Elastic Properties of Poly(ethylene glycol) Nanomembranes and Respective Implications

Abstract

Free-standing poly(ethylene glycol) (PEG) membranes were prepared from amine- and epoxy-terminated four-arm STAR-PEG precursors in a thickness range of 40–320 nm. The membranes feature high stability and an extreme elasticity, as emphasized by the very low values of Young’s modulus, varying from 2.08 MPa to 2.6 MPa over the studied thickness range. The extreme elasticity of the membranes stems from the elastomer-like character of the PEG network, consisting of the STAR-PEG cores interconnected by crosslinked PEG chains. This elasticity is only slightly affected by a moderate reduction in the interconnections at a deviation from the standard 1:1 composition of the precursors. However, both the elasticity and stability of the membranes are strongly deteriorated by a strong distortion of the network imposed by electron irradiation of the membranes. In contrast, exposure of the membranes to ultraviolet (UV) light (254 nm) does not affect their elastic properties, supporting the assumption that the only effect of such treatment is the decomposition of the PEG material with subsequent desorption of the released fragments. An analysis of the data allowed for the exclusion of so called “hot electrons” as a possible mechanism behind the modification of the PEG membranes by UV light.

Rational Design of Porous Poly(ethylene glycol) Films as a Matrix for ssDNA Immobilization and Hybridization

“…To verify this hypothesis, the STAR-NH 2 /STAR-EPX mixing ratio was set to 2:1 (see Section 2 for the experimental details) and 2:1 PEG films were prepared. Please note that the crosslinking reaction still works efficiently at even such a non-optimal mixing ratio, resulting in the formation of stable and robust PEG films, with the swelling and mechanical properties differing only slightly from those of the 1:1 films [ 41 , 44 ]. Additionally, the XP spectra of the 2:1 PEG films were found to be nearly identical to those of the 1:1 prototypes, with the characteristic C 1s, O 1s, and N 1s peaks at BEs of 286.8 eV, 532.8 eV, and 399.6 eV, respectively ( Figure 3 ).…”

“…This technique is also favorable compared to the standard experimental tools used in the field, as fluorescence spectroscopy (FS) and surface plasmon resonance (SPR), which either require DNA labeling (FS) or quite expensive equipment (SPR). In our case, the probe ssDNA-decorated PEG films can both be directly prepared on suitable electrodes and transferred onto them using the established film separation and transfer procedures [ 36 , 38 , 39 , 44 ]. The porous character of these films is of advantage for efficient diffusion of redox species in electrochemical cell, enabling reliable and to a certain extent even quantitative monitoring of hybridization.…”

“…These films had similar thickness and similar properties as the films on the Si/SiO 2 substrates. The stability and robustness of these films was in particular verified by the fabrication of large-area, free-standing PEG membranes which feature extreme elasticity [ 44 ].…”

Poly(ethylene glycol)–Fullerene Composite Films and Free-Standing Nanosheets for Flexible Electronic Devices and Sensors

“…One of the favorable properties of STAR-PEG-based PEG films is the possibility of their separation from the original substrate, followed by either relocation onto a secondary substrate or placement over a window or a supporting mesh as a free-standing nanosheet. , It turned out that this option is also available for the PEG-C60 composite films. To this end, we successfully separated the PEG (reference) and PEG-C60 nanosheets from the primary SiO 2 /Si substrates and placed them onto the secondary substrate with a circular window for the bulge test (see Section for the technical details).…”

“…In the present study, we explored a possibility to prepare PEG-C60 composite films on the basis of a porous PEG matrix, which also gave an additional option to isolate such films as mechanically stable, free-standing nanosheetsan issue that has not been addressed so far, to the best of our knowledge. Note that generally, thin PEG films are prepared by spin-casting of PEG precursors on a solid substrate, followed by cross-linking of individual precursors via UV treatment or chemical coupling. − An efficient alternative approach is thermally activated cross-linking of four-armed STAR-PEG precursors, decorated with the complementary amine (STAR-NH 2 ) and epoxy (STAR-EPX) groups, which can build robust ethanol–amine bridges between individual arms of the precursors upon cross-linking, forming thus a robust PEG matrix. , The resulting PEG films were previously utilized as excellent platforms for suppression of protein adhesion, nanofabrication, electron and UV lithography, and preparation of physical and biological sensors. ,− Moreover, PEG films can be separated from the original substrate and used directly as free-standing nanosheets or transferred to a secondary substrate for further applications. ,, …”