Characterization of Polymer Particles

This chapter restricts itself to a presentation of the methods used to characterize the size and the surface of the polymer particles. Analysis of the polymer itself or the particle morphology is usually performed on the polymer film or on the dried particles and is therefore treated later in Sect 3.3.3. 

Polymer dispersions contain particles with diameters ranging from 10 to about 1500 run. Typically, the particle size is between 100 and 250 run. In the majority of apphcations, particle size and particle size distribution are highly significant factors that determine the properties of a polymer dispersion, such as its flow behavior or its stability (Sect 3.2.1). Measuring particle size is thus an important element when developing polymer dispersions and is also used in in-process control. A broad range of 

LT = transmission through water/trans-mission through dispersion (2.5 cm cuvette, white iight). m = refractive index of the poiymer/refractive index of water. 

For polydisperse dispersions, the measured Kght transmission is the inverse geometric mean of the relative transmissions LTj, LT2,. .. of the respective mass fractions mj, m2.  

The measurement, which takes only a few minutes to perform, can be used to determine particle diameters of between 5 nm and 5 pm. In order to avoid complications due to multiple scattering of the laser light and due to particle interactions, which influence diffusion, the measurements must be carried out on highly dilute samples (10 to 10 %, w/w). 

---