Jack Yarwood

Vibrational relaxation of hydrogen-bonded species in solution. I. Theory

Abstract We present a simple model to describe the phase relaxation of the ν s (XH) mode of a hydrogen-bonded species XH⋯Y in solution in an inert solvent. The major assumptions made are that the ν σ (XH⋯Y) stretching mode of the hydrogen bond can be represented by the Ornstein—Uhlenbeck stochastic process, and that the ν s (XH) phase coherence is lost because of the coupling between the two vibrational modes. The model can be analysed in terms of Kubos theory of a randomly modulated oscillator. An expression is derived for the transition dipole moment autocorrelation function which characterises the line shape of the mid infrared ν s (XH) absorption band, and various limiting cases of the formula are discussed. It is further shown that vibrational relaxation may be expected to influence the far infrared ν σ (XH⋯Y) bandshape and the one-phonon neutron inelastic scattering cross section, and that the parameters required to characterise all three types of spectra are closely related. Experimental tests of the theory are reported in the following paper.

Raman microscopic studies of PVD hard coatings

Abstract A series of PVD ceramic hard coatings (TiN, ZrN, TiAlN, TiZrN and TiCN) were deposited on steel substrates using the cathodic arc/unbalanced magnetron deposition technique. These coatings were characterised using Raman microscopy to elucidate the behaviour of the optic and acoustic phonon modes of the (cubic) crystalline lattices. Defect-induced first- (and second-) order spectra have been observed in the 200–300 and 500–800 cm −1 regions and these have been assigned and correlated with coating composition. Changes in the position, intensity and shape of the principal TO band (640–560 cm −1 ) have been interpreted. Raman microscopy has been shown to be a very useful non-destructive complementary technique to XRD for the characterisation of PVD hard coatings.

Adsorption of polyamine, polyacrylic acid and polyethylene glycol on montmorillonite: An in situ study using ATR-FTIR

Abstract Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD) have been employed to investigate the adsorption of water soluble polymers from aqueous solution onto a clay mineral surface in situ, to gain an understanding of the interactions occurring at the microscopic level in water based muds (WBM). The water soluble polymers studied were; polyethylene glycol (PEG) (molecular weight, M w , 300 and 1000) (neutral), polyamine (FL15) ( M w 5000) (cationic) and polyacrylic acid, PAA, ( M w 2000) (charge dependant on pH) to establish the effect of polymer charge on the nature and extent of adsorption. XRD and ATR-FTIR spectroscopy have shown that water soluble polymers adsorb onto clay dispersions and are stable when deposited as thin solid films. XRD indicates that PEG stacks as either one or two layers whereas PAA and FL15 are restricted to a single layer between the clay lamellae. ATR-FTIR spectroscopy showed that FL15 penetrated the Na–SWy-1 films which contained low loadings of PEG without displacing any of the resident PEG. When a bilayer of PEG was present, FL15 did not penetrate into the film. Both PAA and PEG adsorbed onto FL15 loaded Na–SWy-1 films irrespective of FL15 loading or the molecular weight of the PEG. ATR-FTIR indicated that significant adsorption occurred in under 30 s and the adsorption rate was not influenced by the presence of a second polymer preloaded into the clay.

Studies of molecular motions and vibrational relaxation in acetonitrile. I. Raman spectral studies of the ν1 ν3 and 2ν3 bands in the

Abstract Raman spectroscopic studies on acetonitrile in the liquid and in dilute solutions have been used to investigate the vibrational relaxation-processes wh

A FTIR-ATR study of liquid diffusion processes in PET films: comparison of water with simple alcohols

An in-situ FTIR-ATR method for simultaneously obtaining both kinetic and structural information during liquid sorption into polymers was presented. The kinetics and diffusion profile of the sorption of liquid water and liquid methanol into poly(ethylene terephthalate) (PET) were compared and contrasted. The diffusion of water into PET was shown to follow Fickian kinetics, without significant swelling and the calculated diffusion coefficients (D) varied between 8.57 and 0.52 x 10(-9) cm(2) s(-1) for a crystallinity range of 4-25%. The D values decreased non-linearly with the increase in crystallinity. The average spherulitic crystal size was thought to play a significant role in determining the rate of water sorption. Conversely, the sorption of liquid methanol was accompanied by significant swelling and crystallisation and hence showed non-Fickian or anomalous kinetics. The sorption data were fitted to a dual sorption model which indicated that the rate of diffusion of liquid methanol was faster than that of liquid water, probably due to the accompanying swelling. Increasing the level of crystallinity was shown to decrease the capacity for the polymer to swell and reduced the calculated diffusion coefficients

A Fourier transform infrared study of water-head group interactions in reversed micelles containing sodium bis(2-ethylhexyl) sulfosuccinate (AOT)

Abstract Fourier transform infrared spectroscopy has been employed to study the state of water and water—head group interactions in AOT aggregates or microemulsions in n-heptane. Isotopic dilution of water (4% D2O and in H2O) has been used to monitor the uncoupled ν(OD) band of HOD as a function of W0 (the number of water molecules per head group). It is found that the feature always consists of a single-band profile and there is no evidence of coexisting multiple water species in these systems (on the vibrational time scale). By detailed examination of ν(SO) and ν(CO) bands of the head group it is found that up to W0 = 6 (severely perturbed) water molecules are bound closely to the sulfonate and Na+ ions at the water/organic interface. Beyond this point all the water molecules seem to have a similar vibrational relaxation rate but there are still gradual structural and electronic changes as the water molecules move farther away from the first hydration shell. At values of W0 higher than 12 there is some evidence that the water molecules are similar to those in the bulk, but up to 20 water molecules per head group are probably needed to form well-defined reversed micelles in these systems.

Vibrational relaxation of hydrogen-bonded species in solution. Il. Analysis of vs(XH) absorption bands

Abstract The v s (XH) absorption bands of the following complexes have been recorded in digitised form: phenol (OH)- and phenol (OD)- dioxan in CCl 4 ; phenol (OH)- and phenol (OD)-acetonitrile in CCl 4 ; and phenol (OH)-acetonitrile in CDCl 3 . All these bands are broad and nearly featureless, and have widths at half height ranging from 75 to 148 cm −1 . With one possible exception they appear to be free from Fermi resonances. By least-squares fitting of the theoretical bandshape function derived in part I to the experimental spectra we have been able to estimate the parameters Δ, ω 2 , and τ C which characterise the theoretical autocorrelation function, and also to determine the v s (XH) stretching frequency very accurately. In the case of phenol (OD)-dioxan in CCl 4 the discrepancies between the observed and fitted spectra can be entirely attributed to errors of observation. It is found that the Kubo parameter τ C Δ is close to unity in all cases, showing that the v s (XH) bands are subject to partial (but not extreme) motional narrowing. The v σ (XH⋯Y) vibration is always heavily damped and has a broad spectral density. The changes in the spectral profiles produced by deuteration and change of solvent are easily understood in terms of the theory. Deuteration affects the amplitude of modulation, while changing the solvent affects the value of τ C . In either case τ C Δ changes, and the speed of modulation is altered. Since the system is far from the gaussian (slow modulation) limit, the bandshape changes markedly in consequence.

ATR-FTIR spectroscopic studies of the structure and permeability of sulfonated poly(ether sulfone) membranes. Part 1.—Interfacial water–polymer interactions

Attenuated total reflection (ATR) FTIR spectroscopy has been used to monitor, in situ, the penetration of water into thin sulfonated poly(ether sulfone) films of different thicknesses. Water and polymer IR bands have been analysed to provide information about the molecular state of both diffusant and diffusion medium at the polymer/liquid interface. The hydration process is characterised by intensity enhancements in the aromatic ring and νs(SO3–) vibrational bands of the polymer and by dramatic changes of shape in the ν(OH) profile. These changes have been interpreted in terms of the changing water–polymer interactions as a function of hydration level. In particular, hydration causes considerable electronic perturbation of the conjugated polymer backbone through an ionisation process at the —SO3H groups, giving rise to a stronger interaction between polymer and water and a reduced degree of hydrogen bonding between sorbed water molecules.

Studies of vibrational relaxation in liquid methyl iodide

The intermolecular coupling contribution to the vibrational relaxation function for v 2 of methyl iodide has been deduced using the method of isotopic dilution. The band widths, correlation functions and frequency shifts of both isotropic and anisotropic spontaneous Raman spectra have been studied at 295 and 205 K for solutions of 0·1 mole fraction of CH3I in CD3I and in CS2. Although isotopic dilution leads to a considerable decrease in the rate of vibrational relaxation, neither the corresponding first moment changes nor the I vv-I VH frequency shifts very large. This implies that neither permanent dipole nor other intermolecular interactions lead to appreciable liquid phase ‘order’ in CH3I. This is understood in terms of a model of the intermolecular coupling potential which shows that, for weak ‘order’, the second moment is affected much more than the first moment. Our results for CH3I are different from those predicted by a recently published theory of intermolecular coupling in pure liquids (albeit ...

Depth Profiling of Poly(methyl methacrylate), Poly(vinyl alcohol) Laminates by Confocal Raman Microspectroscopy

We report a molecular depth profiling study of a PMMA/PVOH laminate on quartz using confocal Raman microspectroscopy. It is demonstrated that this technique can be successfully employed to study the hydrogen-bonding interaction between the ester and alcohol groups near the interfacial region. The carbonyl, v(C=O), band of PMMA shows significant broadening in the interfacial region. Various PMMA/PVOH laminates with different PMMA molecular weights have been studied, and it is demonstrated that the PMMA layers with lower molecular weight show a greater degree of interpenetration for a given annealing time.