Temperature-dependent interfacial properties of hydrophobically end-modified poly(2-isopropyl-2-oxazoline)s assemblies at the air/water interface and on solid substrates

We describe herein the properties at the air/water (A/W) interface of hydrophobically end-modified (HM) poly(2-isopropyl-2-oxazoline)s (PiPrOx) bearing an n-octadecyl chain on both termini (telechelic HM-PiPrOx) or on one chain end (semitelechelic HM-PiPrOx) for different subphase temperatures and spreading solvents using the Langmuir film balance technique. The polymer interfacial properties revealed by the π–A isotherms depend markedly on the architecture and molecular weight of the polymer. On cold water subphases (14 °C), diffusion of PiPrOx chains onto water takes place for all polymers in the intermediate compressibility region (5 mN m⁻¹). At higher subphase temperatures (36 and 48 °C), the HM-PiPrOx film exhibited remarkable stability with time. Brewster angle microscopy (BAM) imaging of the A/W interface showed that the polymer assembly was not uniform and that large domains formed, either isolated grains or pearl necklaces, depending on the polymer structure, the concentration of the spreading solution and the subphase temperature. The Langmuir films were transferred onto hydrophilic substrates (silica) by the Langmuir–Blodgett (LB) technique and onto hydrophobic substrates (gold) by Langmuir–Schaefer (LS) film deposition, resulting in the formation of adsorbed particles ranging in size from 200 to 500 nm, depending on the polymer architecture and the substrate temperature. The particles presented “Janus”-like hydrophilic/hydrophobic characteristics.     

An infrared study on Langmuir–Blodgett films of octadecylammonium octadecanoate: FWHM and the vibrational coupling

The monolayer of the mixture of octadecanoic acid and octadecylamine with molar ratio 1:1 has been investigated at the air–water interface. It was found that the monolayer shows a rather stable state at the surface pressure of 30 mN/m and this monolayer can be transferred onto a CaF₂ plate by Langmuir–Blodgett (LB) technique. The infrared spectra of LB films indicated that octadecylammonium octadecanoate is formed by an intermolecular proton exchange between adjacent carboxylic and aminic groups (COO⁻ and NH₃⁺). In three-layer LB film, the CH₂ scissoring mode of the long hydrocarbon chains of octadecylammonium octadecanoate shows a broad band feature at about 1468 cm⁻¹ while this vibrational mode of three-layer LB film of the mixture (1:1) of deuterated stearic acid and octadecylamine (octadecylammonium octadecanoate-d35, C₁₈H₃₇NH₃⁺C₁₇D₃₅COO⁻) only shows a narrow band. The broad feature of the CH₂ scissoring mode in octadecylammonium octadecanoate probably originates from the coupling between the chain of stearic acid and that of octadecylamine while this kind of coupling could be completely removed in octadecylammonium octadecanoate-d35. Another conclusion presented in this paper is that there are no couplings among the chains of fatty acid or among the chains of octadecylamine in LB films of octadecylammonium octadecanoate.     

Studies of the surface wettability and hydrothermal stability of methyl-modified silica films by FT-IR and Raman spectra

Fourier transform infrared (FT-IR) and Raman spectroscopy were employed to study the hydrothermal stability and the influence of surface functional groups on the surface wettability of methyl-modified silica films. The surface free energy parameters of the silica films were determined using the Lifshitz-van der Waals/acid–base approach. The thermal decomposition mechanisms of the CH₃ groups in the methyl-modified silica material are proposed. The results show that with the increase of methyltriethoxysilane (MTES)/tetraethylorthosilicate (TEOS) ratio, the surface free energy and surface wettability of the silica films decrease greatly. This is mainly because of the contribution of the acid–base term; the intensity of Si–CH₃ groups increases at the expense of the intensity of O–H groups in the samples. The surfaces of the methyl-modified silica films exhibited predominantly monopolar electron-donicity. The contact angle on the silica film surface reaches its maximum value when calcination is performed at 350 °C. Thermogravimetric analysis implies that some low molecular weight species, such as H₂, CH₄, and C, are eliminated upon thermal decomposition of the –CH₃ groups. The Si–CH₃ and –CH₃ vibrational bands diminish in intensity as the calcination temperature is increased, disappearing completely when the calcination temperature is increased to 600 °C. When the calcination temperature is increased to 750 °C, the free carbon and CSi₄ species will be formed.     

Rheological properties of reversible thermo-setting in situ gelling solutions with the methylcellulose–polyethylene glycol–citric acid ternary system (2): Effects of various water-soluble polymers and salts on the gelling temperature

The influences of various salts and water-soluble polymers on the phase transition temperature of thermo-setting gels prepared by combining methylcellulose (MC)–sodium citrate (SC)–polyethylene glycol (PEG) at appropriate ratios (the MC–SC–PEG system) were investigated. Concerning cations, comparison of the phase transition temperature between SC and tripotassium citrate (PC) showed a rapid increase in the viscosity of SC between 20 °C and 25 °C and an increase in the viscosity of PC between 30 °C and 35 °C. Concerning the valency of anions, comparisons among SC, disodium tartrate dihydrate (ST), disodium maleate hemihydrates (SM), and sodium sulfate (SS) showed a rapid increase in the viscosity of trivalent SC between 20 °C and 25 °C and changes in the viscosity of the three bivalent sodium salts (ST, SM, and SS) at ≥30 °C. Thus the phase transition temperature decreased with an increase in the valency of anions.Subsequently, the influences of various water-soluble polymers on the gelling temperature were compared. Using polyvinylpyrrolidone (PVP) instead of PEG, the gelling temperature decreased with an increase in the PVP concentration even without the addition of SC. Unlike PVP, the addition of xanthan gum as a viscosity-increasing polysaccharide did not reduce the gelling temperature irrespective of its concentration.Temperature-associated changes in viscosity were observed at a fixed SC concentration with changes in the concentration of PVP or PEG. The gel phase transition temperature increased from 46 °C to 50 °C in gels not containing PVP or PEG. The viscosity did not differ between the addition of PVP or PEG at a low concentration and its absence. However, the viscosity clearly changed after the addition of each agent at a high concentration.     

The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N₂ adsorption–desorption isotherms and potentiometric mass titrations.The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution.     

Kinetic models based in biomass components for the combustion and pyrolysis of sewage sludge and its compost

In the present work, pyrolysis and combustion of the sewage sludge (fresh and composted) have been simulated using five fractions: low stability organic compounds, hemicellulose, cellulose, lignin-plastic, and inorganic compounds. Thermal behavior and kinetic parameters (pre-exponential factor and apparent activation energy) of the main components of the sludge are similar to those reported for hemicellulose, cellulose, and lignin present in lignocellulosic biomass. Comparing non-isothermal thermogravimetric analysis data obtained from fresh and composted sewage sludge, it is possible to measure the efficiency of the composting process. Most of the biodegradable matter is volatized in a temperature range from 150 °C to 400 °C. Non-biodegradable organic matter volatilizes between 400 °C and 550 °C. In both, fresh and composted sludges, oxygen presence increases the mass loss rate at any temperature, but differences between pyrolysis and combustion are focused in two clearly defined ranges. At low temperature (200–350 °C), mass loss is related with a volatilization process. At higher temperature (350–550 °C), mass loss is due to slow char oxidation (oxidative pyrolysis).     

TG-FTIR analysis of switchgrass pyrolysis

Switchgrass is a high yielding perennial grass that has been designated as a potential energy crop. One method of converting switchgrass to energy is by thermochemical conversion to syngas. This requires that the rate of thermal decomposition of switchgrass and the rate of production of components of the syngas be quantified. Ground switchgrass was pyrolyzed at heating rates of 10–40 °C/min in a thermogravimetric analyzer coupled to a Fourier Transform infrared spectrometer. The amount of gases (ppm) that were volatilized during the duration of experiment was quantified. The pyrolysis process was found to compose of four stages: moisture evaporation, hemicellulose decomposition, cellulose decomposition and lignin degradation. The peak temperature for hemicellulose (288–315 °C) and cellulose degradation (340–369 °C) increased with heating rate. FTIR analysis showed that the following gases were given off during the pyrolysis of switchgrass: carbon dioxide, carbon monoxide, acetic acid, ethanol, and methane.     

Comparison of molecular orientation and phase transition behaviors in the two kinds of ordered ultrathin films of reversed duckweed polymer ES-3 studied by infrared grazing reflection-absorption spectroscopy

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection-absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 degrees C for the former while near 80, 105 and 140 degrees C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again.     

Infrared optical constants, dielectric constants, molar polarizabilities, transition moments, dipole moment derivatives and Raman spectrum of liquid cyclohexane

Previous studies have been done in this laboratory focusing on the optical properties of several liquid aromatic and aliphatic hydrocarbons in the infrared. The current study reports the infrared and absorption Raman spectra of liquid cyclohexane. Infrared spectra were recorded at 25 °C over a wavenumber range of 7400–490 cm⁻¹. Infrared measurements were taken using transmission cells with pathlengths ranging from 3 to 5000 μm. Raman spectra were recorded between 3700 and 100 cm⁻¹ at 25 °C using a 180° reflection geometry. Ab initio calculations of the vibrational wavenumbers at the B3LYP/6311G level of theory were performed and used to help assign the observed IR and Raman spectra. Extensive assignments of the fundamentals and binary combinations observed in the infrared imaginary molar polarizability spectrum are reported. The imaginary molar polarizability spectrum was curve fitted to separate the intensity from the various transitions and used to determine the transition moments and magnitudes of the derivatives of the dipole moment with respect to the normal coordinates for the fundamentals.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Rheological investigation of thermal transitions in vesicular dispersion

The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 °C and 43 °C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 °C appears which may correspond to the (ULVs + L_α fragments) → MLVs transition. The thermal-induced MLV’s size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions.     

Rhodamine-conjugated acrylamide polymers exhibiting selective fluorescence enhancement at specific temperature ranges

A simple copolymer, poly(NIPAM-co-RD), consisting of N-isopropylacrylamide (NIPAM) and rhodamine (RD) units, behaves as a fluorescent temperature sensor exhibiting selective fluorescence enhancement at a specific temperature range (25–40 °C) in water. This is driven by a heat-induced phase transition of the polymer from coil to globule. At low temperature, the polymer exists as a polar coil state and shows very weak fluorescence. At >25 °C, the polymer weakly aggregates and forms a less polar domain within the polymer, leading to fluorescence enhancement. However, at >33 °C, strong polymer aggregation leads to a formation of huge polymer particles, which suppresses the incident light absorption by the RD units and shows very weak fluorescence. In the present work, effects of polymer concentration and type of acrylamide unit in the polymer have been investigated. The increase in the polymer concentration in water leads to a formation of less polar domain even at low temperature and, hence, widens the detectable temperature range to lower temperature. Addition of N-n-propylacrylamide (NNPAM) or N-isopropylmethacrylamide (NIPMAM) component to the polymer, which has lower or higher phase transition temperature than that of NIPAM, enables the aggregation temperature of the polymer to shift. This then shifts the detectable temperature region to lower or higher temperature.     

Optimization of the curing conditions of PVC plastisols based on the use of an epoxidized fatty acid ester plasticizer

The use of an epoxidized fatty acid ester (EFAE) as a natural-based plasticizer for plasticized PVC (P-PVC) has been evaluated in this work. The effect of the curing conditions has been studied by following several test techniques such as mechanical properties, thermal behavior, color changes, solvent migration and microstructure. Different curing processes at isothermal conditions (ranging from 160 °C to 220 °C) have been carried at curing times in the 6–16 min range. The optimum mechanical response (tensile strength values in the 9–10 MPa range and elongation at break close to 250%) is obtained for plastisols cured at 200 and 220 °C for 12 and 8 min curing times, respectively. These curing conditions also offer the lowest migration in n-hexane (lower than 11%) which is indicative of plasticizer total absorption. Furthermore, the use of these curing conditions does not lead to thermal degradation as confirmed by color measurements.     

Variation of mechanical and thermal properties of the thermoplastics reinforced with natural fibers by electron beam processing

With restrictions for environmental protection being strengthened, the thermoplastics reinforced with natural fibers (NFs) such as jute, kenaf, flax, etc., appeared as an automobile interior material instead of the chemical plastics. Regardless of many advantages, one shortcoming is the deformation after being formed in high temperature of about 200 °C, caused by the poor adhesion between the natural fibers and thermoplastics. Also, the energy saving in connection with car air-conditioning becomes very important. In this study, the thermal conductivity, tensile strength, and deformation of several kinds of thermoplastic composites composing of 50% polypropylene (PP) and 50% natural fiber irradiated by the electron beam (energy: 0.5 MeV, dose: 0–20 kGy) were measured. The length and thickness of PP and NF are 80±10 mm and 40–120 μm, respectively. The results show that the thermal conductivity and the tensile strength changed and became minimum when the dose of electron beam is 10 kGy, and the deformation after the thermal cycle were reduced by the electron beam.     

Thermal stability of artinite, dypingite and brugnatellite—Implications for the geosequestration of green house gases

The approach to remove green house gases by pumping liquefied carbon dioxide several kilometres below the ground implies that many carbonate containing minerals will be formed. Among these minerals the formation of dypingite, artinite and if the ferric iron is present brugnatellite are possible; thus necessitating a study of the thermal stability of such minerals. The thermal stability of two carbonate bearing minerals dypingite and artinite together with brugnatellite with a hydrotalcite related formulae have been characterised by a combination of thermogravimetry and evolved gas mass spectrometry. Artinite is thermally stable up to 352 °C. Two mass loss steps are observed at 219 and 355 °C. Dypingite decomposes at a similar temperature but over a large number of steps. Brugnatellite shows greater stability with decomposition not occurring until after 577 °C. The thermal decomposition of brugnatellite occurs over a number of mass decomposition steps. It is concluded that pumping liquefied green house gases into magnesium bearing mineral deposits is feasible providing a temperature of 350–355 °C is not exceeded to prevent escape of CO₂ towards the surface. In contrast, the water loss occurring at lower temperatures could have a positive effect on the geosequestration of CO₂ as it probably causes a decrease in the molar volume of secondary carbonate minerals and consequently an increase in aquifer porosity.     

Improved thermal stability of Langmuir-Blodgett films through an intermolecular hydrogen bond and metal complex

Langmuir-Blodgett (LB) films of N-octadecanoyl-L-alanine and its silver and zinc complexes have been investigated by variable-temperature Fourier transform infrared transmission spectroscopy. The thermal stability of LB films is improved through an intermolecular hydrogen bond and metal complex. The intermolecular hydrogen-bonding interaction between hydrophilic head groups in the same monolayers and the metal complex between one head group and another in the neighboring monolayers considerably increase the interaction between the corresponding hydrophobic alkyl chains. It is shown that the transformation of the triclinic subcell packing of the molecules in the LB films prior to and after the silver complex into hexagonal packing occurs before the phase transition accompanied with a change in molecular orientation. The phase transition behavior of the LB films is varied from a small temperature interval to large one depending on the hydrogen bond and metal complex.     

The photophysical properties and morphology of fluorene-alt-benzene based conjugated polymer

A series of fluorene-alt-benzene based conjugated main chain polymers chemically attached with alkyl side chains of different lengths on phenylene rings were designed and synthesized by a palladium catalyzed Suzuki coupling reaction. The UV-vis absorption and fluorescence spectra, thermal stability of spectral property, phase transition behavior and morphology of the synthesized polymers were investigated. With increasing the length of the alkyl side chain, the UV and fluorescence spectra exhibit an obvious blue shift compared with those of the unsubstituted polymer. The alkyl substitution improves the thermal spectral stability of the polymers due to the steric hindrance of the alkyl side chains, thus leading to efficient separation of the main chain backbones. The phase transition behavior is closely related to the length of the alkyl side chains attached on the phenylene rings. The annealed films of the polymers display characteristic nematic liquid crystalline texture. TEM observations indicate that solvent-cast thin deposits of all the polymers show typical fibrillar morphology.     

Thermal behaviors of vinyl esters of long-chain fatty acids and their comblike polymers

Phase transition behaviors of vinyl esters of long-chain fatty acids (C₁₂–C₁₈) and their comblike polymers have been investigated by the thermal analysis combining with X-ray diffraction and infrared spectroscopy. Effect of the length of hydrocarbon chain on the thermal behaviors of both monomers and polymers have been elucidated. Vinyl stearate exhibits three crystalline modifications, α (hexagonal), β₁ (monoclinic, M_∥) and β₂ (monoclinic, O⊥) forms. With shortening of the alkyl chain the polymorphic behaviors become simpler. The thermal behaviors of the resultant polymers are influenced by the packing mode of monomer molecules and the polymerization temperature.     

New cut angle quartz crystal microbalance with low frequency-temperature coefficients in an aqueous phase

In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (dF/dT) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of dF/dT is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low dF/dT values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its dF/dT value is close to zero at ca. 25 °C and its averaged value of |dF/dT| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle.     

四氯合铜酸二烷基铵相变的热分析和红外光谱

用DSC和TG研究了(n-C_nH_(2n+1)NH_3)_2CuCl_4(n=7-12)(记为C_nM)配合物的热稳定性和固-固相变。由红外光谱讨论了C_9Cu三个相的性质。发现C_nM的热稳定性呈奇偶效应; 主相变峰温随链长增长而升高; 相变总ΔH和ΔS也随链增长而加大; 当n≤9时, 高温相为部分无序相; 而n≤10时, 高温相为构象无序相。C_9Cu的主相变主要源自链间堆积结构变化。而在307.7 K的相变主要与烃链有序-无序变化有关。