Color Tunable Poly (N-Isopropylacrylamide)-co-Acrylic Acid Microgel-Au Hybrid Assemblies

• Published in: Advanced functional materials Vol. 21; no. 3; pp. 425 - 433
• Main Authors: Sorrell, Courtney D., Carter, Matthew C. D., Serpe, Michael J.
• Format: Journal Article
• Language: English
• Published: New York WILEY-VCH Verlag 08.02.2011; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Acrylic acid; Color; Color temperature; Deposition; Etalons; Filtering; Glass substrates; Gold; Gold coatings; High temperature; Materials science; metal-polymer hybrid structures; Microgels; Modulation; multilayer materials; Optical properties; ordered assemblies; Polyisopropyl acrylamide; stimuli responsive materials; tunable optical filters
• ISSN: 1616-301X; 1616-3028; 1616-3028
• DOI: 10.1002/adfm.201001714

A new class of materials that are capable of color tunability over 300 nm with a 15 °C temperature change is introduced. The materials are assembled from thermoresponsive poly (N‐isopropylacrylamide)‐co‐acrylic acid (pNIPAm‐co‐AAc) microgels, which are deposited on Au coated glass substrates. The films are also pH responsive; the temperature‐induced color change was suppressed at high pH and is consistent with the behavior of a solution of suspended microgels. The mechanism proposed to account for the observed optical properties suggests that they result from the two Au layers being separated from each other by the “monolithic” microgel film, much like a Fabry‐Pérot etalon or interferometer. It is the modulation of the distance between these two layers, facilitated by the microgel collapse transition at high temperature, that allows the color to be tuned. The sensitivity of the system presented here will be used for future sensing and biosensing applications, as well as for light filtering applications. Color tunable etalons are fabricated by drying thermoresponsive microgels onto a thin Au film (mirror); another thin Au mirror is evaporated onto the monolithic microgel film. When the assemblies are immersed in aqueous solution, they respond to temperature by exhibiting marked shifts in reflectance wavelength. The color tunability is completely reversible and the films are extremely robust.