Complex Crystallization Behavior Research Articles

Crystallization Behavior of Copolyesters Containing Sulfonates.

The polar sulfonate groups in cationic dyeable polyester (CDP) lead to complex crystallization behavior, affecting CDP production's stability. In this study, cationic dyeable polyesters (CDP) with different sulfonate group contents were prepared via one-step feeding of sodium isophthalic acid-5-sulfonate (SIPA), terephthalic acid (PTA), and ethylene glycol (EG). The non-isothermal crystallization behavior of these copolyesters was analyzed by differential scanning calorimetry (DSC). Results show that the crystallization temperature of the sample shifts to lower values with the increase in SIPA content. The relaxation behavior of the molecular chain is enhanced due to the ionic aggregation effect of sulfonate groups in CDP. Therefore, at low cooling rates (2.5 °C/min and 5 °C/min), some molecular chain segments in CDP are still too late to orderly stack into the lattice, forming metastable crystals, and melting double peaks appear on the melting curve after crystallization. When the cooling rate increases (10-20 °C/min), the limited region of sulfonate aggregation in CDP increases, resulting in more random chain segments, and a cold crystallization peak appears on the melting curve after crystallization. The non-isothermal crystallization behavior of all samples was fitted and analyzed by the Jeziorny equation, Ozawa equation, and Mo equation. The results indicate that the nucleation density and nucleation growth rate of CDP decrease with the increase in SIPA content. Meanwhile, analysis of the Kissinger equation reveals that the activation energy of non-isothermal crystallization decreases gradually with the increase in SIPA content, and the addition of SIPA makes CDP crystallization more difficult.

Synthesis of Calamitic Fluorinated Mesogens with Complex Crystallization Behavior.

This work presents the synthesis and self-organization of the calamitic fluorinated mesogen, 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-4-iodobutoxy)ethanesulfonic acid, a potential model for perfluorosulfonic acid membranes (PFSA). The compound is derived in three steps from 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-iodoethoxy)ethanesulfonyl fluoride, achieving a 78% overall yield. The resulting compound exhibits intricate thermal behavior. At 150 °C, a crystal-to-crystal transition is observed due to the partial disordering of calamitic molecules, which is followed by isotropization at 218 °C. Upon cooling, sample ordering occurs through the formation of large smectic liquid crystalline phase domains. This thermotropic state transforms into a layered crystal phase at lower temperatures, characterized by alternating hydrophilic and hydrophobic layers. Using X-ray diffraction, crystalline unit cell models at both room temperature and 170 °C were proposed. Computer simulations of the molecule across varying temperatures support the idea that thermal transitions correlate with a loss of molecular orientation. Importantly, the study underscores the pivotal role of precursor self-organization in aligning channels during membrane fabrication, ensuring controlled and oriented positioning.

Unraveling the Complex Polymorphic Crystallization Behavior of the Alternating Copolymer DMDS-alt-DVE.

A complex crystallization behavior was observed for the alternating copolymer DMDS-alt-DVE synthesized via thiol-ene step-growth polymerization. Understanding the underlying complex crystallization processes of such innovative polythioethers is critical for their application, for example, in polymer coating technologies. These alternating copolymers have polymorphic traits, resulting in different phases that may display distinct crystalline structures. The copolymer DMDS-alt-DVE was studied in an earlier work, where only two crystalline phases were reported: a low melting, L - Tm, and high melting, H - Tm phase. Remarkably, the H - Tm form was only achieved by the previous formation and melting of the L - Tm form. We applied calorimetric techniques encompassing seven orders of magnitude in scanning rates to further explore this complex polymorphic behavior. Most importantly, by rapidly quenching the sample to temperatures well below room temperature, we detected an additional polymorphic form (characterized by a very low melting phase, denoted VL - Tm). Moreover, through tailored thermal protocols, we successfully produced samples containing only one, two, or all three polymorphs, providing insights into their interrelationships. Understanding polymorphism, crystallization, and the resulting morphological differences can have significant implications and potential impact on mechanical resistance and barrier properties.

Over 18% Efficiency of All-Polymer Solar Cells with Long-Term Stability Enabled by Y6 as a Solid Additive.

Morphology control greatly influences the power conversion efficiency (PCE) and long-term stability of all-polymer solar cells (all-PSCs); however, it remains challenging owing to their complex crystallization behavior. Herein, a small amount of Y6 (2 wt%) is introduced as a solid additive into a PM6:PY-DT blend. Y6 remained inside the active layer and interacted with PY-DT to form a well-mixed phase. Increased molecular packing, enlarged phase separation size, and decreased trap density are observed for the Y6-processed PM6:PY-DT blend. The corresponding devices showed simultaneously improved short-circuit current and fill factor, achieving a high PCE of over 18% and excellent long-term stability, with a T80 lifetime of 1180h and an extrapolated T70 lifetime of 9185h at maximum power point tracking (MPP) conditions under continuous one-sun illumination. This Y6-assisted strategy is successfully applied to other all-polymer blends, demonstrating its universality for all-PSCs. This work paves a new way for the fabrication of all-PSCs with high efficiency and superior long-term stability.

A Novel Approach to Analysis of Complex Crystallization Behavior in Zr-Based Bulk Metallic Glass by Non-isothermal Kinetics Studies

The complex crystallization behavior of the Zr40Ti15Cu10Ni10Be25 bulk metallic glass (BMG) produced by suction-casting method was studied with the non-isothermal DSC measurements with the heating rate from 5 to 40 K/min. Three exothermic phenomena were observed for the investigated material. The novel evaluation procedure for qualitative and quantitative analysis of intricate crystallization kinetics for Zr-based BMGs is proposed. The unusual deconvolution of the DSC curves based on a Gaussian function and a two-phase exponential decay function allowed for separate, detailed analysis of overlapped peaks. The activation energies for each crystallization stage were studied based on overall (Kissinger) and local (Kissinger–Akahira–Sunose) procedures. The KAS method applied separately for both low and high heating rates showed a significant difference in local activation energies. Finally, the local Avrami exponent evaluation revealed that the first two stages of crystallization are diffusion-controlled with mainly increasing nucleation rate, whereas the third crystallization is more growth-dominated.

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage.

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0-100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass-crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.

Low- versus Mid-frequency Raman Spectroscopy for in Situ Analysis of Crystallization in Slurries.

Slurry studies are useful for exhaustive polymorph and solid-state stability screening of drug compounds. Raman spectroscopy is convenient for monitoring crystallization in such slurries, as the measurements can be performed in situ even in aqueous environments. While the mid-frequency region (400–4000 cm–1) is dominated by intramolecular vibrations and has traditionally been used for such studies, the low-frequency spectral region (<200 cm–1) probes solid-state related lattice vibrations and is potentially more valuable for understanding subtle and/or complex crystallization behavior. The aim of the study was to investigate low-frequency Raman spectroscopy for in situ monitoring of crystallization of an amorphous pharmaceutical in slurries for the first time and directly compare the results with those simultaneously obtained with mid-frequency Raman spectroscopy. Amorphous indomethacin (IND) slurries were prepared at pH 1.2 and continuously monitored in situ at 5 and 25 °C with both low- and mid-frequency Raman spectroscopy. At 25 °C, both spectral regions profiled amorphous IND in slurries as converting directly from the amorphous form toward the α crystalline form. In contrast, at 5 °C, principal component analysis revealed a divergence in the detected conversion profiles: the mid-frequency Raman suggested a direct conversion to the α crystalline form, but the low-frequency region showed additional transition points. These were attributed to the appearance of minor amounts of the ε-form. The additional solid-state sensitivity of the low-frequency region was attributed to the better signal-to-noise ratio and more consistent spectra in this region. Finally, the low-frequency Raman spectrum of the ε-form of IND is reported for the first time.

Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Oils: Comparison of Phase Transition, Viscosity, and Pour Point

According to the ASTM D97, the pour point is the temperature below which petroleum products cease to flow. To evaluate the relevance of pour point measurements for synthetic lubricating oils, we investigated the crystallization, melting temperature and low-temperature flow behavior of one mineral and five synthetic lubricating oils. The classification of three groups emerged from this process. The formation of paraffin crystals in mineral oils (I) below the crystallization temperature causes shear-thinning behavior and a yield point. The crystallization temperature determined in the thermal analysis and rheology correlates well with the pour point. Synthetic lubricating oils, which solidify glass-like (II), exhibit a steady viscosity increase with falling temperature. The temperature at which viscosity reaches 1000 Pas corresponds well to the pour point. Synthetic oils, especially esters, with complex crystallization behavior (III), exhibit supercooling depending on the shear rate and cooling conditions. For these lubricating oils, the pour point provides no information for low-temperature applicability.

Combination of indirect and direct approaches to the description of complex crystallization behavior in GeSe2-rich region of pseudobinary GeSe2–Sb2Se3 system

The crystallization behavior of the (GeSe2)x(Sb2Se3)1-x system for x = 0.6–0.9 was studied indirectly by using differential scanning calorimetry (DSC) under non-isothermal conditions. DSC experiments revealed a complex behavior consisting of several subprocesses. Using the direct observation method of infrared microscopy and X-ray diffractometry, we found that the overall complicated crystallization process occurred via nucleation and growth of two different crystalline phases, Sb2Se3 and GeSe2. The overall crystallization behavior was analyzed within the current kinetic theory. The deconvoluted DSC curves were fitted using a combination of Gaussian, Johnson-Mehl-Avrami, and autocatalytical models to describe the kinetics of the subprocesses. The combination of the different kinetic models provided reliable kinetic parameters which corresponded well with the direct observation of the crystal growth process followed by microscopy.

Molecular Origins of Polymorphism in Cocoa Butter.

Cocoa butter displays complex crystallization behavior and six crystal polymorphic forms. Although the crystal structure of cocoa butter has been studied extensively, the molecular interactions between cocoa butter triacylglycerols in relation to polymorphic transformations from metastable forms (forms III and IV) to stable crystal forms (forms V and VI) remain largely unknown. In this review, the triclinic polymorphism and melting profiles of the major triacylglycerols in cocoa butter-POP, POS, and SOS-are reviewed, and their binary and ternary phase behaviors in metastable (pseudoβ') and stable (β2) crystal forms are discussed. We also attempt to clarify how the transformation of cocoa butter from form IV to V, as a critical step in the tempering of chocolate, is controlled by POS interactions with both POP and SOS. Moreover, we show how the crystal forms V and VI of cocoa butter are templated by crystal forms β3 and β1 of POS, respectively.

Crystallization of l-glutamic acid under microfluidic conditions and levitation

To gain control over polymorph selection is a pivotal issue in the pharmaceutical, food, and fine chemical industry. However, the mechanisms which affect polymorph selectivity are still not fully chartered. In the present study, we demonstrated the complex crystallization behavior of l-glutamic acid under microfluidic conditions. Amorphous intermediates occur in the early stages of the experiment, which undergo a series of aging steps – such as aggregation/coalescence, growth, or shrinking – before the stable β-polymorph forms. Experiments indicated that the attachment of amorphous particles partly feds crystal growth. This complex mechanism, which was observed under laminar flow conditions, might lead to the preferential formation of a flower-like shape of β-l-glutamic acid. We accompanied these experiments, which were characterized by laminar flow-conditions, with experiments under acoustic levitation in which crystal formation takes place under constant but gentle convection in an evaporating droplet. In these experiments, a similar phenomenon was also observed. However, when crystallization was conducted in a conventional stirred-tank, a mixture of α-form and β-form was formed, characterized by a prism, needle- and plate-like morphologies instead of the distinct flower-like in earlier experiments. This demonstrates that gentle flow conditions, such as a laminar flow in a microfluidic device, preferentially leads to a complex flower-like shape than conventional approaches in a stirred tank.

Crystallization of poly(hexamethylene carbonate)-co-poly(hexamethylene urethane) segmental block copolymers: From single to double crystalline phases

The crystallization behavior of aliphatic poly(hexamethylene carbonate)-co-poly(hexamethylene urethane) (PHCU) segmental block copolymers was studied through non-isothermal differential scanning calorimetry (DSC) experiments at different rates, successive self-nucleation and annealing (SSA), in-situ wide-angle X-ray diffraction (WAXD), and in-situ Fourier transform infrared spectroscopy (FTIR). The crystallization and melting temperatures show linear dependence on the hexamethylene urethane content ([HU]) in PHCU copolymers with high [HU], as well as the similarities of the crystalline structure, indicated an isomorphic-like cocrystallization behavior. However, such behavior was discarded because of the sequential crystallization and sequential melting found by cooling and heating the samples at 1 °C/min, and the cold-crystallization peaks by heating the samples at 10 °C/min, specially at low [HU]. Also, bimodal SSA profiles at low [HU] (≤30 mol%) were found. The fractions at low temperatures could be assigned to the polycarbonate (PC)-rich phase, and those at high temperatures to the polyurethane (PU)-rich phase. The bimodal SSA profile was evident in the PHCU with 10 mol% [HU] (i.e., PHCU-10), which was selected for further analysis. The in-situ WAXD and in-situ FTIR results corroborated the sequential crystallization and melting of the PC- and PU-rich crystals in the PHCU-10 and can be extrapolated to [HU] as high as 30 mol%. The PHCU copolymers had a complex and rate-dependent crystallization behavior, characterized by a single crystallization of the PU-rich phase at high [HU] and double phases including crystallization of both PU- and PC-rich at low [HU].

Super High‐Expansion Poly(Lactic Acid) Foams with Excellent Oil‐Adsorption and Thermal‐Insulation Properties Fabricated by Supercritical CO2 Foaming

AbstractBio‐based and biodegradable poly(lactic acid) (PLA) foams with a high expansion ratio show great application potential in oil‐adsorption and thermal‐insulation, which are crucial for oil‐spill cleanup and energy saving. However, it is difficult to prepare high‐expansion PLA foam due to the poor melt strength and complex crystallization behavior of PLA. Herein, super high‐expansion PLA foams with excellent oil‐adsorption and thermal‐insulation properties are successfully prepared using a modified supercritical CO2 foaming technology without introducing eco‐unfriendly chain extenders or fillers. High‐strength melt at low temperature and low‐strength melt at high temperature are used to prepare closed‐cell and open‐cell foams, respectively. The resulting PLA closed‐cell foam with an expansion ratio of 60 shows a thermal conductivity as low as 31.7 mW m−1 k−1, and the PLA open‐cell foam with an expansion ratio of 43 and exhibits an adsorption capacity of 10.9–31.2 g g−1 for various oils. Based on the prepared PLA foams with tunable structure, the influence of cell structure on the properties of the foam is also studied. Of particular note, reducing the cell size can obviously enhance the surface hydrophobicity of PLA foam. This work provides a green strategy for the preparation of eco‐friendly materials applied in environment protection and energy conservation.

Crystallization behavior of air-plasma-sprayed ytterbium-silicate-based environmental barrier coatings

A combination of characterization techniques has been used to provide new understanding of the complex crystallization behavior of as-sprayed amorphous Yb2Si2O7-based air-plasma-sprayed environmental barrier coatings (EBCs). During crystallization heat-treatment, initially a mixture of metastable α-Yb2Si2O7 and X1-Yb2SiO5 phases form, along with stable β-Yb2Si2O7 and X2-Yb2SiO5 phases. Eventually the metastable phases transform to the stable β-Yb2Si2O7 (major) and X2-Yb2SiO5 (minor) phases. The significant volume expansion associated with these transformations partially contributes towards the anomalous expansion measured in these EBCs after crystallization, but it does not account for all the measured expansion. In this context, in similar EBCs, it is also observed that the porosity increases upon crystallization heat-treatment, primarily in the form of thin, interconnected pores, which also contributes to the measured anomalous expansion. Based on this understanding, guidelines are provided for ‘near-net-shape’ crystallization of phase-pure, dense β-Yb2Si2O7 EBCs that are free of vertical cracks.

Ultrafast scanning calorimetry of newly developed Au-Ga bulk metallic glasses

The isothermal crystallization times and critical cooling rates of the liquid phase are determined for the two bulk metallic glass forming alloys Au49Ag5.5Pd2.3Cu26.9Si16.3 and Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 by using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of Au49Ag5.5Pd2.3Cu26.9Si16.3, a typical crystallization nose was observed, whereas for the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 alloy it is shown that the minimal isothermal nose time does allow for a quantification of the macroscopic critical thickness. It is discussed in contrast to the critical cooling rate, which is found to allow less exact calculations of the critical thickness and thus does not correlate well with the critical cooling rate from macroscopic experiments. Additionally the crystallization data of Au49Ag5.5Pd2.3Cu26.9Si16.3 was modeled using classical nucleation theory with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, enabling a determination of the interfacial energy.

Dapsone Form V: A Late Appearing Thermodynamic Polymorph of a Pharmaceutical.

Five anhydrate polymorphs (forms I-V) and the isomorphic dehydrate (Hydehy) of dapsone (4,4'-diaminodiphenyl sulfone or DDS) were prepared and characterized in an interdisciplinary experimental and computational study, elucidating the kinetic and thermodynamic stabilities, solid form interrelationships, and structural features of the known forms I-IV, the novel polymorph form V, and Hydehy. Calorimetric measurements, solubility experiments, and lattice energy calculations revealed that form V is the thermodynamically stable polymorph from absolute zero to at least 90 °C. At higher temperatures, form II, and then form I, becomes the most stable DDS solid form. The computed 0 K stability order (lattice energy calculations) was confirmed with calorimetric measurements as follows, V (most stable) > III > Hydehy > II > I > IV (least stable). The discovery of form V was complicated by the fact that the metastable but kinetically stabilized form III shows a higher nucleation and growth rate. By combining laboratory powder X-ray diffraction data and ab initio calculations, the crystal structure of form V ( P21/ c, Z' = 4) was solved, with a high energy DDS conformation allowing a denser packing and more stable intermolecular interactions, rationalizing the formation of a high Z' structure. The structures of the forms I and IV, only observed from the melt and showing distinct packing features compared to the forms II, III, and V, were derived from the computed crystal energy landscapes. Dehydration modeling of the DDS hydrate led to the Hydehy structure. This study expands our understanding about the complex crystallization behavior of pharmaceuticals and highlights the big challenge in solid form screening, especially that there is no clear end point.

Fast scanning calorimetry clarifies the understanding of the complex melting and crystallization behavior of polyesteramide multi‐block copolymers

AbstractFast scanning calorimetry has been applied in order to understand the phase transitions in thermoplastic elastomers (TPEs) based on well‐defined multi‐block copolymers made of ‘soft’ polytetrahydrofuran and ‘hard’ terephthalate ester diamides. The intrinsically complex chemical structure of TPEs leads to complex phase transitions. By changing their thermal history over a wide range of temperature (from −100 °C to 200 °C) and cooling rates (from 10 to 4000 °C s−1), we clarify the origins of the various phases present in these materials. In particular, we study the different possibilities for the hard segments to associate depending on their mobility during the quenching phase, forming either strong and stable structures or weaker and metastable ones. Besides, we demonstrate that a minimal cooling rate of 800 °C s−1 is necessary to keep these TPEs (made of short and monodisperse hard segments) amorphous leading to a subsequent cold crystallization when heating back, at around 30 °C. Finally, we validate our interpretations by varying the copolymer composition (from 10 wt% to 20 wt% hard segments), revealing the thermal invariance of poorly organized domains. Based on these data, we also discuss the importance of chain diffusion in the crystallization process. Applying fast scanning calorimetry allows us to link fundamental understanding to industrial application. © 2018 Society of Chemical Industry

Understanding Dissolution and Crystallization with Imaging: A Surface Point of View.

The tendency for crystallization during storage and administration is the most considerable hurdle for poorly water-soluble drugs formulated in the amorphous form. There is a need to better detect often subtle and complex surface crystallization phenomena and understand their influence on the critical quality attribute of dissolution. In this study, the interplay between surface crystallization of the amorphous form during storage and dissolution testing, and its influence on dissolution behavior, is analyzed for the first time with multimodal nonlinear optical imaging (coherent anti-Stokes Raman scattering (CARS) and sum frequency generation (SFG)). Complementary analyses are provided with scanning electron microscopy, X-ray diffraction and infrared and Raman spectroscopies. Amorphous indomethacin tablets were prepared and subjected to two different storage conditions (30 °C/23% RH and 30 °C/75% RH) for various durations and then dissolution testing using a channel flow-through device. Trace levels of surface crystallinity previously imaged with nonlinear optics after 1 or 2 days of storage did not significantly decrease dissolution and supersaturation compared to the freshly prepared amorphous tablets while more extensive crystallization after longer storage times did. Multimodal nonlinear optical imaging of the tablet surfaces after 15 min of dissolution revealed complex crystallization behavior that was affected by both storage condition and time, with up to four crystalline polymorphs simultaneously observed. In addition to the well-known α- and γ-forms, the less reported metastable ε- and η-forms were also observed, with the ε-form being widely observed in samples that had retained significant surface amorphousness during storage. This form was also prepared in the pure form and further characterized. Overall, this study demonstrates the potential value of nonlinear optical imaging, together with more established solid-state analysis methods, to understand complex surface crystallization behavior and its influence on drug dissolution during the development of amorphous drugs and dosage forms.

Influence of pH on morphology, size and polymorph of room temperature synthesized calcium carbonate particles

Calcium carbonate (CaCO3) particles have been used in various applications, including medicine, drug delivery and orthopedics. Having three different polymorphs and exhibiting complex crystallization behavior, it is a challenging task to systematically control physical properties of CaCO3 particles for desired applications. Herein, the influence of pH and [Ca2+]:[CO32−] ratio on the morphology, size and polymorph of room temperature synthesized CaCO3 particles were investigated. Although, in literature, ethylene glycol concentration of precursor solutions is considered as one of the most critical factors controlling polymorph and morphology of CaCO3 particles, present work highlights precursor solution pH to be a stronger factor in controlling room temperature synthesized CaCO3 particle properties. In fact, CaCO3 particle size decreased from micron to sub-micron range and calcite polymorph transformed to vaterite upon decreasing pH of the precursors for all of the precursor solution [Ca2+]:[CO32−] ratios investigated in this study. Importantly, CaCO3 particles with different and distinct morphologies were obtained by altering pH and [Ca2+]:[CO32−] ratios of the precursor solutions. Since requirements for the physical properties of CaCO3 particles are diverse for industrial and medical applications, it is important to understand CaCO3 crystallization behavior for tailored particle synthesis.

Thermo‐structural characterization of (As2Se3)100‐x‐(As2Te3)x glasses for infrared optics

AbstractDifferential scanning calorimetry was used to study thermokinetic behavior of (As2Se3)100−x(As2Te3)x infrared glasses (seven compositions along the pseudo‐binary were investigated). Glass‐transition kinetics was described in terms of the Tool‐Narayanaswamy‐Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. The enthalpy relaxation kinetics was found to be absolutely uninfluenced by changing Se/Te ratio. On the other hand, DSC crystallization behavior changed significantly with increasing As2Te3 content: Te‐rich compositions show marked affinity toward crystallization, whereas in case of the compositions with 0‐34 mol.% As2Te3 crystal growth is significantly suppressed. X‐ray diffraction analysis indicated presence of monoclinic As2Se3, As2Te3, and As2Se(Te)3 phases. The complex crystallization behavior occurring in case of the Te‐rich compositions was described by superposition of two autocatalytic kinetic signals. Based on the information from infrared microscopy the two overlapping crystallization processes can be attributed to the respective formations of spherulitic and needle‐shaped crystallites. Best glass stability was identified in case of the (As2Se3)66(As2Te3)34 composition, which appears to be a potential candidate for optic applications in the far‐infrared region of the spectrum.