Ali R. Mehrabi

The development of combinatorial chemistry methods for coating development: I. Overview of the experimental factory

Abstract Combinatorial chemistry has proven to be a valuable tool for the development of new compounds. The combinatorial methodology is well suited to the development of complex, multicomponent materials that, typically, require extensive experimentation for their development. As a result, coating development appeared to be a good candidate for the application of the combinatorial methodology. A “combinatorial factory” capable of preparing and testing over 100 coatings per day has been developed. The components of the factory consist of: (1) an automated system to prepare liquid coating formulations; (2) a novel coating application process capable of making high density arrays of coatings of controlled thickness; (3) curing of the coating arrays either thermally or with UV light; (4) testing of the coatings using newly developed high throughput screening methods; and (5) a data handling process to quickly identify the most promising coatings produced. Various aspects of the application of the combinatorial methodology to coating development are described.

High-throughput measurement of polymer film thickness using optical dyes

Optical dyes were added to polymer solutions in an effort to create a technique for high-throughput screening of dry polymer film thickness. Arrays of polystyrene films, cast from a toluene solution, containing methyl red or solvent green were used to demonstrate the feasibility of this technique. Measurements of the peak visible absorbance of each film were converted to thickness using the Beer–Lambert relationship. These absorbance-based thickness calculations agreed within 10% of thickness measured using a micrometer for polystyrene films that were 10–50 µm. At these thicknesses it is believed that the absorbance values are actually more accurate. At least for this solvent-based system, thickness was shown to be accurately measured in a high-throughput manner that could potentially be applied to other equivalent systems. Similar water-based films made with poly(sodium 4-styrenesulfonate) dyed with malachite green oxalate or congo red did not show the same level of agreement with the micrometer measurements. Extensive phase separation between polymer and dye resulted in inflated absorbance values and calculated thickness that was often more than 25% greater than that measured with the micrometer. Only at thicknesses below 15 µm could reasonable accuracy be achieved for the water-based films.

Combinatorial Study and High-Throughput Screening of Transparent Barrier Films using Chemical Sensors

The combinatorial study of materials has already proven its value in the areas of biotechnology [1] and the discovery of medicinal compounds [2, 3]. More recently, this methodology has moved into applications such as discovery of organometallic catalysts with special activity [4], optimization of polymer processing [5], and composite design [6]. The primary advantage of the combinatorial technique is the speed at which different materials can be synthesized, formulated, and tested for particular application [sometimes referred to as high-throughput screening (HTS)]. In addition to speed, the amount of material needed for a combinatorial study is far less than that required for conventional methods, which makes combinatorial material discovery more affordable when the materials are expensive. The need for speed in the combinatorial science magnifies the necessity for automation of different steps in the material discovery process. Consequently, a tremendous effort is focused on automating the formulation, synthesis, and screening steps in discovering new materials. Many of these methods are applicable to the screening of any type of functional material, while others are targeted for specific functionality in a particular area of application.

Combinatorial Study and High Throughput Screening of Transparent Oxygen and Moisture Barrier Films

High throughput screening methods for evaluating oxygen and moisture barriers are described. The screening methods are based on the change in a certain optical property, such as absorbance or fluorescence, due to a chemical reaction with oxygen gas or water vapor. The results of these measurements for several cases are presented and their advantages and disadvantages are discussed.