# Effectiveness of Nanotechnology Treatments in Composite Aircraft Applications
## 4 Cleanability Test
### Fluorescence Extraction  
The procedure for removing the residual dirt, often barely visible, from the central portion of the specimen on which the fouling/cleaning procedure was carried out was then started. To do this, 10 mL of distilled water was introduced into the extraction device within 30 min of the fouling procedure, respecting some indications given by the regulation. The first specimen was placed face up within the clamp frame of the extraction fixture. The sealed tube was then placed in the center of the specimen, so that the seal defined the solution extraction area. Once the tube had been locked in the frame with a slight pressure generated by the screwing of the wing nuts, 10 mL of distilled water was added, stirred, and left to rest for 3 min. Finally, with a Pasteur pipette, a portion of the solution obtained was inserted into the test tube, correctly labeled, and placed on the rack, while the subsequent samples were extracted.  
Before proceeding with the measurement, it was necessary to set the wavelength of the ultraviolet source useful for exciting the sodium fluorescein, in our case set at 254 nm and the medium wavelength of the excited fluorescein's fluorescent emission was set at 525 nm. The data thus obtained could finally be processed to obtain the cleanability index  
Figure 14: Fouling solution preparation: (**A**) sodium fluorescein (**B**) mixture of 1% sodium fluorescein and 98% of PEG400 (**C**) ultrasound sonicator (**D**) final mixture with addition of 1% black dye.  
(CI), using the procedure described below. First of all, it was necessary to determine the correct fluorescence:  
\[CF_{treated}=F_{treated}-F_{H2O} \tag{4}\]  
\[CF_{untreated}=F_{untreated}-F_{H2O} \tag{5}\]  
where \(CF_{treated}\) is the corrected fluorescence of the specimen treated with nanotechnologies, \(F_{treated}\) is the fluorescence of the specimen treated with nanotechnologies, and \(F_{H2O}\) is the distilled water fluorescence  
Subsequently, the cleanability index was calculated as:  
\[C_{I}=\frac{CF_{treated}}{CF_{untreated}} \tag{6}\]  
Cleanability index results are included in Table 5.  
With the same amount of time to carry out the cleaning procedure, it can be noted that the Al2024 sample treated with nanotechnologies had a 16% increase in dirt removed, and the raw carbon treated with nanotechnologies had a 7% increase in dirt removed. The painted carbon treated with nanotechnologies had a 15% increase in dirt removed. Finally, the plexiglass treated with nanotechnologies had a decrease in dirt eliminated of 23%. Despite the apparently negative result obtained on the plexiglass, the results obtained on the composite and on the metal are promising in terms of efficacy of nanotechnology in terms of cleaning improvement. Likely, the ability of surfaces treated with nanotechnologies to be easier to clean (at least for CFC and Al2024) is due to the hydrophobicity characteristic that silicon nanoparticles are capable of attributing to the substrate on which they are applied. This property is also observable in Figure 15 where a visual comparison is made on the distribution of dirt in one treated and one untreated specimen. Extraction of the residual dirt and solution samples preparation is shown in Figure 16.