The Materials Characterization Laboratory (MCL) was used for the following abstracts:
“Determining Ligand Induced Charge Transfer Effects on Quantum Dots,” Cale Bowman, Master of Science in Chemistry Candidate
Quantum dots (QDs) are nanometer-sized semiconductors that boast size tunable optical properties that differ from their corresponding bulk material. The tunable nature of the QD band gap allows a range of possible absorption and fluorescence bands, which make QDs ideal for light harvesting applications such as photovoltaics and light emitting applications such as light emitting diodes (LEDs), biosensing, and lasers. The potential for QD devices has not been fully realized yet due to an incomplete knowledge of ligand-QD surface interactions and charge carrier dynamics. In this project, steady state photoluminescence (PL), time-resolved photoluminescence (TRPL) and isothermal titration calorimetry (ITC) techniques are used to study the interaction of different bis(thioether)silane (R2BtsMe) quenching ligands as they are introduced into colloidal CdSe core QD systems. Models used for the steady state PL data were derived from an independent binding site model assuming a static quenching regime supported by TRPL findings. ITC data was fit using the independent binding site model, and yields for Et2BtsMe a site association constant, KL, of 20 M-1 determined from the PL model. There are limits to the ITC, however the data does show some promise toward the usefulness of this technique to directly characterize the thermodynamics of a ligand-QD system, which is similar to an average KL of 24.5 M-1.
"Effects of Weathering on Performance of Intumescent Coatings for Structure Fire Protection in the Wildland-Urban Interface," Babak Bahrani, Master of Fire Protection and Administration
The objective of this study was to investigate the effects of weathering on the performance of intumescent fire-retardant coatings on wooden products. The weathering effects included primary (solar irradiation, moisture, and temperature) and secondary (environmental contaminants) parameters at various time intervals. Wildland urban interface (WUI) fires have been an increasing threat to lives and properties. Existing solutions to mitigate the damages caused by WUI fires include protecting the structures from ignition and minimizing the fire spread from one structure to others. These solutions can be divided into two general categories: active fire protection systems and passive fire protection systems. Passive systems are either using pre-applied wetting agents (water, gel, or foam) or adding an extra layer (composite wraps or coatings). Fire-retardant coating is a passive fire protection method that can be divided into impregnated (penetrant) and intumescent systems. Intumescent coatings are easy to apply, economical, and have a better appearance in comparison to the other passive fire protection methods, and are the main focus of this study. There have been limited studies conducted on the application of intumescent coatings on wooden structures and their performance after long-term weathering exposure. The main concerns of weathering effects are: 1) the reduction of ignition resistance of the coating layer after weathering; and 2) the fire properties of coatings after weathering since coatings might contribute as a combustible fuel and assist the fire growth after Three intumescent coatings were selected and exposed to natural weathering conditions in three different time intervals. Two types of tests were performed on the specimens: a flammability test consisted of a bench-scale performance evaluation using a Cone Calorimeter, and a thermal decomposition test using Simultaneous Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) method (also known as SDT). For each coating type and weathering period, three different radiative heat flux levels were used in the flammability tests. Data obtained from the tests, including flammability and thermal properties, were gathered, analyzed, and compared to non-weathered specimens. The results revealed visible effects of weathering on pre (and up to)-ignition flammability and intumescent properties, especially decreases in Time to Ignition (TTI), Time to Form Intumescent (tintu.), and Intumescent Height (Hintu.) values in weathered specimens. These results validated that ignition resistance of the coating layers decreases according to weathering exposure. On the other hand, the obtained results from weathered specimens for the post-ignition flammability properties, especially Peak Heat Release Rate (PHRR) and Effective Heat of Combustion (EHC) did not show a significant difference in comparison to the non-weathered samples. These results did not support the second concern, and consequently the coating layer did not act as a combustible fuel in the weathering period.