Glass Transition Temperature (glass + transition_temperature)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Glass Transition Temperature

  • high glass transition temperature
  • low glass transition temperature
  • single glass transition temperature


  • Selected Abstracts


    GRINDING SPRAY-DRIED MILK POWDER NEAR the GLASS TRANSITION TEMPERATURE

    JOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2003
    GREGORY R. ZIEGLER
    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

    JOURNAL OF FOOD SCIENCE, Issue 6 2003
    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

    MOLECULAR INFORMATICS, Issue 8-9 2010
    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]


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

    BIOTECHNOLOGY PROGRESS, Issue 2 2000
    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]


    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]


    Dehydration of benzene through fluorine containing aromatic polyamide membrane by pervaporation

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
    P. K. Gutch
    Abstract A series of soluble polyamides were synthesized by direct polycondensation of the 5- tert -butyl isophthalic acid with different diamines. Solution (20%) of the polymers in suitable solvents was used to cast the membranes. The membranes showed selectivity toward the benzene (Bz) in a mixture of Bz/water (H2O). Water affinity of the membrane was found to be lower than that of Bz. The polyamide incorporating hexafluoro isopropylidene moiety was promising for the dehydaration of Bz and breaking of Bz/H2O azeotrope. The polymers exhibited inherent viscosities, ranging from 0.40 to 0.92 dL/g and 10% weight loss in synthetic air up to 474C. Glass transition temperature measured by DSC and DMA reached up to 258C. The membranes were pale yellow in appearance having tensile strength up to 85 MPa, modulus of elasticity up to 2.6 GPa, and elongation at break up to 9.5%, depending upon the exact repeating unit structure. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    The influence of chain-ends on the thermal and rheological properties of some 40/60 PES/PEES copolymers

    POLYMER ENGINEERING & SCIENCE, Issue 8 2009
    Lorenzo Abate
    Four random, differently ended (Cl, NH2, OH, and COO,), polyethersulfone/polyetherethersulfone (PES/PEES) copolymers were studied to investigate the influence of chain ends on thermal and rheological behaviors. The number average molar mass (Mn , 9500 gmol,1) and the PES/PEES ratio (40/60) of all copolymers investigated were checked by 1H NMR spectra. Thermal degradations were carried out in the scanning mode and initial decomposition temperatures (Ti) and activation energy values of degradation (Ea) were obtained. Glass transition temperature (Tg) was determined by differential scanning calorimetry and complex viscosity (,*) by rheological measurements in isothermal heating conditions (T = 270C). All parameters determined were largely affected by copolymer chain ends and decreased according to the same order, OH > NH2 > Cl > COO,. The results were discussed and interpreted. POLYM. ENG. SCI., 2009. 2009 Society of Plastics Engineers [source]


    Synthesis and characterization of novel photosensitive polyimide based on 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2005
    Eun Young Chung
    Abstract A negative type photosensitive polyimide with alicyclic moiety (NPI) was synthesized from 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride and 4,4-diaminobenzophenone by one-step polymerization in m -cresol. Properties of the polyimides were characterized and a photo-crosslinking mechanism was investigated using DEPT 13C-NMR and FT-IR spectroscopy. The negative polyimide showed good photosensitivity on exposure to UV light from a mercury xenon lamp. The polyimide showed remarkable solubility difference after photo- irradiation with an exposure dose of 500,mJ/cm2. The resulting negative pattern of the photo-cured NPI exhibited 10,,m resolution. Glass transition temperature of the photo-crosslinked polyimide was about 307C, which increased by 10C compared to that of the polyimide before UV exposure. Transmittance of NPI after photo-irradiation was about 87% at 500,nm. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Syntheses and properties of cross-linked polymers from functionalized triglycerides

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
    Hui-Ping Zhao
    Abstract A number of functionalized triglycerides were synthesized from glyceryl trioleoate via epoxidation followed by reduction to give glyceryl tris(9-hydroxy)trioleoate (a triol) or hydrolytic ring opening to obtain glyceryl tris(9,10-dihydroxy)trioleoate (a hexaol). A selective monoepoxidation reaction of glyceryl trioleoate was also carried out and the resulting monoepoxide was hydrolyzed to give glyceryl 9,10-dihydroxytrioleoate (a diol). Glyceryl tris(9-hydroxy)trioleoate was brominated followed by displacement with sodium azide and reduction to give glyceryl tris(9-amino)trioleoate (a triamine) and glyceryl tris[9-(N -isopropylamino)]trioleoate. These functionalized triglycerides were crosslinked with 1,4-phenylene diisocyanate. The crosslinked polymers exhibit thermoset characteristics. Thermal analysis results suggest that the polymers are in amorphous states, and their thermal stability was significantly affected by crosslink degree. The crosslinked polymer derived from the diol retained 56% of its weight at 408C, whereas the polymers derived from the aforementioned hexaol with higher crosslink degree retained only 36% of the original weight. Glass transition temperatures of these polymers range from ,1.0C to 10.2C. The thermal stable polymer, 12, derived from the aforementioned diol exhibits a linear viscoelastic character and can be used as thermoplastics. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Synthesis and Properties of Novel Biodegradable/Biocompatible Poly[propylene- co -(ethylene succinate)] Random Copolyesters

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2009
    George Z. Papageorgiou
    Abstract Random biocompatible/biodegradable poly[propylene- co -(ethylene succinate)]s were prepared. Mechanical properties and crystallization rates decreased with propylene succinate content. Glass transition temperatures (Tg) varied between those for the homopolymers. DSC and TMDSC findings showed that multiple melting behaviour of PPESu samples is related to melting,recrystallization,remelting. WAXD observations, eutectic behaviour, and thermodynamic analysis of the equilibrium melting point depression indicated isodimorphic cocrystallization. The copolymers showed enzymatic hydrolysis rates between those of the homopolymers and cytotoxicity/biocompatibility similar to PLA. [source]


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

    ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
    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.

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
    Mater.
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
    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]


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

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
    Mater.
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2009
    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.

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
    Mater.
    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

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
    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,

    ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008
    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]


    Nanopatterning via Pressure-Induced Instabilities in Thin Polymer Films

    ADVANCED MATERIALS, Issue 20 2009
    Ximin He
    The residual stresses in spin-coated films can be exploited to produce highly controlled nanoscale patterns via pressure-induced local rupturing and dewetting of thin films. Residue-free holes as small as 28,nm in diameter formed over large areas by pressing sharp stamps into polymer films at temperatures well below the glass transition temperature. [source]


    The glass transition approach to determination of drying protocols for colour stability in dehydrated pear slices

    INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2005
    Hang-Ing Ling
    Summary Colour stability in dehydrated fruit is often attained by use of sulphite treatment to inhibit browning during processing and storage. However, colour stability may be able to be conferred on products by ensuring that the molecular mobility is restricted in dried fruit by drying to sufficiently low moisture to raise the glass transition temperature (under mild conditions). Pear slices were dehydrated at a low temperature (40 C) to a low final moisture content (below 5%) after it was shown that, for a moisture content of 22% (which is the moisture content of commercial dehydrated pears) pretreatment with sulphite would be necessary to stabilise the colour. The use of longer drying regimes resulted in a moisture content where the food matrix would be closer to the glassy state and conferred colour stability on the dehydrated product compared to a product containing more moisture. For these low-moisture products, pretreatment with sulphite would not be necessary to preserve colour stability. [source]


    Glass transition behaviour of fructose

    INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2004
    Vinh Truong
    Summary The glass transition temperature and the second transition (the endothermic change between the glass transition and melting temperatures) of fructose were studied. The thermal history strongly affected both transitions of fructose. Storage for 10 days at 22 C increased the dynamic glass transition temperature from 16 to 25 C and decreased the second transition of fructose from 110 to 98 C in the first differential scanning calorimetric (DSC) scan. The amplitude of the second transition increased slightly with storage time and reached 260% of the first transition for vacuum oven dried samples. The effect of thermal history on the glass transition temperature of fructose can be removed by scanning the sample in a DSC to 130 C. The effects of water content, glucose and sucrose on the two transitions were also investigated. [source]


    Stability and optimum polymerized condition of polysiloxane,polyacrylate core/shell polymer

    ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2010
    Chengyue Ge
    Abstract The stable emulsion of core/shell latex with little coagulum (no more than 0.5% in quality relative to total monomers) has been prepared at low temperature with potassium-persulfate (KPS), sodium formaldehyde sulfoxylate (SFS), and 2,2,-azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride (VA-044) as composite initiators by staged emulsion polymerization. Reactive surfactants were used to significantly improve the stability of emulsion. More interestingly, reverse core/shell structure was investigated when the organic silicon was added in the late period of polymerization. The effects of the emulsifier, initiators, dosage of organic silicon, and monomer's content on conversion and graft efficiency were studied in detail. Moreover, the stability of emulsion was investigated by the values of zeta potential (,) and coagulum. More importantly, the thermal performance and stability of PSI/PA composite latex was studied by the glass transition temperature (Tg). The results showed that there are appropriate values for all factors to obtain high conversion, graft efficiency, and excellent stability: The dosage of surfactant was about 0.44 g, the dosage of VA-044 was about 1000 mg kg,1, the dosage of organic silicon was about 15%, and the monomer's content was about 30%. In addition, the introduction of organic silicon improved the Tg. 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:161,172, 2010; View this article online at wileyonlinelibrary. DOI 10.1002/adv.20182 [source]


    Synthesis and characterization of hybrid nanocomposites comprising poly(vinyl alcohol) and colloidal silica

    ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2008
    Mousumi De Sarkar
    Abstract Organic,inorganic hybrid composite films were developed using poly(vinyl alcohol) (PVA) and an aqueous dispersion of colloidal silica of initial particle size of 15,30 nm. The hybrid films, prepared with varied proportion of colloidal silica (10,90 phr), were found to be transparent, indicating the nanolevel dispersion of the inorganic component over the polymer. Morphological studies further revealed no significant agglomeration of the silica domains embedded into the polymer matrix. A depression in glass transition temperature of PVA is observed with increasing proportion of silica. The degree of crystallinity also showed a decreasing trend with increasing amount of silica. However, the composite films demonstrated superior mechanical performances, higher resistances to dissolution in boiling water, and lower permeability compared with virgin PVA, owing to the better interaction between PVA and silica as well as the reinforcing action of nanosilica particles in the polymer matrix. 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:152,162, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20129 [source]


    Effects of storage aging on the cure kinetics of bismaleimide prepregs

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2005
    M. Frigione
    The effects of room temperature aging on the subsequent polymerization kinetics of a bismaleimide (BMI) matrix prepreg, for high performance composites, have been characterized by different time and storage conditions. The study has focused on the stability of BMI matrix carbon fiber prepregs, when exposed to controlled environmental conditions before being used in composite manufacturing. The effects of aging on glass transition temperature, reactivity, and processability have been investigated by calorimetry through dynamic, isothermal, and cure-simulating tests. A theoretical kinetic model for epoxy matrix prepregs, developed in previous studies, has been applied to the polymerization of both aged and unaged BMI matrix. The model is able to satisfactorily describe the effect of processing variables such as temperature and degree of reaction during the curing of the composite under different conditions (curing temperature and heating rate). The effects of diffusion-controlled phenomena on the reaction kinetics, associated with changes in glass transition temperature as a function of the degree of polymerization and cross-linking, have been taken into account in the formulation of an nth-order kinetic model. 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 253,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20048 [source]


    Optical and thermo electrical properties of ZnO nano particle filled polystyrene

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
    Mulayam S. Gaur
    Abstract The study of optical and thermally stimulated electrical properties such as optical band gap, refractive index, X-ray spectra, SEM spectra, thermally stimulated discharge current (TSDC), differential scanning calorimetry (DSC) have been undertaken in ZnO nanoparicle filled polystyrene nanocomposite thin film of 30 ,m thickness. The appearance of single TSDC peak at temperature 408 5 K in nanocomposite samples shows the charge carriers injected from deeper trapping levels. It is due to the modification of surface and bulk properties of polystyrene by filling of ZnO nanoparticles. In other hand, the strong interaction of nanoparticles with polymer matrix is the expected reason of improvement of crystallite size, optical energy band gap, refractive index, TSDC, glass transition temperature, and charge storage. It is confirmed from SEM images that the modifications of these properties are caused by creation of clusters in amorphous,crystalline boundaries of pristine polystyrene. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]