title: Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels.
abstract: The surface free energy of a solid determines its surface and interfacial behavior in processes like wetting and adhesion which is crucial for silica aerogels in case of organic liquid absorption and transportation of chemicals at nano-scale for biotechnological applications. Here, we have demonstrated that the surface free energy of aerogels can be tuned in wide range from 5.5892 to 0.3073 mJ/m(2) by modifying their surface using TMCS and HMDZ silylating reagents. The alcogels were prepared by two step acid-base catalyzed process where the molar ratio of precursors Tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH(4)OH:NH(4)F was kept at optimal value of 1:2.7:0.18×10(-4):0.02:0.22×10(-3), respectively. To modify gel surfaces, TMCS and HMDZ concentration have been varied from 3% to 12% and such alcogels were dried at ambient pressure. It is observed from FTIR for aerogels that increase in concentration of silylating reagent resulted increase in hydrophobicity. This leads to increase in contact angle for water from 123° to 155° but leads to decrease in surface free energy from 5.5892 to 0.3073 mJ/m(2). As there is not direct method, we have used Neumann's equation of state to estimate surface energy of aerogels.
authors.affiliation: Air Glass Laboratory, Department of Physics, Shivaji University, Kolhapur, Maharashtra, India.
authors.forename: D B
authors.initials: DB
authors.lastname: Mahadik
authors.forename: A Venkateswara
authors.initials: AV
authors.lastname: Rao
authors.forename: A Parvathy
authors.initials: AP
authors.lastname: Rao
authors.forename: P B
authors.initials: PB
authors.lastname: Wagh
authors.forename: S V
authors.initials: SV
authors.lastname: Ingale
authors.forename: Satish C
authors.initials: SC
authors.lastname: Gupta
mesh_terms: D064751:Ammonium Compounds; D064753:Ammonium Hydroxide; D005459:Fluorides / Q000737:chemistry; D005782:Gels / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D006878:Hydroxides / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D017646:Organosilicon Compounds / Q000737:chemistry*; D019815:Oxalic Acid / Q000737:chemistry; D011312:Pressure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013816:Thermodynamics; D014297:Trimethylsilyl Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D064751:Ammonium Compounds; D005782:Gels; D006878:Hydroxides; D017646:Organosilicon Compounds; D000644:Quaternary Ammonium Compounds; D012821:Silanes; D014297:Trimethylsilyl Compounds; D014867:Water; C040733:tetraethoxysilane; C024822:ammonium fluoride; D064753:Ammonium Hydroxide; C039293:trimethylchlorosilane; D012822:Silicon Dioxide; D019815:Oxalic Acid; C024548:hexamethylsilazane; D005459:Fluorides; D000432:Methanol