New experimental data on the KO2-KOH system

Conclusions The density and magnetic susceptibility were determined for (KO₂)_x(KOH)_1–x preparations of variable composition. The composition vs property curves corroborate the formation of the compound KO₂ · KOH.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 448–450, February, 1971.     

Role of hydration in the phase transition of polypeptides investigated by NMR and Raman spectroscopy

NMR, Raman spectroscopy and ab initio quantum-chemical calculations have been employed to investigate the role of the hydration water in the inverse temperature transition of elastin-derived biopolymers represented by poly(Gly-Val-Gly-Val-Pro) and poly(Ala-Val-Gly-Val-Pro). Temperature and concentration dependences of the Raman spectra measured for water solutions of polymers and of a low-molecular-weight model have been correlated with the vibrational frequencies calculated at the DFT (B3LYP) and MP2 levels for the peptide segment surrounded by a growing number of water molecules. The results indicate strong hydration before the transition that, in addition to water hydrogen-bonded to amide groups, includes hydrophobic hydration of non-polar groups by a dynamic cluster of several water molecules. According to ¹H longitudinal and transverse relaxation of HOD signals in D₂O solutions, the number of water molecules motionally correlated with the polymer is about 4 per one amino acid residue.     

Au-coated ZnO nanorods on stainless steel fiber for self-cleaning solid phase microextraction-surface enhanced Raman spectroscopy

Solid phase microextraction-surface enhanced Raman spectroscopy (SPME–SERS), combining the pretreatment and determination functions, has been successfully used in environmental analysis. In this work, Au-coated ZnO nanorods were fabricated on stainless steel fiber as a self-cleaning SERS-active SPME fiber. The ZnO nanorods grown on stainless steel fiber were prepared via a simple hydrothermal approach. Then the obtained nanostructures were decorated with Au nanoparticles through ion-sputtering at room temperature. The obtained SERS-active SPME fiber is a reproducible sensitivity sensor. Taking p-aminothiophenol as the probe molecule, the RSD value of the SERS-active SPME fiber was 8.9%, indicating the fiber owned good uniformity. The qualitative and quantitative detection of crystal violet and malachite green was also achieved. The log–log plot of SERS intensity to crystal violet and malachite green concentration showed a good linear relationship. Meanwhile, this SERS-active SPME fiber can achieve self-cleaning owning to the excellent photocatalytic performance of ZnO nanorods. Crystal violet was still successfully detected even after five cycles, which indicated the high reproducibility of this SERS-active SPME fiber.     

Dynamics of a low temperature phase transition in liquid crystal TB10A probed by Raman spectroscopy

Raman spectra of TB10A were recorded in the regions, 925-1000 and 1140-1220cm-1 from room temperature down to 20 K, during cooling and heating cycles. The subtle changes in the spectral features of the bands at 975 and 1195cm-1 at 47 K were attributed to a hitherto unreported stable-metastable phase transition in TB10A. The dynamics of the new phase transition have been explained in terms of splitting of the non-planar mode at 975cm-1 owing to strong intermolecular interaction due to close molecular packing in the low temperature phase. The spectral anomaly of the 975cm-1 band, in terms of variation of relative intensity with respect to temperature, also shows the hysterisis linked with the process of stable-metastable-stable modification in TB10A.     

Dynamics of a low temperature phase transition in liquid crystal TB10A probed by Raman spectroscopy

Raman spectra of TB10A were recorded in the regions, 925-1000 and 1140-1220cm-1 from room temperature down to 20 K, during cooling and heating cycles. The subtle changes in the spectral features of the bands at 975 and 1195cm-1 at 47 K were attributed to a hitherto unreported stable-metastable phase transition in TB10A. The dynamics of the new phase transition have been explained in terms of splitting of the non-planar mode at 975cm-1 owing to strong intermolecular interaction due to close molecular packing in the low temperature phase. The spectral anomaly of the 975cm-1 band, in terms of variation of relative intensity with respect to temperature, also shows the hysterisis linked with the process of stable-metastable-stable modification in TB10A.     

Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes

The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition. Unexpectedly, the starch volume fraction (as probed through thermal gravimetry) decreases with T at a higher rate than the free volume fraction (as probed through PALS).     

Raman spectra and phase transition of the phenothiazine crystal

Polarized Raman spectra of single crystals of phenothiazine which undergoes a phase transition around 250 K and is ferroelastic in the low-temperature phase were measured in the lattice-vibrational region for temperatures ranging from 89 to 300 K. The spectra of the high- and low-temperature phases obey the selection rules required for the orthorhombic and monoclinic structures, respectively. Anomalous temperature dependences are observed in the frequency, intensity and linewidth of a band appearing in the lowest-frequency region. This band is attributed mainly to a librational motion of the molecule, and is important in the evaluation of this phase transition. A gradual change of the molecular orientation is inferred to occur over a wide temperature interval in the low-temperature phase along the vibrational coordinate of the above libration. Another strong, low-frequency band, which is characteristic of the phenothiazine spectra, is suggested to arise from mixing between intramolecular and lattice vibrations. This mode is considered to play some role in the phase transition too. The interaction between the low-frequency optical modes and the acoustic modes is briefly discussed in connection with the ferroelasticity of the low-temperature phase. The transition temperature depends on the quality of the specimen; the correct transition temperature is found to be 248.8 K and slightly lower than the previously reported value.     

Recognition of big data mixed Raman spectra based on deep learning with smartphone as Raman analyzer

Raman spectral detection has emerged as a powerful analytical technique due to the advantages of fast acquisition, non-invasion, and low cost. The on-site application is highly dependent on Raman automatic analysis algorithm. However, current Raman algorithm research mainly focuses on small sample Raman spectroscopy (RS) identification with defects of low accuracy and detection rate. It is also difficult to realize rapid RS measurement under big data. In this paper, rapid recognition of mixtures in complex environments was realized by establishing a fast Raman analysis model based on deep learning through data training, self-learning, and parameter optimization. The cloud network architecture was proposed to apply deep learning to real-time detection using Smartphone-based Raman devices. This research solves the technical problems about mixture recognition under big data and thus could be used as a new method for fast and field RS detection in complex environments.     

Free volume microstructure of amorphous polymers at glass transition temperatures from positron annihilation spectroscopy data

The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric glass transition temperatures for a series of amorphous polymers reveals empirical correlations of average lifetime of o-Ps , and of its product with a relative intensityI _3g with appropriateT _g ^DSC values. These trends in terms of free volume mean that both the average size of free volume hole entityv _hg and the fractional free volume grow with increasingT _g ^DSC . The results are discussed considering the chemical microstructure as well as possible mechanisms acting in glass transition. A relation is indicated between geometric and flexibility characteristics of chains and thev _hg andf _g parameters of free volume microstructure on the one side and potential motional processes responsible for solidification of the amorphous system on the other side.     

Resonance Raman spectroscopy of mass selected Al2 in an argon matrix.

In an excitation range of 620-760 nm, resonance Raman spectra of aluminum dimers (Al2) in an argon matrix have been obtained for the first time. Temperature annealing experiments were performed to remove Raman lines attributed site effects caused by the Al2/Ar matrix. We observe a single fundamental at 293.3 (5) cm(-1) along with a progression up to 1149 (1) cm(-1). Taking successive differences of band centers we obtain spectroscopic constants for the ground state fundamental, w(e) = 297.5 (5) cm(-1), the anharmonicity, e(e)x(e) = 1.68 (8) cm(-1). Our results are in close agreement with previous experimental results for Al2 which designate the ground state as a 3piu state, and may be considered as confirmation of this assignment.     

Identification of the diamond-like B-C phase by confocal Raman spectroscopy

The new diamond-like B-C phase was obtained from the graphite-like BC phase in a laser-heated diamond anvil cell at high temperature 2230+/-140 K and high pressure 45 GPa. Raman spectra of the new phase measured at ambient conditions revealed a peak at 1315 cm(-1), which was attributed to longitudinal-optical (LO) mode. The X-Y Raman mapping was used to investigate spatial distribution of the diamond-like phases and was shown to be a powerful tool in studying the sp(2)-to-sp(3) phase transformations occurring in the diamond cell under high temperature and high pressure.     

Evidence for a simple monatomic ideal glass former: the thermodynamic glass transition from a stable liquid phase

Under cooling, a liquid can undergo a transition to the glassy state either as a result of a continuous slowing down or by a first-order polyamorphous phase transition. The second scenario has so far always been observed in a metastable liquid domain below the melting point where crystalline nucleation interfered with the glass formation. We report the first observation of the liquid-glass transition by a first-order polyamorphous phase transition from the equilibrium stable liquid phase. The observation was made in a molecular dynamics simulation of a one-component system with a model metallic pair potential. In this way, the model, demonstrating the thermodynamic glass transition from a stable liquid phase, may be regarded as a candidate for a simple monatomic ideal glass former. This observation is of conceptual importance in the context of continuing attempts to resolve the long-standing Kauzmann paradox. The possibility of a thermodynamic glass transition from an equilibrium melt in a metallic system also indicates a new strategy for the development of bulk metallic glass-forming alloys.     

Using Raman spectroscopy to understand the origin of the phase transition observed in the crystalline sulfur based amino acid l-methionine

We present the Raman spectra of l-methionine (C₅H₁₁NO₂S) monocrystals obtained in the spectral region ranging from 3200 to 50 cm⁻¹ at temperatures from 20 to 375 K. We investigated the dynamics of the different functional groups in l-methionine and related their behaviour to the structural transition previously reported at about 307 K. Additionally, on cooling, changes in the intensities of some Raman bands were associated with conformational changes of at least one of the two l-methionine conformers in the monoclinic unit cell in the interval 160–140 K. Thermal analysis and DFT calculations provide further support to the interpretation of the Raman results.     

Equation of state for polymers based on glass transition data

This paper addresses a method for predicting the participating constants in equation of state (EOS) for compressed polymeric fluids using two scaling constants, the surface tension γ _g and the molar density ρ _g, both at the glass transition point. The theoretical EOS undertaken is the one attributed to Tao and Mason. The second virial coefficients are calculated from a two-parameter corresponding states correlation, which is constructed with two constants as scaling parameters, i.e., the surface tension γ _g and the molar density ρ _g. This new correlation has been applied to the Tao–Mason (TM) EOS to predict the volumetric behavior of several polymer melts. The operating temperature range is from 291.25 to 603.4 K and pressures of up to 202.5 MPa. A collection of 516 data points has been examined for the aforementioned polymers. The average absolute deviation between the calculated densities and the experimental ones is of the order of 0.44%.     

Raman and infrared study of the crystals with molecular anions in the region of a solid-liquid phase transition

It is presented the Raman and infrared (IR) spectroscopic investigations of the thiocyanates: LiSCN, NaSCN, KSCN, RbSCN, CsSCN; nitrates: Ca(NO3)2, Sr(NO3)2, Ba(NO3)2, Pb(NO3)2; and perrhenates: LiReO4, NaReO4, KReO4 in the region of a solid-liquid phase transition. The differences in a pre-melting behavior of this salts were found which can be attributed to a different geometry of the SCN-, NO3- and ReO4- anions.     

Dynamics of phase transitions in a liquid crystal probed by Raman spectroscopy

Raman spectra of the Schiff 's base liquid crystalline compound 5O5, N-(4- n-pentyloxybenzylidene)-4'-n-pentylaniline, have been recorded as a function of temperature from 22 to 80°C in the 1140-1220 cm^-1 and 1550-1640 cm^-1 spectral regions. From careful deconvolution of the spectral features using Lorentzian profiles, precise values of peak positions, integrated intensities and linewidths of some selected Raman bands were obtained. The variations of the Raman spectral parameters with temperature are discussed in terms of changes in the molecular alignment and its effect on intra-/inter-molecular interactions at the Cr-G, G-SmF, SmF-SmC and SmA-N phase transitions. From a detailed study, it is inferred that the increased orientational/vibrational freedom of the alkyl chains, as well as the delocalization of the electron clouds, is responsible for the spectral anomalies at the Cr-G transition. Loss of positional ordering and twist around the -C₆H₄-N= bond takes place at the SmF-SmC transition. In the SmA-N transition, some evidence for the formation of cybotactic clusters was obtained.     

Molecular motions and λ phase transition: Raman and far-ir studies of neat and isotopic mixed hexamethylbenzene crystal

Raman and far-IR studies of hexamethylbenzene (HMB) low temperature crystalline phases (neat and isotopic mixed) are presented. The Raman phonon spectrum changes drastically during the λ-phase transition. Site splittings on two intramolecular modes of HMB-h₁₈ (but on only one corresponding HMB-d₁₈ mode) are observed in the room temperature phase (phase II) spectrum. These splittings disappear in the lower temperature phase (phase III). The methyl torsional bands are identified and a significant shift is observed for them during the phase transition. Also, while the λ-phase transition takes place at 113°K (± 2°K) for HMB-h₁₈ crystal, the transition temperature is 133°K (± 2°K) for HMB-d₁₈. Our results suggest that (for phonon interactions) the symmetry in phase Ill is close to D_3d and reduces to C_i in phase II. Furthermore, the results support the mechanism of phase transition which involves a tilting of the methyl groups out of the benzene ring.     

Dynamics of phase transitions in a liquid crystal probed by Raman spectroscopy

Raman spectra of the Schiff 's base liquid crystalline compound 5O5, N-(4- n-pentyloxybenzylidene)-4'-n-pentylaniline, have been recorded as a function of temperature from 22 to 80°C in the 1140-1220 cm^-1 and 1550-1640 cm^-1 spectral regions. From careful deconvolution of the spectral features using Lorentzian profiles, precise values of peak positions, integrated intensities and linewidths of some selected Raman bands were obtained. The variations of the Raman spectral parameters with temperature are discussed in terms of changes in the molecular alignment and its effect on intra-/inter-molecular interactions at the Cr-G, G-SmF, SmF-SmC and SmA-N phase transitions. From a detailed study, it is inferred that the increased orientational/vibrational freedom of the alkyl chains, as well as the delocalization of the electron clouds, is responsible for the spectral anomalies at the Cr-G transition. Loss of positional ordering and twist around the -C₆H₄-N= bond takes place at the SmF-SmC transition. In the SmA-N transition, some evidence for the formation of cybotactic clusters was obtained.     

Heterogeneous dynamics and dynamic heterogeneities at the glass transition probed with single molecule spectroscopy

We studied the temperature dependence of the structural relaxation in poly(vinyl acetate) near the glass transition temperature with single molecule spectroscopy from Tg-1 K to Tg+12 K. The temperature dependence of the observed relaxation times matches results from bulk experiments; the observed relaxation times are, however, 80-fold slower than those from bulk experiments at the same temperature. We attribute this factor to the size of the probe molecule. The individual relaxation times of the single molecule environments are distributed normally on a logarithmic time scale, confirming that the dynamics in poly(vinyl acetate) is heterogeneous. The width of the distribution of individual relaxation times is essentially independent of temperature. The observed full width at half maximum (FWHM) on a logarithmic time axis is approximately 0.7, corresponding to a factor of about 5-fold, significantly narrower than the dielectric spectrum of the same material with a FWHM of about 2.0 on a logarithmic time axis, corresponding to a factor of about 100-fold. We explain this narrow width as the effect of temporal averaging of single molecule fluorescence signals over numerous environments due to a limited lifetime of the probed heterogeneities, indicating that heterogeneities are dynamic. We determine a loose upper limit for the ratio of the structural relaxation time to the lifetime of the heterogeneities (the rate memory parameter) of Q<80 for the range of investigated temperatures.     

Monitoring the absorption of organic vapors to a solid phase extraction medium applications to detection of trace volatile organic compounds by integration of solid phase absorbents with fiber optic Raman spectroscopy

By combining fiber optic Raman spectroscopy with a C-18 solid phase extraction medium, real time in situ detection of organic vapors is demonstrated. The response of the probe is fully reversible for benzene, trichloroethylene and carbon tetrachloride vapors. Because of the high degree of selectivity afforded by Raman spectroscopy, the composition of mixtures of the vapors can also be determined using the C-18 probe. The detection of ppm levels of benzene in water via headspace analysis using the C-18 probe is demonstrated.