Tunable Composition of Mixed Self‐Assembled Shell‐by‐Shell Structures on Nanoparticle Surfaces

Abstract

of the individual molecules has a decisive influence on the final properties of the resulting suprastructure. In micelles, this can be the size and shape, for vesicles, the diffusion speed through the molecular bilayer, or for self-assembled monolayers (SAMs) the packing density and crystallinity. [1][2][3][4] Properties of such assemblies can be either modified by tuning the individual molecules or by a smart combination of multiple building blocks. [5][6][7][8][9][10][11][12][13] This concept is proven by nature as a highly reliable method to create, for example, cell membranes, which consist of hundreds of different molecules, even for the simplest organisms resulting in remarkably high functionality. [14,15] Among many other tasks, those molecules control the stability, the salt content in cells, the oxygen and nutrient uptake, and the size of these structures. [15] The exact selection of molecule types and stoichiometric composition of membranes play a decisive role in the functioning of the cells. Most prominent examples are amphiphiles that consist of two parts of different polarities, thus making them soluble in orthogonal solvents.All corresponding suprastructures are based on weak hydrophobic interactions as well as intermolecular recognition motifs such as stereo complexation, H-bonding, ionic interactions, etc. [16] But even in simple artificial micelles and vesicles (compared to biological systems), competing forces between two or more molecules can either lead to synergetic effects or segregation of the involved molecules into multiple structures with heterogeneous composition. [17,18] In particular for the combination of highly orthogonal amphiphiles bearing fluorophilic and lipophilic (alkyl-chained) residues, there are only a few examples of synergetic mixtures known. [18,19] However, such orthogonally chained molecules tend to self-assemble to mixed SAMs if they exhibit strong covalent binding anchor groups such as phosphonic acids. The covalent binding drives the self-assembly on, for example, oxide surfaces and prevent the individual molecules from segregating into multiple phases, which allows the formation of SAMs in any stoichiometric mixing ratio. [20] Based on such SAMs, vesicle-like structures (see Scheme 1) can be formed with nanoparticles as template by building up a second layer through non-covalent interactions to a shell-by-shell (SbS) system. [21][22][23][24][25][26] Such unique systems provide the opportunity to switch the polarity of core-shell nanoparticles for adjusted processing, [21] to prepare model bilayers The formation of mixed shell-by-shell (SbS) systems with tunable shell compositions is demonstrated by using molecular self-assembly driven by chemical recognition motifs. Aluminum oxide nanoparticles (AlOx-NPs) act as template surface for a self-assembled monolayer (SAM) of either partially fluorinated fluoroalkyl or alkyl chained phosphonic acid derivatives or defined stoichiometric mixtures of those. By providing an equimolar mixture of corresponding fluoroalkyl and a...

Magnetic Removal of Micro‐ and Nanoplastics from Water—from 100 nm to 100 µm Debris Size

“…To adjust their affinity to a dedicated group of contaminants, they can be functionalized with a self-assembled monolayer. [27][28][29][30][31] Such a layer is composed of organic molecules, which anchor on the SPION's surface and are usually equipped with a functional headgroup that offers the interaction motif with the contaminant. In the case of MNP, this interaction is based on electrostatic as well as Van der Waals interactions, which lead to the formation of aggregates of SPIONs and MNP (Figure 1D).…”

Remediation of charged organic pollutants—binding motifs for highly efficient water cleaning with nanoparticles

“…[46] In order to create a large surface area with dedicated, attractive interaction motifs, long-chained phosphonic acid (PA) derivatives have been established. [43,[47][48][49][50][51][52][53][54][55] PAs tend to form self-assembled monolayers (SAMs), providing long-term stable binding on metal oxide surfaces. [56,57] Core-shell NPs with PA-SAMs have been demonstrated as efficient sorbent materials to remove hydrophobic alkanes, crude oil, aromatic compounds, and even nano-and microplastics.…”