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

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.

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

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

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

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

• Faster formulation of wide array of coatings
• Fast, accurate, and quantitative 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

• 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

Capable of screening 100 to 200 coatings per day

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

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

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

Spin Casting
• 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

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

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

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

The Meniscus and Air Flow

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

• 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

The Result

High-Throughput Screening
Primary
Secondary

• 1 st stage screening
• Test optical clarity, abrasion resistance, and adhesion
• Eliminates ~ 90% of samples
• 2 nd 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

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

Conventional Methods
Property
Optical Clarity
Measurement Method
% Haze (ASTM D1003)
Abrasion Resistance Taber Abrasion (ASTM D1044)
Adhesion Crosshatch Adhesion (ASTM 3359)
Weatherability Accelerated Weathering (ASTM G26)

High-Throughput Screening
Primary: Optical Clarity

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

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

High-Throughput Optical Clarity
• Maximum intensity = optical clarity
• Lower intensity  higher optical clarity
• Relate percent haze to scattered light:
• S
2
= SK/(1 + 100/H)
• S
2
= scattered light
• S = transmitted light + scattered light
• K = constant, relates methods
• H = percent haze

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.

High-Throughput Screening
Primary: Abrasion Resistance

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

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

High-Throughput Abrasion Test
• Air Blast Abrasive Test:
• 50 μm Al
2
O
3 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

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

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

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

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

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

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

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

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

High-Throughput Screening
Primary: Adhesion

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

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

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

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.

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.

Adhesion Evaluation
• Simultaneous measurements of indenter-surface interactions taken to detect the critical load
• Mechanical
• Acoustical
• Electrical
Blade-like micro scratch indenter in the direction of arrow A in previous figure, with the front attack angle, α, and the back attack angle, β. Arrow B shows the direction of movement.

Adhesion Evaluation
• Simultaneous measurements of indenter-surface interactions taken to detect the critical load
• Mechanical
• Acoustical
• Electrical
• Characterize scratch and adhesion resistance
Blade-like micro scratch indenter in the direction of arrow A in previous figure, with the front attack angle, α, and the back attack angle, β. Arrow B shows the direction of movement.

Adhesion Evaluation
• Tungsten-carbide indenter
• Hard
• Conductive (measure electric contact resistance)
• No problems with stress in substrate

Adhesion Evaluation
• Tungsten-carbide indenter
• Hard
• Conductive (measure electric contact resistance)
• No problems with stress in substrate
• Works for clear, non clear, plastic, and metal substrates
• Works for multi-layer coating systems

High-Throughput Screening
Secondary: Weathering

• Similar to current method used by PPG
Key Components:
• Weatherometer
• Automated measurement system

• Sample: 8x6 arrays
• Weathering test
• Weatherometer equipped with Xenon
Lamp with inner and outer filters

• Sample: 8x6 arrays
• Weathering test
• Weatherometer equipped with Xenon
Lamp with inner and outer filters
• Weather cycle consists of:
• 160 min of light (air temp. 45 o C, black panel temp. 70 o C, 50% relative humidity)
• 5 min dark and 15 min of dark and water spray (air temp. 20 o C, 100% relative humidity)

• Weatherometer: accelerates process to approximately 8-fold over that in Miami,
FL.

• Weatherometer: accelerates process to approximately 8-fold over that in Miami,
FL.
• Samples must be subjected to at least
2000 kJ/m
2 at 340 nm of UV exposure in the weatherometer for sufficient weathering

• Weatherometer: accelerates process to approximately 8-fold over that in Miami,
FL.
• Samples must be subjected to at least
2000 kJ/m
2 at 340 nm of UV exposure in the weatherometer for sufficient weathering
• Automated measurement system – generates quantitative data to database.

High-Throughput Screening
Secondary: Integrity

• Yellowness index (YI) measurements
• Deuterium-halogen light source, transmission probe, and portable spectrometer
• Measured over spectral range from 250-800 nm
• Calculates YI value from absorbance values in 400-500 nm range

• Yellowness index (YI) measurements
• Deuterium-halogen light source, transmission probe, and portable spectrometer
• Measured over spectral range from 250-800 nm
• Calculates YI value from absorbance values in 400-500 nm range
• Higher absorbance values  higher yellowness index values

Integrity Evaluation
• Integrity
Measurements
• Halogen 60-W lamp uniformly illuminates the array
• CCD detector collects images of individual coatings for evaluation
• LABView used for image analysis
Spectroscopic system used for YI and integrity evaluation

Integrity Evaluation
• Images of modes of degredation
• A) Good condition
• B) Crack formation
• C) Void formation
• D) Delamination
• after 1738 kJ/m2 exposure

High-Throughput Screening
Secondary: Gloss, Surface Smoothness

Gloss
• Gloss: specular, or mirror-like, reflection of white light from a surface
• White light source is filtered  spectrum similar to the response of the human eye
• Hand-held gloss meters are used with flat and curved surfaces for determining the surface finish of polymer products and painted surfaces for quality control purposes

Gloss
• Gloss meters provide quantitative data on the uniformity and quality of surface treatments
• Are relatively insensitive to vibrations.

Surface Smoothness
• Surface topography contributes mechanical adhesion
• Statistical parameters are obtained from the surface profiles

Surface Smoothness
• Surface topography contributes mechanical adhesion
• Statistical parameters are obtained from the surface profiles
• Most common parameters used:
• R a
= average roughness deviation
• R q
= root mean square roughness deviation
• (equations 1 and 2)
Eqn 1: Eqn 2:

Surface Smoothness
• Non-contact (or optical) profilometers (laser triangulation systems and optical interferometers) measure 3-D surface topography and roughness.
• Surface reflectivity measured with a reflectometer.
• Beam of light (either filtered white light as used for gloss meters or laser) projected onto the target surface at a specific angle
• Amount of light reflected at the same angle is measured.

Surface Smoothness
• Surface roughness causes incident light to be scattered at angles other than that of specular reflection  scatter increases with roughness.
Schematic of surface reflectivity measurement.

Other Considerations
Laser Induced Decohesion Spectroscopy
(LIDS) & Multi-Lens Combinatorial
Adhesion Test (MCAT)

• Possible method of adhesion evaluation
• Photothermal ablation is directed onto the sample
• Produces an internal pressure between the clear coating and a non-clear coating or substrate

• Possible method of adhesion evaluation
• Photothermal ablation is directed onto the sample
• Produces an internal pressure between the clear coating and a non-clear coating or substrate
• Internal pressure creates a blister at the transparent/nontransparent interface
• The blister's internal pressure depends on the laser pulse energy

LIDS
• Blister expands radially into unablated regions, causing sample to fail at a critical pressure
• Measure of curvature, radius, and thickness of the blister  determine the critical pressure
• Critical internal pressure used to quantify adhesion strength

• Developed to measure adhesion across a library in a high throughput fashion
• Utilizes an array of microlenses to conduct adhesion measurements across a sample

MCAT
• The contact area between the array and the substrate is visualized with a Leica
DM IRE2 inverted microscope and measured with Image Pro software
• Labview software is used to record the actuator position and load data during an experiment

MCAT
• Multi-lens arrays may be fabricated to contain anywhere from 100 up to 1000 or even 8100 individual lenses over an area of 1 cm 2

Draw backs for MCAT
• The volume of data collected during each evaluation of a new sample library

Summary

High-Throughput Process
• Application: Robot technology and spin casting to create 6x8 arrays of coating samples
• Spectroscopic determination of optical clarity and abrasion resistance
• Microscratch test with blade-like indenter for adhesion quantification

High-Throughput Process
• Weathering in xenon arc weatherometer
• Spectroscopic determination of yellowness index and coating integrity

High-Throughput Process
• Weathering in xenon arc weatherometer
• Spectroscopic determination of yellowness index and coating integrity
• Quantification of gloss and surface smoothness
• Self-updating computer database

• Automated, reliable processes
• Quantitative analysis
• Comprehensive database

• Automated, reliable processes
• Quantitative analysis
• Comprehensive database
• Test more samples in shorter period of time
• Minimize cost per sample
• Better coatings, faster!

GE’s results
• Combinatorial factory capable of preparing and evaluating ~100-200 coatings/day (2-4 arrays).
• Productivity improvement of at least 10x!
• Measurement throughput improvement of at least 20x!
• (same number of chemists!)