Decrease In Transition Enthalpy Research Articles

Effect of Single and Dual Hydrothermal Treatments on the Resistant Starch Content and Physicochemical Properties of Lotus Rhizome Starches.

Heat-moisture treatment (HMT) changed the morphology and the degree of molecular ordering in lotus rhizome (Nelumbo nucifera Gaertn.) starch granules slightly, leading to some detectable cavities or holes near hilum, weaker birefringence and granule agglomeration, accompanied with modified XRD pattern from C- to A-type starch and lower relative crystallinity, particularly for high moisture HMT modification. In contrast, annealing (ANN) showed less impact on granule morphology, XRD pattern and relative crystallinity. All hydrothermal treatment decreased the resistant starch (from about 27.7–35.4% to 2.7–20%), increased the damage starch (from about 0.5–1.6% to 2.4–23.6%) and modified the functional and pasting properties of lotus rhizome starch pronouncedly. An increase in gelatinization temperature but a decrease in transition enthalpy occurred after hydrothermal modification, particularly for hydrothermal modification involved with HMT. HMT-modified starch also showed higher pasting temperature, less pronounced peak viscosity, leading to less significant thixotropic behavior and retrogradation during pasting-gelation process. However, single ANN treatment imparts a higher tendency of retrogradation as compared to native starch. For dual hydrothermally modified samples, the functional properties generally resembled to the behavior of single HMT-modified samples, indicating the pre- or post-ANN modification had less impact on the properties HMT modified lotus rhizome starch.

Experimental heat transfer analysis of macro packed neopentylglycol with CuO nano additives for building cooling applications

The overall objective of the work reported in this paper was to experimentally study the effect of adding CuO nanoparticles on heat transfer performance of Neopentyl Glycol (NPG) in building cooling applications. Macro packed NPG added with 0.1% weight fraction of CuO nanoparticles were subjected to thermal cycling characterization and the thermal performance study in building application. Heat transfer performance analysis was conducted using the macro packed PCM in a building model with a 100 W incandescent bulb for simulating solar energy source. The differential scanning calorimetry (DSC) analysis showed that thermal cycling caused about 10.4% and 11.05% decrease in enthalpy of transition in the case pure NPG and NPG + 0.1% CuO respectively. The results of Thermogravimetry (TG) analysis and Fourier Transform Infrared (FTIR) analysis respectively confirmed the thermal and chemical stability of NPG +0.1% CuO in the application range of building cooling. The thermal conductivity measurement by T-history method showed an increase of 12.75% due to the addition of 0.1% CuO. The experimental results showed that the lower room temperature was reduced by about 3 °C by the use of macro packed NPG. The addition of CuO nanoparticles accelerated the rate of charging and discharging that lead to the decrease in charging and discharging time of macropacked NPG. It was observed that the addition of 0.1% weight fraction of CuO nanoparticles to NPG resulted in about 6.45% increase in the lower room temperature compared 11.6 7% increase observed in the case of pure NPG.

Adsorption-induced conformational changes of proteins onto ceramic particles: Differential scanning calorimetry and FTIR analysis

Three model proteins, bovine serum albumin, hen's egg lysozyme and bovine serum fibrinogen, were adsorbed from aqueous solution onto finely dispersed ceramic particles, namely different kinds of alumina and hydroxyapatite particles. The influence of adsorption on protein secondary structure was investigated. The FTIR spectroscopic findings were compared with the results of DSC measurements. In almost all cases it was found that adsorption results in destabilisation and structural loss of the bound protein. A decrease in transition enthalpy is correlated with a loss in α-helical structure, which seems to be the most sensitive structure on adsorption-induced rearrangements. A total collapse of structure in the adsorbed proteins was not determined on any ceramic surface. Some residual structure is always retained. Structural changes in the D- or E-domains of fibrinogen could be independently observed by two different calorimetric signals. The two techniques applied in the present study—micro-DSC and FTIR spectroscopy—can be concluded to provide complementary information on adsorption-induced structural changes on both the molecular (thermal stability, overall structure) and the sub-molecular level (secondary structure).

Aqueous solution behavior of thermosensitive (N-isopropylacrylamide-acrylic acid-ethyl methacrylate) terpolymers

A series of N-isopropylacrylamide (NIPAM)-acrylic acid–ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (Tc). Solutions of polymers containing 10% or less of AA display a constant Tc for pH above 5.5, with 15% there is a continuous increase in Tc with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I 1/I 3 ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than Tc, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain.

Characterization of Submicron Particles of Tetragonal BaTiO3

Barium titanate (BaTiO3) powders of varying particle sizes were grown under hydrothermal conditions at a temperature of 240 °C. This was accomplished by varying the hydroxide concentration of the reaction medium as well as the time required for synthesis. The spectroscopic, thermal, and microscopic characteristics of three BaTiO3 powders with average particle sizes 0.09, 0.3, and 0.5 μm were examined. Transmission electron microscopy indicated that all the particles were of single domain. The powder with smallest particle sizes (0.09 μm) contained unreacted titanium dioxide, whereas the larger particles (0.3, 0.5 μm) were pure barium titanate. The Raman spectra showed that all these crystals were tetragonally distorted. Infrared spectra showed primarily Frohlich modes, whose intensities also decreased with particle size. Analysis of the broadening of the powder diffraction patterns suggested that the BaTiO3 powders exhibited small strains. Differential scanning calorimetry showed a decrease in enthalpy of transition (ΔH) values with particle size. The particle size dependence on ΔH is attributed to the transition from a polar to a nonpolar state which occurs due to the bulk dipoles disordering due to interaction with the surface dipoles.

Calorimetric Investigations of Phosphatidic Acid Bilayers

AbstractDifferential scanning calorimetry is a sensitive method for studying the phase transition of phospholipid bilayers. Up to now only few calorimetric investigations of the phase transition of charged phospholipids have been carried out [1–3]. We studied the phase behaviour of dihexadecyl‐phosphatidic acid (DHPA) as a function of the pH of the dispersion [4, 5]. Varying the pH induces different degrees of ionization of the phosphatidic acid head group. At high pH the head group has two negative charges leading to a decrease of the transition temperature to 49°C compared to 70°C at pH 9.0 and a decrease in transition enthalpy to 21.8 kJ/mol compared to 31.4 kJ/mol at pH 9.0. Lowering the pH below 9.0 leads to a gradual protonation of singly charged DHPA. With increasing protonation Tm rises to 74°C at pH 3.5 and then drops to 62°C at pH 1.5.The results obtained by calorimetry indicate, that probably two different phases can exist between pH 9.0 and 1.0. At half protonation at pH 3.5 a particular stable phase with high transition temperature and low transition enthalpy (11.3 kJ/mol) can be observed. Complete protonation leads to a phase, which has the same transition temperature as the melting point of dry crystalline protonated DHPA.The observed variation of the transition enthalpy with pH cannot be explained by assuming, that only the electrostatic potential of the bilayer surface is changed [6]. An influence of the degree of ionization of the head group on the hydrocarbon chain interactions has to be taken into account.From these experiments conclusions can be drawn upon the intermolecular interactions between the head groups of phosphatidic acids.