In the region near an interface, the microscopic properties of a glass forming liquid may be perturbed from their equilibrium bulk values. In this work, we probe how the interfacial effects of additive particles dispersed in a matrix can influence the local mobility of the material and its glass transition temperature, T g . Experimental measurements and simulation results indicate that additives, such as nanoparticles, gas molecules, and oligomers, can shift the mobility and T g of a surrounding polymer matrix (even for relatively small concentrations of additive; e.g. , 5–10% by volume) relative to the pure bulk matrix, thus leading to T g enhancement or suppression. Additives thus provide a potential route for modifying the properties of a polymer material without significantly changing its chemical composition. Here we apply the Limited Mobility (LM) model to simulate a matrix containing additive species. We show that both additive concentration, as well as the strength of its very local influence on the surrounding matrix material, will determine whether the T g of the system is raised or lowered, relative to the pure matrix. We demonstrate that incorporation of additives into the simple LM simulation method, which has successfully described the behavior of bulk and thin film glassy solids, leads to direct connections with available experimental and simulation results for a broad range of polymer/additive systems.
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Temperature dependent perylene fluorescence as a probe of local polymer glass transition dynamics
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.
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- Award ID(s):
- 1905782
- NSF-PAR ID:
- 10413773
- Date Published:
- Journal Name:
- Soft Matter
- Volume:
- 18
- Issue:
- 32
- ISSN:
- 1744-683X
- Page Range / eLocation ID:
- 6094 to 6104
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A new class of high‐temperature dipolar polymers based on sulfonylated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SO2‐PPO) was synthesized by post‐polymer functionalization. Owing to the efficient rotation of highly polar methylsulfonyl side groups below the glass transition temperature (
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2SM00552B
