## 3 Results and Discussion  
### Formation of BSM-PDADCAC Binary Formulations  
In aqueous medium, carboxylated BSMs are negatively charged. An electrostatic interaction of these microspheres with positively charged PDADMAC results in the formation of the polymer-colloid PDADMAC-BSM complexes. The regularities of complexation were revealed via the study of EPM of resulting PDADMAC-BSM particles.  
Figure 1 shows the dependence of EPM on the ratio between a mole concentration of quatermized PDADMAC groups and a mole concentration of carboxylic BSMs groups, Z = [N\({}^{+}\)]/[COO\({}^{-}\)]. Injection of a PDADMAC aqueous solution into a BSL resulted in the adsorption of PDADMAC macromolecules on the microsphere surface, decreasing the negative charge of the particles followed by their complete neutralization at EPM = 0.  
The composition of the electro-neutral PDADMAC-BSM complex was determined using an earlier described approach [48; 49] based on the two main points. At first, positively charged groups of cationic PDADMAC interact completely with negatively charged carboxyl groups at anionic BSMs. As a result, all polycation chains are bound by latex particles, and their surface is completely covered by the polymer. Second, at the EPM = 0, a concentration of the positive PDADMAC groups, involved in the complexation ([N+]\({}_{\text{EPM = 0}}\)), is equal to the concentration of the negative (ionized) BSM groups ([COO-]\({}_{\text{EPM = 0}}\)). These ideas allowed the composition of an electro-neutral complex Z\({}_{0}\) = [N+]\({}_{\text{EPM = 0}}\)/[COOH]\({}_{\text{EPM = 0}}\) = 0.82. A degree of dissociation of the surface carboxylic groups at pH 7 is of \(\alpha\approx\) 0.7 [50]. Extra ionized COO\({}^{-}\) groups (\(\approx\)0.1) were involved in complexation due to a cooperative displacement of protons from carboxylic BSM groups by the interacting PDADMAC [41]. Non-dissociated carboxylic BSM groups, whose fraction was 0.18, did not form ionic bridges with the cationic PDADMAC. The composition of the PDADMAC-BSM complex can be re-calculated in terms of the weight fraction of PDADMAC as \(\text{W}=\text{W}_{\text{PDADMAC}}\)/(W\({}_{\text{BSM }}+\text{W}_{\text{PDADMAC}}\)), where \(\text{W}_{\text{PDADMAC}}\) and \(\text{W}_{\text{BSM}}\) are current weights of PDADMAC and BSM, respectively. For the electro-neutral complex, we get \(\text{W}_{0}=\text{W}_{\text{PDADMAC}}\)/(W\({}_{\text{BSM}}\)(EPM = 0)\) + \(\text{W}_{\text{PDADMAC}}\)(EPM = 0) = 0.02, where \(\text{W}_{\text{PDADMAC}}\)(EPM = 0) and \(\text{W}_{\text{BSM}}\)(EPM = 0) are weights of both components at EPM = 0. The increase in Z was accompanied by the additional binding of PDADMAC and an appearance of the positive charge on the BSM surface. The ultimate positive EPM value was +2 (\(\upmu\)m/s)/(V/cm) and did not change with the further growth in Z. This EPM value corresponded to the maximum adsorption of PDADMAC onto the surface of negative BSMs and the formation of the saturated PDADMAC-BSM complex [49; 51; 52]. The positive charge stabilized the saturated complex particles against aggregation; their size was close to 170 nm as compared with 100 nm for the virgin BSM. Note, the saturation takes place at \(Z_{\text{sat}}\) = 1.5 (see Figure 1) or \(\text{W}_{\text{sat}}\) = 0.036. At W \(>\text{W}_{\text{sat}}\), an accumulation of unbound PDADMAC is observed, and the PDADMAC-BSM binary mixture contains the saturated PDADMAC-BSM complex and unbound PDADMAC. From this standpoint, the weight fraction of PDADMAC W can be considered as the key parameter which describes the composition of the PDADMAC-BSM formulations.