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Materials Science at Oregon State University

Graduate Student Seminars - Sean Smith and Dmytry Khvostenko

Date: Thursday, Mar 1st
Presenter: Sean Smith and Dmytry Khvostenko, OSU Materials Science


Sean Smith abstract:
Atomic Layer Deposition Coated Cellulose Nanocrystal Aerogels

Cellulose nanocrystal aerogels are a renewable material with a unique microstructure and impressively high mechanical properties, making them attractive as a potential low cost renewable alternative for fiber reinforced polymers with potential applications such as plastic casings for cell phones and laptops. Unfortunately, the sensitivity of cellulose aerogels to temperature and oxygen limits their ability to be incorporated into polymers which require high temperature processing (>200 C) in oxygen containing environments. Atomic layer deposition (ALD) allows surface limited deposition of highly uniform and conformal thin films of inorganic oxides over high aspect ratio porous and large surface area structures. Thin ALD Al2O3 coatings have been shown to make effective oxygen and water permeation barriers. In this work, we form a hybrid organic/inorganic nanocomposite by conformally coating cellulose aerogel scaffolds with a thin layer of oxide. Using tri-methyl aluminum and water, a thin layer of Al2O3 was coated onto a cellulose aerogel produced from wood. Energy dispersive x-ray spectroscopy indicates the depth of penetration of Al2O3 into the aerogel. Thermogravimetric analysis is used to discover if cellulose nanocrystal aerogels coated with Al2O3 by ALD have improved temperature and oxidation resistance, which should allow for an extended processing window for incorporation of cellulose nanocrystal aerogels into polymers. It is anticipated that the hard, wear-resistant Al2O3 coating should result in a nanocomposite with improved mechanical properties, increased allowable processing temperature and improved barrier properties.

Dmytry Khvostenko abstract:
Effect of Bacteria on Mechanical Properties of Dental Composites

One problem in restorative dentistry is bacterial biofilm development at the tooth-filling interface which can lead to demineralization of tooth tissue and secondary caries. Furthermore, bacterial exposure may also be deleterious to the composite mechanical properties. Bioactive glass (BAG) added as an antimicrobial agent may help mitigate this problem and enhance composite durability. In phase I of this study fatigue crack growth, fracture toughness and 3-point beam bending experiments are being performed on bulk composite samples after two different soaking treatments: 1) 24 hours in distilled water and 2) 60 days in trypticase soy agar broth with streptococcus mutans bacteria. BAG containing composite behavior will be compared to a commercial composite (Heliomolar). In phase II, the issue of demineralization of marginal tooth structure will be examined by in-vivo fatigue testing of tooth samples restored with BAG containing composites to assess the effect of combined mechanical loading and exposure to bacteria.