Cellulose (2018) 25:3781–3795
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Fig. 5 Average a side scattering and b forward scattering of PEC particle populations at different cation/anion ratios of polycations with 700 kDa CMC and DS 0.8–0.95
the wavelength of the incoming light, the precise angle that the light is collected, the internal structure of the cells, the presence of strongly absorbing materials within the cell, and refractive index of the cell. It has been shown that osmotic swelling of cells, as well as damages from freezing and thawing of cells will lower their measured FSC. Especially interesting is the fact that changes in lipid packing within a cell can affect the FSC, without changes in cell volumes. It has also been reported that highly textured surfaces or internal structures lower the FSC of a cell. With the explanations of FCM data from medical science, it is clear that SSC and FSC give information about very different properties of the PEC particles. The SSC of a particle gives information about the amount of dense and light scattering surfaces. The FSC of a particle gives information about the trans- parency of a particle, as well as the complexity of its external or internal texture. The light scattering in both side and forward direction are still connected to particle size, even though the dependence is indirect. An attempt to diminish the influence of particle size by combining the SSC and FSC of PEC particles into one single term, in the form of FSC/SSC values, gave new correlations. The FSC/SSC values of PECs formed from polyDADMAC and CMC at low cation/anion ratio was 2.4, but decreased to about 1.1 with increasing cation/anion ratio (Fig. 6). The size estimation of these PEC particles from SSC and FSC were almost the same at the highest examined cation/anion ratio. The FSC/SSC of PECs from Raifix 25035 and CMC were slightly higher at low cation/anion ratio, but also decreased after the theoretical neutralization point was
Fig. 6 Determined FSC/SSC values of particle populations from different cation/anion ratios of polycations with 700 kDa CMC
exceeded. The FSC/SSC values of PECs formed from Raifix 01015 SW or Raisabond 15 with CMC were higher throughout the studied cation/anion interval, yet similar to each other. PolyDADMAC, with a charge density of about 4 meq/g, gave lower FSC/SSC values than Raifix 25035 (1.9 meq/g), which in its turn gave lower values than Raifix 01015 SW and Raisabond 15 (0.8 and 0.9 meq/g, respectively). The results indicated that the FSC/SSC values decreased with increasing charge density of the polycation, while the properties of the polyanion was kept constant. Furthermore, the results indicated that for most combinations the FSC/SSC values seemed to decrease after the theoretical point of neutralization. In order to understand these results, available literature about the adsorption behavior of polyelec- trolytes onto model surfaces need to be considered, since the interactions between two dissolved poly- electrolytes may exhibit similar mechanisms.
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