Transition Temperature (transition + temperature)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Transition Temperature

  • glass transition temperature
  • high glass transition temperature
  • low glass transition temperature
  • phase transition temperature
  • single glass transition temperature
  • superconducting transition temperature

  • Selected Abstracts


    ABSTRACT The fine grinding of chocolate is typically accomplished on five-roll mills. Chocolate manufacturers consider milk powder, a component of milk chocolate, difficult to grind. Spray-dried milk powders comprise a glassy lactose matrix in which fat globules, air vacuoles and protein are entrapped. the glassy-rubbery transition in commercial milk powders usually lies between 60,70C, depending on the moisture content. A mixture of 60% wt/wt commercial whole milk powder, Tg, 60C, and 40% wt/wt cocoa butter was ground in a three-roll refiner at temperatures of 40, 50, 60, 70 and 75C. Below Tg the particles exhibited brittle fracture, while above Tg plastic deformation was evident and particles became highly asymmetric. the amount of fat liberated from the lactose matrix, so-called free fat, particle density, and mean particle size increased with grinding temperature. However, the Casson yield value and plastic viscosity of finished "white chocolate" coatings, manufactured to a constant free fat content, increased with grinding temperature, suggesting an influence of particle shape on flow behavior. [source]

    Influence of Cooling Rate on Glass Transition Temperature of Sucrose Solutions and Rice Starch Gel

    C.-L. Hsu
    ABSTRACT: The study's objectives were to determine the influence of cooling rate through the primary zone of freezing on Tg in sucrose solutions and rice starch gels. The influence of cooling rate, water content, and annealing on Tg were evaluated. Results indicated that the observed Tg values for sucrose solutions were lower after rapid cooling (70% solids: rapid cooling ,66.7C; slow cooling ,64.6 C; 30% solids: rapid cooling ,34.6 C; slow cooling ,33.3 C). The Tg values of annealed samples are higher than the Tg of both rapidly and slowly cooled samples (70%: ,44.2 C; 30%: ,32.7 C). The Tg of the rice starch gel was ,9.0 C after rapid cooling and ,7.5 C after slow cooling. [source]

    QSPR Analysis of Copolymers by Recursive Neural Networks: Prediction of the Glass Transition Temperature of (Meth)acrylic Random Copolymers

    Carlo Giuseppe Bertinetto
    Abstract The glass transition temperature (Tg) of acrylic and methacrylic random copolymers was investigated by means of Quantitative Structure-Property Relationship (QSPR) methodology based on Recursive Neural Networks (RNN). This method can directly take molecular structures as input, in the form of labelled trees, without needing predefined descriptors. It was applied to three data sets containing up to 615 polymers (340 homopolymers and 275,copolymers). The adopted representation was able to account for the structure of the repeating unit as well as average macromolecular characteristics, such as stereoregularity and molar composition. The best result, obtained on a data set focused on copolymers, showed a Mean Average Residual (MAR) of 4.9,K, a standard error of prediction (S) of 6.1,K and a squared correlation coefficient (R2) of 0.98 for the test set, with an optimal rate with respect to the training error. Through the treatment of homopolymers and copolymers both as separated and merged data sets, we also showed that the proposed approach is particularly suited for generalizing prediction of polymer properties to various types of chemical structures in a uniform setting. [source]

    ChemInform Abstract: Pressure Dependence of the Superconducting Transition Temperature of Magnesium Diboride.

    CHEMINFORM, Issue 30 2001
    M. Monteverde
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Competitive Enzymatic Fluorescence Immunoassay for Human IgG by Using a Temperature-Sensitive Phase Separating Polymer with Regulated Phase Transition Temperature

    Peng LIN
    Abstract A new enzymatic fluorescence immunoassay for human IgG was developed using a temperature-sensitive polymer, poly(N -isopropylacrylamide-co-acrylamide) [P(NIP-AA)], as a carrier. The lower critical solution temperature of the P(NIP-AA) containing molar fraction of 8% for AA was 37 C. In a competitive immunoassay, immobilized IgG and the standard IgG (or sample) competed for binding to a horseradish peroxidase labeled antibody at 33 C in homogeneous format. After changing the temperature to separate the polymer-immune complex, the complex precipitate was re-dissolved and determined by coupling with the fluorescence reaction of hydrogen peroxide and p -hydroxyphenylacetic acid. The calibration graph for human IgG was linear over the range of 100,1000 ng/mL with a detection limit of 2.0 ng/mL. The method is rapid, sensitive and simple. The immune reaction efficiency was improved. In addition, the sensitivity of this method was close to that using traditional microtitration plates as carriers. However, the assay was much faster (the assay time decreased from 100,120 to 30 min). The method has been applied to the determination of the human IgG levels in human sera with satisfactory results. [source]

    The Structure of Water in PEO-Based Segmented Block Copolymers and its Effect on Transition Temperatures

    Debby Husken
    Abstract The effect of water on block copolymers that contain hydrophilic PEO flexible segments is studied. The polyether phase consisted of either PEO or mixtures of PEO and hydrophobic PTMO, monodisperse crystallisable T6T6T was used as hard segments. Water absorption as a function of relative humidity and PEO content were studied. The PEO melting temperature and crystallinity were strongly reduced when the copolymer absorbed water, while the PTMO phase remained unaffected by its presence. Freezing water was present in the PEO-based copolymers when the PEO phase contained ,30 vol.-% water, its relative amount being almost independent of PEO concentration and molecular weight and the presence of hydrophobic PTMO segments. [source]

    Glass Transition Temperatures and Fermentative Activity of Heat-Treated Commercial Active Dry Yeasts

    Carolina Schebor
    Differential scanning calorimetry thermograms of various samples of commercial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperatures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumulate in large amounts in baker's yeast. The effect of heat treatment at various temperatures on the fermentative activity (as measured by the metabolic production of CO2) of dry yeast was studied. First-order plots were obtained representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentative activity were observed in vitrified yeast samples. The dependence of rate constants with temperature was found to follow Arrhenius behavior. The relationship between the loss of fermentative activity and glass transition was not verified, and the glass transition was not reflected on the temperature dependence of fermentative activity loss. [source]

    Conformational aspects of segmented poly(ester-urethanes)

    S. Ioan
    Abstract Segmented poly(ester-urethanes) containing hard and soft segments, were obtained from aromatic diisocyanates with thiodiglycol or diethylene glycol as chain extenders, and poly(ethylene glycol)adipate usig a multistep polyaddition process. Transition temperatures by differential scanning calorimetry and thermo-optical analysis were employed to characterize polyurethane materials. Changes in the conformation of these polyurethanes were analyzed also, by viscometer measurements in N,N-dimethyl-formamide. The obtained data revealed that the thermal curves are influenced by the soft and hard segment structures in the temperature range studied. [source]

    Correlation between the residual resistivity ratio and the power-law of the normal-state resistivity in MgB2

    I. M. Obaidat
    Abstract MgB2 polycrystalline superconducting specimens were irradiated with several doses of ,-rays up to 100 MR. An increase in the normal state resistivity and a broadening of the resistive transition to the superconducting state were observed with increasing ,-irradiation dose. Although very small changes to the superconducting transition temperature were obtained after ,-irradiation, different temperature dependence of normal-state resistivity and different residual resistivity ratios, RRR were obtained for different doses. We have found a correlation between RRR and the power law dependence of resistivity, n as the irradiation dose increases. This correlation may be an indication that the electron-phonon interaction is important in these samples. These results are attributed to the disorder caused by ,-rays. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination Sphere and Spin Transition around Room Temperature

    Birgit Weber
    Abstract The reaction of iron(II) acetate with the tetradentate Schiff base like ligand H2L1 {[3,3,]-[4,5-dihydroxy-1,2-phenylenebis(iminomethylidyne)bis(2,4-pentanedion)]} leads to the formation of the complex [FeL1(MeOH)]. Reaction of this complex with pyridine (py) or N,N,-dimethylaminopyridine (dmap) leads to the two N4O2 -coordinated complexes [FeL1(py)2]py (1) and [FeL1(dmap)2]MeOH0.5dmap (2). Both complexes are spin-crossover compounds that were characterised by using magnetic measurements, X-ray crystallography and temperature-dependent 1H NMR spectroscopy. Special attention was given to the role of the two hydroxy groups on the phenyl ring in the formation of a hydrogen-bonding network and the influence of this network on the spin-transition properties. Although only a gradual spin crossover was observed for both complexes, the transition temperature was shifted to higher temperatures relative to that of the complexes with no additional hydroxy groups at the Schiff base like ligand. The hydrogen-bonding network was responsible for this effect.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Microstructure and Mechanical Properties of New AlCoxCrFeMo0.5Ni High-Entropy Alloys

    Chin-You Hsu
    Effects of Co content on microstructures and hot hardness of a new high-entropy alloy system, AlCoxCrFeMo0.5Ni (x,=,0.5 to 2.0) were investigated. As cobalt content increases, the microstructure changes from dendrite to polygrain type and the constituent phases change from BCC,+,, at x,=,0.5 to BCC,+,FCC,+,, at x,=,2.0. The alloy hardness varies from Hv 788 at x,=,0.5 to Hv 596 at x,=,2.0. This can be explained with the relative amount of hard , phase, medium hard BCC phase and soft FCC phase. All the AlCoxCrFeMo0.5Ni alloys possess higher hardness level than that of Ni-based superalloys In 718/In 718 H from room temperature to 1273,K. They obey the Westbrook equation presenting the normal heating behavior. Both alloys of x,=,0.5 and 1.0 exhibit a transition temperature higher than that of Co-based alloy T-800 by about 200,K. They also have a high hot hardness of Hv 347 at 1273,K, which is higher than those of In 718 and In718 H by Hv 220. The strengthening mechanism for their superiority is proposed. The AlCoxCrFeMo0.5Ni alloy system has great potential in high-temperature applications. [source]

    Asymmmetric Diamino Functionalization of Nanotubes Assisted by BOC Protection and Their Epoxy Nanocomposites

    Yao Zhao
    Abstract Homogenous dispersion and strong interfacial bonding are prerequisites for taking full advantage of the mechanical properties of nanotubes in a composite. In order to simultaneously achieve both conditions, a highly efficient and mechanically non-destructive functionalization of nanotubes is developed. With fluoronanotubes as the precursor, asymmetric diamine molecules, N -BOC-1,6-diaminohexane, are used to replace fluorines on the wall of fluoronanotubes and construct covalent bonding to the surface of the nanotubes. A BOC de-protection reaction is conducted and the resulting exposed amino groups create strong covalent bonds with the matrix in the course of epoxy ring-opening etherification and curing chemical reactions. In comparison with the conventional functionalization based on symmetric diamine molecules, the functionalized nanotubes derived from the BOC-protected diamine molecule are more dispersed within the epoxy matrix. Dynamic mechanical analysis shows that the functionalized nanotubes have better crosslinking with the matrix. The composites reinforced by the nanotubes demonstrate improvement in various mechanical properties. The Young's Modulus, ultimate tensile strength, and storage modulus of composites loaded with 0.5 wt% functionalized nanotubes are enhanced by 30%, 25%, and 10%, respectively, compared with the neat epoxy. The increase of the glass transition temperature, as much as 10 C, makes the composites suited for engineering applications under higher temperatures. The new functionalization method allows for an competitive enhancement in the composite performance in use of relatively low cost raw nanotubes at a small loading level. The reinforcement mechanism of the functionalized nanotubes in the epoxy resin is discussed. [source]

    Organic Electronics: High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal Treatment (Adv. Funct.

    Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95 1) and high thermal stability (glass transition temperature = 181 C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source]

    High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal Treatment

    Jaeyoung Jang
    Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95 1) and high thermal stability (glass transition temperature = 181 C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source]

    Domain V of m-calpain shows the potential to form an oblique-orientated ,-helix, which may modulate the enzyme's activity via interactions with anionic lipid

    FEBS JOURNAL, Issue 22 2002
    Klaus Brandenburg
    The activity of m-calpain, a heterodimeric, Ca2+ -dependent cysteine protease appears to be modulated by membrane interactions involving oblique-orientated ,-helix formation by a segment, GTAMRILGGVI, in the protein's smaller subunit. Here, graphical and hydrophobic moment-based analyses predicted that this segment may form an ,-helix with strong structural resemblance to the influenza virus peptide, HA2, a known oblique-orientated ,-helix former. Fourier transform infrared spectroscopy showed that a peptide homologue of the GTAMRILGGVI segment, VP1, adopted low levels of ,-helical structure (, 20%) in the presence of zwitterionic lipid and induced a minor decrease (3 C) in the gel to liquid-crystalline phase transition temperature, TC, of the hydrocarbon chains of zwitterionic membranes, suggesting interaction with the lipid headgroup region. In contrast, VP1 adopted high levels of ,-helical structure (65%) in the presence of anionic lipid, induced a large increase (10 C) in the TC of anionic membranes, and showed high levels of anionic lipid monolayer penetration (,SP = 5.5 mNm,1), suggesting deep levels of membrane penetration. VP1 showed strong haemolytic ability (LD50 = 1.45 mm), but in the presence of ionic agents, this ability, and that of VP1 to penetrate anionic lipid monolayers, was greatly reduced. In combination, our results suggest that m-calpain domain V may penetrate membranes via the adoption of an oblique-orientated ,-helix and electrostatic interactions. We speculate that these interactions may involve snorkelling by an arginine residue located in the polar face of this ,-helix. [source]

    The assembly factor P17 from bacteriophage PRD1 interacts with positively charged lipid membranes

    FEBS JOURNAL, Issue 20 2000
    Juha M. Holopainen
    The interactions of the assembly factor P17 of bacteriophage PRD1 with liposomes were investigated by static light scattering, fluorescence spectroscopy, and differential scanning calorimetry. Our data show that P17 binds to positively charged large unilamellar vesicles composed of the zwitterionic 1-palmitoyl-2-oleoyl-phosphatidylcholine and sphingosine, whereas only a weak interaction is evident for 1-palmitoyl-2-oleoyl-phosphatidylcholine vesicles. P17 does not bind to negatively charged membranes composed of 1-palmitoyl-2-oleoyl-phosphatidylglycerol and 1-palmitoyl-2-oleoyl-phosphatidylcholine. Our differential scanning calorimetry results reveal that P17 slightly perturbs the phase behaviour of neutral phosphatidylcholine and negatively charged multilamellar vesicles. In contrast, the phase transition temperature of positively charged dimyristoylphosphatidylcholine/sphingosine multilamellar vesicles (molar ratio 9 : 1, respectively) is increased by approximately 2.4 C and the half width of the enthalpy peak broadened from 1.9 to 5.6 C in the presence of P17 (protein : lipid molar ratio 1 : 47). Moreover, the enthalpy peak is asymmetrical, suggesting that lipid phase separation is induced by P17. Based on the far-UV CD spectra, the ,-helicity of P17 increases upon binding to positively charged micelles composed of Triton X-100 and sphingosine. We propose that P17 can interact with positively charged lipid membranes and that this binding induces a structural change on P17 to a more tightly packed and ordered structure. [source]

    Curvature properties of novel forms of phosphatidylcholine with branched acyl chains

    FEBS JOURNAL, Issue 10 2000
    Richard M. Epand
    We studied the properties of a series of phosphatidylcholine molecules with branched acyl chains. These lipids have previously been shown to have marked stimulatory effects on the side-chain cleavage activity of cytochrome P450SCC (CYP11A1), an enzyme of the inner mitochondrial membrane. The synthetic lipids used were diacyl phosphatidylcholines with the decanoyl, dodecanoyl or tetradecanoyl chain having a hexyl, octyl or decyl straight chain aliphatic branch at the 2-position. All three lipids lowered the bilayer to hexagonal phase transition temperature of dielaidoyl phosphatidylethanolamine, the lipids with longer acyl chains being more effective in this regard. As pure lipids all of the forms were found by X-ray diffraction to be predominantly in the hexagonal phase (HII) over the entire temperature range of 7,75 C. The properties of the HII phase were unusual with regard to the small size of the lattice spacings and the small temperature dependence of the spacings. We used tetradecane to relieve hydrocarbon packing constraints to determine the intrinsic radius of curvature of the lipid monolayer. The elastic bending modulus was measured in the presence of tetradecane by introducing an osmotic gradient across the hexagonal phase cylinders with aqueous solutions of poly(ethylene glycol). The elastic bending modulus was found to be higher than that observed with other lipids and to increase with temperature. Both the small intrinsic radius of curvature and the high elastic bending modulus indicate that the presence of these lipids in bilayer membranes will impose a high degree of negative curvature strain. [source]

    The RadA protein from a hyperthermophilic archaeon Pyrobaculum islandicum is a DNA-dependent ATPase that exhibits two disparate catalytic modes, with a transition temperature at 75 C

    FEBS JOURNAL, Issue 4 2000
    Maria Spies
    The radA gene is an archaeal homolog of bacterial recA and eukaryotic RAD51 genes, which are critical components in homologous recombination and recombinational DNA repair. We cloned the radA gene from a hyperthermophilic archaeon, Pyrobaculum islandicum, overproduced the radA gene product in Escherichia coli and purified it to homogeneity. The purified P. islandicum RadA protein maintained its secondary structure and activities in vitro at high temperatures, up to 87 C. It also showed high stability of 18.3 kcalmol,1 (76.5 kJmol,1) at 25 C and neutral pH. P. islandicum RadA exhibited activities typical of the family of RecA-like proteins, such as the ability to bind ssDNA, to hydrolyze ATP in a DNA-dependent manner and to catalyze DNA strand exchange. At 75 C, all DNAs tested stimulated ATPase activity of the RadA. The protein exhibited a break in the Arrhenius plot of ATP hydrolysis at 75 C. The cooperativity of ATP hydrolysis and ssDNA-binding ability of the protein above 75 C were higher than at lower temperatures, and the activation energy of ATP hydrolysis was lower above this break point temperature. These results suggest that the ssDNA-dependent ATPase activity of P. islandicum RadA displays a temperature-dependent capacity to exist in two different catalytic modes, with 75 C being the critical threshold temperature. [source]

    Plant fructans stabilize phosphatidylcholine liposomes during freeze-drying

    FEBS JOURNAL, Issue 2 2000
    Dirk K. Hincha
    Fructans have been implicated as protective agents in the drought and freezing tolerance of many plant species. A direct proof of their ability to stabilize biological structures under stress conditions, however, is still lacking. Here we show that inulins (linear fructose polymers) isolated from chicory roots and dahlia tubers stabilize egg phosphatidylcholine large unilamellar vesicles during freeze-drying, while another polysaccharide, hydroxyethyl starch, was completely ineffective. Liposome stability was assessed after rehydration by measuring retention of the soluble fluorescent dye carboxyfluorescein and bilayer fusion. Inulin was an especially effective stabilizer in combination with glucose. Analysis by HPLC showed that the commercial inulin preparations used in our study contained no low molecular mass sugars that could be responsible for the observed stabilizing effect of the fructans. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature of dry egg PtdCho by more than 20 C in the presence of inulin. A direct interaction of inulin with the phospholipid in the dry state was also indicated by dramatic differences in the phosphate asymmetric stretch region of the infrared spectrum between samples with and without the polysaccharide. [source]

    The ,-to-, Transition in BiFeO3: A Powder Neutron Diffraction Study

    Donna C. Arnold
    Abstract High-temperature powder neutron diffraction experiments are conducted around the reported ,,, phase transition (,930,C) in BiFeO3. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator,metal transition, both the ,- and ,-phase of BiFeO3 exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The ,-orthorhombic phase is observed to persist up to a temperature of approximately 950,C before complete decomposition into Bi2Fe4O9 (and liquid Bi2O3), which subsequently begins to decompose at approximately 960,C. [source]

    Sensors: Glass Fibers with Carbon Nanotube Networks as Multifunctional Sensors (Adv. Funct.

    A semiconductive interphase between a glass fi ber and an epoxy matrix is achieved by coating carbon nanotubes on the glass fiber, as reported by S.-L. Gao, E. Mder, et al. on page 1885. The interphase at the nanoscale provides multifunctional sensibility, which can be observed by electric force microscopy. The resulting composites with an ultra-high anisotropic electrical property are capable of detecting piezoresistive effects as well as the local glass transition temperature. [source]

    Glass Fibers with Carbon Nanotube Networks as Multifunctional Sensors

    Shang-lin Gao
    Abstract A simple approach to deposit multiwalled carbon nanotube (MWNT) networks onto glass fiber surfaces achieving semiconductive MWNT,glass fibers is reported, along with application of fiber/polymer interphases as in-situ multifunctional sensors. This approach demonstrates for the first time that the techniques of conducting electrical resistance measurements could be applicable to glass fibers for in situ sensing of strain and damage; the techniques were previously limited to conductive and semiconductive materials. The electrical properties of the single MWNT,glass fiber and the "unidirectional" fiber/epoxy composite show linear or nonlinear stress/strain, temperature, and relative humidity dependencies, which are capable of detecting piezoresistive effects as well as the local glass transition temperature. The unidirectional composites containing MWNT,glass fibers exhibit ultrahigh anisotropic electrical properties and an ultralow electrical percolation threshold. Based on this approach, the glass fiber,the most widely used reinforcement in composites globally,along with the surface electrical conductivity of MWNTs will stimulate and realize a broad range of multifunctional applications. [source]

    Orientation Control of Linear-Shaped Molecules in Vacuum-Deposited Organic Amorphous Films and Its Effect on Carrier Mobilities

    Daisuke Yokoyama
    Abstract The molecular orientation of linear-shaped molecules in organic amorphous films is demonstrated to be controllable by the substrate temperature. It is also shown that the molecular orientation affects the charge-transport characteristics of the films. Although linear-shaped 4,4,-bis[(N -carbazole)styryl]biphenyl molecules deposited on substrates at room temperature are horizontally oriented in amorphous films, their orientation when deposited on heated substrates with smooth surfaces becomes more random as the substrate temperature increases, even at temperatures under the glass transition temperature. Another factor dominating the orientation of the molecules deposited on heated substrates is the surface roughness of the substrate. Lower carrier mobilities are observed in films composed of randomly oriented molecules, demonstrating the significant effect of a horizontal molecular orientation on the charge-transport characteristics of organic amorphous films. [source]

    High-Strain Shape-Memory Polymers

    Walter Voit
    Abstract Shape-memory polymers (SMPs) are self-adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures. In this study, the glass transition temperature (Tg) is adjusted between 28 and 55,C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA). Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a Tg of 28,C, at 663% for a Tg of 37,C, and at 553% for a Tg of 55,C. A new compound, 4,4,-di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape-memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%. The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape-memory cycle caused large-scale disfiguration. The materials in this study are intended to enable future applications where both recoverable high-strain capacity and the ability to accurately and independently position Tg are required. [source]

    Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole

    Ju Huang
    Abstract Soluble molecular red emitters 1a/1b are synthesized by Stille coupling from 2-(3,5-di(1-naphthyl)phenyl)thiophene precursors. The compounds show emission maxima at ca. 610,nm in CH2Cl2 solution and 620,nm in solid films. Replacing the n -hexyl substituent by 4- sec -butoxyphenyl produces a marked increase of glass transition temperature (Tg) from 82,C to 137,C and increases the solubility in toluene and p -xylene, thus improving the film-forming properties. Cyclic voltammetry shows that the compounds can be reversibly oxidized and reduced around +1.10 and ,1.20,V, respectively. A two-layered electroluminescent device based on 1b produces a pure red light emission with CIE coordinates (0.646, 0.350) and a maximal luminous efficiency of 2.1,cd A,1. Furthermore, when used as a solution-processed red emitter in optically pumped laser devices, compound 1b successfully produces a lasing emission at ca. 650,nm. [source]

    Synthesis and Structure,Property Relations of a Series of Photochromic Molecular Glasses for Controlled and Efficient Formation of Surface Relief Nanostructures

    Roland Walker
    Abstract This paper reports on the synthesis and properties of a new series of photochromic molecular glasses and their structure,property relations with respect to a controlled and efficient formation of surface relief nanostructures. The aim of the paper is to establish a correlation between molecular structure, optical susceptibility, and the achievable surface relief heights. The molecular glasses consist of a triphenylamine core and three azobenzene side groups attached via an ester linkage. Structural variations are performed with respect to the substitution at the azobenzene moiety in order to promote a formation of a stable amorphous phase and to tune absorption properties and molecular dynamics. Surface relief gratings (SRGs) and complex surface patterns can easily be inscribed via holographic techniques. The modulation heights are determined with an equation adapted from the theory for thin gratings, and the values are confirmed with AFM measurements. Temperature-dependent holographic measurements allow for monitoring of SRG build-up and decay and the stability at elevated temperatures, as well as determination of the glass transition temperature. SRG modulation heights of above 600,nm are achieved. These are the highest values reported for molecular glasses to date. The surface patterns of the molecular glasses are stable enough to be copied in a replica molding process. It is demonstrated that the replica can be used to transfer the surface pattern onto a common thermoplastic polymer. [source]

    Original article: Glass transition temperature of hard chairside reline materials after post-polymerisation treatments

    GERODONTOLOGY, Issue 3 2010
    Vanessa M. Urban
    doi:10.1111/j.1741-2358.2009.00312.x Glass transition temperature of hard chairside reline materials after post-polymerisation treatments Objective:, This study evaluated the effect of post-polymerisation treatments on the glass transition temperature (Tg) of five hard chairside reline materials (Duraliner II-D, Kooliner-K, New Truliner-N, Ufi Gel hard-U and Tokuso Rebase Fast-T). Materials and methods:, Specimens (10 10 1 mm) were made following the manufacturers' instructions and divided into three groups (n = 5). Control group specimens were left untreated. Specimens from the microwave group were irradiated with pre-determined power/time combinations, and specimens from the water-bath group were immersed in hot water at 55C for 10 min. Glass transition (C) was performed by differential scanning calorimetry. Data were analysed using anova, followed by post hoc Tukey's test (, = 0.05). Results:, Both post-polymerisation treatments promoted a significant (p < 0.05) increase in the Tg of reline material K. Materials K, D and N showed the lowest Tg (p < 0.05). No significant difference between T and U specimens was observed. Conclusion:, Post-polymerisation treatments improved the glass transition of material Kooliner, with the effect being more pronounced for microwave irradiation. [source]

    Directed Helical Growth: A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization (Adv. Funct.

    Crystalline helices (PLLA crystallization directed by helical confined microdomains) and crystalline cylinders (phase transformation of helical nano structures dictated by crystallization) are obtained by controlling the crystallization temperature of PLLA with respect to the glass transition temperature of PS in PS-PLLA block copolymers; this process is described by J.-W. Chiang et al. on page 448. A spring-like behavior of the PLLA helical nanostructures embedded in the PS matrix can be driven by crystallization, so as to dictate the transformation of the helices, resulting in crystalline cylinders that might represent a possible avenue for the design of switchable large-strain actuators. [source]

    A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization

    Yeo-Wan Chiang
    Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source]

    Fabrication of Reversibly Crosslinkable, 3-Dimensionally Conformal Polymeric Microstructures,

    Luke A. Connal
    Abstract Multifaceted porous materials were prepared through careful design of star polymer functionality and properties. Functionalized core crosslinked star (CCS) polymers with a low glass transition temperature (Tg) based on poly(methyl acrylate) were prepared having a multitude of hydroxyl groups at the chain ends. Modification of these chain ends with 9-anthracene carbonyl chloride introduces the ability to reversibly photocrosslink these systems after the star polymers were self-assembled by the breath figure technique to create porous, micro-structured films. The properties of the low Tg CCS polymer allow for the formation of porous films on non-planar substrates without cracking and photo-crosslinking allows the creation of stabilized honeycomb films while also permitting a secondary level of patterning on the film, using photo-lithographic techniques. These multifaceted porous polymer films represent a new generation of well-defined, 3D microstructures. [source]