- Polymer processing
- Polymer rheology
- Non-linear viscoelasticity
- Profile and film extrusion
- Rheological characterization
- Polymer processing instabilities
- Melt fracture in extrusion
- Processing aids
- Extrusion coating (wire, cable, sheet)
- Processing of polyolefins
- Processing of fluoropolymers
- Paste extrusion of PTFE
- Wire coating
- Food rheology (cheese and dough)
- Rheology of biomaterials
- Linear and nonlinear stability analysis of processing operations
- Nano-patterning of metallic and polymeric surfaces (superhydrophobicity)
Non-Newtonian fluid mechanics is often distinguished from its Newtonian counterpart by the additional requirement that first a constitutive equation be specified as part of the problem statement and secondly a suitable wall boundary condition other than the no-slip be imposed as a necessary ingredient. It is also accepted that diverse fluids and diverse wall materials lead to diverse interfacial behaviors. Therefore, the main thrust of this part of the research program is both a theoretical and an experimental study of diverse polymer-wall interfaces. The development of proper relationships that describe the behavior of such interfaces under flow conditions are necessary in order to gain a better understanding of phenomena such as sharkskin, gross melt fracture and stick-slip. The identification of processing aids that can eliminate such phenomena is a key element in our studies.
Polymer flow instabilities and more specifically melt fracture phenomena in polymer processing is of particular importance. Application of interest include extrusion, film blowing, blow moulding and coating flows (wire, cable and sheet) of polyolefins, fluoropolymers and other commodity polymers. Methods to enhance the rate of production by eliminating or postponing these phenomena to higher shear rates are also of interest. Processing aids such as fluoroelastomers (VitonÒ, DynamarÒ, KynarÒ), stearates and their combination with boron nitride and clays are examined in extrusion and other polymer processing operations in order to evaluate their effectiveness.
The rheology and processing of polymer blends are also of particular interest to the research program of Professor Hatzikiriakos. During the processing of polymer blends, there is a variety of phenomena that may take place. At increasing shear/extensional rates, the polymer blends may phase-separate (shear induced de-mixing) and then at higher rates may mix again (shear induced mixing) or vice versa. These effects are dramatic as the homogeneous region in their (polymer blends) phase diagram may be shifted or enlarged by 20 K under flow conditions. This part of the research program focuses on the rheological and thermodynamic behavior of polymer blends under flow (shear/extensional) conditions. The phase behavior of model as well of industrial importance polymer blends is studied both experimentally and theoretically. The results from these fundamental studies are used in order to gain a better understanding on the resulting morphology during processing and its effects on the mechanical properties of final products.
Another aspect of the research program in polymer rheology is the development of new techniques to measure the nonlinear rheological viscoelastic properties of molten plastics. The key element of this part of the program is to use the rheological properties measured in the laboratory in order to gain a better understanding of the behavior of a thermoplastic and other polymeric systems in a melt processing operation such as film blowing, film extrusion, film casting, blow molding and coating flows (wire, cable and sheet). Complex fluids, semisolids and solids are of particular importance as well i.e. polymer blends, gels, cheese, dough, and biomaterials such as biological tissues.
The research interests/efforts of Professor Hatzikiriakos include an integrated study of the paste extrusion process of polytetrafluoroethylene (PTFE) and other polymers (UHMWPE, PEEK), metals and metal oxides. Relevant tests for the rheological characterization of complex materials such as PTFE paste is of primary interest. Other areas of interest include experimental and computational studies of polymer processing operations such as film blowing, film casting, pipe extrusion, profile extrusion, blow molding, thermoforming and embossing.
Finally, tribological properties of metallic and polymeric surfaces are also of interest. Nano-patterned surfaces after laser irradiation that render the material superhydrophobic exhibit reduced coefficient of friction in many cases. This makes them candidates for many important applications in ice and snow sports, as well as in biological and medical systems.
Professor Hatzikiriakos and his students have published over 240 papers in journals and conference proceedings. He has edited a book entitled Polymer Processing Instabilities: Understanding and Control (Marcel Dekker) . His group is actively collaborating with the University of Crete and the National Technical University of Athens. Professor Hatzikiriakos also serves as an expert witness in polymer patent litigation and dispute and as a consulting engineer to the polymer industry.
- T. Ebrahimi, S.G. Hatzikiriakos, and P. Mehrkhodavandi, “Synthesis and Rheological Characterization of Star-shaped and Linear Poly(hydroxybutyrate),” Macromolecules, 48, 6672-6681 (2015).
- S.G Hatzikiriakos, “Slip Mechanisms in Complex Fluid Flows,” Soft Matter, 11, 7851-7856 (2015).
- M. Ansari, D. Vavlekas, J.L. McCoy, S.G. Hatzikiriakos, “Paste Extrusion and Mechanical Properties of PTFE,” International Polymer Processing, XXX, 603-614 (2015).
- E.Behzadfar, M. Ansari, V.K. Konaganti, S.G. Hatzikiriakos, “Extrudate Swell of HDPE Melts: I. Experimental”, J. Non-Newtonian Fluid Mechanics, 225, 86-93 (2015).
- V.K. Konaganti, M. Ansari, E. Mitsoulis, S.G. Hatzikiriakos, “Extrudate Swell of a HDPEMelt: II. Modeling using Integral and Differential Constitutive Equations”, J.Non-Newtonian Fluid Mechanics, 225, 94-105 (2015).
- I. Yu, T. Ebrahimi, S.G. Hatzikiriakos, and P. Mehrkhodavandi, “Star-shaped PHB-PLA Block Copolymers: Immortal Polymerization with Dinuclear Indium Catalysts,” Dalton Transactions, 44, 14248-14254 (2015).
- S. Toosi, S. Moradi, S. Kamal, and S. G. Hatzikiriakos, “Superhydrophobic Laser Ablated PTFE Substrates,” J. Applied Surface Sci., 349, 715-723 (2015).
- M. Ebrahimi, M. Ansari and S.G. Hatzikiriakos, “Wall Slip of Polydisperse Linear Polymers using Double Reptation,” J. Rheology, 59, 885-901 (2015).
- S. Moradi, S. Kamal, and S. G. Hatzikiriakos, “Laser Ablation Induced Micro/Nano-Patterns on Stainless Steel Substrates and their Wettability” Surface Innovations, 3, 151-163 (2015).
- M. Derakhshandeh, B. Jazrawi, G. Hatzikiriakos, A.K. Doufas and S.G. Hatzikiriakos, “Flow Induced Crystallization of Polypropylenes in Capillary Flow,” Rheol. Acta, 54, 207-221 (2015).
- S. Safiei-Sabet, W. Hamad and S.G. Hatzikiriakos, “Ionic Strength Effects on the Microstructure and Shear Rheology of Cellulose Nanocrystal Suspensions,” Cellulose, 21, 3347-3359 (2014).
- M. Derakhshandeh, G. Mozaffari, A.K. Doufas and S.G. Hatzikiriakos, “Quiescent Crystallization of Polypropylenes: Experiments and Modelling,” Journal of Polymer Science Part B: Polymer Physics, 52, 1259-1275 (2014).
- A.H. Anvari, E. Mitsoulis, and S.G. Hatzikiriakos, “Capillary Flow of Milk Chocolate,” J. Non-Newtonian Fluid Mech., 210, 56-65 (2014).
- N.H. Othman, M. Ansari, Th. Zisis, , E. Mitsoulis, and S.G. Hatzikiriakos, “Entry Flows of Polylactides with Slip,” J. Non-Newtonian Fluid Mech., 210, 78-84 (2014).
- M. Derakhshandeh, A.K. Doufas and S.G. Hatzikiriakos, “Quiescent and Shear-Induced Crystallization of Polypropylenes,” Rheologica Acta, 53, 519-535 (2014).
- Y. Amintowlieh, C. Tzoganakis, S.G. Hatzikiriakos, and A. Penlidis, “Effects of Processing Variables on Polypropylene Degradations and Long Chain Branching with UV Irradiation,” Polymer Degradation and Stability, 104, 1-10 (2014).
- S. Moradi, P. Englezos and S. G. Hatzikiriakos “Contact Angle Hysteresis in Superhydrophobic Metallic Surfaces”, Langmuir, 30, 3274-3284 (2014).
- H. Sharifi, S. G. Hatzikiriakos and P. Englezos, “Rheological Evaluation of Kinetic Hydrate Inhibitors in Brine/n-Heptane Solutions,” AIChE, 60, 2654-2659 (2014).
- E. Behzadfar and S.G. Hatzikiriakos, “The Diffusivity of CO2 in Bitumen using Rheometry,” Energy and Fuels, 28, 1304-1311 (2014).
- E. Behzadfar and S.G. Hatzikiriakos, “Rheology of Bitumen: Effects of Temperature, Pressure and CO2 Concentration,” Fuel, 116, 578-587 (2014).