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Abstract 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 Δf_nand dissipation ΔΓ_nshifts as a function of harmonic numbern, 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. 

Chain adsorption to nanofiller interfaces creating bound layers has become central to understanding property changes in polymer nanocomposites. We determine the impact different kinds of adsorbed layers can have on the local glass transition temperature Tg of polymer matrices in a model film system using a localized fluorescence method. This work compares the adsorption and desorption of adsorbed layers grown in solution with the solution washing characteristics of adsorbed layers formed in the melt, leveraging knowledge about polymer adsorption in solution to infer the structure of adsorbed layers formed in the melt. In the limit of zero concentration after a long time in solution, we find that both kinds of adsorbed layers reach the same limiting adsorbed amount h∞(c → 0) ≈ 1 nm, appearing to evolve to the same thermodynamic equilibrium state of a near monolayer of surface coverage. We propose that melt annealing leads to a coarsening of polymer segment–surface contacts, increasing the length of trains and shrinking loops and tails, slowing the subsequent kinetics of these adsorbed chains in solution. Considering how the pyrene-labeled chains intermix with the adsorbed layer enables us to discriminate between the impact of tails, loops, and trains as threading of loops takes longer. We find that large fluffy loops, tails, and trains have little to no impact on the local Tg. A large 30 K increase in local Tg is observed for 30-min solvent washed well-annealed films at long intermixing times that we attribute to the threading of small tight loops. 

Interfaces of glassy materials such as thin films, blends, and composites create strong unidirectional gradients to the local heterogeneous dynamics that can be used to elucidate the length scales and mechanisms associated with the dynamic heterogeneity of glasses. We focus on bilayer films of two different polymers with very different glass transition temperatures ( $T_{\text{g}}$) where previous work has demonstrated a long-range (∼200 nm) profile in local $T_{\text{g}}\left(z\right)$is established between immiscible glassy and rubbery polymer domains when the polymer–polymer interface is formed to equilibrium. Here, we demonstrate that an equally long-ranged gradient in local modulus $\tilde{G}\left(z\right)$is established when the polymer–polymer interface ( $\approx$5 nm) is formed between domains of glassy polystyrene (PS) and rubbery poly(butadiene) (PB), consistent with previous reports of a broad $T_{\text{g}}\left(z\right)$profile in this system. A continuum physics model for the shear wave propagation caused by a quartz crystal microbalance across a PB/PS bilayer film is used to measure the viscoelastic properties of the bilayer during the evolution of the PB/PS interface showing the development of a broad gradient in local modulus $\tilde{G}\left(z\right)$spanning $\approx$180 nm between the glassy and rubbery domains of PS and PB. We suggest these broad profiles in $T_{\text{g}}\left(z\right)$and $\tilde{G}\left(z\right)$arise from a coupling of the spectrum of vibrational modes across the polymer–polymer interface as a result of acoustic impedance matching of sound waves with $\lambda \sim 5$nm during interface broadening that can then trigger density fluctuations in the neighboring domain. 

We demonstrate how the temperature dependence of perylene's fluorescence emission spectrum doped in bulk polymer matrices is sensitive to the local glass transition dynamics of the surrounding polymer segments. Focusing on the first fluorescence peak, we show that the intensity ratio I Ratio ( T ) = I Peak ( T )/ I SRR between the first peak and a self referencing region (SRR) has a temperature dependence resulting from the temperature-dependent nonradiative decay pathway of the excited perylene dye that is influenced by its intermolecular collisions with the surrounding polymers segments. For different polymer matrices, poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(2-vinyl pyridine) (P2VP), and polycarbonate (PC), we demonstrate that I Ratio ( T ) exhibits a transition from a non-Arrhenius behavior above the glass transition temperature T g of the polymer to an Arrhenius temperature dependence with constant activation energy E below the T g of the polymer matrix, indicating perylene's sensitivity to cooperative α-relaxation dynamics of the polymer matrix. This transition in temperature dependence allows us to identify a perylene defined local T peryleneg of the surrounding polymer matrix that agrees well with the known T g values of the polymers. We define a fluorescence intensity shift factor in analogy with the Williams–Landel–Ferry (WLF) equation and use literature WLF parameters for the polymer matrix to quantify the calibration factor c f needed to convert the fluorescence intensity ratio to the effective time scale ratio described by the conventional WLF shift factor. This work opens up a new characterization method that could be used to map the local dynamical response of the glass transition in nanoscale polymer materials using appropriate covalent attachment of perylene to polymer chains. 

Polymers exist in the glass state for a wide range of applications. The slow and limited crystallizability of polymers means that solid polymer materials are either wholly or in part glassy, giving them great importance. The glass is a nonequilibrium amorphous state that occurs because the cooperative molecular dynamics become kinetically trapped on cooling as the available thermal energy for molecular motion decreases. This article aims to provide the reader with a molecular picture of what this packing frustration that causes glass formation means for polymers. Experimental considerations for accurately measuring the glass transition temperature 𝑇𝑔 given this nonequilibrium nature will be discussed. Basic concepts underpinning theoretical efforts to model the glass transition will be summarized to provide the reader with a lexicon and paradigm for understanding different approaches used in the field to capture the main characteristics of glasses. Current research areas of interest in polymer glasses will be briefly outlined. Hopefully, this article will provide the beginning investigator a starting point for their own studies.