**4. Hydrophilic or hydrophobic**

The term 'hydrophobe' (hydrophobic) is borrowed from ancient Greek (hẏdor = water and phob = repellent). Hydrophobic describes a water-repellent property of a substance. This means that the substance does not dissolve in water and cannot be wetted by water. The term 'hydrophil' (hydrophilic) is also borrowed from the ancient Greek

**Figure 5.** *Contact angle measurement: superhydrophobic, P. Körber.*

**Figure 6.** *Contact angle measurement: hydrophobic, P. Körber.*

**Figure 7.** *Contact angle measurement: hydrophilic, P. Körber.*

*Investigation on Building Materials with the SEM in the ESEM Mode to Demonstrate… DOI: http://dx.doi.org/10.5772/intechopen.104292*

(hẏdor = water and phílos = loving). Hydrophilic means that a substance is water-friendly, water-loving. Hydrophilic describes a water-accepting property of a substance. This means that the substance can be dissolved in water and wetted with water (**Figures 5**–**7**).

### **5. Investigations in the ESEM on building materials**

The examination method described here for building materials in the ESEM can be used in particular for the question in the hydrophobicity of the substance to be examined. During the investigation in the ESEM, condensation processes are carried out, which provide information on how water-absorbent the examined substance is [23].

The procedure for examining building materials in the ESEM is explained below on the basis of a subsequent waterproofing of capillary building materials using injection agents. Such an injection method is used in particular in historic buildings made of solid building materials and in renovations [9].

Investigations in the ESEM are particularly useful when the question arises to what extent a building material is capillary-active or to what extent the capillarity of the building material has changed. Such changes are conceivable, for example, through the use of injection agents in building waterproofing. In the case of injection agent seals, for example, on brick masonry, the penetration of the injection agent changes the capillarity of the building material in such a way that the transfer of water in the building material is impeded or prevented. In this way, it is possible to subsequently create a cross-section seal in masonry walls. For such a procedure, it is necessary to prove the changed capillarity of the building material. This proof documents the sealing success. In this respect, the condensation in the ESEM is predestined to provide evidence for the use of injection agents for the subsequent sealing. The advantage of the examination method in the ESEM is that very small sample quantities can be evaluated in a very short time. The ESEM investigations on building materials are therefore qualitative, microscopic (imaging) detection methods. In addition to these microscopic methods, there are also macroscopic detection methods to investigate the changed capillarity in building materials [24–29].

The qualitative microscopic (imaging) detection method in the ESEM as described here can also be used by verifying the macroscopic, also qualitative, detection methods. It can provide comprehensive information about the changes in the capillary building material under the influence of the injection agent used.

Furthermore, the extent to which an injection material was used at all and to which the building material now exhibits hydrophobic properties after use can be verified. With the exact measurements, the hydrophobicity of the building material can be gradually verified. A comparative examination of the building material before and after injection is possible. With the qualitative microscopic (imaging) detection method, as with the macroscopic investigations, local samples are taken from the injection level using mini core drillings and are analysed in the laboratory in the ESEM.

Essentially, significantly less material has to be removed from the structure for the verification method described here.

To examine the building material in the ESEM, samples are to be taken from the injection level. In addition, reference samples of the masonry without adding the injection agent are required.

The reference samples and the samples from the injection level are subjected to condensation in the ESEM. In the ESEM mode, condensation on a microscopic scale can be brought about within the pores of the building material (bricks and mortar). The condensation process is recorded using pictures and, if necessary, using film. During the condensation process, there is a time window in which the contact angle of the forming water droplets can be measured. The measurement of the contact angle can be carried out directly in the ESEM.

In addition, the measurement can also be carried out retrospectively on the images generated in the ESEM. The measured contact angles can be used to determine whether the substance is hydrophobic or hydrophilic. The examination results consist of an imaging procedure that can be evaluated afterwards. In particular, comparisons with the reference samples are possible.

**Figure 8.** *Condensation process on a brick sample in the ESEM, P. Körber.*

*Investigation on Building Materials with the SEM in the ESEM Mode to Demonstrate… DOI: http://dx.doi.org/10.5772/intechopen.104292*

#### **Figure 9.**

*Condensation process on a brick sample in the ESEM, P. Körber.*

**Figure 10.** *Condensation process on a mortar sample in the ESEM, P. Körber.*

#### **Figure 11.**

*Condensation process on a brick sample in the ESEM, P. Körber.*

#### **Figure 12.** *Measurement of the contact angle in the ESEM, P. Körber.*

*Investigation on Building Materials with the SEM in the ESEM Mode to Demonstrate… DOI: http://dx.doi.org/10.5772/intechopen.104292*

The qualitative microscopic, imaging detection method described here can be flanked and verified by macroscopic examinations. The macroscopic investigations can serve as a calibration function for the ESEM measurements. In this way, serial tests can be carried out, in which differentiated proof of the sealing success of the subsequent building sealing with injection agents can be provided [29].

In **Figure 8a**–**f**, shown below, it becomes clear how the condensation water droplets form in the ESEM. After the time window for the formation of the drops has expired, these attract each other and then merge into one another, so that the time window for the measurement is over. The maximum achievable contact angle is relevant for the measurement.

The following figures show examples of the formation of condensation water droplets in the ESEM on brick and mortar samples (**Figures 9**–**11**). **Figure 12** shows the contact angle measurement, which takes place directly in the ESEM.
