Fig 1.
Schematic diagram of the PDMS system for preparation of ultrasoft PDMS elastomers; m ≈ 2090; x ≈ 700, y ≈ 51, calculated from 5–7 mol% of hydrosilane group.
Right hand side shows a detail of the PDMS network.
Fig 2.
Silicone elastomers exhibit a large linear range.
Amplitude sweeps for neat silicone elastomers (system 1) with r = 1 (A) and r = 0.71 (B) measured at 20°C. Storage (solid symbols) and loss (open symbols) modulus are plotted against strain amplitude. Squares ω = 62.83 rad/s; circles ω = 6.283 rad/s; and triangles ω = 0.6283 rad/s. The dashed lines indicate the limits of the linear regime. Raw data can be found in S1 Dataset.
Fig 3.
Reducing the catalyst concentration decreases elasticity of elastomers.
Frequency dependence of storage (G', solid symbols) and loss modules (G", open symbols) of neat silicone networks (system 1) prepared at r = 0.71 and measured at 1% strain. Squares: 0.5 ppm catalyst; circles: 0.37 ppm catalyst. Red line: power law expected for a critical gel (see discussion). Raw data can be found in S3 Dataset.
Fig 4.
The stoichiometric ratio controls viscoelastic response.
Frequency dependence of storage (G', solid symbols) and loss modules (G", open symbols); squares stoichiometric ratio r = 1.28; circles: r = 1.00; triangles: r = 0.71. Red line: power law expected for a critical gel (see discussion). Raw data can be found in S4 Dataset.
Table 1.
Dependence of the equilibrium shear modulus G0 on the stoichiometric ratio r.
Table 2.
Dissipation factors of neat silicone networks.
Fig 5.
The loss module may be approximated by power laws in some regions.
The local slope of G'' in a double logarithmic plot, i.e. the effective exponent n, as a function of angular frequency; (triangles) elastomer with r = 1.21; (squares) r = 0.84; (stars) r = 0.71. Raw data can be found in S5 Dataset.
Table 3.
Dependence of sol fraction on stoichiometric ratio.
Fig 6.
Change of rheological properties due to addition of inert filler polymers.
Frequency dependence of the storage (G', solid symbols) and loss modules (G", open symbols) at a strain of 1%. All samples: r = 0.71 and 0.5 ppm catalyst; Squares: neat system; Circles: 25% (v/v) of 139 kg/mol inert PDMS added; Triangles: 25% (v/v) of 68 kg/mol inert PDMS added; Diamonds: 25% (v/v) of 28 kg/mol inert PDMS added. Raw data can be found in S7 Dataset.
Fig 7.
Inhibition results in ultrasoft elastomers.
Frequency dependence of the storage (G', solid symbols) and loss modules (G", open symbols). All measurements 1% strain and stoichiometric ratio 1.28. Squares: 0.5 ppm catalyst and cinhibitor = 0% (neat system); Circles: 0.5 ppm catalyst and winhibitor = 0.25%; Triangles: 1.0 ppm catalyst and cinhibitor = 2%. Raw data can be found in S8 Dataset.
Fig 8.
Cortical neurons behave normally when grown on our silicone elastomer substrates.
Cortical neurons, grown 5 days on soft PDMS elastomer without inhibitor, system 1, r = 0.71, 0.5 ppm catalyst (A) and with inhibitor, system 3, r = 3.18, 1 ppm catalyst, 2.16% inhibitor (B). Please note that a stoichiometric ratio as high as shown in B) can be achieved only in system 3 due to its long work time.
Fig 9.
Rheological response of weakly crosslinked elastomers can be described by an empirical model.
Fitting of rheological data of neat elastomers (system 1) using the modified Maxwell model, Eqs 5 and 6; frequency dependence of storage (G', solid symbols) and loss modules (G", open symbols); Diamonds: r = 1.28; Triangles, left: r = 1.14; Squares: r = 1.00; Circles: r = 0.92; and Triangles, up: r = 0.71; red lines are fit curves. Raw data can be found in S9 Dataset.
Fig 10.
The loss factor tan δ = G''/G' is independent of filler molecular weight.
All samples stoichiometric ratio 0.71 and 0.5 ppm catalyst. Squares: Neat elastomer (system 1); all other systems 25% inert silicone polymer added with molecular weights of 28 kg/mol (circles), 68 kg/mol (up triangles), and 139 kg/mol (down triangles), respectively. Raw data can be found in S10 Dataset.
Fig 11.
The equilibrium shear module of silicone elastomers is controlled by the concentration of hydrosilane cSi-H.
Data for PDMS elastomers: Squares, black: system 1, at a catalyst concentration of 0.5 ppm (solid symbols) and less (open symbols); Crosses: system 2; Squares, red: system 3; Dashed line is an empirical fit, Eq 7, cf. text. Numerical values can be found in S11 Dataset.