Freestanding Ultrathin Nanoparticle Membranes Assembled at Transient Liquid–Liquid Interfaces

Abstract

as well as noncovalent [ 17,19 ] reticulation or through the coassembly of the NPs with polymers, [ 29 ] DNA [ 30 ] or peptides. [ 31 ] Besides the classical thin-fi lm assembly on a solid substrate (drop casting, [ 32 ] spincoating, [ 27,33 ] layer-by-layer deposition [ 8 ] ) followed by a detachment step, interfacial assembly, and especially liquid-liquid assembly, is a very effi cient way to obtain well-defi ned fi lms or membranes [34][35][36][37] (please note that in this context, we defi ne as membrane any freestanding thin layer, regardless of selective mass-transport properties). These approaches rely on the possibility of NPs to adsorb and pack into a dense network at an interface. This can occur if the free energy of the nanoparticles bound at the interface is lower than that of the NPs in either of the two phases. [38][39][40] The surface of NPs should thus possess specifi c wetting properties to guarantee a stable adsorption at the interface. Such behavior can be obtained using nanoparticles with a Janus-type anisotropic surface functionalization [ 41 ] or having systems that will spontaneously break their symmetry in situ. [ 42 ] This can also be obtained by carefully modifying locally the properties of one of the solvents to create a layer of intermediate characteristics, for instance, by injecting locally a compatibilizing reagent such as ethanol [ 43 ] or by applying an electric fi eld. [ 44 ] Hereby, we propose an innovative approach to achieve the formation of ultrathin free-standing and mechanically resilient membranes. The membranes are constituted of gold nanoparticles (AuNPs) that are reticulated by bridging mercaptopropyltrimethoxysilane (MPTMS) ligands which can cross-link through the formation of Si O Si bonds. Our approach relies on the formation of an unstable oil-in-water emulsion, in which AuNPs assemble at the surface of the oil droplets. Upon coalescence of the droplets, the decreasing available surface causes the AuNPs to close-pack and cross-link via the MPTMS ligands, forming an ultrathin membrane that remains freestanding in the water-phase. This dynamic interfacial assembly guarantees the presence of only a few NP-layers, with monolayer-thin domains easily obtained over several square-millimeters. Furthermore, the membranes can then be transferred onto solid or holey support substrates. This synthetic route is compatible with the presence of functional dopants that are physically immobilized in the AuNPs network, making this a promising way to form functional membranes by combining targeted properties through co-assembly. Since the preparation procedure involves the intimate contact of the water and oil phases A synthetic route is presented for the realization of ultrathin freestanding nanoparticle membranes that are built of gold nanoparticles protected with trimethoxysilane-bearing ligands. The mechanism relies on interfacial assembly in an oil-water mixture. Upon shaking, nanoparticles are transported to the liquid-liquid interface of the oil droplets and form a network thr...

Free‐Standing 2D Nanoassemblies

“…Reproduced with permission. [109] Copyright 2016, Wiley-VCH. d) Crosslinking through dithiol molecules.…”

“…For example, a free-standing gold nanoparticle assembly has been fabricated by forming of Si-O-Si between hydrolysed mercaptopropyltrimethoxysilane ligands in a suitable pH environment ( Figure 4c). [109] To form closely-packed nanoassemblies, the constituent building blocks need to be close enough to each other so that the cross-linking can happen to lock the nanoparticles in place.…”

A Peptide‐Based Method for the Fabrication of 1D Rail‐Like Nanoparticle Chains and 2D Nanoparticle Membranes: Higher‐Order Self‐Assembly

“…Molecular self‐assembly is particularly suitable for bottom‐up techniques because of its versatility and capability for forming nanoscale ordered templates and practical components. Inspired by nature, self‐assembling systems including bacterial S‐layers, DNA strands, biopolymers,, peptides and proteins are rapidly becoming superior templates for directing the nucleation, deposition, and assembly of metal or semiconducting nanoparticle into 1D nanowires or 2D nanomembranes or arrays . In general, both 1D and 2D structures have attracted attention in the fields of catalysis, materials science, and medicine, all of which generally require a simpler production process.…”

Polymer Nanosheet Containing Star‐Like Copolymers: A Novel Scalable Controlled Release System

“…Recently, polymer nanosheet (PNS), a polymer‐based free‐standing film with nano‐order thickness, is a promising candidate for many applications due to its unique properties, such as high transparency, high aspect ratio, high permeability and selectivity, and high flexibility . Miyashita and co‐workers fabricated the free‐standing ultrathin films with the controllable thickness from 3.3 to 1 µm by utilizing Langmuir–Blodgett technique (LB film).…”

“…[15,17,18,[26][27][28] However, the practical application of these PCL-based nanodevices is hindered by the difficulties in largescale fabrication.Recently, polymer nanosheet (PNS), a polymer-based freestanding film with nano-order thickness, is a promising candidate for many applications due to its unique properties, such as high transparency, high aspect ratio, high permeability and selectivity, and high flexibility. [29][30][31][32][33][34] Miyashita and co-workers fabricated the free-standing ultrathin films with the controllable thickness from 3.3 to 1 µm by utilizing Langmuir-Blodgett technique (LB film). The film can be used as biosensors, nonlinear optical materials, optical gating devices, and molecular photoswitching devices.…”