Ultrathin, freestanding, stimuli-responsive, porous membranes from polymer hydrogel-brushes

Abstract

The fabrication of freestanding, sub-100 nm-thick, pH-responsive hydrogel membranes with controlled nano-morphology, based on modified poly(hydroxyethyl methacrylate) (PHEMA) is presented. Polymer hydrogel-brush films were first synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequently detached from silicon substrates by UV-induced photo-cleavage of a specially designed linker within the initiator groups. The detachment was also assisted by pH-induced osmotic forces generated within the films in the swollen state. The mechanical properties and morphology of the freestanding films were studied by atomic force microscopy (AFM). Inclusion of nanopores of controlled diameter was accomplished by performing SI-ATRP from initiator-coated surfaces that had previously been patterned with polystyrene nanoparticles. Assembly parameters and particle sizes could be varied, in order to fabricate nanoporous hydrogel-brush membranes with tunable pore coverage and characteristics. Additionally, due to the presence of weak polyacid functions within the hydrogel, the membranes exhibited pH-dependent thickness in water and reversible opening/closing of the pores.

Loops and Cycles at Surfaces: The Unique Properties of Topological Polymer Brushes

“…Alternatively, the interfacial physicochemical properties of polymer brushes can be conveniently varied by applying different polymer architectures or topologies, beyond linearity, often keeping constant the overall polymer composition. By this approach, the introduction of crosslinks, side chains or branchings along the grafted polymers enabled the precise tuning of brush swelling, its nanomechanical and nanotribological characteristics, while increasing the surface concentration of functional groups available for post‐modification …”

Using Polymers to Impart Lubricity and Biopassivity to Surfaces: Are These Properties Linked?

“…Recent studies have demonstrated how precise tuning of brush architecture can be exploited to independently modulate friction and/or protein resistance. This is the case for crosslinked brushes or brush-hydrogels, which have already proven to be extremely versatile films for a variety of materials formulations, including nanostructured and responsive membranes, [67] metal nanoparticles (NPs)-polymer hybrid coatings with tunable optical [68] and catalytic properties, [69] and supports for cell manipulation. [70 -72] As an example, the conformational restrictions that occur upon crosslinking densely grafted poly(hydrox-yethyl methacrylate) (PHEMA) brushes with oligo (ethylene glycol) dimethacrylates (OEGDMA) during surface-initiated atom transfer radical polymerization (SI-ATRP), [73] lead to an increase in the amount of protein fouling that occurs upon exposure to serum.…”

Fabrication techniques enabling ultrathin nanostructured membranes for separations

“…After deposition and post‐treatment of the nanospheres, the areas that are left uncovered are most commonly etched for pattern transfer; however, Kang et al . functionalized them in order to selectively direct the deposition of a modified poly(hydroxyethyl methacrylate) (PHEMA) hydrogel to those open areas between nanospheres (Fig. A).…”

“…Cross‐sectional schemes of nanoporous membranes fabricated through NSL: (A) PHEMA hydrogel brush membrane fabricated using PS nanospheres , (B) SiN membrane fabricated through a Cr etch mask produced from PS nanospheres , (C) aluminum oxide membrane fabricated by patterned anodization through PS nanospheres , and (D) polymeric membrane lifted‐off from its processing substrate by dissolving a cellulose acetate sacrificial layer .…”