Viscosity-average Molar Mass
Viscosity-average Molar Mass - Related Videos
01:54
Molar Mass
0 Views •
2020
The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, water, H2O, and hydrogen peroxide, H2O2, are alike in that their respective molecules are composed of hydrogen and oxygen atoms. However, because a hydrogen peroxide molecule contains two oxygen atoms, as opposed to the water molecule, which has only one, the two substances exhibit very different properties. Atoms and molecules are extremely...
01:27
Determination of Molar Masses of Polymers II
0 Views •
2026
Polymer samples typically consist of macromolecular chains with a distribution of lengths, resulting in a range of molar masses rather than a single discrete value. Conventional descriptors such as the number-average molar mass and weight-average molar mass quantify this distribution but do not fully capture polymer behavior in solution..The viscosity-average molar mass provides a more realistic description of polymer behavior in solution because it accounts for the enhanced contribution of...
03:43
Applications of the Ideal Gas Law: Molar Mass, Density, and Volume
0 Views •
2020
The volume occupied by one mole of a substance is its molar volume. The ideal gas law, PV = nRT, suggests that the volume of a given quantity of gas and the number of moles in a given volume of gas vary with changes in pressure and temperature. At standard temperature and pressure, or STP (273.15 K and 1 atm), one mole of an ideal gas (regardless of its identity) has a volume of about 22.4 L — this is referred to as the standard molar volume. For example, one mole each of hydrogen, oxygen,...
01:24
Determination of Molar Masses of Polymers I
0 Views •
2026
Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
08:04
Viscosity of Propylene Glycol Solutions
0 Views •
2023
Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA Viscosity is a measure of a fluid's resistance to flow, and it is a useful parameter in the design of efficient product processing and quality control in a wide range of industries. A variety of viscometers are used to obtain the most accurate readings of experimental materials. The standard method of measuring viscosity is through a glass tube viscometer, which...
FAQs
The constants K and a convert an intrinsic-viscosity measurement into the reported value of Mᵥ. K sets the scale of the relationship, while a determines how strongly the calculated molar mass changes as intrinsic viscosity changes. Because both constants belong to a particular polymer–solvent system and temperature, using mismatched values can make calculations or comparisons unreliable.
Hydrodynamic volume links molecular dimensions to the resistance a dissolved chain creates as solution flows. Chains that occupy more effective volume can produce a larger viscosity response, so the measurement reflects chain size in its dissolved environment rather than an isolated chain mass alone. This makes the result useful for assessing solution behavior when direct chain-mass measurements are unavailable.
Solvent and temperature are part of the measurement conditions because they influence the polymer–solvent relationship used in the calculation. The Mark–Houwink–Sakurada constants K and a are defined for a particular system and temperature, so changing either condition can affect the connection between intrinsic viscosity and Mᵥ. Consistent conditions are therefore essential for meaningful comparisons.
A typical workflow begins by measuring the intrinsic viscosity of dissolved polymer under a specified temperature and solvent condition. The measured value is then inserted into [η] = K(Mᵥ)^a, using constants established for that polymer–solvent–temperature combination. The resulting Mᵥ can support sample comparisons when measurement and reference conditions are suitably aligned.
Changes in viscosity-average molar mass across controlled samples can indicate altered polymer chain characteristics associated with degradation. By measuring samples under the same solvent and temperature conditions, researchers can distinguish changes in the viscosity response from simple differences in test conditions. This supports monitoring of polymer stability and evaluation of degradation during research or quality-control studies.
The measurement is useful for comparing polymer batches, checking consistency, and evaluating how chain characteristics may affect solution behavior. It also provides information relevant to processing and formulation, where dissolved-polymer viscosity matters. When individual chain masses are not measured directly, viscosity-based results offer a practical molecular-weight characterization approach for examining material performance.