  It is widely agreed that phase change materials (PCMs) are of high interest
for sustainable energy future. Many of the applications require anti-leakage
properties of PCM, that can be accomplished through PCM encapsulation. In this
study, scalable and considerably simplified approach based on the microfluidics
principles was successfully designed for polyvinylidene fluoride (PVDF) hollow-
and for leakage-free paraffin-core/PVDF-sheath fibers production. The required
device can be as simple as syringe+tube+glass capillary. The fibers were
created by PVDF/N,NDimethylformamide (DMF) solution and PVDF/DMF/paraffin
emulsion injection in water followed by solvent extraction process. The
proposed approach results in a hollow PVDF or PVDF/paraffin composite fibers
with the PCM content between 32-47.5% according to DSC and TGA measurements.
SEM study of the fibers morphology has shown that PCM is in the form of slugs
along the fibers. Such PCM distribution is maintained until the first melting
cycle. Later, molten PCM spreads within the fiber under capillary forces that
was captured by infrared camera. Elastic modules and stress vs. strain were
measured to characterise mechanical properties of designed fibers. Finally, the
composite fibers have shown outstanding retention capacity with only 3.5% of
PCM mass loose after 1000 melting/crystallisation cycles.
