Optical Properties of Nanocomposite Films: Size-tuned vs. Shape-tuned Silver Nanoparticles

Abstract

Color change is a desirable response when designing user-friendly chemical sensors. However, when preparing colored nanocomposites sensors, it can be challenging to transfer the color from solution into films. This work demonstrates that films of various colors can be prepared by blending premade nanoparticles with poly(vinyl alcohol) (PVA); however, the color in solution differed from the color in film. While, this color discrepancy and the appearance of the films depended on how the optical properties of nanoparticles were tuned, UV-visible spectroscopy and Transmission Electron Microscopy (TEM) showed that changes in nanoparticle's morphology was not the cause of the color discrepancy. Reflecting the polydispersity of nanoparticles in solution, more homogeneous colored films were obtained by controlling the size of nanoparticles rather than their shape. This work shows how to readily prepare silver-PVA nanocomposite films of various colors, which may facilitate the design of nanocomposites intended for chemical sensing based on the optical properties of silver nanoparticles.

Color Transferability from Solution to Solid Using Silica Coated Silver Nanoparticles

“…Colored films were prepared by embedding nanoparticles in PVA using the drop cast method . In a typical preparation, nanoparticle solution was mixed in a 1:1 ratio with 10% PVA solution.…”

“…Synthesis of Silver Nanoparticles in Solutions. Colored solutions of silver nanoparticles were prepared as reported previously 11 using the simultaneous multiple asymmetric reduction technique (SMART) synthesis, where the morphology of nanoparticles is controlled by varying the amount of ascorbic acid in the presence of sodium borohydride. 22 In a typical synthesis, a 1.0 L solution of 0.18 mM silver nitrate with 0.145 mM PVP was prepared in a volumetric flask; then, aliquots of 100 mL were placed in 500 mL Erlenmeyer flasks.…”

“…In all of these works, the color of the particles in solution is not the same as the color in the solid. In some cases, this color change has been attributed to morphological changes of the nanoparticles caused by incompatibility with the environment or synthesis conditions. , Some authors have attempted to prevent these changes by protecting the metallic core with a silica shell. ,, Color changes upon embedding in a matrix can still be observed, however, even if nanoparticles preserve their shape and size or are protected with a silica shell. , …”

“…Polymer nanocomposites colored with silver nanoparticles can be obtained by embedding silver nanoparticles in a polymeric matrix. While most works obtained yellow-colored materials − or varied the color using an external stimulus, − recent work in our lab has shown that nanocomposites of various colors can be obtained by tuning the color of nanoparticles in solution and then embedding them in a polymer . In all of these works, the color of the particles in solution is not the same as the color in the solid.…”

“…12,13 Some authors have attempted to prevent these changes by protecting the metallic core with a silica shell. 12,14,15 Color changes upon embedding in a matrix can still be observed, however, even if nanoparticles preserve their shape and size 11 or are protected with a silica shell. 12,14 As a shell, silica is attractive for studies related to color changes because it prevents the aggregation of metallic cores, is optically transparent, and can be tailored to different morphologies and surface functionalities.…”