Hydrophilic macroions represent a transition stage between small ions (following Deby-Huckel theory) and large colloids (DLVO theory). We found that such macroions show completely different solution behavior than either of previously known systems. Study on their behavior is of a great interest to understand the missing region in between. Dendrimers like PAMAM and PPI with the ability of being charged at different levels in solution can be a good candidate to fit this model.<br/>PPI dendrimer’s surface amines can be protonated and become charged, which will induce electrostatic repulsion between dendrimers and makes them stay individual in solution.<sup> </sup>Initiation of assembly process needs the overcoming of this electrostatic repulsion. Presence of oppositely charged counterions and reduction of solvent polarity were both necessary to induce enough screening effect to overcome the repulsive force.<br/>We suggested that the electrostatic interaction between PPI dendrimer and oppositely charged counter-anions can be considered as a major driving force yielding dendrimer molecules to form hollow spherical nanoparticles with known structure and controllable size. Nanoparticles’ sizes -measured using light scattering techniques- can be controlled based on dielectric constant and pH of the solution. It was shown that decreasing solution polarity will increase the size of nanoparticles. We also investigated the effect of changing pH on formed spheres. It was observed that changing pH at the same time will alter the dendrimer surface charge and ionic strength of solution which each have opposite effect on the size of spheres. At different pH and solution polarity either of above factors can be dominant and affect more on the nanoparticle’s sizes. This resulted in creation of a transition between “low polarity, high pH” and “higher polarity and lower pH” conditions in solutions.

Monovalent counter-ion mediated self-assembly of dendrimers

249th National Meeting (2015)

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