Meaning
Characterisation methods used in conjunction with chromatography provide absolute measurements of molecular mass and size in solution. Multi angle light scattering detects the intensity of laser light deflected by polymer chains at several different positions simultaneously. This technique eliminates the need for external calibration standards and provides a direct view of the polymer architecture.
Detection Geometry
Sensor placement around the sample cell allows for the calculation of the radius of gyration of the molecules. In a multi angle light scattering system, the detectors are typically arranged in a semi-circle to capture the scattering profile from low to high angles. This arrangement is useful for detecting large aggregates or very high molecular weight fractions that might be missed by a single angle detector.
Absolute Mass
Calculation of the molar mass is based on the physical principles of light scattering rather than the time it takes for a chain to pass through a column. Multi angle light scattering provides a mass measurement that is independent of the polymer shape or its interaction with the column packing. This makes it the preferred tool for studying branched polymers or copolymers where the hydrodynamic volume does not have a simple relationship with mass.
Branching Distribution
Structural analysis reveals how long chains are attached to the main polymer backbone. By comparing the molar mass to the size of the molecule, multi angle light scattering can quantify the degree of long chain branching in a sample. This information is required for polyethylene producers who need to control the melt strength and the processing stability of their resins in film blowing operations.
Modern systems integrate this data with viscosity detectors to provide a complete picture of the polymer molecular configuration.
