Source of funding: National Science Centre, No 2014/13/D/ST8/03140, 2015-2017
Project manager/ principal investigator: Arkadiusz Gradys,Ph.D.
Significance of the project
In recent decades, it may be observed an increasing scientific and practical interest in studies on confinement effects, which manifest, with decrease in size, as deviations in the behavior as observed in bulk. Depending on system geometry, various confinement effects may be observed. One of the important issues relates to the effects in phase transitions and structure formation.
Research Project Objectives
The objective of the project was to explore physical phenomena at sub-micrometer scale, specifically, to study the confinement effects on phase transitions and structure properties. There were performed experimental investigations on confinement effects in quasi-one dimensional geometry- an issue, as yet, not well studied. The term “quasi one-dimensional geometry” is understood as fiber / rod geometry, meaning that restriction in size is realized in two dimensions, the third dimension being considered as macroscopic.
Scientific hypothesis
There exist confinement effects in quasi one-dimensional geometry and critical sizes of confinement leading to deviation in the kinetics of phase transitions, due to restrictions in molecular mobility and diffusion, and deviation of thermodynamic parameters due to decrease in entropy related with increase in orientation of molecules and supermolecular structure, in comparison to parameters of macroscopic (bulk) systems.
Results
Using the coaxial electrospinning process, sub-micron “core-shell” fibers were obtained. By specific thermal treatment, it was possible to control the thickness of the thermo-shrinkable fibers. This enabled the studies of the effect of the fiber thickness on various aspects related to crystallization and structure of the substance encapsulated in the fiber core: 1) crystallization behavior and mechanisms, crystallization rate, 2) characteristic temperatures of crystal melting and glass transition, 3) crystal structure orientation. The studies revealed that the critical fiber thickness to see a deviation from the macroscopic scale is below 1 micron.
The results have broadened the current knowledge on the confinement effects, which have a high potential for use in nanoengineering and medical engineering.
