scholarly journals Silicon-Oxygen Region Infrared and Raman Analysis of Opals: The Effect of Sample Preparation and Measurement Type

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 173
Author(s):  
Neville J. Curtis ◽  
Jason R. Gascooke ◽  
Allan Pring
Keyword(s):  
Ir Spectroscopy ◽  
High Refractive Index ◽  
Structural Features ◽  
Longitudinal Optical ◽  
Attenuated Total Reflection ◽  
Silica Glasses ◽  
Specular Reflectance ◽  
Primary Means ◽  
Infrared Wavelengths ◽  
Non Destructive

An extensive infrared (IR) spectroscopy study using transmission, specular and diffuse reflectance, and attenuated total reflection (ATR) was undertaken to characterise opal-AG, opal-AN (hyalite), opal-CT and opal-C, focussing on the Si-O fingerprint region (200–1600 cm−1). We show that IR spectroscopy is a viable alternative to X-ray powder diffraction (XRD) as a primary means of classification of opals even when minor levels of impurities are present. Variable angle specular reflectance spectroscopy shows that the three major IR bands of opal are split into transverse optical (TO) and longitudinal optical (LO) components. Previously observed variability in powder ATR is probably linked to the very high refractive index of opals at infrared wavelengths, rather than heterogeneity or particle size effects. An alternative use of ATR using unpowdered samples provides a potential means of non-destructive delineation of play of colour opals into opal-AG or opal-CT gems. We find that there are no special structural features in the infrared spectrum that differentiate opal from silica glasses. Evidence is presented that suggests silanol environments may be responsible for the structural differences between opal-AG, opal-AN and other forms of opaline silica. Complementary studies with Raman spectroscopy, XRD and scanning electron microscopy (SEM) provide evidence of structural trends within the opal-CT type.

Accelerated Discovery of High-Refractive-Index Polyimides via First-Principles Molecular Modeling, Virtual High-Throughput Screening, and Data Mining

2019 ◽  
Author(s):  
Mohammad Atif Faiz Afzal ◽  
Mojtaba Haghighatlari ◽  
Sai Prasad Ganesh ◽  
Chong Cheng ◽  
Johannes Hachmann
Keyword(s):  
Data Mining ◽  
Refractive Index ◽  
High Throughput ◽  
First Principles ◽  
High Throughput Screening ◽  
Large Scale ◽  
Computational Study ◽  
High Refractive Index ◽  
Structural Features ◽  
Learning Program

<div>We present a high-throughput computational study to identify novel polyimides (PIs) with exceptional refractive index (RI) values for use as optic or optoelectronic materials. Our study utilizes an RI prediction protocol based on a combination of first-principles and data modeling developed in previous work, which we employ on a large-scale PI candidate library generated with the ChemLG code. We deploy the virtual screening software ChemHTPS to automate the assessment of this extensive pool of PI structures in order to determine the performance potential of each candidate. This rapid and efficient approach yields a number of highly promising leads compounds. Using the data mining and machine learning program package ChemML, we analyze the top candidates with respect to prevalent structural features and feature combinations that distinguish them from less promising ones. In particular, we explore the utility of various strategies that introduce highly polarizable moieties into the PI backbone to increase its RI yield. The derived insights provide a foundation for rational and targeted design that goes beyond traditional trial-and-error searches.</div>

scholarly journals Spectroscopy as a useful tool for the identification of changes with time in post-mortem vitreous humor for forensic toxicology purposes

2021 ◽  
Author(s):  
Anna Wójtowicz ◽  
Agata Mitura ◽  
Renata Wietecha-Posłuszny ◽  
Rafał Kurczab ◽  
Marcin Zawadzki
Keyword(s):  
Ir Spectra ◽  
Forensic Toxicology ◽  
Principal Component ◽  
Hierarchical Cluster ◽  
Vitreous Humor ◽  
Attenuated Total Reflection ◽  
Glass Slides ◽  
Added Benefit ◽  
Ft Ir ◽  
Non Destructive

AbstractVitreous humor (VH) is an alternative biological matrix with a great advantage of longer availability for analysis due to the lack of many enzymes. The use of VH in forensic toxicology may have an added benefit, however, this application requires rapid, simple, non-destructive, and relatively portable analytical analysis methods. These requirements may be met by Fourier transform infrared spectroscopy technique (FT-IR) equipped with attenuated total reflection accessory (ATR). FT-IR spectra of vitreous humor samples, deposited on glass slides, were collected and subsequent chemometric data analysis by means of Hierarchical Cluster Analysis and Principal Component Analysis was conducted. Differences between animal and human VH samples and human VH samples stored for diverse periods of time were detected. A kinetic study of changes in the VH composition up to 2 weeks showed the distinction of FT-IR spectra collected on the 1st and 14th day of storage. In addition, data obtained for the most recent human vitreous humor samples—collected 3 and 2 years before the study, presented successful discrimination of all time points studied. The method introduced was unable to detect mephedrone addition to VH in the concentration of 10 µg/cm3. Graphic abstract

scholarly journals Applications of neutron reflectometry in biology

2020 ◽  
Vol 236 ◽  
pp. 04002 ◽  
Author(s):  
Yuri Gerelli
Keyword(s):  
Thin Films ◽  
Structural Features ◽  
Neutron Reflectometry ◽  
Protein Films ◽  
Biologically Relevant ◽  
Buried Interfaces ◽  
Biological Thin Films ◽  
Non Destructive

Over the last 10 years, neutron reflectometry (NR) has emerged as a powerful technique for the investigation of biologically relevant thin films. The great advantage of NR with respect to many other surface-sensitive techniques is its sub-nanometer resolution that enables structural characterizations at the molecular level. In the case of bio-relevant samples, NR is non-destructive and can be used to probe thin films at buried interfaces or enclosed in bulky sample environment equipment. Moreover, recent advances in biomolecular deutera-tion enabled new labeling strategies to highlight certain structural features and to resolve with better accuracy the location of chemically similar molecules within a thin film. In this chapter I will describe some applications of NR to bio-relevant samples and discuss some of the data analysis approaches available for biological thin films. In particular, examples on the structural characterization of biomembranes, protein films and protein-lipid interactions will be described.

Quantitative non-destructive analysis of paper fillers using ATR-FT-IR spectroscopy with PLS method

2019 ◽  
Vol 411 (20) ◽  
pp. 5127-5138 ◽  
Author(s):  
Signe Vahur ◽  
Liisa Eero ◽  
Jaan Lehtaru ◽  
Kristina Virro ◽  
Ivo Leito
Keyword(s):  
Ir Spectroscopy ◽  
Destructive Analysis ◽  
Ft Ir ◽  
Non Destructive ◽  
Pls Method ◽  
Ft Ir Spectroscopy

Characterising the Morphology of Polymer Articles Using Polarised FTIR Reflectance and Raman Microscopies.

1997 ◽  
Vol 3 (S2) ◽  
pp. 839-840
Author(s):  
N.J. Everall ◽  
J.M. Chalmers
Keyword(s):  
Data Analysis ◽  
Molecular Orientation ◽  
Multivariate Calibration ◽  
Mechanical Performance ◽  
Raman Microscopy ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Specular Reflectance ◽  
Calibration Techniques ◽  
Polymer Crystallinity

The optical and mechanical performance of polymer articles is often very strongly influenced by the crystallinity and degree of molecular orientation in the polymer. It is therefore important to have available techniques for measuring and mapping these parameters over article surfaces and through wall thicknesses, on scales from centimetres to microns. It is also desirable that these techniques do not in themselves perturb the morphology of the polymer, for example by introducing excess orientation or crystallinity through sectioning.In this paper we will show how Raman microscopy can provided a useful approach for mapping polymer crystallinity on the micron scale, particularly when coupled with multivariate calibration techniques for data analysis. The acquisition and treatment of data to obtain crystallinity information will be described in detail. We will also describe the development and application of polarised FTIR specular reflectance and attenuated total reflection (ATR) microbeam techniques for quantifying and mapping surface orientation of polymer articles.

scholarly journals ATR-FTIR Spectroscopy, a New Non-Destructive Approach for the Quantitative Determination of Biogenic Silica in Marine Sediments

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 3927 ◽  
Author(s):  
Dora Melucci ◽  
Alessandro Zappi ◽  
Francesca Poggioli ◽  
Pietro Morozzi ◽  
Federico Giglio ◽  
...  
Keyword(s):  
Ftir Spectroscopy ◽  
Marine Sediments ◽  
Biogenic Silica ◽  
Standard Addition ◽  
Silica Content ◽  
Attenuated Total Reflection ◽  
Sediment Samples ◽  
Analyte Signal ◽  
Micro Organisms ◽  
Non Destructive

Biogenic silica is the major component of the external skeleton of marine micro-organisms, such as diatoms, which, after the organisms death, settle down onto the seabed. These micro-organisms are involved in the CO2 cycle because they remove it from the atmosphere through photosynthesis. The biogenic silica content in marine sediments, therefore, is an indicator of primary productivity in present and past epochs, which is useful to study the CO2 trends. Quantification of biosilica in sediments is traditionally carried out by wet chemistry followed by spectrophotometry, a time-consuming analytical method that, besides being destructive, is affected by a strong risk of analytical biases owing to the dissolution of other silicatic components in the mineral matrix. In the present work, the biosilica content was directly evaluated in sediment samples, without chemically altering them, by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Quantification was performed by combining the multivariate standard addition method (MSAM) with the net analyte signal (NAS) procedure to solve the strong matrix effect of sediment samples. Twenty-one sediment samples from a sediment core and one reference standard sample were analyzed, and the results (extrapolated concentrations) were found to be comparable to those obtained by the traditional wet method, thus demonstrating the feasibility of the ATR-FTIR-MSAM-NAS approach as an alternative method for the quantification of biosilica. Future developments will cover in depth investigation on biosilica from other biogenic sources, the extension of the method to sediments of other provenance, and the use higher resolution IR spectrometers.

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