Temperature-dependent FTIR Research Articles

Reactive extrusion fabrication of thermoplastic starch with Ca2+ heterodentate coordination structure for harvesting multiple-reusable PBAT/TPS films

Creating multiple-reusable PBAT/TPS (PT) films presents a novel solution to reduce carbon emissions from disposable packaging, addressing challenges like the high creep of PBAT and the glycerol migration of TPS. Consequently, adopting reactive extrusion to fabricate reversible cross-linking TPS with high shape memory performance, low migration, and homogeneous dispersion in PBAT matrix was a fascinating strategy. Herein, starch, glycerol and CaCl2 (calcium chloride) were extruded to fabricate TPS-Ca with Ca2+ heterodentate coordination structure and confirmed by XPS, 1H NMR and temperature-dependent FTIR. The results of DMA, dynamic rheology, flow activation energy and SEM revealed that TPS-Ca exhibited significant temperature-sensitive reversible properties and robust melt flow capability, enabling micro-nano scale dispersion in PBAT. Noteworthy, PBAT/TPS-Ca (PT-Ca) would recover 100 % length within 20 s by microwave heating after being loaded under the hygrothermal environment. Meanwhile, the migration weight of glycerol decreased from 2.5 % to 1.2 % for the heat-moisture-treated PBAT/TPS (HPT) and PBAT/TPS-Ca (HPTCa). Remarkably, the tensile strength and elongation at the break of HPT-Ca increased to 20.0 MPa and 924 %, respectively, due to reduced stress concentration sites in the phase interface. In summary, our study provides a streamlined strategy for fabricating multiple-reusable PT, offering a sustainable solution to eliminate carbon emissions linked to disposable plastic.

Chemical interaction between the sugar moieties in N, N-di-glycated alanine derivatives

The chemistry of N,N-diglycated amino acids remains unexplored due to their transient nature in the Maillard reaction. Their increased reactivity is attributed to the presence of high concentrations of open ring forms in at least one of their sugar moieties. The N,N-diglycated alanine derivatives were generated in situ via dissociation from their stable precursors the bis[N,N-diglycated alanine]iron(II) complexes, in the alanine/glucose/FeCl2 model system heated at 110 °C for 2 h. The thermal degradations of these complexes were followed in the reaction mixture, using isotope-labelled reactants, such as [13C-3] alanine and [13C–U] glucose, and ESI/qTOF/MS analysis. The N,N-diglycated amino acids exhibited a unique and characteristic chemical interaction between the neighbouring sugar moieties generating hitherto unknown heterocyclic moieties. The origin of these products was tracked by identifying ions incorporating one C-3 atom from alanine and between seven to 12 carbon atoms from the sugar moieties in the same structure. Temperature-dependent FTIR spectra of di-glycated alanine generated through ball milling provided further evidence for their reactivity.

Gelation, self-assembly, and acid responsive properties of an unsymmetrical 1,3,4-oxadiazole derivative

ABSTRACT A novel unsymmetrical 1,3,4-oxadiazole derivative (2-POXD-B8) was synthesized. 2-POXD-B8 can form organogel in methanol. The gelation and self-assembly behavior of 2-POXD-B8 were researched by SEM, XRD, UV–vis, and temperature-dependent FT-IR, etc. π–π interaction and van der Waals force are viewed as the main driving forces in the self-assembly process. In addition, 2-POXD-B8 showed acid-responsive properties in different states, including gel state and film state. A dual-channel acid response by reversible solution–gel transition and fluorescence changes was observed in the methanol gel system. The protonation of 2-POXD-B8 is the reason for its acid-responsive property.

The Signature of Fluctuations of the Hydrogen Bond Network Formed by Water Molecules in the Interfacial Layer of Anionic Lipids

As the water molecules found at the interface of lipid bilayers exhibit distinct structural and reorientation dynamics compared to water molecules found in bulk, the fluctuations in their hydrogen bond (HB) network are expected to be different from those generated by the bulk water molecules. The research presented here aims to gain an insight into temperature-dependent fluctuations of a HB network of water molecules found in an interfacial layer of multilamellar liposomes (MLVs) composed of anionic 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) lipids. Besides suspending DMPS lipids in phosphate buffer saline (PBS) of different pH values (6.0, 7.4, and 8.0), the changes in HB network fluctuations were altered by the incorporation of a non-polar flavonoid molecule myricetin (MCE) within the hydrocarbon chain region. By performing a multivariate analysis on the water combination band observed in temperature-dependent FTIR spectra, the results of which were further mathematically analyzed, the temperature-dependent fluctuations of interfacial water molecules were captured; the latter were the greatest for DMPS in PBS with a pH value of 7.4 and in general were greater for DMPS multibilayers in the absence of MCE. The presence of MCE made DMPS lipids more separated, allowing deeper penetration of water molecules towards the non-polar region and their restricted motion that resulted in decreased fluctuations. The experimentally observed results were supported by MD simulations of DMPS (+MCE) lipid bilayers.

Nucleation Retardation of Polyamide 6,6 by Tuning Hydrogen Bonding Reorganization via Nigrosine for High-Speed Injection Molding Applications

The mechanism of regulating hydrogen bond organization for polyamide 6,6 (PA 6,6) by nigrosine was investigated by temperature-dependent FTIR and in situ synchrotron X-ray diffraction during cooling/heating processes. The intermolecular interaction between amide groups and nigrosine was verified by the FTIR spectroscopy method. Upon melt cooling, the formation of H-bonds is promoted by nigrosine at the initial stage (regime I) with increased enthalpy change (ΔH1), which results from denser molecular coils as the interaction with nigrosine increases the ability to form H-bonds between adjacent amide groups, while at a lower temperature (regime II), the ΔH1 decreases with increasing nigrosine as nigrosine restrains the mobility of PA 6,6 chains that retards the formation of H-bonds between nonadjacent amide groups. Moreover, the ordering arrangement of H-bonds into 2-D hydrogen bond sheets (H-sheets) is hindered for both the regime I′/II′ stages with decreased ΔH2 due to the decreased mobility of chain segments, which retards the nucleation of PA 6,6 crystallization. The crystal perfection index (CPI) was investigated by WAXD, and it was found to decrease with the increase of nigrosine. Combined with microstructure analysis, we proposed that partial nigrosine can insert between H-sheets, which therefore tunes the Brill transition behavior of PA 6,6. Overall, the regulation mechanism of nigrosine on PA 6,6 crystallization has been established via interaction with amide groups to tune the organization of H-sheets. The retardation effects on crystallization can improve the flowability of PA 6,6 for high-speed injection molding applications.

Dynamic Multicomponent Reactions-Directed Self-Assembled G-quadruplex Inherent Antibacterial Hydrogel.

Nowadays, inherent antibacterial hydrogels have gained significant attention due to their utilization against infectious bacteria. Herein, we focus on the development of an injectable, self-healable, dynamic, and G-quadruplex hydrogel with inherent antibacterial activity. The dynamic self-assembled hydrogel is constructed upon multicomponent reactions (MCR) among guanosine, 2-formylphenylboronic acid, and amino acid/peptides in the presence of potassium ions. The role of amino acid/peptides in the formation of the G-quadruplex hydrogel is studied in detail. The G-quadruplex structure is formed via the π-π stacking of G-quartets. The formation of G-quadruplex is investigated by thioflavin T binding assay, CD spectroscopy, and PXRD. The formation of the dynamic imino-boronate bond in the hydrogels is well characterized by temperature-dependent 11B NMR (VT-NMR) and FT-IR spectroscopy. Furthermore, HR-TEM images and rheological experiments reveal the fibrillar networks and viscoelastic property of the hydrogels. The presence of the dynamic imino-boronate ester bonds makes the hydrogel injectable and self-healable in nature. These dynamic G-quadruplex hydrogels show potential antibacterial activity against a series of Gram-positive and Gram-negative bacteria. The hydrogels have been used for the entrapment and sustained release of an anticancer drug doxorubicin over 48 h at different pHs (4.8, 7.4, and 8.5) and temperature without the influence of any external stimuli. Such injectable and self-healable hydrogels could be used in various applications in the field of biomedical science.

Imparting Reprocessability, Quadruple Shape Memory, Self-Healing, and Vibration Damping Characteristics to a Thermosetting Poly(urethane-urea)

The advent of dynamic covalent bond chemistry (DCBC) has sparked renewed research interest in reprocessability of thermosetting polymers. However, combining reprocessability with stimuli-responsiveness remains a challenge for futuristic applications. Usually, a combination of complementary DCBCs is employed to integrate reprocessability with shape memory as well as self-healing (SH) attributes in a single polymeric system. In the present work, we report two-component poly(urethane-urea) (PUU) networks, with varied hard segment (HS) concentrations, that exhibit quadruple shape memory (QSM), efficacious vibration damping, thermally activated intrinsic SH as well as multiple cycles of thermal reprocessability. The component A is an isocyanate capped bi-soft segment blend of polybutadiene diol and polypropylene glycol, while the second component comprises an aromatic diamine chain extender solubilized in an oligomeric polyoxypropylene triol. The networks characterized through FTIR as well as small- and wide-angle X-ray scattering (SAXS and WAXD) revealed a phase-separated morphology with extensive hydrogen-bonding (H-bonding) interactions in the HS domains of the PUU networks. Dynamic mechanical analysis (DMA) measurements revealed broad dissipation factor (tan δ) vs temperature and frequency profiles of the networks, which could be leveraged for efficacious passive vibration damping applications. A dissociative mechanism of urethane and urea bond exchange, evidenced from temperature-dependent FTIR studies enabling facile stress relaxation, is proposed to be the mechanistic origin of the reprocessability and SH of the networks. A broad dissipation factor (tan δ) vs temperature profiles endowed the networks with QSM characteristics. We posit that the study is relevant for expanding the scope of DCBCs for development of reprocessable thermosetting polyurethanes with multiple smart functionalities.

Tri-block segmented thermoplastic elastomers of N-(aminohexyl)-N-hexylterephthalamide (6T6M) and functionalised polystyrene: Synthesis, characterization and thermal property

Abstract Low molecular weight polystyrene (PSt) containing 1,6-hexamethylenediisocyanate (HMDI) is prepared and used as soft segment. Hard segments (HS) n-(aminohexyl)-n-hexylterephthalamide (6T6M) is prepared and used for the preparation of thermoplastic elastomer. The molecular weight of the copolymer increased by increasing the hard segment content and thereby varied the HS content from 24 to 8 wt%. Inherent viscosity results prove that the synthesized polymer showed expected molecular weight and linear relationship is obtained between inherent viscosity and molecular weight of the copolymer. The 1HNMR spectrum showed expected peak which confirms the product formation. Temperature dependent FT-IR studies of the polymer reveals that the crystallinity of the HS is very high (about 90%) and the hydrogen bonding highly reversible. The thermogravimtric analysis confirms that the polymer is stable upto 420 °C. Differential calorimetric analysis showed two transition namely Tg of soft segment Tm of HS. The XRD analysis confirms the formed material is semicrystalline in nature. Swelling behaviors and solvent resisitivity confirms that the copolymer showed excellent resistivity than the PSt. Therefore the prepared copolymer is highly thermal stable with excellent solvent resisitivity.

Hydrogen-bonding stabilized columnar mesophases in hexasubstituted triphenylene 2,3-Dicarboxamides

A series of new mixed tail triphenylene derivatives having four β-alkoxy and two adjacent β-carboxamide side chains have been prepared and characterized. The synthesis was carried out by amidation of the triphenylene 2,3-dicarboxylic methyl ester with various primary amine. All the dicarboxamides exhibit an enantiotropic Colh phase, except compound TPC6-(CONHC6H13)2 bearing the shortest hexyloxy chains. Effects of variation in lengths of alkoxy and N-alkyl chains on mesogens were also studied and the pronounced influence of lengths of alkoxy chains turned out to be more important than that of N-alkyl chains. Furthermore, the intermolecular hydrogen bonding induced by amide functions in TPC8-(CONHC4H9)2 does indeed enhance the mesophase stability in comparison to the non-hydrogen bonding ester TPC8-(COOC4H9)2, as reflected by higher clearing temperatures and evidenced by temperature-dependent FT-IR studies. Although the compound TPC6-(CONHC6H13)2 was found to decompose to imide compound on the hot stage before clearing in the course of the POM experiment, only it shows good gelation property in single toluene, indicating that the intermolecular hydrogen bonding is not the only factor responsible for the formation of gel in these molecules.

Physicochemical properties and thermal-responsive phase separation of poly(ethylene glycol)-based ionic liquids

• A series of PEGylated ionic liquids were synthesized. • Physico-chemical properties of PEGylated ionic liquids were measured. • AOT-based PEGylated ILs exhibit good surface activity in aqueous solutions. • PEGylated ionic liquids exhibit typical low critical solution temperature phase behavior. • Thermal-regulated phase separation system has great promise to separate metal ions. How to design thermal-responsive functional ionic liquids that can respond in a reversible manner still remains a challenge for the construction of ionic liquid-based smart systems, and they easily find applications in various scientific fields, including phase transfer catalysis, smart soft materials, controlled drug delivery and green separation. In this work, a series of PEGylated ionic liquids were prepared, and their structures were confirmed by NMR and FTIR spectra. The thermal properties of these ionic liquids were characterized by DSC and TGA. In addition, their physicochemical properties were measured in detail, including density and viscosity. Different models were used to fit the density and viscosity data. The critical micelle concentrations of the Aerosol OT-based PEGylated ionic liquids were also determined by the surface tension method, and they exhibited good surface activity. Furthermore, these PEGylated ionic liquids exhibit typical low critical solution temperature phase behavior. To illuminate the underlying mechanism of thermal-induced phase separation, temperature-dependent FTIR spectra were used to analyze the interaction between ionic liquids and water molecules. Finally, the thermally regulated PEGylated IL phase separation system was proposed as an efficient strategy to separate heavy metal ions and rare earth metal ions from water media. The results presented here offer key information to design new thermoresponsive ionic liquids and their applications.

Self- blowing non-isocyanate polyurethane foam: Synthesis, characterization and properties

Polyurethane (PU) foams are inevitable for many applications from comfort materials or energy saving to aerospace. Today, greener routes for their production have gained thoughtful attention among the scientific community by avoiding mainly the use of toxic isocyanates. An easily scalable process for the realization of self-blown isocyanate-free PU (poly (hydroxy urethane)-PHU) foams by exploiting suitable amines and cyclic carbonates is demonstrated in this work. The foaming is attributed to the release of CO2, from the reaction of cyclic carbonate of resorcinol diglycidyl ether (RDGCC) with amine terminated oligomeric phenyl hydroxy amine (AOPHA), where a parallel reaction of the hydroxyl groups and amino groups with the cyclic carbonate groups are competing during polymerization and culminate in poly (hydroxy urethane) foam. The released gas was confirmed as CO2 from GC–MS and temperature dependent FTIR. The realized flexible PHU foam is thermally stable (>250 ℃) with adhesive strength between Al-Al as 1.5 to 2.0 MPa, and with a closed cell structure possessing a density of 480 kg/m3.

Co-pyrolysis characteristics and flammability of polylactic acid and acrylonitrile-butadiene-styrene plastic blend using TG, temperature-dependent FTIR, Py-GC/MS and cone calorimeter analyses

The plastic blend (PLA-ABS) of polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) is a promising material with great toughness and environmental-friendly potentials. Nevertheless, little research has focused on PLA-ABS co-pyrolysis and combustion. This work explores the pyrolysis characteristics and flammability of PLA-ABS blend with a mass ratio of 1:1. The thermogravimetric analysis shows that during the co-pyrolysis of PLA-ABS the individual pyrolysis of PLA and ABS is much faster than the corresponding pyrolysis rate of PLA and ABS alone. The FTIR analyses of solid residues indicate that PLA and ABS do not react chemically in the solid phase, hence the volatile products of co-pyrolysis are similar to those of pure materials. Through Py-GC/MS experiments, characteristic products of ABS induced by PLA-ABS co-pyrolysis at 330 °C were identified where the original ABS has not started to pyrolyze. This finding concludes that the co-pyrolysis enhances the depolymerization of components, leading to the characteristic products appearing at a lower temperature. Finally, the cone calorimeter experiments show that the PLA-ABS blend produces the highest peak heat release rate during combustion which is 93%–182% and 5%–15% higher than that of PLA and ABS, respectively. The cone calorimeter results further confirm the enhanced depolymerizations induced by co-pyrolysis.

Water does not dance as ions sing: A new approach in elucidation of ion-invariant water fluctuations

Aqueous solutions of salts composed from monovalent ions are explored using temperature-dependent FT-IR spectroscopy in transmission. Water combination band, being extremely sensitive to the network of hydrogen bonds due to the contribution of water librations (ρLH2O), is analyzed in uni- and multivariate fashion. Univariate analysis of the combination band maximum (νmax) reveals that perturbation of water hydrogen bond network by ions is primary driven by electrostatic interactions between water and ions. Using multivariate curve resolution with alternating least squares and evolving factor analysis this band is separated into two components that represent low- and high-density water. The observed asymmetry in their behavior is interpreted in terms of fluctuations of a hydrogen bond network of two water components. The significance of the found phenomenon is unambiguously confirmed by performing analogous analysis in the spectral range that contains partial signature of water linear bending (δHOH) and is free from ρLH2O, in which the asymmetry is absent. Additionally, we show that this phenomenon, namely ion-invariant behavior of water fluctuations, persists even in the regime of high ionic strengths. Although ions indeed participate in shaping of water hydrogen bond network, this straightforward approach shows that its temperature-dependent fluctuations are ion-independent.

Core-shell microgels synthesized in continuous flow: deep insight into shell growth using temperature-dependent FTIR.

While core-shell microgels have been intensively studied in their fully synthesized state, the formation mechanism of the shell has not been completely understood. Such insight is decisive for a customization of microgel properties for applications. In this work, microgels based on a N-isopropylmethacrylamide (NiPMAM) core and a N-n-propylacrylamide (NnPAM) shell are synthesized in a continuous flow reactor. The shell growth is studied depending on the solution's time of residence inside the reactor. PCS experiments reveal a significant decrease of the volume phase transition temperatures of the core and the shell, with increasing residence time. At early stages, a decreased swelling capacity is found before a discrete NnPAM shell is formed. Temperature-dependent FTIR spectroscopy shows that the decreased swelling capacity originates from a pronounced interpenetrated network (IPN) between NnPAM and NiPMAM. AFM images resolve heterogeneously distributed shell material after 3 min, pointing to an aggregation of NnPAM domains before the distinct shell forms. The combination of diffusional properties, AFM images and vibrational information confirms a deeply interpenetrated network already at early stages of the precipitation polymerization, in which the shell material heavily influences the swelling properties.

Synthesis and liquid crystalline behavior of hydrazide-functionalized triphenylenedicarboxyimides

ABSTRACT Seven hydrazide-functionalised triphenylenedicarboxyimides (TDIs) which contain a benzamide group bearing different polar substitutes connected to the imide N atom have been studied with the aim to establish the effect of hydrogen bonding and polar substituents on their mesomorphism properties. Six of seven hydrazides each form two types of hexagonal columnar liquid crystalline (LC) phase, including a low-temperature Colho phase and a high-temperature Colhd phase, which were confirmed by characteristic pseudo focal conic fan-shaped textures and XRD measurements. Temperature-dependent FT-IR studies indicated that hydrogen bonding is not strong enough to exist in the LC phases of these hydrazides and disfavours the stabilisation of the columnar mesophase. Nevertheless, dipole–dipole effects were found to favour the mesophase stabilities of these compounds, and the position of the lateral substituent attached to the end benzene ring has a significant impact on the self-assembly by affecting the overall dipole moment.

Determination of solid-phase reaction mechanism and chlorine migration behavior of co-pyrolyzing PVC[sbnd]CaCO3 based polymer using temperature-dependent FTIR and XRD analysis

This paper investigates the pyrolysis of outer sheath polymer of a PVCCaCO3 based cable. TG-DSC-MS, temperature-dependent FTIR, XRD and XPS experiments were conducted to study the pyrolysis characteristics and chlorine migration law for solid products. The results show that the pyrolysis can be divided into three stages induced by co-pyrolysis of PVC and CaCO3. In the first stage, the PVC dehydrohalogenation takes place producing the majority of HCl. CaCO3 does not participate in the solid-phase reaction. In the second stage, the cyclization of olefin chains occurs with a low HCl production. The CaCO3 reacts under high temperature, absorbing HCl in crystal lattice producing CaCl2 and CO2. In the third stage, the CaCO3 continues consuming HCl, meanwhile it starts pyrolyzing above 800 °C, generating CaO and CO2. The final residue mainly consists of CaCl2 and CaO and the organic Cl is ignorable. As the Cl-capturing reactions occur under high temperature with a low HCl production, the efficiency of CaCO3 reducing HCl is low, which explains the findings in previous study. This paper reveals the solid-phase reaction scheme and the law of Cl migration of the PVCCaCO3 based polymer pyrolysis, providing fundamentals for modeling and contributing to the understanding of cable pyrolysis for incineration industry.

Design of high-energy-dissipation, deformable binder for high-areal-capacity silicon anode in lithium-ion batteries

• The efficient energy-dissipation binder is harnessed on silicon anodes. • A synergized static and dynamic strategy is used to release the stress. • The mechanism is clarified by in-situ IR and finite element simulations. • Unprecedented cycling performances are achieved at high areal capacity. Although silicon has the highest theoretical capacity among the existing anode materials, its practical application is highly hindered by huge interface stress arising from large volume change upon cycling. Herein, an efficient energy-dissipation engineering was harnessed on high-capacity silicon anodes through a synergized “static” (chemically crosslinking) and “dynamic” (physically crosslinking) binder. In this dual network, the disassociation of non-covalent hydrogen bonds greatly facilitates the dispersion and release of unfavorable stress, while the permanent chemical bonding network enables a deformable network to sustain the electrode structure. Such a strategy effectively avoids both materials and electrodes deterioration and promises a better Si-based anode: a high areal capacity of 2 mAh cm −2 with capacity retention of 91.3% after 200 cycles. Meanwhile, the energy-dissipation mechanism was further clarified by temperature-dependent FTIR and finite element simulations.

Application of MCR-ALS with EFA on FT-IR spectra of lipid bilayers in the assessment of phase transition temperatures: Potential for discernment of coupled events

Temperature-dependent transmission FT-IR spectroscopy and DSC measurements were conducted on lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Lipid multibilayers made from 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, which do not form a ripple phase, were examined as a reference. Spectra were analyzed using multivariate curve resolution technique with alternating least squares and evolving factor analysis (MCR-ALS with EFA) and lipid phase transition temperatures were determined. Polar parts of lipid molecules exert greater response on a ripple phase formation than non-polar ones. However, vibrational signatures of hydrocarbon chains with intramolecular origins display certain qualitative differences that pave the way for future work oriented on uncoupling the events that drive ripple phase formation.

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Formation and phase transition of the disordered Form I’ in electrospun PEO-thiourea complex nanofibers

A new crystal modification named as Form I′, a disordered counterpart of Form I, was for the first confirmed for the PEO (Poly (ethylene oxide))-thiourea complex nanofibers prepared by electrospinning technique. The Form I′ has the same thiourea molar fraction (0.4) as the Form I, but is more disordered and less thermally stable. During the heating process, an unexpected cold crystallization peak around 93.0 °C was observed for the Form I′ in the DSC heating scan. It arises from the phase transition from Form I′ to Form I. Temperature-dependent FTIR demonstrates that the Form I’ to Form I phase transformation undergoes a sequential process during the heating period.