Free-Standing and Reactive Thin Films Fabricated by Covalent Layer-by-Layer Assembly and Subsequent Lift-Off of Azlactone-Containing Polymer Multilayers

Abstract

We report an approach to the fabrication of freestanding and amine-reactive thin films that is based on the reactive layer-by-layer assembly and subsequent lift-off of azlactone-containing polymer multilayers. We demonstrate that covalently crosslinked multilayers fabricated using the azlactone-functionalized polymer poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) and a primary amine-containing polymer [poly(ethyleneimine) (PEI)] can be delaminated from planar glass and silicon surfaces by immersion in mildly acidic aqueous environments to yield flexible freestanding membranes. These freestanding membranes are robust and can withstand exposure to strong acid, strong base, or incubation in high ionic strength solutions that typically lead to the disruption and erosion of polymer multilayers assembled by reversible weak interactions (e.g., 'polyelectrolyte multilayers' assembled by electrostatic interactions or hydrogen bonding). We demonstrate further that these PEI/PVDMA assemblies contain residual reactive azlactone functionality that can be exploited to chemically modify the films (either directly after fabrication or after they have been lifted off of the substrates on which they were fabricated) using a variety of amine-functionalized small molecules. These freestanding membranes can also be transferred readily onto other objects (for example, onto the surfaces of planar substrates containing holes or pores) to fabricate suspended polymer membranes and other film-functionalized interfaces. In addition to planar, two-dimensional freestanding films, this approach can be used to fabricate and isolate threedimensional freestanding membranes (e.g., curved films or tubes) by layer-by-layer assembly on, and subsequent lift-off from, the surfaces of topologically complex substrates (e.g., the curved ends of glass tubing, etc.). The results of this investigation, when combined, suggest the basis of methods for the fabrication of stable, chemically-reactive, and flexible polymer thin films and membranes of potential utility in a variety of fundamental and applied contexts.

Superhydrophobic Thin Films Fabricated by Reactive Layer-by-Layer Assembly of Azlactone-Functionalized Polymers

“…We have described in several recent reports a ‘reactive’ layer-by-layer approach25 to the assembly of covalently crosslinked multilayered films that exploits the versatile reactivity of azlactone-functionalized polymers 26–30. Polymers bearing azlactone functionality, such as poly(2-vinyl-4,4-dimethylazlactone) (PVDMA, Eq.…”

Covalently Crosslinked and Physically Stable Polymer Coatings with Chemically Labile and Dynamic Surface Features Fabricated by Treatment of Azlactone-Containing Multilayers with Alcohol-, Thiol-, and Hydrazine-Based Nucleophiles

“…16,23 For films treated with decylamine, the peak corresponding to the azlactone functionality at 1819 cm -1 was completely consumed, suggesting exhaustive reaction of the azlactone groups with the incoming amine-based nucleophile and consistent with the results of past studies. 16,23,25 For films treated with decanol, the intensity of the azlactone carbonyl stretch at 1819 cm -1 was nearly fully consumed, and a carbonyl C=O stretch at 1724 cm -1 appeared, consistent with the formation of ester bonds upon the ring-opening of the azlactone groups with this alcohol-based nucleophile. Finally, for films treated with decanethiol, the azlactone peak was also consumed and close inspection of the data reveals a shoulder on the amide C=O stretch (near 1652 cm -1 ) that we attribute to the C=O carbonyl stretching of thioester functionality.…”

Covalent Layer‐by‐Layer Assembly Using Reactive Polymers

“…Subsequent work demonstrated the versatility of this azlactone-based approach as a means to coat and modify the interfacial properties of a variety of different materials and more complex substrates, including the surfaces of glass [54][55][56][57][58][59][60]143], soft materials (e.g., polymer-based substrates) [59,61], paper [62], cotton thread and commercial wound dressings (Figure 15.12e,f) [62], protein-based surfaces (e.g., horsehair) [62], inorganic microparticles (for the fabrication of hollow microcapsules Figure 15.12g,h) [63], and, owing to the ability to perform covalent assembly in organic solvents that are immiscible with water, liquid/liquid interfaces formed between organic and aqueous phases (for the fabrication of suspended membranes; Figure 15.12i) [64]. In each of these studies, the presence of amine-reactive azlactone functionality on the surface (or within the bulk) of the films provided a convenient and straightforward platform for further postfabrication modification of surface properties by exposure to a broad range of different amine-functionalized molecules (including amine-functionalized small molecules [54,55,[57][58][59][60][61][62][63], proteins [55,61], peptides [65], functional polymers [61], and amine-functionalized droplets of thermotropic liquid crystals [56]).…”

“…Buck et al [57] demonstrated that PEI/PVDMA films fabricated on untreated (nonsilanized) silicon substrates could be induced to delaminate and lift off to yield cross-linked, stable, and amine-reactive freestanding thin films (Figure 15.12j) that can be postfunctionalized and physically transferred onto the surfaces of other objects. Other examples of this approach using other reactive polymers are discussed in the following section.…”