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.
Employing a quartz crystal microbalance (QCM) as a MHz‐viscoelastic sensor requires extracting information from higher harmonics beyond the Sauerbrey limit, which can be problematic for rubbery polymer films that are highly dissipative because of the onset of anharmonic side bands and film resonance. Data analysis for QCM can frequently obscure the underlying physics or involve approximations that tend to break down at higher harmonics. In this study, modern computational tools are leveraged to solve a continuum physics model for the QCM's acoustic shear wave propagation through a polymer film with zero approximations, retaining the physical intuition of how the experimental signal connects to the shear modulus of the material. The resulting set of three coupled equations are solved numerically to fit experimental data for the resonance frequency Δfn and dissipation ΔΓn shifts as a function of harmonic number n, over an extended harmonic range approaching film resonance. This allows the frequency‐dependent modulus of polymer films at MHz frequencies, modeled as linear on a log–log scale, to be determined for rubbery polybutadiene (PB) and polydimethylsiloxane (PDMS) films, showing excellent agreement with time–temperature shifted rheometry data from the literature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.