Phase Transition Of Polymer Research Articles

Effect of Host-Guest Complexation on the Thermoresponsive Behavior of Poly(oligo ethylene glycol acrylate)s Functionalized with Dialkoxynapththalene Guest Side Chains.

The combination of thermoresponsive polymers with supramolecular host-guest interactions enables accurate tuning of the phase transition temperature, while also providing additional response mechanisms based on host-guest complexation. Most studies focused on a single thermoresponsive polymer to demonstrate the effect of host-guest complexation on the responsive behavior. In this work, the effect of the polymer structure on the host-guest complexation and thermoresponsive behavior is reported. Therefore, different poly(oligoethylene glycol acrylate)s, namely, poly(2-hydroxyethylacrylate) (PHEA), poly(methoxy diethylene glycol acrylate), poly(methoxy triethylene glycol acrylate), and poly(methoxy tetraethylene glycol acrylate), are synthesized functionalized with 1,5-dialkoxynaphthalene guest molecules in the side chain. Their complexation with the cyclobis(paraquat-p-phenylene) tetrachloride host is studied to understand the effect of polymer structure on the supramolecular association and the polymer phase transition, revealing that the oligoethylene glycol side chains lead to weaker host-guest complexation and also have a smaller increase in the cloud point temperature compared to PHEA.

DPOLY: Deep Learning of Polymer Phases and Phase Transition

Machine learning (ML) and artificial intelligence (AI) have the remarkable ability to classify, recognize, and characterize complex patterns and trends in large data sets. Here, we adopt a subclass of machine learning methods viz., deep learnings and develop a general-purpose AI tool - dPOLY for analyzing molecular dynamics trajectory and predicting phases and phase transitions in polymers. An unsupervised deep neural network is used within this framework to map a molecular dynamics trajectory undergoing thermophysical treatment such as cooling, heating, drying, or compression to a lower dimension. A supervised deep neural network is subsequently developed based on the lower dimensional data to characterize the phases and phase transition. As a proof of concept, we employ this framework to study coil to globule transition of a model polymer system. We conduct coarse-grained molecular dynamics simulations to collect molecular dynamics trajectories of a single polymer chain over a wide range of temperatures and use dPOLY framework to predict polymer phases. The dPOLY framework accurately predicts the critical temperatures for the coil to globule transition for a wide range of polymer sizes. This method is generic and can be extended to capture various other phase transitions and dynamical crossovers in polymers and other soft materials.

Photochemical-induced phase transitions in photoactive semicrystalline polymers.

The emergent photoactive materials obtained through photochemistry make it possible to directly convert photon energy to mechanical work. There has been much recent work in developing appropriate materials, and a promising system is semicrystalline polymers of the photoactive molecule azobenzene. We develop a phase field model with two order parameters for the crystal-melt transition and the trans-cis photoisomerization to understand such materials, and the model describes the rich phenomenology. We find that the photoreaction rate depends sensitively on temperature: At temperatures below the crystal-melt transition temperature, photoreaction is collective, requires a critical light intensity, and shows an abrupt first-order phase transition manifesting nucleation and growth; at temperatures above the transition temperature, photoreaction is independent and follows first-order kinetics. Further, the phase transition depends significantly on the exact forms of spontaneous strain during the crystal-melt and trans-cis transitions. A nonmonotonic change of photopersistent cis ratio with increasing temperature is observed accompanied by a reentrant crystallization of trans below the melting temperature. A pseudo phase diagram is subsequently presented with varying temperature and light intensity along with the resulting actuation strain. These insights can assist the further development of these materials.

Role of Joule heating in the electro-induced metal-insular transition of a composite film filled with VO2

Vanadium dioxide is a typical representative of a strong electronic correlation system. Triggered by stimuli such as heat and electric fields, VO2 can undergo a reversible transition from insulating to metallic phase and has therefore attracted attention of many researchers. In this work, a hydrothermal method was used to prepare nano-VO2 particles with phase transition. According to the phenomenology, finite element simulation and theoretical calculation models of the electro-induced phase transition (E-MIT) in the VO2-filled Polyethylene glycol were established. Electrode-gap effect on the phase-transition voltage of E-MIT was discussed. Furthermore, the phase transition and heat distribution processes were analyzed. The results revealed that high-temperature conductive channels are formed in the VO2 structure during the electro-induced phase transition. Moreover, position of these channels is determined by the high-voltage edge effect of the electrode and the heat dissipation effect of the material. The ideal adiabatic E-MIT process was also evaluated. The phase change voltage curve of the theoretical model was well matched with the simulation model. The results reveal that the temperature in the channel is significantly lower than the typical phase change temperature when a phase transition occurs. In addition, owing to an applied voltage, the resistance of the VO2 composite material can drop suddenly even if the temperature rise is small. The analysis results verified that Joule heating is an important factor in the electro-induced phase transition of VO2-filled polymers. The experimental results are helpful in understanding the E-MIT mechanism of VO2 composite materials and the subsequent application of these materials.

Formation of Single Double-Layered Coacervate of Poly(N,N-diethylacrylamide) in Water by a Laser Tweezer.

We demonstrate liquid-liquid phase separation involving both coacervation and coil-to-globule phase transition of a thermoresponsive polymer. By focusing a near-infrared laser beam into an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM), a single phase-separated polymer microdroplet can be formed and stably trapped at the focal point. Such droplet formation is induced by a local elevation in temperature (induced by a photothermal effect) and an optical force. The technique allows us to selectively analyze a single polymer droplet trapped at the focal point. In this study, we applied this technique to poly(N,N-diethylacrylamide) (PDEA) in water and generated a double-layered PDEA droplet. Such an inhomogeneous and complex microstructure has not been previously observed both in steady-state heating of a PDEA solution and in the PNIPAM system. Moreover, we used micro-Raman spectroscopy to clarify that PDEA underwent dehydration due to a coil-to-globule phase transition. Despite this, the polymer concentration (Cpoly) of the trapped PDEA droplet was very low and was around 30 wt %. Cpoly depended on the molecular weight of PDEA and the laser power that regulates the temperature elevation. These results strongly indicate that PDEA undergoes coacervation in addition to a coil-to-globule phase transition. This study will help provide us with a fundamental understanding of the phase separation mechanisms of thermoresponsive polymers.

Relaxor Ferroelectric Polymers: Insight into High Electrical Energy Storage Properties from a Molecular Perspective

Relaxor ferroelectric polymers exhibit both high dielectric constants and low remnant polarization and thus deliver much higher energy densities and greater charge–discharge efficiencies than normal ferroelectrics for capacitive energy storage applications. Herein, dielectric energy storage behavior of several newly discovered relaxor ferroelectric polymers is studied from a molecular perspective. It is observed that the homopolymers exhibit very slim polarization–electric field loops and the highest charge–discharge efficiencies among ferroelectric polymers, which are attributed to the highly disordered chain conformation as evidenced from the scanning probe microscopy results. Based on the findings on the relaxor homopolymers, the benchmark relaxor ferroelectric terpolymers is revisited and insights into their outstanding capacitive performance are provided. Moreover, it is found that the disordered chain conformation in relaxor ferroelectric polymers remains as the ground state at varied temperatures and applied electric fields, which is in stark contrast to relaxor perovskites whose ground state is strongly dependent on temperatures and external electric fields. The discovery of the absence of thermal‐ and field‐induced phase transition in relaxor ferroelectric polymers makes this class of ferroelectric materials more attractive for advanced electronic and energy applications.

Reentrant Phase Transition and Out-of-Equilibrium Behavior of Liquid Polyphosphate Condensate

Liquid-liquid phase transition (LLPT) of multivalent polymers has emerged as a ubiquitous process of self-assembly in biological cells, as well as in the design of soft biomaterial and artificial cells lacking membranes. One of the most conserved linear multivalent biopolymers is inorganic polyphosphate (polyP), which is present in all three domains of life. In bacteria, polyphosphate forms membrane-less granules as a starvation survival response. However, the mechanism of polyP granule biogenesis remains unclear.

Fabrication of thermoresponsive metal-organic nanotube sponge and its application on the adsorption of endocrine-disrupting compounds and pharmaceuticals/personal care products: Experiment and molecular simulation study.

Thermoresponsive metal-organic nanotube modified (MONT-pNIPAM, pNIPAM=poly N-isopropylacrylamide) sponge was synthesized using the dip-coating method and served as an adsorbent for endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal care products (PPCPs) removal. The material was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and N2 sorption-desorption. Nonlinear regression-based equations were derived to optimize pH and ionic strength during process. Though thermoresponsive polymer phase transition between dissolve and aggregate, realizing the adsorption tunnel "ON-OFF" under the temperature control. Adsorption kinetics and isotherms were investigated on the basis of a static experiment. The pseudo-second-order kinetic model and the Langmuir isotherm were fitted well to characterize adsorption. At an initial concentration of 50mgL-1, maximum adsorption capacity were 128mg/g, 184mg/g and partition coefficient were 1.09mgg-1 μM-1, 1.13mgg-1 μM-1 for dibutyl phthalate (DBP) and parachlorometaxylenol (PCMX), respectively. The density-functional theory (DFT) was applied to calculate the interaction energy and investigate the possible mechanism. Combining the experimental data with theoretical calculation, results demonstrated that the MONT-pNIPAM sponge was a highly efficient adsorbent material that was suitable for the removal of EDCs/PPCPs from water.

Comparison of Conformational Phase Behavior for Flexible and Semiflexible Polymers.

We employ the recently introduced generalized microcanonical inflection point method for the statistical analysis of phase transitions in flexible and semiflexible polymers and study the impact of the bending stiffness upon the character and order of transitions between random-coil, globules, and pseudocrystalline conformations. The high-accuracy estimates of the microcanonical entropy and its derivatives required for this study were obtained by extensive replica-exchange Monte Carlo simulations. We observe that the transition behavior into the compact phases changes qualitatively with increasing bending stiffness. Whereas the collapse transition is less affected, the first-order liquid-solid transition characteristic for flexible polymers ceases to exist once bending effects dominate over attractive monomer-monomer interactions.

Investigation of the influence of the nano-nuclei habit on the specifics of phase transitions in long-chain molecular crystals and polymers

The thermodynamic parameters of a long chain molecular crystals (LCMCs) set are analyzed. We revealed the dependence of LCMC’s melting points with a different chain length on the habitus of the first-order phase transition’s elementary volume. It was shown that LCMCs with the same chemical structure of the “core” (normal alkanes {CH3(CH2)nCH3}, normal alkanols {CH3(CH2)nCOH}, diols {COH(CH2)nCOH}, carboxylic {CH3(CH2)nCOOH} and dicarboxylic {COOH(CH2)nCOOH} acids) lose their individual thermodynamic properties and approach the properties of polymethylene with an increase in the number of –CH2– groups.

Observing the Current Change with Increasing Temperature in Thermo-Responsive Polymer Solution Using Electrochemical Method

The behavior of redox in thermo-responsive polymer solution while heating was electrochemically observed and analyzed in this research. Temperature responsive polymers are intensively applied to various research fields and industries such as drug carriers, lithium ion batteries, temperature sensitive films, and sensor technology. For this reason, measuring the critical point and analyzing the phase transition of temperature stimuli responsive polymer are very important.In previous studies, the phase behavior of polymers according to the temperature was examined by measuring the transmittance of solution using ultraviolet–visible (UV-vis) spectroscopy and the size of polymer particles in solution using dynamic light scattering (DLS). As an electrochemical method, a collision method was used for detecting current decrease caused by aggregated polymer which blocked the electrode surface. These methods, however, were unable to track the behavior of polymer in solution during continuous temperature increase in real time easily. The temperature was increased at intervals of 5 ℃ to measure the absorbance of solution in UV-vis spectroscopy and only specific temperature and time could be used to observe the blocking signal in the electrochemical collision method. In this study, we offer the easy and novel way to monitor the thermal induced change of polymer and redox with continuous temperature increase using the electrochemical system.Lower critical solution temperature (LCST) polymer was used as the thermo-responsive polymer in this research. Dissolving the LCST polymer in organic media containing the redox, we measured the current with increasing temperature in real time. The experiment was conducted using electrochemical method with an ultramicroelectrode (UME) and the current transition according to the temperature growth was monitored. As a result, the specific current changes were obtained. Analyzing these specific current changes can be used to confirm the phase transition behavior of the temperature responsive polymer and redox in polymer solution. This study will be applied for further research with controlling the various conditions.

Temperature dependence of elastic constants in unidirectional carbon fiber reinforced shape memory polymer composites

The work describes a model to predict the elastic constants of unidirectional carbon fiber reinforced shape memory polymer composites (SMPCs) with different fiber volume fractions within the temperature range of 293 K to 393 K. The model is based on a theoretical description of the phase transition of the shape memory polymer (SMP). Two glassy phase volume fraction functions are developed, one based on the Eyring equation, the other based on the normal distribution equation. The longitudinal and transverse moduli, axial and transverse shear moduli, and axial Poisson's ratio are derived by using the glassy phase volume fraction function and modified rule of mixture. The axial Poisson's ratio increases with the temperature increase, while the other four constants decrease nonlinearly with rising temperatures. An inverse identification of the elastic constants at different temperature via numerical and experimental modal analysis from a flat SMPC laminate shows that the model proposed is adequate to describe the temperature dependence of the elastic constants of the laminate.

Side-chain crystallization and segment packing of poly(isobutylene-alt-maleic anhydride)-g-alkyl alcohol comb-like polymers

A series of poly(isobutylene-alt-maleic anhydride)-g-alkyl alcohol (PIAM-Cn) comb-like polymers were fabricated through the esterification process between poly(isobutylene-alt-maleic anhydride) (PIAM) and n-alkyl alcohol with various side-chain lengths changing from n = 10, 16, 18, 22 to 26. Side-chain crystallization, phase transition, segment conformation, and relaxation behavior of PIAM-Cn comb-like polymers have been in-depth investigated by DSC, variable-temperature X-ray scattering and FTIR, as well as dielectric spectroscopy. For PIAM-Cn comb-like polymers, the phase transition temperature, enthalpy and side-chain crystallization behavior show an obvious dependence upon the side-chain length, and a minimum requirement of carbon atoms to form the side-chain crystallites is 9. The phase transition process from regular orthorhombic packing, irregular hexagonal packing manner to the amorphous state of PIAM-C26 is well confirmed in combination with the other PIAM-Cn (n = 10, 16, 18, 22), showing the varied local packing of and conformational variation of side alkyl chains. Moreover, the chain segment relaxation of PIAM-Cn (n = 10, 18) indicates the restricted local stacking process originated from the cooperation motion of the PIAM backbone and the side chain. A proposed three-phase model is used to describe the chain motion and segment packing manner of comb-like polymers. Also, the phase transition and chain segment relaxation behavior of comb-like polymers are further interpreted from the aspect of side-chain crystallization.

Reprogrammable Ferromagnetic Domains for Reconfigurable Soft Magnetic Actuators.

Soft magnetic materials have shown promise in diverse applications due to their fast response, remote actuation, and large penetration range for various conditions. Herein, a new soft magnetic composite material capable of reprogramming its magnetization profile without changing intrinsic magnetic properties of embedded magnetic particles or the molecular property of base material is reported. This composite contains magnetic microspheres in an elastomeric matrix, and the magnetic microspheres are composed of ferromagnetic microparticles encapsulated with oligomeric-PEG. By controlling the encapsulating polymer phase transition, the magnetization profiles of the magnetic composite can be rewritten by physically realigning the ferromagnetic particles. Diverse magnetic actuators with reprogrammable magnetization profiles are developed to demonstrate the complete reprogramming of complex magnetization profile.

Intelligent optimization system for powder bed fusion of processable thermoplastics

Powder bed fusion (PBF) represents a class of additive manufacturing processes with the unique advantage of being able to fabricate functional products with complex three-dimensional geometries. PBF has been broadly applied in highly value-added industries, including the biomedical device and aerospace industries. However, it is challenging to construct a comprehensive knowledgebase to guide material selection and process optimization decisions to satisfy the product standards of various industries based on a poor understanding of process-structure-property/performance relationships for each type of thermoplastic. In this paper, an intelligent optimization system is proposed to establish quantitative relationships between process parameters and multiple optimization objectives, including mechanical properties, productivity, energy efficiency, and degree of material degradation. Polyurethane is considered as a representative thermoplastic because it is sensitive to thermal-induced degradation and has a relatively narrow process window. Material and powder properties as functions of temperature are investigated using systematic material screening. Numerical models are created to analyze the interactions between laser beams and polymeric powders by considering the effects of chamber thermal conditions, laser parameters, temperature-dependent properties, and phase transitions of polymers, as well as laser beam characteristics. The theoretically predicted features of melting pools are validated experimentally and then utilized to develop quantitative relationships between process parameters and multiple optimization objectives. The established relationships can guide process parameter optimization and material selection decisions for polymer PBF.

Controllable synthesis and spontaneous phase transition of photonic coordination polymer to produce a strong second-harmonic generation response

Herein, a novel photonic coordination polymer material was constructed by aggregation-induced emission luminogen (AIEgen) containing a tripyridyl moiety used as the linking ligand. It displayed a spontaneous direct centrosymmetric to noncentrosymmetric phase transition in a single crystal. The two crystals, before and after the phase transition, were both controllably synthesized and characterized by single-crystal X-ray diffraction. After being exposed to air, the centrosymmetric metastable phase (1-α) transitioned to a new stable phase with a noncentrosymmetric structure (1-β). Interestingly, the 1-β structure exhibited a strong phase-matching second-harmonic generation (SHG) response, about 4.5 times higher than that of KH2PO4 (KDP). In order to better understand the relationship between the structure and the nonlinear optical properties, the dipole moments were calculated and discussed. Remarkably, the noncentrosymmetric phase with high thermal stability for 1-β retained and improved the initial photoluminescent properties of the AIEgen ligand after the structural phase transition from 1-α, and simultaneously produced the excellent SHG property, which are beneficial for the design and construction of excellent optical materials.

Phase Control of Polyamide 6 via Extension‐Dominated Polymer Blend Reactive Extrusion

Control of the crystalline phase transition of polymers is critical to improve mechanical properties and to achieve good levels of thermal properties in polymer engineering. Current methods control the transition process by using thermal methods that is, annealing above the glass transition temperature (Tg) to get the targeting crystalline phase. It requires precise control of the temperature and process time and is limited to a small scale. In contrast, a novel processing‐based method developed in our group by combining the use of reactive processing technique and extensional mixing elements (EME) allows different sizes of minor phase droplets in immiscible polymer blends to be achieved by controlling the degree of aggressiveness of the EME. The use of EME can confine polyamide crystalline structure into the γ‐phase from the α‐phase. The reactive processing benefits in stabilizing these droplets and in freezing the corresponding crystalline morphologies in droplets. Crystalline phase transition of the minor phase in these droplets is therefore observed as the size of droplet decreases from micro to submicron. Furthermore, phase transition can be precisely controlled by tuning additives and EME blocks. POLYM. ENG. SCI., 60:1019–1028, 2020. © 2020 Society of Plastics Engineers

Reversible Phase Transition of Porous Coordination Polymers.

Porous coordination polymers or metal-organic frameworks with reversible phase-transition behavior possess some attractive properties, and can respond to external stimuli, including physical and chemical stimuli, in a dynamic fashion. Their phase transitions can be triggered by adsorption/desorption of guest molecules, temperature changes, high pressure, light irradiation, and electric fields; these mainly include two types of transitions: crystal-amorphous and crystal-crystal transitions. These types of porous coordination polymers have received much attention because of their interesting properties and potential applications. Herein, reversible phase transition porous coordination polymers are summarized and classified based on different stimuli sources. Corresponding typical examples are then introduced. Finally, examples of their applications in gas separation, chemical sensors, guest molecule encapsulation, and energy storage are also presented.

Role of constituents for the chirality isolation of single-walled carbon nanotubes by the reversible phase transition of a thermoresponsive polymer.

The simple sorting procedure and continuous use of poly(N-isopropylacrylamide) (PNIPAM), a well-known thermoresponsive polymer, have a high potential for the mass production of single-walled carbon nanotubes (SWCNTs) with a specific electronic structure. However, knowledge of efficient single-chirality sorting methods with mixed surfactant systems is not applicable. In this work, we explored experimental conditions by controlling the interaction among PNIPAM, sodium cholate (SC) and SWCNTs. An optimization of the PNIPAM and SC concentrations as well as the addition of sodium borate achieved the selective release of (6,4) nanotubes into the liquid phase after the PNIPAM phase transition. The sorting mechanism with PNIPAM was explained by the difference in the micelle configuration on the SWCNTs and the hydrophobic collapse of PNIPAM in the presence of a sodium salt. The one-step sorting procedure for obtaining SWCNTs with a single chirality via PNIPAM will help promote their widespread application.

Autonomous Shrinking/Swelling Phenomenon Driven By Macromolecular Interchain Cross-Linking via β-Cyclodextrin–Triazole Complexation

Molecular recognition-induced autonomous dynamic motions, which feature in living systems, have been attracting much interest because such biological functions can promote the consequent development of sophisticated functional materials. To realize molecular recognition-induced autonomous dynamic motions using synthetic materials and manipulate them, herein, we designed poly(NIPAM-co-triaz–CD), which bears a cyclodextrin (CD) host and a triazole guest in the side chains of the polymer itself; subsequently, we investigated its phase transition behavior. 2D NOESY NMR analysis evidenced that triazole in the polymer side chains was included into the CD cavity, and DLS measurements indicated that the CD–triazole complexation resulted in the formation of interchain cross-linking. Poly(NIPAM-co-triaz–CD) exhibited autonomous shrinking/swelling of the polymer chains that occurred by itself in water due to the interchain cross-linking via the CD–triazole complexation. Thus, this study enabled the poly(NIPAM) itself to generate the artificial molecular recognition-induced autonomous phenomenon. These findings not only present a unique methodology for polymer phase transition phenomena but also provide a new platform for designing molecular recognition polymeric materials.