Dental Materials Properties Lecture 2

Wettability and Surface Properties

• Wettability indicates a liquid's affinity for a solid, measured through the contact angle of a liquid drop.
• Contact angle of 180° signifies no wetting, while 0° indicates complete wetting.
• Surface energy is the excess energy at a material's surface compared to its bulk, influenced by attraction forces among surface molecules.

Adhesion and Bonding

• Adhesion describes the attraction between two contacting surfaces, crucial for material bonding.
• Micromechanical bonding relies on interfacial forces, enhanced when an adhesive penetrates a rough surface.
• Bonding can occur via chemical forces, mechanical interlocking, or a combination of both.

Surface Tension and Cohesion

• Surface tension is the tendency of fluid surfaces to minimize area, resulting from molecular attraction imbalances at the surface.
• Cohesion refers to the attraction between molecules of the same species, influencing liquid properties.

Terminology in Materials Science

• Stress is defined as force per unit area within a material under external load.
• Strain quantifies deformation as the change in length divided by the original length.
• Shear stress measures time-dependent plastic strain in a solid under consistent load.

Viscosity and Flow Behavior

• Viscosity is the measurement of a fluid's resistance to flow; it describes how substances deform and flow.
• Rheology studies the flow characteristics indicating how materials behave under various forces.
• Newtonian fluids have a consistent viscosity, while non-Newtonian fluids exhibit varied flow properties:
  • Dilatant: Flow decreases with increased strain until reaching a constant.
  • Pseudoplastic: Flow increases with increased strain.
  • Plastic: Resembles rigid material until a minimum strain is applied.