Dear Anik,

Please specify the test conditions. The temperature and atmosphere have an impact on the wetting behavior. Additionaly, impurities and contaminants also influence the wetting. Make sure you have identical test conditions. This is important.

Best regards,

dear Anik Mazumder ; you have to make your test in a specific pure environment avoide of impurities, because it effects on the wettability property of the coated samples, you can read more in this reference;

Article Tunable Surface Properties of Aluminum Oxide Nanoparticles f...

Thank you for your answers Mahmood H. and Nelson Filipe Lopes Dias . Actually during the experimental sample preparation, the samples were cleaned with water jet and acetone for 15 mins and were baked at 180 degree centigrade for 30 mins after each cleaning. The experiments were carried out in atmospheric condition after the samples cooled down. However, immediately after this cleaning only the hydrophobic nature can be observed. After prolonged atmospheric exposure for 48 hours makes this hydrophobicity to disappear and after 7days of exposure, contact angle as low as 30 degree can be observed. I thought of the atmospheric impurity reason but in that case is it possible for the hydrophobicity to disappear after certain time.

I would be really grateful if you kindly comment to help me figure out the phenomena and suggest other test method to investigate it further.

Mahmood H. Thank you sir for the reference. I have gone through it earlier but in our case we did not perform any nano-scale modifications. However, if modifications related to plasma spray coating is present, kindly suggest some investigating procedure to confirm the same

dear Anik Mazumder; I advice you not to use water jet and acetone in cleaning just dip it in water and repeat your same tests.

Mahmood H. should I should include baking after dipping it in water? To remove residual water from surface and cracks.

dear Anik Mazumder ;

I think no need just dry it in air for few minutes because the heating may be effect on your coating if the base metal is not pure. also the heating should be in low rate avoiding the thermal stresses which caused by the thermal conductivity difference.

if you want to read more about the annealing of anodized coating usually made for forming a self-organized anodization layer.

Effects of Annealing Treatment of Aluminum Substrate on Nanopore Arrangements in Anodic Alumina

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.430.7167&rep=rep1&type=pdf

Mahmood H. Thank you very much for your inputs. I will definitely try out the suggested options

with my pleasure hope to get a good results

Mahmood H. I tried dipping in water and subsequent air drying but landed in the same result. while alumina monolith is hydrophilic with ~40 degree contact angle, plasma spray coated alumina shows contact angle of nearly ~110 degree. No literature whatsoever mentions any hydrophobicity of alumina. Secondly, this characteristics is temporary and contact angle degrades with a time period of 48 hours.@

Anik Mazumder please see this paper

Anik Mazumder

dear sir can you provide me your paper which shows degraded hydrophobicity property with time. I want to create hydrophilic surface through plasma of alumina.

Konok Das

I am attaching the relevant literature for your reference