Controlling the Aggregation of Particles to Tune Materials Properties

Colloids and polymeric systems constitute building blocks of choice for designing and controlling material properties. One major parameter is therefore the aggregation state of the polymer/particles complexes and its control to achieve desired properties. In this presentation, two examples will be given to illustrate this principle. The first example relates to paper surface hydrophobation, often referred to as surface sizing, where typically a combination of stabilized hydrophobic nanoparticles and an excess of starch is applied on the paper web in the paper making process. This study focused on the combination of the surface sizing particles of different charges (cationic, anionic and amphoteric) and anionic starch. The mixtures were investigated by turbidity, light scattering and SAXS measurements. While amphoteric and anionic particles were not affected by the starch addition, cationic particles aggregated strongly at low starch concentration. At higher starch concentration the stability was restored. We could correlate this behavior with the higher efficiency of the cationic particles in the hydrophobation of the paper surface compared to the amphoteric and the anionic particles. The effect of the size of the aggregate in the hydrophobation efficiency will also be discussed.