Reversible Assembly of Tunable Nanoporous Materials from “Hairy” Silica Nanoparticles

Abstract

Membranes with 1-100 nm nanopores are widely used in water purification and in biotechnology, but are prone to blockage and fouling. Reversibly assembled nanoporous membranes may be advantageous due to recyclability, cleaning, and retentate recovery, as well as the ability to tune the pore size. We report the preparation and characterization of size-selective nanoporous membranes with controlled thickness, area, and pore size via reversible assembly of polymer brush-grafted ("hairy") silica nanoparticles. We describe membranes reversibly assembled from silica particles grafted with (1) polymer brushes carrying acidic and basic groups, and (2) polymer brushes carrying neutral groups. The former are stable in most organic solvents and easily disassemble in water, whereas the latter are water-stable and disassemble in organic solvents.

Free‐Standing 2D Nanoassemblies

“…[58, 62-63, 76, 80, 127, 129] Another group demonstrated the suitability of the approach extended to silica spheres with the size of 390 nm to form free-standing membranes. [130] In another example, the cooperative effect from both the entanglements between PS chains, as well as strong vdW force between PS ligands and the Ag nanoparticles could facilitate the fabrication of the macroscopic 2D silver nanoassemblies that freely suspend over a wire loop larger than 1 cm. [131] Although the thickness of the entangled PS layers is only a few nanometers (3-6 nm) , they are mechanically robust, chemically stable, yet solvent and ion-permeable.…”

Percolation analysis for estimating the maximum size of particles passing through nanosphere membranes

“…1.1579 . 1.1678 (7) Figure 11. Graph of the various models that can be used to estimate the particle size cut-off as a function of the silica particle size and volume fraction within the membrane.…”

“…If this equation is applied to cutoff experiments for different membranes [1,19], the overlap of the brushes can be estimated (assuming that the volume fraction is known to be ~ 0.64). Two sizes of spheres were experimentally tested: 280 nm and 460 nm silica spheres, with 24 nm and 30 nm length brushes, respectively.…”

“…Hairy nanoparticle (HNP) membranes, comprised of a hard sphere silica core with polymeric brushes stretching from the surface, represent a new class of low-cost, self-assembled nanoporous membranes that can be used to separate nanoscale moieties, such as viruses, nanoparticles and biomacromolecules. [1] An SEM image of a dry HNP membrane in shown in Figure 1(a), and a figurative illustration of the structure of the particles is shown in Figure 1 The size of the pores in the membrane can be altered by changing the diameter of the silica spheres and the length of the polymer brushes. Predicting the size of particulates that can pass between the HNPs that comprise the membrane is difficult; the membranes are not ordered and the silica sphere sizes and polymer brush lengths can vary greatly.…”

A comparative study of the self-assembly of achiral and chiral hairy nanoparticles with polystyrene cores and poly(2-hydroxyethylmethacrylate) hairs

“…33 Most of these applications require control in the pore size, functional membrane surface, chemical and thermal stability. 34,35 It has been demonstrated that an amphiphilic phase separated copolymer of PS-b-PHEMA synthesized by ATRP has the ability to self-assemble into honeycomb patterned porous membranes. 36 From the perspective of functional bionanomaterial engineering, the PS-b-PHEMA copolymers are of signicant interest.…”