Extended PDMS stiffness range for flexible systems

Abstract

a b s t r a c tThe use of polymers in the context of flexible systems such as flexible sensors leads to an incompatibility issue: on the one hand, the flexibility of the polymer must not be to the detriment of the fabrication process, e.g. excessive thermal expansion leading to process failure and on the other hand, certain applications will require high flexibility and also a specific mechanical stiffness, e.g. artificial skin, smart clothes, flexible screen. In other words, a compromise is necessary between rigidy for processing and controlled flexibility for applications. In this context it is crutial to be able to tune the mechanical properties of such polymers. Polydimethylsiloxane (PDMS) is a very versatile and useful soft polymeric material -Elastic modulus typically ≈1 MPa. This paper investigates the stiffness tunability of PDMS by varying the hardening agent to PDMS base ratio over 19:1 to 2:1, and using two extreme curing processes, i.e. 120 min at 100 • C and 2 days at 165 • C. It was observed that the stiffness of PDMS can be accurately controlled from 800 kPa to 10 MPa with a rupture limit higher than 20%. To our knowledge this is the highest reported elastic modulus in PDMS by combining mixing ratio and curing temperature. The impact of such a stiffness variation on potential functional properties such as the rupture limit, Poisson's ratio and material's wetting contact angle is also analysed. We observe that the wetting contact angle depends on the bulk mechanical properties of the PDMS. The observations will be of use to all technological communities who are engaged in using PDMS-type polymers for their specific applications.

Capturing strain stiffening using Volume Controlled Cavity Expansion

“…NH behavior and when analyzed against the Ogden model, it is possible to capture an exponent of N = 2.40 ± 0.14, again nearly identical to the NH response. 4 Figure 3: Variation of the average shear modulus measured for PDMS samples as a function of the cross-linking density, in comparison with our previous measurements [46], as well as the measurements of Wang et al [92] and Seghir and Arscott [93].…”

“…Unfortunately, there are no reports of measurements of such second constants reported in literature for comparable samples. Seghir and Arscott [93] use a generalized MR to analyze their results, but only report the shear modulus as presented in Fig.3. Kim et al [94] report softer responses for PDMS films of 15:1 (less than half the shear modulus measured here) and thus a fair comparison is not possible.…”

Photo-hardenable and patternable PDMS/SU-8 hybrid functional material: A smart substrate for flexible systems

“…In this study, different PDMS mixing ratios and baking processes are required to mix with the SU‐8—for an easier understanding of the preparation of the PDMS, the authors direct readers to refer to our previous work in which the tunability of PDMS stiffness is demonstrated and analyzed depending on the base/curing agent mixing ratio, baking time, and temperature. PDMS mixtures were first prepared by mixing the base and the curing agent with different weight ratios (10:1, 4:1, and 2:1).…”

Polynomial fitting techniques applied to opto-mechanical properties of PDMS Sylgard 184 for given curing parameters

“…Study and characterization of PDMS's mechanical, chemical and optical properties are reported for specific cases in the literature; some fabrication methods are also mentioned to modify properties such as (a) curing and baking conditions, (b) different proportions of curing base agent, (c) different types of PDMS and other polymers, (d) inclusion of other molecules or particles and (e) elaboration of samples with different forms and sizes [13,[28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”

“…Mechanical properties measurements of PDMS's samples are also detailed for predetermined synthesis parameters; relevant examples are the components´ratio of base mixture: catalyst (ratios varying from 2:1 to 33:1) [9,16,21,28], the curing temperature applied (from room temperature up to 310°C) [30,35], or the curing time (18 min to 48 h) [32,41]. Reports indicate that Young's modulus, compressive and shear moduli vary in the ranges of 12 kPa-3 GPa, 117.8 MPa-186.9 MPa and 100 kPa-3 MPa, respectively [14,18,22,35,37,42,43].…”