Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.

https://science.sciencemag.org/content/sci/277/5330/1232.full.pdf

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

/pdf/progress-challenges-and-opportunities-in-two-dimensional-1sweg4hljr.pdf

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Unilamellar colloids of graphite oxide (GO) were prepared from natural graphite and were grown as monolayer and multilayer thin films on cationic surfaces by electrostatic self-assembly. The multilayer films were grown by alternate adsorption of anionic GO sheets and cationic poly(allylamine hydrochloride) (PAH). The monolayer films consisted of 11−14 A thick GO sheets, with lateral dimensions between 150 nm and 9 μm. Silicon substrates primed with amine monolayers gave partial GO monolayers, but surfaces primed with Al13O4(OH)24(H2O)127+ ions gave densely tiled films that covered approximately 90% of the surface. When alkaline GO colloids were used, the monolayer assembly process selected the largest sheets (from 900 nm to 9 μm) from the suspension. In this case, many of the flexible sheets appeared folded in AFM images. Multilayer (GO/PAH)n films were invariably thicker than expected from the individual thicknesses of the sheets and the polymer monolayers, and this behavior is also attributed to folding...

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/Che%20Mat11,%20771.pdf

Layer-by-Layer Assembly of Ultrathin Composite Films from Micron-Sized Graphite Oxide Sheets and Polycations

Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important. Here, we demonstrate that both structural features can be reproduced by sequential deposition of polyelectrolytes and clays. This simple process results in a nanoscale version of nacre with alternating organic and inorganic layers. The macromolecular folding effect reveals itself in the unique saw-tooth pattern of differential stretching curves attributed to the gradual breakage of ionic crosslinks in polyelectrolyte chains. The tensile strength of the prepared multilayers approached that of nacre, whereas their ultimate Young modulus was similar to that of lamellar bones. Structural and functional resemblance makes clay– polyelectrolyte multilayers a close replica of natural biocomposites. Their nanoscale nature enables elucidation of molecular processes occurring under stress.

Nanostructured artificial nacre

The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-bylayer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed.

/pdf/biomedical-applications-of-layer-by-layer-assembly-from-1i20r8iian.pdf

Biomedical Applications of Layer‐by‐Layer Assembly: From Biomimetics to Tissue Engineering

Layer-by-Layer Assembly of Intercalation Compounds and Heterostructures on Surfaces: Toward Molecular "Beaker" Epitaxy

The exfoliation of acid-exchanged K4Nb6O17 with tetra(n-butyl)ammonium hydroxide in water produces a colloidal suspension of individual sheets, which roll into loosely bound tubular structures The tubule shape can be made permanent via precipitation of the colloid with alkali cations Atomic force microscopy and transmission electron micrographs reveal that the tubules have outer diameters ranging from 15 to 30 nm and that they are 01 to 1 μm in length The observed curling tendency, preferential folding, and cleavage angles of the individual sheets are interpreted in terms of the crystal structure of the parent solid, K4Nb6O17 The driving force for tubule formation appears to be relief of strain that is inherent in the asymmetric single sheets This driving force is absent in bilayer colloids formed early in the exfoliation process, which are found only as flat sheets Tubules in colloidal suspensions that have been subjected to turbulence have a tendency to unroll into flat sheets on surfaces, indica

Nanoscale Tubules Formed by Exfoliation of Potassium Hexaniobate

Monolayer and multilayer thin films consisting of anionic α-zirconium phosphate (α-ZrP) sheets and polycations (poly(allylamine hydrochloride) (PAH), cytochrome c) were characterized by transmission electron microscopy (TEM), ellipsometry, UV−visible absorbance spectroscopy, reflectance FT-IR, XPS, and X-ray diffraction. Titration and powder X-ray diffraction experiments confirm that exfoliation of α-ZrP begins to occur when enough tetra(n-butylammonium) hydroxide (TBA+OH-) has been added to exceed single-layer packing of TBA+ ions (x ≈ 0.50) in the intercalation compound Zr(HPO4)2-x(TBA+PO4-)x·nH2O. The identical contrast of many sheets in TEM micrographs suggests that the suspension is unilamellar. Alternately dipping cationic substrates into α-ZrP-containing suspensions and aqueous PAH gives a multilayer film that resembles the corresponding bulk intercalation compound. X-ray photoelectron spectra of multilayer films show that they are Zr-rich, relative to α-ZrP, consistent with some corrosion during t...

Characterization of Zirconium Phosphate/Polycation Thin Films Grown by Sequential Adsorption Reactions

The intercalation and exfoliation reactions of α-zirconium phosphate, Zr(HPO4)2·H2O (α-ZrP), were studied microscopically by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The reaction of α-ZrP with tetra(n-butylammonium) hydroxide (TBA+OH-) initially produces intercalation compounds, which then transform to unilamellar colloids. The rate-determining step in intercalation is the opening of the interlamellar galleries. Subsequent diffusion of TBA+ ions into the opened galleries is rapid. The hydrolysis reaction of α-ZrP colloids proceeds from the edges inward, forming ∼4-nm hydrated zirconia particles that decorate the edges of the sheets. The reaction does not go to completion, as it is limited by equilibrium associated with the release of phosphate into the solution. The hydrolysis reaction is negligible at 0 °C, which permits the synthesis of hydrolysis-free unilamellar colloids. Remarkably, these colloids form monolayer films on amine-derivatized silicon surfaces with a high ...

Chemistry on the Edge: A Microscopic Analysis of the Intercalation, Exfoliation, Edge Functionalization, and Monolayer Surface Tiling Reactions of α-Zirconium Phosphate

Hyuk Nyun Kim

Papers

Layer-by-Layer Assembly of Intercalation Compounds and Heterostructures on Surfaces: Toward Molecular "Beaker" Epitaxy

Nanoscale Tubules Formed by Exfoliation of Potassium Hexaniobate

Characterization of Zirconium Phosphate/Polycation Thin Films Grown by Sequential Adsorption Reactions

Chemistry on the Edge: A Microscopic Analysis of the Intercalation, Exfoliation, Edge Functionalization, and Monolayer Surface Tiling Reactions of α-Zirconium Phosphate