Local Glass Transition Temperature T_g(z) Within Polystyrene Is Strongly Impacted by the Modulus of the Neighboring PDMS Domain

Abstract

Profiles in the local glass transition temperature T g(z) within polystyrene (PS) next to polydimethylsiloxane (PDMS) domains were determined using a localized fluorescence method. By changing the base to cross-linker ratio, we varied the cross-link density and, hence, the Young’s modulus of PDMS (Sylgard 184). The local T g(z) in PS at a distance of z = 50 nm away from the PS/PDMS interface was found to shift by 40 K as the PDMS modulus was varied from 0.9 to 2.6 MPa, demonstrating a strong sensitivity of this phenomenon to the rigidity of the neighboring domain. The extent the T g(z) perturbation persists away from the PS/PDMS interface, z ≈ 65–90 nm before bulk T g is recovered, is much shorter for this strongly immiscible system compared with the weakly immiscible systems studied previously, which we attribute to a smaller interfacial width, as the χ parameter for PS/PDMS is an order of magnitude larger.

Physically intuitive continuum mechanics model for quartz crystal microbalance: Viscoelasticity of rubbery polymers at MHz frequencies

“…We were able to find DMA data for the same Sylgard 184 PDMS elastomer we use published by Tiwari et al, where they measured the frequency‐dependent Young's modulus E ( ω ) from −140 °C to 120 °C in 5 °C increments, and then time–temperature shifted the data to create a master curve at a reference temperature of 20 °C 50 . Although this study by Tiwari et al used slightly different curing conditions and base to cross‐linker ratio, our previous literature compilation of Sylgard 184 PDMS Young's modulus values suggests these small differences are not significant, and the Tiwari et al modulus curve should be a decent representation for our PDMS 35 …”

“…The storage and loss moduli are again modeled using Equations (), treating the frequency dependence of the shear modulus as linear on a log–log scale. For PDMS, we use the popular Sylgard 184 elastomer kit to make cross‐linked PDMS samples (9 to 1 base to cross‐linker ratio by mass) with a zero‐frequency elastic modulus E ≈ 1.95 ± 0.19 MPa 35,37 …”

“…Polydimethylsiloxane (PDMS) films cross‐linked at a base to cross‐linker ratio of 9:1 by mass were prepared using the Sylgard 184 kit manufactured by Dow Corning. After mixing the base and cross‐linking agent for ≈1 min, the PDMS mixture was diluted with heptane for spin‐coating (at ≈30 wt% of the PDMS mixture in heptane) 35 . PDMS films were then cured at 70 °C for 2 h to match the curing schedule of Refs.…”

“…The optical layer model was comprised of a transparent Cauchy layer for the polymer film, atop a semi‐infinite silicon substrate with a 1.25 nm native oxide layer 38 . For ellipsometric modeling of spin‐coated PDMS films, an additional thickness non‐uniformity parameter was included in the fit, with values typically between 3% and 7% 35 …”

Water‐assisted mechanical testing of polymeric thin‐films

“…Recently, Gagnon and Roth demonstrated the influence of the base to crosslinker ratio of PDMS substrates on the T g of PS using fluorescence labeling. 100 In this report, a 10-15 nm thick pyrene-labeled probe layer was used to characterize the influential distance of PDMS on the T g of a bulk (>500 nm) PS film. The PDMS substrate was observed to substantially reduce the T g of PS at a length scale of 65-90 nm with a higher base to crosslinker ratio of 17:1, demonstrating the most significant influence.…”