ABSTRACT
TiO2 films generally undergo contact angle relaxation in the dark. It has been suggested that carbon contamination and the loss of surface OH generated by UV may be the major causes. However, the mechanisms for the long-lasting hydrophilicity have not been fully understood. Here, we studied contact angle relaxation of amorphous, mixed-phase, and anatase, and a new mechanism is proposed. After UV exposure and oxygen plasma treatment, the films' relaxation was observed over short-term (1 day) and long-term (>30 days) scales with XPS analysis using two quantitative parameters: relative amount and binding energy (B.E.) shifting. One day after plasma treatment, we observed that the donor-acceptor complex (DAC) and Ti-OH peaks of anatase shifted toward lower B.E., while the other films showed no shift or positive B.E. shifting. Interestingly, the relaxation of the amorphous and mixed-phase TiO2 occurred over time despite the large number of total OH groups (IOH/Ibulk > 75%) and DAC (IDAC/Ibulk > 110%), and only the anatase film showed superhydrophilicity (â¼10°) for 90 days. Also, the B.E. of all OH peaks increased over time, indicating that polarizable hydroxyls relaxed in the dark. Although the greater binding strength of Ti-OH and DAC on the anatase surface maintains long-lasting hydrophilicity, the loss of polarizable OH causes relaxation on the less-reactive TiO2 films. Carbon contamination can also contribute to the relaxation over time. Taken together, we conclude that the surface energy, polarizable OH, and contaminants are the major factors affecting relaxation; this study gives a full picture of the mechanism integrated over some of the previously reported models.
ABSTRACT
The contact angle relaxation of TiO2 surfaces is an important problem that must be understood, particularly for long-lasting hydrophilicity under dark conditions. The relaxation of sputtered anatase TiO2 thin films over a long time (â¼22 days) in an atmospheric environment was observed using quantitative XPS analysis. A new peak was identified as H2O within a donor-acceptor complex at â¼2.57 eV above the lattice oxygen peak. This donor-acceptor complex turns out to be a key factor for long lasting hydrophilicity, and our model is presented. Adventitious carbon contamination was not the main cause of the contact angle relaxation. Instead, samples with lower amounts of donor-acceptor complexes ( IDAC/ Ibulk ≤ â¼5%) underwent contact angle relaxation over time, and samples with a high density of donor-acceptor complexes ( IDAC/ Ibulk ≥ â¼10%) showed good hydrophilicity (contact angle ≤20°) over 22 days. Larger amounts of basic Ti-OH relative to acidic OHbridge ( ITi-OH/ Ibridge ≥ 1) resulted in greater amounts of donor-acceptor complexes ( IDAC/ Ibulk ≥ â¼10%). Thus, basic Ti-OH groups interact with H2O by forming a strong electrostatic donor-acceptor complex, leading to long-lasting hydrophilicity. Indeed, TiO2 was transformed to show long lasting hydrophilicity by high-density oxygen plasma treatment by forming sufficient Ti-OH groups and H2O molecules in the donor-acceptor complexes. Contact angle relaxation is closely related to the interactions between water molecules and the TiO2 surface in the dark. It is suggested that the relaxation depends on the number of electrostatic donor-acceptor complexes. This study provides new insight by linking theoretical studies with the experimental contact angle at the TiO2 surface in an ambient environment and is the first study that provides the presented relaxation mechanism.
ABSTRACT
OBJECTIVE: Quantitative electroencephalography (qEEG) has been increasingly used to evaluate patients with attention deficit hyperactivity disorder (ADHD). The aim of this study was to assess the correlation between qEEG data and symptom severity in patients with ADHD. METHODS: Fifteen patients with ADHD and 20 healthy controls (HCs) were recruited. Electroencephalography was assessed in the resting-state, and qEEG data were obtained in the eyes-closed state. The Korean version of the ADHD Rating Scale (K-ARS) and continuous performance tests (CPTs) were used to assess all participants. RESULTS: Theta-band (4-7 Hz) power across the brain was significantly positively correlated with inattention scores on the K-ARS, reaction times and commission errors on the CPTs in ADHD patients. Gamma-band (31-50 Hz) power was significantly positively correlated with the results of the auditory CPTs in ADHD patients. The theta/alpha (8-12 Hz) and theta/beta (13-30 Hz) ratios were significantly negatively correlated with commission and omission errors on auditory CPTs in ADHD patients. No significant correlations between qEEG relative power and K-ARS and CPT scores were observed in HCs. CONCLUSION: Our results suggest that qEEG may be a useful adjunctive tool in patients with ADHD.
ABSTRACT
Lycium chinense has been used as a traditional medicine for centuries in Asia because of its positive effects on health. However, its functional components have not been elucidated. This study determines the levels of health-promoting lipophilic compounds, including carotenoids, tocopherols, and phytosterol, and those of 42 hydrophilic metabolites, including sugars, organic acids, alcohols, amines, and amino acids, in L. chinense fruit from 11 cultivars. The metabolite profiles were subjected to a principal component analysis (PCA), Pearson correlation analysis, and hierarchical clustering analysis (HCA). PCA showed the Cheongdang (LM-3) cultivar to be distinct from the others. The correlation results for a total of 55 compounds revealed strong correlations between the metabolites that participated on closely related pathways. The Cheongdang cultivar appears to be most suited for functional food production because of its high carotenoid, tocopherol, and phytosterol levels. These results indicate the usefulness of metabolite profiling as a tool for assessing the quality of food.
