Faculty Advisor or Committee Member

Germano S. Iannacchione, Advisor




"A novel approach to a light scattering experiment that employs a lounge image capture assay has been developed for both static and dynamic measurement on a wide variety of samples. In this work, the 'Development and Application of an Area Recorded Generalized Optical Scattering Technique', abbreviate as ARGOS, an approach is based on the placement of a translucent screen where the scattered light, now converted to a diffuse light, is imaged as a function of time. The placement and size of the screen determines the range of scattering wave-vectors, while the time between images determines the fastest dynamic resolvable . The overall experimental stability determines the slowest dynamic resolvable and so can be made arbitrarily long. The scattering intensity is measured by a camera whose dynamic range (number of bits per pixel), resolution, and speed determines the sensitivity and accuracy of intensity of the scattered light. The system allows for an extremely well-defined scattering experiment geometry, where images may be manipulated to extract structure (i.e. average I(q)over t) and dynamics (average I(q,t) over q) for a wide range of samples(liquids and solids). A number of innovation were developed. Instead of a beam stop to block the high intensity thru-beam, a thru-beam attenuator was developed such that the exact center of the scattering geometry is determined for each image acquired. A variety of image processing algorithms were also developed to correct for dead pixels, camera response, and intensity normalization. Of particular use was the development of the root-mean-square difference(RSD) image to probe dynamic. Here, the first image is taken as the time-zero reference image and subtracted from all succeeding images where averaged over a speci ed q and plotted as a function of time revealing the build up image changes due to dynamics. The technique was validated for both static and dynamic measurements with a set ofdilute suspended latex spheres in water (sizes ranging from 0.01 to 2micro m). The static light scattering result in terms of particle radius and dimension closely matched the expected values. The dynamic light scattering results could only several the end of the dynamics of these suspended latex spheres due to Brownian motion because of the speed limitation of the camera. However, sedimentation dynamics that are much slower, were early observed. The ARGOS technique was then applied to two biological systems, the evolution of a dilute suspension of E. Coli bacteria through the life-cycle and the evolution of the same suspended bacteria but infected with the MS2 bacteria-phage virus. High temporal resolution data were obtained of the bacteria life-cycle which werecorrelated with size, structure, and dynamics that revealed potentially new insights on behavior not well understood in the literature . The MS2 infected bacteria revealed the effect of the bacteria-phage on every character of the E. Coli life-cycle. The successful development and implementation of ARGOS here has also revealed avenues to greatly improve the performance."


Worcester Polytechnic Institute

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scattering analysis, Light scattering