Extended Veytsman statistics for the solid–fluid transition in the framework of lattice fluid

Lattice fluid can describe a vapor–liquid transition but not a solid–fluid transition. In this work, we propose a simple and analytic term which yields a solid–fluid transition when coupled with a lattice based equation of state (EOS). The proposed term is derived based on the two assumptions that (1) solid can be considered as highly associated phase affected by strong attractive force and (2) this force is distinct from the conventional attractive forces yielding a vapor–liquid transition. To formulate these assumptions, we extend Veytsman statistics by modifying its density dependency. The derived term was combined with a quasi-chemical nonrandom lattice fluid theory (QLF) developed by the authors. The combined model was found to require only two parameters besides 3 QLF parameters for physical properties calculation of three phases. When tested against equilibrium properties of 8 components, the combined model was found to closely reproduce melting pressure, sublimation pressure, and vapor pressure, but underestimate solid density as well as heat of melting at the triple point temperature. It was found that the present approach can yield a solid–liquid transition at all temperatures.     

Powder X‐Ray Diffraction Investigation of Xylazine Hydrochloride Solid Phase Transformation Kinetics

The kinetics of the solid‐state phase transformation of xylazine hydrochloride form X to A has been investigated using powder X‐ray diffraction and differential thermal analysis. Three different kinetic models have been used to describe transition kinetics: the Avrami–Erofeev equation, the Cardew equation, and the methodology for simulation of solid‐state phase transition kinetics by the combination of nucleation and nuclei growth processes. The latter has been recently developed and has been tested in this paper for the case of a real solid‐state transition. The relative humidity, mechanical pressure, temperature, and sample‐preparation effect on phase‐transition kinetics have been investigated, and rate constant changes have been analyzed.     

Phase transition of syndiotactic polypropylene in electrospun nanofibers during progressive heating

By means of high-temperature electrospinning process, syndiotactic polypropylene (sPP) nanofibers with an average diameter of 127 nm were obtained using a rotating disc as a collector. The aligned fibers were subjected to progressive heating for fiber melting. During heating, structural evolution of the sPP nanofibers was investigated in situ by means of two-dimensional wide-angle and small-angle X-ray scattering with synchrotron radiation sources. It was found that the as-spun fibers consist of the antichiral form I (9 %), mesophase (31 %), and amorphous phase (60 %), in the absence of isochiral form II. Upon heating, the mesophase started to melt and completely disappeared at 90 °C. The melting of the mesophase directly produced amorphous chains at 35–60 °C, and brought up the isochiral form II at low temperatures (60–70 °C), as well as the antichiral form I at high temperatures (70–110 °C). These events were in accordance with the DSC heating curve, which exhibited a small endotherm centered at 52 °C for the mesophase melting, followed by a shallow and broad exotherm associated with two phase-transition events, i.e., the crystal reorganization and the crystallization of supercooled liquid. The former is likely due to the solid–solid transition of meso→II phase as suggested by Lotz et al. (Macromolecules 31:9253, 1998), and the latter is relevant with crystallization of amorphous chains to develop the thermodynamic stable form I phase at high temperatures.     

Thermodynamic aspects of capillarity and electrocapillarity of solid interfaces

In the previous paper (Gutman, JOSSEC 18:3217–3237, 2014), we have shown that the main problem in capillarity and electrocapillarity of solid surfaces is the lack of clarity in determining the surface stress and basic equations. Now, we continue the survey of efforts to solve this problem and show origins of erroneous results, accenting some important items: comparative analysis of Gibbs and Guggenheim approaches in surface thermodynamics (a geometrical dividing surface and finite-thickness surface layer, respectively), transformation of fundamental equations on per-unit-area basis to obtain Gibbs adsorption equation for finite-thickness surface layer, different attempts to derive the thermodynamic definition of “surface stress” in frames of Gibbs’ theory (including Shuttleworth’s approach), atomistic calculations of surface stress, surface stress in rational continuum mechanics, “modifications” of Gibbs–Duhem relations made for solid interface, and Maxwell relations in capillarity and electrocapillarity of solid interface. It is shown that the erroneous Shuttleworth’s approach is present in an explicit or implicit form in all efforts to introduce the surface stress in frames of Gibbsian theory (although Gibbs did not introduce surface stress). Therefore, “modernizations” or “generalizations” of the Gibbs–Duhem relation, the Gibbs adsorption equation, and the Lippmann equation to adopt them for a solid surface are unnatural and not necessary. Therefore, we recommend withdrawing the Shuttleworth equation and its consequences from circulation, including the IUPAC Recommendations.     

Preparation of molecularly imprinted polymeric fibers using a single bifunctional monomer for the solid‐phase microextraction of parabens from environmental solid samples

In this study, molecularly imprinted polymer fibers for solid‐phase microextraction have been prepared with a single bifunctional monomer, N,O‐bismethacryloyl ethanolamine using the so‐called “one monomer molecularly imprinted polymers” method, replacing the conventional combination of functional monomer and cross‐linker to form high fidelity binding sites. For comparison, imprinted fibers were prepared following the conventional approach based on ethylene glycol dimethacrylate as cross‐linker and methacrylic acid as monomer. The recognition performance of the new fibers was evaluated in the solid‐phase microextraction of parabens, and from this study it was concluded that they provided superior performance over conventionally formulated fibers. Ultimately, real‐world environmental testing on spiked solid samples was successful by the molecularly imprinted solid‐phase microextraction of samples, and the relative recoveries obtained at enrichment levels of 10 ng/g of parabens were within 78–109% for soil and 83–109% for sediments with a relative standard deviation <15% (n = 3).     

A diffuse‐interface modeling for liquid solution–solid gel phase transition of physical hydrogel with nonlinear deformation

A diffuse‐interface model is presented in this paper for simulation of the evolution of phase transition between the liquid solution and solid gel states for physical hydrogel with nonlinear deformation. The present domain covers the gel and solution states as well as a diffuse interface between them. They are indicated by the crosslink density in such a way that the solution phase is identified as the state when the crosslink density is small, while the gel as the state if the crosslink density becomes large. In this work, a novel order parameter is thus defined as the crosslink density, which is homogeneous in each distinct phase and smoothly varies over the interface from one phase to another. In this model, the constitutive equations, imposed on the two distinct phases and the interface, are formulated by the second law of thermodynamics, which are in the same form as those derived by a different approach. The present constitutive equations include a novel Ginzburg–Landau type of free energy with a double‐well profile, which accounts for the effect of crosslink density. The present governing equations include the equilibrium of forces, the conservations of mass and energy, and an additional kinetic equation imposed for phase transition, in which nonlinear deformation is considered. The equilibrium state is investigated numerically, where two stable phases are observed in the free energy profile. As case studies, a spherically symmetrical solution‐gel phase transition is simulated numerically for analysis of the phase transition of physical hydrogel.     

Three-stage melting of an annelide-type copper complex. A new type of organized phase: Tegma crystals

The solid—solid phase transition of an annlide type copper complex are described. As the temperature is raised, three different constituents of the complex successively melt. In the temperature range 77–95°C, the polyethylene oxide chains and the paraffinic tail are both in a very mobile state while the copper complex sub-units still form a two-dimensional crystalline array.     

Features of colloidal disperse structure formation in petroleum bitumen

Temperature-modulated differential scanning calorimetry has been employed to analyze the structure-related thermal properties of petroleum bitumen. This method enables one to distinguish between “order–disorder” and glass transitions, thereby making it possible to monitor and identify structure-related phase transformations, the signals from which are invisible or overlapped in the thermograms of conventional differential scanning calorimetry. Bitumen has been shown to be a colloidal disperse system only under certain temperature–time conditions. Its dispersed phase may be represented by aggregates of two types with colloidal sizes. Saturated hydrocarbons form a solid crystalline phase in accordance with the regularities of first-order structural phase transitions and nucleation mechanism of phase separation. Asphaltenes and resins form a solid amorphous phase for a relatively long time as a result of a structural relaxation glass transition by the spinodal mechanism of phase separation.     

Effects of temperature and water on the γ → α crystalline transition of nylon 6 caused by stretching in the chain direction

The effects of temperature and water on the crystal transition of nylon 6 from the γ phase to the α phase, which is caused by stretching along the chain direction, were investigated. The γ-phase fibers with high crystallite orientation were stretched at constant load under various conditions. An inversion of the effect of water on the transition occurs at about ?60°C. Stretching in the wet state is more effective for the transition at higher temperature. In contrast, at low temperatures water in the crystalline regions actsasa cohesive agent for the chains and increases the activation energy for the transition. Thus, dry stretching is more effective than wet stretching at very low temperature. The fraction of transformed α-phase crystallites increases abruptly over a narrow range of stress. Thus the critical stress can be determined for the transition. The critical stress changes appreciably with temperature; the higher the temperature, the lower the critical stress. The relation between stretching temperature and critical stress was analyzed by Flory's equation for the shift of transition temperature by stress. About 220°C. was estimated as the zero-stress transition temperature. The heat content of the γ-phase crystal was estimated to be smaller by 500 cal./mole than that of the α-phase crystal. This result suggests that the free energy of the γ-phase crystal is lower than that of the α-phase crystal at temperatures lower than the transition point. The irreversible strain of a sample in which the crystal transition has taken place is very small at low temperature. This small extension of the sample is evidence that the γ → α transition produced by stretching along the chain axis is a crystal-crystal transition.     

Determining the boundaries of second-type phase transitions in Ag–Mg–Cd alloys by means of diffusion couples

The interaction between elements in the transition zones of diffusion couples Mg + AgCd–alloy are studied. Isothermal sections of the Ag–Mg–Cd ternary system at 573 K are constructed. The existence of a Heusler phase based on H–Ag₂MgCd compound is found in the field of the solid β′-solution. It is shown that the interdiffusion of components prevents the formation of ordered phases in the transition zones of bimetals, allowing us to determine the boundaries of second-type phase transitions in solid solutions.     

Biodegradable PEO/cellulose‐based solid–solid phase change materials

A series of poly(ethylene oxide) (PEO) blends with cellulose (CEL) or cellulose derivatives—carboxymethyl cellulose (CMC), cellulose acetate (CAC), and cellulose ether (CET)—has been investigated as phase change materials for thermal energy storage. For PEO/CEL blends solid–solid phase transition has been observed in the whole concentration's range; for PEO/CMC and PEO/CET blends solid–solid phase transition has been found for PEO content 25 or 50 and 25 wt%, respectively. Otherwise, solid–liquid phase transition takes place. MTDSC investigations revealed that for PEO/CEL and PEO/CMC blends transition the strongest recrystallization effect (as evidenced by exothermic effect in reversing heat flow) as melting process occurred. FTIR analysis shows a shift of the stretching vibration bands of both the proton‐donor O? H groups from CEL and PEO due to intermolecular hydrogen interactions between the blends' components. Copyright © 2010 John Wiley & Sons, Ltd.     

Annealing behavior of gel‐spun polyethylene fibers at temperatures lower than needed for significant shrinkage

The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003     

Forms of solid solution ordering upon decreasing temperature

The work reports different forms of solid solution ordering: from the well-known atom redistribution processes over positions and the decomposition of the solid solution to the formation of superstructures, modulated structures, rotation of atomic groups, splitting of sites. For each ordering form as a crystal chemical phenomenon the position of atoms, molecules, and vacancies in the crystal structure of the solid solution is considered and the place of these processes among the main crystal chemical phenomena is determined. The manifestation of order–disorder processes in phase diagrams of systems is also analyzed: from the classical heterogeneous decomposition of solid solutions to the formation of ordered chemical compounds and other phase transitions. The necessity of a thorough study of the atomic-molecular nature of the solid solution ordering by modern X-ray diffraction crystallographic methods and high-resolution electron microscopy is demonstrated. For each ordering form examples are given, the driving force of the process is distinguished, and a brief literature review is presented.     

LCST‐type liquid–liquid and liquid–solid phase transition behaviors of hyperbranched polyglycerol bearing imidazolium salt

A hyperbranched polyglycerol bearing imidazolium tosylate units ( ITHB ) was synthesized through the imidazolium salt‐modification of hyperbranched polyglycerol ( HB ). ITHB was found to possess novel reversible lower critical solution temperature (LCST)‐type liquid–liquid and liquid–solid phase transition behaviors in a methanol/chloroform mixed solution. The phase transition temperatures of the liquid–liquid phase transition (PTT_1to2) and liquid–solid phase transition (PTT_2toSus) increased with increasing the ratio of methanol in the mixed solution and decreasing the concentration of ITHB . Additionally, increasing the molecular weight of ITHB decreased the PTT values. The liquid–liquid phase transition was caused by the aggregation of ITHB , which was proved by dynamic light scattering measurement. In contrast, the liquid–solid phase transition was caused by the solvation cleavage between the imidazolium rings and solvents, which was proved by ¹H NMR measurement. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Thermal actuation performance modification of coiled artificial muscle by controlling annealing stress

Twisted and coiled polymer (TCP) is a promising linear artificial muscle fabricated from nylon or other polymeric fibers, whose geometric structure is similar to a coil spring. TCP muscle is actuated reversibly with negative coefficients of thermal expansion. Twisting, coiling, and annealing are the main fabricating procedures. Annealing is the key process to form TCP muscles with stable performance. To modify and enhance actuation performance, it is necessary to explore and reveal influences of annealing process on thermal actuation (contraction strain, nominal modulus, and geometrical characteristic). Therefore, a new TCP fabrication and test platform is first established, which can quantize key geometrical and force parameters by multiple precise sensors. Then, four types of TCP muscles using nylon 6 fibers with varied diameters are fabricated and annealed under different conditions. As one of the important factors in annealing process, the nominal tensile stress is adjusted and controlled. Meanwhile, the contraction strain and nominal modulus are tested compared with the general annealing method. Finally, the experiment results show that contraction strain can be enhanced about two times (nominal modulus decreases accordingly) by increasing annealing stress, and the actuation performance can be remodeled reversibly by adjusting annealing stress and annealing repetitively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 383–390     

Study on the thermoresponsive two phase transition processes of hydroxypropyl cellulose concentrated aqueous solution: from a microscopic perspective

In this paper, it was discovered that during the heating process from 35 to 63 °C, hydroxypropyl cellulose (HPC) concentrated aqueous solution (20 wt%) would first go through coil-to-globule transition and then sol–gel transition with temperature elevation. The microdynamic mechanisms of the two phase transitions were thoroughly illustrated using mid and near infrared spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique. Mid infrared spectroscopy is an effective way to study the hydrophobic interactions in HPC molecules. And near infrared spectroscopy is a potent method to study hydrogen bonds between HPC molecules and water molecules. Boltzmann fitting and PCMW could help determine the exact transition temperatures of each involving functional groups in the two processes. Moreover, 2Dcos was used to discern the sequential moving orders of the functional groups during the two phase transitions. Depending on the structure of HPC and the thermodynamic conditions, the dominating associative elements in either process might vary. During the coil-to-globule transition, HPC molecules precipitated to form an opaque system with mobility.It was discovered that the driving force of the coil-to-globule transition process in microdynamics could only be the dehydration and hydrophobic interactions of C–H groups. However, in the sol–gel transition, the system crosslinked to form a physical network with no mobility. The driving force of this process in microdynamics was primarily the self-assembly behavior of O–H groups in HPC “active molecules”.     

THE MECHANICAL VIEW OF THE SURFACE TENSION IS FALSE

The concept of surface tension is usually introduced as a force per unit length originated from the “stress tensor” at the liquid surface (and vaguely extended to solids). This mechanical model of the surface tension, a paradigm for many workers in the field, is wrong. The inferences from the model, however, are correct in the more common uses. Some contradictions may appear but not sufficient to abandon such a simple and intuitive concept. The origin of the surface tension, of a liquid or solid surface, is in the molecular interactions, when some other phase is put in contact with such a surface. Recent developments using the surface tension components allow to predict interfacial surface tensions and to measure surface tension of solids. Although the power of this approach is evident, its use is only incipient because some results, particularly the presence of negative interfacial tensions, are difficult to interpret using the erroneous vision of surface tension as a consequence of a “stress tensor” at the liquid (or solid) surface. We present here some properties of liquids useful to fundament the concept of surface tension and briefly refer to Laplace's equation, Young's equation and capillarity, attempting to correct some misinterpretations.     

Structure development and physical properties achieved in the drawing and/or annealing of PEN fibers

As‐spun poly(ethylene‐2,6‐naphthalate) (PEN) fibers (i.e., precursors) prepared from high molecular weight polymer were drawn and/or annealed under various conditions. Structure and property variations taking place during the treatment process were followed via wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering, differential scanning calorimetry (DSC), and mechanical testing. Both the WAXS and DSC measurements of the cold‐drawn samples stretched from a low‐speed‐spun amorphous fiber indicate that strain‐induced crystallization can occur at a temperature below the glass‐transition temperature and that the resultant crystal is in the α‐form modification. In contrast, when the same precursor was subjected to constrained annealing, its amorphous characteristics remained unchanged even though the annealing was performed at 200 °C. These results may imply that the application of stretching stress is more important than elevated temperatures in producing α‐form crystallization. The crystalline structure of the hot‐drawn samples depends significantly on the morphology of the precursor fibers. When the precursor was wound at a very low speed and in a predominantly amorphous state, hot drawing induced the formation of crystals that were apparently pure α‐form modification. For the β‐form crystallized precursors wound at higher speeds, a partial crystalline transition from the β form to the α form was observed during the hot drawing. In contrast with the mechanical properties of the as‐spun fibers, those of the hot‐drawn products are not improved remarkably because the draw ratio is extremely limited for most as‐spun fibers in which an oriented crystalline structure has already formed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1424–1435, 2000