Phase Transition Temperature Values Research Articles

Mesoporous Silica and Oligo (Ethylene Glycol) Methacrylates-Based Dual-Responsive Hybrid Nanogels.

Polymeric-inorganic hybrid nanomaterials have emerged as novel multifunctional platforms because they combine the intrinsic characteristics of both materials with unexpected properties that arise from synergistic effects. In this work, hybrid nanogels based on mesoporous silica nanoparticles, oligo (ethylene glycol) methacrylates, and acidic moieties were developed employing ultrasound-assisted free radical precipitation/dispersion polymerization. Chemical structure was characterized by infrared spectroscopy and nuclear magnetic resonance. Hydrodynamic diameters at different temperatures were determined by dynamic light scattering, and cloud point temperatures were determined by turbidimetry. Cell viability in fibroblast (NIH 3T3) and human prostate cancer (LNCaP) cell lines were studied by a standard colorimetric assay. The synthetic approach allows covalent bonding between the organic and inorganic components. The composition of the polymeric structure of hybrid nanogels was optimized to incorporate high percentages of acidic co-monomer, maintaining homogeneous nanosized distribution, achieving appropriate volume phase transition temperature values for biomedical applications, and remarkable pH response. The cytotoxicity assays show that cell viability was above 80% even at the highest nanogel concentration. Finally, we demonstrated the successful cell inhibition when they were treated with camptothecin-loaded hybrid nanogels.

Thermal and Mesomorphic Investigations of 1:1 Supramolecular Assemblies of 4-[(4-(n-Alkoxy)phenylimino)methyl]benzoic Acids Having Symmetrical and Un-Symmetrical Terminal Chain Lengths

Thermal and mesomorphic properties of possible 1:1 supramolecular complexes (SMCs) (Im/In) designed from two members of 4-[(4-(n-alkoxy)phenylimino)methyl]benzoic acid with symmetrical or un-symmetrical alkoxy terminal flexible chains (carbons of m and n = 6, 8 and 16), were analyzed by differential scan-calorimetry (DSC), thermogravemetric (TG) analysis, and their mesophases identified by polarized optical microscopy (POM). The equimolecular mixtures of the two acids possess symmetrical and un-symmetrical terminal lengths. The mesomorphic properties of the binary mixtures were examined as a function of the total alkoxy chain length on both sides. Results revealed that the nematic mesophase temperature range increases as the total terminal length increases for all designed un-symmetrical mixtures. A comparison was constructed between the formed SMCs and of those of the previously prepared 4-n-alkoxyphenylazo benzoic acids as well as the 4-n-alkoxy benzoic acids, to examine the impact of mesogenic core on the mesomorphic properties. The comparison indicated that as the mesogenic portion lengthens the thermal mesophase stability exhibits higher values of phase transition temperatures; whereas, the azo and Schiff base moieties exhibited near thermal properties.

Thermodynamic description of the ternary systems of the core sulphate system Na2SO4–K2SO4–MgSO4–CaSO4

The ternary subsystems of the quaternary sulphate system Na2SO4–K2SO4–MgSO4–CaSO4 were thermodynamically assessed using the available experimental information on phase equilibria. The dataset containing all binary sub-systems, published earlier, was extended to describe phase equilibria of the four sub-ternary systems. Furthermore, a first dataset covering the entire quaternary system has been generated. In the absence of the experimental information on the high order systems the proposed dataset can be used for interpolative and predictive thermodynamic calculations. Ternary interaction parameters were embedded in the framework of the modified associate species model for the description of the liquid phase. The solubility between langbeinite compounds (K2Me2(SO4)3 with Me = Ca, Mg) was treated with a multi-sublattice model. The resulting new databank being compatible with the general oxide database is used for the representation of phase equilibria in the ternary subsystems. To validate the thermodynamic dataset, the calculated values of phase transition temperatures are compared with the experimental results of the selected compositions of the ternary systems obtained by differential thermal analysis (DTA).

Biobased Thermoplastic Elastomers: Structure-Property Relationship of Poly(hexamethylene 2,5-furanodicarboxylate)-Block-Poly(tetrahydrofuran) Copolymers Prepared by Melt Polycondensation.

A series of poly(hexamethylene 2,5-furanodicarboxylate)-block-poly(tetrahydrofuran) (PHF-b-F-pTHF) copolymers were synthesized using a two-stage procedure, employing transesterification and polycondensation. The content of pTHF flexible segments varied from 25 to 75 wt.%. 1H nuclear magnetic resonance (NMR) and Fourier transformed infrared spectroscopy (FTIR) analyses were applied to confirm the molecular structure of the materials. Differential scanning calorimetry (DSC), dynamic mechanical measurements (DMTA), and X-ray diffraction (XRD) allowed characterizing the supramolecular structure of the synthesized copolymers. SEM analysis was applied to show the differences in the block copolymers’ morphologies concerning their chemical structure. The influence of the number of flexible segments in the copolymers on the phase transition temperatures, thermal properties, as well as the thermo-oxidative and thermal stability was analyzed. TGA analysis, along with tensile tests (static and cyclic), confirmed the utilitarian performance of the synthesized bio-based materials. It was found that an increase in the amount of pTHF caused the increase of both number-average and weight-average molecular weights and intrinsic viscosities, and at the same time causing the shift of the values of phase transition temperatures toward lower ones. Besides, PHF-b-F-pTHF containing 75 wt.% of F-pTHF units was proved to be a promising thermoplastic shape memory polymer (SMP) with a switching temperature of 20 °C.

Effect of varying the vanadium thickness layer of V2O5/V/V2O5 film on its microstructural and thermochromic properties

In this study, V2O5/V/V2O5 sandwich-structured films were deposited on glass substrates by electron beam evaporation. The thickness of the first (bottom) V2O5 layer was 40 nm and the last (top) layer was 20 nm, while that of the sandwiched vanadium layer varied up to 12 nm for different samples. The effects of varying the thickness of the sandwiched vanadium layer on microstructural and thermochromic properties of the as-deposited and thermal annealed films were investigated. Ultrahigh-resolution scanning electron microscopy revealed the presence of nanostructures with various irregular shapes on the surfaces of all films. Also, the atomic force microscopy revealed an average roughness of ∼10–38 nm for increasing thickness of the sandwiched vanadium layer. X-ray powder diffraction measurements showed the presence of the monoclinic VO2 (M) crystal structure of the films with (011) preferred orientation at 27.94° for both 7 and 12 nm thicknesses of the sandwiched vanadium layers. The varying thickness of the sandwiched vanadium layers enhanced phase transition temperature values to ∼33.92 and ∼29.11 °C for both 7 and 12 nm thicknesses of the sandwiched layers, respectively. These enhanced transition temperature values, as a result of thickness variation of the sandwiched vanadium layers, pointed toward utilization of this method in the successful synthesis of VO2 films for thermochromic windows application and optoelectronics.

How do biological stimuli modulate conformational changes of biomedical thermoresponsive polymer?

Continuing efforts to develop stimuli-responsive polymers (SRPs) as novel smart materials/biomaterials are anticipated to upgrade the quality life of humans. The details of the molecular, physico chemical and biophysical interactions between SRPs and proteins are not fully understood. Indeed, protein - polymer interactions play a major role in a wide range of biomedical/biomaterial applications. In this regard, we have demonstrated the influence of proteins (β-lactoglobulin (BLG) and stem bromelain (BM) as biological stimuli) on the phase transition behavior of biomedical thermoresponsive poly(N-isopropylacrylamide) (PNIPAM). In order to predict these, we have used a set of biophysical techniques to unveil the influence of biological stimuli on the phase transition behavior of PNIPAM. Absorption spectroscopy, steady-state fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) were operated at room temperature to examine the changes in absorbance, fluorescence intensity, molecular interactions and surface morphologies, respectively. Furthermore, temperature dependent fluorescence spectroscopy and dynamic light scattering (DLS) studies were also performed to analyze conformational changes, agglomeration behavior, particle size, coil to globule transition and phase behavior. The significant variations obtained in the phase transition temperature values, conformational changes and agglomeration behavior clearly reflects the different molecular interplay induced in presence of biological stimuli. The results demonstrated that the added proteins act as biological stimuli via preferential interactions between the amide group of the polymer and water molecules. The present study can be useful for the design and development of the next generation smart responsive materials/biomaterials.

Mesogenic properties of PAA/6BA binary liquid crystal complexes

A novel supramolecular liquid crystal complex has been designed and formed from pure liquid crystals para-azoxyanisole (PAA) and 4-hexylbenzoic acid (6BA). Thermal and microstructural properties of formed PAA/6BA binary liquid crystal complex system are investigated by differential scanning calorimeter (DSC), polarized optical microscopy (POM) and X-ray diffractometer (XRD). Fourier transformed infrared spectroscopy (FTIR) is used to confirm the formation of hydrogen bond between the PAA and 6BA molecules. The XRD results show that the molecular ordering of the hydrogen bonded PAA/6BA complex is arranged in the orthorhombic structure. The DSC and POM results clearly indicate that the PAA/6BA binary complex exhibits liquid crystalline properties due to the hydrogen bonds formed between the PAA and 6BA molecules. The PAA/6BA complex shows the phase transition peaks indicating Cr→N→I and I→N→SmA→Cr phase sequence during continuous heating and cooling, respectively, by DSC. These phase sequences have also been confirmed by POM observations. Furthermore, the effect of the heating rate on the phase transition temperature values is investigated. As the heating rate increases, the phase transition temperature values increase as well. Moreover, the activation energies for the phase transitions of the PAA/6BA liquid crystal complex are calculated by using Kissinger, Ozawa and Takhor methods. The calculated results clearly show that the phase transitions are regular.

Thermal and optical characterization of liquid crystal 4′-hexyl-4-biphenylcarbonitrile/4-hexylbenzoic acid mixtures

We present the thermal and optical properties of binary mixtures formed from hydrogen-bonded liquid crystal 4-hexylbenzoic acid (6BA) and 4-hexyl-4′-biphenylcarbonitrile (6CB) mesogens. Phase transition temperatures and enthalpy values are evaluated by differential scanning calorimetry (DSC) and phases identified by polarized optic microscopy (POM). The experimental results obviously show that the 6BA/6CB binary mixtures exhibit nematic and smectic phases. The most interesting result is that although the smectic phase is not observed in pure components 6BA and 6CB, it is observed in their some binary mixtures. The thermal properties like phase peak temperatures, enthalpy changes and thermal span of binary mixtures are affected by depending on the mixture ratio. The nematic range increase in the binary mixture compared to the individual mesogen, and also the phase transition temperature values and the nematic thermal stability factor increase as heating rate increases. Furthermore, the calculated activation energy values show that the reorientation of the molecules during the phase transitions of the mixture occurs on an orderly basis.

Apolipoprotein B-100-targeted negatively charged nanoliposomes for the treatment of dyslipidemia

BackgroundAnionic nanoliposomes can interact with serum lipoproteins and regulate lipid metabolism through several mechanisms. This study aimed to evaluate the lipid-modifying effects of anionic immunoliposomes targeted against apoB, an important component of atherogenic lipoproteins. MethodsTwo sets of nanoliposomes (20mM) were prepared with low (including soy phosphatidylcholine [SPC] and egg phosphatidylglycerol [EPG]) and high (including hydrogenated soy phosphatidylcholine [HSPC] and distearoyl phosphatidylglycerol [DSPG]) phase transition temperature values without cholesterol. In each set, the anionic phospholipid (EPG or DSPG) constituted 75% of total phospholipid content. Immunoliposomes were prepared by conjugating a monoclonal antibody against apoB-100 to the liposomal surface using a post-insertion technique. Fluorescently-labeled immunoliposomes were assessed for their uptake by J774.A1 macrophages. Lipid-modifying effects of immunoliposomes were tested at different doses (50, 100 or 200μmole/g weight) using a tyloxapol-induced hyperlipidemic mouse model. Blood sampling was performed 1h after the injection of each immunoliposomal formulation. ResultsApoB-targeted HSPC/DSPG and SPC/EPG nanoliposomes were both taken up by cultured macrophages but the uptake rate was higher with the former formulation. Both immunoliposomal formulations significantly reduced serum LDL-cholesterol concentrations of hyperlipidemic animals at all tested doses (p<0.001) and this effect lasted for at least 48h. Significant reductions of serum levels of apoB, non-HDL-C, total cholesterol and triglycerides, and elevations of HDL-C levels were also observed. ConclusionIntravenous injection of a single dose of apoB-targeted anionic nanoliposomes improves serum lipid profile parameters. These findings might have implications for the treatment of patients with severe dyslipidemias or statin intolerance.

A simple and effective approach for the treatment of dyslipidemia using anionic nanoliposomes

The present study was undertaken to evaluate the anti-dyslipidemic effects of nanoliposomes with different phospholipid compositions. Three sets of liposomal formulations (20Mm; 100nM in size) were prepared with low (SPC), medium (POPC) and high (HSPC) phase transition temperature values with and without cholesterol and anionic phosphatidyl glycerol (HSPC/DSPG; POPC/DMPG; SPC/EPG). The liposomal preparations were characterized for their size and zeta potential (dynamic light scattering), J774A.1 macrophages uptake (flow cytometry) and lipid-modifying effects (tyloxapol-induced hyperlipidemic mouse model). Anionic formulations displayed the highest rate of uptake by macrophages. Among them, HSPC/DSPG and SPC/EPG liposomes had the best lipid-modifying activity. These two formulations exerted favorable impact on all lipid profile parameters by reducing LDL-C (by up to 76% [HSPC/DSPG] and 86% [SPC/EPG]), total cholesterol (by up to 52% [HSPC/DSPG] and 68% [SPC/EPG]), triglycerides (by up to 88% [HSPC/DSPG] and 73% [SPC/EPG]), apoB (by up to 44% [HSPC/DSPG] and 35% [SPC/EPG]) and elevating HDL-C (by up to 85% [HSPC/DSPG] and 75% [SPC/EPG]) concentrations. Atherogenic indices were also effectively reduced following HSPC/DSPG (by up to 69%) and SPC/EPG (by up to 79%) injections. Empty, cholesterol-free nanoliposomal formulations containing 75% anionic phospholipid (PG) might serve as effective and rapid acting anti-dyslipidemic agents. Further research is warranted to confirm the observed anti-dyslipidemic effects of anionic nanoliposomes in diet-induced hyperlipidemic models, and also to evaluate the potential protective effects in regressing atheromatous lesions.

Thermal and Optical Properties of Some Hydrogen-Bonded Liquid Crystal Mixtures

Phase transition properties of the mixtures of hydrogen-bonded nematic liquid crystals (HBLC) 4-hexylbenzoic acid (6BA), 4-(octyloxy)benzoic acid (8OBA), and 4-(decyloxy)benzoic acid (10OBA) have been investigated by means of differential scanning calorimetry (DSC) and polarize optic microscope (POM). The DSC and POM results clearly indicate the existence of smectic and nematic phase transitions in binary mixtures. The phase transition temperature values of 6BA/10OBA mixtures have clearly increased with increasing heating rate. The activation energies were calculated for the phase transitions of 6BA/10OBA liquid crystal (LC) mixture. The optical transmittance of these mixed hydrogen-bonded nematic liquid crystals was investigated in terms of temperature variations through electrooptic methods. The electrooptic experiments indicate that, while low in the nematic phase, the optical transmittance is very high at the nematic-isotropic phase transition. The transmitted light intensity values of 6BA/8OBA mixture are somewhat higher than those of other binary mixtures, 6BA/10OBA and 8OBA/10OBA, a result associated with the different alkyloxy chain lengths.

Thermal and mesomorphic properties of ternary mixtures of some hydrogen-bonded liquid crystals

The thermal and mesophase behaviour of ternary mixtures formed from hydrogen-bonded nematic liquid crystals 4-hexylbenzoic acid, 4-(octyloxy)benzoic acid and 4-(decyloxy)benzoic acid were investigated by differential scanning calorimetry (DSC) and phases identified by polarised optic microscopy (POM). The DSC and POM results clearly indicate that the produced mixtures display liquid crystalline properties. The phase transition temperature values obtained in the DSC experiments are in line with the POM observations. Investigation of the thermal properties of ternary mixtures reveals that the nematic range of the produced mixtures is affected in a way that is dependent on both the mixture ratio and the difference in the alkyloxy chain lengths. Furthermore, the phase transition temperature values of ternary mixture increase with increasing heating rate, and the calculated activation energy values show that the reaction arising during the phase transitions of the mixture is regular.

Determining excitation temperature of fragmented C60via momentum distributions of fragments

Hot C(60) molecules under nanosecond laser excitation decay by a variety of fragmentation channels. An experimental search has been made to determine the excitation temperature of fragmented C(60)via analyzing the momentum distributions of the prompt ionic fragments C(n)(+) (n ≤ 58). It was found that all the C(60) precursors appearing as these ionic fragments have almost the same temperature and the temperature shows little variation with the laser fluences in our limited range. The results provide a clear evidence that a first-order phase transition in the fragmented C(60) is occurring at this temperature. The value of phase transition temperature is found to be about 6050 ± 250 K, which is in a good agreement with the most recent estimations based on the molecular dynamics simulation. This approach offers an experimental opportunity for studying the fragmentation thermodynamics of more complex polyatomic molecules under excitation temperature determined conditions.

Synthesis and liquid crystal properties of phthalocyanine bearing a star polytetrahydrofuran moiety

A new polymeric ligand, 6-(3,4-dicyanophenylthio)-hexyl-2-polytetrahydrofuranacetate ( 2) and its liquid crystalline polymeric phthalocyanine, 2,9,16,23-tetrakis-{6-(polytetrahydrofuran-2-carboxylate)-hexylthio-phthalocyaninatocobalt(II) ( 3), {Co[Pc(S-C 6H 13OCO-poly-THF) 4]}(CoPcLC) have been synthesized. The ligand and the phthalocyanine, bearing polytetrahydrofuran moieties (poly-THF), were characterized using elemental analysis, FTIR, 1H and 13C NMR, and UV–Vis techniques. CoPcLC ( 3) promotes a greater interaction between the mesogens, resulting in solution aggregations together with a red-shift in the Q-band in the presence of the soft Ag + ion. The dielectric anisotropy and phase transition temperature values of CoPcLC doped with 4-cyano-4′-n-pentylbiphenyl (5CB) were found to be 7.17 and 40.5 °C, respectively. The dielectrical anisotropy behaviour of the liquid crystals changes from the positive to the negative type. The current–voltage characteristics of the liquid crystals show a non-linear behaviour.

Temperature Dependence of Thermo-Mechanical Properties of Banana Fiber-Reinforced Polyester Composites

Using a Dynamic Mechanical Analyzer (DMA), mechanical properties like modulus and phase transition temperature of polyester composites of banana fibers (treated and untreated) are measured simultaneously. The shifting of phase transition temperature is observed in some treatments. The performance of the composite depends to a large extent on the adhesion between polymer matrix and the reinforcement. This is often achieved by surface modification of the matrix or the filler. Banana fiber was modified chemically to achieve improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkalies were used to modify the fiber surface. Chemical modification was found to have a profound effect on the fiber/matrix interaction, which is evident from the values of phase transition temperatures. Of the various chemical treatments, simple alkali treatment with 1% NaOH was found to be the most effective.

Diffuse phase transition of Fe doped lead ytterbium tantalate ceramics

The effect of different concentration of Fe on the phase transition behavior of Lead ytterbium tantalate is investigated by dielectric and differential scanning calrimetry measurements. The samples are prepared through solid state reaction method and it has been found that the sintering temperature significantly lowered when the proportion of Pb(Fe 1/2Ta 1/2)O 3 increased. It has been observed that the doping in small amounts (0≤ x≤0.2) of Fe could meliorate the dielectric and ferroelectric properties. The diffuseness in the mode of phase transition increases and the phase transition temperature decreases as a function of Fe content. It is revealed that the dielectric data and heat capacity data follow a similar trend in the variation of the mode of phase transition and phase transition temperatures. The phase transition temperature values obtained from the heat capacity measurement well agreed with the values obtained from dielectric measurement.

Otrzymywanie i niektore wlasciwosci multiblokowych kopoli (amido-b-amidow)

The paper concerns the polymers built of oligoamide hard blocks and oligoamide soft blocks (KPAA, formula I). Oligo(laurolactam) (PA12) was used as hard block and the product of reaction of dimerized fatty acid and hexamethylene diamine (PA6,36) was used as a soft one. Effects of molar ratio of these blocks on the following properties of KPAA have been investigated: limiting viscosity number ([2]), degrees of swelling in water and benzene (Q H 2 O , Q b e n z , respectively), tensile properties and values of phase transition temperatures (Table 1, Fig. 1). It was found that fulfilling of various requirements concerning functional properties was possible when KPAA composition was properly chosen.

Relationship of Loss of Membrane Functionality and Hard‐to‐Cook Defect in Aged Beans

ABSTRACTMicrosomal membranes were prepared from fresh beans (Phaseolus vulgaris) and from samples kept 9 mo at various temperatures and humitidies. Increasing storage severity produced progressively hard‐to‐cook (HTC) beans as well as higher solids loss and lower water‐holding capacity during soaking. Membrane phase transition temperature (PTT), calcuated from spin label electron paramagnetic resonance data, also increased and showed a highly significant (r = 0.997) correlation with cooked hardness. Fatty acid analysis of membrane lipids demonstrated higher PTT values were due to a significant increase in proportion of saturated fatty acids. These data reflect membrane deterioration during aging that could explain solids loss and water‐holding capacity changes. Changes in the membrane may be the primary event in initiation of the HTC defect.

The Role of Liposome Composition on the Stabilization of Ancitabine

AbstractReduction in the ancitabine hydrolysis rate in an alkaline medium was achieved by liposome encapsulation of stable ancitabine solutions. The degree of success was gauged using stabilization ratios which compare rates of hydrolysis of free and encapsulated ancitabine under identical conditions. Stabilization ratios as high as 22 were observed when the phase transition temperature (PTT) values were 16 to 26°C higher than the storage temperature. Liposomes composed of phospholipids with PTT values below storage temperatures were ineffective. Increased liposome permeability was evidenced by rapid, nearly complete, release of encapsulated ancitabine at temperatures above the PTT. The inclusion of cholesterol in the liposomes reduced the maximum stabilization ratios from 22 to 4.