Linkam has been chosen by Salerno University's Polymer Technology Group to study the effect of temperature and steady shear flow on the nucleation rate of spherulites in isotactic polypropylene.
One of the research programmes of professors Giuseppe Titomanlio, Roberto Pantani and their colleagues at Salerno is the study of polymer crystallisation enhanced by flow.
This has attracted interest because it implies the possibility of controlling the final morphology and the resulting mechanical and functional properties of semicrystalline polymers.
An improved understanding of the fundamentals of flow-enhanced crystallisation effects can help to tailor advanced transformation processes such as injection moulding and extrusion.
During these processing operations, the polymer melt is subjected to complex and intense flow fields (shear, elongational or mixed), during or soon after which the polymer crystallises.
The crystallisation kinetics and the morphology of the semicrystalline polymer in the final product, and subsequently its properties and quality, depend upon the orientation of the melt by effect of the flow.
The observation of changes in morphology and the measurement of nucleation density under both steady shear and quiescent conditions were performed using a polarised light microscope (Olympus BH-41) equipped with a Linkam shearing cell (CSS450).
The Linkam system was chosen for its ability to accurately control changes in temperature and shear rate on the micro scale.
The Salerno University group was able to show clear differences under varying shear rates and temperature cycles, which provided a different thermal history to the samples.
Pantani said: 'Prior to our having the CS450, understanding the analysis was just qualitative.
'Now we are able to complete unique quantitative analyses.
'We have been able to calculate the evolution of the nucleation density during the crystallisation under shear using our own specialised image analysis software.
'The values of nucleation rate were obtained by a linear fitting of the evolution of nucleation density for all the shear rates and temperatures applied in this work,' he added.
The CSS450 optical shearing system allows the structural dynamics of complex fluids to be directly observed via a standard optical microscope while they are under precisely controlled temperature and various shear modes.
Using the cell, it is possible to study the micro-structure evolution of complex fluids in great detail for many physical processes, for example the coarsening of binary fluids during their phase separations, the flow-induced mixing and demixing of polymer blends, the defects dynamics of liquid crystals and the aggregation of red blood cells and their deformation by effect of flows.
It is then possible to correlate the micro-structural dynamics with rheological data, thus gaining insight into the rheology of complex fluids.
