An estimation of the Young’s modulus of bacterial cellulose filaments

An estimation, using a Raman spectroscopic technique, of the Young’s modulus of a single filament of bacterial cellulose is presented. This technique is used to determine the local molecular deformation of the bacterial cellulose via a shift in the central position of the 1095 cm^–1 Raman band, which corresponds to the stretching of the glycosidic bond in the backbone of the cellulose structure. By calculating the shift rate with respect to the applied strain it is shown that the stiffness of a single fibril of bacterial cellulose can be estimated. In order to perform this estimation, networks of fibres are rotated through 360° and the intensity of the 1095 cm⁻¹ Raman band is recorded. It is shown that the intensity of this band is largely independent of the angle of rotation, which suggests that the networks are randomly distributed. The modulus is predicted from a calibration of Raman band shift against modulus, using previously published data, and by using Krenchel analysis to back-calculate the modulus of a single fibril. The value obtained (114 GPa) is higher than previously reported values for this parameter, but lower than estimates of the crystal modulus of cellulose-I (130–145 GPa). Reasons for these discrepancies are given in terms of the crystallinity and structural composition of the samples.     

Elastic coils: deformation micromechanics of coir and celery fibres

Natural fibres, such as flax and hemp, are typically chosen as reinforcing elements in composites to replace traditional glass fibres due to their high stiffness, strength and low strain to failure. Some plant fibres such as coir and celery however possess high strains to failure, which could be utilised in a composite to enhance toughness. This paper reports on the use of Raman spectroscopy to follow the molecular deformation of single fibres of coir and celery. The technique is also used to characterise the orientation of the cellulose structure within the fibres. It is shown by mechanical testing of fibres that both celery and coir possess a non-linear stress–strain curve. Coir fibres however exhibit high strain to failure, whereas celery fibres are shown to have a much lower value of this parameter, despite having a similar coiled fibrillar structure. It is shown by using polarised Raman spectroscopy, and rotating the specimens with respect to the polarisation axis of the laser and measuring the intensity of the 1095 cm⁻¹ Raman band, that both celery and coir fibres combine both axial and transverse orientation, due to their coiled structures. This is also confirmed by birefringence measurements. By following the shift in the central position of this Raman band as a function of cyclic deformation of the fibres, it is shown that the coir fibres recover their molecular deformation, whereas the celery does not show the same level of recovery. This difference between the fibres is postulated to be due to the fact that coir possesses an interlaced fibrillar structure, which remains intact, whereas the celery sub-fibrils unravel and orient towards the fibre axis during deformation.     

Applications of FT Raman Spectroscopy and Micro Spectroscopy Characterizing Cellulose and Cellulosic Biomaterials

FT Raman spectroscopy and micro spectroscopy were used for the investigation of cellulose, cellulose derivatives and cellulosic plant fibres. Lattice structures of cellulose, polymorphic modifications I and II, as well as amorphous structure, were clearly identified by means of FT Raman vibrational spectra. Chemometric models were developed utilizing univariate calibration as well as methods of multivariate data analyses of FT Raman spectral data for the fast prediction of cellulose properties. Cellulose properties like the degree of crystallinity Xc_Raman, the degree of substitution DS_CMC, DS_AC and cellulose reactivity were determined. In situ/ in vivo FT Raman micro spectroscopy was used for the characterization of cellulose structures of flax and hemp fibres. Orientational and stress dependent FT Raman experiments were carried out.     

FT-IR studies on the mechanical response of the crystalline fraction in ultrastrong polyethylene tapes

FT-IR spectra of UHMW-PE tapes with different moduli have been studied in dependence of mechanical deformation and stress. Small spectral variations have been revealed in the difference spectra. Band shifts of the 730/720 cm^–1 doublet have been observed under stress relaxation and upon stretching. A clear correlation between the shift of crystalline bands and the Young's modulus could be determined. Polarized measurements demonstrated variations in the mechanical response of nearly perfectly oriented and non-oriented crystallites. Crosslinking was performed by blending the polyethylene with 10% polysilane and UV-irradiation of the drawn material. The band shift increases as the linkage between oriented crystal blocks is improved with higher draw ratios and chemical crosslinking.     

Mechanical Properties of Regenerated Cellulose Fibres for Composites

Summary: A broad variety of regenerated cellulose fibres was subjected to single fibre tensile tests in order to determine the modulus of elasticity, tensile strength, and failure strain. The results were compared to glass fibres and flax fibres, which are considered the most important technical and natural fibres, respectively. With regard to their modulus of elasticity and tensile strength, regenerated cellulose fibres showed clearly lower values than glass fibres, even when their low density was taken into account. The average modulus of elasticity and tensile strength of regenerated cellulose fibres was also lower than the values measured for flax fibres, but when variability was considered, both fibres performed similarly. In terms of interfacial shear strength with polypropylene, lyocell fibres performed significantly less well than sized glass fibre and ramie fibre. The most important difference between regenerated cellulose fibres and both glass and flax fibres is their high failure strain and thus high work to fracture. The high work to fracture of regenerated cellulose fibres makes them particularly useful for composite applications where high fracture toughness is required.     

Confinement of CdS Nanocrystals in a Sonogel Matrix

CdS/silica xerogel composites have been prepared using a sonocatalytic method. The confinement effects of CdS semiconductor nanocrystallites have been analyzed through UV-VIS absorption and Raman scattering. The blue shift of the absorption band and the shape of the Low Frequency Inelastic Raman Scattering (LOFIRS) spectra make it possible to evaluate the size of nanocrystallites, which are contrasted with previous results obtained through other techniques. Moreover, in the 200–700 cm^–1 region of Raman shift, resonant effects are discussed, through the longitudinal optical mode lines.     

Investigation of the dislocation of natural fibres by Fourier-transform infrared spectroscopy

Dislocations were thought the weakest link in natural fibres which had negative effects on the tensile strength of the fibres. This paper presents a systematic approach to examine the dislocations in hemp fibres firstly by optical microscopy (OM) and field emission scanning electron microscopy (FE-SEM) for the morphologies of the dislocations and then by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) for the crystallinity index and hydrogen bonds and main chemical compositions of the dislocation regions in hemp fibres. The results showed that (i) dislocations resulted in fibril distortion and intensified amorphous features of hemp fibres; (ii) crystallinity index reduced from 48.4% examined by FTIR and 56.0% by XRD determination for hemps without dislocations to 41.3% for the dislocation regions; (iii) the FT-IR spectra showed much higher absorbance of hemp fibres without dislocations which was two times that of dislocation regions across the whole range of wavenumbers; (iv) deconvolving spectra in O-H stretching region showed a lower number of hydrogen bonds, weaker inter- and intra-molecular hydrogen bonding in the dislocation regions, indicating a possible decrease in the tensile strength of hemp fibres; (v) the FT-IR spectra indicated the removal of the hemicelluloses in dislocation regions and hence possible loss of lignin because of disappearing the bands at 1368 cm⁻¹, 1363 cm⁻¹ and 1506 cm⁻¹; (vi) the spectra in fingerprint region gave rise to the ratio of syringyl (S)/guaiacyl (G) of 0.9 in dislocation regions which was lower than that (1.1) of hemp without dislocation, this means a significant reduction of lignin content and a higher cellulose content in the dislocation regions.     

In vivo molecular evaluation of guinea pig skin incisions healing after surgical suture and laser tissue welding using Raman spectroscopy

The healing process in guinea pig skin following surgical incisions was evaluated at the molecular level, in vivo, by the use of Raman spectroscopy. After the incisions were closed either by suturing or by laser tissue welding (LTW), differences in the respective Raman spectra were identified. The study determined that the ratio of the Raman peaks of the amide III (1247 cm⁻¹) band to a peak at 1326 cm⁻¹ (the superposition of elastin and keratin bands) can be used to evaluate the progression of wound healing. Conformational changes in the amide I band (1633–1682 cm⁻¹) and spectrum changes in the range of 1450–1520 cm⁻¹ were observed in LTW and sutured skin. The stages of the healing process of the guinea pig skin following LTW and suturing were evaluated by Raman spectroscopy, using histopathology as the gold standard. LTW skin demonstrated better healing than sutured skin, exhibiting minimal hyperkeratosis, minimal collagen deposition, near-normal surface contour, and minimal loss of dermal appendages. A wavelet decomposition–reconstruction baseline correction algorithm was employed to remove the fluorescence wing from the Raman spectra.     

Study of Adsorption, Condensation, Orientation, and Reduction of Quinoline Molecules on a Pure Mercury Electrode Using Raman Microprobe Spectroscopy

Quinoline is known to adsorb on a mercury electrode surface with several differentorientations and it sometimes blocks other electrochemical reactions. The Ramanmicroprobe technique has been applied successfully to observe reorientations ofquinoline adsorbed on the mercury surface from neutral and basic aqueoussolutions. The orientation-distance profile from the mercury surface was also studied.A Raman band intensity of quinoline (1373 cm^–1) relative to the intensity ofperchlorate ion (931 cm^–1) was measured. The peak positions did not shift evenwhen the applied potential was altered, but the relative peak intensity changed.It was concluded that the adsorbed quinoline changes its orientation from a flatat –0.1 > E > –0.3V, to a standing at E < –0.5 V, passing through a mixtureof the two orientations when –0.3 > E > –0.5 V.     

IR-analysis of H-bonded H2O on the pure TiO2 surface

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Raman spectra in the libration region of concentrated aqueous solutions of lithium-6 and lithium-7 halides. Evidence for tetrahedral Li(OH2) 4 +

The Raman spectra of saturated solutions of⁶LiCl and⁷LiCl have been decomposed into Gaussian components, one of which is a polarized band that occurs at 360 cm^–1 when the ion is⁶Li⁺ and shifts to 335 cm^–1 when the ion is⁷Li⁺. Equivalent bands occur in the spectra of saturated solutions of⁶LiBr and⁷LiBr at 343 and 320 cm^–1, respectively. These bands are assigned to solvent-separated ion aggregates. The Raman spectra of 8.0 and 3.5 m solutions of the isotopic lithium chlorides have been decomposed into five Gaussian components, three of which are assigned to water librations. In addition, there is a polarized band at 440 cm^–1 independent of the lithium isotope used, and a depolarized band which occurs at 385 cm^–1 in the⁶LiCl solutions and 360 cm^–1 in the⁷LiCl solutions. We interpret these two additional bands as theA ₁ andF ₂ stretching modes of Li⁺ tetrahedrally solvated by water molecules.     

Natural rubber nanocomposites with SiC nanoparticles and carbon nanotubes

Single-walled carbon nanotubes (SWNTs) and SiC nanoparticles were dispersed in natural rubber (NR) polymer solution and subsequently evaporated the solvent to prepare NR nanocomposites. Using this technique, nanoparticles can be better dispersed in the NR matrix. The influence of nano-fillers on the mechanical properties of the resulting nanocomposites was quantified.Mechanical test results show an increase in the initial modulus with nanoscale reinforcements for up to 50% strain compared to pure NR. The modulus and strength of natural rubber with 1.5% SiC nanoparticles appear to be superior to those of SWNTs with the same filler content. In addition to mechanical testing, these nanocomposites were studied using the SEM and Raman spectroscopy techniques in order to understand the morphology of the resulting system and the load transfer mechanism, respectively. The Raman spectrum of the SWNT/NR system is characterized by a strong band at 1595 cm⁻¹ (G mode—C-C stretching) and other two bands at 1300 cm⁻¹ (D mode-disorder induced) and 2590 cm⁻¹ (D* band). A shift of the 2590 cm⁻¹ Raman band to the lower wavenumber was observed after subjecting SWNT/NR sample to cyclic stress testing. Ageing SWNT/NR specimen in distilled water for 30 days also provided a similar result. The Raman shift in aged samples indicates internal stress transfer from the natural rubber matrix to the SWNTs implying the existence of bonding at the interface.     

Differentiation of solvated spironolactone samples by FT-Raman and FT-IR diffuse reflectance spectroscopy

Summary Five solvates of spironolactone were prepared by crystallization from absolute methanol, acetonitrile, absolute ethanol, ethyl acetate, and benzene, and characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and by FT-Raman spectroscopy. Of these solvates, all were found to be monosolvated except that formed with acetonitrile which gave a spironolactone-acetonitrile (2:1) complex as determined by elemental microanalysis. Distinctive IR and Raman spectral features of the solvates are discussed. Remarkable similarity is seen in the Raman spectra (1800–400 cm^–1) of the solvates obtained from methanol, ethanol, and ethyl acetate. The Raman spectrum of the benzene solvate is particularly useful for showing the presence of benzene because of the very intense band near 1000 cm^–1 which is unique to the Raman effect.Presented at the 36th Canadian Spectroscopy Conference, 1–3 August 1990, at Brock University, St. Catharines, ON, Canada     

Direct observation of a 220 cm structure in the lowest π–π* absorption band in the vapour phase of trans-azobenzene

In this work we present the first direct observation of a 220 cm⁻¹ progression in the absorption spectrum of trans-azobenzene in the vapour phase. The mode at 220 cm⁻¹ is essential to explain both the electronic absorption spectrum and the Raman excitation profiles of the most intense Raman bands of trans-azobenzene in the 1000–1600 cm⁻¹ shift range. Our data in the vapour phase assure that this frequency pertains to an internal molecular mode.     

Far-infrared spectrum,conformational stability,barriers to internal rotation,normal coordinate calculations,and vibrational assignment for chloroacetaldehyde

The far infrared spectrum [350 to 25 cm^–1] of gaseous chloroacetaldehyde, ClCH₂CHO, has been recorded at a resolution of 0.10 cm^–1. The first excited-state transition of the asymmetric torsion of the more stable near s-cis [chlorine atom s-cis to the aldehyde hydrogen atom] conformer has been observed at 26.9 cm^–1, with seven additional upper state transitions falling to higher frequency. Additionally, the fundamental torsional transition of the s-trans conformer has been observed at 58.9 cm^–1 with two excited states also falling to higher frequency. From these data, the asymmetric torsional potential coefficients have been determined to be:V ₁=414±11;V ₂ = 191±3;V ₃=–203±5;V ₄=44±1 andV ₆=–26±1 cm^–1. The s-cis to s-trans barrier is 500±5 cm^–1 (1.43±0.01 kcal mol^–1) with the s-cis conformer being more stable by 267±19 cm^–1 (0.76±0.05 kcal mol^–1) than the s-trans form. The Raman [4000 to 100 cm^–1] and infrared (4000 to 400 cm^–1] spectra of the gas have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Complete vibrational assignments are proposed for both conformers based on band contours, depolarization values, and group frequencies. The assignments are supported by ab initio Hartree-Fock gradient calculations employing the 3–21G^* basis set to obtain the frequencies and the potential energy distributions for the normal vibrations for both rotamers. Additional ab initio calculations at the MP4/6-31G^* level have been carried out to determine the structural parameters for both conformers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.This contribution taken in part from the thesis of C. L. Tolley which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Investigation of silicate mineral sanidine by vibrational and NMR spectroscopic methods

Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 Å confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200–950, 770–720, 590–540 and 650–640 cm⁻¹. The Raman spectrum shows the strongest band at 512 cm⁻¹ characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV–vis–NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm⁻¹ due to the combination of fundamental OH– stretching. The bands at 11236 and 8196 cm⁻¹and the strong, well-defined band at (30303 cm⁻¹ attest the presence of Fe²⁺ and Fe³⁺, respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe³⁺ at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The ²⁹Si NMR spectrum shows two peaks at −97 and −101 ppm corresponding to T2 and T1, respectively, and one peak in ²⁷Al NMR for Al(IV).     

Clathrate and inclusion compounds. Part 11 [1]. A pre-resonance Raman study of the β-quinol/SO2 clathrate

A pre-resonance Raman study of the yellow -quinol/SO₂ clathrate has been carried out using 609.8, 586.8, 514.5, 488.0 and 457.9 run excitation. Pre-resonance enhancement is observed for the guest v_l (Al) band at 1147 cm^–1 and the host band at 1257 cm^–1. These observations are consistent with a charge transfer interaction arising from the LUMO of S0₂ (S 3pz) and the HOMO of quinol, which consists mainly of the ring electrons.     

Raman Combinations and Stretching Overtones from Water, Heavy Water, and NaCl in Water at Shifts to ca. 7000 cm−1

Photographic Raman spectra were obtained at shifts to ca. 7000 cm^–1 for pure water and for a saturated aqueous solution of NaCl using argon ion laser excitation. Raman spectra were also obtained photoelectrically for H₂O and D₂O between ca. 2500 and ca. 7000 cm^–1 using 248-nm excimer laser excitation and boxcar detection. Overtone and combination assignments are presented for H₂O and D₂O. The first IR OH-stretching overtone from water occurs 215 cm^–1 above the first Raman OH-stretching overtone because the IR overtones are dominated by asymmetric stretching. The second OH-stretching Raman overtone from water is estimated to occur near 10,020 ± 20 cm^–1, with 9950 cm^–1 as a lower limit.     

Spectra and structure of small ring compounds. LIX

The Raman (3200 to 10 cm^–1) and far infrared (380 to 60 cm^–1) spectra of gaseous fluorocyclobutane,c-C₄H₇F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm^–1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm^–1)=(1.76±0.05)10³X+(4.88±0.28)10⁴X²+(2.12 ±0.16)10³ exp(–5.66±0.41)10X² with a reduced mass function ofg ₄₄= 0.00386–0.00295X+0.03485X²+0.1228X³ +0.3459X⁴, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm^–1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm^–1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c^–1) and gas (413±43 cm^–1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G^*, and 6-31 G^** basis sets.For part LVIII, seeStruct. Chem. 1991,2, 195.Taken in part from the thesis of M. J. Lee, which has been submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May 1991.     

Excitation energy dependence of the Raman spectrum of single-walled carbon nanotubes

We investigate the excitation energy dependence of Raman modes in the 600–1200 cm⁻¹ range. The main features are first, two lines around 860 and 1060 cm⁻¹ independent of the energy and second, energy-dependent couples of lines, each of them composed of one first-order mode and one substractive combination band. In each couple, the frequency of the lines is found to follow a linear, strong and opposite energy dependence.