Advisor, PhD
CHBE 243

Research Summary

Rheology of Polymers, Blends and Suspensions, Associating Polymers, Non-Newtonian Fluid Mechanics, Polymer Processing

Research interests + projects

  • Polymer rheology (ionomers and hydrogen bonding polymers)
  • Non-linear viscoelasticity (ionomers and hydrogen bonding polymers)
  • Rheological characterization
  • Polymer processing (extrusion, film blowing, blow molding and coating)
  • Polymer processing instabilities (melt fracture)
  • Processing aids
  • Processing of polyolefins and fluoropolymers
  • Paste extrusion of PTFE
  • Food rheology (cheese and dough)
  • Rheology of biomaterials (nanocrystalline cellulose)

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 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 these 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 molding and coating flows (wire, cable and sheet) of polyolefins, fluoropolymers and other 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, stearates and their combination 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 several degrees 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 polymers such as polyolefins, ionomers and hydrogen bonding polymers. 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 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, polyelectrolyte hydrogels (based on nanocrystalline cellulose), cheese, dough, and biomaterials such as nanocrystalline based materials.

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.

Professor Hatzikiriakos and his students have published over 240 papers. He has edited a book entitled Polymer Processing Instabilities: Understanding and Control. 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.

Selected publications + presentations

A. Abbasi Moud, J. Poisson, Z.M. Hudson and S.G. Hatzikiriakos, “Yield stress and wall slip of kaolinite networks,” Physics of Fluids, 33, 053105 (2021)

D. Gilmour, T. Tomkovic, N. Kuanr, M. Perry, H. Gildenast, S.G. Hatzikiriakos and L. Schafer, “Catalytic amine functionalization and polymerization of cyclic alkenes creates adhesive and self-healing materials” ACS Applied Polymer Materials, 3, 2330-2335 (2021)

P. Keyvani, K. Nyamayaro, P. Mehrkhodavandi, and S.G. Hatzikiriakos, “Cationic and Anionic Cellulose Nanocrystalline (CNC) Hydrogels: A Rheological Study,” Physics of Fluids, 33, 043102 (2021)

K. Nyamayaro, V. Triadafilidi, P. Keyvani, J. Rottler, P. Mehrkhodavandi, and S.G. Hatzikiriakos, “The rectification mechanism in polyelectrolyte gel diodes,” Physics of Fluids, 33, 032010 (2021)

T. Raeisi Gahrooee, A. Abbasi Moud, M. Danesh and S.G. Hatzikiriakos, “Rheological Characterization of CNC-CTAB Network below and above CMC,” Carbohydrate Polymers, 257, 117552 (2021)

K. Nyamayaro, P. Keyvani, F. D’Acierno, J. Poisson, Z. Hudson, C. Michal, J. Madden, S.G. Hatzikiriakos, P. Mehrkhodavandi, “Towards biodegradable electronics: Ionic diode based on a cellulose nanocrystals-agarose hydrogel,” ACS Applied Materials and Interfaces, 12, 52182-52191 (2020)

N. Ghahramani, K. Iyer, A.K. Doufas and S.G. Hatzikiriakos, “Rheology of Thermoplastic Vulcanizates (TPVs),” J. Rheology, 64, 1325-1341 (2020)

M. Danesh, D. Mauran, S. Hojabr, R. Berry, M. Pawlik and S.G. Hatzikiriakos “Yielding of Cellulose Nanocrystal Suspensions in the Presence of Electrolytes,” Physics of Fluids, 32, 093103 (2020)

M. Najm and S.G. Hatzikiriakos, “Flow-Indiced Fractionation Effects on Slip of Polydisperse Polymer Melts,” Physics of Fluids, 32, 073109 (2020)

Z. Zhang, and S.G. Hatzikiriakos, “Entry Pressure Correlations in Capillary Flow,” Physics of Fluids, 32, 073106 (2020)

T. Tomkovic and S.G. Hatzikiriakos, “Rheology and Processing of Polytrafluoroethylene (PTFE) Paste Extrusion” Canadian J. Chem. Eng., 98, 1852-1865 (2020)

N. Kuanr, T. Tomkovic, D.J. Gilmour, M.R. Perry, S-J. Hsiang, E. van Ruymbeke, S.G. Hatzikiriakos, and L.L. Schafer, “Hydrogen Bonding in Dynamic Crosslinking of Catalytically Synthesized Poly(Aminonorbornenes),” Macromolecules, 53, 2649-2661 (2020)

M. Zuliki, S. Zhang, T. Tomkovic and S.G. Hatzikiriakos, “Capillary Flow of Sodium and Zinc Ionomers,” Physics of Fluids, 32, 023106 (2020)

M. Zuliki, S. Zhang, K. Nyamajaro, T. Tomkovic and S.G. Hatzikiriakos, “Rheology of Sodium and Zinc Ionomers: Effects of Neutralization and Valency,” Physics of Fluids, 32, 023104 (2020)

D. Ranjbar, M. Raeiszadeh, L. Lewis, M. J. MacLachlan, and S. G. Hatzikiriakos, “Adsorptive Removal of Congo Red by Surfactant Modified Cellulose Nanocrystals: a Kinetic, Equilibrium, and Mechanistic Investigation,” Cellulose, 27, 3211-3232 (2020)

D. Ranjbar and S.G. Hatzikiriakos, “Effect of Ionic Surfactants on the Viscoelastic Properties of Chiral Nematic Cellulose Nanocrystal Suspensions,” Langmuir, 36, 293-301 (2020)

V. Triandafilidi, S.G. Hatzikiriakos, and J Rottler, “Poisson-Boltzmann and Molecular Dynamics Simulations of Polyelectrolyte Gel Diodes in the Static Regime,” Soft Matter, 16, 1091-1101 (2020)

T. Tomkovic, E. Mitsoulis and S.G. Hatzikiriakos, “Contraction Flow of Ionomers and their Corresponding Copolymers: Ionic and Hydrogen Bonding Effects,” Physics of Fluids, 31, 033102 (2019)

T. Wright, T. Tomkovic, S.G. Hatzikiriakos, and M.O. Wolf, “Photoactivated Healable Vitrimeric Copolymers,” Macromolecules, 52, 36-42 (2019)