Jack L. Koenig

Raman Spectrum of Graphite

Raman spectra are reported from single crystals of graphite and other graphite materials. Single crystals of graphite show one single line at 1575 cm−1. For the other materials like stress‐annealed pyrolitic graphite, commercial graphites, activated charcoal, lampblack, and vitreous carbon another line is detected at 1355 cm−1. The Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k‐selection rule. The intensity of this band allows an estimate of the crystallite size in the surface layer of any carbon sample. Two in‐plane force constants are calculated from the frequencies.

A review of polymer dissolution

Abstract Polymer dissolution in solvents is an important area of interest in polymer science and engineering because of its many applications in industry such as microlithography, membrane science, plastics recycling, and drug delivery. Unlike non-polymeric materials, polymers do not dissolve instantaneously, and the dissolution is controlled by either the disentanglement of the polymer chains or by the diffusion of the chains through a boundary layer adjacent to the polymer–solvent interface. This review provides a general overview of several aspects of the dissolution of amorphous polymers and is divided into four sections which highlight (1) experimentally observed dissolution phenomena and mechanisms reported to this date, (2) solubility behavior of polymers and their solvents, (3) models used to interpret and understand polymer dissolution, and (4) techniques used to characterize the dissolution process.

The structure of γ-aminopropyltriethoxysilane on glass surfaces

Abstract The structure of γ-aminopropyltriethoxysilane (APS) has been studied in aqueous solution and as a solid using Fourier transform infrared spectroscopy. The monomeric aminosilane forms an internal cyclic chelate structure when hydrolyzed. Two vibrational bands have been found near 1575 and 1600 cm −1 in condensed aminopropylsiloxane polymer. The band at 1575 cm −1 is assigned to the NH 2 deformation mode of the acceptor amine groups involved in strong hydrogen bonding and the band at 1600 cm −1 is assigned to the NH 2 groups. Heat treatment causes the formation of nonring chain-structured aminosilanes. In the study of the structure of APS coupling agent on high-surface-area silica gel (Cab-O-Sil) and E-glass fibers, it was found that the aminosilane adsorbed on silica as essentially a monolayer and the amino group chemically interacted with the glass surface. The adsorbed APS on E-glass fiber exists as a multilayer, and formed a predominately cyclic ring structure in the coupling agent interphase.

Infrared and raman spectroscopy of carbohydrates. : Part II: Normal coordinate analysis of α-D-glucose.

Abstract A theoretical study of the vibrational spectra of α- D -glucose has been made by normal coordinate analysis. The predicted vibrational frequencies are compared with those observed in the infrared and Raman spectra of α- D -glucose, both as a crystalline solid and in aqueous solution. The computed potential-energy distribution shows that most of the modes are highly coupled vibrations. In most cases, this distribution is compatible with the experimental band-assignments, based on deuterium exchange methods, and the like. Overall, the agreement between the observed and calculated data is considered reasonably satisfactory for a molecule as large as α- D -glucose.

Infrared and raman spectroscopy of carbohydrates : Part IV. Identification of configuration- and conformation-sensitive modes for D-glucose by normal coordinate analysis

Abstract A theoretical study of the normal modes of vibration for D -glucose has been made by normal coordinate analysis. The calculated modes for β- D -glucose are shown to be in good agreement with the observed infrared and Raman frequencies, and the computed potential-energy distribution is compatible with previous experimental band-assignments. Lines at 840 cm−1 for α- D -glucose and at 898 cm−1 for the β-form, which are sensitive to the anomeric configuration, are predicted to occur at 845 and 901 cm−1, respectively. These two modes have been found to be similar, consisting essentially of a C-1-H deformation coupled to a mixed CH2 vibration. The band in the 1150 cm−1 region, which is characteristic of pyranose sugars, is predicted to be a complex ring-mode in each case. Also, the modes that are dependent upon the crystal structure for amylose and cellulose and occur at approximately 1432, 1334, and 1263 cm−1 are described as complex vibrations involving CH2, C-O-H, and C-C-H motions.

Infrared and raman spectroscopy of carbohydrates : Part III: raman spectra of the polymorphic forms of amylose

Abstract The Raman spectra of V a -, Vh h -, and B -amylose have been recorded, and are interpreted in terms of the proposed mechanism for conversion from the V- into the B-form. Lines occurring at 1263 and 946cm -1 with V-amylose shift to 1254 and 936 cm -1 on conversion into the B -form; at the same time intensity changes are observed for the lines at 2940 and 1334 cm -1 . These effects are consistent with the mechanism proposed for V→B conversion, involving an extension of the helix and changes in the intramolecular hydrogen-bonding. In addition, the spectra of amylose dissolved in aqueous salt solution and in methyl sulfoxide have been recorded. The results indicate that amylose does not adopt the V-conformation in methyl sulfoxide solution.

Application of Fourier Transform Infrared Spectroscopy to Chemical Systems

The advantages of Fourier transform infrared spectroscopy (FTIR) over dispersive infrared spectroscopy are outlined. The use of data processing with specific reference to difference spectroscopy is discussed in light of these advantages. Applications of FTIR to identification, quality control, and quantitative infrared analysis arc indicated. The use of difference spectroscopy to improve the quality of the spectra of the desired components is illustrated for a variety of chemical systems. The role of FTIR is thus illustrated in the analytical chemical laboratory.

An infrared study of phase‐III poly(vinylidene fluoride)

Infrared spectra representative of crystalline regions of cast films of phase‐III poly(vinylidene fluoride) (PVF2) have been obtained by absorbance subtraction techniques using a FT‐IR instrument. The spectra contain more bands than previously reported and are not consistent with current models for the crystal structure. Several possible models and their relationship to the corresponding crystalline spectra of phase II and phase I are discussed.

Orientational Measurements in Polymers Using Vibrational Spectroscopy

Abstract The mechanical properties of polymers are strongly influenced not only by the structure of the material but by the magnitude of the molecular orientation. Thus a great deal of interest exists in information about the molecular orientation in samples introduced by drawing or other forming processes. Several techniques of evaluation of this orientation exist such as birefringence, x-ray diffraction, sonic modulus, and fluorescence measurements [l, 2]. Vibrational analysis of oriented polymers provides a method of determining independently the molecular orientation both in the crystalline and amorphous phases of polymers. By using vibrational techniques, a number of macromolecules have been studied in the solid state for a variety of different processes. It is the purpose of this review to summarize the recent theoretical and experimental results which have occurred since the review of Zbinden [3]. Infrared and Raman measurements will be reported since they are complementary to each other in their a...

Magic-angle cross-polarization carbon 13 NMR study of aminosilane coupling agents on silica surfaces

Abstract The high-resolution solid-state carbon 13 nuclear magnetic resonance spectra of γ-aminopropyltriethoxysilane (APS) and N-2-aminoethyl-3-aminopropyltrimethoxysilane (AAPS) condensed as bulk polymers and adsorbed on glass surfaces have been investigated. It is shown that the 13 C NMR resonance peaks of the low-cured and high-cured polyaminopropylsiloxanes are chemically shifted from one to another. The hydrogen-bonded APS propyl chain produces an upfield shoulder on the central methylene carbon resonance peak in a cross polarization with magic-angle sample-spinning (CPMASS) experiment. Measurements of the chemical shifts of non-heat-treated and heat-treated APS/glass samples were also made and the chemical shift trends are discussed in terms of oriented and extended conformational effects of propyl units. Three molecular structure models of APS are proposed involving a hydrogen bonding interaction by the amine and SiOH groups. The chemical shifts induced by electric field effects on the β-carbon nucleus for different APS isomers have been calculated and the results agree with the observed resonances.