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Dielectric properties of poly(vinylidene fluoride)-grafted-BaTiO3 (PVDF-g-BT) core-shell structured nanocomposites obtained from Reversible Addition Fragmentation chain Transfer (RAFT) polymerization of VDF were investigated by Broadband Dielectric Spectroscopy (BDS). The dielectric constant increased along with the BT content, about +50% by addition of 15 vol% of BT, which was around 40% more than expected from predictions using the usual dielectric modeling methods for composite materials, to be ascribed to the effect of the interfacial core-shell structure. The known dielectric relaxations for PVDF were observed for the neat polymer as well as for its nanocomposites, not affected by the presence of nanoparticles. A relaxation process at higher temperatures was found, due to interfacial polarization at the amorphous-crystalline interface, due to the high crystallinity of materials produced by RAFT. Isochronal BDS spectra were exploited to detect the primary relaxation of the amorphous fraction. Thermal analysis demonstrated a very broad endotherm at temperatures much lower than the usual melting peaks, possibly due to the ungrafted fraction of the polymer that is more easily removable by repeated washing of the pristine material with acetone.

Effective converse piezoelectric coefficient (d33,eff) mapping of poly(vinylidene fluoride) (PVDF) nanofibers with ceramic BaTiO3 nanoparticle inclusions obtained by electrospinning was carried out by piezoresponse force microscopy (PFM) in a peculiar dynamic mode, namely constant-excitation frequency-modulation (CE-FM), particularly suitable for the analysis of compliant materials. Mapping of single nanocomposite fibers was carried out to demonstrate the ability of CE-FM-PFM to investigate the nanostructure of semicrystalline polymers well above their glass transition temperature, such as PVDF, by revealing the distribution of piezoelectric activity of the nanofiber, as well as of the embedded nanoparticles employed. A decreased piezoelectric activity at the nanoparticle site compared to the polymeric fiber was found. This evidence can be rationalized in terms of a tradeoff between the dielectric constants and piezoelectric coefficients of the component materials, as well as on the mutual orientation of polar axes.

The free electron fraction is the fraction of electrons, produced inside the cavity of an ionization chamber after irradiation, which does not bind to gas molecules and thereby reaches the electrode as free electrons. It is a fundamental quantity to describe the recombination processes of an ionization chamber, as it generates a gap of positive charges compared to negative ones, which certainly will not undergo recombination.The free electron fraction depends on the specific chamber geometry, the polarizing applied voltage and the gas thermodynamic properties. Therefore, it is necessary to evaluate such fraction in an accurate and easy way for any measurement condition.In this paper, a simple and direct method for evaluating the free electron fraction of ionization chambers is proposed.We first model the capture process of the electrons produced inside an ionization chamber after the beam pulse; then we present a method to evaluate the free electron fraction based on simple measurements of collected charge, by varying the applied voltage. Finally, the results obtained using an Advanced Markus chamber irra-diated with a Flash Radiotherapy dedicated research Linac (ElectronFlash) to estimate the free electron fraction are presented.The proposed method allows the use of a conventional ionization chamber for measurements in ultra-high -dose -per-pulse (UHDP) conditions, up to values of dose -per-pulse at which the perturbation of the electric field due to the generated charge can be considered negligible.

Glycerol is one of the glass-forming liquids selected by Robert H. Cole in 1950 to start his study of molecular dynamics by dielectric spectroscopy. Seventy-one years have gone by and remarkably no consensus has been reached on the nature and identity of the relaxation processes observed in the dielectric spectra. The macroscopic dielectric relaxation data allow different interpretations to yield contrasting results, and it is not possible to determine which one is most plausible. Coming to the rescue is the application of the nuclear γ-resonance time-domain interferometry (TDI) to glycerol by Saito et al. [Phys. Rev. E 105, L012605 (2022)10.1103/PhysRevE.105.L012605]. Their microscopic TDI data potentially can decide which interpretation of the dielectric spectra of glycerol is most plausible. The attempt was made by Saito et al., but there is a problem in their analysis of the dielectric data of glycerol and hence their conclusion is untenable. In this paper, we critically compare four major interpretations with the TDI data in an effort to identify the most plausible interpretation of the relaxation processes constituting the dielectric spectra of glycerol.

Ultra-High dose -per-pulse regimens (UHDP), necessary to trigger the "FLASH" effect, still pose serious challenges to dosimetry. Dosimetry plays a crucial role, both to significantly improve the accuracy of the radiobiological experiments necessary to fully understand the mechanisms underlying the effect and its dependencies on the beam parameters, and to be able to translate such effect into clinical practice. The standard ionization chamber in UHDP region is significantly affected by the effects of the electric field generated by the enormous density of charges produced by the dose pulse.This work describes the theory and the conceptual design of a gas chamber (the ALLS chamber) which overcomes the above-mentioned problems.

Macromolecular crowding influences protein mobility and stability in vivo. A precise description of the crowding effect on protein thermal stability requires the estimate of the combined effects of excluded volume, specific protein-environment interactions, as well as the thermal response of the crowders. Here, we explore an ideal model system, the lysozyme protein in powder state, to dissect the factors controlling the melting of the protein under extreme crowding. By deploying state-of-the art molecular simulations, supported by calorimetric experiments, we assess the role of the environment flexibility and of intermolecular electrostatic interactions. In particular, we show that the temperature-dependent flexibility of the macromolecular crowders, along with specific interactions, significantly alleviates the stabilizing contributions of the static volume effect.

Recently, in polymeric liquids, unexpected solid-like shear elasticity has been discovered, which gave rise to a controversial discussion about its origin (1⇓–3). The observed solid-like shear modulus G depends strongly on the distance L between the plates of the rheometer according to a power law G ∝ L − p with a nonuniversal exponent ranging between p = 2 and p = 3 . Zaccone and Trachenko (4) have published an article in which they claim to explain these findings by a nonaffine contribution to the liquid shear modulus. The latter is represented as Δ G ∝ − ∑ λ = L , T 1 V … [↵][1]1To whom correspondence may be addressed. Email: giancarlo.ruocco{at}roma1.infn.it. [1]: #xref-corresp-1-1

The dielectric spectra of methyl m-toluate (MMT) in supercooled liquid and glassy states were measured over wide ranges of temperature T at ambient and elevated pressures P. We found that the frequency dispersion of the loss peak contributed by the structural α-relaxation is invariant to changes of P and T, while keeping the loss peak frequency fα(T,P) constant. This isochronal superposition property of the α-relaxation holds for different choices of fα(T,P). The invariant frequency dispersions for the same fα(T,P) are also indicated by the fractional exponent βKWW in the Fourier transform of the Kohlrausch-Williams-Watts (KWW) function. Similarly, the fragility m index of MMT keeps approximately constant on varying pressure, largely different from H-bonded glass formers. The secondary β-relaxation at a frequency higher than fα(T,P) is found to shift to lower frequencies by elevating pressure in concert with the α-relaxation. The ratio τα(T,P)/τβ(T,P) is approximately unchanged to variations of T and P while keeping τα(T,P) constant. These properties observed in MMT offer experimental evidence of the dynamic correlation between α- and β-relaxations in pure small-molecule glass-formers.

The correlation between the vibrational dynamics, as sensed by the Debye-Waller factor, and the primary relaxation in the presence of secondary Johari-Goldstein (JG) relaxation, has been investigated through molecular dynamics simulations. Two melts of polymer chains with different bond length, resulting in rather different strength of the JG relaxation are studied. We focus on the bond-orientation correlation function, exhibiting higher JG sensitivity with respect to alternatives provided by torsional autocorrelation function and intermediate scattering function. We find that, even if changing the bond length alters both the strength and the relaxation time of the JG relaxation, it leaves unaffected the correlation between the vibrational dynamics and the primary relaxation. The finding is in harmony with previous studies reporting that numerical models not showing secondary relaxations exhibit striking agreement with experimental data of polymers also where the presence of JG relaxation is known.

According to the Coupling Model (CM), secondary relaxation belonging to a special class has strong connection to the α-relaxation. These Johari-Goldstein (JG) β-relaxations are predicted to be ubiquitous, and its relaxation time is approximately equal to the primitive relaxation time and the surface diffusion time. These predictions cannot be tested directly in ethylcyclohexane (ECH) because the JG β-relaxation is unresolved and overlapping the α-relaxation to modify its dispersion. To capture the actual dispersion of the α-relaxation we considered surface diffusion data, adiabatic calorimetry data of the JG β-relaxation, and dielectric data of cyanocyclohexane (CNCH). We demonstrated the dispersion of the α-relaxation is actually narrower than known before. The primitive relaxation times calculated are now in agreement with τJG(T) and with τsurface(T), and in accord with the CM predictions.

International audience; The attainable lateral resolution of electrostatic force microscopy (EFM) in an ambient air environment on dielectric materials was characterized on a reference sample comprised of two distinct, immiscible glassy polymers cut in a cross-section by ultramicrotomy. Such a sample can be modeled as two semi-infinite dielectrics with a sharp interface, presenting a quasi-ideal, sharp dielectric contrast. Electric polarizability line profiles across the interface were obtained, in both lift-mode and feedback-regulated dynamic mode EFM, as a function of probe/surface separation, for different cases of oscillation amplitudes. We find that the results do not match predictions for dielectric samples, but comply well or are even better than predicted for conductive interfaces. A resolution down to 3 nm can be obtained by operating in feedback-regulated EFM realized by adopting constant-excitation frequency-modulation mode. This suggests resolution is ruled by the closest approach distance rather than by average separation, even with probe oscillation amplitudes as high as 10 nm. For better comparison with theoretical predictions, effective probe radii and cone aperture angles were derived from approach curves, by also taking into account the finite oscillation amplitude of the probe, by exploiting a data reduction procedure previously devised for the derivation of interatomic potentials.

We employ differential scanning calorimetry, IR spectroscopy, X-ray powder diffraction and dielectric spectroscopy to characterize binary mixtures of m-fluoroaniline (mFA), a rigid-molecule glass former, with two non-self-associating molecules containing benzene rings, namely m-xylene (mX) and a distyrene derivative (DS). The addition of mX suppresses the formation of H-bonded mFA clusters. While both mX and DS dilute the H-bond density of mFA, they have opposite effects on the glass transition temperature (Tg) and structural relaxation time of mFA, with mX acting as a plasticiser and DS as an antiplasticiser. While the mFA-DS mixtures can be studied in the supercooled liquid regime at DS molar mass fraction as high as 0.9 without undergoing phase separation, the mFA-mX mixtures remain homogeneous at low temperatures only up to a mX molar fraction of 0.5. All homogeneous mixtures display a structural relaxation which shifts according to the Tg of the mixture, and a secondary relaxation which remains virtually invariant with respect to that of pure mFA. For mX molar fraction higher than 0.5, the mixtures phase-separate into almost pure crystalline mX domains and a mFA-rich amorphous phase. Upon partial crystallization the structural relaxation time and Tg of the remaining amorphous fraction shift to larger values, consistent with the increased effective mFA concentration. At the same time, the secondary relaxation time undergoes a dramatic shift of more than two decades. These findings allow identifying the secondary relaxation in the rigid-molecule mFA glass former as a local reorientational motion of a m-fluoroaniline moiety around one of its H-bonds, a rotation that is strongly affected if the mobility of the H-bond sharing species is quenched by crystallization.

Determining the pressure dependence of dynamic moduli in unconsolidated sediments is still an open problem in applied geophysics. This is because several petrophysical parameters affect the elastic response of the granular medium during compression. Effective medium theories based on the Hertz–Mindlin contact law estimate the effective moduli from petrophysical parameters. Among them, the Pride and Berryman model assumes that new contacts between grains are progressively created during compression. Furthermore, the gaps around rattlers are distributed following a power law with distance and the global strain can change either linearly or quadratically with the local strain. This identifies two types of strain accumulation. Quadratic strain accumulation is associated with grain rotation. We simplified this model by assuming a flat distribution of gaps around rattlers and we applied this simplified model to published ultrasonic measurements. By means of these measurements, we studied how the strain-accumulation mechanism affects the coordination number during isotropic compression. The coordination numbers were estimated by applying a DEM-based correction to the average-strain model. We observe that the majority of the experimental trends lay between the linear and the quadratic accumulation trends. Based on this result, we assume that the strain accumulation is a combination of the two mechanisms and we propose a formula to estimate the contribution of each mechanism. Furthermore, we note that, in the studied datasets, rotation affects larger grains (diameter approximately 500 μm) more than smaller grains (diameter approximately 100 μm). If further validated, this correlation could guide the determination of pressure trends for sands.

In recent years, there is a growing interest in improving the physicochemical stability of amorphous pharmaceutical solids due to their very promising applications to manufacture medicines characterized by a better water solubility, and consequently by a higher dissolution rate than those of their crystalline counterparts. In this review article, we show that the molecular mobility investigated both in the supercooled liquid and glassy states is the crucial factor required to understand molecular mechanisms that govern the physical stability of amorphous drugs. We demonstrate that pharmaceuticals can be thoroughly examined by means of the broadband dielectric spectroscopy, which is a very useful experimental technique to explore different relaxation processes and crystallization kinetics as well. Such studies conducted in the wide temperature and pressure ranges provide data needed in searching correlations between properties of molecular dynamics and crystallization process, which are aimed at developing effective and efficient methods for stabilizing amorphous drugs.

Two solubility limited pharmaceuticals bezafibrate and fenofibrate, belonging to BCS class II drugs, were compared, by investigating molecular dynamics of the former and compared with the neat and as a probe in an apolar host polystyrene of mole. wt. 800 (PS800) of the latter by broadband dielectric spectroscopy (BDS), other supporting thermal and spectroscopic experimental means and density functional theory (DFT) calculations. The BDS experiments from frozen glassy state to vibrant molten state of the title drugs were done to explore the role of parameters describing their complex molecular dynamics and the stabiliy of amorphous phase, such as glass transition temperature (Tg), temperature dependence of α-relaxation times (τα), width of structural dispersion and its role on the occurrence of Johari-Goldstein (JG) β-relaxation, fragility index (m) and apparent activation energy of secondary processes. Realizing that most of the pharmaceuticals have narrow α-dispersion which limits the visibility of JG β-relaxation as a separate process in the dielectric window, to resolve the conundrum, we have further explored the amorphous dynamics of fenofibrate as a probein an apolar host polystyrene of molecular weight 800 (PS800) having higher Tg than the polar probe. The Tg of bezafibrate and PS800-fenofibrate mixture were determined to be 298 K and 275 K respectively, whereas the fractional exponent of Kohlrausch–Williams–Watts function βKWW of bezafibrate was determined to be 0.68 which is closer to that of fenofibrate, whereas that of PS800-fenofibrate mixture was found to be much broader with a value of 0.39, all in the vicinity of Tg. Even though βKWW decreased in binary mixture of fenofibrate when compared to its pure form due to concentration fluctuations and other aspects, but cold crystallization tendency was absent and Tg is elevated than that of fenofibrate. Due to higher Tg than that of fenofibrate, amorphous bezafibrate is more stable than fenofibrate. Finally, using quantum computational calculations using DFT, the relevant flexible parts of the two drug molecules, whose motions manifests the secondary γ-relaxation was identified by calculating potential energy barriers and dipole moments on relaxed dihedral angle scans, as no experimental technique is available for this purpose.

Adopting an agnostic approach, the quality factor Q of tantala glass is drawn via in silico mechanical spectroscopy in wide ranges of temperature (10-300 K) and frequency (500 MHz

Cangialosi and co-workers found two steps in the enthalpy recovery deep in the glassy state of high and low molecular weight bulk polystyrene (PS). We attribute the first step to the segmental α-relaxation and the second step to the sub-Rouse modes and explain the two-step enthalpy recovery by the dynamic properties of the two processes in bulk PS by the coupling model (CM). The two-step enthalpy recovery was found in nanometer thin films of polystyrene (PS). On decreasing film thickness h, the first step was shifted to much lower temperature than the second step, and the effect is explained by the segmental α-relaxation shifting to lower temperature much more than the sub-Rouse modes, as predicted by the CM. Furthermore, the dependences of the faster and slower processes of the two-step enthalpy relaxation on film thickness are analogues of two effects observed on decreasing h of freestanding polystyrene films. One effect is the observation of two transitions by ellipsometry. We associated the lower tran...

Although by now the glass transition temperature of uncrystallized bulk water is generally accepted to manifest at temperature T near 136 K, not much known are the spectral dispersion of the structural alpha-relaxation and the temperature dependence of its relaxation time tau_alpha-bulk(T). Whether bulk water has the supposedly ubiquitous Johari-Goldstein (JG) beta-relaxation is a question that has not been answered. By studying the structural alpha-relaxation over a wide range of temperatures in several aqueous mixtures without crystallization and with glass transition temperatures T close to 136 K, we deduce the properties of the alpha-relaxation and the temperature dependence of tau_alpha(T) of bulk water. The frequency dispersion of the alpha-relaxation is narrow, indicating that it is weakly cooperative. A single Vogel-Fulcher-Tammann (VFT) temperature dependence can describe the data of tau_alpha(T) at low temperatures as well as at high temperatures from neutron scattering and GHz-THz dielectric relaxation, and hence, there is no fragile to strong transition. The T-scaled VFT temperature dependence of tau_alpha(T) has a small fragility index m less than 44, indicating that water is a "strong" glass-former. The existence of the JG beta-relaxation in bulk water is supported by its equivalent relaxation observed in water confined in spaces with lengths of nanometer scale and having Arrhenius T-dependence of its relaxation times tau_conf(T). The equivalence is justified by the drastic reduction of cooperativity of the alpha-relaxation in nanoconfinement and rendering it to become the JG beta-relaxation. Thus, the tau_conf(T) from experiments can be taken as tauJG_bulk(T), the JG beta-relaxation time of bulk water. The ratio tau_alphaBulk(Tg)/tau_betaBulk(Tg) is smaller than most glass-formers, and it corresponds to the Kohlrausch alpha-correlation function, exp[-(t/tau_alphaBulk)^(1-n)], having (1-n) = 0.90. The dielectric data of many aqueous mixtures and hydrated biomolecules with T higher than that of water show the presence of a secondary nu-relaxation from the water component. The nu-relaxation is strongly connected to the alpha-relaxation in properties, and hence, it belongs to the special class of secondary relaxations in glass-forming systems. Typically, its relaxation time tau_nu(T) is longer than tau_betaBulk(T), but tau_nu(T) becomes about the same as tau_betaBulk(T) at sufficiently high water content. However, tau_nu(T) does not become shorter than tau_betaBulk(T). Thus, tau_betaBulk(T) is the lower bound of tau_nu(T) for all aqueous mixtures and hydrated biomolecules. Moreover, it is tau_betaBulk(T) but not tau_alpha(T) that is responsible for the dynamic transition of hydrated globular proteins.

Influence of different factors on nematic alignment and relaxation dynamics in supercooled mixture of liquid crystals E7 was investigated by means of dielectric and rheo-dielectric spectroscopy. Results show that elevated pressure or application of strong oscillatory shear aligned the nematic director parallel to the electrodes. On the other hand, if after the shear treatment a static electric field is applied an alignment of the nematic director perpendicular to the electrodes is even better than in the sample quenched and aligned by bias field without the shear treatment.

The relaxation dynamics in two van der Waals bonded liquids and one hydrogen-bonding molecular liquid are studied as a function of pressure and temperature by incoherent neutron scattering using simultaneous dielectric spectroscopy. The dynamics are studied in a range of alpha relaxation times from pico- to milliseconds, primarily in the equilibrium liquid state. In this range, we find that isochronal superposition and density scaling work not only for the two van der Waals liquids but also for the hydrogen-bonding liquid, though the density scaling exponent is much smaller for the latter. Density scaling and isochronal superposition are seen to break down for intra-molecular dynamics when it is separated in time from the alpha relaxation, in close agreement with previous observations from molecular dynamics simulations.

Summary Pride and Berryman (2009) proposed a model to predict pressure dependence of effective elastic bulk modulus for unconsolidated sediments, by progressively allowing the creation of new contacts during compression. They assume that the gaps around rattlers are distributed according to a power law with distance, in addition, the model allows two different strain-accumulation mechanisms: linear or quadratic, the latter being associated with grain rotation ( Goddard, 1990 ). We have observed that the model of Pride and Berryman can be simplified without losing its generality, assuming a flat distribution of gaps around rattlers, given appropriate values for the maximum gap. We have used this simplified model to study how the strain-accumulation mechanism affects the coordination number during isotropic compression. We tested our model on sand data from Zimmer (2003). We observed that the majority of the experimental trends lay between the pure linear and the pure quadratic accumulation trends. We conclude that the strain accumulation in unconsolidated sediments can be well described as a combination of the two mechanisms. We noted also that rotation affects larger grains (diameter approx. 500 micron) more than smaller grains (diameter approx. 100 micron).

Secondary relaxations with properties closely related to the α-relaxation have fundamental importance in glass-forming substances including polymers. To distinguish these secondary relaxations from those involving intramolecular degrees of freedom, they are called the Johari–Goldstein (JG) β-relaxations. Acting as the precursor of the α-relaxation, the JG β-relaxation is supposedly ubiquitous in all glass-formers, a thesis supported by experiments on a variety of glass-formers. Notwithstanding, the JG β-relaxation has not been identified definitively in the hydroxyl-terminated polypropylene glycols (PPGs) with various molecular weights, despite these polymers have been intensively studied experimentally in the last several decades. The difficulty of finding the JG β-relaxation is due to the presence of a faster intramolecular γ-relaxation and a slower relaxation originating from residual water. This is demonstrated in two recent papers by Gainaru et al. Macromolecules 2010, 43, 1907, and Kaminski et al. M...

Mixtures of methyltetrahydrofuran (MTHF) with tristyrene and high molecular weight polystyrene involve an exceptionally large difference in the glass transition temperatures of the two components not realized in other binary mixtures studied before. The extensive study of the molecular dynamics of these mixtures by various experimental techniques by Blochowicz et al. has revealed the presence of a new α'-relaxation not found before in other mixtures and also the more familiar α- and β-relaxations, but their properties are more extreme. Attention was focused on the new α'-relaxation by Blochowicz et al. in interpreting it to originate from MTHF in confinement and explaining its properties by the Mode Coupling Theory. In a different direction, we concentrate on the highly unusual properties of the α- and β-relaxations. Earlier, we had success in explaining the properties of these two relaxations and their connection in other mixtures by the coupling model. In this paper, we apply the same model to explain the highly unusual dynamics of the α- and β-relaxations found in the mixtures of MTHF with tristyrene and polystyrene. Possible relation between the α'- and the β-relaxations also is explored.

In this article we report on the design, manufacture and testing of a high-pressure cell for doing simultaneous dielectric and neutron spectroscopy. This cell is a unique tool for studying dynamics on different timescales, from kilo- to picoseconds, covering universal features such as the alpha relaxation and fast vibrations at the same time. The cell, constructed in cylindrical geometry, is made in high-strength aluminum alloy and operates up to 500 MPa in a temperature range between roughly 2 and 320 K. In order to measure the scattered neutron intensity and the sample capacitance simultaneously, a cylindrical capacitor is positioned within the bore of the high-pressure container. The capacitor consists of two concentric electrodes separated by insulating spacers. The performance of this setup has been successfully verified by collecting simultaneous dielectric and neutron spectroscopy data on dipropylene glycol, using both backscattering and time-of-flight instruments. We have carried out the experiments at different combinations of temperature and pressure in both supercooled liquid and glassy state., A.S. and H.W.H. contributed equally to this work

One fundamental challenge in biophysics is to understand the connection between protein dynamics and its function. Part of the difficulty arises from the fact that proteins often present local atomic motions and collective dynamics on the same time scales, and challenge the experimental identification and quantification of different dynamic modes. Here, by taking lyophilized proteins as the example, we combined deuteration technique and neutron scattering to separate and characterize the self-motion of hydrogen and the collective interatomic motion of heavy atoms (C, O, N) in proteins on the pico-to-nanosecond time scales. We found that hydrogen atoms present an instrument-resolution-dependent onset for anharmonic motions, which can be ascribed to the thermal activation of local side-group motions. However, the protein heavy atoms exhibit an instrument-resolution-independent anharmonicity around 200 K, which results from unfreezing of the relaxation of the protein structures on the laboratory equilibrium time (100-1000 s), softening of the entire bio-macromolecules.

In a series of papers on binary glass-forming mixtures of tripropyl phosphate (TPP) with polystyrene (PS), Kahlau et al. [J. Chem. Phys. 140, 044509 (2014)] and Bock et al. [J. Chem. Phys. 139, 064508 (2013); J. Chem. Phys. 140, 094505 (2014); and J. Non-Cryst. Solids 407, 88-97 (2015)] presented the data on the dynamics of the two components studied over the entire composition range by several experimental methods. From these sets of data, obtained by multiple experimental techniques on mixtures with a large difference ΔTg ≈ 200 K between the glass transition temperatures of two starting glass formers, they obtained two α-relaxations, α1 and α2. The temperature dependence of the slower α1 is Vogel-Fulcher like, but the faster α2 is Arrhenius. We have re-examined their data and show that their α2-relaxation is the Johari-Goldstein (JG) β-relaxation with Arrhenius T-dependence admixed with a true α2-relaxation having a stronger temperature dependence. In support of our interpretation of their data, we made dielectric measurements at elevated pressures P to show that the ratio of the α1 and α2 relaxation times, τα1(T,P)/τα2(T,P), is invariant to variations of T and P, while τα1(T,P) is kept constant. This property proves unequivocally that the α2-relaxation is the JG β-relaxation, the precursor of the α1-relaxation. Subsequently, the true but unresolved α2-relaxation is recovered, and its relaxation times with much stronger temperature dependence are deduced, as expected for the α-relaxation of the TPP component. The results are fully compatible with those found in another binary mixture of methyltetrahydrofuran with tristyrene and PS with ΔTg ≈ 283 K, even larger than ΔTg ≈ 200 K of the mixture of TPP with PS, and in several polymer blends. The contrast between the two very different interpretations brought out in this paper is deemed beneficial for further progress in this research area.

The relaxation dynamics in two van der Waals bonded liquids and one hydrogen-bonding molecular liquid are studied as a function of pressure and temperature by incoherent neutron scattering using simultaneous dielectric spectroscopy. The dynamics are studied in a range of alpha relaxation times from pico- to milliseconds, primarily in the equilibrium liquid state. In this range, we find that isochronal superposition and density scaling work not only for the two van der Waals liquids but also for the hydrogen-bonding liquid, though the density scaling exponent is much smaller for the latter. Density scaling and isochronal superposition are seen to break down for intra-molecular dynamics when it is separated in time from the alpha relaxation, in close agreement with previous observations from molecular dynamics simulations.

Atomic force microscopy (AFM) allows profiling of solid surfaces with nanometer-scale resolution. For characterization of interphases, the transition region can be imaged by suitable sample preparation, exposing a cross-sectional surface by, for example, cleavage or cutting by microtomy. A variety of different properties can be measured along with topography that may indicate different materials or phases on the sectioned surface. Electrical properties of interfaces can be investigated by AFM-based electrostatic probes, namely, Kelvin probe microscopy for contact potential difference and electrostatic force microscopy for surface charge density, capacitance, and dielectric permittivity. All such distinctive properties can be characterized at the interface with state-of-the-art spatial resolution of 20-30 nm. Buried interfaces can also be detected, facilitating, for instance, the study of nanocomposites. Local dielectric spectroscopy (electrical permittivity as a function of frequency) can be probed to monitor changes of materials properties like glass transition across an interface section. In this chapter, AFM electrostatic probes will be described, and examples of application to interphase characterization will be shown.

Evaluating abnormal pore pressure (overpressure zones) is a major safety issue in well drilling for oil and gas exploration. Nevertheless, presently, the problem of assessing the dependence of elastic moduli with pressure in unconsolidated media is still an open question even for the simple case of dry materials and packing of identical spherical grains. This is because the effective medium theory (EMT) based on the Hertz-Mindlin contact theory fails to predict the measured trend in laboratory data. To overcome this issue, we test a modified grain contact theory (GCT) model that fits elastic moduli with pressure proposed by Saul et al. (2013). We optimized this method by allowing a non linear relation between the calibration parameter and porosity and a simpler relation between pressure and porosity. We show that this model can predict the Vp and Vs pressure trends using published laboratory datasets by performing a blind test on Santa Cruz agglomerate samples.

Measurements of several metallic glasses under strain reveal that the materials relieve stress through a two-step process that has previously been seen only in “softer” glasses.

When the thickness is reduced to nanometer scale, freestanding high molecular weight polymer thin films undergo large reduction of degree of cooperativity and coupling parameter n in the Coupling Model (CM). The finite-size effect together with the surfaces with high mobility make the a-relaxation time of the polymer in nanoconfinement, tau(nano)(alpha)(T), much shorter than tau(bulk)(alpha)(T) in the bulk. The consequence is avoidance of vitrification at and below the bulk glass transition temperature, T-g(bulk), on cooling, and the freestanding polymer thin film remains at thermodynamic equilibrium at temperatures below T-g(bulk). Molecular dynamics simulations have shown that the specific volume of the freestanding film is the same as the bulk glass-former at equilibrium at the same temperatures. Extreme nanoconfinement renders total or almost total removal of cooperativity of the alpha-relaxation, and tau(nano)(alpha)(T) becomes the same or almost the same as the JG beta-relaxation time tau(bulk)(beta)(T) of the bulk glass-former at equilibrium and at temperatures below T-g(bulk). Taking advantage of being able to obtain tau(bulk)(beta)(T) at equilibrium density below T-g(bulk) by extreme nanoconfinement of the freestanding films, and using the CM relation between tau(bulk)(alpha)(T) and tau(bulk)(beta)(T), we conclude that the Vogel-Fulcher-Tammann-Hesse (VFTH) dependence of tau(bulk)(alpha)(T) cannot hold for glass-formers in equilibrium at temperatures significantly below T-g(bulk). In addition, tau(bulk)(alpha)(T) does not diverge at the Vogel temperature, T-0, as suggested by the VFTH-dependence and predicted by some theories of glass transition. Instead, tau(bulk)(alpha)(T) of the glass-former at equilibrium has a much weaker temperature dependence than the VFTH-dependence at temperature below T-g(bulk) and even below T-0. This conclusion from our analysis is consistent with the temperature dependence of tau(bulk)(alpha)(T) found experimentally in polymers aged long enough time to attain the equilibrium state at various temperatures below T-g(bulk).

A simple experimental method for piezoresponse force microscopy (PFM) measurements for reliable evaluation of piezoelectric surface displacements even on compliant surfaces is proposed based on atomic force microscopy (AFM) operated in frequency-modulation (FM) dynamic mode with constant excitation (CE), by using non-contact mode cantilevers. Surface displacement by piezoelectric effect after application of an electric potential to the conductive AFM probe translates into a likewise variation of the probe oscillation amplitude, while the related electrostatic forces mainly affect the oscillator resonant frequency, and cantilever bending is limited due to their high stiffness. Our non-contact CE-FM-PFM method is shown to reduce electrostatic force contributions as compared to contact-PFM modes. Converse piezoelectric effect mapping is demonstrated on poly(vinylidenefluoride) nanofibers obtained by electrospinning.

The research of dynamics of protein is predominantly focused on the hydrated or solvated state, which is close to the physiological condition of biological relevance. Eclipsed by the hydrated and solvated counterparts, the dynamics of dry proteins are seldom studied in earnest. Studied occasionally, the data of dry proteins were not addressed, possibly due to the preconceived notion that dry proteins are bio inactive, and thus are uninteresting and unimportant. Actually lyophilized dry proteins are important for the pharmaceutical industry as the therapeutic proteins are often stored in lyophilized conditions to achieve long-term stability, which is of direct connection to the dynamics of protein in dry state. In order to uncover the intrinsic dynamics of dry proteins that previous studies overlooked or ignored, we analysed quasielastic neutron scattering, Mossbauer, and Brillouin light scattering data of various dry proteins. We demonstrate the existence of a novel transition of the dry protein dynamics at temperatures around 200 K, with the exact value dependent on the kind of protein. The transition temperature of dry proteins is found here independent of the time/frequency of the measurement, in stark contrast to the well-documented dynamical transition observed in hydrated proteins, the temperature of which is strongly depending on the time window probed experimentally. In addition we point out that this transition in dry proteins is analogous to those observed before in the glassy state of various glass-forming materials, the origin of which is the change of the caged molecule dynamics in response to the change of the temperature dependence of density when crossing the secondary glass transition temperature Tgβ for the Johari-Goldstein β-relaxation. We show that the transition of various dry proteins also occurs around Tgβ, thus suggesting that the underlying microscopic mechanism is the same as the one identified and explained before for many glass-formers of different types. The presence of the transition is independent of the trace amount of water in supposedly dry proteins, although the value of Tgβ can vary somewhat. The novel transition in dry proteins has impact on bio-pharmaceutical research and applications because of the connection to the Johari-Goldstein β-relaxation, which can affect long-term stability of lyophilized dry proteins.

The dynamic transition found by Mossbauer spectroscopy and neutron scattering in hydrated and solvated proteins has been an active research area for the past three decades. By now a consensus among some researchers has been reached that it originates exclusively from relaxation of the hydration water (HW) coupled to the protein. The dynamic transition temperature Td depends on energy resolution of the spectrometer and is higher than the glass transition temperature Tg. Recently demonstrated is the presence of yet another transition at Tg, which is independent of the resolution of the spectrometer and coexists with the dynamic transition at a higher temperature Td. The transition at Tg is similar to that found in various kinds of glass-formers by neutron and dynamic light scattering at short times when molecules are mutually caged via the intermolecular potential. Like in the case of conventional glass-formers, the transition at Tg of hydrated proteins has been explained by the sensitivity of the extent of the caged dynamics to change of specific volume and entropy on crossing Tg. The caged dynamics are terminated by the onset of relaxation of HW, which in turn gives rise to the dynamic transition at Td > Tg. Despite these important roles played by the caged dynamics and the HW relaxation in the observed dual transitions of the hydrated proteins, their exact nature is still unclear. In this paper we clarify their nature in hydrated proteins by use of various experimental data, with the assist of the results from studies of mixtures of water with hydrophilic solutes, taking advantage of the fact that the properties are similar in both systems.

We investigate by thorough Molecular Dynamics simulations the thermodynamic scaling (TS) of a polymer melt. Two distinct models, with strong and weak virial-energy correlations, are considered. Both evidence the joint TS with the same characteristic exponent $\gamma_{ts}$ of the fast mobility - the mean square amplitude of the picosecond rattling motion inside the cage -, and the much slower structural relaxation and chain reorientation. If the cage effect is appreciable, the TS master curves of the fast mobility are nearly linear, grouping in a bundle of approximately concurrent lines for different fragilities. An expression of the TS master curve of the structural relaxation with one adjustable parameter less than the available three-parameters alternatives is derived. The novel expression fits well with the experimental TS master curves of thirty-four glassformers and, in particular, their slope at the glass transition, i.e. the isochoric fragility. For the glassformer OTP the isochoric fragility allows to satisfactorily predict the TS master curve of the fast mobility with no adjustments.

We probe the temperature- and pressure-dependent specific volume (v) and dipolar dynamics of the amorphous phase (in both the supercooled liquid and glass states) of the ternidazole drug (TDZ). Three molecular dynamic processes are identified by means of dielectric spectroscopy, namely the α relaxation, which vitrifies at the glass transition, a Johari-Goldstein βJG relaxation, and an intramolecular process associated with the relaxation motion of the propanol chain of the TDZ molecule. The lineshapes of dielectric spectra characterized by the same relaxation time (isochronal spectra) are virtually identical, within the studied temperature and pressure ranges, so that the time-temperature-pressure superposition principle holds for TDZ. The α and βJG relaxation times fulfil the density-dependent thermodynamic scaling: master curves result when they are plotted against the thermodynamic quantity Tv γ , with thermodynamic exponent γ approximately equal to 2. These results show that the dynamics of TDZ, a system characterized by strong hydrogen bonding, is characterized by an isomorphism similar to that of van-der-Waals systems. The low value of γ can be rationalized in terms of the relatively weak density-dependence of the dynamics of hydrogen-bonded systems.

The effect of confinement on structural relaxation in ultrathin poly(vinyl acetate) films has been studied by local dielectric spectroscopy. This scanning probe method allows the investigation of dielectric relaxation at nanometer scale of supported ultrathin films having a free surface. Measurements have been performed at ambient pressure and controlled atmosphere on films with decreasing thickness. A deviation of dynamic properties from the bulk behavior, showing up as an increase of the relaxation rate, was observed starting from film thickness of 35 nm, which corresponds to about 3 times the gyration radius of polymer chains. A 2-fold increase of relaxation rate was measured for the thinnest investigated film of 18 nm. Local dielectric spectroscopy is therefore an effective method to elucidate confinement effects on relaxation dynamics in ultrathin polymer films with a free upper surface.

Orientationally disordered (OD) mixed crystals formed between cyanoadamantane (CN-A) and chloroadamantane (Cl-A) have been thermodynamically characterized by means of thermal analysis and X-ray diffraction. The dynamics of these OD mixed crystals has been studied by means of broad band dielectric spectroscopy. Results evidence that dynamics of the α-relaxation process associated with the overall molecular tumbling slows down when molecules of CN-A are substituted by molecules of Cl-A.

In this Letter, we present results of dielectric measurements of water-propylene glycol oligomer mixtures at ambient and high pressure. The ? relaxation process that emerges with the addition of water exhibits unexpected behavior at elevated pressure. These features indicate local motions of water molecules as the origin of this relaxation process. In addition, we observe a pressure-induced change of the dynamics in the water-related relaxation; such a crossover occurs near the glass transition of the mixture and significantly differs from properties observed for confined water.