Page 113 - Carrahers_Polymer_Chemistry,_Eighth_Edition

76 Carraher’s Polymer Chemistry

Solvent reservoir
Injector
Filter
Pump
Degasser

DAWN DSP
or miniDAWN
Columns
RI Detector
Waste

UV Detector
(optional)
OPTILAB DSP DAWN DSP

Plumbing
Computer
Electrical

FIGURE 3.19 Typical SEC-MALS setup, including refractive-index refractometer. (Used with permission
of Wyatt Technology Corporation, Santa Barbara, CA 93117; wyatt@wyatt.com)

time that is being measured; photon correlation spectroscopy (PCS) with the name emphasizing the
particular mathematical technique employed to analyze the light-scattering data; and quasielastic-
light scattering (QELS) with name emphasizing the fact that no energy is lost between the collision
between the particle and the light photon.
The effect of subtle particle changes as a function of temperature, sample preparation, time,
solvent, and other changes can be measured using DLS. Such changes can then be related to perfor-
mance variations eventually interrelating structure shape and biological/physical property.
Another variation that is useful employing coupled light scattering is referred to as a tri-
ple detection set. The set consists of three detectors—a light-scattering detector, a differential-
refractometer detector, and a capillary-differential viscometer. It functions in concert with a GPC
and light-scattering source. The GPC separates the polymer mixture into molecular weight frac-
tions. According to the Einstein equation the intrinsic viscosity times the molecular weight is
equal to the hydrodynamic volume or size of polymers in solution. Thus, the molecular weight
is determined using light-scattering photometry; viscometry gives the intrinsic viscosity, and the
equation is solved for size.
In general, light-scattering photometry has a limit to determining molecular size with the
lower limit being about 10 nm. The addition of the viscometer allows molecular sizes to be deter-
mined for oligomeric materials to about 1 nm. The assembly allows an independent measure of
size and molecular weight as well as additional conformational and aggregation information,

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