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Dendritic Polymers as Biocompatible Oil Spill Dispersants: Effectiveness and Mechanisms with Crude Oil Ying Tu Masters Thesis Defense Thesis Committee: Dr. David Ladner (Advisor) Dr. David Freedman Dr. Tanju Karanfil 1

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Outline Background and Motivation Literature Review and Hypothesis Experiment Methodology Results and Discussion Conclusions and Recommended future work 2

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Oil spill dispersants 3 A U.S. Air Force Reserve plane sprays Corexit over the Deepwater Horizon oil spill in the Gulf of Mexico (http://en.wikipedia.org/wiki/Corexit) BP Deepwater Horizon oil rig ablaze (Photo: U.S. Coast Guard)

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Dendritic polymers 4 Dendrimers Branch Out, Chemical & Engineering News, June 13, 2005, Volume 83, Number 24, pp. 30-36. Dendritic polyethylenimine is a highly functional aliphatic polyamine with a globular structure. (http://www.hyperpolymers.com/prodinf.html) Dendrimer terminal groups NH OH o NH 2 NH OH o Amino Amidoethanol Succinamic Acid PAMAM HY-PEI Same chemical structure but different molecular weight; 1.2, 1.8, 10, 70, 750 kDa.

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Model compounds study and hypothesis 5 N.K. Geitner, P. Bhattacharya, M. Steele, R. Chen, D.A. Ladner, and P.C. Ke*, Understanding Dendritic Polymer-Hydrocarbon Interaction for Oil Dispersion, RSC Advances 2 (2012), 9371. C16 partitioned into polymer C16 capping by polymer C16 end to end interaction Hydrophobic interaction C16-polymer complexation Dendritic polymers are capable of encapsulating both polyaromatic and linear hydrocarbons

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A few oil/water emulsion stabilization mechanisms 6 Venkataraman, P. & Tang, J. (2013) Attachment of a Hydrophobically Modified Biopolymer at the OilWater Interface in the Treatment of Oil Spills. Applied Materials and Interfaces: 35723580. Ye, A., Zhu, X. & Singh, H. (2013) Oil-in- water emulsion system stabilized by protein-coated nanoemulsion droplets. Langmuir: the ACS journal of surfaces and colloids 29: 1440310.

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Objectives Test and verify the hypothesis that dendritic polymers can disperse oil Develop methods to adequately characterize the effectiveness of the dendritic polymers Gain a fundamental understanding of the interactions of dendritic polymers with crude oil 7

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8 Small vials trialmethod development and preliminary results Dispersant to oil ratio (DOR) 0.02 Mixing time 30 min Mixing speed 200 rpm Settling time 15 min

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Higher volume effectiveness test 9 Sample preparation 120 ml artificial seawater 100 l crude oil Dispersant with DOR 0.02 Mixing and Settling Mixing at 200 rpm for 30 min Settling for 15 min in separatory funnel Drain each 30 ml water column segment into centrifuge tubes Oil extraction and analysis Add 10 ml dichloromethane (DCM) in each 30 ml mixture UV spectrophotometer at 340 nm 105 ml 45 ml 75 ml 15 ml

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HY-PEI dispersion effectiveness -effects of molecular weight 10

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HY-PEI dispersion effectiveness -effects of molecular weight 11 Larger polymers were more effective, but on an equal-mass basis increasing size gave diminishing returns Further analysis confirms that larger size polymers entrap more oil molecules.

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PAMAM dispersion effectiveness -effects of surface charge 12 Positively charged dendrimers were the most effective dispersants

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Interfacial tension test 13 Video frames of oil drop shapes varied with time. 0.0125g/L HY-PEI 10kDa at time of 20 s, 70 s and 115 s. Needle diameter is 0.632 mm. As the age of drop increasing, the drop shapes became elongated. Oil phase: crude oil only Water phase: dispersant solution prepared with artificial seawater at concentrations of 0.1, 0.05, 0.025 & 0.0125 g/L Record videos from 0 to 120 s

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14 Crude oil only HY-PEI 70kDa (DOR 0.02) Corexit (DOR 0.02)

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Dynamic interfacial tension 15 Data were recorded for 120 seconds or until the drop separated from the needle. The 100 mg/L data are not shown for some materials because drops were not sufficiently stable. For clarity, symbols are shown on only the final data point of each series.

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Oil droplet size distribution Dynamic light scattering Coulter counter Microscope image analysis 16

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Dynamic light scattering 17 Polymer Designation HY-PEI 1.2kDa HY-PEI 1.8kDa HY-PEI 10kDa HY-PEI 70 kDa HY-PEI 750kDa MW (g/mol)1200180010,00070,000750,000 Polymer diameter (nm)2.002.056.0910.9632.03 Oil drop size (nm)1.96 x 10 4 1.28 x 10 4 674681725 Polymer size

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Coulter counter & Microscope imaging 18 Size distribution graph was obtained by analyzing 20 microscope images in a Matlab script Microscope pictures of oil drops taken under 40x magnification; many drops are out of focus. Diluted oil-water-dispersant mixture measured by Coulter counter; most oil drops smaller than 7 m.

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Conclusions Method development Small volume resulted in significant variability in effectiveness results. High volume gave more reproducible results. A conceptual model of oil-dendritic polymer interactions was developed. Hybrid Pickering surfactant mechanism. Other possibilities exist. Positively charged dendrimers were more effective than the neutral or negatively charged dendrimers. This suggests an adsorption, charge reversal mechanism. 19

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Conclusion 20 http://schema-root.org/technology/chemical/agents/dispersants/ Gong, Y., Zhao, X., Cai, Z., OReilly, S. E., Hao, X., & Zhao, D. (2014). A review of oil, dispersed oil and sediment interactions in the aquatic environment: influence on the fate, transport and remediation of oil spills. Marine Pollution Bulletin, 79(1-2), 1633. Surfactant mechanism Pickering emulsion mechanism Our mechanism: hybrid Pickering-surfactant

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Recommended future studies Use equal molar ratios on high volume effectiveness tests Examine the polymer with equal charge but different surface functional groups Further develop oil droplet size measurement techniques 21

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Acknowledgements 22 Thanks to Dr. Ladner for all the instruction and guidance kindly provided during this research Thanks to Dr. Freedman and Dr. Karanfil for helping me with thesis writing Thanks to our coworkers Nick Geitner, Dr. Ding from Clemson Physics and Astronomy Thanks to EPA Thanks to our group members Erin Partlan, Mengfei Li, Muriel Steele, Peng xie for helping me with experiments Thank you all audience for coming to my thesis defense RD835182