On the influence of PDMS (polydimethylsiloxane) substrate surface energy in wrinkling of DLC (diamond-like carbon) thin films

Abstract

We have explored the influence of surface energy of the PDMS (polydimethylsiloxane) substrate on the wrinkling of diamond-like carbon thin films. The surface energy of PDMS can be tuned by exposure to oxygen plasma or by shallow-implantation of gold. The result is an increase in the wrinkling wavelength and amplitude. By means of a tri-layer wrinkling model, we discuss whether the major contribution to the wavelength variation is via the surface energy of the substrate or via the mechanical properties of the interface layer resulting from the surface treatment. We conclude that the surface energy of the substrate is an important property that must be considered in order to provide a complete description of wrinkling phenomena.

Barrier Diamond-like Carbon Coatings on Polydimethylsiloxane Substrate

“…On the other hand, the application of tests with a variable tensile force of DLC coatings on PDMS substrates allows us to know other important properties of such a composite, e.g., coating adhesion to the substrate or the presence of a cross-linked substrate interlayer [ 34 ]. Similar relationships also apply to other coatings on PDMS substrates, such as SiOx, gold [ 27 , 33 ], silver, molybdenum [ 29 ], or polymer coatings [ 28 ]. As already described in our previous work regarding DLC coatings on PDMS, substrates deposited by the RF PACVD method are uniform and crack-free.…”

“…The use of DLC coatings on substrates such as PDMS is inevitably combined with the appearance of wrinkles on the surface of polymers. It is an issue that has been widely described in the literature [ 10 , 27 , 28 , 29 , 30 , 31 , 32 ]. Most often, wrinkles on modified PDMS surfaces are described as the result of mismatching the elasticity modulus of the coating and the polymer substrate [ 26 , 27 , 31 ].…”

“…It is an issue that has been widely described in the literature [ 10 , 27 , 28 , 29 , 30 , 31 , 32 ]. Most often, wrinkles on modified PDMS surfaces are described as the result of mismatching the elasticity modulus of the coating and the polymer substrate [ 26 , 27 , 31 ]. However, when analyzing this issue in more detail, it is worth noting that the formation of wrinkles is the effect of mismatching the deformation of the formed coating when the compressive stress exceeds the threshold value [ 29 , 30 , 32 ].…”

“…However, when analyzing this issue in more detail, it is worth noting that the formation of wrinkles is the effect of mismatching the deformation of the formed coating when the compressive stress exceeds the threshold value [ 29 , 30 , 32 ]. There are a number of mathematical models describing the wavelength and amplitude of the wrinkles, depending on the material properties of the substrate, the coating, and even the intermediate layer that may be formed during the modification processes [ 27 ]. Changes in the mentioned parameters, which, in fact, perfectly describe the surface geometry, are often reflected in changes in the value of surface free energy [ 27 ].…”

“…There are a number of mathematical models describing the wavelength and amplitude of the wrinkles, depending on the material properties of the substrate, the coating, and even the intermediate layer that may be formed during the modification processes [ 27 ]. Changes in the mentioned parameters, which, in fact, perfectly describe the surface geometry, are often reflected in changes in the value of surface free energy [ 27 ]. Wrinkles on the surface of DLC coatings produced on the PDMS substrate may also be the result of the applied additional tensile stresses [ 10 , 33 ]; however, in this case, cracks in the coating very often occur.…”