Polymerization in a small droplet on a superhydrophobic surface
Item
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Title
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Polymerization in a small droplet on a superhydrophobic surface
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Identifier
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d_2009_2013:a6e8f7e9ca71:12023
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identifier
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12719
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Creator
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Lin, Fang-Ju,
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Contributor
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Alan M. Lyons
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Date
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2013
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Language
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English
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Publisher
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City University of New York.
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Subject
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Polymer chemistry | droplet | heat resistance | photo-polymerization | superhydrophobic surface
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Abstract
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Droplets of fluids have been used as small volume reactors in microfluidic applications, including polymerase chain reaction, as well as synthesis of small-molecules, polymers, and gel particles. More recently, reactions within individual droplets on superhydrophobic surfaces have been studied. However, the fundamentals of polymerization reactions in a droplet on a superhydrophobic surface have not been reported. To address this issue, firstly, a temperature- and atmosphere-controlled environmental chamber was designed to maintain a constant volume of the droplet on superhydrophobic surface by insuring an equilibrium solvent vapor pressure, eliminating extraneous evaporation or condensation of water. A new technique, micro-dilatometry, was developed to measure the change in volume of the droplet in real-time as a function of photopolymerization conditions. Experimental parameters include photoinitiator concentration, UV light intensity and surface type. In this way, polymerization rate could be calculated in isolated 10 uL droplets. Droplets on a superhydrophobic surface can be easily and completely lifted off the surface with a syringe because of the weak interactions between liquid and solid surface. Because of this unique aspect of superhydrophobic surfaces, small droplets could be easily analyzed in an external instrument such as NMR or GPC. The percent conversion of monomer to polymer, calculated by micro-dilatometry, was verified by NMR for the same droplet. The molecular weight of the formed polymer could also be measured by injecting the droplet into a GPC. These results demonstrated good correlation between micro-dilatometry and NMR for percent conversions ranging from 5 - 18%. Above 18% conversion, experiments demonstrated significant deviations between micro-dilatometry and NMR. Main reason of these discrepancies is proofed to be changes in the vapor pressure of water within the droplet as the concentration of solute molecules decreased significantly during polymerization. Using the micro-dilatometry technique, the kinetics of polymerization of acrylamide was studied. The polymerization rate within isolated 10 uL droplets was found to be significantly higher than in a well-stirred vial. In addition, the molecular weight of polymers formed in droplets was found to be larger than in the well-stirred system. A hypothesis is presented to explain the higher polymerization rate and molecular weight in small isolated droplets.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Chemistry
