**3. Synthesis and characterization of organic hybrid microspheres**

The purpose of this work on the synthesis of organic-inorganic microcontainers is to create a material where it can be used by industry for the ultimate purpose of self-healing of concrete. In other words, a study was carried out to find a synthetic path that is easy, fast, but also easily adaptable to the final product. For these reasons, polymer microspheres were combined, changing parameters in the experimental process to achieve a size of microspheres, approximately 1 μm. The purpose of using microspheres at this size was to interact with *St. aureus*, the size of which is 0.5–1.5 μm.

### **3.1 Water traps**

The purpose of producing water traps with a desired size of 1 μm and then incorporating them into the material is when they come into contact with the bacterium and their nutrient, to adsorb and retain the bacterium on their surface. Spherical water traps were made up by a two-step process, which initially includes the cross-linked polymethacrylic acid (PMAA) spheres through submersion polymerization after distillation, and then the conversion of carboxylic groups into corresponding calcium salts through the treatment of microtraps with Ca (OH)2 solution. Methacrylic acid (MAA) and dimethacrylate glycolic acid ester (EGDMA) were used as monomers in a crusader role, in acetonitrile solvent with azodisisobutyronitrile (AIBN) beginning. Acetonitrile, being a nonprimary, polar solvent, favors polymer-polymer interactions, that is, hydrogen bonds between the carboxylic edges of polymer chains. MAA together with EGDMA are dissolved in acetonitrile in a 250 ml triple-blooded spherical flask. A freezer, thermometer, and N2 supply are installed in this bottle. After an hour of stirring, the AIBN is added, which has been dissolved in a solvent quantity before. Stirring continues at the same temperature for another hour. In order to distill the solvent, the temperature of the experiment increases to the boiling point of acetonitrile (80°C). After a certain amount of solvent has been collected, the reaction is terminated, and the resulting final solution is in the form of an emulsion. Finally, after the solution is allowed to reach ambient temperature, the sample is centrifuged twice, rinsed with acetonitrile, and then dried. PMAA spheres acquire the ability to absorb water when the carboxylic groups are converted into the corresponding calcium salts. The experimental procedure is as follows: 2 g PMAA spheres dissolve in acetonitrile and spread through ultrasound. After the sample has been dispersed homogenously, add 0.74 g of 0>1 M Ca (OH)2 solution. The mixture becomes clear (depending on the ratio of monomers—the less EGDMA is added, the clearer the solution becomes). After stirring for 30 minutes, the sample is centrifuged, rinsed with acetonitrile, and left to dry. Four different sized water traps were made up, changing the ratio of monomers in each case (**Figure 2**).

One can conclude from **Table 1** that the submersion polymerization after distillation gives uniform polymeric microspheres with different functional groups. **Figure 3** shows the SEM image of sample 2 together with the elemental analysis 2 before **Figure 3A** and after **Figure 3B** treatment with Ca (OH)2.

According to the SEM images and the data in **Table 1**, the experimental process of composing water traps shows repeatability by giving spherical particles, with a similar diameter and small size distribution. The diameter shown in **Table 1** was calculated from the average of the diameters of hundreds of water traps with the corresponding standard deviation of each. The dispersion indicator is close to one and proves that there is a good size distribution. Also, the elemental analysis

### **Figure 2.**

*Vaccination of microorganisms in petri dish.*


**Table 1.**

*n = [EGDMA]/[MAA] molar ratio and size of water traps for 4 n compositions.*

### **Figure 3.**

*(A) SEM image and EDS analysis of sample 2 as well as %w/w of data before modification with Ca (OH)2. (B) SEM and EDS analysis of sample 4 as well as the % w/w of data after modification with Ca (OH)2.*

(**Figure 3B**) in each sample case confirms the existence of Ca, after its modification, which means that the water microtraps are now capable of absorbing water. **Figure 3** confirms that statement via dynamic light scattering measurements.

For small amounts of water, up to 10% v/v of the total amount of solvent, the differences in hydrodynamic diameter are not significant, but as the percentage increases, there is a fairly large difference in size. This difference is evident when the percentage of water exceeds 15%, and this is probably due to the interaction of trap-water with water. These interactions may relate to the development of hydrogen bonds between particles and water but also between the particles themselves. The elucidation of the water absorbing mechanism needs further work (**Figure 4**). *Self-Healing of Concrete through Ceramic Nanocontainers Loaded with Corrosion Inhibitors… DOI: http://dx.doi.org/10.5772/intechopen.93514*

**Figure 4.** *Change in hydrodynamic diameter depending on different quantities of water.*

### **3.2 Ca(OH)2 @SiO2 modified water traps**

The purpose of the Ca (OH)2@SiO2 modification of the water traps is to give the adsorbed water traps a durable shell that will protect the bacterium and LB when it is introduced into cement. The SiO2 shell synthesis process was done using the sol-gel method. For the more durable and complete coating of activated water traps, six experiments were carried out, each increasing the amount of the TEOS reagent. The experimental procedure is the same in all six experiments carried out and is as follows: in 150 ml boiling glass, the amount of traps is dissolved in acetonitrile, and the solution is left to ultrasound for 20 minutes and then for another while stirring, in order to spread the sample well in the solvent. Then the ammonia is added, and the stirring continues for another 15 minutes. TEOS is then added to the sample and the solution is left stirring for about 20 hours. Finally, each sample is centrifuged, rinsed, and left to dry. The whole experimental process takes place at ambient temperature. To make up the SiO2 shell around the water traps, a water emulsion in oil (W/O emulsion) was created. Due to the organic solvent used (acetonitrile), when aqueous solution is added to it, water drops are created inside the solvent. In this case, due to the ability of water traps to retain water, the role of the aqueous phase in a W/O emulsion is made up of particles that have adsorbed water. The water comes from the solution of NH3 30%. Thus, in the middle of the water traps and acetonitrile, when the precursor TEOS compound is added, hydrolysis and condensation take place there. This overlays silicon-shelled water traps (**Figure 5**).

**Figure 6** shows the size of the nanospheres as a function of Rw (H2O/ Si ratio). This graph was determined by keeping all parameters constant except the quantity of the added water in the experiments. Note that the amount of modified water microtraps covered was the same in all experiments, (0.5 g).

**Figure 7** shows the SEM micrographs of the modified nanotraps. The SEM image and the corresponding EDS elemental analysis are reported for the sample of the experiment corresponding to the one with the largest amount of TEOS added.

**Figure 5.**

*Schematic representation of the coating of modified water traps with SiO2 in a W/O emulsion.*

**Figure 6.** *The corresponding Rw ratio for each case of SiO2@Ca (OH)2 modified water traps.*

**Figure 7.** *SEM micrograph. EDS analysis of the experiment with 21 ml of TEOS as well as the %w/w of each element.*

*Self-Healing of Concrete through Ceramic Nanocontainers Loaded with Corrosion Inhibitors… DOI: http://dx.doi.org/10.5772/intechopen.93514*
