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Fig. 2 The measured turbidity values of polyelectrolyte complexes (PECs) of polyDADMACs or different cationic starches with CMCs (250 kDa) of DS 0.7, 0.9, and 1.2. The presented turbidity values were determined after 24 h of PEC formation
Fig. 3 Two logarithmic flow cytometry dot plots of PECs in aqueous media, using a mixture of polyDADMAC (100–200 kDa) ? CMC (250 kDa, DS 0.9) with a cation/anion ratio of 0.5:1. The properties of the measured particles are plotted as a their side scattering (SSC) versus forward scattering (FSC), and b their FSC versus intensity in the red spectrum (hydrophobicity)
0.5:1 mixture of polyDADMAC (100–200 kDa) with CMC (250 kDa, DS 0.9). The colloidal PEC particles interacted with the added hydrophobic dye, which was seen in the recorded intensities of the particles in the red spectra (Fig. 3b). The added Nile red was most likely adsorbed on the surface of the PECs. Nile red is an environment-sensitive fluorophore, which is almost non-fluorescent in hydrophilic environments, while it undergoes a fluorescent enhancement and large absorption and blue shifts in hydrophobic environ- ments. The fluorescence in the red spectrum has commonly been used as a measurement of particle hydrophobicity (Va¨ha¨salo et al. 2003; Strand et al. 2013). The PECs were quite hydrophilic; the low intensities of the PEC particles in the red spectra indicated that the particles were hydrophilic, even
though the chemical environment could activate the hydrophobic dye to some extent. A hydrophilic nature of the PECs was very much suspected, since these consist of kinetically frozen structures of polyelec- trolytes that were previously soluble in water (Dautzenberg and Karibyants 1999).
Particle count
PECs of polyDADMAC or three different commer- cially available cationic starches with CMC of 250 and 700 kDa were prepared at different cation/anion ratios. Noticeable variations in the number of particles per l L was seen when 250 kDa CMC was used as polyanion, while the particle count remained more stable when 700 kDa CMC was used (Fig. 4a, b). Adsorption experiments have previously shown that
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