Molecular Motion Research Articles

Diffusion-Ordered Spectroscopy (DOSY) as a Powerful NMRMethod to Investigate Molecular Mobitiesand IntermolecularInteractions in Complex Oil Mixtures.

Studying the characteristics and molecular mechanisms of liquid self-diffusion coefficient and viscosity changes is of great significance for, e.g., chemical and petroleum processing. As an example of a highly complex liquid, asphaltene-free high-acid and high-viscosity crude oil and its extracted fractions were studied by comparing their 1H DOSY diffusion maps. The crude oil exhibited a polydisperse diffusion distribution, including multiple diffusion portions with diffusion coefficients much smaller than that of any single fraction in independent diffusion. The main mechanism that leads to the decreases in the diffusion coefficients of crude oil is attributed to diffusion resistance enhanced by Dynamical Molecular-Interaction Networks (DMINs), rather than by enlargement of the diffusion species caused by molecular aggregation. Constructed through the synergistic interactions of various polar molecules in crude oil, DMINs dynamically bind polar molecules, trap polarizable molecules, and spatially hinder the free motion of non-polar molecules. Overall, this reduces the diffusion coefficients of all molecular. This study demonstrates that DOSY is a powerful NMR method to investigate molecular motion abilities in complex mixtures. In addition, the insights in the influence of the interaction matrix on the molecular mobility also help to understand the contribution of "structural viscosity" to the viscosity of heavy oil.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer.

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Microwave‐Responsive Flexible Room‐Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

AbstractThe development of flexible, room‐temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4‐biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg=−27.1 °C), which exhibits a remarkable UV‐light‐dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase‐dependent RTP materials while demonstrating a promising approach toward microwave detection.

Exploring the Impact of Intermolecular Interactions on the Glassy Phase Formation of Twist-Bend Liquid Crystal Dimers: Insights from Dielectric Studies

The formation of the nematic to twist-bend nematic (NTB) phase has emerged as a fascinating phenomenon in the field of supramolecular chemistry, based on complex intermolecular interactions. Through a careful analysis of molecular structures and dynamics, we elucidate how these intermolecular interactions drive the complex twist-bend modulation observed in the NTB. The study employs broadband dielectric spectroscopy spanning frequencies from 10 to 2 × 109 Hz to investigate the molecular orientational dynamics within the glass-forming thioether-linked cyanobiphenyl liquid crystal dimers, namely, CBSC7SCB and CBSC7OCB. The experimental findings align with theoretical expectations, revealing the presence of two distinct relaxation processes contributing to the dielectric permittivity of these dimers. The low-frequency relaxation mode is attributed to an “end-over-end rotation” of the dipolar groups parallel to the director. The high-frequency relaxation mode is associated with precessional motions of the dipolar groups about the director. Various models are employed to describe the temperature-dependent behavior of the relaxation times for both modes. Particularly, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics in accordance with findings from infrared (IR) spectroscopy. Here, as the longitudinal correlations of dipoles intensify, the m1 mode experiences a sudden upsurge in enthalpy, while the m2 mode undergoes continuous changes, displaying critical mode coupling behavior. Interestingly, both types of molecular motion exhibit a strong cooperative interplay within the lower temperature range of the NTB phase, evolving in tandem as the material’s temperature approaches the glass transition point. Consequently, both molecular motions converge to determine the glassy dynamics, characterized by a shared glass transition temperature, Tg.

Effect of Pressure and Temperature Variation on Wax Precipitation in the Wellbore of Ultradeep Gas Condensate Reservoirs

Summary To investigate the wax precipitation mechanism of condensate in a wellbore during the ultradeep gas condensate reservoir development, condensate samples were prepared in this work. Changes in the temperature and pressure of fluid flow in the wellbore are simulated by a high-temperature and high-pressure pressure/volume/temperature (PVT) system. This simulation explores their influences on the wax precipitation of the condensate produced from the target reservoir. The results show that the temperature decrease weakens the wax molecular movement activity and promotes the precipitation of wax, resulting in the expansion of the pressure range in which wax precipitation occurs in the system. Meanwhile, decreasing the pressure promotes wax aggregation by increasing van der Waals forces between wax molecules, thereby increasing the wax precipitation rate. At different temperatures, the wax precipitate amount first increases and then decreases with decreasing pressure, which is determined by the wax solubility and remaining content in the system. Since the solubility of a low carbon number component is more sensitive to temperature and pressure changes than that of a high carbon number component, in the early stages of experimental temperature and pressure decreases, the precipitation of coarse crystalline wax with carbon numbers ranging from C16 to C30 is more active than that of microcrystalline wax with carbon numbers exceeding C30. The remaining amount of the former component in the system decreases rapidly, and its precipitation capacity weakens, thus increasing the amount of the latter component in the precipitated wax during the later stage of experiments; this trend corresponds to the shift of the curve peak of the wax carbon number distribution to an abscissa interval with the relatively high carbon numbers. This work can provide reference data for the prediction of the well depth at which the wax precipitation occurs and the wax composition, aiming to promote the implementation of wellbore wax blockage prevention programs.

Promoting organic room temperature phosphorescence through in situ polymerization

AbstractOrganic room temperature phosphorescence materials (RTP) have attracted much attention for their wide application in organic light‐emitting diodes, anti‐counterfeiting, and sensors. In this work, a series of organic luminogens containing carbonyl and aromatics were fixed in a three‐dimensional polymethyl methacrylate (PMMA) network by in situ polymerization. All organic luminogens‐doped in situ PMMA (s‐PMMA) columns achieved longer RTP lifetimes than those of doped commercial PMMA (c‐PMMA) films, especially, the RTP lifetime of NMP2O in these PMMA matrixes increased from 1.82 ms to 156.34 ms by about 86 times. It is mainly due to the restriction of molecular motions by highly entangled polymer chains and rigid environments to efficiently inhibit the non‐radiative transitions. Also, the excellent shielding effect toward oxygen by the in situ polymerization process can avoid possible quenching effects on triplet excited states, beneficial to RTP emission. Thus, it affords an efficient approach to achieving persistent RTP for three‐dimensional displaying applications.

Excited-State Dynamics Simulations of a Light-Driven Molecular Motor in Solution.

Molecular motors, where light can be transformed into motion, are promising in the design of nanomechanical devices. For applications, however, finding relationships between molecular motion and the environment is important. Here, we report the study of excited-state dynamics of an overcrowded alkene in solution using a hybrid quantum mechanics/molecular mechanics (QM/MM) approach combined with excited-state molecular dynamics simulations. Using QM/MM surface-hopping trajectories, we calculated time-resolved emission and transient absorption spectra. These show the rise of a short-lived Franck-Condon state, followed by the formation of a dark state in the first 150 fs before the molecular motor relaxes to the ground state in about 1 ps. From the analysis of radial distribution functions, we infer that the orientation of the solvent with respect to the molecular motor in the electronic excited state is similar to that in the ground state during the photoisomerization.

On Relative Importance of Vehicular and Structural Motions in Defining Electrolyte Transport

Molecular motions of ionic and neutral electrolyte species determine transport properties at the continuum scale. These molecular motions can be classified as vehicular (e.g., cations moving with a solvation shell of neighboring solvent molecules) and structural (e.g., cations hopping from one solvation shell to another) motions. While literature studies have described the presence, and relative importance, of each of these motions in various electrolytes, a clear link to macroscopic transport properties has not been made. We herein establish this link by using the fluctuation-dissipation theorem to develop theoretical expressions connecting the molecular displacements to Stefan-Maxwell diffusivities. To illustrate the usefulness of the proposed equations, we study LiPF6 in propylene carbonate as an exemplar electrolyte. We show that its transport behavior improves at all concentrations when structural diffusion of cations is promoted. On the other hand, boosting the cation vehicular diffusion negatively affects the concentrated compositions. We extend this understanding to a generalized electrolyte of a salt dissolved in a solvent. Our theory suggests that while structural diffusion influences Stefan-Maxwell diffusivities globally, vehicular diffusion is only relevant under certain conditions. Such guidelines are critical for a bottom-up design of electrolyte transport.

Biomimetic mineralization-based In situ growth of AuNCs@ZIF-8 on paper fibers for visual detection of copper ions

As one of the essential trace elements in life activities, copper ion (Cu2+) plays a very important role in human health. However, copper-containing pesticides are usually used for sterilization and disinfestation in agriculture. Thus, the residues of copper-containing pesticides in agricultural samples increase the risk of excessive intake of Cu2+ for human. The development of an effective method for detecting Cu2+ is still an important task. Herein, a detecting system based on AuNCs@ZIF-8 modified paper and smartphone platform was developed for visual detection of Cu2+ in agricultural samples. Herein, a detecting system based on AuNCs@ZIF-8 modified paper and smartphone platform was developed for visual detection of Cu2+ in agricultural samples. In the detecting system, gold nanoclusters (AuNCs) were packaged by ZIF-8 to limit their molecular motion and enhance the fluorescence effectively. In the meanwhile, by ultrasound-assisted biomimetic mineralizing, AuNCs@ZIF-8 composites were uniformly synthesized in situ on the surface of the paper fibers to indicate Cu2+ by fluorescence quenching. A portable visual monitoring system consisted of the prepared Cu2+ paper sensor and a smartphone platform was then successfully built and applied to on site detecting Cu2+ in agricultural samples. The limit of detection (LOD) was 4.57 μM and recovery rate varied from 96.50 % to 121.58 %. The developed detecting system for Cu2+ has the advantages of easy preparation and operation, and is very suitable for the use in agricultural products and farmland.

Near-infrared-II photoacoustic imaging and photo-triggered synergistic treatment of thrombosis via fibrin-specific homopolymer nanoparticles

The formation of an occlusive thrombus in the blood vessel is the main culprit for numerous life-threatening cardiovascular diseases that represent the leading cause of morbidity and mortality worldwide. Herein, we develop a polymer nanoplatform that integrates long-wavelength second near-infrared (NIR-II) photoacoustic imaging-based thrombosis detection and antithrombotic activity. We design and synthesize a semiconducting homopolymer with strong absorption in the NIR-II region and molecular motion that boosts photothermal conversion and photoacoustic signal. We dope the homopolymer with a thermosensitive nitric oxide donor to formulate a nanoplatform, on which a fibrin-specific ligand is functionalized to ensure selective thrombus targeting. We show that with strong NIR-II light harvesting capability, bright photoacoustic signal and active thrombus accumulation ability, the NIR-II photoacoustic nanoprobes are able to sensitively and selectively delineate thrombi. We find that the nanoplatform also displays rapid and efficient blood clot removal activity with nearly complete blood flow restoration in both carotid thrombosis models and low extremity arterial thrombosis models under NIR-II light trigger by integrating a thrombus-localized photothermal effect and on-demand nitric oxide release. This nanoplatform offers a versatile approach for the diagnosis and treatment of life-threatening diseases caused by various thrombotic disorders.

Hydrogen Bond Reorganization‐Enabled Dielectric Pulsing Effects in Polar Polymers

AbstractPhase transition and relaxation, both essentially molecular motions, are critical mechanisms that determine the mechanical, electrical, optical, and thermal behaviors of polymer materials. For decades, hydrogen bonding has played an essential role in the modulation of molecular motions and material properties. However, in the design of stimulus‐responsive dielectric materials and the modulation of their properties, the role of hydrogen bonding has been rarely investigated, and its effect on dielectric response behavior remains elusive. Here, observations and proof that hydrogen bond reorganization is able to act as the origin of the dielectric pulsing effect in polar semicrystalline polymers by in situ testing is presented. A two‐step hydrogen bond reorganization drives molecular chain relaxation in polar semicrystalline polymers causing a strong dielectric response behavior, opening up the possibility of modulating dielectric response behavior through hydrogen bonding. Moreover, electrode polarization can synergize with interfacial and dipolar polarizations to enhance the dielectric pulsing effect. This study also provides a blow‐spinning method for preparing large‐area, flat, flexible, lightweight, and recyclable thermo‐responsive dielectric films by continuous, efficient, and low‐cost processing.

A ReaxFF and DFT study of effect and mechanism of an electric field on JP-10 fuel pyrolysis

To investigate the sustainable use of electric fields in improving aviation fuel combustion efficiency, a ReaxFF molecular dynamics simulation was conducted using exo-TCD (exo-tetrahydrocyclopentadiene) as the major component of JP-10 fuel. The study aimed to investigate the pyrolysis efficiency and the mechanism of electric field modulation at different temperatures. It elucidates that the pyrolysis reaction activation energy and molecular motion are the key factors affected by the co-effect of temperature and electric field. A filed strength of 10−5 V/Å was shown to increase both the reaction barriers and the probability of collision for JP-10 molecule pyrolysis, which promotes a higher reaction rate in weak electric fields with high-temperature pyrolysis. The DFT calculation was used to analyze the electronic structure and reaction potential of the JP-10 molecule under the electric field, which further discloses the effect mechanism of electric field on the pyrolysis reaction pathway. This study provides a detailed explanation of combined effects of temperature and electric field effect on aviation fuel pyrolysis to enable effective combustion of aviation fuels.

Simulation of oriented NMR spectra: Combining molecular dynamics and chemical shift tensor calculations.

Solid state NMR is widely used to study the orientation and other structural features of proteins and peptides in lipid bilayers. Using data obtained by PISEMA (Polarization Inversion Spin Exchange at Magic Angle) experiments, periodic spectral patterns arise from well-aligned α-helical molecules. Significant problems in the interpretation of PISEMA spectra may arise for systems that do not form perfectly defined secondary structures, like α-helices, or the signal pattern is disturbed by molecular motion. Here, we present a new method that combines molecular dynamics simulation with tensorial orientational constraints (MDOC) and chemical shift tensor calculations for the simulation and interpretation of PISEMA-like spectra. The calculations include the spectra arising from non α-helical molecules and molecules with non-uniform intrinsic mobility. In a first step, dipolar or quadrupolar interaction tensors drive molecular rotations and reorientations to obtain the proper mean values as observed in corresponding NMR experiments. In a second step, the coordinate snapshots of the MDOC simulations are geometry optimized with the isotropic 15 N chemical shifts as constraints using Bond Polarization Theory (BPT) to provide reliable 15 N CS tensor data. The averaged dipolar 1 H-15 N couplings and the δzz tensor components can then be combined to simulate PISEMA patterns. We apply this method to the ß-helical peptide gramicidin A (gA) and demonstrate that this method enables the assignment of most PISEMA resonances. In addition, MDOC simulations provide local order parameters for the calculated sites. These local order parameters reveal large differences in backbone mobility between L- and D-amino acids of gA.

Integrating Electron Paramagnetic Resonance Spectroscopy and Computational Modeling to Measure Protein Structure and Dynamics.

Electron paramagnetic resonance (EPR) has become a powerful probe of conformational heterogeneity and dynamics of biomolecules. In this Review, we discuss different computational modeling techniques that enrich the interpretation of EPR measurements of dynamics or distance restraints. A variety of spin labels are surveyed to provide a background for the discussion of modeling tools. Molecular dynamics (MD) simulations of models containing spin labels provide dynamical properties of biomolecules and their labels. These simulations can be used to predict EPR spectra, sample stable conformations and sample rotameric preferences of label sidechains. For molecular motions longer than milliseconds, enhanced sampling strategies and de novo prediction software incorporating or validated by EPR measurements are able to efficiently refine or predict protein conformations, respectively. To sample large-amplitude conformational transition, a coarse-grained or an atomistic weighted ensemble (WE) strategy can be guided with EPR insights. Looking forward, we anticipate an integrative strategy for efficient sampling of alternate conformations by de novo predictions, followed by validations by systematic EPR measurements and MD simulations. Continuous pathways between alternate states can be further sampled by WE-MD including all intermediate states.

Inducing Motions of Polymers in Liquid Nitrogen with Light.

Polymer materials that show macroscopic deformation in response to external stimuli are feasible for novel soft actuators including microactuators. Incorporation of photochromic moieties, such as azobenzenes, into polymer networks enables macroscopic deformation under irradiation with light through photoisomerization. Under cryogenic conditions, however, it has been difficult to induce macroscopic deformation as polymers lose their soft nature due to the severe restrictions of molecular motions. Here, activation of molecular motions and macroscopic deformation in liquid nitrogen only with light for polymers containing photochromic moieties is reported. Photoinduced bending of polymer networks with normal azobenzenes in liquid nitrogen is enabled by preliminary UV irradiation at room temperature to produce cis-isomers. To realize photoinduced deformation directly in liquid nitrogen, polymer networks are functionalized with bridged azobenzenes, which exist as cis-isomers in thermodynamic equilibrium. The films with bridged azobenzenes exhibit reversible photoisomerization and bending upon irradiation with light in liquid nitrogen without the need of preliminary irradiation, implying that the change in conformation of polymer chains can be isothermally induced even under cryogenic conditions. Achievement of flexible motions under cryogenic conditions through isothermal processes will greatly expand the operating temperature range of soft actuators.

Cinematographic study ofstochastic chemical events at atomic resolution.

The advent of single-molecule atomic-resolution time-resolved electron microscopy (SMART-EM) has created a new field of 'cinematic chemistry,' allowing for the cinematographic recording of dynamic behaviors of organic and inorganic molecules and their assembly. However, the limited electron dose per frame of video images presents a major challenge in SMART-EM. Recent advances in direct electron counting cameras and techniques to enhance image quality through the implementation of a denoising algorithm have enabled the tracking of stochastic molecular motions and chemical reactions with sub-millisecond temporal resolution and sub-angstrom localization precision. This review showcases the development of dynamic molecular imaging using the SMART-EM technique, highlighting insights into nanomechanical behavior during molecular shuttle motion, pathways of multistep chemical reactions, and elucidation of crystallization processes at the atomic level.

Surface Glass Transition Temperature Region of Diarylethene Films Determined by Nano-Marangoni Effect.

For the last two decades, research has addressed whether the glass transition temperature and the molecular motions on the surface of organic films are significantly different from those inside the bulk glasses. It is reported that the surface of the photochromic diarylethene film prepared by vacuum deposition has fluidity and the vacuum deposition of small amount of rubrene molecules induces surface tension fluctuations, generating dents due to the Marangoni flow in nanoscale. The depth of the dents increases in proportion to these radii for the colorless diarylethene film with a bulk glass transition temperature (Tg) close to room temperature. On the other hand, in the colored diarylethene obtained by UV irradiation to the colorless film, the depth becomes constant at a certain level. The Tg distribution in the depth direction is clarified based on an analysis of the dent depth. By approximating the obtained Tg depth distribution with an exponential function, the outermost surface Tg is about 100 K lower than the bulk Tg in the case of photoisomerized diarylethene.

Infrared Spectroscopy of Li+ Solvation in Diglyme: Ab Initio Molecular Dynamics and Experiment.

Infrared (IR) spectra of solutions of the lithium salt LiBF4 in diglyme, CH3O(CH2CH2O)2CH3, are studied via IR spectroscopy and ab initio molecular dynamics (AIMD) simulations. Experiments show that the major effects of LiBF4, compared to neat diglyme, are the appearance of a new broad band in the 250-500 cm-1 frequency region and a broadening and intensity enhancement of the diglyme band in the 900-1150 cm-1 region accompanied by a red-shift. Computational analysis indicates that hindered translational motions of Li+ in its solvation cage are mainly responsible for the new far-IR band, while the changes in the mid-IR are due to Li+-coordination-dependent B-F stretching vibrations of BF4- anions coupled with diglyme vibrations. Molecular motions in these and lower frequency regions are generally correlated, revealing the collective nature of the vibrational dynamics, which involve multiple ions/molecules. Herein, a detailed analysis of these features via AIMD simulations of the spectrum and its components, combined with analysis of the generalized normal modes of the solution components, is presented. Other minor spectral changes as well as diglyme conformational changes induced by the lithium salt are also discussed.

Characterization of material degradation mechanism of carbon fiber reinforced epoxy resin composites under ultraviolet radiation and salt‐fog synergistic environment

AbstractThe influence of harsh environment conditions on carbon fiber reinforced polymer composites (CFRP) restricts their popularization and usage in outdoor marine applications. Although many studies have been conducted on the service characteristics of CFRP under different conditions, the effect of ultraviolet (UV) radiation and salt‐fog synergistic aging has not been researched in detail. The primary focus of this work is to understand the aging degradation mechanism and mechanical response of CFRP in this harsh environment. The test samples were exposed to UV and salt‐fog synergistic environment. Then the physicochemical properties, dynamic/static mechanical behavior of all samples were characterized. The results show that the CFRP exposed to UV and salt‐fog environment represent noticeable synergistic aging effects. The matrix plasticization and particle washing caused by UV radiation and water condensation will intensify the erosion effect of chloride ions, thus leading to significant deterioration of the fiber‐matrix interface and interlaminar bonding. After aging, the deformation resistance of the material reduces, the molecular chain movement intensifies, the cross‐linking density of the resin matrix decreases, and the maximum decline of glass transition temperature reaches 32.36%. Compared with the tensile performance, the degradation of interlaminar shear performance is more serious, of which the interlaminar shear performance are mainly determined by the matrix and interlaminar properties. Besides, for the aged samples, more serious irreversible deformation appears during the loading process.Highlights The CFRP shows noticeable synergistic aging effects under UV and salt‐fog aging, which the matrix plasticization and particle washing caused by ultraviolet radiation and water condensation will intensify the erosion effect of chloride ions. The decrease of the cross‐linking density of CFRP materials is the primary cause for the deformation resistance reduction and properties degradation. Compared with the tensile performance, the degradation of interlaminar shear performance is more serious.

Thermal and structural properties of polyzwitterions: Effects of monomer chemistry and salt addition

Thermal and structural properties of polyzwitterions (PZI)s comprising the sulfobetaine moiety were studied as a function of LiCl addition and variations in monomer chemistry. The polyzwitterions chosen for this study are: poly(sulfobetaine methacrylate), PSBMA; poly(sulfobetaine acrylate), PSBA; and, poly(ethyl sulfobetaine methacrylate), PESBMA. When LiCl salt is added, the Li+and Cl− ions disrupt the dipole-dipole electrostatic interaction of the PZI side groups. Fourier transform infrared spectroscopy shows that the vibrational frequencies of the symmetric and asymmetric S=O bonds increase as LiCl content increases. Structural studies by wide angle X-ray scattering show that all the PZIs are amorphous, and the average interatomic spacing, d, increases in the order: dPSBA(= 0.456±0.006nm) < dPSBMA (= 0.474±0.015nm) < dPESBMA (= 0.493±0.011nm). Upon the addition of LiCl, d-spacing for a given PZI decreases as LiCl content increases. Thermogravimetry showed that PZIs had degradation onset temperatures Td ∼ 300°C. As LiCl content increases, the onset temperature of degradation decreases suggesting that the disruption of dipole-dipole crosslinks destabilizes the polymer. All the PZIs are hydrophilic and hygroscopic, and a drying procedure was developed so that well-defined glass-to-liquid transitions could be observed in the dry solid state. PZIs without LiCl have glass transition temperatures, Tg, increasing in the order: Tg,PSBA(= 200±1°C) < Tg,PESBMA (= 204±1°C) < Tg,PSBMA (= 237±1°C). As the LiCl content increases, Tg decreases, and the liquid state heat capacity increases, in all PZIs. The specific heat capacity increment at Tg was studied for PSBA as a function of LiCl content. In PSBA, the heat capacity increment reached a maximum for molar ZI:LiCl content at and above 1:1, and its value agreed well with predictions based on an empirical bead model of polymers. Thermal data on the dry state of PZI-LiCl complexes suggest an analogy between electrostatically crosslinked, fully amorphous PZIs and semicrystalline polymers. The dipolar crosslinks confine the molecular motion of PZIs just as crystal domains confine the molecular motion of the amorphous phase in semicrystalline polymers.