Document Type

Dissertation

Date of Degree

Summer 2015

Degree Name

PhD (Doctor of Philosophy)

Degree In

Chemistry

First Advisor

Christopher M. Cheatum

Second Advisor

Amanda J. Haes

Abstract

The overarching objective of the investigations discussed herein is the development of a model experimental system for surface-enhanced infrared absorption (SEIRA) spectroscopy, with potential applicability in higher order infrared spectroscopic techniques, specifically, surface-enhanced two-dimensional infrared (SE-2D IR) spectroscopy.

Theoretical predictions that accurately predict the stability of functionalized nanoparticles enable guided design of their properties but are often limited by the accuracy of the parameters used as model inputs. Hence, first, such parameterization limitations for the extended DLVO (xDLVO) theory are overcome using a size-dependent Hamaker constant for gold, interfacial surface potentials, and tilt angles of self-assembled monolayers (SAMs), which collectively improves the predictive power of xDLVO theory for modeling nanoparticle stability. Measurements of electrical properties of functionalized gold nanoparticles validate the predictions of xDLVO theory using these new parameterizations illustrating the potential for this approach to improve the design and control of the properties of functionalized gold nanoparticles in various applications.

Next, a series of experiments were conducted to elucidate the behavior of various infrared active molecules in the presence of spherical gold nanoparticles of average diameter ∼20 nm. Here, the spectroscopic anomalies, specifically the shifted vibrational frequency and the dispersive lineshape observed in the infrared spectra for SCN- in the presence of gold nanoparticles provide direct evidence of SIERA.

Nevertheless, it was evidenced that nanomaterial with plasmonic properties that extends into the infrared wavelengths are imperative in observing efficient infrared enhancements. Hence, nanomaterial indicating plasmonic properties extending into the infrared wavelengths were synthesized via a straightforward, seedless, one-pot synthesis. The gold nanostars prepared here indicated plasmonic behavior clearly extending into the near infrared, with simple plasmonic tunability via changing the buffer concentration used during synthesis.

The systematic understanding achieved here in terms of theoretical prediction of nanoparticle stability, origin of infrared spectral anomalies in the presence of nanomaterials, and the preparation of infrared plasmonic material, collectively provides a resilient framework for the further investigation of surface-enhanced infrared spectroscopic techniques including SEIRA and SE-2D IR spectroscopies.

Public Abstract

Nanoparticles are materials that are on the order of one billionth of a meter in size and particles of such small size behave in very unique ways allowing them to exhibit many properties important to industrial and scientific applications. These properties rely on the fact that the nanoparticles exist as individual structures, not combined with its neighboring particles. Hence, here we conduct modifications on an existing model such that the stability of a specific type of nanoparticle can be theoretically predicted.

Spectroscopy or the study of the interactions between light and matter is important in many chemical analyses. Metal nanoparticles are widely used to increase the efficiency of the above light - matter interactions thereby allowing to efficiently identify chemical species, determine their structure, and understand how they behave under given conditions. Here, we use gold nanoparticles to demonstrate that this interesting characteristic of metal nanoparticles can be extended into novel scientific techniques, allowing increased efficiency in identifying or even understanding chemical substances.

Preparation of competent nanoparticles for such applications is important, but at the same time challenging. Here we demonstrate a new method of preparing gold nanoparticle that are shaped in the form of stars, hence being named ‘nanostars’. The prepared nanostars demonstrate many unique, interesting, and tunable properties, suggesting their efficient applicability in many scientific applications. The overall understanding attained in the series of investigations conducted here, will be imperative in the design, preparation, and application of new and exciting forms of nanoparticles in many novel scientific applications.

Keywords

publicabstract, Nanospheres, Nanostars, SE-2D IR, SEIRA, Surface enhancement, xDLVO

Pages

xix, 158 pages

Bibliography

Includes bibliographical references (pages 147-158).

Copyright

Copyright 2015 A. K. Lahiru Anuradha Wijenayaka

Included in

Chemistry Commons

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