Differential Scanning Calorimetric Measurements Research Articles

Synthesis and electrical properties of hydrogen bonded liquid crystal polymer

In this study, a new polystyrene based side chain liquid crystalline polymer (EP-PS-LC11)) has been prepared from polystyrene having ethylpiperazine moiety as a hydrogen bond acceptor polymer and 11-(4-cyanobiphenyl-4(-oxy)undekan-1-ol (LC11) as a bond donor by molecular self-assembly processes via hydrogen bond formation between nitrogen of ethylpiperazine on polymer chain and hydroxyl group of the LC11. The formation of hydrogen bond has been confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the EP-PS-LC11 has been investigated by a differential scanning calorimeter (DSC) and polarized optical microscopy. The thermal behaviors of the H-bonded liquid crystalline polymer have been investigated by DSC measurements. The dielectric properties and ac conductivity mechanism of EP-PS-LC11 have also been investigated by impedance spectroscopy within the frequency interval of 5Hz–15MHz. The dielectric relaxation type of EP-PS-LC11 has been analyzed by fitting dispersion curves of ε′-ω. The system obeys nearly Debye and non-Debye type relaxations for the low and high frequency regions. In addition, it has been revealed that since the dielectric strength decreases by increasing frequency, the LC composite molecules can align more easily at high frequency. Moreover, the variation of imaginary component of dielectric constant with frequency shows two relaxation peaks. While the low frequency relaxation peak corresponds to molecular vibration, the high frequency relaxation peak is attributed to molecular orientation. The frequency dependence of ac conductivity has also been analyzed by means of frequency exponent, s. Depending on the frequency deal with, the system exhibit nearly dc, correlated barrier hopping (CBH) and super linear power law (SLPL) behaviors.

Preparation and thermal characterization of sodium acetate trihydrate/expanded graphite composite phase change material

The sodium acetate trihydrate (SAT)/expanded graphite (EG) composite phase change material (PCM) was firstly prepared by absorbing liquid SAT into a porous network of EG, in which SAT acted as the PCM. EG prepared at microwave irradiation power of 800 W for 30 s with maximum volumes has the largest sorption capacity for SAT. At the mass fraction of SAT <95 %, SAT uniformly disperse in the pores of EG without liquid leakage evidenced from scanning electron microscopy characterization. X-ray diffraction results further show that PCM is just a combination between SAT and EG without any chemical reaction. Differential scanning calorimeter measurements indicate that the melting temperature and latent heat of the composite PCM are 59.5 °C and 202 J g−1, respectively, close to those of pure SAT. The thermal conductivity of the composite PCM can be as high as 1.589 W m−1 K−1.The form-stable SAT/EG composite with SAT mass fraction of 95 % has great potential in thermal energy storage due to its moderate melting point, significant latent heat storage capacity, form-stable property, direct usability without need for an extra storage container, and high thermal conductivity.

Structural characterization, vibrational spectroscopy accomplished with DFT calculation, thermal and dielectric behaviors in a new organic-inorganic tertrapropylammonium aquapentachlorostannate dihydrate compound

In this work a novel compound tertrapropylammonium aquapentachlorostannate dihydrate was synthesized and characterized by; single crystal X-ray diffraction, vibrational spectroscopy, differential scanning calorimetric and dielectric measurement. The crystal structure refinement at room temperature reveled that this later belongs to the monoclinic compound with P121/c1 space group with the following unit cell parameters a = 8.2699(3) Å, b = 12.4665(4) Å, c = 22.3341(7) Å and β = 92.94(0)°. The crystal arrangement can be described by stacked organic-inorganic layers in the c direction with two independent water molecules placed between each two layers. The detailed interpretations of the vibrational properties of the studied compound were performed using density functional theory (DFT) with the B3LYP/LanL2DZ basis set, and has enabled us to make the detailed assignments by comparative study of the experimental and calculated Raman and IR spectra. The differential scanning calorimetry (DSC) measurement disclosed two anomalies in the temperature range 356–376 (T1) K and at 393 K (T2) characterized by the dehydration of the sample and probably a reconstruction of a new structure after T2 transition. The temperature dependences of dielectric permittivity show a relaxation process around T2 anomaly indicating the occurrence of the disorder at high temperature. The dependence of the exponent m(T) on temperature, extracted from the straight lines of log(ε″) with log (ω), suggests that the correlated barrier hopping is the appropriate model for the conduction mechanism.

Monitoring dehydration of the organic–inorganic [(C3H7)4N][SnCl5(H2O)]·2H2O compound using simultaneous thermal and Raman studies

In this work we report the experimental studies of the structural phase transition in the [(C3H7)4N]SnCl5(H2O)]·2H2O compound by differential scanning calorimetric (DSC) and Raman spectroscopic. The X-ray powder diffraction study of the [(C3H7)4N][SnCl5(H2O)]·2H2O sample at room temperature showed that this compound is monoclinic and has P121/c1 space group. Differential scanning calorimetric disclosed two types of phase transitions in the temperature range 356–376 (T1) K and at 393K (T2) characterized, by a loss of water molecules and probably a reconstruction of new anionic parts after T2 transition. The Raman scattering spectra recorded at various temperatures in the wavenumber range from 100 to 3800cm−1 covering the domains of existence of changes in the vicinity of the two phase transitions detected by DSC measurement. A detailed study of the spectral parameters (wave number, reduced intensity and the full width at half maximum) as a function of temperature of a chosen band, associated with (νs(SnO)+νs(SnCl)), based on an order–disorder model allowed us to obtain information relative to the activation energy and correlation length.

Effect of the dispersion degree of asphaltene on wax deposition in crude oil under static conditions

This paper summarizes the experimental work done on the wax deposition in a waxy crude oil, considering the impact of the dispersion degree of asphaltene. Asphaltene from Venezuela residue was added into the waxy crude oil at several concentrations, and the dispersion degree of asphaltene was determined by the size distribution of asphaltene measured with microscopic observation and software analysis. Based on the size distribution of asphaltene, it shows two types of asphaltenes: dispersed asphaltenes (<2μm) and aggregated asphaltenes (>2μm). By using a differential scanning calorimeter (DSC) measurements and coldfinger experiments, it is shown that the dispersed asphaltenes can inhibit the wax precipitation, and the concentration gradient of wax molecules between the bulk and deposit surface is increased, favoring wax deposition. The aggregated asphaltenes can provide crystal cores, promote wax molecules to precipitate in advance, and decrease the concentration gradient of wax molecules, depressing the wax deposition. Additionally, it is found that the dispersed asphaltenes play little role in hindering wax molecule diffusion towards the deposition surface. Furthermore, the idea that the n-paraffin component in deposits is a function of the dispersion degree of asphaltene is supported by the high-temperature gas chromatography (HTGC) measurements.

Enormous lattice distortion through an isomorphous phase transition in an organic–inorganic hybrid based on haloantimonate(iii)

Bis(diisobutylammonium) octabromodiantimonate(III), [(i-C4H9)2NH2]2Sb2Br8, has been synthesized. The differential scanning calorimetric measurements indicate a reversible, first-order phase transition at 222/229 K (cooling/heating). The single crystal X-ray diffraction studies reveal that the phase transition is isomorphous and is accompanied by a huge distortion of the crystal lattice. By comparison of the crystal structures of [(i-C4H9)2NH2]2Sb2Br8 and [(i-C4H9)2NH2]2Sb2Cl8, an analogous mechanism of the phase transition of the former is proposed. The change of the electronic structure of the complex during the phase transition was analyzed by UV-vis spectroscopy. A low-frequency dielectric relaxation process appears over phase I (below the room temperature) and corresponds to the dynamics of dipolar diisobutylammonium cations. The detailed analysis of the molecular motions of the organic cations studied by means of proton magnetic resonance (1H NMR) in a wide temperature range indicates a leading role of the methyl groups in the relaxation mechanism. A variable-temperature investigation of the infrared spectra of [(i-C4H9)2NH2]2Sb2Br8 confirms, in turn, the influence of the diisobutylammonium cation dynamics on the molecular mechanism of the structural transformation at 229 K.

Infrared thermography method for fast estimation of phase diagrams

Phase change materials (PCM) are widely used today in thermal energy storage applications. Pure PCMs are rarely used because of non adapted melting points. Instead of them, mixtures are preferred. The search of suitable mixtures, preferably eutectics, is often a tedious and time consuming task which requires the determination of phase diagrams. In order to accelerate this screening step, a new method for estimating phase diagrams in record time (1–3h) has been established and validated. A sample composed by small droplets of mixtures with different compositions (as many as necessary to have a good coverage of the phase diagram) deposited on a flat substrate is first prepared and cooled down to ambient temperature so that all droplets crystallize. The plate is then heated at constant heating rate up to a sufficiently high temperature for melting all the small crystals. The heating process is imaged by using an infrared camera. An appropriate method based on singular values decomposition technique has been developed to analyze the recorded images and to determine the transition lines of the phase diagram. The method has been applied to determine several simple eutectic phase diagrams and the reached results have been validated by comparison with the phase diagrams obtained by Differential Scanning Calorimeter measurements and by thermodynamic modelling.

Enhanced CO oxidation activity of CuO/CeO2 catalyst prepared by surfactant-assisted impregnation method

A modified CuO/CeO2 catalyst was prepared by surfactant-assisted impregnation method and showed better catalytic activity for low temperature CO oxidation than that from conventional impregnation method. The physicochemical properties of different CuO/CeO2 catalysts were characterized by thermogravimetric and differential scanning calorimetric measurements (TG-DSC), X-ray diffraction (XRD), N2 adsorption-desorption, Raman spectroscopy, H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of O2 (O2-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results suggested that the addition of hexadecyl trimethyl ammonium bromide (CTAB) into the impregnation solution could improve the dispersion of CuO species, which could facilitate Cu2+ incorporating into CeO2 lattice and strengthened the synergistic effects between CuO and CeO2, making the lattice oxygen more active, and eventually resulting in enhanced activity for CO oxidation.

Transparent and flexible amorphous cellulose-acrylic hybrids

Amorphous cellulose and poly(methyl methacrylate) (PMMA) blends in the form of free standing transparent hybrid films were prepared by dissolving both polymers in trifluoroacetic acid (TFA). Ultraviolet–visible (UV–vis) measurements indicated that the transparency of the films was always maintained regardless of cellulose-PMMA proportions. In addition, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements were carried out in order to characterize the chemical composition, intermolecular interactions and the crystallinity of the hybrid films. Thermo-gravimetric analysis (TGA), differential scanning calorimeter (DSC) and tensile test measurements demonstrated that amorphous cellulose improved the thermal and mechanical properties of PMMA considerably. Scanning electron microscope (SEM) and atomic force microscopy (AFM) measurements showed that hybrid films had no micron scale phase separation or segregation, resulting in highly uniform and homogenous miscibility between amorphous cellulose and PMMA. The wetting characteristics of the hybrid films were also studied by water contact angle measurements. Hybrid films showed better water barrier properties in comparison to commercial paper packaging. Furthermore, the hybrid films exhibited relative high dissolution resistance to common organic solvents, which dissolve PMMA completely. Considering the recent interest in polymer blends based on natural and synthetic macromolecules, these new transparent hybrids can have various potential applications particularly in general packaging and biomedical technologies.

Bio-based polymyrcene with highly ordered structure via solvent free controlled radical polymerization

Monomers from renewable resources, such as terpenes, recently came into the focus of interest of polymer chemists. This work describes the first reversible addition fragmentation chain transfer (RAFT) polymerization of myrcene, a simple monoterpene, with 2-ethylsulfanylthiocarbonylsulfanyl-propionic acid ethyl ester chain transfer agent (CTA), in bulk. The polymerizations showed pseudo first order kinetics and the molar masses of the produced polymers increased linearly with the conversion, while the dispersities (Ð) were in the range of 1.1–1.4. Chain extension studies using the preliminary synthesized polymyrcene as macroCTA in the polymerization of styrene resulting in block-copolymer with low Ð. The copolymer formation confirmed the trithiocarbonate chain ends of the used polymer. These results clearly confirm the controlled nature of the polymerization for the selected system. The microstructure of the polymer was also investigated. Low glass transition temperatures of the produced polyterpenes (≈−60°C) were determined by differential scanning calorimetric measurements that clearly indicate the dominance of the 1,4 polymyrcene structure. The microstructure was quantified by NMR spectroscopy validating a composition of the polymer at least 96% 1,4 units, with the coexistence of cis and trans isomers. These results confirm the controlled nature not only in terms of dispersity, functionality and molar mass, but also of microstructure of the RAFT polymerized monoterpene with the applied CTA.

The effect of sulphur on the glass transition temperature in anorthite–diopside eutectic glasses

The effect of sulphur dissolved in anorthite–diopside eutectic (AD) glasses on the glass transition temperature (Tg) has been investigated via Differential Scanning Calorimetric measurements (DSC) and Thermogravimetric Analysis (TGA) under moderately reducing to oxidizing conditions.In a series of AD glasses, we have measured the change in Tg as a function of S content present as SO42− (HS− is also identified to a lesser extent) and H2O content. The AD glasses investigated have S contents ranging from 0 to 7519ppm and H2O contents ranging from 0 to 5.3wt.%. In agreement with previous studies, increasing H2O content induces a strong exponential decrease in Tg: volatile free AD glass has a Tg at 758±13°C and AD glass with 5.18±0.48wt.% H2O has a Tg at 450±11°C. The change in Tg as a function of H2O is well-reproduced with a third-order polynomial function and has been used to constrain Tg at any H2O content. The effect of S on Tg is almost inexistent or towards a decrease in Tg with increasing S content. For instance, at ~2.4wt.% H2O, the addition of S induces a change in Tg from 585±10°C with 0ppm S to 523±3°C with 2365±138ppm S; a further increase in S up to 7239±90ppm S does not induce a dramatic change in Tg measured at 529±2°C.The limited effect of S on the glass transition temperature contrasts with recent spectroscopic measurements suggesting that S dissolution as SO42− groups provokes an increase in the polymerization degree. We propose an alternative view which reconciles the spectroscopic evidence with the Tg measurements. The dissolution of S as SO42− does not induce the formation of SiOSi molecular bonding through consumption of available non-bridging oxygens (NBO) but instead we suggest that SiOS molecular bonds are formed which are not detectable by DSC measurements but mimic the increase in glass polymerization. Therefore, spectroscopic measurements must be used with caution in order to extract melt physical properties.

Research on the critical temperature of thermal decomposition for large cartridge emulsion explosives

Emulsion explosives are one type of main industrial explosives. The emergence of the large cartridge emulsion explosives has brought new security incidents. The differential scanning calorimeter (DSC) and the accelerating rate calorimeter (ARC) were selected for the preliminary investigation of the thermal stability of emulsion explosives. The results showed that the initial thermal decomposition temperatures were in the range of 232–239 °C in nitrogen atmosphere (220–232 °C in oxygen atmosphere) in DSC measurements and 216 °C in ARC measurements. The slow cook-off experiments were carried out to investigate the critical temperature of the thermal decomposition (Tc) of the large cartridge emulsion explosives. The results indicated that the larger the diameter of the emulsion explosives, the smaller the Tc is. For the large cartridge emulsion explosives with diameter of 70 mm, the Tc was 170 °C at the heating rate of 3 °C h−1. It is a dangerous temperature for the production of the large cartridge emulsion explosives and it should cause our attention.

Effect of superparamagnetic iron oxide nanoparticles on fluidity and phase transition of phosphatidylcholine liposomal membranes.

Superparamagnetic iron oxide nanoparticles (SPIONs) with multifunctional properties have shown great promise in theranostics. The aim of our work was to compare the effects of SPIONs on the fluidity and phase transition of the liposomal membranes prepared with zwitterionic phosphatidylcholine lipids. In order to study if the surface modification of SPIONs has any influence on these membrane properties, we have used four types of differently functionalized SPIONs, such as: plain SPIONs (primary size was shown to bê11 nm), silica-coated SPIONs, SPIONs coated with silica and functionalized with positively charged amino groups or negatively charged carboxyl groups (the primary size of all the surface-modified SPIONs was ~20 nm). Small unilamellar vesicles prepared with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine lipids and multilamellar vesicles prepared with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipids were encapsulated or incubated with the plain and surface-modified SPIONs to determine the fluidity and phase transition temperature of the bilayer lipids, respectively. Fluorescent anisotropy and differential scanning calorimetric measurements of the liposomes that were either encapsulated or incubated with the suspension of SPIONs did not show a significant difference in the lipid ordering and fluidity; though the encapsulated SPIONs showed a slightly increased effect on the fluidity of the model membranes in comparison with the incubated SPIONs. This indicates the low potential of the SPIONs to interact with the nontargeted cell membranes, which is a desirable factor for in vivo applications.

Self-Assembly, Supramolecular Organization, and Phase Behavior of L-Alanine Alkyl Esters (n = 9-18) and Characterization of Equimolar L-Alanine Lauryl Ester/Lauryl Sulfate Catanionic Complex.

A homologous series of l-alanine alkyl ester hydrochlorides (AEs) bearing 9-18 C atoms in the alkyl chain have been synthesized and characterized with respect to self-assembly, supramolecular structure, and phase transitions. The CMCs of AEs bearing 11-18 C atoms were found to range between 0.1 and 10 mM. Differential scanning calorimetric (DSC) studies showed that the transition temperatures (Tt), enthalpies (ΔHt) and entropies (ΔSt) of AEs in the dry state exhibit odd-even alternation, with the odd-chain-length compounds having higher Tt values, but the even-chain-length homologues showing higher values of ΔHt and ΔSt. In DSC measurements on hydrated samples, carried out at pH 5.0 and pH 10.0 (where they exist in cationic and neutral forms, respectively), compounds with 13-18 C atoms in the alkyl chain showed sharp gel-to-liquid crystalline phase transitions, and odd-even alternation was not seen in the thermodynamic parameters. The molecular structure, packing properties, and intermolecular interactions of AEs with 9 and 10 C atoms in the alkyl chain were determined by single crystal X-ray diffraction, which showed that the alkyl chains are packed in a tilted interdigitated bilayer format. d-Spacings obtained from powder X-ray diffraction studies exhibited a linear dependence on the alkyl chain length, suggesting that the other AEs also adopt an interdigitated bilayer structure. Turbidimetric, fluorescence spectroscopic, and isothermal titration calorimetric (ITC) studies established that in aqueous dispersions l-alanine lauryl ester hydrochloride (ALE·HCl) and sodium dodecyl sulfate (SDS) form an equimolar complex. Transmission electron microscopic and DSC studies indicate that the complex exists as unilamellar liposomes, which exhibit a sharp phase transition at ∼39 °C. The aggregates were disrupted at high pH, suggesting that the catanionic complex would be useful to develop a base-labile drug delivery system. ITC studies indicated that ALE·HCl forms a strong complex with DNA, suggesting that the AEs may find use in DNA therapeutics as well.

Structure-reinforcement correlation and chain dynamics in graphene oxide and Laponite-filled epoxy nanocomposites

The present work attempts at a relative deduction of correlations between structure-reinforcement and chain dynamics in Laponite- and graphene oxide (GO)-dispersed epoxy nanocomposites. The fillers were reasonably well dispersed in the epoxy matrix as revealed by wide-angle X-ray diffraction, transmission electron microscopy and small-angle X-ray scattering studies. The scattering from the nanocomposites exhibited power-law behaviour at low q region with fractal dimensions, implying presence of platelets and tactoids of varying thicknesses. A comprehensive study on the thermomechanical properties of the nanocomposites was made in terms of tensile, dynamic mechanical analysis and flexural and fracture toughness measurements. The studies revealed simultaneous reinforcement as well as toughening effects in the nanocomposites; ~42 and ~34 % increases in flexural strength and mode I fracture toughness (K IC), respectively, with 0.1 wt% GO; and ~25 and ~20 % enhancements in flexural modulus and K IC with 0.1 and 0.3 wt% Laponite, respectively. A unique phenomenon of bimodal distribution of glass transition temperatures was observed as two overlapped peaks in terms of Gaussian contributions in the tan δ versus temperature profiles of the nanocomposites (from dynamic mechanical analysis) and derivative of reversible heat capacity with respect to temperature, dC p,rev/dT versus temperature profiles (from modulated differential scanning calorimetric measurements); as against a single symmetric profile for the unfilled matrix. We attempt to understand the nanofiller-induced alteration in the primary relaxation mechanisms as well as notable reinforcement and toughening effects by invoking the filler/polymer interactions, filler dispersion and fractographic investigations.

Study of Sustainability and Scalability in the Cp*Rh(III)-Catalyzed Direct C–H Amidation with 1,4,2-Dioxazol-5-ones

The practical aspects of Cp*Rh(III)-catalyzed direct C–H amidation with 1,4,2-dioxazol-5-ones were investigated on the operational safety, use of green solvent, and scalability. Differential scanning calorimeter (DSC) measurement showed that 3-phenyl-1,4,2-dioxazol-5-one is thermally stable while benzoyl azide, a conventionally employed precursor of acyl nitrene, rapidly decomposes to isocyanate. It was confirmed that the replacement of acyl azide with 1,4,2-dioxazol-5-one brings not only high reactivity but also improvement in safety. In respect to a green process development, functional group tolerant Cp*Rh(III) catalyst exhibited high reactivity in ethyl acetate, successfully replacing 1,2-dichloroethane solvent used in the original report. Upon the validation on safety and environmental concerns, scalability was also tested. Two different types of arenes bearing pyridyl and oxime directing groups showed excellent conversions on tens of gram scale reactions, and single recrystallization gave desired pr...

Mapping the Complex Phase Behaviors of Aqueous Mixtures of κ-Carrageenan and Type B Gelatin.

We report a detailed and complete phase diagram for an aqueous mixture of oppositely charged gelling biopolymers, type B gelatin and κ-carrageenan (KC) at pH 7.0. The phase diagram is studied in the ionic strength-temperature coordinate by means of turbidity, rheological and differential scanning calorimetric measurements, and macroscopic phase compositional analysis. Seven phase regions are identified, including (I) compatible region, (II) electrostatically induced associative phase separation (EIAPS) region, (III) hydrogen bonding induced associative phase separation (HBIAPS) region, (IV) coexistence of EIAPS and HBIAPS, (V) segregative phase separation (SPS) region, (VI) coexistence of HBIAPS and SPS, and (VII) SPS trapped by gelation. The HBIAPS reported for the first time here is attributed to the extensive hydrogen bonding formation between gelatin and KC above their conformational transition temperatures, as probed by addition of urea and methylene blue as well as by 2D (1)H-(1)H NOESY NMR. NaCl is found to have dual effects on HBIAPS. The electrostatic complexation at lower ionic strength facilitates the formation of hydrogen bonds between gelatin and KC and hence the HBIAPS. It is believed that the local structural arrangement of gelatin molecules or the change in local solvent environment prior to triple helix formation during cooling enables the formation of hydrogen bonds with KC.

New Er3+ doped antimony oxide based glasses: Thermal analysis, structural and spectral properties

The novel oxide glass compositions based on Sb2O3 are elaborated and characterized, in the system (90-X)Sb2O3–10Na2O–XBi2O3 (SNB). We are interested in bismuth rates incorporated into the glass, its effect on the different physical properties that have been measured, and especially, in radiative and spectroscopic properties of erbium doped SNB glasses. Differential scanning calorimeter (DSC) measurements show an improvement of the stability factor,ΔT, of the glasses, which can indicate a reinforcement of the network. Both FTIR and Raman spectra have also been considered in terms of bismuth influence. As a function of composition, we have principally measured optical absorption, visible and infrared emission, and lifetime. The Judd–Ofelt parameters measured from the absorption spectra have been used to calculate the radiative lifetime (τr) and the stimulated emission cross section. The spectroscopic quality factor χ = Ω4/Ω6 = 0.73, low phonon energy of ∼600–700 cm−1, a reduced quenching effect, and a high quantum efficiency of 90% for the 1.53 μm measured emission, by pumping at 980 nm, are in favor of promising laser applications.

Superhydrophobic behavior of polyimide–siloxane mats produced by electrospinning

In this study, a series of novel superhydrophobic polyimide-siloxane electrospun mats was prepared using an electrospinning process. Segmented poly- imide-siloxane copolymers were prepared using 4,4 0 -oxydianiline (ODA) and 3,3 0 ,4,4 0 -benzophenone tetracarboxylic dianhydride (BTDA) as hard segments and aminopropyl terminated polydimethylsiloxane (APPS) and BTDA as soft segment. The polyimide-siloxane copolymers were synthesized by varying the APPS loading (10 and 20 mol%) and also the molecular weight of APPS (1000 and 2500 g/mol), respectively. Electrospinning of the polyamic acids was followed by thermal imidization to construct the electrospun polyimide-siloxane mats. The electrospun mats were characterized by FTIR, scanning electron microcopy (SEM), thermo- gravimetric analysis (TGA), differential scanning calorimeter (DSC) and contact angle measurement. According to SEM results, the polyimide-siloxane electrospun mats have nano-roughness morphology. Bead on string type surface morphology that has been generated by electrospinning yields stable superhydrophobicity with a contact angle of 167.

Tuning the Dynamic Fragility of Acrylic Polymers by Small Molecules: The Interplay of Hydrogen Bonding Strength

High-Tg polymers exhibit high fragilities in general. Here, we report for the first time that small molecules with double phenolic end groups are effective to independently mediate the dynamic fragility (m) and glass transition temperature (Tg) of acrylic polymers. Broad band dielectric spectrometer (BDS), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimeter (DSC) measurements showed that the addition of small molecules with a concentration lower than 30 wt % leads to a narrower relaxation time distribution of the intermolecular cooperative rearrangement motion because of the formation of hydrogen bonding networks. These acrylic polymers exhibited a significant decrease in m while showing a linear increase in Tg by changing the loading of the small molecules. Further experimental results demonstrated that m decreases monotonically with intermolecular hydrogen bonding strength for a given host polymer matrix. The m/Tg value diminishes with increasing small molecule content,...