Comparative Evaluation of the Photodegradation of Stearic Acid by TiO2 - Modified Cement Under UV Irradiation Through Water Contact Angle and Absorbance Studies
Aniedi Nyong,
Edet Nsi,
Joachim Awaka-Ama,
Godwin Udo
Issue:
Volume 9, Issue 1, March 2020
Pages:
1-7
Received:
22 November 2019
Accepted:
17 December 2019
Published:
23 March 2020
Abstract: The photodegradation of stearic acid has been studied through evaluation of changes in the contact angles of water and from absorbance measurements. The photodegradation of 0.02 M stearic acid coatings and solutions were initiated by TiO2 nanoparticles of average size of 9.80 ± 2.92 nm embedded in cements in 1.66 wt.%, 3.33 wt.%, 5.0 wt.% and 6.67 wt.% to generate modified cement composites with photocatalytic capability. It was noted that the photodegradation efficiencies increased with the increase in the weight-percent of TiO2 present in the modified cement samples. A modified Cassie-Baxter and the Langmuir-Hinselwood models were used to compute the rate constants, based on changes in the contact angles of water and in the concentration of the stearic acid respectively, on exposure to the UV light source. The modified Cassie-Baxter model successfully provided a route to relate the changes in water contact angle to the rate of photodegradation of a hydrophobic, long-chain stearic acid. The values of the rate constant estimated from both models increased with increase in the amount of TiO2 present in the modified cement samples. However, the rate constant values obtained from the modified Cassie-Baxter model were lower than those obtained from the Langmuir-Hinselwood model. The values of these rate contants were in the range of 0.11-0.50 hr-1 and 0.78-1.33 hr-1 as btained from the modified Cassie-Baxter and Langmuir-Hinselwood models respectively. This disparity in the values was attributed to a higher mobility of the charge carriers and free-radicals that induced the photodegradation in liquid medium as compared to the solid medium.
Abstract: The photodegradation of stearic acid has been studied through evaluation of changes in the contact angles of water and from absorbance measurements. The photodegradation of 0.02 M stearic acid coatings and solutions were initiated by TiO2 nanoparticles of average size of 9.80 ± 2.92 nm embedded in cements in 1.66 wt.%, 3.33 wt.%, 5.0 wt.% and 6.67 ...
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Study on the Cure Behavior of a Novel Photocurable Material Using UPLC-Q-TOF-MS
Chunfu Chen,
Dayong Sun,
Masao Kanari,
Daoqiang Lu
Issue:
Volume 9, Issue 1, March 2020
Pages:
8-14
Received:
24 February 2020
Accepted:
10 March 2020
Published:
23 March 2020
Abstract: An UPLC-Q-TOF-MS method is developed for cure degree measurement and cure behavior analysis on a novel photocurable adhesive material which is composed of specially designed acrylate oligomers, acrylate monomers, photo-initiators and additives such as ultra-violet absorbent, antioxidant stabilizer, optical stabilizer, etc. The photocurable adhesive material, in both cured and uncured state, were separated by Ultra-Performance Liquid Chromatography (UPLC) and the low molecular weight components were detected and determined quantitatively by high resolution Quadrupole Time-Of-Flight mass spectrometry (Q-TOF-MS) under Atmosphere Pressure Chemical Ionization (APCI) mode. Cure behaviors of all photo-reactive components in the photocurable adhesive material such as acrylate monomers and photo-initiators were studied by quantitatively measuring the amount of each reactive components in different stages of curing. Both the conversion of each acrylate monomers and photo-initiators at different curing energy conditions were calculated and discussed. Nearly full cure was obtained at cure energy of 200 mJ/cm2 for 4-hydroxybutyl acrylate and acryloyl morphine, as well as the two bifunctional monomers, 1,6-hexandiol diacrylate and dimethylol tricyclodecane diacrylate. Only 42.7% and 85.0% conversion were achieved for benzyl acrylate and isobornyl acrylate, respectively while consumption of TPO, a photo-initiator, was 38.0% at this cure energy. The results showed that a minimum 2000 mJ/cm2 energy condition is needed to achieve full cure of all acrylate monomers and enough decomposition of photo-initiator. This study indicated that UPLC-Q-TOF-MS is an effective and precise analytical method for cure degree measurement and cure behavior analysis on the photocurable materials.
Abstract: An UPLC-Q-TOF-MS method is developed for cure degree measurement and cure behavior analysis on a novel photocurable adhesive material which is composed of specially designed acrylate oligomers, acrylate monomers, photo-initiators and additives such as ultra-violet absorbent, antioxidant stabilizer, optical stabilizer, etc. The photocurable adhesive...
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