Resumen de Device and strategy for surface energy measurement
In this Ph.D. Thesis, we have developed a new measurement method to measure the contact angle and the surface energy in hydrophobic samples with a device based on confocal technology. This new measurement method incorporates the correction of the effect of the roughness of the surface in the contact angle measurement.
The developed measurement method includes the measurement with the confocal device of the Developed Interfacial Area Ratio (Sdr) of the surface under study as well as several parameters of a liquid drop placed on the surface, such as the height and the apparent diameter of the drop. On the other hand, the developed measurement method also includes three mathematical models to calculate the contact angle from a combination of the height (h) and the apparent diameter (L) of the drop measured by the confocal device, and the volume of the dispensed drop (V) indicated by the liquid dispenser. We have verified the validity of each mathematical model by evaluating the introduced error in the calculation of the contact angle.
A validation study has also been performed by comparing the calculated contact angles by means of the developed mathematical model that uses exclusively the height and the apparent width of the drop measured with the confocal device with the contact angles measured by a current commercial contact angle meter applying the height-width fitting method. This allowed us to verify the developed measurement method to calculate contact angles on different hydrophobic samples.
Furthermore, we have corrected the effect of the surface roughness of a subset of hydrophobic samples on the calculated contact angles according to Wenzel’s model. Our method uses the Sdr parameter measured with the confocal device to calculate the roughness ratio factor required to correct the calculated contact angle with the effect of the roughness.
Finally, by doing the measurement with water and diiodomethane, we have evaluated the total surface energy as well as its dispersive and polar components according to OWRK’s method from the previously corrected contact angles, obtaining accurate surface energy values.
Therefore, we can conclude that the work reported in this Ph.D. Thesis has been able to demonstrate the validity of the developed measurement methodology for evaluating the contact angle and the surface energy on hydrophobic samples with a confocal device. The advantage of this new technique is that it allows to take into account and correct the effect of the roughness in the evaluation of the surface energy, using a single device.
