Jul 2026· Journal of Polymer Science· 0 citations· 51 references
Abstract
The glass transition temperature (
T
g
) and underlying segmental dynamics are fundamental parameters governing the thermomechanical and macroscopic properties of polymeric materials. Honoring the 65th birthday of Professor Sindee L. Simon, this perspective first highlights several of her pioneering contributions to the understanding of structural recovery and nanoconfinement in polymers, using Flash differential scanning calorimetry (Flash DSC). While physical confinement heavily dictates the behavior of traditional linear polymers, semirigid conjugated polymers, the cornerstone of modern flexible electronics, experience an intrinsic “self‐confinement” arising from nanoscopic domains between their highly rigid backbones and packed, flexible side chains. This unique architecture yields extreme dynamic heterogeneity and vanishingly small heat capacity changes (Δ
C
p
), rendering traditional DSC largely ineffective. Inspired by Professor Simon's methodologies, this perspective will describe how the application of Flash DSC to conjugated polymers successfully overcomes these kinetic and thermodynamic barriers, isolating elusive thermal transitions. We explain how understanding and manipulating polymer dynamics directly impacts macroscopic device engineering: from maintaining viscoelastic mechanical compliance in soft wearable electronics to engineering stable organic photovoltaics. Finally, we highlight the necessity of a multi‐modal approach, coupling Flash DSC with the microscopic structural resolution of neutron scattering to fully map the evolving dynamic landscape of conjugated polymers.
Melt memory in semicrystalline polymers is the remarkable ability of polymer chains to retain structural information from a prior crystalline state after being heated above the melting temperature. This phenomenon can induce extraordinary self-nucleation and strongly influence crystallization kinetics and final material properties, yet its molecular origin remains unresolved. Here, using molecular dynamics simulations of linear polymer chains in which the strength of nonbonded interchain interactions is systematically tuned, we show that enhanced interchain attractions stabilize nanoscale regions of increased density and extended trans-planar conformations that persist in the melt, as revealed by analyzing the dynamics through a density-field approach. These residual ordered regions in the melt act as self-nuclei upon cooling, providing a molecular explanation for experimental observations of persistent melt memory in polar polymers. By varying a single chemically meaningful parameter, i.e., the strength of interchain attraction, our model bridges weakly interacting polyolefins and polymers with stronger dipolar or hydrogen-bonding interactions, establishing a direct link between molecular cohesion and memory retention. The results demonstrate that melt memory originates from the interaction-mediated survival of localized structural order in the melt rather than from a completely randomized chain state. These findings provide a molecular framework connecting the chemical structure, intermolecular forces, and macroscopic crystallization behavior, offering new principles for controlling polymer solidification and designing semicrystalline materials with tailored properties.
A. de Nicola, A. Müller, Dario Cavallo et al.· Journal of the American Chem...· 0 citations
United-atom molecular dynamics simulations were performed to investigate the structure, dynamics, and mechanical-viscoelastic properties of natural rubber (NR)/Eucommia ulmoides gum (EUG) blends. The systems were modeled as fully amorphous matrices to isolate the intrinsic behavior of the disordered phase. Results reveal that incorporating rigid EUG chains into flexible NR induces a counterintuitive acceleration of segmental dynamics─manifested as a decreased glass transition temperature and enhanced chain diffusion─driven by local segmental ordering that facilitates chain sliding. Under uniaxial deformation, tensile strength exhibits a nonmonotonic composition dependence, with optimal reinforcement at 20% EUG content, arising from a balance between the orientational reinforcement of rigid segments and the delayed onset of cavitation. Linear viscoelastic analysis shows that enhanced dynamics shift the α-relaxation peak to higher frequencies and slightly increase energy dissipation. This contrasts with the reduced hysteresis reported for real materials, a discrepancy that stems from the absence of crystalline constraints and chemical cross-links in our amorphous models. By delineating the intrinsic role of amorphous-phase dynamics, this work provides molecular-level insights into the structure-property relationships of biobased elastomers.
The insertion of small molecules into glassy polymer matrices is strongly influenced by the non-equilibrium dynamical state of the polymer. Using atomistic molecular dynamics simulations, we investigate sorbitol insertion into dry and hydrated poly(vinyl acetate) (PVAc) slabs and analyse how limited polymer mobility in the glass affects the potential of mean force (PMF). In the dry slab, the polymer chains are kinetically trapped below the glass transition temperature and cannot relax on accessible simulation timescales. As a result, direct PMF calculations yield an artificially large, non-equilibrium free-energy barrier dominated by steric constraints and kinetic trapping. In contrast, water-induced plasticization enhances local mobility, allowing relaxation around the solute and producing a substantially lower, more physically meaningful insertion barrier. To overcome the non-ergodicity of the dry glass, we introduce a local annealing strategy. Here, the solute is heated, promoting local relaxation of polymer chains in the immediate vicinity of the solute, prior to re-equilibration into a glassy state. This method reduces the insertion barrier by more than 70% and yields an equilibrium-like free-energy profile without disrupting, melting or softening the entire polymer film. The approach provides a practical and general route for modelling solute insertion in glassy polymers, where full equilibration is not computationally achievable on the timescales of atomistic simulation.
Ajeeth Kanagarajan, M. R. Wilson· Soft Matter· 0 citations
Mechanochemical activation has been extensively investigated in solutions and soft polymeric materials, where force transmission along stretched chains dominates the response. In contrast, activation behavior in higher-modulus, glassy thermosets remains poorly understood, and the role of the material environment itself has not been systematically quantified. Here, we investigate spiropyran (SP) mechanophores incorporated into a high-performance poly(dicyclopentadiene) (pDCPD) network fabricated directly by polymerization into its final form. This chemically faithful synthesis preserves network integrity and enables the quantitative analysis of mechanophore activation under tensile and compressive loading. We find that activation is absent in the elastic regime and emerges only beyond the macroscopic yield point. These results demonstrate that the mechanochemical response in this glassy network is governed by deformation and irreversible segmental mobility rather than tension magnitude alone, establishing motion-induced activation as distinct from the behavior previously observed in soft materials. The SP-pDCPD system thus provides a quantitative framework for understanding mechanochemical activation in high-performance glassy polymers.
Fangbai Xie, S. D. Ekim, F. Kern et al.· Journal of the American Chem...· 0 citations
The advancement of stretchable organic photovoltaics is hindered by a fundamental trade-off between high optoelectronic performance and mechanical durability, in particular, a challenge rooted in the complex microstructure of conjugated polymers and their blends. This review addresses a critical literature gap on the microstructure of various conjugated polymer systems by systematically examining how multiscale microstructural evolution, from solution-state aggregation to solid-state morphology and dynamic response under strain, can be characterized, understood, and rationally controlled. Analysis begins with how advanced X-ray and neutron scattering techniques elucidate the formative solution-aggregation structures that dictate the final solid-state morphology. Subsequently, multiscale characterization methods for thin films are reviewed, alongside material design strategies, such as elastomeric modifiers, engineered to optimize phase-separated morphologies for simultaneous conductivity and mechanical flexibility. A key focus is the transition beyond static X-ray scattering analysis to explore the dynamic evolution of microstructure under mechanical stretching, thereby underscoring the pivotal role of in situ and operando characterization in revealing deformation and failure mechanisms. By integrating insights across these scales, this review aims to distill rational design principles, offer a coherent processing-structure-performance framework, and provide a complete picture for the predictive design of next-generation intrinsically robust stretchable photovoltaics and related electronics.
M. Gao, Junjiang Wu, Yanhou Geng et al.· Advances in Materials· 0 citations
In this work, the dynamics and viscoelasticity of styrene butadiene rubber (SBR) are systematically explored for different temperatures (T) and pressures (P), where the coarse-grained model and potential functions are developed by the iterative Boltzmann inversion approach. The simulation results reveal that the dynamics at the monomer and chain scales display different dependencies on T and P. Thus, a time-T-P superposition principle (TTPSP) holds at both the monomer and chain scales for the translational dynamics. However, TTPSP fails at the monomer scale for the relaxation dynamics while remaining valid at the chain scale at a high T. Meanwhile, a low T enhances dynamical heterogeneity, while a high P reduces fragility, which also reduces the monomer mobility. The universal correlations among the relaxation time, corresponding peak height, Debye-Waller factor, T, and P are derived. These indicate the reduced anisotropy of cage shapes at a high P value and some decoupling or coupled relationships. Finally, the storage modulus, loss modulus, and viscosity of SBR are analyzed, which exhibit a gradual increase with decreasing T or increasing P. Interestingly, the viscoelastic properties present a strong relationship with local chain stiffness. TTPSP holds for viscoelasticity at a high T, while it breaks down over the entire T range, which mainly originates from the complex multiscale dynamical behavior of SBR. In summary, this work provides a comprehensive understanding of how temperature and pressure influence the dynamics and viscoelasticity of the SBR.
Yang Zhang, Xiangbao Wang, Ruibin Ma et al.· Langmuir· 0 citations
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