1. Time Dependent Response of Polymers: PEEK Performance By Andrew Darmawan Supervisors Dr. Rebecca PowlesProf. David Mckenzie

2. Elastic Materials Copper Stress (σ) Elongation (Δ) Strong Inter-atomic Forces Crystalline atomic structure Elongation (Δ) Stress (σ) Viscous Materials Weaker Inter-molecular forces Free molecules

3. Viscoelastic materials are those for which the relationship between stress and strain depends on time. E.g. Polymers. When stress (σ) is instantaneously increased: Instantaneous increase in strain Continued straining with time at a non-constant rate (called creep) When stress (σ) is instantaneously released: Some instantaneous strain recovery Delayed recovery Illustration by David Zinn

4. Pitch drop experiment Started in 1927 by University of Queensland Professor Thomas Parnell. A drop of pitch falls every 9 years Pitch can be shattered by a hammer Pitch drop experiment apparatus

5. VentrAssist™ LVAS Left Ventricular Assist System (LVAS) Used as alternative to heart transplant or a bridge to recovery Only one moving part

6. Evolution of the heart pump Aluminium 1.2.3. Titanium 4. Why Polymers? Easier manufacture (injection molding) Cheaper Density is a better match with the human body ? 5. Polymers

7. PEEK (Poly ether ether ketone) Properties Specific Gravity1.3-1.32 Tensile Strength 97-100Mpa Tensile Elastic Modulus (Young's Modulus) 3.6Gpa Glass transition temperature (T g ) 417K Melting temperature (T m ) 607K Crystallinity42% Chain Structure Why PEEK? Biocompatible Strong Smooth ketone ether

8. Experiment 1: Newton’s Rings Light is reflected from both sides of a thin film Interference occurs The interference pattern represents a contour map of the surface. Reflective polymer Air film (made by indentation) Optical flat t

9. Experiment 1: Newton’s Rings Apparatus Camera Sample with optical flat Laser Paper Beam splitter

10. Results 10min 4300min 480min 60min

11. Experiment 2: Surface Profiler Pin dragged across surface Produces a profile of the indentation. Tencor Alpha-step

15. Conclusions: Surface profiling is a useful method for measuring the time dependant response of polymers. PEEK has a time dependant response to indentation (appears to be exponential) (the sample recovered by approximately 8% in 87 minutes) Cross-linked polymer Recommended topics for further research: Long term recovery of PEEK Ways we can speed up recovery eg. Temperature Cross-linking in PEEK and its effect on recovery properties Use of surface profiling on other materials (viscoelastic or not) Creep characteristic of PEEK Instantaneous recovery of PEEK after indentation Non-cross linked polymer

16. Other applications…

17. Summary 1.Elastic and Viscous materials 3. Ventracor’s VentrAssist™ 4. PEEK5. Experiment 1: Newton’s Rings 6. Experiment 2: Surface Profiler 2. Viscoelastic Materials