Experimental determination of the cooperative length scale of a glass-forming liquid near the glass transition temperature

1999 ◽  
Vol 59 (1) ◽  
pp. 612-617 ◽  
Author(s):  
A. K. Rizos ◽  
K. L. Ngai
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Experimental Determination ◽  
Length Scale ◽  
Glass Forming

Possible Causes of the Change of Dynamics in Glass-Forming Materials Subjected to Reduced Dimension

1996 ◽  
Vol 455 ◽  
Author(s):  
K. L. Ngai ◽  
A. K. Rizos
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Bulk Material ◽  
Three Dimensions ◽  
Radius Of Gyration ◽  
Length Scale ◽  
Glass Forming ◽  
Reduced Dimension

ABSTRACTThere is currently many ongoing investigations of the change in the glass transition temperature when a material is reduced in dimension from the normal bulk state. The reduction in dimension can be accomplished by casting the material as thin films with or without a substrate or putting it in nanometer size pores. In this work, we explore possible causes of the change in dynamics of the bulk material when the glass-former is subjected to such modifications. The existence of a growing cooperative length scale L(T) with decreasing temperature in bulk fragile glass-forming liquids reaching the size of approximately 1.5–2.0 nm at the glass transition temperature is the basis of our consideration. When the reduced dimension is comparable to L(Tg), cooperative dynamics within a lengthscale equal to L(Tg) can no longer be maintained in all three dimensions throughout the sample. The imposed reduction of the cooperative length scale speeds up the dynamics and causes a reduction of the glass transition temperature. For polymeric glass-formers particularly at higher molecular weights, reduction of one dimension in thin films engenders orientation of the polymer chains when their radius of gyration becomes comparable to the film thickness. The latter is known to cause also a reduction of the glass transition temeperature.

scholarly journals Physical Aging Behavior of a Glassy Polyether

Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 954
Author(s):  
Xavier Monnier ◽  
Sara Marina ◽  
Xabier Lopez de Pariza ◽  
Haritz Sardón ◽  
Jaime Martin ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Physical Aging ◽  
Glassy State ◽  
Aging Behavior ◽  
Scanning Calorimetry ◽  
Narrow Temperature Range ◽  
Glass Forming ◽  
Fast Scanning Calorimetry

The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state.

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