Combinatorial Science - Coating Screening
Coating screening can be carried out using a variety of methods depending on the goals of the specific study.
This automated system uses the hardware and software developed by First Ten Angstroms to measure the surface energy of coatings. The coating surface energy station has been modified to receive two standard 4x8 inch metal coating panels that have been prepared by the coating application station. Each of the 24 elements within a library is subjected to three water droplets and three methylene iodide (MI) droplets. The contact angle of each is measured using image analysis and the readings are averaged for both water and MI. The Owens-Wendt method is then used to calculate the surface energy of the coating patch.
Dynamic contact angle measurements are also possible with this instrument. The plot below indicates the difference between advancing and receding contact angles for water on a single coating patch. Advancing droplets are created by pumping liquid into the droplet with a fine tip glass pipette. Receding angles are then generated by pumping the liquid back out of the droplet.
Coating friction, tack, wear, and chemical resistance measurements can be performed on coatings applied to glass and metal substrates using this Symyx Tools bench top system. The essential element of this tool is a disposable steel sphere fitted to a dual axis force transducer mounted to the end of an XYZ robotic arm. The spherical probe, selected from more than 100 loaded on the deck, is then brought into contact with the coating at a specified force and moved back and forth or up and down depending on the measurement being made. Challenge liquids or lubricants can be dispensed onto the coating using a pipette tip. For wear measurements, an optical profilometer and digital camera have been installed to monitor the groove formed by the abrasive action of the probe. Substrates of the micro titer plate format can be automatically delivered to the unit using a Velocity 11 BenchCell 2xTM for unattended operation.
The Symyx Parallel DMTATM system measures the viscoelastic response of an array of 96 polymers or coatings as a function of temperature, or isothermally. Modulus, glass transition temperature (Tg) and crosslink density can be determined for individual samples.
A polymer or coating formulation is deposited onto a KaptonTM substrate and dried or cured. The thickness of each specimen is measured using a laser profilometer.
The array is then placed in the pDMTA where it is vibrated against an array of force transducers to determine viscoelastic properties as a function of temperature.
The software provides real time data viewing of the viscoelastic properties of each of the 96 samples on the KaptonTM substrate. The effect of the KaptonTM substrate is subtracted from the data, yielding the modulus-temperature relationship for the materials being tested.
A Symyx® automated pull-off adhesion system is used to determine the adhesive strength of coatings to the substrate and adhesive strength of an epoxy to a coating surface (“pseudo-barnacle” adhesion).
Aluminum studs, or “pseudo-barnacles” are glued to the surface of the coatings, 3 studs for each patch for a total of 72 measurements per experiment are performed. The adhesive is deposited by hand using a screen printing process.
The studs are pulled off the panels, one at a time in an automated fashion as the pull force is increased linearly. Force and displacement transducers record all experimental data while the software displays the data in real time. Pull forces upwards of 100 lbs can be generated with this apparatus.
The maximum force at failure is measured automatically with 3 replicates for each of the 24 coating samples in a single experiment. Results are related back to experimental parameters for screening and analysis.
An automated system for measuring color and gloss has been developed at NDSU. This system is compatible with all of the flat substrates generated by the CMRL. The on-board computer up-loads the data to a central database for easy access through a web based browser. Color measurements are made with an X-rite integrating sphere spectrophotometer while gloss measurements are made with a BYK-Gardner gloss meter reading at 3 different angles. This system is particularly useful for studying the long term effects of weathering or corrosion on paint samples since the readings are taken at precisely the same spot from day to day and month to month.
An automated dry film thickness measurement station has been developed by NDSU to measure the thickness of coatings deposited onto our array panels. The system is outfitted with a Fischerscope MMSTM system with measurement probes for both aluminum and steel substrates. The thickness data is automatically up loaded to a central database and is accessible through a web portal. This system is valuable in the long-term study of self-polishing ablative coatings since the same measurement points can be consistently read from day to day and month to month.
A workflow has been developed to assess polymer and coating surfaces for bacterial growth and removal. Coatings are deposited into modified 24-well microtiter plates. The wells are inoculated with bacteria and bacterial growth is assessed after incubation. A novel waterjet has been developed to determine the water pressure needed to remove bacterial biofilm from the coating surface. Coatings are thus screened for anti-bacterial properties as well as fouling release properties.