Something about amber: Fictive temperature and glass transition temperature of extremely old glasses from copal to Triassic amber

Observation of Boson Peak of Fragile Baltic Amber Glass by Terahertz Time-Domain Spectroscopy

Amber is a fragile (in Angell's classification) natural glass that has performed maturation processes over geological time. The terahertz dynamics of Baltic amber that was about 40 million years old were studied by terahertz time-domain spectroscopy (THz-TDS) in the frequency range of 0.2 and 6.0 THz. In general, the intensity of a boson peak is weak for fragile glass. In the terahertz transmission spectra of Baltic amber in the previous study, no boson peak was observed upon slow cooling. However, in the present study, upon rapid cooling down to 15 K, the boson peak was observed clearly at 0.36 THz by the suppression of ice nucleation of confined water. The dynamic correlation length determined by the boson peak frequency was compared with the static structure correlation length and the scale of the medium-range order as determined by the first sharp diffraction peak of X-ray diffraction (XRD) in the recent literature. It was found that the dynamic correlation length determined by THz-TDS was closely related to the static correlation length determined by the XRD analysis.

Pressure dependence of intermediate-range order and elastic properties of glassy Baltic amber

Amber is a unique example of a fragile glass that has been extensively aged below its glass transition temperature, thus reaching a state that is not accessible under normal experimental conditions. We studied the medium-range order of Baltic amber by x-ray diffraction (XRD) at high pressures. The pressure dependences of the low-angle XRD intensity between 0 and 5 Å^{-1} were measured from 0 to 7.3 GPa by the energy-dispersive XRD. The first diffraction peak at 1.1 Å^{-1} and ambient pressure has a doublet structure consisting of the first sharp diffraction peak (FSDP) at 1.05 Å^{-1} and the second feature at 1.40 Å^{-1}. The peak position and the width of the FSDP increase as the pressure increases, while the intensity of the FSDP decreases. Below P_{0}=2.4 GPa, the rapid increase of the FSDP peak position was observed, while above P_{0}, the gradual increase was observed. Below P_{0}, voids and holes in a relatively low-density state are suppressed, whereas above P_{0}, the suppression becomes mild. Such a change suggests the crossover from the low- to high-density state at P_{0}. There is a close correlation between the pressure dependence of XRD and previously reported sound velocity results. The correlation between the mean-square fluctuation of the shear modulus on the nanometer scale and fragility in amber and other glass formers is also discussed.

Highly stable petroleum pitches provide access to the deep glassy state

Differential scanning calorimetry (DSC) was used to study the fast aging behavior of two petroleum pitch materials despite being only three to five years old. We observe that these highly aromatic pitches with broad distributions of both molecular weight and aromaticity exhibit large enthalpic relaxation endotherms in initial DSC heating scans, and 20-32 °C reductions in the fictive temperature and 0.35-0.87 of θK, which are indicative of aged glasses similar to ultrastable glasses and 20 MA aged amber. Quantifying the degree of thermodynamic stability relative to the Kauzmann temperature vs. the aging time demonstrates that these materials age just as quickly as low fragility metallic glasses. Additionally, we observe that pitches age faster than polymers reported in the literature when compared using down-jump experiments. We hypothesize that the fraction of higher aromaticity of pitch molecules plays a crucial role in faster dynamics. The unique aging behavior and the ability to produce pitches in bulk quantities using pilot-scale equipment, while being possible to tailor their molecular composition, make them a useful material for studying complex aging dynamics in the deep glassy state.

The overview of analytical methods for studying of fossil natural resins

The review presents methods that are used frequently for multi-analytical study of fossil resins. The preliminary characterization relies on physical methods such as microhardness, density and fluorescence in UV light measurements. The spectroscopic methods: infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy are also presented in the paper. Besides that, the review also contains examples of the application of chromatographic methods: gas chromatography, thin layer chromatography, high-performance liquid chromatography, two-dimensional gas chromatography coupled to time-of-flight mass spectrometry as well as sample preparation methods for chromatographic studies such as pyrolysis. Additionally, thermal methods such as thermogravimetric analysis and differential scanning calorimetry also are covered by the review. Beside the examples of application, a detailed description with development history and perspective for further improvement are presented for each method. Moreover, fit-for-purpose assessment of each method is illustrated based on many examples from literature. The paper also contains examples of the application of multivariate statistical analysis and chemometric methods for comparing multiple properties of different fossil resin specimens for differentiation and classification purposes.

Recent developments in using the molecular decay dating method: a review

The dating of organic findings is a fundamental task for many scientific fields. Radiocarbon dating is currently the most commonly used method. For wood, dendrochronology is another state‐of‐the‐art method. Both methods suffer from systematic restrictions, leading to samples that have not yet been able to be dated. Molecular changes over time are reported for many materials under different preservation conditions. Many of them are intrinsically monotonous. These monotonous molecular decay (MD) patterns can be understood as clocks that start at the time when a given molecule was formed. Factors that influence these clocks include input material composition and preservation conditions. Different wood species, degrees of pyrolysis, and pretreatments lead to different prediction models. Preservation conditions might change the speed of a given clock and lead to different prediction models. Currently published models for predicting the age of wood, paper, and parchment depend on infrared spectroscopy. In contrast to radiocarbon dating, dating via MD does not comprise a single methodology. Some clocks may deliver less precise results than the others. Ultimately, developing a completely different, new dating strategy‐such as MD dating–will help to bring to light a treasure trove of information hidden in the darkness of organic findings.

Chemical and spectroscopic signatures of resins from Sumatra (Sarolangun mine, Jambi Province) and Germany (Bitterfeld, Saxony-Anhalt)

Fossil resins from Miocene coal deposit (Sarolangun mine, Jambi Province, Sumatra, Indonesia) have been analysed using spectroscopic methods: Raman Spectroscopy (RS), Fourier Transform-Infrared Spectroscopy (FT-IR), ¹³C Nuclear Magnetic Resonance (¹³C NMR), Fluorescence Spectroscopy (FS), and Gas Chromatography-Mass Spectrometry (GC-MS) in order to describe their diagnostic features. Simultaneously, glessite, a fossil resin from Upper Oligocene Bitterfeld deposit (Saxony-Anhalt, Germany), originating from similar botanical sources (i.e. angiosperms) was tested with the same analytical methods in order to find similarities and differences between the resins. The resins differ in colour, transparency and amounts of inclusions (resins from Sumatra-yellow, and transparent with few inclusions; glessite-brown-red, translucent with wealth of inclusions). In general, the IR and RS spectra of these resins are very similar, probably because the glessite colour-changing additives can be very subtle and non-observable in the infrared region. The RS spectra revealed also a slight difference in intensity ratio of the 1650/1450 cm^-1 bands (0.56 and 0.68 for Sumatra and Germany resins, respectively), indicating a differences in their maturation process. The resins from Sumatra seem to be more mature than glessite from Germany. The excitation-emission (EM-EX) and synchronous spectra showed unique, chemical compositions of these resins, which are different one from another. The GC-MS data for Sumatran resins, dominated by sesquiterpenoids and triterpenoids (amyrin), confirmed their botanical origin (angiosperms as their biological affinities). The sesquiterpenoid biomarkers with cadine-structures suggested the glessite underwent more advanced polymerization processes, which does not correlate with its RS spectrum. The geological factors, the environmental conditions of resin deposition, and later various diagenesis processes may have influenced the maturation and crosslinking of compounds. Despite the genetic similarity of the resins from various part of the world, Sumatra and Germany, advanced techniques such as Gas Chromatography-Mass Spectrometry and Fluorescence Spectroscopy were the most useful to find the differences between them. These differences are predominantly a result of different diagenetic transformations of the resins.

Fossil Resins–Constraints from Portable and Laboratory Near-infrared Raman Spectrometers

Comparative studies of fossil resins of various ages, botanical sources, geological environments, and provenience were provided via a handheld portable Near-Infrared (NIR)-Raman spectrometer and benchtop instrument both working with laser line 1064 nm. The recorded Raman spectra of individual fossil resins were found to be sufficiently similar irrespective to the device type applied, i.e., handheld or benchtop. Thus, the portable equipment was found to be a sufficient tool for the preliminary identification of resins based on botanical and geographical origin criteria. The observed height ratio of 1640/1440 cm−1 Raman bands did not correlate well with the ages of fossil resins. Hence, it may be assumed that geological conditions such as volcanic activity and/or hydrothermal heating are plausible factors accelerating the maturation of resins and cross-linking processes.

A simple mean-field model of glassy dynamics and glass transition

We propose a phenomenological model to describe the equilibrium dynamic behavior of amorphous glassy materials. It is assumed that a material can be represented by a lattice of cooperatively re-arranging regions (CRRs), with each CRR having two states, the low-temperature "solid" and the high-temperature "liquid". At low temperatures, the material exhibits two characteristic relaxation times, corresponding to the slow large-scale motion between the "solid" CRRs (α-relaxation) and the faster local motion within individual CRRs (β-relaxation). At high temperatures, the α- and β-relaxation times merge, as observed experimentally and suggested by the "Coupling Model" framework. Our new approach is labeled "Two-state, two (time)scale model" or TS2. It is shown that the TS2 treatment can successfully describe the "two-Arrhenius" relaxation time behavior described in several recent experiments. We also apply TS2 to describe the pressure- and molecular-weight dependence of the glass transition temperature in bulk polymers, as well as its dependence on film thickness in thin films.

LOOKING AT THE GLASS TRANSITION: CHALLENGES OF EXTREME TIME SCALES AND OTHER INTERESTING PROBLEMS

The behavior of glass-forming materials is examined with emphasis on the below-glass transition behavior. A major question that is related to the super-Arrhenius behavior of the dynamics of glass-forming systems is whether the apparent divergence at finite temperature continues below the kinetic or laboratory glass transition that is related to the limits of measurement and is standardized so that the material relaxation time is near 100 s. The problem arises because as the temperature decreases, the time scales required to reach equilibrium (or metastable equilibrium) become geologically long. Yet the apparent finite temperature divergence is fundamental to many theories of glasses; therefore, it becomes essential to find ways to finesse the extreme time scales related to the so-called Kauzmann paradox to bring new information to the ongoing conversation concerning the existence or not of an ideal glass transition at either the Kauzmann temperature or the Vogel–Fulcher–Tammann temperature. After describing the framework of the glassy state that is formed by the early ideas of a fictive temperature, we examine the use of extremely low fictive temperature glasses as a means to potentially get around the long time-scale problem. The challenge is to find ways to create such glasses and measure their properties. In addition to looking at the dynamic behavior of a 20-million-year-old amber and a vapor-deposited amorphous perfluoropolymer whose fictive temperature was the same as the Kauzmann temperature for the material, we also examine the possibility of directly testing the thermodynamics of an ideal glass transition by making athermal solutions of a poly(α-methyl styrene) and its pentamer, where we find that the entropy surface determined from extrapolation of the heat capacity to zero pentamer shows no distinct transition at as much as 180 K below the Kauzmann temperature. The significance of the dynamics of the stable glasses and the thermodynamics of the polymer solutions is discussed in terms that challenge the idea of an ideal glass transition. We also look in more detail at the ability to use vapor deposition to make ethylbenzene, a small-molecule organic, into an ultra-stable glass with a fictive temperature that is possibly below the Kauzmann temperature of this material. We end with remarks on the question of decoupling of different relaxation mechanisms as something not treated by current theories of glass, and we consider some open questions related to the fact that the glass transition remains an unresolved and important problem.

Tracking the Connection between Disorder and Energy Landscape in Glasses Using Geologically Hyperaged Amber

Fossil amber offers the unique opportunity to investigate an amorphous material that has been exploring its energy landscape for more than 110 million years of natural aging. By applying different X-ray scattering methods to amber before and after annealing the sample to erase its thermal history, we identify a link between the potential energy landscape and the structural and vibrational properties of glasses. We find that hyperaging induces a depletion of the vibrational density of states in the terahertz region, also ruling the sound dispersion and attenuation properties of the corresponding acoustic waves. Critically, this is accompanied by a densification with structural implications different in nature from that caused by hydrostatic compression. Our results, rationalized within the framework of fluctuating elasticity theory, reveal how upon approaching the bottom of the potential energy landscape (9% decrease in the fictive temperature) the elastic matrix becomes increasingly less disordered (6%) and longer-range correlated (22%).

Testing the paradigm of an ideal glass transition: Dynamics of an ultrastable polymeric glass

A major challenge to understanding glass-forming materials is obtaining equilibrium data far below the laboratory glass transition temperature T _g. The challenge arises because it takes geologic aging times to achieve the equilibrium glassy state when temperatures are well below T _g. Here, we finesse this problem through measurements on an ultrastable amorphous Teflon with fictive temperature T _f near to its Kauzmann temperature T _K. In the window between T _f and T _g, the material has a lower molecular mobility than the equilibrium state because of its low specific volume and enthalpy. Our measurements show that the determined scaled relaxation times deviate strongly from the classical expectation of divergence of time scales at a finite temperature. The results challenge the view of an ideal glass transition at or near to T _K.