Free Surface-Induced Glass-Transition Temperature Suppression of Simulated Polymer Chains

2019 ◽  
Vol 123 (14) ◽  
pp. 9237-9246 ◽  
Author(s):  
Chaofu Wu
Keyword(s):  
Glass Transition ◽  
Free Surface ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Polymer Chains

scholarly journals Used of Chemically Modified Titanium Dioxide Particles to Mediate the Non-isothermal Cold Crystallization of Poly(latic acid)

2020 ◽  
Vol 64 (2) ◽  
Author(s):  
J. A. Gonzalez-Calderon ◽  
Guadalupe Mendoza ◽  
M. G. Peña-Juárez ◽  
Elias Perez
Keyword(s):  
Titanium Dioxide ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Chemical Modification ◽  
Dicarboxylic Acid ◽  
Crystallization Process ◽  
Polymer Chains ◽  
Cold Crystallization ◽  
Crystal Formation

In this work, the effect of the chemical modification of titanium dioxide particles on the non-isothermal crystallization process of polylactic acid (PLA) was studied. Cold crystallization in some polymers occurs above the glass transition temperature (Tg) when the polymer chains gain sufficient mobility to organize themselves into the ordered structure (i.e. the crystal structure) by folding the chains. Cold crystallization in general is caused by the ordering of the molecular chains in the crystalline PLA due to the increased mobility during heating. Through an analysis of the cool crystallization process in DSC at different cooling rates, it was observed that the behavior of PLA and its composites made with titanium dioxide, neat and functionalized with dicarboxylic acids, can be described through the models used for crystallization of the polymer carrying out during cooling, such as Mo’s and Jeziorny’s model. In addition, it was determined that the chemical modification of TiO2 performed with silane increases the crystallization rate in the last step of the process; while the chemical modification with dicarboxylic acid has an accelerated effect on the crystal formation process attributed to the affinity between the aliphatic part of this group and the polymer chains. Also, it was shown that the inclusion of the silanized particles has no effect on the energy requirement compared to the pure PLA process; however, the addition of particles with the dicarboxylic acid decreases the energy value required to complete the crystalline state due to affinity at the surface to immobilize the polymer chains. Finally, it is emphasized that the activation energy required to perform the crystallization of PLA and its composites has positive values, which is an indicator that the crystallization was performed while heating, after reaching and passing the glass transition temperature and before melting.

scholarly journals Boson peak, elasticity, and glass transition temperature in polymer glasses: Effects of the rigidity of chain bending

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Naoya Tomoshige ◽  
Hideyuki Mizuno ◽  
Tatsuya Mori ◽  
Kang Kim ◽  
Nobuyuki Matubayasi
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Low Frequency ◽  
Peak Frequency ◽  
Boson Peak ◽  
Polymer Chains ◽  
Coarse Grained ◽  
Elastic Response ◽  
Bending Rigidity

AbstractThe excess low-frequency vibrational spectrum, called boson peak, and non-affine elastic response are the most important particularities of glasses. Herein, the vibrational and mechanical properties of polymeric glasses are examined by using coarse-grained molecular dynamics simulations, with particular attention to the effects of the bending rigidity of the polymer chains. As the rigidity increases, the system undergoes a glass transition at a higher temperature (under a constant pressure), which decreases the density of the glass phase. The elastic moduli, which are controlled by the decrease of the density and the increase of the rigidity, show a non-monotonic dependence on the rigidity of the polymer chain that arises from the non-affine component. Moreover, a clear boson peak is observed in the vibrational density of states, which depends on the macroscopic shear modulus G. In particular, the boson peak frequency ωBP is proportional to $$\sqrt{G}$$G. These results provide a positive correlation between the boson peak, shear elasticity, and the glass transition temperature.

Study on Glass Transition Temperature of Amorphous Polymer Thin Film

2012 ◽  
Vol 482-484 ◽  
pp. 1457-1460
Author(s):  
Yi Jin Ren
Keyword(s):  
Thin Film ◽  
Glass Transition ◽  
Free Surface ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Film Thickness ◽  
Amorphous Polymer ◽  
Dominant Factor ◽  
Polymer Thin Film ◽  
Air Interface

The glass transition temperaure Tg of amorphous polymer thin film was investigated. The opposite experimental results, the increase or decrease in Tg of thin film with decreasing film thickness, were found. It was believed that the free surface near the polymer-air interface has a smaller chain ends density, leading to the decrease in Tg; while the polymer-substrate interface has a larger chain ends density, resulting in the increase in Tg. However, there are a competition between the both, and the interaction of polymer and substrate is a dominant factor to affect Tg of thin film. In addition, the multilayer model of thin film was proposed to explain the effect of the free surface and the interface on the Tg of thin film.

Diffusivity and glass transition of polymer chains in polymer nanocomposites

2019 ◽  
Vol 21 (41) ◽  
pp. 23209-23216 ◽  
Author(s):  
Huan Zhang ◽  
Dan-Dan Sun ◽  
Yi Peng ◽  
Jian-Hua Huang ◽  
Meng-Bo Luo
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Polymer Nanocomposites ◽  
Polymer Chains

Diffusivity and glass transition temperature of polymer nanocomposites are governed by a dynamic confinement parameter.

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