Related Experiment Video
Updated: Jun 12, 2026
09:32
Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
Published on: January 26, 2016
Glass transition dynamics and surface layer mobility in unentangled polystyrene films
Zhaohui Yang1, Yoshihisa Fujii, Fuk Kay Lee
1Department of Physics, Boston University, Boston, MA 02215, USA.
Science (New York, N.Y.)
|June 26, 2010
Summary
The glass transition temperature (T(g)) of polymer films decreases as film thickness reduces. This phenomenon is attributed to a mobile surface liquid layer that influences polymer flow in thin films.
Area of Science:
- Polymer Science
- Materials Science
- Physical Chemistry
Background:
- Polymers typically solidify into a glassy amorphous state below their glass transition temperature (T(g)).
- A significant debate exists regarding the influence of film thickness on polymer T(g) and the underlying mechanisms.
- Understanding these thickness-dependent effects is crucial for polymer applications in thin-film technologies.
Purpose of the Study:
- To investigate the relationship between polymer film thickness and glass transition temperature (T(g)).
- To elucidate the origin of observed changes in T(g) with decreasing film thickness.
- To quantify the impact of film thickness on polymer viscosity and dynamics.
Main Methods:
- Viscosity measurements of unentangled, short-chain polystyrene films on silicon substrates at varying temperatures.
- Analysis of temperature-dependent viscosity data to determine transition temperatures.
- Application of hydrodynamic equations to model film behavior and surface effects.
Main Results:
- A decrease in the viscosity transition temperature was observed with decreasing polymer film thickness.
- This observed transition temperature shift aligns with previously reported changes in the glass transition temperature (T(g)) of polymer films.
- Hydrodynamic modeling suggests the dominance of a highly mobile surface liquid layer in the thinnest films studied.
Conclusions:
- The study confirms that polymer T(g) is dependent on film thickness, with thinner films exhibiting lower transition temperatures.
- A mobile surface liquid layer, exhibiting Arrhenius dynamics, is identified as the primary cause for the altered flow behavior in thin polymer films.
- This surface layer significantly influences and can dominate the flow dynamics in nanoscale polymer films.
Related Concept Videos
01:08Molecular Weight of Step-Growth Polymers
Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
01:21Polymer Classification: Crystallinity
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
01:09Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the concentration...
01:26Polymer Classification: Stereospecificity
Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...