1. Temporal Thin Film Stability Studies Using Silver Nanoparticles
Madeline I. Vara ‘10, Nolan T. Flynn
Department of Chemistry
Wellesley College
Introduction
Nanoparticle Characterization
Silver nanoparticles (AgNPs) are of great interest for electo-optical and biotechnology application because of their novel antimicrobial, electrical and thermal properties.
Our research focuses on the formation of AgNP thin films on planar substrates, looking at functionalization of these films and their stability in water over time. Although prior research has been conducted in our lab using AuNP films, similar studies have not been conducted with AgNPs. We looked to continue stability studies using AgNPs and examined altering various steps of the thin film formation procedure
AgNP Synthetic Methods
AgNPs were characterized using both ultraviolet-visible (UV-vis) spectroscopy transmission electron microscopy (TEM).
UV-vis spectroscopy was used to give a general characterization of our nanoparticle solutions. Peaks at longer wavelengths indicate larger particles, whereas peaks at lower wavelengths indicate smaller particles.
TEM was used to take direct images of our samples, providing us with information on our AgNP size and shape uniformity and dispersity.
We synthesize our nanoparticles using general chemical reductions. We dissolve our silver salt (silver nitrate) into solution, then add a reducing agent to reduce the Ag+ to Ag0, thus allowing the formation of silver nanoparticles (AgNP).
AgNO3 + 1e- → Ag0 + NO3−
nAg0 → AgNPs
reduce
Trisodium Citrate Reduction Method
Add trisodium citrate to silver nitrate solution
Stir at 100 °C for 2 hours
Stir and let cool to room temperature
Citrate concentration affects NP size
Self-Assembled Alkanethiol Monolayer on AgNPs
Sodium Borohydride (NaBH4) Reduction Method
Add NaBH4 to silver nitrate (AgNO3) solution
Stir at room temperature for 45 minutes
Thin Film Formation and Characterization
Slides were cleaned using a piranha (3:1 H2SO4:H2O2) bath. Thin films were formed on the slides by immersion for 24 hours into solutions containing the material. Slides were first submerged into solutions of 3-aminopropyltrimethoxysilane (APTMS), which binds to the substrate and acts as a coupling agent for the AgNPs. The slides were then immersed into AgNP solutions, and then finally into solutions containing 2mM dodecanethiol (DT) for AgNP functionalization with the alkanethiol.
The quality of the slides and the films being formed was qualitatively monitored by optical flatbed scanning and quantitatively monitored through contact angle goniometry.Several variables in thin film formation that were modified included the relative concentration of coupling agent (APTMS) used, the type of slide substrate (glass, quartz, and Indium-Tin Oxide (ITO) coated slides), as well as the size of the AgNPs being deposited. Traditionally, glass slides and 0.18% APTMS have used in thin film formation procedures.
The NaBH4 reduction method produces highly uniform, monodisperse AgNPs of approximately 18 nm diameter. The citrate reduction method has yielded promising results for forming AgNPs of larger size. However, we have encountered difficulties in controlling the exact size distribution of the nanoparticles formed and in maintaining nanoparticle stability for further use thin film stability studies.
APTMS Concentration
Substrate
Conclusion
Our work has shown
We have been able to synthesize smaller AgNPs using NaBH4 reduction methods
Though more costly that glass, ITO has shown the greatest degree of thin film formation out of all of the substrates
Using 1% APTMS yielded the highest quality slides up through DT-functionalization of AgNPs
Different syntheses and/or deposition methods may need to be further investigated in order to fully study thin film stability using larger AgNPs
Thus far, results with AgNP thin films have correlated with results seen using AuNP thin films
Acknowledgments
Vachik Hacopian (BISC), Wellesley College,
Office of the Dean of Wellesley College