TiO₂-coated Hollow Glass Microspheres with Superhydrophobic and High IR-reflective Properties Synthesized by a Soft-chemistry Method

The overall goal of this experiment is to synthesize superhydrophobic, highly IR-reflective hollow glass microspheres in a single step. This technique can help with the development of simple masses to synthesize HGM with multiple functions, such as the self-cleaning and IR-reflective properties. The advantage of this mass is that it is a performer in the single-stat, making the mass simple and energy-saving compared with the existing mass.

The implications of this technique extended toward a better understanding of sliding angles as HGM samples with different coatings can have similar connected angles but different sliding angles. To prepare the hollow glass microspheres, first place over five grams of original HGM in a 500-milliliter beaker. Add 200 milliliters of absolute ethanol to the mixture of broken and unbroken HGM.

Allow the mixture to sit for 30 minutes to ensure that all unbroken HGM have floated to the top, leaving only broken HGM at the bottom of the beaker. Use a clean scoop to collect the unbroken HGM from the surface of the ethanol. Dry the unbroken HGM at 80 degrees Celsius for four hours.

Repeat this process as needed to obtain five grams of unbroken HGM. To begin the synthesis, combine five grams of unbroken HGM, 47.5 milliliters of absolute ethanol, and 2.5 milliliters of deionized water. Add it into a three-necked flask.

And then stir the mixture at 400 RPM for 20 minutes. Place 30 milliliters of absolute ethanol, 15 grams of tetrabutyl titanate, and one gram of PFOTES in a beaker and stir until dissolved. Pour the mixture into a pressure-equalized dropping funnel.

Connect the dropping funnel to the three-necked flask and reduce the stirring rate 350 RPM. Add the TBT-PFOTES mixture to the HGM suspension at a rate of one drop every seven seconds. The dropping speed must be carefully set to the correct rate and stay in that rate until the mixture have been completely added.

Once addition of the TBT-PFOTES mixture is complete, continue stirring at 350 RPM until three hours have elapsed since the start of addition. Then, pour the HGM mixture into a hydrothermal reactor with a well-fitting cover. Insert the reactor into an appropriately-sized steel sleeve and seal the reactor.

Heat the HGM mixture at 180 degrees Celsius for six hours. Once the reaction is complete, allow the reactor to cool to room temperature. Open the hydrothermal reactor and use a large, clean scoop to collect the suspended HGM samples.

Dry the samples at 80 degrees Celsius for four hours to obtain MCHGM. To synthesize PFOTES or titanium oxide single-coated HGM, follow this procedure without addition of TBT or PFOTES respectively. Perform X-ray defraction and measure the reflectivity and thermal conductivity of the coated and uncoated HGM samples.

Acquire scanning electron microscopy images and perform energy dispersive X-ray spectroscopy. Use a contact angle goniometer to measure the contact angle between the HGM surface and a 10-microliter drop of water. To measure the sliding angle, first apply double-sided tape to a glass slide.

Evenly distribute the HGM powder sample over the double-sided tape. Place 0.05 milliliter drop of water on the powder surface. Place the coated slide on the goniometer motor platform.

While monitoring the water drop, tilt the glass slide at a rate of one degree per second. When the water drop begins to move, stop tilting the slide and record the sliding angle. The successful coating of HGM samples was confirmed by EDS.

Fluorine was detected in both F-SCHGM and MCHGM, and titanium was detected in both titanium-SCHGM and MCHGM. The single PFOTES coating was not observable by SEM. But rough coatings were observed for titanium-SCHGM and MCHGM.

The coated HGM samples were compared to the starting material and to standard anatase titanium oxide by X-ray defraction. The MCHGM and titanium-SCHGM samples both showed peaks matching anatase titanium oxide indicating that the titanium coating was in the anatase form. Both titanium-SCHGM and MCHGM showed about 5%higher reflectivity values than uncoated or F-SCHGM.

A small increase in thermal conductivity was also observed for titanium-SCHGM and MCHGM. The measured contact angle of uncoated HGM was 59 degrees. Titanium SCHGM did not show a large increase from this contact angle, but both F-SCHGM and MCHGM did.

Further, MCHGM had a much lower sliding angle than F-SCHGM, indicating greater hydrophobicity compared to F-SCHGM. Once mastered, this technique can be done in nine hours if it is performed properly. While attempting this procedure, it is important to remember to precisely set the TBT-PFOTES addition rate to one drop every seven seconds.

After its development, this technique paved the way for the researchers in the hidden civilization field to explore highly IR-reflective HGM with superhydrophobic self-cleaning properties to protect the surface from falling.