Document Type

Thesis

Date of Degree Completion

Spring 2016

Degree Name

Master of Science (MS)

Department

Chemistry

Committee Chair

Dion Rivera

Second Committee Member

Anthony Diaz

Third Committee Member

Yingbin Ge

Abstract

Indicator inks are an important part of the continued consumption of packaged goods. This thesis is focused on understanding the kinetics and reaction mechanism for a unique indicator ink that is based upon the oxidation of indigotetrasulfonate (ITS) encapsulated in the polyelectrolyte poly(diallyldimethylammonium chloride) (polyDADMAC). Sodium bisulfite (NaHSO3) was used as the initial oxygen scavenger and to drive the reduction of the ITS. Studies were predominantly done in solution phase through the dilution of the ink systems. Fluorescence spectroscopy was the primary method used to determine the kinetic decay rates and interaction between the ITS dye molecules and the polyDADMAC. The reduced form of the ITS displayed a significant fluorescence output compared to the oxidized form, making fluorescent studies a very selective and sensitive method for characterization. Inks with different concentrations of polyDADMAC or NaHSO3, and constant concentrations of ITS, were studied at various temperatures in order to gain an understanding of the rate and activation energy of the reaction. Ink solutions consisted of either 4.9%, 9.8% or 14.7% polyDADMAC iv concentrations and 2.04x10-3 mol, 4.08x10-3 mol or 6.13x10-3 mol NaHSO3 amounts. Results indicate that two separate kinetic regimens exist for the oxidation of the dye. The initial decay occurs over a 6 minute time scale while the slower decay take place after the initial oxidation has been completed. The initial oxidation has been attributed to ITS molecules on the outside of the macromolecular complex, and longtime oxidation has been attributed to ITS molecules encapsulated inside the complex. It was found that the energy barriers for the reaction were consistent across dilution factors, indicating that the complex was not breaking apart over the time period of the experiments. When the amount of NaHSO3 was varied, the highest activation energy was seen in the lowest concentration. This suggests that the removal of competing charges for the positively charged polyDADMAC induced stronger electrostatic interaction between the remaining ITS and NaHSO3 molecules. When NaCl was introduced to the system, the energy barrier decreased significantly, indicating that the Na+ and Cl- ions were breaking apart the macromolecular complex.

Available for download on Tuesday, October 26, 2021

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