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Conclusions
Acknowledgments This work is a part of the project ExtBioNet, appointed by the Academy of Finland. The work is part of the activities of the Process Chemistry Centre (PCC) at A˚ bo Akademi University. Special thanks to Frida Sjo¨gren, MSc worker at the laboratory of Wood and Paper Chemistry, A˚ bo Akademi University, for skillful laboratory work. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unre- stricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Com- mons license, and indicate if changes were made. Open Access
Polyelectrolyte complexes (PECs) were prepared from common papermaking additives at different cation/ anion ratios. The polycations were different cationic starches and polyDADMACs, while the polyanions were CMCs of various molar masses and charge densities. The colloidal, light scattering PEC particles were studied by turbidity measurements, as well as by flow cytometry (FCM). Turbidity maxima of the different PEC mixtures were located close to the theoretical point of neutralization between the poly- cation and polyanion. The turbidity response varied with polyelectrolyte charge density. The formed PECs were in most cases stable for 24 h, but certain combinations close to the theoretical point of neutral- ization resulted in unstable complexes. The light scattering properties of PECs in side direction (SSC) and in forward direction (FSC) were recorded by FCM analyses. It was seen that the SSC and FSC of the analyzed particles were influenced by very different particle properties, and a new term was suggested to better understand the properties of these particles in suspension; FSC/SSC. It was shown that the calculated FSC/SSC values were connected to the structural density of particles. The hydrophobicity of PECs was also analyzed by FCM. All of the measured PEC combinations were very hydrophilic, and it was seen that the hydrophobicity of the particles was lowest close to the theoretical point of neutralization. Finally, a coagulating PEC mixture was studied by FCM analysis as a function of time. It was shown that the initial particle count decreased by 75% over a short period of time. The PECs were initially of medium density, but quickly formed large, swollen particles due to secondary aggregation amongst the initial particles. After 53 min, only about 1% of the particles remained in suspension. It is suggested that FCM can be used to study polyelectrolyte complexes in suspension. FCM pro- vides relevant information about the structural density and hydrophobicity of these particles. With FCM it would be possible to simultaneous analyze PEC properties and their interactions with other particles in suspension. When dealing with research or produc- tion of PECs, FCM techniques can be very useful for categorizing the formed particles.
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