Pretransition Effects Research Articles

Exact pretransition effects in kinetically constrained circuits: Dynamical fluctuations in the Floquet-East model.

We study the dynamics of a classical circuit corresponding to a discrete-time version of the kinetically constrained East model. We show that this classical "Floquet-East" model displays pre-transition behavior which is a dynamical equivalent of the hydrophobic effect in water. For the deterministic version of the model, we prove exactly (i) a change in scaling with size in the probability of inactive space-time regions (akin to the "energy-entropy" crossover of the solvation free energy in water), (ii) a first-order phase transition in the dynamical large deviations, (iii) the existence of the optimal geometry for local phase separation to accommodate space-time solutes, and (iv) a dynamical analog of "hydrophobic collapse."

Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic, and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry.

High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity c_{p}(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase (N_{F}) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (N_{x}). From the detailed data of h(T) and c_{p}(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (x_{DIO}). The x_{DIO} dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N_{x}-N transition of DIO was as low as L=0.0075±0.0005J/g and L=0.23±0.03J/g for the N_{F}-N_{x} transition, which is about twice the previously reported value of 0.115 J/g for the N_{F}-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x_{DIO}. At all the N_{x}-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N_{F} to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c_{p}(T) resulted in an effective critical exponent α=0.88±0.1 for DIO and this value decreased in the mixtures with decreasing x_{DIO} toward α=0.50±0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.

Nonlinear Dielectric Effect in the Vicinity of Solid–Liquid Phase Transition of 1-Decanol

The motivation to perform nonlinear dielectric effect (NDE) experiments in the vicinity of the freezing–melting region of 1-decanol was the intention to observe a pretransition anomaly in supercooled liquid, similar to that announced already for nitrobenzene. In the case of 1-decanol the pretransition effects related to supercooling were not observed, but we found interesting NDE behavior in the solid state approaching the melting temperature. To our best knowledge, it is the first time that NDE was measured in the solid state close to solid–liquid phase transition. In our opinion, the observed behavior could be interpreted as an effect of appearance of the rotator phase and premelting.

Solvation in Space-time: Pretransition Effects in Trajectory Space.

We demonstrate pretransition effects in space-time in trajectories of systems in which the dynamics displays a first-order phase transition between distinct dynamical phases. These effects are analogous to those observed for thermodynamic first-order phase transitions, most notably the hydrophobic effect in water. Considering the (infinite temperature) East model as an elementary example, we study the properties of "space-time solvation" by examining trajectories where finite space-time regions are conditioned to be inactive in an otherwise active phase. We find that solvating an inactive region of space-time within an active trajectory shows two regimes in the dynamical equivalent of solvation free energy: an "entropic" small solute regime in which uncorrelated fluctuations are sufficient to evacuate activity from the solute, and an "energetic" large solute regime which involves the formation of a solute-induced inactive domain with an associated active-inactive interface bearing a dynamical interfacial tension. We also show that as a result of this dynamical interfacial tension there is a dynamical analog of the hydrophobic collapse that drives the assembly of large hydrophobes in water. We discuss the general relevance of these results to the properties of dynamical fluctuations in systems with slow collective relaxation such as glass formers.

Pre-Transition Effects Mediate Forces of Assembly between Transmembrane Proteins: Recent Results on the Orderphobic Effect

Pre-Transition Effects Mediate Forces of Assembly between Transmembrane Proteins: Recent Results on the Orderphobic Effect

Pre-transition effects mediate forces of assembly between transmembrane proteins.

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order-disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to this phenomenon as the 'orderphobic effect'. The effect is mediated by proximity to the order-disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.

Pre-Transition Effects Mediate Forces of Assembly between Transmembrane Proteins: The Orderphobic Effect

We present a mechanism for a generic and powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the host membrane. Using large scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order-disorder interface, and the stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial free energy. In analogy with the hydrophobic effect, we refer to this phenomenon as the "orderphobic effect". The effect is mediated by proximity to the order-disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from the orderphobic effect are significantly larger than those that could arise from membrane elasticity for the membranes we examine.

Comparative study of structure formation and mechanical behavior of age-hardened Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys

This work sets out to study the peculiar effects of aging treatment on the structure and mechanical behavior of cold-rolled and annealed biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) (at.%) shape memory alloys by means of transmission electron microscopy, X-ray diffractometry, functional fatigue and thermomechanical testing techniques. Dissimilar effects of aging treatment on the mechanical behavior of Zr- and Ta-doped alloys are explained by the differences in the ω-phase formation rate, precipitate size, fraction and distribution, and by their effect on the alloys' critical stresses and transformation temperatures. Even short-time aging of the TNZ alloy leads to its drastic embrittlement caused by “overaging”. On the contrary, during aging of the TNT alloy, formation of finely dispersed ω-phase precipitates is gradual and controllable, which makes it possible to finely adjust the TNT alloy functional properties using precipitation hardening mechanisms. To create in this alloy nanosubgrained dislocation substructure containing highly-dispersed coherent nanosized ω-phase precipitates, the following optimum thermomechanical treatment is recommended: cold rolling (true strain 0.37), followed by post-deformation annealing (600°C, 15–30min) and age-hardening (300°C, 30min) thermal treatments. It is shown that in TNT alloy, pre-transition diffraction effects (diffuse reflections) can “mask” the β-phase substructure and morphology of secondary phases.

Synthesis, Characterization, and Dilatometric Studies on N-(p-n-Alkoxybenzylidene)-p-n-pentyloxyanilines Compounds

Synthesis, textural characterization, differential scanning calorimetry, and dilatometry studies are carried out on a new homologous series of N-(p-n-alkoxy benzylidene)-p-n-pentyloxy anilines (nO.O5) where n = 1–18. The lower homologues of this series (n = 1–5) and a higher homologue (n = 16) exhibit monotropic Liquid Crystal (LC) phase. The other members of the series show enantiotropic LC phases, while 18O.O5 is a nonliquid crystal. The dilatometric studies on 7O.O5, 10O.O5, 13O.O5 and 16O.O5 reveal the first-order nature of Isotropic to Nematic Phase (IN), Isotropic to Smectic A Phase (IA), Nematic to Smectic C Phase (NC), Smectic A to Smectic B Phase (AB), Smectic C to Smectic B Phase (CB), and Smectic A to Krystal Phase (AK) transitions. The pretransition effects are estimated from dilatometry results. The results are compared with the available data on nO.m compounds.

Atomic Structure of Alloys Close to Phase Transitions

AbstractPhase transitions are often accompanied by pre-transition effects. These effects have been studied on an atomic scale by high resolution electron microscopy. For the diffusion controled phase transitions we discuss short range ordering effects in Ni-Mo and Cu-Pd. For the displacive transitions we discuss the martensitic nucleation in Ni-Al and the nanoscale domain formation in the Ni-Ti R phase.

Transition State Treatment of Nuclear Multifragmentation: Summary of results

The Transition State Treatment of Nuclear Fragmentation has been used to study a number of aspects of the break-up of heavy ions during medium-energy reactions. This manuscript presents a review of the transition state method and a summary of results. In particular, the post- and pre-transition effects are investigated, and the break-up volume—a parameter used by other models—is studied.

Infrared Dichroism and Vibrational Spectroscopy of a Side Chain Polyacrylate Liquid Crystalline Polymer

Abstract The infrared spectra of a polyacrylate side chain liquid crystalline polymer has been recorded and investigated as a function of temperature and the angle of polarisation of the IR incident beam. Variations in the absorbance and frequency are found to be governed by the phase transitions. The order parameter for various vibrational bands has been calculated from the infrared dichroism measurements. It is found that the liquid crystalline polymer alignment achieved by a surface treatment with polyvinyl-alcohol followed by rubbing of the windows does yield reasonable values of the order parameter. The order parameter for the alkyl chain is found to be only 15° of the maximum value; this shows a conformational disorder for the macromolecule in terms of the configuration of chains. Study of the vibrational frequency of bands with temperature shows a definite existence of the pre-transition effects especially for SmA phase. Frequencies for most of the vibrational modes are seen to change abruptly at S...

Electron microscopy observations of pretransition effects in alloys

Abstract A number of alloy systems show structural modifications upon approaching a phase transition. This can be an ordering (or disordering) effect or a deformation modulation. High-resolution electron microscopy allows one to deduce significant information on the transformation process. Examples considered are Co-Pt and Cu3Pd for the ordering alloys and Ni—Al where ‘tweed’ shows a prefiguration of the martensite product.

Free transition phenomena and electrical birefringence in the isotropic phase of liquid crystalline polymers having mesogenic groups in the side chain

The electrical birefringence (Kerr effect) in the isotropic phase of thermotropic liquid crystalline comb-like polyacrylic polymer having cyanobiphenyl groups in the side chains is studied. The presence of pretransition effects over several degrees before the temperature of transition into the nematic state in both its equilibrium electrooptical properties and in relaxation phenomena is established. On the basis of a comparison of the electrooptical properties of the polymer and its low molecular weight analogues, conclusions are arrived at on the mechanisms of motion of the polymer chain responsible for the electrical birefringence. Two mechanisms of the Kerr effect dispersion of various types and having different relaxation times and different relations with the temperature are observed.

X-ray studies of tilted hexatic phases in thin liquid-crystal films.

X-ray-diffraction studies of the structures and phase transitions of the tilted hexatic phases (smectic $F$ and smectic $I$ in thin liquid-crystal films of 4-$n$-heptyloxybenzylidene-4-n-$n$-heptylaniline (70.7) are reported. The measured correlation lengths were strongly anisotropic in both phases. The smectic-$I$ to smectic-$F$ transition is first order as expected from the symmetry change. The smectic-$F$ to smectic-$G$ transition is first order with strong pretransition effects and becomes nearly second order as the film thickness is decreased.

X-ray topographic investigations of phase transitions in crystals

In recent years, X-ray topography has increasingly been applied to the study of phase transitions in single crystals. In principle, the following investigations can be performed with this technique: (a) The revelation of the domain configuration, that arises during the transition into a phase having a lower-symmetry and the characterization of the different kinds of domains. The domains can be imaged by domain contrast or by the contrast of their boundaries. (b) The characterization of domain boundaries by analysing their X-ray contrast in different imaging reflections. (c) The observation of the ȁphase boundaryȁ between the transformed and non-transformed crystal regions. The appearance of this boundary in X-ray topographs depends strongly on the character of the transition. The boundary can be expected to have a high strain gradient and to exhibit strong X-ray contrast for first-order transformations. Second-order transformations can be expected to show zero or only faint contrast in the transition region. In addition, the imaging of the phase boundary may reveal the existence of an intermediate (and frequently incommensurate) phase sandwiched between the ȁmainȁ phases involved in the transition. (d) The observation of pre-transition effects, i.e. the formation of strained regions, crystal defects and/or domains prior to the transformation. The main features of X-ray topographic imaging of domains, domain boundaries and phase boundaries are briefly surveyed. Some examples selected from studies of the following transitions are given: (1) The first-order paraelectric-antiferroelectric transition of copper formation tetrahydrate at -38°C. (2) The first-order paraelectric-antiferroelectric transition of ammonium sulphate at about -50°C. (3) The second-order paraelectric-ferroelectric transition of rubidium hydrogen sulphate at about -8°C. (4) The second-order paraelectric-ferroelectric transitions of Rochelle salt at -18°C and +24°C. In these four cases, the formation of domains during the transition into the lower-symmetry ȁferroicȁ phases and their disappearance during re-transformation is observed. Due to the fine-scale domain configurations in copper formate tetrahydrate, ammonium sulphate and rubidium hydrogen sulphate, and the poor spatial resolution of X-ray topography, a clear resolution of domains is not obtained. In Rochelle salt, well-resolved domains in the form of lamellae parallel (010) and (001) are observed. As expected, the first-order phase boundaries of copper formate tetrahydrate and ammonium sulphate appear on the topographs by strong kinematical contrast demonstrating the high strain gradient present in the boundaries. In rubidium hydrogen sulphate and in (100) plates of Rochelle salt (normal to the ferroelectric axis) no X-ray contrast is observed in the transition region, which indicates the absence of a strain gradient in these cases. This transition, however, is recognizable by the vanishing of domains. In (001) plates of Rochelle salt diffuse extended contrast is observed revealing the presence of a long-range strain gradient in the transition region. In ammonium sulphate, strain which develops in the paraelectric phase prior to the transition is observed. The use of X-ray topography for the study of phase transitions is restricted by the poor spatial resolution of this method and by the rather long exposure times. The latter disadvantage can largely be overcome by the application of synchrotron radiation and image intensifiers (real-time topography).

Liquid Crystals in my Memories and Now—the Role of Anisotropic Viscosity in Liquid Crystals Research

Abstract The viscosity coefficients of nematic substances for corresponding orientation geometry introduced and measured for PAA and PAP by the author in the thirties are discussed from the actual point of view. The great universality of these coefficients of viscosity and their utility for describing several dynamical phenomena has been shown. There is a quantitative agreement between the experimental data of those investigations and continuum hydrodynamical theory of nematics with the numerical values of viscosities measured by the author. As a new field of application of flow in definite orientation geometry, the properties of smectics and closely connected problems of phase transitions, pretransition effects and reentrant phase has been discussed.

Scaled Particle Theory of a System of Spherocylinders: Extension of Calculations to High Pressures

Abstract The viscosity coefficients of nematic substances for corresponding orientation geometry introduced and measured for PAA and PAP by the author in the thirties are discussed from the actual point of view. The great universality of these coefficients of viscosity and their utility for describing several dynamical phenomena has been shown. There is a quantitative agreement between the experimental data of those investigations and continuum hydrodynamical theory of nematics with the numerical values of viscosities measured by the author. As a new field of application of flow in definite orientation geometry, the properties of smectics and closely connected problems of phase transitions, pretransition effects and reentrant phase has been discussed.

High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

Abstract We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q 2⊥ + γ2 q 2 z). Unless the elastic constant C44 is more than an order of magnitude smaller than previously reported values of ∼ 108 ergs/cm3 the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.

Compressibility and Thermal Expansion Anomalies in the Isotropic Liquid Crystal Phase

Abstract De Gennes' theory of pretransition effects in the isotropic liquid crystal phase is generalized to include number density and orientational fluctuations. Order fluctuations produce more efficient local packing of rod-shaped molecules with a resulting fluid contraction. This mechanism is proposed to explain the anomalous rise in compressibility and thermal expansivity of liquid crystals above the clearing temperature.