pH-Gated Porosity Transitions of Polyelectrolyte Multilayers in Confined Geometries and Their Application as Tunable Bragg Reflectors

Abstract

Polyelectrolyte multilayers with alternating porous and fully dense regions have been assembled from poly(acrylic acid) (PAA), poly(allylamine hydrochloride) (PAH), and poly(sodium 4-styrenesulfonate) (SPS) in appropriate combinations. The porous zones were developed postassembly via immersion of the heterostructure film into an aqueous acidic medium followed by rinsing in deionized water. Properly assembled PAH/PAA regions exhibit a reversible, pH-gated nanoporosity transition while PAH/SPS regions remain unchanged upon treatment at low pH. The application of these structures as one-dimensional dielectric mirrors and vapor sensors has been investigated. Organic liquid crystal molecules were also successfully loaded selectively into the nanoporous regions via a capillary force driven wicking action. Potential applications for drug delivery and as Bragg stacks with tunable refractive index layers are also discussed.

Bottom-up assembly of photonic crystals

“…The first generation of optical-quality LbL structures with photonic properties surfaced from polyelectrolyte multilayers assembled from poly(acrylic acid) (PAA)/ poly(allylamine hydrochloride) (PAH) and PAA/poly(sodium 4-styrenesulfonate) (SPS) layers showing alternating porous and dense regions induced by a reversible, pH-gated nanoporosity transition in the PAA/PAH layers. 79 Subsequently, Cohen and co-workers demonstrated a photonic signature in TiO 2 /SiO 2 nanoparticle-based systems assembled by polyelectrolyte-assisted LbL deposition, followed by calcination of the films to remove the polymer components. 80 However, as compared to spin-and dip-coating protocols, fabrication of one high and low RI layer requires the deposition of about 20 nanoparticle/polymer bilayers owing to their small size of about 3-4 nm after calcination.…”

Stacking the Nanochemistry Deck: Structural and Compositional Diversity in One‐Dimensional Photonic Crystals

“…[38] The potential of polyelectrolyte multilayer systems exhibiting pH-gated nanoporosity and their use as dielectric mirrors for vapor sensing has been demonstrated in a comprehensive study by Rubner and co-workers. [39] The first example of a solventvapor tunable hybrid organic-inorganic Bragg mirror was recently fabricated by chemical vapor deposition of alternating layers of titania and poly(2-hydroxyethyl methacrylate). [40] Along these lines, our group is currently extending the scope of materials and assembly protocols suitable to introduce specific sensitivity and functionality into hybrid hydrogel-based Bragg mirrors.…”

Dielectric function of two-phase colloid–polymer nanocomposite

“…Nanocomposite materials consisting of noble-metal colloids in polymer matrices have huge potential for applications as surface coatings, [1][2][3] for biomedical devices as implants 4,5 or drug delivery, 6,7 and in optoelectronic devices. 8,9 The collective excitation of electrons at the colloid-surface determines the characteristic (optical)…”