Calorimetry Studies (calorimetry + studies)

Distribution by Scientific Domains

Kinds of Calorimetry Studies

  • differential scanning calorimetry studies
  • scanning calorimetry studies


  • Selected Abstracts


    Rheological and thermal properties of poly(ethylene oxide)/multiwall carbon nanotube composites

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008
    T. N. Abraham
    Abstract Poly(ethylene oxide) (PEO) based nanocomposites were prepared by the dispersion of multiwall carbon nanotubes (MWCNTs) in aqueous solution. MWCNTs were added up to 4 wt % of the PEO matrix. The dynamic viscoelastic behavior of the PEO/MWCNT nanocomposites was assessed with a strain-controlled parallel-plate rheometer. Prominent increases in the shear viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content. Dynamic and isothermal differential scanning calorimetry studies indicated a significant decrease in the crystallization temperature as a result of the incorporation of MWCNTs; these composites can find applications as crystallizable switching components for shape-memory polymer systems with adjustable switching temperatures. The solid-state, direct-current conductivity was also enhanced by the incorporation of MWCNTs. The dispersion level of the MWCNTs was investigated with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Crystallization pathways and kinetics of carbamazepine,nicotinamide cocrystals from the amorphous state by in situ thermomicroscopy, spectroscopy, and calorimetry studies

    JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007
    K. Seefeldt
    Abstract The work presented here was motivated by the premise that the amorphous state serves as a medium to study cocrystal formation. The molecular mobility inherent to amorphous phases can lead to molecular associations between different components such that a single crystalline phase of multiple components or cocrystal is formed. Cocrystallization pathways and kinetics were investigated from amorphous equimolar phases of carbamazepine and nicotinamide using hot-stage polarized microscopy (HSPM), hot-stage Raman microscopy (HSRM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). Nonisothermal studies revealed that amorphous phases generate cocrystals and that thermal history affects crystallization pathways in significant ways. Two different pathways to cocrystal formation from the amorphous phase were identified: (1) at low heating rates (3°C/min) a metastable cocrystalline phase initially nucleates and transforms to the more stable cocrystalline phase of CBZ,NCT, and (2) at higher heating rates (10°C/min) individual components crystallize, then melt and the stable cocrystalline phase nucleates and grows from the melt. Isothermal studies above the Tg of the amorphous equimolar phase also confirm the nucleation of a metastable cocrystalline phase from the amorphous state followed by a solid phase mediated transformation to the stable cocrystalline phase. Cocrystallization kinetics were measured by image analysis and by thermal analysis from small samples and are described by the Avrami,Erofeev model. These findings have important implications for the use of amorphous phases in the discovery of cocrystals and to determine the propensity of cocrystallization from process-induced amorphization. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1147,1158, 2007 [source]


    Living free-radical polymerization (reversible addition,fragmentation chain transfer) of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate: A route to architectural control of side-chain liquid-crystalline polymers

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003
    Xiaojuan Hao
    Abstract Side-chain liquid-crystalline polymers of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate with controlled molecular weights and narrow polydispersities were prepared via reversible addition,fragmentation chain transfer (RAFT) polymerization with 2-(2-cyanopropyl) dithiobenzoate as the RAFT agent. Differential scanning calorimetry studies showed that the polymers produced via the RAFT process had a narrower thermal stability range of the liquid-crystalline mesophase than the polymers formed via conventional free-radical polymerization. In addition, a chain length dependence of this stability range was found. The generated RAFT polymers displayed optical textures similar to those of polymers produced via conventional free-radical polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2949,2963, 2003 [source]


    Using Differential Scanning Calorimetry to Follow How Gelcasting Proceeds

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007
    BoonSing Ng
    Differential scanning calorimetry studies on aqueous low-toxicity monomer,crosslinker gelcasting systems loaded with zirconia powder provided information on the onset and kinetics of the polymerization reaction. A simple procedure was developed to determine the relative importance of the individual components on the gelation process. It was found that the thermal stability and dissociation of the initiator control the gelation rate and that the zirconia particles accelerate the gelation. [source]


    Functional properties and retrogradation behaviour of native and chemically modified starch of mucuna bean (Mucuna pruriens)

    JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2003
    Kayode O Adebowale
    Abstract Mucuna bean (Mucuna pruriens) starch was isolated and subjected to chemical modification by oxidation and acetylation. The proximate analysis of the non-starch components of the native starch on a dry weight basis was 92 g kg,1 moisture, 5 g kg,1 ash, 2 g kg,1 fat, 7 g kg,1 crude fibre and 19 g kg,1 protein. Chemical modification reduced the values for all the non-starch components except the moisture level. For all the samples, swelling power and solubility increased as the temperature increased in the range 50,90 °C. The swelling power of mucuna native starch (MNS) and mucuna acetylated starch (MAS) increased with increasing acidity and alkalinity, while that of mucuna oxidised starch (MOS) only increased with increasing pH in the acidic range. The maximal solubility of all the starches was observed at pH 12. All the starch samples absorbed more oil than water. The lowest gelation concentration followed the trend MAS < MNS < MOS. Chemical modification reduced the gelatinisation temperature (Tp), while peak viscosity (Pv), hot paste viscosity (Hv) and cold paste viscosity (Cv) decreased after oxidation but increased following acetylation. The setback tendency of the native starch was reduced significantly after chemical modification. However, the breakdown value of MNS, 65 BU (Brabender units), was lower than that of MOS (78 BU) but higher than that of MAS (40 BU). Differential scanning calorimetry studies of gelatinisation and retrogradation revealed that chemical modification reduced the onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc). Oxidation and acetylation reduced the gelatinisation and retrogradation enthalpies of the native starch. The enthalpy of retrogradation of the starches increased as the length of storage increased. Copyright © 2003 Society of Chemical Industry [source]


    Metal-exchanged clay and zeolite additives as smoke suppressants and fire retardants for poly(vinyl chloride)

    JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2009
    Alexander G. Zestos
    Cone calorimetry studies showed that various metal-exchanged clays and zeolites containing only 3,4% of Cu(II), Cu(I), Zn(II), or Al(III) were effective smoke suppressants and fire retardants for plasticized poly(vinyl chloride). Copper(II)-Zn(II) and Cu(II)-Al(III) synergism for smoke and heat reduction was observed with binary blends of the clays, and the effectiveness of the additives was usually improved considerably by heating plasticizer-additive mixtures under very high shear before combining them with the polymer. Possible mechanisms of action of the additives are described. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers [source]


    Low density polyethylene and grafted lignin polyblends using epoxy-functionalized compatibilizer: mechanical and thermal properties

    POLYMER INTERNATIONAL, Issue 12 2005
    RRN Sailaja
    Abstract Lignin was graft copolymerized with methyl methacrylate using manganic pyrophosphate as initiator. This modified lignin was then blended (up to 50 wt%) with low density polyethylene (LDPE) using a small quantity of poly[ethylene- co -(glycidyl methacrylate)] (PEGMA) compatibilizer. The mechanical properties of the blend were substantially improved by using modified lignin in contrast to untreated lignin. Differential scanning calorimetry studies showed loss of crystallinity of the LDPE phase owing to the interaction between the blend components. Thermogravimetric analysis showed higher thermal stability of modified lignin in the domain of blend processing. This suggested that there is scope for useful utilization of lignin, which could also lead to the development of eco-friendly products. Copyright © 2005 Society of Chemical Industry [source]


    Strategy for selecting and characterizing linker peptides for CBM9-tagged fusion proteins expressed in Escherichia coli

    BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007
    Mojgan Kavoosi
    Abstract The influence of linker design on fusion protein production and performance was evaluated when a family 9 carbohydrate-binding module (CBM9) serves as the affinity tag for recombinant proteins expressed in Escherichia coli. Two bioinformatic strategies for linker design were applied: the first identifies naturally occurring linkers within the proteome of the host organism, the second involves screening peptidases and their known specificities using the bioinformatics software MEROPSÔ to design an artificial linker resistant to proteolysis within the host. Linkers designed using these strategies were compared against traditional poly-glycine linkers. Although widely used, glycine-rich linkers were found by tandem MS data to be susceptible to hydrolysis by E. coli peptidases. The natural (PT)xP and MEROPSÔ-designed S3N10 linkers were significantly more stable, indicating both strategies provide a useful approach to linker design. Factor Xa processing of the fusion proteins depended strongly on linker chemistry, with poly(G) and S3N10 linkers showing the fastest cleavage rates. Luminescence resonance energy transfer studies, used to measure average distance of separation between GFP and Tb(III) bound to a strong calcium-binding site of CBM9, revealed that, for a given linker chemistry, the separation distance increases with increasing linker length. This increase was particularly large for poly(G) linkers, suggesting that this linker chemistry adopts a hydrated, extended configuration that makes it particularly susceptible to proteolysis. Differential scanning calorimetry studies on the PT linker series showed that fusion of CBM9 to GFP did not alter the Tm of GFP but did result in a destabilization, as seen by both a decrease in Tm and ,Hcal, of CBM9. The degree of destabilization increased with decreasing length of the (PT)xP linker such that ,Tm,=,,8.4°C for the single P linker. Biotechnol. Bioeng. 2007;98: 599,610. © 2007 Wiley Periodicals, Inc. [source]


    Selective Guest Encapsulation by a Cobalt-Assembled Cage Molecule

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005
    Roger G. Harrison Prof.
    Abstract Metal-assembled resorcinarene-based cages enclose space and entrap organic molecules from water. Addition of cobalt(II) ions to a neutral, aqueous solution of a resorcinarene that has iminodiacetic acids attached to its upper rim results in the formation of cages. These cages not only entrap organic molecules, but they do so in a selective manner. Guests with optimum size, shape, and polarity are preferentially entrapped. For example, selection of p -xylene is twenty thousand times more favorable than that of m -xylene. The enthalpy of resorcinarene deprotonation and cage formation was calculated by performing calorimetry studies and ranged from ,305 to ,348 kJ,mol,1. The change in enthalpy of guest encapsulation varied by as much as 43 kJ,mol,1. The differences in change in free energy of guest encapsulation varied by ,16 kJ,mol,1. The changes in enthalpy and free energy of guest encapsulation were used to calculate the changes in entropy, which ranged from ,97 to +37 J,mol,1,K,1. An enthalpy,entropy compensation of guest encapsulation was observed. [source]