Glossary

Attenuated Total Reflectance –ATR
is an FTIR accessory that allows the measurement samples to be examined directly in the solid or liquid state without further preparation.
Activation Energy
is the energy needed to cause motion. Frequency-dependent activation energy can be used to identify transition types.
Additives
are materials added to polymers to tune their properties, protect from UV, etc.
Alloys
are mechanically-blended combinations of polymers, as opposed to the term’s usage in metals.
Alpha transition
is the next transition in temperature below the melt. Normally this is the Tg but in certain materials may be a crystal-crystal slip as in PP.
Amorphous
is an unorganized structure that allows random folding and intertwining. Glass is amorphous because of the lack of light-scattering crystals; amorphous polymers are clear.
Amorphous content
is the fraction of the polymer in the amorphous phase. It is important for solubility studies in pharmaceuticals and clarity in polymers. Relative values can be obtained via measuring the degree of crystallinity or the strength of the Tg in the DSC, and by comparing the area of loss modulus peak at Tg.
Amorphous phase
is the unordered portion of the chemical structure.
Amplitude
is the height of sinusoidal displacement.
Anisotropy
is the directionality of material properties within a sample.
Annealing
is the slow, controlled cooling of a material from its melt temperature to room temperature. Annealing normally uses controlled cooling rates below 5°C/min for polymers. This is used to further study the effects of structural ordering within the material.
Backbone
refers to a polymer’s primary structure, which is typically a continuous chain of carbon atoms.
Beta transition
is the second transition below the metal and is often associated with toughness.
Blending
refers to the mixing of two polymers. A blend can have one or more Tg depending on how it was made.
Branching
refers to the number of side chains in a polymer. It can be estimated by comparing the terminal zone of the storage modulus in a frequency scan.
Calorie
is the amount of heat required to raise one gram of H2O by 1°C.
Cole-Cole Plot
is a plot of E’ versus E” (or tan δ) used to check the validity of a TTS study. It is also called a wicket plot because a successful one looks like a wicket.
Compatibility of polymer
is how well two or more different polymers combine with each other in a blend.
Complex modulus
is the bulk-sample behavior in a DMA experiment and is an indicator of viscoelasticity.
Compliance
is the ratio of sample strain-to-sample stress in the linear region of creep ramp. It is also the inverse of shear modulus.
Compression
is a test geometry in which disks or rectangles are deformed using some arrangement of plates (plate and tray, sintered parallel plates, cone- and plate-measuring systems). This gives compressive modulus, an important value used in Finite Element Analysis (FEA).
Copolymer
is a polymer made with two polymers. Copolymers can be block or random. Some are purely mechanical mixtures, such as HIPS.
Creep
is the deformation of a sample under stress while temperature is held constant. This gives time dependent behavior as a function of pressure (stress) or temperature.
Crosslink
is a chemical bond between two or more polymer chains.
Crossover point
normally refers to the intersection of the storage modulus and complex viscosity curves plotted against frequency on a log-log-log plot.  In a curing study, it is also the crossover of E’ and E” (where tan δ =1).
Crystalline
is a highly organized physical structure that is compacted in very low energy states.
Crystalline phase
is a highly ordered structure with closely packed and ordered orientation of a polymer backbone. This is typically the lowest energy state of a polymer. Crystal structure is also important in metallurgy since workability and hardness depend on different crystalline forms.
CTE-Coefficient of thermal expansion
is the expansion of a material on heating. See dilatometry, LCTE, and TMA below. Understanding this is vital for handling materials that will undergo thermal changes in their end use.
Cure of thermosets
is the forming of a chemical connection between polymer backbones.
Cure rate (kinetics)
allows one to predict how a material will behave. This can be done in DMA or DSC.
Curie Point
is the loss of magnetism in a metal upon heating. It is related to the metal’s chemical composition and is often used as a standard to calibrate TGAs and DT/TGAs.
Crystallization Temperature
is the temperature where crystallization occurs.  Normally, it is the extrapolated onset temperature or the peak temperature of the crystallization peak. On cooling, it represents the transition of a liquid phase to a solid. It can be seen upon heating in some semi-crystalline materials such as PET when enough mobility in the amorphous phase allows the formation of new crystals.
Dynamic Mechanical Analysis (DMA)
is the measurement of stiffness and modulus using forced oscillations as a function of time, temperature, stress, strain, or frequency.
Differential Scanning Calorimetry (DSC)
is an analytical technique that measures the heat flow rate to or from a sample specimen under a controlled temperature program in a controlled atmosphere.
Differential Thermal Analysis (DTA)
is a simpler form of DSC, often called heat flux DSC or single-furnace DSC. The term today is normally only used for instruments that operate above 700°C.
DT/TGA (also called an STA)
is an instrument that performs both DTA and TGA on the same sample simultaneously; hence, DTA and TGA are combined into DT/TGA, or alternatively called a simultaneous analyzer (STA).
Damping
is the dissipation (loss) of mechanical energy and modeled by a dashplot. In DMA, it is another term for tan delta.
Deborah number
is a unitless measure of viscosity obtained by the time of the experiment divided by the time of the property measured.
Degree of cure
is how cured a material is, normally estimated by either the Tg, the modulus values in DMA, or the residual cure in the DSC.
Degree of polymerization
is a measure of how far a polymerization reaction has gone. See degree of cure.
Derivative curves
are often used to see the rate of change in a property and help detect transitions. The most commonly used one is the derivative of the weight loss in the TGA, in which it helps one understand the changes a material undergoes as it combusts.
Dilatometer
measures volumetric expansion by translating a three-dimensional expansion into a deflection. This gives bulk (volumetric) expansion of irregularly shaped samples or fluids and can also determine the bulk modulus, which can be used with other values to calculate Poisson’s ratio.
Elastic
refers to a material’s ability to return to its original shape. Normally it is modeled by a spring.
Elastomers
are materials that exhibit elastic properties and may be thermoplastic or thermoset.
End use properties
are the properties (tests) used for deciding a polymer’s suitability for a task.
Entanglements
are the physical (steric) interference of polymer movement by other chains.
Equilibrium modulus
is calculated from the recovery portion of creep-recovery analysis or slope of creep strain extrapolated back to intercept the start of the creep cycle.
Endothermic Event
is a thermal event in which a material absorbs energy, i.e.,  melting.
Evolved Gas Analysis (EGA)
is the connection of a TGA to another instrument to determine the off-gas components. FTIR is the most common; however, MS, GCMS, and IR-GCMS are also used. Instruments connected like this are called hyphenated techniques and written as TG-IR (for TGA coupled to an FTIR).
Exothermic Event
is a thermal event in which a material releases energy, i.e., crystallization.
Fast-Scanning DSC
is a DSC technique that employs controlled heating rates above 300°C/minute. It is used to observe subtle thermal events, kinetically trap polymorphic forms, and suppress curing, degradations, and recrystallizations.
Flexural
is a testing geometry in which samples are deformed using three-point bending, four-point bending, and single- or dual-cantilever measuring systems. These are the easiest geometries to use.
Fluid bath
is an alternative furnace that allows the sample to be immersed into a solution.
Fluid region
is where the sample flows like water with free chain movement, and inter-chain slipping occurs. Tan delta is much higher than 1.0 and the fluid region above the Tm in crystalline materials. The material here often follows the power law and is often studied in terms of shear and shear rate.
Force
is an application of mechanical energy, the load applied to a sample in TMA and DMA.
Force motor
applies a force to the sample, causing sample deflection.
Frequency scan
observes sample strain while increasing frequency of oscillation, while holding stress and temperature constant. This is used for fingerprint-type identification of polymers, identifying the resonant and harmonic frequencies, determining the degree of shift in the glass transition temperature, and for calculating TTS and activation energy.
Friction
is the force required to overcome surface-molecular interaction between two materials.
Fourier Transform Infrared Spectrometer –FTIR
simultaneously collects spectra over a wide wavenumber range. This gives a significant advantage over dispersive instruments and is now the industry standard.
Functional group
is a chemical group, such as CHO, attached to a polymer backbone.
Gel point
is the point at which a curing system approaches infinite molecular weight. The polymer often becomes incompressible at this point. In DMA it is taken as either the onset of the increase of storage modulus during an isothermal cure; the point at which E’ and E” intersect; or the point at which frequency dependence in E’ disappears.
Glass transition (Tg)
is the temperature range at which an amorphous material softens without changing state. It appears differently in the DSC, TMA, and DMA getting agreement between the methods is often a point of contention. Even within on method, there are often various values. This is aggravated by the assumption Tg is a temperature, when it is a temperature range we pick an indicator for. Depending who you ask, you can get 4 different numbers by DSC, two by TMA, and seven by DMA. Of these methods, DMA is the most sensitive to weak Tgs.
Glass Transition Temperature (Tg)
is the temperature reported as an indicator of the glass transition region.
Glassy
refers to the hard, springy, or rock-like state of a polymer. It does not imply clarity.
Heat
is a form of energy. Heat is not temperature.
Heat Capacity (Cp)
is the amount of heat required to raise a material’s unit mass one degree in temperature. Cp = Q/m T, where: Cp = specific heat, Q = heat added, m = mass of material, T = change in temperature.
Heat History
is the effect on the polymer caused by the last thermal cycle. In polymers, heat history is erasable by heating the material slightly above the melt temperature and then cooling a material to below its glass transition temperature.
Heat of Fusion (hf,)
is the amount of heat per unit mass needed to change a substance from a solid to a liquid at its melting point. See Delta H.
Heterogeneity
refers to an inconsistent material content within a sample. For example, the X, Y, or Z axis in carbon fiber composites will have different mechanical properties and CTEs.
Homogeneity
refers to the consistency of material content within a sample. A homogenous material is the same in all directions. In DMA and TMA, this means that testing in the X, Y, or Z axis will be the same.
Hooke’s law
describes the elastic behavior of springs and defines spring constant.
Humidity Generator
is an alternative furnace or device that allows the sample to be studied in a controlled humidity environment.
Hyphenation
is the coupling of two instruments together and refers to the hyphen used to separate them. For example, a TGA connected to an FTIR is written TG-IR.
Hysteresis
refers to the energy stored after each cyclic deformation causes the difference between loadings.
Impact modifiers
are modifier or additives used specifically to make a polymer less brittle on impact.
Isotropy
refers to the consistency of material properties within a sample.
Isothermal
describes the process of holding a material at a certain temperature and observing its changes over time. One example of an isothermal experiment is observing the cure of an epoxy at a set temperature.
Isothermal Kinetics
are kinetics calculated by isothermal temperatures instead of ramping rates.
Joule
is the SI unit of energy and is approximately equal to 4.18 calories.
Leathery
is a polymer state described as tough, but flexible.
Linear coefficient of expansion
is the normalized change in a material upon heating. Also called a CTE, it is the main reason for TMA and it is needed for proper design and understanding of products. Everything has a CTE.
Melt viscosity
is a traditional test for polymer processing. It approximates the complex viscosity of a frequency scan at melt temperature.
Modifiers
are a type of polymer additive.
Molecular Weight
is the sum of the atoms’ combined atomic weights in a molecule. In polymers, molecular weight is normally a distribution and can be Mn (number average), Mw (weight average) or Mz (viscosity average). This is important in polymers for determining the materials properties like the Tg. After monomer type, molecular weight is the single most important property of polymers, especially for determining materials properties. It affects the Tg, the moduli, and the vertical movement of the frequency scan’s crossover point.
Modulus
is the ratio of stress to strain. Moduli for different geometries are different, although shear, bulk, and tensile can be interconverted.
Melting Point (Tm)
is the temperature at which a material melts. For polymers, it is measured as the peak temperature of an endothermic event in DSC and DT/TGA. For metals and pure organics, it is not the peak temperature, but the extrapolated onset temperature (To) of the endothermic event.
Modulated Temperature DSC
is the general name for techniques applying a nonlinear heating rate to a sample. TAI’s trademarked version is MDSC™ and applies a sinusoidal heating rate over a standard ramp. This separates the heat flow into a reversible and a non-reversible component, allowing the detection of buried transitions and the measurement of thermal conductivity. Other companies use different methods: PerkinElmer’s StepScan™ uses a series of heating and holding steps, and returns a Cp and Kinetic curve.
Morphology
refers to the crystalline and non-crystalline (amorphous) properties of materials.
Newton’s law
describes the behavior of flowing materials.
Omega ω
is the symbol for frequency in radians per second.
Orientation
is the non-crystalline organization in which polymer backbones become closely packed in one direction.
Period
is the time it takes to complete one event, normally an oscillation.
Permanent set or irrecoverable flow
is the change in a material’s form after a material has been deformed. It is normally studied in a Creep test and is irreversible.
Phase
refers to part of or section of a polymer. For example, many types of polyurethane have rubbery and crystalline phases.
Phase lag (δ)
is the delay between applied force and material response. It is also called the phase angle and is the delta (δ) in tan δ.
Photo Calorimetry
is the study of reactions in the DSC that are driven by UV light. This requires a modified DSC. Similarly one can do photo-TMA or photo-DMA.
Plasticity
is the deformation of polymers stressed beyond the yield point.
Poisson’s ratio
is the ratio of the change in sample depth and width as the sample length is changed, and is typically about 0.35 for polymers.
Polymer transitions
are changes in a polymer’s physical appearance or behavior as a sample. The glass transition and the melt are examples of such.
Proportional limit
is the greatest stress a material can withstand without permanently deforming. It is the upper limit for DMA testing.
Quench Cooling
is a DSC technique that employs rapid cooling rates above 300˚C/minute. This is used to further study the effects of rapid crystallization on a material. Quenching normally implies that the cooling rate is not controlled.
Rate
How fast something happens, e.g. how fast you heat or cool in degrees per minute.
Recovery
is the return of a material to a relaxed state. Most commonly used in Creep studies, where it defines the material’s response after the applied stress is removed. It gives time-dependent relaxation behavior as a function of pressure (stress) or temperature.
Recovery time
is the time in which the sample stops changing after a recovery analysis.
Relaxation time
is the time needed for molecules to relax after applying a stress to a material. A single relaxation time for the material is required for the WLF to be valid.
Resonance
is the amplification of natural harmonics within a sample. At this point, the data becomes useless in most DMA experiments. Because of this, resonance often limits the upper frequency you can apply to a material.
Resonant Frequency
is the frequency at which resonance occurs and the amplification of natural harmonic oscillation.
Rheology
is the study of flow and deformation in materials.
Roller Kinetics
are a method of using isothermal or temperature-scanning cure studies to calculate the activation energy for curing.
Rubbery
is a springy, putty-like state of polymers.
Rubbery plateau
is when the main backbone chain exhibits gradual slippage and the Tan delta is often near 1.0. This is above the Tg and the modulus here is related to cross-linking or entanglements.
Scanning
is a heating or cooling run at a controlled rate.
Specific Heat
is the heat capacity of a substance per unit mass. For engineering purposes, specific heat and heat capacity can be assumed to be equivalent.
Start-up Transient
is the initial change in the baseline at the very beginning of a DSC scanning run before the instrument is in complete scanning rate control. If multiple segments are used, each segment will have a start-up transient.
Semi-crystalline polymers
are polymers that have some of their backbones organized into crystals and some randomly arranged (or organized).
Shear Sliding
is used in axial-type DMA to get at the shear modulus, G. It is a fixture that holds two samples so they exhibit shear behavior.
Side chain
is a branch of the main polymer backbone.
Sinusoidal
refers to a cyclic event related to a sine wave, and is how force is applied in most DMAs.
Solid-solid phase transitions
are small transitions caused by changes in the solid state. They are called polymorphism in pharmaceutical or eutectic transitions in liquid crystals and metals.
Spring constant
is the slope of a spring’s stress-strain relationship according to Hooke’s law.
Static modulus
is the slope of the stress-vs-strain curve in the linear region of a stress strain plot. In extension, this is Young’s modulus.
Steric effects
are the effects of the physical position of atoms relative to each other within a molecule.
Storage modulus (E’)
is the in-phase component of a DMA signal and an indicator of elasticity.
Strain Ratio
is the ratio between the change in length and the original length of an extension sample.
Strain Percent or Percent Strain
is the engineering strain multiplied by 100 to report conventional units.
Stepper Motor
is a secondary motor in older DMAs that shifts the force motor to compensate for sample stretching or contraction.
Stress
Stress is the load applied to a sample, calculated by dividing the force by surface area?
Structure
is the physical position of molecules relative to each other. In polymers, you can have primary, secondary, tertiary, and quaternary structure.
Structure-property relations
are how specific parts of the polymer contribute to specific behavior of the material. Studying these is a major area of applied polymer science.
Thermogravimetric Analysis (TGA)
is tracking the change in a sample’s mass as a function of time and/or temperature.
Thermal Mechanical Analysis (TMA)
is the measurement of changes in sample size or volume as a function of temperature. It works by applying a weak static force and measuring sample response normally while changing temperature. One observes sample height as temperature is increased. TMA can give the coefficient of thermal expansion and identify thermal transitions, like Tg.
Tangent delta
is the tangent of the phase angle and also the ratio of loss to elasticity (E’/E’). It is also called damping and is an indicator of a sample’s viscoelasticity.
Temperature
is the degree of heat measured on a definite scale.
Temperature Scan
is running a sample under a controlled heating or cooling rate while controlling other variables. It is used for characterizing thermally-dependent behavior, like the Tg.
Tensile
is a test method for films or fibers in which they are deformed using extension measuring systems.
Terminal zone
is the onset point in a frequency scan in which the storage modulus dramatically decreases.
Terpolymer
is a copolymer with three repeating units.
Thermal expansion
is the change in a sample’s dimensions as it is subjected to a controlled temperature program.
Thermal history
is the previous thermal conditioning applied to the sample. A second DSC scan after a controlled cooling is used to remove thermal history in thermoplastic polymers. It is also called heat history.
Thermoplastics
are materials that reversibly change when heated and can be heated multiple times without changing the material. The melting and cooling of polystyrene is an example.
Thermosets
are materials that irreversibly change when heated—for example,  the hardening of the proteins in a cooked egg.
Thermosetting Polymers
have their backbones chemically bonded (cross-linked) between chains.
Time scan or isothermal scan
observes the sample change while holding temperature and any other conditions constant. Often used for curing, aging, environmental effects, etc.
Time-dependent behavior
is the sample’s behavior over time. An effect of the viscoelastic nature of polymer, it is often a concern in mechanical methods.
Time-Temperature Superposition
is a mathematical technique that allows one to predict behavior in materials outside the measured frequencies or time. The WLF model is the most commonly used.
Tougheners
are additives used to make a polymer less brittle. Often seen in the DMA as step changes in E’ at low temperature. Also called plasticizers, they tend to low the Tg.
Toughness
is a material’s ability to absorb mechanical energy without fracturing or deforming. In DMA, it is often related to the beta transition.
Ultimate strength
is the greatest stress a material can withstand without failing or breaking apart.
UV Furnace
is a furnace or adapter that allows the irradiation of a sample in order to study photo-curing or degradation.
Viscoelasticity
is a material’s ability to exhibit both elastic and viscous behavior.
Viscosity
is a material’s ability to flow and deform.
Vitrification Point
is the point at which curing systems reach a viscosity so high that it limits further curing. It is normally taken as the onset plateau of storage modulus during Time Scan isothermal cure. It is also detectable using modulated temperature DSC.
Yield point
is the point at which stress causes a material to permanently deform.
Yield strength
is the amount of stress that will cause a permanent physical change in a sample’s shape.
Young’s modulus
is the ratio of stress to strain when stress is increasingly applied to a sample.
Watt
is the power expended when one joule of work is done in one second.
WLF or Williams–Landel–Ferry Model
is a model of polymer behavior used to predict wide-frequency ranges or long times. Developed for rubber, the WFL equation is empirical and remains the most common model used for TTS.