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TOUGHNESS OF DOUBLE NETWORK HYDROGELS
- 1. TOUGHNESS OF DOUBLE NETWORK HYDROGELS Department of Chemistry Bangladesh University of Engineering & Technology (BUET), Dhaka-1000, Bangladesh. Presented by Md. Mahamudul Hasan Rumon Student ID: 0419032707 October- 2018 1
- 2. Contents Hydrogel Toughness Stress Vs Strain curve Toughness mechanism Structure of DN hydrogel
- 3. Hydrogel • Three-dimensional hydrophilic polymer chain network with an interstitial fluid i,e Wet & Soft Material • Possess the ability to absorb a large amount of water/biological solutions up to thousands of times their dry weight • Shows many unique properties based on swelling/deswelling being stimuli- responsive Reversible responsiveness due to change of any one of following stimulus • 𝑃𝐻 • Temperature • Electric Field • Magnetic Field • Light • Pressure • Sound • Ionic Strength • Molecular Species Opens up the opportunity to convert chemical potential into mechanical work Applications • Biomedical Engineering • Hygiene Products • Agricultural Applications • Electronics • Robotics • Cosmetics • Food Processing • Water Treatment • Actuators & Sensors
- 4. Toughness Ability of a material to absorb energy deformation without fracturing Amount of energy per unit volume that a material can absorb before rupturing
- 5. Stress Vs Strain Curve
- 7. Toughness mechanism Case 1: very high strength, with minimum elongation at break Case 2: very high elongation at break, but low stiffness and strength Case 3: good stiffness and strength with a higher elongation Highly crosslinking (Low toughness) High toughness Physical bonding (Low toughness)
- 8. The optimum Case 3 is only realized under some preconditions: By introducing physical and chemical crosslinking in the system avoiding larger, critical defects, no critical stress concentrations, no brittle fracture yield point at a high yield stress and initiating a lot of small, localized yield events stabilizing the deformation by strain hardening and preventing premature crack propagation.
- 9. Other relevant mechanisms are to increase toughening efficiency a) multiple microcrack and void Formation b) bridging mechanism c) multiple initiation of crazes d) nanovoid formation and yielding fibrillation
- 10. Classical methods Figure adapted from internet
- 11. Fig: Structure of a double network hydrogel