Mechanical characterization of crosslinking effect in polydimethylsiloxane using nanoindentation

Abstract

Polydimethylsiloxane (PDMS) is one of the widely-used silicone-based organic polymers. It can serve as a substrate to grow cells, mainly because of its controllable range of mechanical properties. Varying the degree of crosslinking in the polymer network allows tuning its mechanical properties in a range similar to living tissues. To study the PDMS stiffness effect on the growth and behaviour of cells, it is of significant importance to explore the mechanical properties of a series of PDMS samples cured to different crosslink densities. In this paper, nanoindentation tests were conducted using spherical, Berkovich, cube corner and conical indenters to characterize PDMS mechanical properties. To interpret the nanoindentation data, the nano-JKR force curve method was successfully extended to include Berkovich, cube corner and conical indenters by conducting a numerical simulation in which the adhesive interactions are represented by an interaction potential and the surface deformations are coupled by using half-space Green's functions discretized on the surface.

Apparent depth‐dependent modulus and hardness of polymers by nanoindentation: Investigation of surface detection error and pressure effects

“…Based on our results and discussion above, it is better to test the stiff polymers with spherical probes, Berkovich probes can lead to large pressure beneath the probe compared with spherical probe, which then gives higher modulus. While for the softest materials, such as PDMS, it has been shown by Jin and co‐workers that if the complete loading history is obtained, the correct modulus can be determined for different probe geometries. In all events, care should be taken to assure good detection of the surface or serious errors can occur with nanoindentation methods.…”

“…For example, Han and co‐workers have reported several orders of magnitude of surface stiffening in their indentation studies of polydimethylsiloxane (PDMS) rubber in which a Berkovich probe was used. At the same time, other nanoindentation experiments with either Berkovich probe or spherical probe have reported much weaker or no surface stiffening for PDMS or other compliant materials . Such an extreme surface stiffening cannot be explained by pressure effects on the rubber modulus.…”

“…A third factor is the surface detection error, which has two sources: adhesion force and instrument surface detection criterion setting. It has been shown that for soft materials, the adhesion force between the sample surface and probe causes a “snap in” phenomenon, where the probe jumps on to the sample surface which results in a negative load at the initial loading. This, then, leads to a surface detection error and inaccurate modulus estimation.…”

Investigating the effect of silver nanorods embedded in polydimethylsiloxane matrix using nanoindentation and its use for flexible electronics

“…For indentation, the sample was cut into 1 x 1 cm 2 pieces using surgical blades and placed directly onto the UNHT sample holder and pressed with tweezers to develop full contact with the stage to avoid the air between the film and sample holder. 61,62 The area for indentation testing was carefully chosen by an optical microscope. In case of the quasi-static indentation, the load varied from 30 to 200 μN with a constant loading-unloading time of 30 s and holding time 10 s at maximum load.…”

Elastic modulus of thermoplastic elastomers investigated with the instantaneous volumetric strain method

“…The spherical indentation method is commonly used to measure the K ( t ) values of elastoplastic materials . Congrui et al . conducted a nanoindentation test with spherical indenters to characterize the mechanical properties of polydimethylsiloxane.…”