## 3 Results and Discussion  
### The Effects of Different Monomer Ratios on the Performance of the Various Synthesized PSA Emulsions  
Of the two monomers in the PSA emulsion, St is a hard monomer due to its benzene ring structure, while butyl acrylate is a soft monomer due to its linear structure. The use of different ratios of soft and hard monomers leads to significant changes in the rigidity of  
Figure 2: (**a**) Flexural strength tests of PSA emulsion-modified mortar. (**b**) Compressive strength tests of PSA emulsion-modified mortar. (**c**) The fracture toughness test setup for PSA emulsion-modified mortar. the polymer chain segment in the emulsion and significant changes in its performance [29]. Thus, a series of PSA emulsions with different monomer ratios were initially characterized with the aim of investigating the effects of the soft and hard monomer ratios on the performance of PSA emulsions. Firstly, the basic performance of the various synthesized PSA emulsions was tested; the results are shown in Table 4. The PDI is used to describe the uniformity of the molecular weight distribution in the polymer; the smaller the PDI value, the more uniform the molecular weight distribution. It shows that the series of PSA emulsions synthesized using pre-emulsified semicontinuous seeded emulsion polymerization have a high conversion (\(\geq\)95%) and low PDI (<0.08), which indicates that this polymerization method is more suitable for the polymerization of the present system and the emulsion particles are well dispersed during polymerization. The hydrodynamic diameter is the particle size of the composite particles in the emulsion state. The hydrodynamic diameter of the emulsion is approximately 160 nm. The zeta potential refers to the potential difference between the surface of polymer particles and the surrounding fluid, which is an important indicator for characterizing the stability of the polymer dispersion system; the higher the absolute value of the zeta potential, the better the stability. The zeta potentials are all negative values, indicating that the surface is negatively charged, and the absolute value of the zeta potential is more than 50 mV, which indicates that the anionic emulsifier and nonionic emulsifier compounding system used in this paper can effectively stabilize the PSA emulsion [30]. The test results of the glass transition temperature (T\({}_{\text{g}}\)) and the minimum film-forming temperature (MFFT) show that, as the content of the hard monomer (St) gradually increases in the mixed monomers, the T\({}_{\text{g}}\) and MFFT also gradually increase. This is mainly because the increase in the content of the hard monomer enhances the rigidity of the polymer chain segments and reduces the free movement of these segments, hence the T\({}_{\text{g}}\) gradually increases. One of the most important steps in the film forming process of the polymer latex is the mutual fusion between the latex particles. Therefore, the movement of the chain segments is extremely crucial. This also leads to a strong correlation between the MFFT and T\({}_{\text{g}}\) in general; thus, the MFFT also gradually increases with an increase in the St content. However, the MFFts of the PSA emulsions in this paper are significantly lower than the conventional curing temperature of mortar, which is 20 \({}^{\circ}\)C. This ensures that the PSA emulsions have good film forming properties in mortar. The TEM results of the microstructure of PSA emulsions are shown in Figure 3a. The latex particles show a more uniform spherical structure, with sizes similar to the DLS test results. The latex particles can be easily bonded together to form a film under a low St content, while the granular structure of the latex particles becomes more obvious as the St content gradually increases. This is mainly because the PSA emulsion with the low St content easily forms a film during the TEM sampling process.