The dielectric response of phenothiazine-based glass-formers with different molecular complexity.

We examined a series of structurally related glass-forming liquids in which a phenothiazine-based tricyclic core (PTZ) was modified by attaching n-alkyl chains of different lengths (n = 4, 8, 10). We systematically disentangled the impact of chemical structure modification on the intermolecular organization and molecular dynamics probed by broadband dielectric spectroscopy (BDS). X-ray diffraction (XRD) patterns evidenced that all PTZ-derivatives are not 'ordinary' liquids and form nanoscale clusters. The chain length has a decisive impact on properties, exerting a plasticizing effect on the dynamics. Its elongation decreases glass transition temperature with slight impact on fragility. The increase in the medium-range order was manifested as a broadening of the dielectric loss peak reflected in the lower value of stretching parameter ßKWW. A disagreement with the behavior observed for non-associating liquids was found as a deviation from the anti-correlation between the value of ßKWW and the relaxation strength of the α-process. Besides, to explain the broadening of loss peak in PTZ with the longest (decyl) chain a slow Debye process was postulated. In contrast, the sample with the shortest alkyl chain and a less complex structure with predominant supramolecular assembly through π-π stacking exhibits no clear Debye-mode fingerprints. The possible reasons are also discussed.

Correlation between configurational entropy, excess entropy, and ion dynamics in imidazolium-based ionic liquids: Test of the Adam-Gibbs model.

The Adam-Gibbs (AG) model, linking thermodynamics with molecular dynamics of glass-forming liquids, plays a crucial role in the studies of the glass transition phenomenon. We employ this approach to investigate the relationship between ion dynamics and thermodynamics in three imidazolium-based ionic liquids in the current work. We show that the AG relation, -log10σdc ∝ (TSc)-1 (where σdc, T, and Sc denote the dc-conductivity, absolute temperature, and configurational entropy, respectively), does not work when the whole supercooled liquid state is considered. Meanwhile, a linear relationship between -log10σdc and (TSe)-1 (where Se denotes the excess entropy) was observed in the entire supercooled range. On the other hand, the generalized AG model log10σdc ∝ (TSc α)-1 with an additional free parameter α successfully describes the relation between σdc and Sc. The determined α values being less than unity indicate that the configurational entropy is insufficient to govern the ion dynamics. Meanwhile, we found a systematical decrease in α with the elongation of the alkyl chain attached to the imidazolium ring.

Fast secondary dynamics for enhanced charge transport in polymerized ionic liquids.

Segmental dynamics is considered as a major factor governing ionic conductivity of polymerized ionic liquids (PILs), envisioned as potential electrolytes in fuel cells and batteries. Our dielectric studies performed in T-P thermodynamic space on ionene, composed of the positively charged polymer backbone and freely moving anions, indicate that other relaxation modes, completely ignored so far, can affect the charge transport in PILs as well. We found that fast mobility manifested by a secondary ß process promotes segmental dynamics and thereby increases ionic conductivity making the studied material a first coupled PIL of superionic properties. The molecular mechanism underlying such a ß process has been identified as Johari-Goldstein relaxation giving experimental proof that fast secondary relaxations of intermolecular origin exist also in PILs and thereby reveal a universal character.

Structurally Related Scaling Behavior in Ionic Systems.

We examine the density scaling properties of two ionic materials, a classic aprotic low molecular weight ionic liquid, 1-butyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide ([BMIm][BETI]), and a polymeric ionic liquid, poly(3-methyl-1,2,3-triazolium bis(trifluoromethylsulfonyl)imide) (TPIL). Density scaling is known to apply rigorously to simple liquids lacking specific intermolecular associations such as hydrogen bonds. Previous work has found that ionic liquids conform to density scaling over limited ranges of temperature and pressure. In this work, we find that the dc-conductivity of [BMIm][BETI] accurately scales for density changes of 17%; however, there is a departure from scaling for TPIL for even more modest variations of temperature and pressure. The entropy of both ionic samples conforms to density scaling only if the scaling exponent is allowed to vary linearly with the magnitude of the entropy.

The relation between molecular dynamics and configurational entropy in room temperature ionic liquids: Test of Adam-Gibbs model.

In this communication, the Adam-Gibbs model connecting molecular dynamics with configurational entropy is tested for the first time for ionic liquids. For this purpose, we investigate simultaneously the shear viscosity η and configurational entropy Sc of an aprotic ionic liquid: 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm TFSI). Comparing the Sc data obtained by the combination of Vogel-Fulcher-Tammann and Adam-Gibbs equations to the Sc points determined directly from the calorimetric experiment, good agreement is found in the entire supercooled liquid region. These results indicate the validity of the Adam-Gibbs model in materials with electrostatic interactions being dominated. These important findings not only generalize the applications of the Adam-Gibbs theory but also provide an opportunity to gain insight into the relationship between thermodynamics and molecular dynamics in ionic liquids.

Experimental Evidence for a State-Point-Independent Density-Scaling Exponent in Ionic Liquids.

This Letter addresses a fundamental issue of condensed-matter physics, which is the validity of the density-scaling concept. For this purpose, the ambient and high-pressure conductivity measurements of two selected ionic liquids (ILs), with the different contribution of H-bonding interactions, were performed in the dynamic range of 13 orders of magnitude and corresponding to the density changes as large as 20%. All experimental data obtained within one compound are shown to superimpose each other when plotted as a function of ρ^{γ}/T. These results clearly show that for studied ILs the scaling exponent is a state-point-independent parameter that is in odds with the recent findings for van der Waals liquid [Sanz et al., Phys. Rev. Lett. 122, 055501 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.055501].

Experimental and theoretical UV characterizations of acetylacetone and its isomers.

Cryogenic matrix isolation experiments have allowed the measurement of the UV absorption spectra of the high-energy non-chelated isomers of acetylacetone, these isomers being produced by UV irradiation of the stable chelated form. Their identification has been done by coupling selective UV-induced isomerization, infrared spectroscopy, and harmonic vibrational frequency calculations using density functional theory. The relative energies of the chelated and non-chelated forms of acetylacetone in the S0 state have been obtained using density functional theory and coupled-cluster methods. For each isomer of acetylacetone, we have calculated the UV transition energies and dipole oscillator strengths using the excited-state coupled-cluster methods, including EOMCCSD (equation-of-motion coupled-cluster method with singles and doubles) and CR-EOMCCSD(T) (the completely renormalized EOMCC approach with singles, doubles, and non-iterative triples). For dipole-allowed transition energies, there is a very good agreement between experiment and theory. In particular, the CR-EOMCCSD(T) approach explains the blue shift in the electronic spectrum due to the formation of the non-chelated species after the UV irradiation of the chelated form of acetylacetone. Both experiment and CR-EOMCCSD(T) theory identify two among the seven non-chelated forms to be characterized by red-shifted UV transitions relative to the remaining five non-chelated isomers.

The effect of birth hospital type on the outcome of very low birth weight infants.

OBJECTIVE: To test the hypothesis that the likelihood of death or major morbidity is reduced for very low birth weight (VLBW; <1500 g) infants who are born at hospitals with subspecialty perinatal and neonatal care compared with other available birth sites. METHODS: A population-based cohort study was conducted of all live births of 500 to 1499 g at the 19 hospitals in the greater Cincinnati region from September 1, 1995, through December 31, 1997 (N = 848). Primary outcome was the risk-adjusted, predischarge mortality or morbidity, including bronchopulmonary dysplasia, severe intracranial hemorrhage, severe retinopathy of prematurity, or necrotizing enterocolitis for VLBW infants who were born at subspecialty perinatal centers compared with those who were born at nonsubspecialty centers. RESULTS: The odds of death or major morbidity for VLBW infants who are born at nonsubspecialty perinatal centers is twice that of infants who are born at subspecialty centers despite controlling for demographic (odds ratio [OR]: 2.64; 95% confidence interval [CI]: 1.7-4.2) and practice characteristics (OR: 1.96; 95% CI: 1.2-3.2). The effect of birth hospital type on death or major morbidity was greater for infants of 1000 to 1499 g birth weight (OR: 3.42; 95% CI: 2.0-6.1) than for infants of 500 to 999 g birth weight (OR: 2.1; 95% CI: 1.0-4.8). CONCLUSION: The current study lends strong support to existing Academy of Pediatrics and American College of Obstetricians and Gynecologists recommendations that deliveries at <32 weeks' gestational age occur at subspecialty perinatal centers.

Hazards of delivery room resuscitation using oral methods of endotracheal suctioning.

Between 1978 and 1982 at least eight physicians at our institution were exposed to infectious secretions while performing mouth-to-tube resuscitation. A questionnaire revealed that 74% of responding pediatric physicians accidentally ingested secretions in 1982. The risk of cross-contamination between newborn patients and resuscitating physicians with the oral methods of oropharyngeal and endotracheal suctioning is considerable.