Polarized FTIR Spectroscopy Research Articles

Characterization of polyethylene films drawn by machine direction orientation and consequences on their photooxidation

The effect of uniaxial drawing by Machine Direction Orientation (MDO) on polyethylene films was first studied by complementary analytical methods. XRD and polarized FTIR spectroscopy revealed the transformation of the initial spherulitic structure of PE into microfibrils composed of small crystalline blocks connected by amorphous chains oriented along the drawing direction. No stress-induced crystallization was observed upon MDO processing, but the permeability to oxygen was reduced by 30 % owing to this morphology change. In a second time, the effect of photooxidation on undrawn and MDO-drawn films was studied. There was no difference in the photooxidation kinetics and stoichiometry between them. A slight reorganization of the polymer structure due to physical ageing was observed before any photooxidation, but no change in orientation occurred upon photochemical ageing. Finally, the oxygen permeability of undrawn and MDO-drawn films decreased owing to the changes brought by photooxidation, especially the formation of polar functions within the initially apolar polyethylene and the occurrence of chemicrystallization.

Comparative study of vulcanization system on strain-induced crystallization of epoxidized natural rubber

Vulcanization systems and epoxidation degree play an important role for the microstructure and macro-property of epoxidized natural rubber (ENR). Effect of sulfur (S), dicumyl peroxide (DCP) and itaconic acid (IA) vulcanization systems on the strain-induced crystallization (SIC), molecular chain orientation and microstructure evolution of ENRs were compared by WAXD, polarized FTIR spectroscopy and AFM modulus images. Results demonstrated that ENR-10 with 10% epoxidation degree showed the best mechanical properties, and its tensile strength and elongation of break increased by 137%, 167%, and 19%, 20% compared with the ENR-10-DCP and ENR-10-IA, respectively. ENR-10-DCP and ENR-10-IA had a similar higher molecular chain orientation than ENR-10-S which resulted in the stress larger than ENR-10-S at strain lower than 1. While at high strain, the heterogeneous microstructure, rapid growth of molecular chain orientation and earliest SIC led to the mechanical properties of ENR-10-S being significantly higher than ENR-10-DCP and ENR-10-IA. In addition, compared with NR-S, the introduction of epoxy groups could promote the molecular chain orientation and SIC, thus ENR-10-S showed better mechanical strength than NR-S.

Comparative study on the molecular chain orientation and strain-induced crystallization behaviors of HNBR with different acrylonitrile content under uniaxial stretching

Molecular chain orientation and strain-induced crystallization (SIC) behaviors of hydrogenated nitrile butadiene rubber (HNBR) with acrylonitrile content of 19%, 33%, 41%, 44%, i.e., HNBR-19 to HNBR-44, were characterized by using polarized FTIR spectroscopy and synchrotron radiation WAXD. Results demonstrated that the hydrogenated butadiene and acrylonitrile segments showed different orientation behaviors in these HNBRs. Orientation decreased with increasing acrylonitrile content, except for HNBR-44. HNBR-19 had the highest SIC ability and the crystals were composed of only hydrogenated butadiene homopolymer segments. HNBR-33 could not crystallize. As for HNBR-41 and HNBR-44 with high acrylonitrile content, HNBR-44 showed the better SIC ability and hydrogenated butadiene-acrylonitrile alternating copolymer segments were proved to participate in the crystallization. Relationship between microstructure and stress-strain characteristics was also discussed and results revealed that the relatively homogeneous crystal structure, higher crystal orientation and rapidly increasing molecular chain orientation were attributed to the highest stress value of HNBR-44 after SIC occurred.

Molecular orientation in aligned electrospun polyimide nanofibers by polarized FT-IR spectroscopy

Quantitative explanation on the improved mechanical properties of aligned electrospun polyimide (PI) nanofibers as the increased imidization temperatures is highly required. In this work, polarized FT-IR spectroscopy is applied to solve this problem. Based on the polarized FT-IR spectroscopy and the molecular model in the fibers, the length of the repeat unit of PI molecule, the angle between the fiber axis and the symmetric stretching direction of carbonyl group on the imide ring, and the angle between the PI molecular axis and fiber axis are all investigated. The Mark-Howink equation is used to calculate the number-average molar mass of PI molecules. The orientation states of PI molecules in the electrospun nanofibers are studied from the number-average molar mass of PI molecules and the average fiber diameter. Quantitative analysis of the orientation factor of PI molecules in the electrospun nanofibers is performed by polarized FT-IR spectroscopy.

A novel mouse model of intervertebral disc degeneration shows altered cell fate and matrix homeostasis

Intervertebral disc degeneration and associated low back and neck pain is a ubiquitous health condition that affects millions of people world-wide, and causes high incidence of disability and enormous medical/societal costs. However, lack of appropriate small animal models with spontaneous disease onset has impeded our ability to understand the pathogenetic mechanisms that characterize and drive the degenerative process. We report, for the first time, early onset spontaneous disc degeneration in SM/J mice known for their poor regenerative capacities compared to “super-healer” LG/J mice. In SM/J mice, degenerative process was marked by decreased nucleus pulposus (NP) cellularity and changes in matrix composition at P7, 4, and 8 weeks with increased severity by 17 weeks. Distinctions between NP and annulus fibrosus (AF) or endplate cartilage were lost, and NP and AF of SM/J mice showed higher histological grades. There was increased NP cell death in SM/J mice with decreased phenotypic marker expression. Polarized microscopy and FTIR spectroscopy demonstrated replacement of glycosaminoglycan-rich NP matrix with collagenous fibrous tissue. The levels of ARGxx were increased in, indicating higher aggrecan turnover. Furthermore, an aberrant expression of collagen X and MMP13 was observed in the NP of SM/J mice, along with elevated expression of Col10a1, Ctgf, and Runx2, markers of chondrocyte hypertrophy. Likewise, expression of Enpp1 as well as Alpl was higher, suggesting NP cells of SM/J mice promote dystrophic mineralization. There was also a decrease in several pathways necessary for NP cell survival and function including Wnt and VEGF signaling. Importantly, SM/J discs were stiffer, had decreased height, and poor vertebral bone quality, suggesting compromised motion segment mechanical functionality. Taken together, our results clearly demonstrate that SM/J mouse strain recapitulates many salient features of human disc degeneration, and serves as a novel small animal model.

Supramolecular organization of a H-bonded perylene bisimide organogelator determined by transmission electron microscopy, grazing incidence X-ray diffraction and polarized infra-red spectroscopy.

An organogelator based on a N,N'-substituted H-bonding perylenebisimide (PBI-C10) self-assembles to form either a green J-type (form I) or a red H-type (form II) aggregate structure. The molecular packing of both polymorphs was determined from a combination of Transmission Electron Microscopy (TEM) (low dose electron diffraction and high resolution), Grazing incidence X-ray diffraction and polarized infrared spectroscopy. To that aim, highly oriented films have been prepared by mechanical rubbing at controlled film temperature and DFT calculations were performed to identify representative vibrational IR bands and their associated polarizations. H-Bonding between amides generates either a rectangular columnar phase (form I) in the dried gel or a hexagonal packing of supramolecular 21/1 helices with a long period of 97 Å (form II) in annealed thin films. In aligned films of form I, polarized FTIR spectroscopy helps determine the orientation of both intermolecular H-bonds and the PBI core with respect to the substrate. In form II, PBI-C10 molecules assemble into pairs to form off-centered 21/1 helices whose helical axis is made of strongly H-bonded amides. TEM investigations show that three 21/1 helices are packed in a frustrated trigonal structure formed by H-bonding. The Form I → Form II transformation implies a redistribution of a single population of strong intra-columnar H-bonds between amides in form I to a mixture of strong and weak H-bonds in the supramolecular helices, the strong H-bonds forming the spine of the helices.

Tailored conditions for controlled and fast growth of surface-grafted PNIPAM brushes

Abstract Surface-initiated Atom Transfer Radical Polymerization is an established technique for synthesis of polymer brushes via “grafting from” method. However, dynamic behavior of surface-tethered macromolecules during their growth requires more detailed studies to obtain uniform polymer brush films. It was addressed here by varying solvent composition in grafting of poly(N-isopropylacrylamide) brushes. Complementary in situ (quartz crystal microbalance) and ex situ (atomic force microscope, spectroscopic ellipsometry) techniques were employed to investigate the influence of methanol molar fraction (xMe) in methanol/water polymerization mixture on the brush growth. Grazing-angle polarized FT-IR spectroscopy was used to monitor macromolecular arrangement in the brushes. While achieving controlled, uniform and relatively fast growth of macromolecules is challenging a compromise may be reached by tuning solvent composition. The most balanced conditions with this respect were found in a narrow solvent composition window at ca. xMe ≈ 0.16 and below 0.31. The results may be applied for tailoring polymerization conditions of other polymer brush systems.

Temperature dependence of molecular conformation in uniaxially deformed isotactic polypropylene investigated by combination of polarized FTIR spectroscopy and 2D correlation analysis

Evolution of molecular conformation in uniaxially deformed isotactic polypropylene (iPP) as a function of temperature is investigated by time-resolved polarized Fourier-transform infrared spectroscopy. It is observed that oriented crystals (microfibrils) induced by deformation possess better thermal stability compared with isotropic spherulites. 2D correlation analysis reveals that the relaxation process of ordered helices in deformed iPP could be divided into two regions referring to the melting of different crystalline structures. No obvious sequential change of ordering conformations observed in low temperature region is attributed to melting of defective or destructed crystals. However, notable sequential changes of helices occur in the high temperature region; interestingly, long helices are more thermally stable than short helices. The central region of microfibrils is suggested to consist of a large amount of long helical bundles, and the short ordering segments are primarily located in the outer lateral surfaces. A physical picture of the conformational distribution in deformation-induced microfibrils is thus gained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 673–684

러빙한 유리 기판을 이용한 반응성 액정 배향

고분자 배향막이 없는 순수 유리 기판을 이용하여 광반응성 액정의 배향을 유도하였다. 유리 기판을 러빙하여 액정 배향을 유도한 경우, 고분자 배향막을 사용하여 유도한 경우와 같이 액정을 러빙 방향과 평행하게 배향할 수 있는 것을 편광 FTIR, 편광현미경, 복굴절 측정 등의 실험을 통해서 알 수 있었다. 순수 유리 기판을 러빙하여 액정 배향을 유도하는 메커니즘은 러빙 과정에서 유리 표면에 묻어나온 고분자들이 러빙 방향으로 늘어서 분자간 상호작용을 통하여 액정 분자들의 배향을 유도하는 것이다. Alignments of photo-reactive mesogen were induced using bare glass substrates without a polymer alignment layer. It was found by using polarized FTIR spectroscopy, polarized microscopy, and birefringence measurement experiments that the reactive mesogen could be aligned along the rubbing direction although the glass substrate without an alignment layer was used. The induction mechanism of the rubbed bare glass is ascribed to that polymers from rubbing clothes are coated on the glass substrate along the rubbing direction and lead the alignment of liquid crystals through intermolecular interactions.

Carboxylic acid-grafted mesoporous material and its high catalytic activity in one-pot three-component coupling reaction

A new carboxylic acid functionalized mesoporous organic polymer has been synthesized via in situ radical polymerization of divinylbenzene and acrylic acid using a mesoporous silica as a seed during the polymerization process under solvothermal conditions. The mesoporous material MPDVAA-1 has been thoroughly characterized employing powder XRD, solid state 13C cross polarization magic angle spinning-nuclear magnetic resonance, FT-IR spectroscopy, N2 sorption, HR-TEM, and NH3 temperature programmed desorption-thermal conductivity detector (TPD-TCD) analysis to understand its porosity, chemical environment, bonding, and surface properties. The mesoporous polymer was used as a catalyst for a three comp onent Biginelli condensation between various aldehydes, β-keto esters, and urea/thioureas to give 3,4-dihydropyrimidine-2(1H)-ones. The reactions were carried out under conventional heating as well as solvent-free microwave irradiation of solid components, and in both the cases, the mesoporous polymer MPDVAA-1 proved to be a powerful, robust, and reusable catalyst with high catalytic efficiency.

Morphology and crystalline structure of inclusion compounds formed between poly(ethylene glycol) and urea

The poly(ethylene glycol) (PEG, with M w 2000)-urea inclusion compound (IC) crystallized at high temperature region showed two typical orientations, flat-on and edge-on crystals. 2D-XRD and polarized FTIR spectroscopy revealed that the PEG chains within urea channels were perpendicular to the substrate in flat-on oriented crystals, while PEG chain axes were parallel to the substrate and lay along the growth direction in the edge-on crystals. FTIR absorption bands of PEG in the ICs are sensitive to orientation of the crystals. A scheme of PEG chain packing in the urea IC channel was proposed, which could explain the orientation of the crystal nucleus causing the two types of morphologies. Furthermore, functioning of PEG2000 chain end with analine had significantly influence on the morphology and orientation of the inclusion compound crystals, due to the defects caused by large terminal groups included in the urea channel.

Centimeter-scale giant spherulites in mixtures of polar polymers and crystallizable diluents: Morphology, structure, formation and application

A series of giant spherulites at centimetre scale were effectively constructed from the mixtures of polyacrylonitrile (PAN)/dimethyl sulfone (DMSO2), although neither PAN nor DMSO2 itself forms spherical morphology during crystallization. A detailed investigation was carried out on the morphology, microstructure, and formation mechanism by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray diffraction, polarized FTIR spectroscopy, and differential scanning calorimetry. These giant spherulites constituted of PAN phase and DMSO2 crystals alternately distributed in divergent patterns. The fast crystallization of DMSO2 dominates the large growth rate and the macroscopic size, while PAN composes the skeleton of the giant spherulites. The cooperative deposition of PAN beside DMSO2 crystals originates from dipole–dipole interaction between the nitrile groups of PAN and the sulfone groups of DMSO2, accounting for the branching and splaying in the giant spherulites. These macroscopic morphologies were universally observed in other mixtures of PAN/dimethyl sulfoxide, PAN/maleic anhydride, poly(vinylidene fluoride)/DMSO2, and cellulose acetate/DMSO2. We propose that the giant spherulites can be formed by introducing suitable diluent crystallization and appropriate polymer–diluent interaction. Furthermore, this spherulitic pattern has been used as a template to direct the oriented growth of calcium carbonate based on the molecular orientation in the giant spherulite.

Solvent Effects on Template Wetting Nanofabrication of MEH-PPV Nanotubules

Template wetting is simple, solution-based nanofabrication technique that has previously been demonstrated for a number of different polymers. Like other solution-based polymer processing methods, it is reasonable to expect that the choice of solvent will have a significant impact on the properties of the resulting structures. This work examines the impact of wetting solvent on the properties of poly(2-methoxy-5-2′-ethylhexyloxy-1,4-phenylenevinlyene) (MEH-PPV) nanotubules formed using this method. The strength of solvent−polymer interaction was found to positively correspond to the degree of polymer chain alignment in the resulting nanotubules. Alignment was indicated by the level of dichroism observed using polarized FTIR spectroscopy, with no preferential alignment observed when using the poorest solvent (chlorobenzene) and dichroic ratios greater than 10 observed when “good” solvents chloroform and tetrahydrofuran were employed. The degree of alignment in turn correlated to a greater effective conjuga...

Molecular Orientation and Crystalline Structure of Aligned Electrospun Nylon 6 Nanofibers: Effect of Gap Size

We studied the effect of gap size on molecular orientation and crystalline structure of theuniaxially well-aligned nylon 6 nanofibers produced in the gap of the negatively charged metal plates. As evidenced by polarized FT-IR spectroscopy, relative intensity in several absorbance bands, including the N-H stretching, amide I, II, and III vibrations were found to be different in the parallel and perpendicular polarized FT-IR spectra. Moreover, X-ray analysis indicated that the metastable γ-form was predominant in the as-spun nylon 6 nanofiber, and was transformed into the thermodynamically stable α-form by increasing the cap size. These results suggested that the polymer chains were oriented perpendicular to the fiber direction. Molecular orientation to the fiber axis was enhanced as increasing the gap size.

Spectroscopic and electrical evaluation of poly(3-hexylthiophene) nanotubules made using template wetting nanofabrication

The unique properties of conjugated polymer nanostructures as compared to thin films of the same materials have fueled the investigation of a number of different polymer nanofabrication techniques. Here we examine the optoelectronic properties of poly(3-hexylthiophene)P3HT nanotubules made using one of the simplest of these techniques, template wetting nanofabrication. Comparison is made with results from our previous study in which in poly(2-methoxy-5-(2́-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) nanotubules prepared in this manner were shown to have dramatically different properties in comparison with thin films due to increased molecular order in the nanostructures. With semicrystalline P3HT, the differences are much more subtle, we believe due to the greater inherent order in this material. In P3HT nanotubules, a small bathochromic shift (∼0.05 eV) in the onset of Uv–vis absorption was observed indicating increased long range order and a greater effective conjugation length in the polymer. Polarized FTIR spectroscopy indicated a small degree of preferential alignment of the inter-ring C–C bond with the axis of the nanotubules as the stretching vibration for this bond showed a dichroic ratio of 1.73. The degree of increased conjugation length and chain alignment in P3HT nanotubules indicated by both the UV–vis and polarized FTIR spectra were much smaller than that previously observed for MEH-PPV. No significant improvement in mobility as measured from the current voltage characteristics of simple single carrier devices based on the P3HT nanotubules was observed, in sharp contrast to previously studied MEH-PPV where more than an order of magnitude increase was seen. Unlike in amorphous MEH-PPV, the increase in molecular order suggested by spectral data was insufficient to significantly impact mobility of semicrystalline P3HT when using template wetting nanofabrication for either of the 100 or 200 nm nanotubules examined.

Electrical conductivity anisotropy of dry and hydrous olivine at 8 GPa

The effects of dissolved H 2O on the electrical conductivity and its anisotropy in olivine (Fo 90) at 8 GPa were investigated by complex impedance spectroscopy. At nominally anhydrous conditions, conduction along [1 0 0] and [0 0 1] is slightly higher than along [0 1 0] in contrast to observations made at lower pressures in earlier studies. Increasing H 2O content increases conductivities but activation energies are lower and H 2O concentration dependent. The use of polarized FTIR spectroscopy to determine H 2O concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non-polarized infrared spectroscopy. We show that at H 2O concentrations of a few hundred wt ppm or less, that the dominant conduction mechanism at mantle temperatures continues via small polarons, such as that observed for anhydrous olivine. Our results also suggest that at depths greater than 200 km, the presence of H 2O may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed. This can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes. However, while electrical anisotropy of anhydrous olivine remains weak at 8 GPa, it is nevertheless enhanced by elevated concentrations (>several hundred wt ppm) of dissolved H 2O. At these conditions dominated by proton hopping, conductivity along [0 1 0] is highest, approximately an order of magnitude greater than along [1 0 0]. Additionally, at 1000 wt ppm and 1500 °C, an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine. Thus, in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy, significant amounts of dissolved hydrogen can be expected.

Hexacoordinated Oligosilanes from a Hexacoordinated Silicon(IV) Complex Containing an O,N,N,O Salen-type and Thiocyanato-N Ligands

Two new neutral hexacoordinated silicon complexes with SiN(4)O(2) (6) and SiN(3)O(2)C (7) coordinating frameworks were synthesized by reaction of the O,N,N,O-donor salen-type ligand 1,2-bis[[(2-hydroxy-4-methoxyphenyl)(phenyl)methylene]amino]ethane (H(2)salen*) with Si(NCS)(4) and HMeSi(NCS)(2), respectively. The complexes 6 [Si(salen*)(NCS)(2)] and 7 [Si(salen*)Me(NCS)] were studied in the solid-state by (29)Si and (15)N CP/MAS NMR and in solution by (1)H, (13)C, and (29)Si insensitive nuclei enhanced by polarization transfer (INEPT) NMR, UV/vis and FT-IR spectroscopy. Elemental analysis and single-crystal X-ray diffraction analysis were used to confirm the composition and structure for compounds 6 and 7. Both complexes contain the dianionic salen-type ligand coordinated in an equatorial fashion to the silicon center, while the axial positions are occupied by two thiocyanato-N ligands for 6 and one thiocyanato-N and one methyl ligand for 7. Complex 6, which contains two Si-NCS functional groups, was used as monomer to produce a mixture of linear oligosilanes with a hexacoordinated silicon backbone (formulated SCN-[Si(salen*)](n)-NCS, n = 2-8) 8, via a Wurtz-type coupling reaction. Oligomers 8 were identified by solid-state (29)Si cross polarization-magic angle spinning NMR and solution (1)H and (29)Si NMR spectroscopy, matrix assisted laser desorption ionization-time of flight (MALDI-TOF), gel-permeation chromatography (GPC), FT-IR, UV/vis spectroscopy and thermogravimetric analysis (TGA). Conclusive evidence of the oligomeric nature of 8 was provided by MALDI-TOF spectrometry and was supported by quantitative solution (29)Si NMR and GPC studies.

A New Method for the Time-Resolved Analysis of Structure and Orientation: Polarization Modulation Infrared Structural Absorbance Spectroscopy

Polarization modulation infrared linear dichroism (PM-IRLD) is often used for measurements of molecular orientation with high sensitivity and good time resolution. However, PM-IRLD is unable to provide the structural absorbance spectrum because it does not measure separately the parallel and perpendicular spectra. Here we propose a new method, named polarization modulation infrared structural absorbance spectroscopy (PM-IRSAS), to overcome this limitation of PM-IRLD. PM-IRSAS measures the dichroic difference and structural absorbance spectra simultaneously and, therefore, allows quantitative analysis of molecular orientation and conformation with 200 ms time resolution. The PM-IRSAS method was first validated through comparison with conventional polarized FT-IR spectroscopy using drawn polymer films. Second, it was demonstrated that the PM-IRSAS method can provide a quantitative analysis of dynamic orientation and conformation changes in PET films during deformation and crystallization processes.

FTIR study of the structures of vapor deposited PMDA–ODA film in presence of copper phthalocyanine

Orientation structure of vacuum deposited thin layer polyimide matrix in presence of copper phthalocyanine as a “guest”, by means of polarization and derivative FTIR spectroscopy has been studied. The polymer layers (500 nm thick) prepared by vacuum co-deposition of polyimide precursors – oxydianiline and pyromellitic dianhydride and copper phthalocyanine (9%), followed by mixed treatment (microwave and thermal) have been investigated. The SEM investigation of layers that are microwave and thermally treated at temperatures 200 and 300 °C have no considerable difference in the surface structure. FTIR analysis of spectra in the range of molecular vibration 1300–700 cm −1 demonstrates that polyimide films thermally treated at 200 °C showed lower order structure than polyimide films treated at 300 °C. After derivatization of the polyimide spectra two bands at 1125 cm −1 and 1116 cm −1 have appeared which are related to two types C–N deformation vibration. The structure of the layers treated at higher temperature (300 °C) is higher order and is fixed in one plane (after derivatization single narrow band at 1114 cm −1 has appeared; the band at 903 cm −1 is missing). It was found that after microwave treatment the time of thermal treatment has no considerable influence. Preliminary microwave treatment allows reducing of the duration of thermal treatment.

Potential protonation sites in the Al2SiO5 polymorphs based on polarized FTIR spectroscopy and properties of the electron density distribution

Potential protonation sites for, kyanite, sillimanite, and andalusite, located in a mapping of the (3, −3) critical points displayed by their L(r) = −∇2ρ(r) distributions, are compared with polarized single-crystal FTIR spectra of kyanite and sillimanite determined earlier and with andalusite measured in this study. For andalusite, seven peaks were observed when the electric vector, E, is parallel to [100]: four intense ones at 3,440, 3,460, 3,526, and 3,597 cm−1 and three weaker ones at 3,480, 3,520, and 3,653 cm−1. Six peaks, three intense ones at 3,440, 3,460, and 3,526 cm−1 and three weaker ones at 3,480, 3,520, and 3,653 cm−1 when E parallels [010]. No peaks were observed when E is parallel to [001]. The concentration of water in andalusite varies between 110 and 168 ppm by weight % H2O. Polarized FTIR spectra indicate that the OH vector is parallel to (001) in andalusite and sillimanite and \( {\left( {11\ifmmode\expandafter\bar\else\expandafter\=\fi{1}} \right)} \) in kyanite. Examination of the L(r) (3, −3) critical points in comparison with the polarized FTIR indicates that H prefers to bond to the oxygen atoms O1 and O2 in andalusite and O2 and O4 in sillimanite which correspond to the underbonded oxygen atoms and those with the largest L(r) maxima. In kyanite, comparison of the FTIR spectrum and the critical points indicates that H will preferentially bond to the two 4-coordinated O2 and O6 atoms.