Condis Phase Research Articles

Microscopic Mechanism of the Large Electrocaloric Effect in Vinylidene Difluoride-Based Polymers

The molecular mechanism of the large electrocaloric effect in ferroelectric vinylidene difluoride-based polymers was proposed. The mechanism involves the electric field-induced phase transition between the ferroelectric β-phase and the paraelectric conformationally disordered (condis) phase. The condis phase is characterized by the absence of a three-dimensional crystallographic order: there is only two-dimensional translational symmetry in the plane perpendicular to the chain direction. Due to conformational disorder, the entropy of the condis phase is higher than that of the β-phase. A high entropy change at the transition from the β to the condis phase causes a large electrocaloric effect. Molecular dynamics simulations of the poly(vinylidene fluoride-co-trifluoroethylene) (poly(VDF-co-TrFE)) copolymer and poly(vinylidene fluoride–ter–trifluoroethylene–ter–chlorofluoroethylene) (poly(VDF-ter-TrFE-ter-CFE)) and poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) (poly(VDF-ter-TrFE-ter-CTFE)) terpolymers were performed. The electrocaloric effect was determined from simulations using two techniques: (i) direct calculation of the temperature drop in adiabatic conditions and (ii) calculation of the entropy difference between β and condis phases from the pair histograms of dihedral angles. Both techniques predict similar temperature drops that validate the proposed molecular mechanism.

Effect of mesogenic organic salts on vulcanization and physical properties of rubber compounds

The effect of mesogenic organic salts as reinforcing fillers for non-ionic elastomers such as natural rubber and styrene–butadiene rubber has been investigated. The influence of cation size (thallium and sodium) and organic chain length (thallium(I) pentanoate and thallium(I) dodecanoate) on vulcanization parameters, physical and mechanical characteristics and rheological behaviour has also been analysed. In general, the maximum torque of the vulcanizates increases in the presence of the salts and is clearly manifested in a noticeable increase in tensile modulus and strength of the composites. The thallium(I) salts are more effective reinforcements than the sodium salt, and the length of the organic chain has hardly any influence on the mechanical properties. The composites based on the thallium(I) dodecanoate salt show a very peculiar rheological behaviour with a ‘plateau’ in the elastic modulus and loss modulus versus temperature plots which is related to solid phase I, existing between 83.5 and 127 °C, characterized as a plastic condis phase. This issue is especially interesting for the fabrication of devices such as sensors to control, for instance, the security (resistance of a material) as a function of temperature. © 2013 Society of Chemical Industry

Effect of Mesogenic Organic Salts on Vulcanization and Physical Properties of Natural Rubber Compounds

ABSTRACTThe effect of mesogenic organic salts as reinforcing fillers for natural rubber has been investigated. The influence of cation size (thallium and sodium) and organic chain length (thallium (I) pentanoate and dodecanoate) on the vulcanization parameters, physical and mechanical characteristics and rheological behavior has also been analyzed. In general, the maximum torque of the vulcanizates increases in the presence of the salts and is clearly manifested in a sensible increase in tensile modulus and strength of the composites. The reinforcing effect of these salts is noticeable in the natural rubber matrix. The thallium (I) salts are more effective reinforcements than the sodium salt, and the length of the organic chain hardly has any influence on the mechanical properties. The composites based on the thallium (I) dodecanoate salt show a very peculiar rheological behavior with a “plateau” in the G’ and G” vs temperature graphics which is related with solid phase I, existing between 83.5 ºC and 127 ºC, characterized as a plastic condis phase. This issue is especially interesting for the fabrication of devices such as sensors to control, for instance, the security (resistance of a material) as a function of temperature.

The role of calorimetry in the structural study of mesophases and their glass states

Four mesomorphic states of matter are known: liquid crystal, plastic crystal, condis phase, and rotator phase, all of them are solid phases, except liquid crystal, which is fluid. Plastic crystal (also called ODIC, orientational disordered crystal), rotator phase, and even condis phase have been considered the same phase by many authors. Differences between them will be established to define their own characteristics. Two organic salts series have been used for discussion in this presentation: (1) thallium(I) alkanoate series, that presents a condis mesophase, and (2) lead(II) alkanoate series, that present a rotator one, both forming a smectic A-like liquid crystal phase. Based in the literature data of the alkyl ammonium bromide series it can be established that the short chain length members would present a rotator phase, and, the large chain ones, a condis phase. Five different glass states are known (four with partial crystalline order), corresponding with the above mentioned mesophases, and the ordinary (amorphous) glass state.

The phase diagram of poly(4-hydroxybenzoic acid) and poly(2,6-hydroxynaphthoic acid) and their copolymers from X-ray diffraction and thermal analysis

Homopolymers and copolymers of 4-hydroxybenzoic acid (HBA) and 2,6-hydroxynaphthoic acid (HNA) have been studied with differential scanning calorimetry and temperature-resolved wide angle X-ray diffraction. All polymers have more than one disordering transition between the glass transition (between 400 and 430K) and decomposition (between 710 and 750K). The first transition in PHBA at 616–633K is from orthorhombic rigid crystals to a conformationally disordered pseudo-hexagonal phase (condis phase). The two higher transitions are first, a further disordering process to a hexagonal condis crystal, and then a change to an anisotropic melt (liquid crystal) at about 800K, with increasing decomposition above 750K. In PHNA, orthorhombic crystals change above 600K to an orthorhombic condis crystal structure, which go to an anisotropic melt at 750K, and subsequent decomposition. In addition, using empirical entropy rules that account for the changes during the transitions from the crystal to the disordered mobile phases, an effort is made to understand the disorder and mobility, and to arrive at a non-equilibrium phase diagram of the copolymer system. The existence of a single, but up to 200K wide, glass transition and remaining high crystallinity of the copolyesters, indicate partial solubility of the repeating units in all phases. The new data are compared to and brought into agreement with the large number of prior measurements and often unclear interpretations.

Reversibility of the low-temperature transitions of polytetrafluoroethylene as revealed by temperature-modulated differential scanning calorimetry

Temperature-modulated differential scanning calorimetry reveals distinct differences in the kinetics of the low-temperature phase transitions of polytetrafluoroethylene. The triclinic to trigonal transition at 292 K is partially reversible as long it is not complete. As soon as the total sample is converted, supercooling is required to nucleate the reversal of the helical untwisting involved in the transition. The trigonal phase can be annealed in the early stages after transformation with a relaxtion time of about 5 minutes. The dependence of the reversing heat capacity on the modulation amplitude, after a metastable equilibrium has been reached, is explained by a non-linear, time-independent increase of the heat-flow rate, perhaps caused by an increased true heat capacity. The order-disorder-transition at 303 K from the trigonal to a hexagonal condis phase is completely reversible and time-independent. It extends to temperatures as low as the transition at 292 K or even lower. Qualitatively, the thermal history and crystallization conditions of polytetrafluoroethylene do not affect the transition kinetics, that is, melt-crystallized film and as-polymerized powders show similar transition behaviors, despite largely different crystallinities. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 750–756, 2001

Thermal analysis of paraffins as model compounds for polyethylene

The n-paraffins C50H102, C44H90, and C26H54 were analyzed with standard and temperature-modulated differential scanning calorimetry. Crystallization and ordering from the melt to the condis phase showed practically no supercooling. These observations were confirmed with hot-stage microscopy and a melting-point apparatus. Only the organization of the C26H54 condis crystals to fully ordered crystals showed a supercooling of 4.0 K. The measurement of the apparent reversing heat capacity with a 0.05-K modulation amplitude revealed that the melting of C50H102 was completed within 1.0 K and the isotropization of C26H54 was completed within less than 0.6 K, but 62–78% of the total transitions occurred over a much narrower temperature range of 0.1 K or less. The link to polyethylene was made with fractions of the masses 15,520, 2150, and 560 Da. The 560-Da sample corresponded to C40H82 and showed also almost no supercooling, whereas the others, with folded and extended-chain crystals, supercooled by about 10 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2810–2822, 2000

Local composition in Lennard-Jones systems of particles with flexible shape

A two-dimensional Lennard-Jones system of particles with flexible shape is studied by Monte Carlo simulations. Each particle involves an internal degree of freedom characterizing a gradual change in shape from circular to elliptical with maximum anisotropy. The condis crystal,† which is characterized by translational order and a mixture of particle shapes, is analysed in detail. The simulations show that in the condis phase the shape flexibility of the particles does not allow (i) stable interfaces formed by particles of both limiting intraparticle states and (ii) the formation of blocks of particles with similar shape.

The phase diagram of an ensemble of Lennard-Jones particles with flexible shape

A model representing a 2-dimensional Lennard-Jones system of particles with flexible shape is presented. Each particle involves an internal degree of freedom characterizing a gradual change in shape from circular to elliptical. An NVT Monte Carlo simulation procedure is performed in order to analyse the structure and the phase behaviour of the modified Lennard-Jones system. Depending on the model parameters one of these four phases is found: (i) an ordered crystal, which is composed solely of particles with either circular or elliptical shape, (ii) a mesophase characterized by a mixture of particles with different shapes while translational order remains (condis phase), (iii) a mesophase of elliptical particles exhibiting translational order and orientational disorder (plastic phase), and (iv) the melt.

The phase diagram of an ensemble of Lennard-Jones particles with flexible shape

A model representing a 2-dimensional Lennard-Jones system of particles with flexible shape is presented. Each particle involves an internal degree of freedom characterizing a gradual change in shape from circular to elliptical. An NVT Monte Carlo simulation procedure is performed in order to analyse the structure and the phase behaviour of the modified Lennard-Jones system. Depending on the model parameters one of these four phases is found: (i) an ordered crystal, which is composed solely of particles with either circular or elliptical shape, (ii) a mesophase characterized by a mixture of particles with different shapes while translational order remains (condis phase), (iii) a mesophase of elliptical particles exhibiting translational order and orientational disorder (plastic phase), and (iv) the melt.

High pressure effect on molecular motions in the paraelectric phase of a vinylidene fluoride and trifluoroethylene copolymer ([formula omitted]) studied by n.m.r.

The 19F n.m.r. spin-lattice relaxation times in both the laboratory and the rotating frame have been measured in a 7030mol% random copolymer of vinylidene fluoride and trifluoroethylene, over a range of pressures from 0.1 to 200 MPa in the paraelectric phase. Molecular motions have been investigated in this condis phase, and correlation times were obtained as a function of pressure and temperature. Activation parameters have been determined and discussed in terms of a thermally activated model and compared with literature data.

Analysis of the thermal properties and motion in crystalline trans-1,4-poly(butadiene)

A new analysis of the disordering transition of semicrystalline trans-1,4-poly(butadiene) is presented, based on an improved calculation of the transition enthalpy from the crystal form I to the mesophase II (condis phase). In the past it had been overlooked that the experimental heat capacity starts to deviate more than one hundred kelvins below the peak temperature of the disordering transition temperature T d from that contributed by the amorphous fraction and the crystal. An assessment of the additional entropy of disordering at lower temperature suggests that by the time the glass transition is reached on cooling, all the mesophase is converted to the fully ordered crystal form I.

Monte-Carlo simulation of solid-solid transition to conformationally disordered state

A Monte-Carlo simulation of the CONDIS phase transition is presented based on a simple three-parameter model for particles with one internal degree of freedom. The parameters themselves can be deduced in principle from atomistic calculations. It is shown that these calculations yield a solid-liquid as well as a solid-CONDIS crystal solid phase transition depending on the energy difference between both states of the particle

Atomistic calculations on the high-temperature condis phase of poly(trans-1,4-butadiene) (PTBD)

The structure of the low-temperature phase of poly(trans-1,4-butadiene) was calculated by means of semiempirical atomistic potentials. Without using any symmetry assumptions there is good agreement with experimental data. In order to understand the high-temperature phase, packing energy calculations were performed with different chain conformations. There are a great number of possible packing modes. They show an approximately linear relation between defect volume and defect energy. The results of these calculations are taken as a basis for a thermodynamic treatment (cooperative pair theory) of the phase transition. The experimental transition enthalpy can only partially be explained by intermolecular interactions, and the defect energy of the various intramolecular equilibrium conformations is not sufficient to explain the difference. A refined treatment with a simultaneous inter-and intramolecular minimization of the energy reveals that the chains are not in their intramolecular equilibrium state. This results in an additional intramolecular defect energy which seems to lead to an understanding of the experimental transition data.

Solid-state deformation of trans-1,4-polybutadiene

Abstract The uniaxial deformation behaviour of trans -1,4-polybutadiene was investigated. Trans -1,4-polybutadiene exhibits a solid-solid phase transition to a mobile pseudo-hexagonal, conformational disordered (condis), crystal structure at a temperature of approximately 65°C. Trans -1,4-polybutadiene cannot be deformed to high draw ratios via tensile drawing in the pseudo-hexagonal condis phase. Using coextrusion, trans -1,4-polybutadiene can be deformed, in the pseudo-hexagonal condis phase, to high (extrusion) draw ratios. Structures possessing a high degree of chain orientation in the extrusion direction and a strongly enhanced Young's modulus and tensile strength can be produced.

The high temperature transition of polyethylene into a Condis phase, described on the basis of the cluster-entropy hypothesis (CEH)

On the basis of atomistic calculations a rotator model of the high temperature Condis phase of polyethylene is proposed. Its cooperative statistical treatment (using CEH for the lateral packing of chains) explains the first order transition from the all-trans crystal as well as the transition dataT t ,ΔS t ,ΔV t . We found that the normal melting (i. e. at pressures below the triple point) is also governed by the onset of the Condis phase.

The thermal properties of polypropylene

AbstractThe thermodynamic properties of isotactic polypropylene in the fully crystalline, glassy, and molten state are established from 0 to 500 K based on data bank heat capacities and the vibrational frequency spectrum. The seven skeletal vibrations are described by θ3 and θ1 of 91 and 714 K for crystalline polypropylene. For the calculation of Cp − Cv, a Lindemann A0 value of 1.5 × 10−3 K mol/J was found. Calculated and experimental heat capacity data show agreement within an average error of −0.3 ± 1.6%. Glassy polypropylene was similarly treated up to the glass transition temperature at 260 K (θ3 = 78 K, θ1 = 633 K, average heat capacity error −0.6 ± 2.8%). The residual 0 K entropy of glassy polypropylene is 1.9 J/K mol. Partially crystalline polypropylene is shown through high‐sensitivity DSC measurements to have a glass transition range from 260 to 380 K. Similarly, high‐sensitivity DSC has been used to characterize the condis phase of polypropylene (conformationally disordered polypropylene) which was prior called “smectic mesophase” or “paracrystalline.” Its heat of transformation to the stable crystal phase is 600 J/mol.