method for abrasion resistance determination.

  44. Data Acquisition Programs • Programs constructed using LabView • National Instruments • Kaleidagraph • Synergy Software • Programs constructed using MatLab • The Mathworks Inc.

  45. High-Throughput Screening Primary: Adhesion

  46. Adhesion • Occurs when interfacial and intermolecular forces hold two surfaces together

  47. Adhesion • Occurs when interfacial and intermolecular forces hold two surfaces together • Measuring: corresponds to the forces or work required to terminate the adhering system

  48. Adhesion • Occurs when interfacial and intermolecular forces hold two surfaces together • Measuring: corresponds to the forces or work required to terminate the adhering system • Quantified through a micro scratch test using a blade-like indenter

  49. Adhesion Evaluation • Indenter positioned with a selected angle of attack between the front side and the coating surface Blade-like micro scratch indenter with a sharp angle between edge RE and the front side, and rounded angle γ with radius R1.

  50. Adhesion Evaluation • Indenter positioned with a selected angle of attack between the front side and the coating surface • Drawn across surface with constant or progressively increasing load Blade-like micro scratch indenter with a sharp angle between edge RE and the front side, and rounded angle γ with radius R1.