Edward Bormashenko, PhD, Professor, Ariel University
The research was performed according to the milestones supplied in the proposal.
Study of the relevant papers and reviews devoted to bio-inspired non-stick surfaces.
Undergraduate and graduate students studied the papers and books published in the period of 1997-2013 devoted to bio-inspired non-stick surfaces. The relevant papers published in Langmuir, Soft Matter, Current Opinion in Colloid and Interface Science, Journal of Colloid and Interface Science, Colloids and Surfaces A were studied. The main results reported in the papers were presented and discussed at the Laboratory weekly scientific seminar.
2. Preparing FD-POSS powder. Fluorinated Polyhedral Oligomeric silsesquioxane (FD-POSS) powder has been successfully synthesized according to the protocol reported in the paper: J. M. Mabry, A. Vij, S.T. Iacono, B. D. Viers, Fluorinated Polyhedral Oligomeric silsesquioxane (FD-POSS), Angew. Chem. Int. Ed. 47 (2008) 4137-4140. Synthesized FD-POSS powder was studied with high resolution SEM and ESEM. The SEM image of a particle of the FD-POSS powder is supplied in Figure 1. It was recognized from the high resolution SEM and ESEM images that the particles of synthesized FD-POSS powder possess highly developed micro-porous surface, which strengthened their inherent hydrophobicity according to the Cassie-Baxter wetting hypothesis.
3. Assembly and adjustment of the experimental unit for cavitation rheology. We started, but did not accomplish this item. We plan to finish it during next year.
4. Manufacturing liquid marbles. Liquid marbles with the volume of 10-50 µl comprising crude oil were prepared using synthesized FD-POSS powder and lab-made superhydrophobic surface (the 10 µl liquid marble is shown in Figure 2). Liquid marbles containing crude oil were prepared as follows: 10-50 µl drops of crude oil were deposited using a precise micro-syringe on a lab-made superoleophobic surface, manufactured as described in: Bormashenko et al. Robust technique allowing manufacturing superoleophobic surfaces, Applied Surface Science, 270 (2013) 98 103. Superoleophobic surface was covered with a layer of the FD-POSS powder. Rolling of crude oil droplets resulted in the formation of liquid marbles containing crude oil enwrapped with FD-POSS powder, such as depicted in Figure 1.
We established that manufactured liquid marbles containing crude oil demonstrated extremely low adhesion to a diversity of solid substrates including steel, glass and plastics. We also established that marbles remained stable when supported by water, as depicted in Figure 3.
5. Study of the effective surface tension of marbles with the "maximal height" method, illustrated with Figure 4. The effective surface tension of marbles containing crude oil was established with the "maximal height" method according to:
as 30.2 ±0.5 mJ/m2. The maximal height of marbles H and the apparent contact angle θ were measured precisely with the Ramé-Hart Advanced Goniometer Model 500-F1. The established value of the effective surface tension is in accordance to the values of the effective surface tension of liquid marbles containing organic liquids reported recently by other groups.
6. Acquaintance with the Mathematica software. Undergraduate and graduate students studied and demonstrated good skills with the Mathematica software, exploited successfully for the calculation of the effective surface tension of marbles with the "maximal height" method. Skills necessary for the study of the effective surface tension of marbles with the analysis of marbles' shape, planned for the next year of the Research Program of the Proposal, were gained by the students.
Main results: Main scientific and technological ideas in the field of manufacturing of non-stick surfaces were assimilated by undergraduate and graduate students. FD-POSS powder was synthesized successfully and SEM and ESEM imaged. Liquid marbles containing crude oil were successfully manufactured. The liquid marbles remained stable, when supported by steel, glass, plastics and water. The effective surface tension of marbles was established with the maximal height method. Students gained skills in the manufacturing superoleophobic surfaces, use of the optical goniometer and the Mathematica software.
Figure 1. SEM image of the particles of FD-POSS powder. Scale bar is 50 µm.
Figure 2. 10 µl liquid marble containing crude petroleum coated with the FD-POSS powder.
Figure 4. Scheme illustrating establishment of the effective surface tension of liquid marbles containing crude oil γeff with the maximal height method. H is the maximal height, θ is the apparent contact angle.