Information-rich High-Throughput Screening of Curing Formulations Via the Large Sample Array Calorimeter
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Information-rich High-Throughput Screening of Curing Formulations Via the Large Sample Array Calorimeter Pamela J. Stirn, Tom C. Hofelich, and Ramasamy R. Tamilarasan Dow Chemical Company, Midland, MI ABSTRACT This paper describes the use of an automated Large Sample Array Differential Scanning Calorimeter (LSA-DSC or LSA) for process optimization. The LSA was designed specifically for screening studies of multi-variable arrays where a large number of samples need to be examined simultaneously. It is ideal for kinetic evaluation of both biological and chemical reactions. The LSA can be used in either a temperature scanning (DSC) or isothermal (IMC) mode. An example where this equipment was used to optimize epoxy formulations will be presented. These formulations were prepared with high throughput techniques and evaluated using the LSA-DSC to determine the cure kinetics. INTRODUCTION Determining a formulation for an epoxy that would facilitate low temperature curing was the scope of the project. The speed of which the business could obtain these results affected their success in the marketplace. For this project a combinatorial approach was utilized to develop various formulations. The high throughput design incorporated a robot, balance, vortex/heater and linear shaker. The most critical aspect of high throughput is having an analytical instrument that can keep up with the large number of samples being prepared. The development of the high throughput technique required a large amount of the time because of its many challenges. These challenges and their solutions will be presented. The analytical technique able to measure the set of samples simultaneously will also be explained.
EXPERIMENTAL DETAILS A Cavro robotic platform was utilized for the formulation process, see Figure 1. The platform consists of two programmable robot arms, one is liquid handling with a probe arm and syringe, and the other is a custom developed gripper arm able to lift and move the LSA vials. Included on the platform was an analytical balance to weigh the components by difference. The balance takes an average of ten readings for zeroing and weighing, to allow for equilibration. The robot is programmed to move and weigh vials, and add reagents. The program reads the formulation information from an Excelï›› spreadsheet. The spreadsheet contained information such as the number of formulations, the reagent vial position, and the weight ratio of the components. A sample spreadsheet is shown in Table I. Absence of the vial position for any reagents indicated that the component was a solid and had to be added manually. The resulting weights were determined and stored in the spreadsheet.
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Figure 1: A Cavro robotic platform showing the gripper arm transporting a vial to the balance. An array of 10 amines and 16 catalysts was prepared for the epoxy curing formulations. A typical formulation was prepared as follows. A given volume of epoxy was added to LSA vials using a Cavro liquid handling robot. LSA vials were crimped sealed glass vials and
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