Physical characterization of thin films and lung surfactant systems

Friction is something that affects our everyday life, but a phenomenon that is not well understood at the molecular level. Previous work has shown that fatty acid Langmuir-Blodgett thin films are molecularly smooth surfaces and a perfect candidate for the study of molecular scale friction. The natural defects of the fatty acid films provided a unique look at friction properties. The number of layers in the film affects the friction as well as the chain length. Odd chained fatty acids have a higher friction than the even chained fatty acids, due to the more disordered packing of the odd-chained tails.A major portion of the friction study was to calibrate the AFM and determine its usefulness in molecular scale friction studies. Many calibration methods were explored and one was found to be suitable for quantitative friction. This method uses the resonance frequency of the cantilever to calculate the spring constants of the cantilever. Even though the cantilever can be evaluated to a sufficient degree, I feel the AFM is not a suitable instrument for quantitative friction. Noise and data inconsistencies do not allow for data to be compared from experiment to experiment. The AFM is a useful tool in comparing the frictional properties of 2 surfaces within the same sample.Another section of my work employed AFM to investigate the collapse and recovery of lung surfactant films. Lack of proper lung surfactant (LS) function is a serious condition known as respiratory distress syndrome (RDS). RDS is a potentially fatal condition that arises from premature birth or acute lung injury. There is a need for artificial replacement LS due to the high cost of the natural surfactants and inconsistency of the natural mixtures. Over the course of my research, I investigated the biophysical properties of LS in order to help design better artificial replacement LS. The main property we investigated was the collapse and recovery of the LS that would occur curing a normal breathing cycle. My research has led to a greater understanding of LS collapse and recovery mechanisms and to more standardized testing of LS properties.