Electron Diffraction of Water in No Man's Land

A generally accepted understanding of the anomalous properties of water will only emerge if it becomes possible to systematically characterize water in the deeply supercooled regime, from where the anomalies appear to emanate. This has largely remained elusive because water crystallizes rapidly between 160 K and 232 K. Here, we present an experimental approach to rapidly prepare deeply supercooled water at a well-defined temperature and probe it with electron diffraction before crystallization occurs. We show that as water is cooled from room temperature to cryogenic temperature, its structure evolves smoothly, approaching that of amorphous ice just below 200 K. Our experiments narrow down the range of possible explanations of the origin for the water anomalies and open up new avenues for studying supercooled water

Flash Melting Amorphous Ice

Water can be vitrified if it is cooled at rates exceeding $3*10^5$ K/s. This makes it possible to outrun crystallization in so-called no man's land, a range of deeply supercooled temperatures where water crystallizes rapidly. One would naively assume that the process can simply be reversed by heating the resulting amorphous ice at a similar rate. We demonstrate that this is not the case. When amorphous ice samples are flash melted with a microsecond laser pulse, time-resolved electron diffraction reveals that the sample transiently crystallizes despite a heating rate of more than $5*10^6$ K/s, demonstrating that the critical heating rate for outrunning crystallization is significantly higher than the critical cooling rate during vitrification. Moreover, we observe different crystallization kinetics for amorphous solid water (ASW) and hyperquenched glassy water (HGW), which suggests that the supercooled liquids formed during laser heating transiently retain distinct non-equilibrium structures that are associated with different nucleation rates. These experiments open up new avenues for elucidating the crystallization mechanism of water and studying its dynamics in no man's land. They also add important mechanistic details to the laser melting and revitrification process that is integral to the emerging field of microsecond time-resolved cryo-electron microscopy.Comment: arXiv admin note: text overlap with arXiv:2211.0441

In situ studies of phase transitions in rapidly annealed metallic glasses and properties of obtained composites using ultrafast experimental techniques

Metallic glasses (MGs) are very attractive for structural applications due to their large elastic strain, high strength and hardness, resulting from their unique atomic structure. However, MGs are brittle. Preparing metallic glass–crystal composites (MGCCs) from parent glass through thermal treatment is a useful method to induce ductility and work hardening. Thus, besides the direct applications of as-prepared MGs, the glasses can be used as a starting material to be processed, for example, by thermoplastic forming or thermal treatment to design components with desired shape and/or properties. In this view, it is of high importance to know the phase- transformation mechanisms and kinetics upon heating MGs, especially for rapid heating, which has not been sufficiently studied yet. CuZrAl-based alloys, with near CuZr equimolar compositions, are suitable for producing MGCCs with improved plasticity owing to their good glass-forming ability and the formation of ductile B2 CuZr phase upon crystallization. However, the crystallization mechanism(s) and products have mainly been elucidated by extrapolating the available knowledge of the binary CuZr system. In the present work, a set of complementary techniques including resistive (Joule) heating, in situ high-energy synchrotron X-ray diffraction, conventional and ultrafast differential scanning calorimetry and containerless solidification during electromagnetic levitation is used to map the phase evolution ― crystallization and solid-state phase transformations ― in Cu₄₇.₅Zr₄₇.₅Al₅, Cu₄₇.₅Zr₄₈Al₄Co₀.₅ and Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MGs during isokinetic and isothermal annealing. The resistive heating devices, custom-built at the Leibniz Institute for Solid State and Materials Research Dresden – IFW Dresden, enable heating rates Φ to range from 10¹ up to 10⁵ K s⁻¹ in a vacuum. Using the obtained experimental data, continuous-heating-transformation (CHT) diagrams for a heating rate range exceeding six orders of magnitude, covering the entire supercooled liquid region, and time-temperature-transformation (TTT) diagrams are constructed. The transformation maps reveal the competition between the Cu₁₀Zr₇, B2 CuZr and τ4 (Cu₂ZrAl) phases during crystallization. The formation of the primary phase and transformation sequence depends on the MG composition as well as on the heating rate. The critical heating rate to bypass the crystallization increases from ~30 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG to ~40 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG and to ~90 000 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, reflecting their glass-forming ability. The optimum heating rate to obtain glass–crystal composites with the predominant and desired B2 CuZr phase is evaluated to be Φ > 1 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG, Φ > 1 500 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, and Φ > 4 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG. Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG shows an increased propensity for the formation of brittle Cu₁₀Zr₇ intermetallic phase, compared to Cu₄₇.₅Zr₄₇.₅Al₅ and Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MGs. The TTT diagram for the isothermal heating of Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ shows an apparent double-nose shape which corresponds to the primary crystallization of Cu₁₀Zr₇ at lower temperatures and B2 CuZr at higher temperatures

The Role of Nuclear Quantum Effects in Supercooled Water and Amorphous Ice

Water is one of the most important substances on Earth and plays a fundamental role in numerous scientific and engineering applications. Interestingly, water behaves much differently than other liquids. For example, water shows an anomalous density maximum at 277 K, the solid phase (ice) is less denser than the liquid, and its thermodynamic response functions, such as the specific heat CP and isothermal compressibility κT, also increase anomalously upon cooling. In the glassy state, water can exist in two different forms, low-density and high-density amorphous ice (LDA and HDA). While water has been scrutinized for many centuries, the origin for the anomalous thermodynamic and dynamical properties of liquid and glassy water are not fully understood. A scenario that explains water anomalous behavior is provided by the liquid-liquid phase transition hypothesis (LLPT). The LLPT hypothesis postulates that water at low temperature can exist as two distinct liquids, a low-density and a high-density liquid (LDL and HDL), that are separated by a first-order phase transition line that ends at a liquid-liquid critical point (LLCP). The LLPT hypothesis is currently the explanation best-supported by experiments and computational studies. Most computational studies that focused on the phase behavior of liquid and glassy water have been performed using classical molecular dynamics simulations where nuclear quantum effects (NQE) are neglected. This can be troublesome because water is a light molecule and NQE are known to influence the structural and dynamic properties of water even at ambient conditions. For example, in H2O and D2O, the temperature of the density maxima, glass transition temperature and melting temperature are shifted by δT = 4 − 10 K, a clear sign of NQE. We note that classical MD simulations can not be used to study isotope effects (H2O and D2O) because in this technique the water O and H atoms are modeled as point particles that interact with other water molecules through electrostatic and short range interactions. In order to incorporate NQE in computer simulations one must use path integral techniques such as path integral molecular dynamics (PIMD) or path integral Monte Carlo (PIMC). In this dissertation, I will discuss results from extensive PIMD simulations using the q-TIP4P/F water model in order to explore the behavior of H2O and D2O at low temperature, including the supercooled liquid and glass states. I will show that our PIMD simulations indicate that H2O and D2O, both exhibit a LLCP at low temperatures, implying that the LLPT hypothesis is still valid when NQE are taken into account. In particular, while the phase diagram we have obtained from our PIMD simulations for H2O and D2O are qualitatively similar, NQE shift the LLCP for H2O towards lower temperatures and pressures, consistent with estimations from experiments in glassy water. I will also show that while PIMD simulations of q-TIP4P/F water can reproduce some of the thermodynamic, dynamic, and structural properties of light and heavy water remarkably well, there are notable exceptions between our simulations and experiments. For example, the CP(T) and κT(T) from our PIMD simulations deviate from experiments at low temperatures, implying that introducing NQE does not necessarily reproduce the density and entropy fluctuations observed experimentally in supercooled water. After discussing the results we have obtained from our PIMD simulations for supercooled water, I will then discuss the results I have obtained for glassy water from PIMD simulations. Our PIMD simulations show that NQE play a relevant role for glassy water at low temperatures. For example, we find from our PIMD simulations that the density of LDA and ice Ih indicate the presence of a density maximum at low temperatures, while MD simulations show that the density of LDA and ice Ih to increase monotonically upon isobaric cooling

On the glass transition of bulk and confined polyamorphic liquids: A molecular dynamics simulations study

Supercooled liquids and the glass transition are not satisfactorily understood to date. The temperature dependence of dynamical properties eludes theoretical prediction. No model can be successfully applied to all liquids. One liquid is particularly complex in its supercooled regime - water. This seemingly simple liquid exhibits the most anomalies of any neat liquid, and most of these are thought to be related to the existence of two distinguishable liquid phases with different density in the supercooled regime, i.e., water exhibits polyamorphism. However, most of the relevant temperature range lies in the so-called no-man's land, a region of the phase diagram in which bulk water rapidly crystallizes and which is therefore experimentally inaccessible to the bulk liquid. Therefore, experimental studies often exploit the fact that crystallization of water is suppressed in nanoscopic confinements or water mixtures. The present work deals with both areas of research, water's polyamorphism and dynamics of supercooled liquids, confined and mixed, with the use of molecular dynamics simulations. They allow for detailed analysis and systematic variation of the liquid and enable easy supercooling. Partial charges of the TIP4P/2005 and SPC/E water models were scaled which led to strong shifts of dynamics in temperature. These were reconciled by using the high-temperature activation energy as the relevant energy scale as long as structural properties were the same. For the TIP4P/2005 model and a set of reduced charges, isochore crossing in the phase diagram confirmed the existence of a liquid-liquid critical point (LLCP) in the supercooled regime at positive or negative pressures, depending on the molecular polarity. The two-structure equation of state (TSEOS) formalism was used to describe the data and determine the location of the LLCP. In addition, reduction of the partial charges accelerated dynamics at the LLCP and simulations with elongated boxes in the double metastable regime allowed for the coexistence of high-density (HDL) and low-density (LDL) liquid phases and the determination of their dynamics as a function of temperature. The results are in agreement with observations from isochoric and isobaric simulations and translational motion was observed for all state points. It was found that the temperature dependence of the dynamics at a constant fraction of the low-density state (LDS) is Arrhenius-like. Thus, the presumed fragile-to-strong transition (FST) of water is not caused by a transition from fragile HDL to strong LDL but by the fast transition between these liquid states when the system is cooled through the Widom line at constant pressure. This is consistent with experimental observations slightly above water's glass transition temperature Tg and reinforces the question of whether HDL or LDL on their own exhibit an FST. Models for the temperature dependence of reactive mixtures were tested but were unable to describe simulation results at the lowest studied temperatures. A family of functional forms for the temperature dependence of dynamical properties of supercooled liquids was derived. These functions allow their description over the entire temperature range from the boiling point to the glass transition and with or without an FST. The second-order functions predict a high and low-temperature Arrhenius regime connected by an intermediate fragile regime. Knowledge of the path in the phase diagram of charge-scaled water-like systems, whether they cross the Widom line at increased charges or not, allowed for more rigorous testing of these functional forms. They are sensitive to deviations from Vogel-Fulcher-Tammann (VFT) behavior and apply well to data from charge-scaled water and silica simulations, which have a pronounced FST, as well as to real liquids. The possibility that supercooled liquids in general have a low-temperature Arrhenius regime and the characteristics of such FSTs were discussed. Simulations of charge-scaled water models in chemically neutral pores were performed and static and dynamic length scales associated with changes of water's structure and dynamics near the pore wall were extracted. These correlation lengths were used to test theories of the glass transition and discussed in the context of water's two phases. Signs of crossing the Widom line could not be found in the temperature dependence of the correlation lengths within the moderately supercooled temperature range. The slowdown at the pore wall relative to the pore center was characterized using two empirical functions for additional activation energies caused by the liquid-confinement interface. Furthermore, the potential energy landscape (PEL) imprinted on the liquid was quantified using a novel approach based on Boltzmann statistics and predicted and measured mobility gradients are in agreement. Lastly, the origin of slow solvent processes observed in dielectric spectroscopy studies of dynamically asymmetric binary mixtures was determined in simulations. For mixtures of picoline and poly-methylmethacrylate and of water and polylysine, fractions of slow solvent molecules were not found. Instead, the PEL imprinted by the slow polymer molecules causes preferred locations and orientations for the solvent molecules. A mechanism was proposed in which the solvent molecules exchange fast compared to the relaxation of the polymer molecules but have correlated orientations. This causes long-lived cross correlations that can be misinterpreted as slow solvent contributions in coherent measurements. Other sources of cross correlations were quantified and the dependency on measured molecular property and correlation function were discussed. The dynamical heterogeneity of solvent dynamics was traced back to the variation of the local solvent concentration and it is broad but unimodal. The same observations, slowly decaying cross correlations and absence of self correlation on these time scales, were made for other binary mixtures, suggesting that these effects are relevant to a wide range of systems

Synthesis, Relaxation Dynamics and Rheology of Supramolecular Polymers

A supramolecular polymer is a complex assembly of molecules held together by noncovalent bonds, such as hydrogen bonding, host-guest interactions or coordinative bonds. The last few decades great developments have been made in the research and application of supramolecular polymers, and a wide variety of supramolecular polymers have been prepared. These supramolecular polymers have been applied within many application areas, especially for medical applications such as drug or DNA delivery into living cells, and controlled drug release. However, many fundamental aspects such as the relaxation dynamics and rheological properties over a wide temperature range as well as the detailed structure-properties relationships are still not well understood for supramolecular polymers. This thesis addresses this, and aims at a better understanding of how the supramolecular interactions affect the structure, relaxation dynamics and rheological properties of different supramolecular polymer systems over a wide timescale or temperature range ranging from the glassy to the melt states. The goal is to determine the structure-property relationships, and to provide guidelines for the design and synthesis of new supramolecular polymers. In this thesis, the dynamics of four different supramolecular polymers are investigated. The first system is based on a comb-like polymeric backbone of poly(2-ethylhexyl acrylate) (PEHA) to which a random distribution of 2-ureido-4[1H]-pyrimidinone (UPy) supramolecular side-groups are added. A series of polymers with varying side-group UPy contents have been synthesised using the reversible addition fragmentation chain transfer (RAFT) polymerization. The second system is based on poly(propylene glycol) (PPG) for which the chain ends were functionalised using supramolecular hydrogen-bonding UPy-groups. The unfunctionalized PPG is a viscous liquid at room temperature whereas the end-functionalised UPyPPG is a rubbery material due to the formation of long extended chains formed through multiple hydrogen bonds. For this supramolecular polymer system, we have investigated two possible application areas: (i) the use of blends of PPG and UPyPPG with lithium salts in polymer electrolytes for Li-ion batteries and (ii) the use together with UV curable components for self-healing coatings. The third system is based on hydroxyl-capped polytetrahydrofuran (PTHF) with varying molecular weights and the fourth is a set of alkane diols of different chain-length. For both these systems, intermolecular supramolecular hydrogen bond interactions via the chain-ends will become more important for shorter chains. Generally, the relaxation dynamics, thermodynamic response and rheological response were determined using a range of experimental techniques, including broadband dielectric relaxation spectroscopy, differential scanning calorimetry (both in the standard and modulated mode), shear and extensional rheology and nuclear magnetic resonance relaxometry

Ultrafast Hydration Dynamics Near Extended Macromolecular Interfaces

Liquid water is arguably the most complex, but interesting chemical, enabling development and sustenance of life. The tetrahedral geometry of the water molecule allows the formation of a dense network of hydrogen bonds which undergoes rapid fluctuations at picosecond timescales. This ultrafast making and breaking of hydrogen bonds near an extended macromolecular interface may govern various biochemical kinetics, such as enzymatic activity, protein folding and membrane formation and disruption. Having a better understanding of interfacial hydration dynamics has implications to tune enzymatic activity, design targeted drugs and develop efficient desalination techniques. This dissertation elucidates the complex origin of the slowdown in hydration dynamics near the interfaces of micelle, protein and polymer. To completely capture the timescale and perturbation of hydration dynamics by an extended interface, surface charge cannot be excluded. Using the thiocyanate anion (SCN–) as a vibrational probe in the infrared and in conjunction with magnetic resonance spectroscopy, we find that the thiocyanate anion strongly associates with an interfacial model system of dodecyltrimethylammonium bromide (DTAB) micelles. Ultrafast two-dimensional infrared (2D-IR) spectroscopy of the SCN– probe in a range of DTAB micelle sizes shows little if any size dependence to the time scale for spectral diffusion, which is found to be ~3.5 times slower compared to bulk water (both D2O and H2O). We conclusively find that the SCN– spectral dynamics in cationic micelles is largely dominated by hydration contributions and offers a promising probe for interfacial hydration near positively charged interfaces. Graph theoretical analysis of water hydrogen bond network is implemented to map its network topology obtained using molecular dynamic simulations in confined protein (Hen Egg White Lysozyme) geometries. The observed power-law dependence for average path length on system size reveals that the bulk hydrogen bond networks cannot be considered random, but rather consists of a giant lattice-like component. At small protein separations (5-10 Å) with reduced hydrogen bond connectivity, similar global network structures are observed, indicating the maintenance of a completely unperturbed network topology. A Monte Carlo simulation on square lattices devoid of surface heterogeneity of real proteins reveals that the slowdown in hydration dynamics falls off exponentially near flat interfaces and converges within 2-3 shells with no evidence of cooperative effects. However, we conclusively find that protein surface residues become significantly slow when crowded and remains decoupled with interfacial hydration dynamics. The long-range collective influences by an interface may be due to complex chemical patterning of the surface. Poly(ethylene oxide) is well known for its water structuring ability and bio-compatibility by forming strong a rigid hydration shell. In small poly(ethylene oxide) polymers, high charge density cations slaves PEG-200 to adopt a cyclic conformation, even at low salt concentrations. Probing the CN stretching frequency of the thiocyanate counter anion shows significantly slow spectral diffusion (~5-fold) time scale offering evidence for direct interactions between the polymer and cations contrary to currently accepted water mediated mechanism. The lack of correlation with the Hofmeister ordering of the cations implies that PEG-cation interactions are highly specific. While complete maintenance of bulk-like dynamics in concentrated DNA duplex confirms weak DNA-water interactions. The diverse range of dynamical timescales for water fluctuations near macromolecular interfaces may require simultaneous probing of chemical groups present on macromolecular interfaces and water directly, a feat that is now possible using the recently developed broadband mid-infrared light source.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149890/1/vproy_1.pd

Enhancement and maximum in the isobaric specific-heat capacity measurements of deeply supercooled water using ultrafast calorimetry

Significance The importance of molecular understanding of the structure, dynamics. and properties of liquid water is recognized in many scientific disciplines. Here, we study experimentally the structure and thermodynamics of bulk liquid water as it is supercooled by evaporation down to ∼228 K. The unique aspect of this work is the use of ultrafast calorimetry that enables us to determine the specific-heat capacity of water to unprecedentedly low temperatures. The observed maximum of about 218 J/mol/K at 229 K is consistent with the liquid–liquid critical point model and supports a proposed fragile-to-strong transition at ∼220 K to explain the steep decrease in the estimated self-diffusion coefficient below 235 K.</jats:p