Characterizing Polymer Brushes via Surface Wrinkling

Abstract

We apply surface wrinkling to measure the mechanical properties of poly(2-hydroxyethyl methacrylate) polymer brush layers tethered to the surface of a flexible poly(dimethylsiloxane) (PDMS) substrate. A facile modification scheme based on hydrochloric acid treatment was employed to introduce hydroxyl groups to the surface of PDMS, which served to covalently attach initiator groups for subsequent polymerization. Upon mechanical compression of the brush layer on PDMS, a wrinkling instability occurs whose wavelength yields a Young’s modulus for the brush layer that is comparable to the corresponding polymer in the bulk. Moreover, we show that the wrinkling wavelength can provide an accurate measure of the brush thickness, which is often difficult to assess on transparent, flexible substrates. When using thermal strain to generate wrinkled surfaces, the patterns are stable at room temperature but can be erased by solvent treatment, which relaxes the applied strain and thus imparts reversibility to the wrinkled surfaces.

Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films

“…It has been reported elsewhere [1][2][3][4][5] that the buckling wavelength increases with increasing the number of layers. The Young' modulus, however, should not be affected by thickness over a certain thickness range [9][10][11][12][13] which is also demonstrated here in figure 5b. Young's modulus is calculated as 1.106 (±0.145) GPa and 2.181 (± 0.083) GPa for PVAm-NFC and PVAm-SiO 2 -PVAm-NFC, respectively.…”

“…It is, though, very difficult to evaluate the properties of nanometer sized films due to handling properties of these types of free-standing films [8]. However, following the development of the use of Strain Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) [9][10][11][12] it was recently shown that it is possible to use the SIEBIMM technology to evaluate the mechanical properties of nanometer sized films of NFC and PEI [13]. Furthermore, by using high resolution optical methods [14], it should also be possible to determine the optical properties of thin films deposited on the same types of supports (i.e PolyDiMethylSiloxane) (PDMS) as used for the SIEBIMM technology.…”

“…Thus, the most critical parameters in the SIEBIMM technique that determines Young's modulus of a thin film are the buckling wavelength λ and the film thickness d f . Buckling of a thin film on an elastic Polydimethylsiloxane (PDMS) substrate can be achieved by a mechanical compression or thermal induction [12]. Whereas the thickness of polymer thin films increases with increasing relative humidity, due to moisture uptake, the Young's modulus of the film was found to decrease with increasing relative humidity [15].…”

Surface Wrinkling: A Versatile Platform for Measuring Thin‐Film Properties

“…We have been successful at growing polymer brushes from PDMS surfaces that have been oxidized in a mild acid solution and reacted with a silanebonded initiator in order to grow polymers via atom-transfer radical polymerization (ATRP). [ 38 ] This technique produces polymer fi lms on the PDMS surface with low polydispersity (and hence low roughness) and with a fi nal thickness that is completely tunable by simply varying the polymerization time. Surface wrinkling can play an important role in characterizing the properties of polymer brush layers on soft substrates such as PDMS.…”

Self-assembled porous templates allow pattern transfer to poly(dimethyl siloxane) sheets through surface wrinkling

“…Rogers et al 12 showed the buckling of GaAs ribbons and its application for electronics. Stafford et al 13 showed that microwrinkles formed when grafting polymer brushes onto PDMS surfaces. Many other studies have reported the formation of microwrinkles and their applications.…”