2.6. Hydrodynamic Diameter (HD) and Polydispersity Index (PDI) Measurements

A Zetasizer Nano ZS ZEN3600 device (Malvern Instruments, Malvern, UK) was applied to perform dynamic light scattering (DLS) measurements. The selected measurement principle enabled determining hydrodynamic diameters (HD) and polydispersity index (PDI) of the aqueous polymer particle dispersion, according to the definition in ISO 13321:1996E and ISO 22412:2008 [20,21,22]. The standard red He–Ne laser with an output power of 4.0 mW, and wavelength of λ = 633 nm, was used as the incident beam. A sensitive avalanche photodiode detector (APD) placed at a 173° angle enabled the application of a non-invasive backscattering (NIBS) system. The attenuator for the laser beam adjusted the laser power during the measurement sequence by setting it automatically. An optically translucent polyacrylic disposable DTS-0012 cuvette (Malvern Instruments, Malvern, UK) was filled with 1.0 mL of the polymer dispersion and placed in a temperature-controlled cell. The sample was transparent, homogenous without any precipitation, purified by dialysis, and not diluted. The DLS measurements were recorded at every one degree with increasing temperature from 18 to 45 °C. The number of runs in one measurement was adapted automatically in the range from 10 to 100. The equilibration time before start measurements at the new temperature was 240 s. The PDI and HD were calculated based on the cumulants analysis. All presented HD and PDI data are the average of five measurements at each temperature. The Zetasizer software (version 7.10) was used to interpret data from DLS measurements; it also enabled the use and design of custom standard operating protocols ensuring repeatability of measurements.