Flexible and Robust 2D Arrays of Silver Nanowires Encapsulated within Freestanding Layer-by-Layer Films

• Published in: Advanced functional materials 2006-10, Vol.16 (15), p.2024-2034
• Main Authors: Gunawidjaja, R., Jiang, C., Peleshanko, S., Ornatska, M., Singamaneni, S., Tsukruk, V. V.
• Format: Article
• Language: English
• Subjects: Arrays; Layer-by-layer assembly; metal; Nanowires; Nanowires, metal; Polymer nanocomposites; Silver; Thin films
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200600430

Freestanding layer‐by‐layer (LbL) films encapsulating controlled volume fractions (ϕ = 2.5–22.5 %) of silver nanowires are fabricated. The silver nanowires are sandwiched between poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS) films resulting in nanocomposite structures with a general formula of (PAH/PSS)10PAH Ag(PAH/PSS)10PAH. The Young's modulus, toughness, ultimate stress, and ultimate strain are evaluated for supported and freestanding structures. Since the diameter of the nanowires (73 nm) is larger than the thickness of the LbL films (total of about 50 nm), a peculiar morphology is observed with the silver nanowires protruding from the planar LbL films. Nanowire‐containing LbL films possess the ability to sustain significant elastic deformations with the ultimate strain reaching 1.8 %. The Young's modulus increases with increasing nanowire content, reaching about 6 GPa for the highest volume fraction, due to the filler reinforcement effect commonly observed in composite materials. The ultimate strengths of these composites range from 60–80 MPa and their toughness reaches 1000 kJ m–3 at intermediate nanowire content, which is comparable to LbL films reinforced with carbon nanotubes. These robust freestanding 2D arrays of silver nanowires with peculiar optical, mechanical, and conducting properties combined with excellent micromechanical stability could serve as active elements in microscopic acoustic, pressure, and photothermal sensors. A planar 2D array of silver nanowires is encapsulated between polymer layers by a layer‐by‐layer assembly process, yielding novel freestanding polymer nanocomposite membranes. These films exhibit a filler reinforcement phenomenon due to the presence of the silver nanowires, as suggested by the membrane response during buckling and bulging experiments shown in the figure. These robust elastic membranes could potentially serve as active elements in sensing devices due to their characteristic optical and mechanical properties.