Multi angle laser light scattering MALLS

5 Multi angle laser light scattering (MALLS) 

Early instruments employed low (forward) angle laser light scattering (LALLS) but these have been replaced by multi-angle instruments. MALLS instruments use Lorenz-Mie (often referred to as Mie) theory or Fraunhofer diffraction theory. 

Refractive index consists of two parts, a real part that describes the refracted light and an imaginary (complex) part that describes absorption. In the case of very small particles, or particles where the complex part of the refractive index is near zero, light is transmitted through the partieles and interferes with the diffracted radiation. The interaction between the transmitted and diffracted radiation results in anomolous scattering and can be catered for in the Fraunhofer theory if both parts of the refractive index are known. 

Non-spherical particles are measured over all orientations and this causes a broadening in the measured size distribution. Textured particles tend to give enhanced weighting to the fine end of the distribution. 

The measurement volume is controlled by the width of the laser beam (10-25 mm) and the path length in the sample cell. The number of large particles in a broad distribution is low, which requires an extended measurement time in order to obtain an accurate estimate of their frequency. Since large particles are present in a small number of sweeps they are lost in the averaging process. They can, however, be distinguished by comparison of the sweeps using cross-correlation and principle component studies [132]. 

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Recently, Kulicke et al. [145] applied the principle of Flow-Field-Flow-Frac-tionation (F4) in combination with multi angle laser light scattering (MALLS) to characterize PDADMAC. Differential and integral molar mass distributions have been published for PDADMAC. One advantage of this method seems to be that it can be extended to the investigation of the mass distribution of aggregated and particulate components. 

In Multi Angle Laser Light Scattering (MALLS), the light scattered at various different angles is simultaneously measured and the extrapolation at low 6 values is done automatically. 

The CALLS detector is insensitive to low MW and low concentration species. Therefore, the determined by this method may be erroneously high. Another commercially available MW detector is a Multi Angle Laser Light Scattering (MALLS) photometer. It should be noted that a good chromatographic... 

Fig. 6.1. Determination of the exponent a from the slope and the constant K[ from the intersection with the y-axis when plotting log [q] as a function of log M. Values for the intrinsic viscosity [q] of the polycation poly(acrylamide-co-(A/,A/,A/-trimethyl-A/-[2-methacryloethyl]-ammoniumchloride) (PTMAC) in 0.1 mol/l NaN03 solution are taken from Fig. 4.2. The copolymer consists of 8 mol% TMAC and 92 mol% AAm. Molar mass values were determined with multi-angle laser light scattering (MALLS), data from [102]...

As mentioned in Chap. 1, randomly hyperbranched chains are even more complicated than dendrimers. It has not been completely clear whether they are fractal objects [11, 12] and whether those previously reported M-dependent intrinsic viscosities from an on-line combination of the size exclusion chromatograph (SEC) with viscosity and multi-angle laser light scattering (MALLS) detectors actually captured its structure-property relationship [11, 13]. In the next section, we ll discuss our experimental results in detail. 

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