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1. Local Glass Transition Temperature T _g ( z ) Profile in Polystyrene next to Polybutadiene with and without Plasticization Effects

   https://doi.org/10.1002/macp.201700328  

   Kasavan, Benjamin L.; Baglay, Roman R.; Roth, Connie B. (November 2017, Macromolecular Chemistry and Physics)

   Abstract Rubber toughening of glassy polystyrene (PS) has been manufactured commercially for decades as high impact polystyrene, where rubbery poly‐butadiene (PB) inclusions are added to modify the PS matrix response to deformation and impact. In this study, measurements of the local glass transition temperatureT_g(z) of PS next to PB rubber are presented, expanding the previous data to a polymer with a much lowerT_gvalue (PBT_g^bulk= −96 °C). After accounting for a small molecule additive present in the commercial PB sample that would otherwise migrate over to the PS domain causing plasticization, it is found that theT_g(z) profile in PS next to PB is consistent with previous results. It is also demonstrated that these broad and asymmetric experimentally observedT_g(z) profiles are not caused by the migration of low molecular weight chains across the interface by comparing samples made with two different poly(n‐butyl methacrylate) molecular weights. 

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2. Fast crystallization below the glass transition temperature in hyperquenched systems

   https://doi.org/10.1063/5.0136306  

   Lucas, Pierre; Takeda, Wataru; Pries, Julian; Benke-Jacob, Julia; Wuttig, Matthias (February 2023, The Journal of Chemical Physics)

   Many phase change materials (PCMs) are found to crystallize without exhibiting a glass transition endotherm upon reheating. In this paper, we review experimental evidence revealing that these PCMs and likely other hyperquenched molecular and metallic systems can crystallize from the glassy state when reheated at a standard rate. Among these evidences, PCMs annealed below the glass transition temperature T g exhibit slower crystallization kinetics despite an increase in the number of sub-critical nuclei that should promote the crystallization speed. Flash calorimetry uncovers the glass transition endotherm hidden by crystallization and reveals a distinct change in kinetics when crystallization switches from the glassy to the supercooled liquid state. The resulting T g value also rationalizes the presence of the pre- T g relaxation exotherm ubiquitous of hyperquenched systems. Finally, the shift in crystallization temperature during annealing exhibits a non-exponential decay that is characteristic of structural relaxation in the glass. Modeling using a modified Turnbull equation for nucleation rate supports the existence of sub- T g fast crystallization and emphasizes the benefit of a fragile-to-strong transition for PCM applications due to a reduction in crystallization at low temperature (improved data retention) and increasing its speed at high temperature (faster computing). 

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3. Development of broad modulus profile upon polymer–polymer interface formation between immiscible glassy–rubbery domains

   https://doi.org/10.1073/pnas.2312533120  

   Gagnon, Yannic J; Burton, Justin C; Roth, Connie B (January 2024, Proceedings of the National Academy of Sciences)

   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. 

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4. Validation of quartz crystal rheometry in the megahertz frequency regime

   https://doi.org/10.1002/polb.24812  

   Delgado, David E.; Sturdy, Lauren F.; Burkhart, Craig W.; Shull, Kenneth R. (March 2019, Journal of Polymer Science Part B: Polymer Physics)

   ABSTRACT The utility of the quartz crystal microbalance (QCM) as a high‐frequency rheometer operating at 15 MHz was demonstrated. High‐frequency data obtained from a series of rubbery materials were compared with results obtained from traditional dynamic mechanical analysis (DMA) at much lower frequencies. The high‐frequency data enable meaningful shift factors to be obtained at temperatures much further above glass‐transition temperature (T_g) than would otherwise be possible, giving a more complete picture of the temperature dependence of the viscoelastic properties. The QCM can also be used to quantify mass uptake and changes in viscoelastic properties during sample oxidation. The viscoelastic response spanning the full range of behaviors from the rubber to glassy regimes was found to fit well with a six‐element model consisting of three power‐law springpot elements. One of these elements is particularly sensitive to the behavior in the transition regime where the phase angle is maximized. The value of this quantity is obtained from the maximum phase angle, which can be obtained from a temperature sweep at fixed frequency, proving a means for more detailed frequency‐dependent rheometric information to be obtained from a fixed‐frequency measurement at a range of temperatures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019,57, 1246–1254 

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5. Different temperature- and pressure-effects on the water-mediated interactions between hydrophobic, hydrophilic, and hydrophobic–hydrophilic nanoscale surfaces

   https://doi.org/10.1063/5.0097908  

   Engstler, Justin; Giovambattista, Nicolas (August 2022, The Journal of Chemical Physics)

   Water-mediated interactions (WMIs) are responsible for diverse processes in aqueous solutions, including protein folding and nanoparticle aggregation. WMI may be affected by changes in temperature and pressure, and hence, they can alter chemical/physical processes that occur in aqueous environments. Traditionally, attention has been focused on hydrophobic interactions while, in comparison, the role of hydrophilic and hybrid (hydrophobic–hydrophilic) interactions have been mostly overlooked. Here, we study the role of T and P on the WMI between nanoscale (i) hydrophobic–hydrophobic, (ii) hydrophilic–hydrophilic, and (iii) hydrophilic–hydrophobic pairs of (hydroxylated/non-hydroxylated) graphene-based surfaces. We find that hydrophobic, hydrophilic, and hybrid interactions are all sensitive to P. However, while hydrophobic interactions [case (i)] are considerably sensitive to T-variations, hydrophilic [case (ii)] and hybrid interactions [case (iii)] are practically T-independent. An analysis of the entropic and enthalpic contributions to the potential of mean force for cases (i)–(iii) is also presented. Our results are important in understanding T- and P-induced protein denaturation and the interactions of biomolecules in solution, including protein aggregation and phase separation processes. From the computational point of view, the results presented here are relevant in the design of implicit water models for the study of molecular and colloidal/nanoparticle systems at different thermodynamic conditions. 

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