Fabrication techniques enabling ultrathin nanostructured membranes for separations

Abstract

The fabrication of nanostructured materials is an area of continuous improvement and innovative techniques that fulfill the demand of many fields of research and development. The continuously decreasing size of the smallest patternable feature has expanded the catalog of methods enabling the fabrication of nanostructured materials. Several of these nanofabrication techniques have sprouted from applications requiring nanoporous membranes such as molecular separations, cell culture, and plasmonics. This review summarizes methods that successfully produce through-pores in ultrathin films exhibiting an approximate pore size to thickness ratio of one, which has been shown to be beneficial due to high permeability and improved separation potential. The material reviewed includes large-area, parallel, and affordable approaches such as self-organizing polymers, nanosphere lithography, anodization, nanoimprint lithography as well as others such as solid phase crystallization and nanosphere lens lithography. The aim of this review is to provide a set of inexpensive fabrication techniques to produce nanostructured materials exhibiting pores ranging from 10 to 350 nm and exhibiting a pore size to thickness ratio close to one. The fabrication methods described in this work have reported the successful manufacture of nanoporous membranes exhibiting the ideal characteristics to improve selectivity and permeability when applied as separation media in ultrafiltration.

Use of Nanosphere Self-Assembly to Pattern Nanoporous Membranes for the Study of Extracellular Vesicles

“…34 High permeability, at the nanoscale, can be obtained through membranes with a pore size to thickness ratio close to one. 34,35 Such platform should provide ultrathin membranes with close control on pore size over the range of small EVs. Another reason for minimal thickness is to improve tissue barrier function in a direct co-culture format by allowing physical contact and fast exchange of soluble factors, [36][37][38] establishing a more physiologically relevant model.…”

Micro‐Phase Separation within Epoxy Resin Yields Ultrathin Mesoporous Membranes with Increased Scalability by Conversion from Spin‐ to Dip‐Coating Process

“…Therefore, manufacturing procedures are often complex and sophisticated and do not satisfy the requirements or are not well suited for a production exceeding lab‐scale. The most feasible strategies and the resulting materials were recently reviewed where inorganic materials prevail. The control of size and distribution of pores is typically accompanied with a compromise with respect to production speed or scale.…”

“…However, polymer‐based approaches can be favorable due to the availability of feasible routes for mass‐ and large‐scale production with widely established and reliable techniques. In terms of polymeric membranes with thicknesses equivalent to several molecular layers, frequent approaches utilize block copolymers, etching, lithography, and self‐assembly of particles or combinations of those . Walheim et al laid a basis for another bottom‐up technique in the regime of self‐assembly where phase segregation in binary and ternary mixtures during spin‐coating was used to obtain functional nanostructured thin films .…”

“…The fabrication procedure relies on a ternary polymer blend in an organic solvent where one of the components forms a microemulsion within a continuous phase of the other two. This process and most of the other approaches to fabricate ultrathin separation membranes rely on spin‐coating for thin film formation . Although spin‐coating is a very versatile and popular method for casting of ultrathin polymer films, such films are limited in lateral size by the nature of the technique and are therefore only partially scalable.…”

“…This process and most of the other approaches to fabricate ultrathin separation membranes rely on spincoating for thin film formation. [9] Although spin coating is a very versatile and popular method for casting of ultrathin poly mer films, such films are limited in lateral size by the nature of the technique and are therefore only partially scal able. To generate a thin film, the coating substrate is revolved at high speeds so that disk diameters of tens of centimeters are the upper limit.…”