LBL Assembled Laminates with Hierarchical Organization from Nano- to Microscale: High-Toughness Nanomaterials and Deformation Imaging

Abstract

Layer-by-layer assembly (LBL) can generate unique materials with high degrees of nanoscale organization and excellent mechanical, electrical, and optical properties. The typical nanometer scale thicknesses restrict their utility to thin films and coatings. Preparation of macroscale nanocomposites will indicate a paradigm change in the practice of LBL, materials manufacturing, and multiscale organization of nanocomponents. Such materials were made in this study via consolidation of individual LBL sheets from polyurethane. Substantial enhancement of mechanical properties after consolidation was observed. The resulting laminates are homogeneous, transparent, and highly ductile and display nearly 3x higher strength and toughness than their components. Hierarchically organized composites combining structural features from 1 to 1 000 000 nm at six different levels of dimensionality with a high degree of structural control at every level can be obtained. The functionality of the resulting fluorescent sandwiches of different colors makes possible mechanical deformation imaging with submicrometer resolution in real time and 3D capabilities.

Controlled loading and release of methylene blue from LbL polyurethane/poly(acrylic acid) film

“…It should be mentioned that when exposed to the MB solutions in the pH range 5.0–9.0, films swelled and had a cotton‐like appearance (pictures not shown). The film was strongly hydrated due to quaternary ammonium groups in the side chains of PU, and a low crosslinking density between hydrophilic groups along the backbone of PU and PAA.…”

“…PAA is one of the most popular weak polyelectrolytes for the fabrication of LbL multilayer films. Kotov's group found that PU/PAA polyelectrolyte combination exhibits exponential layer‐by‐layer (e‐LbL) growth and displays exceptional mechanical properties . However, to the best of our knowledge, the controlled loading and release of drug in the film by a change in ionic strength or pH value in solution have not been reported.…”

Porous Materials with Tunable Structure and Mechanical Properties via Templated Layer-by-Layer Assembly

“…[6][7][8][9][10] The total thickness of an LbL assembled film is determined by the number of times an alternating deposition cycle of anionic and cationic species is repeated, 11,12 but the nano-to microscale thickness per deposition cycle typical for LbL assembly is a major limitation of the technique and an impediment to utilizing the resulting materials for macroscale applications. 13 LbL assembly of conformal coatings onto three-dimensional porous templates, such as foams, colloidal crystals, and hollow tubes has been implemented for a variety of applications, [14][15][16][17][18][19] but these studies have largely focused on modifying the surfaces of these materials rather than altering the porous structure and bulk mechanical behavior. In this work, a polymer nanoclay composite coating is deposited onto open-cell foam templates using LbL assembly, emulating a general strategy that is used to produce porous materials from thin films.…”

Layer-by-Layer Polyelectrolyte Deposition: A Mechanism for Forming Biocomposite Materials

“…19–22 Recent advances in multilayer assemblies have shown that the method is flexible and can be expanded to the processing of hollow nanospheres and capsules, which are useful as drug delivery vehicles 23–29 and contrast agents for magnetic resonance imaging 30 , as well as to create hierarchically organized assemblies that can yield robust nanomaterials. 31 Another well-known complex formed by polyelectrolytes is that of complex coacervates which is a dense fluid phase of electrically neutralized cationic and anionic polyelectrolytes that is phase separated from the bulk solution 16 . Complex coacervation has been used for the encapsulation of drugs 32 and food flavors.…”