Fabrication of Large Nanomembranes by Radical Polymerization of Multifunctional Acrylate Monomers

Abstract

Nanomembranes and naosheets are among the most interesting nanomaterials.1,2 They are characterized by one nanometer dimension and two micro-to-macroscopic dimensions. This unique dimensional combination produces interesting features that are not attainable with other nanomaterials of different dimensionality such as nanocrystals, 3,4 nanoparticles, [5][6][7] and nanotubes. 8-10The macroscopic robustness is essential for application of such features particularly in case of giant nanomembranes. We have shown recently that high cross-linking density is effective for attaining sufficient robustness of nanomembranes with large aspect ratios (size/thickness).11 For example, a hybrid membrane of cross-linked acrylate and zirconia/silica possessed superior robustness with a thickness of only 35 nm. 12,13 In the subsequent studies, we demonstrated that epoxy and other thermosetting resins similarly gave robust nanomembranes with equally large aspect ratios.14,15 These results imply that robust nanomembranes become available only if high crosslinking density is introduced. In the above case of the hybrid nanomembrane, 12 however, it was not possible to obtain stable (i.e., free-standing) nanomembranes from the organic component alone. This failure can result from insufficient crosslinking density and/or from insufficient robustness of crosslinked acrylate chains, since successful fabrication of robust nanomembranes is possible from thermosetting resins.Here, we report fabrication of free-standing nanomembranes from acrylic components alone. According to the above supposition, we employed a precursor which contains a higher amount of the double-bond moiety on one hand and a precursor mixture which contains a rigid molecular backbone on the other. They are a tetra-functional acrylic monomer of pentaerythritol tetraacrylate (PETA, Aldrich) and a bisphenol Afunctionalized acrylic oligomer (Kayarad R-280, Nippon Kayaku, with 20 wt % 2-hydroxypropylacrylate), respectively.The fabrication procedure of nanomembranes is similar to that of our previous study.14 Firstly, thin layers of poly(styrene-4-sulfonic acid) [PSS; M w ¼ 1:0 Â 10 5 , Aldrich] or poly(4-hydroxystyrene) [PHS; M w ¼ 4:5 Â 10 3 , Aldrich] were formed on Si-wafer by spin-coating. These layers act as water-soluble and ethanol-soluble sacrificial layers, respectively. Chloroform solutions (1 wt %) of acrylic precursors and a photo-initiator (Darocure4265, Ciba-Geigy, 5 wt % relative to the acrylic precursor) were then spin-coated, and UV irradiation was performed on the sample under vacuum. A high pressure mercury lamp (Hamamatsu, Lighteningcure LC5) was used as a light source, and irradiation was done through a slide glass as a filter. Chemicals used in this study together with the bi-functional aliphatic acrylate (hexanediyl diacrylate; HDODA) used in our previous study are summarized in Figure 1. Figure 2 shows ATR-FT-IR (Thermo Nicolet, Nexus670 FT-IR) spectra of an R-280 film which was directly fabricated on a gold substrate under otherwise the identical condit...

Manipulation of surface properties: the use of nanomembrane as a nanometre-thick decal

“…We have reported that robust nanomembranes are fabricated from a variety of densely crosslinked materials such an inorganic/organic hybrid, 29 thermosetting resins, 30,31 and photopolymers. 32 Because a nanomembrane layer was formed on a substrate coated with a sacrificial polymer, dissolution of the sacrificial layer detaches the nanomembrane into/onto a solvent (see ESI † for more details). One definitive advantage of the process is the easy transfer of a nanomembrane onto other solid substrates.…”

Dynamic Actuation of Soft 3D Micromechanical Structures Using Micro‐Electromechanical Systems (MEMS)

“…The elastic modulus of PEGDA (Mn 575) has a broad reported range of moduli of ≈10 kPa up to ≈100 MPa, depending on photoinitiator concentration in the resist and degree of polymerization of the final polymer . Acrylate‐based polymers such as PETA can have moduli ranging from 0.1 to 4 GPa . It is important to point out that, although linear fits of the force‐displacement curves were used to calculate the structure spring constants, it can be seen from Figure d that the response of PEGDA springs was not linear.…”

Giant nanomembrane of covalently-hybridized epoxy resin and silica

“…17,18 Its importance is supported even in the case of acrylate polymers, and robust nanomembranes were available from pentaerythritol tetraacrylate (PETA) that would lead to higher cross-linking density. 19 Structural rigidity of precursor materials may also contribute to the macroscopic robustness. In the case of acrylic monomers, Kayarad-R280 provides a robust nanomembrane, in spite of its functional group density which is not greater than that of HDODA.…”

“…This difference appears to arise from the presence of rigid molecular components in Kayarad-R280. 19…”

“…[14][15][16] This finding was then extended to fabrication of large, free-standing nanomembranes from representative thermosetting resins. [17][18][19] It was clear that high-density cross-linking was the essential feature to attain sufficient robustness that is required for coexistence of nanometre thickness and macroscopic size. 20 One of the conventional approaches to reinforce robustness of organic polymer membranes is hybridization with silica and other inorganic components.…”