Savvas G. Hatzikiriakos

Biography

  Dr. Savvas G. Hatzikiriakos is a Professor at The University of British Columbia, Vancouver Campus.  

Research Interest

  Polymer processing Polymer rheology Non-linear viscoelasticity Plasticity 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 Tribology 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.