Abstract
The elastic modulus and hydrophilicity of cross-linked poly(dimethylsiloxane) (PDMS) are tunable via cross-linker concentration and the addition of a simple surfactant, C12E4, before curing. However, the surfactant concentration, [C12E4], reduces the elastic modulus (73% lower for 6.3% w/w) because it reduces the extent of curing. This is likely because the hygroscopic surfactant results in water poisoning of the catalyst. Three distinct time-dependent hydrophilicity profiles were identified using water contact angle analysis with [C12E4] determining which profile was observed. This indicates the concentration-dependent phase behavior of C12E4 within PDMS films. Changes in phase behavior were identified using small-angle neutron scattering (SANS) and a compatibility study. No surface excess or surface segregation of surfactant was observed at the PDMS–air interface. However, a surface excess revealed by neutron reflectivity against a D2O interface indicates that the increase in hydrophilicity results from the migration of C12E4 to the film interface when exposed to water.
Highlights
Poly(dimethylsiloxane) (PDMS) is a polymer that has use in microfluidic devices,[1−4] fouling-release coatings,[5−9] and cell cultivation.[10,11] When cross-linked to form a network, its biocompatibility, low bulk modulus, deformability, low roughness, and low surface energy have made the polymer a favorable material for these applications,[12] and by learning to better control some of these properties, the functionality of PDMS in these applications can be improved.PDMS does have limitations
Similar observations regarding the trend in the tangent elastic modulus with cross-linker concentration and the different nonlinear rheologies have been reported by Seghir and Arscott when curing Sylgard 184 for 2 h at 100 °C.66
Available PDMS can be tuned by adjusting the concentration of durham.ac.uk the cross-linker used when curing and that the nonlinear rheology is different when using more or less than the concentration of cross-linker recommended by the manufacturer
Summary
Poly(dimethylsiloxane) (PDMS) is a polymer that has use in microfluidic devices,[1−4] fouling-release coatings,[5−9] and cell cultivation.[10,11] When cross-linked to form a network, its biocompatibility, low bulk modulus, deformability, low roughness, and low surface energy have made the polymer a favorable material for these applications,[12] and by learning to better control some of these properties, the functionality of PDMS in these applications can be improved. D2O could not be obtained without enriched layers of d25− C12E4 near the water interface While this increase in SLD could be due to the penetration of D2O into the PDMS matrix, such a layer was not needed to fit the reflectivity curve from a pure PDMS film against D2O (shown in Figure 10), suggesting arises from the phase separation of components into small domains, capable of scattering light. The low-Q Porod exponent of the fit for the 0.87% w/w d25−C12E4 cured sample was ∼2, whereas the higher concentrations showed m ≃ 3 This change in the small-angle scattering behavior between low and high concentrations shows that the low-Q features are likely not inherent to the PDMS matrix.
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