Transparency of Temperature-responsive Shape-memory Gels Tuned by a Competition between Crystallization and Glass Transition

Wang, Youhao; Gong, Jin; Hu, Wenbing

doi:10.1007/s10118-020-2456-0

Cited by 8 publications

(6 citation statements)

References 43 publications

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“…Finally, Flash DSC 1 executed the experiment program to achieve the heat flow rates for the evaluations of the enthalpy changes during isothermal crystallization. Like in our previous Flash DSC measurements, − the temperature dependence of isothermal crystallization kinetics in half–half symmetric racemic PLA blends with five molecular weights were measured. During these measurements, PLA samples were easily ruined after long-term repeating experiments, and new samples with different sample mass were loaded.…”

Section: Methodsmentioning

confidence: 99%

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

Liú

Wang

et al. 2022

Macromolecules

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High molecular weights switch the harvests of crystallinity from stereocomplex crystals to homocrystals in the symmetric racemic poly(lactic acid) (PLA) blends. We performed Flash DSC measurement of isothermal crystallization kinetics of symmetric racemic PLA blends with five molecular weights in combination with confocal Raman spectroscopy to identify their polymorphic crystal phases. The results confirmed crystallization kinetics as responsible for the molecular weight selection of polymorphic crystals. We further employed Tammann analysis on the crystal nucleation kinetics in the low-temperature region to reveal that higher molecular weights have little influence on homocrystal nucleation; rather, they suppress the nucleation rates of stereocomplex crystals, making homocrystals dominant. The observation was interpreted by the correlation hole of neighboring monomers among higher molecular weight polymers, which hinders intermolecular nucleation of alternatingly racemic polymers as favored for stereocomplex crystals.

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Section: Methodsmentioning

confidence: 99%

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

Liú

Wang

et al. 2022

Macromolecules

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“…Therefore, side‐chain crystallization or packing is the most probably interpretation 28–30 . This indicates the C18 side chain of PSA 22 are extended and packing paralleled with each other between the perpendicular aligned main chain.…”

Section: Resultsmentioning

confidence: 99%

“…According to the equation d = 2π/ q , the long periods of P(SA‐ETPTA) and PVA are 0.15 and 0.07 Å −1 , respectively, which can be distinguished from each other. Crystallization of PSA segment is mainly side chain crystallization, which will be detailed in the following discussion 22 …”

Section: Resultsmentioning

confidence: 99%

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A poly(vinyl alcohol)/poly(stearyl acrylate) core‐shell fibers with robust performance realized by taking advantages of the phase change property

Wang

Zheng

et al. 2021

J of Applied Polymer Sci

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A phase change fiber with long‐term stability, temperature dependent transparency and melt‐healing properties were prepared using polyvinyl alcohol (PVA) as the shell layer and polystearyl acrylate (PSA) lightly crosslinked by ethoxylated trimethylolpropane triacrylate (ETPTA) as the core layer. It was found the PVA/P(SA‐ETPTA) core‐shell fiber exhibited a melt enthalpy of 43 J/g (coagulation bath temperature −15 °C, core layer diameter 0.2 mm, spinning rate 1.0 mm/s) and an extremely high stability after 100 heating–cooling cycles. The as‐spun core‐shell fiber was fragile, but the flexibility was greatly improved after it was drawn to 800% of the original length. The PVA shell forming tunneling for the P(SA‐ETPTA) core layer, which could heal after fracture on condition of PSA melting. The melting and crystallization of PSA side chains enabled a temperature dependent light transmittance of the PVA/P(SA‐ETPTA) fibers, which was ascribed to the phase separation between PSA and PETPTA around the melting point of the PSA composition. As a whole, the core‐shell fibers showed robust performance as a phase change fiber. Further aggregate structure and orientation structure investigation on the PVA/P(SA‐ETPTA) fiber was detected by wide angle X‐ray diffraction and small angle X‐ray scattering.

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“…The time evolution of melting enthalpy could provide a kinetic analysis to demonstrate the acceleration effects of low-temperature annealing on high-temperature crystallization, similar with our previous investigation. ,, The melting enthalpy was obtained from the integration of the melting peak on the heating curves shown in Figure b–d. The results for various crystallization periods at various temperatures are summarized in Figure a–c.…”

Section: Resultsmentioning

confidence: 99%

Glassy Alfa-Relaxation Promotes Surprising Homo-Crystal Nucleation in the Low-Molar-Mass Enantiomeric Poly(lactic acid) Blend

Liú

Xie

et al. 2022

Macromolecules

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Low-molar-mass enantiomeric poly(lactic acid) (PLA) blends commonly harvest stereo-complex crystals that hold alternatingly packed enantiomeric polymers favoring more intermolecular nucleation than intramolecular nucleation. Structural relaxation in polymer glassy states often promotes early-stage crystal nucleation for the high-temperature crystallization. By means of fast-scanning differential scanning calorimetry measurements, we first identified enthalpy relaxation as dominated by beta-relaxation below 35 °C and by alfa-relaxation above 35 °C in the glassy states of the symmetric enantiomeric PLA blends (20 kDa, L/D = 7:3). We then employed the two-stage Tammann analysis on crystal nucleation during isothermal annealing for 300 s at 30 °C in comparison to 40 °C, followed with isothermal crystallization at various high temperatures. The results of high-temperature crystallization showed that in comparison to the parallel cases without prior annealing, the annealing with beta-relaxation at 30 °C promotes stereo-complex crystal nucleation, probably because only very small stereo-complex crystal nuclei could survive due to their relatively high melting points. In contrast, the annealing with alfa-relaxation at 40 °C surprisingly promotes homo-crystal nucleation for the high-temperature crystallization below 120 °C, probably because the relatively large-scale but limited molecular cooperation under these circumstances favors intramolecular chain-folding nucleation of homo-crystals more than intermolecular fringed-micelle nucleation of stereo-complex crystals. The homo-crystal nuclei could not survive at a temperature of 120 °C and above and hence leave the rest stereo-complex crystal nuclei as dominant again for the high-temperature crystallization. Our observations revealed a strong competition between intermolecular crystal nucleation and intramolecular crystal nucleation at the early stage of polymer crystal nucleation.

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Transparency of Temperature-responsive Shape-memory Gels Tuned by a Competition between Crystallization and Glass Transition

Cited by 8 publications

References 43 publications

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

A poly(vinyl alcohol)/poly(stearyl acrylate) core‐shell fibers with robust performance realized by taking advantages of the phase change property

Glassy Alfa-Relaxation Promotes Surprising Homo-Crystal Nucleation in the Low-Molar-Mass Enantiomeric Poly(lactic acid) Blend

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