Glass Prelim 2 overview
Viscosity Resistance of a liquid to flow; governed by structural relaxation.
Newtonian behavior Constant viscosity independent of shear rate.
Non-Newtonian behavior Viscosity varies with applied stress; common near the glass transition.
Elastic behavior Instant recovery after deformation.
Viscous behavior Continuous, time-dependent deformation.
Viscoelastic behavior Combination of elastic and viscous responses; typical of glass near Tg.
Stress relaxation Decrease of stress with time under constant strain.
Describes viscoelastic relaxation using elastic and viscous elements in
Maxwell model
series.
Voigt model - Describes time-dependent strain (creep) using elastic an
Kelvin
viscous elements in parallel.
Creep Time-dependent deformation under constant stress.
Burgers model Combines Maxwell and Kelvin-Voigt to represent full viscoelastic beha
Dynamic mechanical analysis Measures time- and temperature-dependent mechanical response.
Storage modulus Represents stored elastic energy.
, Glass Prelim 2 overview
Loss modulus Represents dissipated energy as heat.
Loss tangent Ratio of viscous to elastic response; measures damping.
Structural relaxation Rearrangement of glass toward equilibrium.
Non-exponential relaxation Relaxation described by a broad distribution of times.
Aging Slow structural evolution of glass below Tg.
Physical aging Reversible densification over time at constant temperature.
Structural rejuvenation Recovery of less relaxed structure through heating or mechanical ener
temperature superposition - Combines data across temperatures to
Time
describe viscoelastic behavior.
Classification based on temperature dependence of viscosity; fragile =
Fragile vs. strong liquids
highly non-Arrhenius, strong = near-Arrhenius.
Fragility index Quantifies deviation from Arrhenius viscosity.
Time-dependent process as glass approaches supercooled liquid
Glass relaxation
structure.
Molecular mobility depends on available free space; viscosity rises as
Free volume theory
volume decreases.
Viscosity Resistance of a liquid to flow; governed by structural relaxation.
Newtonian behavior Constant viscosity independent of shear rate.
Non-Newtonian behavior Viscosity varies with applied stress; common near the glass transition.
Elastic behavior Instant recovery after deformation.
Viscous behavior Continuous, time-dependent deformation.
Viscoelastic behavior Combination of elastic and viscous responses; typical of glass near Tg.
Stress relaxation Decrease of stress with time under constant strain.
Describes viscoelastic relaxation using elastic and viscous elements in
Maxwell model
series.
Voigt model - Describes time-dependent strain (creep) using elastic an
Kelvin
viscous elements in parallel.
Creep Time-dependent deformation under constant stress.
Burgers model Combines Maxwell and Kelvin-Voigt to represent full viscoelastic beha
Dynamic mechanical analysis Measures time- and temperature-dependent mechanical response.
Storage modulus Represents stored elastic energy.
, Glass Prelim 2 overview
Loss modulus Represents dissipated energy as heat.
Loss tangent Ratio of viscous to elastic response; measures damping.
Structural relaxation Rearrangement of glass toward equilibrium.
Non-exponential relaxation Relaxation described by a broad distribution of times.
Aging Slow structural evolution of glass below Tg.
Physical aging Reversible densification over time at constant temperature.
Structural rejuvenation Recovery of less relaxed structure through heating or mechanical ener
temperature superposition - Combines data across temperatures to
Time
describe viscoelastic behavior.
Classification based on temperature dependence of viscosity; fragile =
Fragile vs. strong liquids
highly non-Arrhenius, strong = near-Arrhenius.
Fragility index Quantifies deviation from Arrhenius viscosity.
Time-dependent process as glass approaches supercooled liquid
Glass relaxation
structure.
Molecular mobility depends on available free space; viscosity rises as
Free volume theory
volume decreases.
