Polymer Types
Specific Volume vs Temperature
Molecular Motion
Elastic Modulus vs Temperature
Parameters
Temperature Control
Molecular Factors
Display Options
Property Comparison
| Property | Glassy State (T < T_g) | Rubbery State (T > T_g) |
|---|---|---|
| Mechanical Behavior | Brittle, rigid | Tough, flexible |
| Elastic Modulus | 10³-10⁴ GPa | 1-10 GPa |
| Molecular Motion | Frozen (vibrational only) | Segmental motion |
| Thermal Expansion | Low coefficient | High coefficient |
| Applications | Plastics, glasses | Rubbers, elastomers |
Physical Principles
Instructions
- Select different polymer types to see their T_g values
- Adjust temperature to cross T_g and observe state changes
- Watch molecular motion animation - frozen in glassy state, active in rubbery state
- Modify molecular factors to see how they affect T_g
- Use heating animation to observe continuous transition
What is Glass Transition?
The glass transition is a reversible transition in amorphous polymers from a hard and relatively brittle glassy state into a viscous or rubbery state as temperature increases. The glass transition temperature (T_g) is where this transition occurs. Unlike melting (first-order transition), glass transition is second-order, characterized by changes in heat capacity, thermal expansion, and mechanical properties.
Specific Volume vs Temperature
The volume-temperature (V-T) curve shows specific volume vs temperature. Below T_g: glassy state with low thermal expansion. Above T_g: rubbery state with high expansion. Slope change at T_g indicates increased free volume and chain mobility.
Molecular Motion
In glassy state (T < T_g): polymer chains frozen, only small vibrational motions possible. Lack of large-scale motion makes material brittle and stiff. Above T_g: sufficient thermal energy enables segmental motion - chain portions can rotate and move. This mobility transforms mechanical properties from rigid to flexible.
Elastic Modulus vs Temperature
Elastic modulus decreases dramatically at T_g by factor of 10³-10⁴. Glassy: high modulus (GPa) due to restricted mobility. Rubbery: low modulus (MPa) as chains gain mobility. This drastic change determines useful temperature range: plastics below T_g for rigidity, rubbers above T_g for flexibility.
Factors Affecting T_g
Molecular weight: higher MW increases T_g due to chain entanglement. Cross-linking: creates covalent bonds between chains, restricts mobility, raises T_g. Plasticizers: small molecules that increase free volume and mobility, lower T_g. Chain flexibility, side groups, intermolecular forces also influence T_g.
Applications
Understanding glass transition is crucial for: selecting materials for specific temperature ranges, designing processing conditions, predicting material behavior, developing polymer blends, and optimizing formulations. Examples: polystyrene cups (T_g ≈ 100°C), rubber tires (T_g ≈ -70°C), impact-modified plastics.