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1.
The phase transition behavior and isothermal micro-phase separation kinetics of polyester-based thermoplastic elastomer were studied using the synchrotron X-ray scattering (SAXS) method. The structural changes occurring during heating period were investigated by determining the changes of the one-dimensional correlation function, interfacial thickness and Porod constant. Based on the abrupt increases of the domain spacing and interfacial thickness, a major structural change occurring well below the melting transition temperature is suggested. Those changes are explained in terms of melting of the thermodynamically unstable hard domains or/and the interdiffusion of the hard and soft segments in the interfacial regions. SAXS profile changes during the micro-phase separation process were also clearly observed at various temperatures and the separation rate was found to be sensitively affected by the temperature. The peak position of maximum scattering intensity stayed constant during the entire course of the phase separation process. The scattering data during the isothermal phase separation process was interpreted with the Cahn-Hilliard diffusion equation. The experimental data obtained during the early stage of the phase separation seems to satisfy the Cahn-Hilliard spinodal mechanism. The transition temperature obtained from the extrapolation of the diffusion coefficient to zero value turned out to be about 147±2°C, which is close to the order-disorder transition temperature obtained from the Porod analysis. The transition temperature was also estimated from the invariant growth rate. By extrapolating the invariant growth rate to zero, a transition temperature of about 145±2°C was obtained.  相似文献   

2.
In situ melting and crystallization of short-linear α-1,4-glucan (short-chain amylose, or SCA) from debranched waxy starches were investigated by synchrotron wide-angle X-ray diffraction. Amorphous SCA was prepared by dissolving completely debranched waxy starches in alkaline solution and neutralized by hydrochloric acid. When hydrated with 50% water at 25 °C, all amorphous SCA crystallized immediately and gave a B-type structure. The SCA from debranched waxy potato starch had a longer average chain length and a higher melting temperature but relatively lower crystallinity upon hydration; it was not completely melted at 100 °C and retained its original B-type structure during rapid cooling. In contrast, the SCA from debranched waxy wheat and waxy maize starches had a large portion of low molecular weight fractions, a higher crystallinity upon hydration, and a lower melting temperature. These differences suggest that amylopectin short chains crystallized more readily but their crystals were weaker than those of long chains. After the B-type crystals of hydrated SCA from waxy wheat and waxy maize starches melted, they reformed into the A-type polymorph upon rapid cooling. The thermal properties showed that the A-type polymorph of debranched waxy wheat and waxy maize starches had a higher melting temperature than their B-type structure.  相似文献   

3.
This study investigated the main origin of the thermochromism of a novel compound, 1,3-bis(hydroxyethylamino)-4,6-dinitrobenzene (BDB). In order to unravel the relative dependence of reversible color change between yellow and orange on proton transfer reaction and crystal-crystal phase transformation, kinetic experiments were executed. The recovery rates of thermochromic transition, proton transfer reaction, and crystal-crystal phase transformation were calculated from the data measured through UV-vis spectrophotometry, IR spectrometry, and X-ray diffractometry with a lapse of time at fixedtemperatures (30, 40, and 50 °C) after cooling from heated temperature (150 °C). The kinetic experiments revealed that the recovery takes place more quickly at lower temperature. At each fixed-temperature, the recovery rate is in the order of the crystal-crystal phase transformation > the proton transfer reaction > the thermochromic transition. It is concluded that the proton transfer reaction is the main origin for thermochromism of BDB in solid state and the crystal-crystal phase transformation is a collateral one.  相似文献   

4.
We reported the controlled surface morphologies and the cell culture of polyelectrolyte multilayer coated nylon 6 fibrous mats with different number of layers. Polyelectrolyte multilayer coated nylon 6 fibers were successfully prepared by an alternative deposition of alginic acid sodium salt and chitosan via a Layer-by-Layer (LbL) electrostatic self-assembly. The surface morphology, stiffness, and hydrophilicity of polyelectrolyte multilayer coated nylon 6 fibrous mats could be finely tuned by regulating the number of polyelectrolyte nanocoating. It was observed that the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth, indicating a dense and harder nanocoating of polyelectrolytes onto nylon 6 fibers. Compared to pure nylon 6 fibrous mat (tensile strength ～10.6±1 MPa), the tensile strength of polyelectrolyte coated nylon 6 fibrous mats was largely increased to 35.2±2 MPa for 5 bilayers coated fiber mats. In addition, it was found that at an initial stage after 1 day of cell culturing, the electrospun nylon 6 fibrous mats coated with 5 bilayer of alginic acid and chitosan show the highest cell affinity (good adhesion), while the electrospun nylon 6 fibrous mats coated with 10 bilayer show the lowest cell affinity. After cell seeding for 3 days, it was observed that rate of proliferation is enhanced by increasing the number of bilayer up to 3 bilayers (good proliferation), and then drastically decreased with further increasing the number of bilayer.  相似文献   

5.
The subzero properties of wheat doughs were measured by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA) over the temperature range −90 to +40 °C and by1H-nuclear magnetic resonance (NMR) T2relaxation over the range −45 to 0 °C. The experiments revealed two transitions in the dough: one independent of frequency at −10 °C (attributed to ice melting) and one dependent on frequency at −30 °C (attributed to a glass transition). The glass transition temperatures measured by DMTA moved to higher temperatures during frozen storage when the optimal water content of dough was used. A reduction in the water content eliminated this phenomenon. A similar effect of water reduction was observed by NMR studies, in which amplitude ratios and decay times were used to calculate the phase transitions. However, the glass transition recorded by NMR was independent of frozen storage with optimal water content. The changes of water state in frozen doughs were studied by ultracentrifugation (the amount of liquid phase) and NMR (freezable water based on liquid amplitude ratios). Frozen storage increased the liquid phase in dough with optimal water content. Thus, ice crystals are growing during frozen storage resulting in the concentration of polymers and a higher glass transition observed by DMTA. The increase of liquid phase during storage was substantially lower when the water content of dough was decreased. Ice crystals» growth can be minimised by reducing water content. The experiments were carried out with four different flours. The measurement of glass transition temperature by DMTA, DETA or NMR did not reveal great differences in doughs made from different flours. The amount of liquid phase was strongly flour dependent.  相似文献   

6.
Thermoplastic polyurethanes were prepared using 90 % acetylated softwood kraft lignin, polyethylene glycol and 4,4-methylene diphenyl diisocyanate. Due to the glass transitions of the compatible soft and hard segment mixtures, the polyurethanes exhibited the first glass transitions at ?40 to 10 °C, and the transition temperatures increased with increasing hard segment content. Due to the glass transitions of the microphase separated hard domains, the second glass transitions occurred at 150 °C. The viscous responses during the second transitions decreased as the separated hard domains-induced chemical and physical crosslinks increased. The Young’s modulus and tensile strength increased with increasing hard segment content, whereas the breaking strain decreased. The phase morphology changed from an isolated hard domain structure to an interconnected one as the physical crosslinks increased, which caused drastic changes in the increasing or decreasing tendency of the tensile strength or breaking strain. Because of the phase morphology, the polyurethanes exhibited viscoplasticity or viscoelasticity.  相似文献   

7.
The low molecular weight glutenin subunits (LMW-GS) are major components of the glutenin polymers which determine the elastomeric properties of wheat (Triticum aestivum L.) gluten and dough. They comprise a complex mixture of components and have proved to be difficult to purify for detailed characterisation. The mature LMW subunit proteins comprise two structural domains, with one domain consisting of repeated sequences based on short peptide motifs. DNA sequences encoding this domain and a whole subunit were expressed in Escherichia coli and the recombinant proteins purified. Detailed comparisons by spectroscopy (CD, FT-IR) and dynamic light scattering indicated that the repetitive and non-repetitive domains of the proteins formed different structures with the former having an extended conformation with an equilibrium between poly-L-proline II-like structure and type II' β-turns, and the latter a more compact globular structure rich in α-helix. Although the structures of these two domains appear to form independently, dynamic light scattering of the whole subunit dissolved in trifluoroethanol (TFE) suggested that they interact, leading to a more compact conformation. These observations may have relevance to the role of the LMW-GS in gluten structure and functionality.  相似文献   

8.
The effects of sucrose, NaCl, and ascorbic acid on dielectric relaxations of frozen wheat doughs were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency using a 10 g bowl Micro-Mixer. DEA measurements were made at a heating rate of 1 °C/min from −150 to 10 °C. Before the measurements, samples were equilibrated at −30 °C for 15 min to allow maximum ice formation, and then cooled at 1 °C/min to −150 °C. The frequencies used were 0·1, 0·5, 1, 5, 10, 20, 50, 100 and 1000 Hz. The dissipation factor (tan δ) of DEA showed an α-relaxation (glass transition), two low temperature relaxations (β and γ) and ice dissolution. Added NaCl had a markedly depressed the glass transition temperature (Tg′) and onset of melting of ice temperature (Tm′), probably because of the higher conductivity of the frozen material, and the decreased transition temperatures of the unfrozen solute phase. At the higher frequencies, the α-relaxation coincided with melting of ice, and all relaxation temperatures (α, β and γ) increased with increasing frequencies.  相似文献   

9.
Samples of semen from 12 pigs, three from Yorkshire, Landrace, Duroc and Mexican Hairless each where obtained to study cryopreservation methods. Three stages of boar semen cryopreservation were evaluated: none (fresh stage), cooling at 5 degrees C and freezing at -196 degrees C then thawing to 56 degrees C for 12 sec. Perinuclear theca damage and domain alterations were selected as indices of seminal quality, as measured by electronic and fluorescence microcopy, respectively according to two lineal models considering by separately the effect of semen preservation and breed. Integrity and absence of perinuclear theca significantly (p < 0.001) decreased and increased, respectively according to a decrease in temperature of cryopreservation, from 87.4 to 58.8% and from 0.8 to 26.2%, respectively. This same significant (p < 0.001) effect was found for acrosomal and post-acrosomal membrane distribution of domains, from 92.1 to 76.8% and from 3.1 to 13.1% in this same order. Slight but highly significant (p < 0.001) differences were observed when theca integrity was evaluated as affected by breed, with highest and lowest values for Yorkshire and Pel6n Mexicano pigs, respectively. No breed effect was encountered for presence of acrosomal domains. A strong interdependence was found between perinuclear theca damage and domain distribution. In this connection, a highly significant (p < 0.001) positive, interdependence was observed between the theca damage and acrosomal domain (r = 0.87), while this same relationship was although highly significant (p < 0.001), negative in nature for equatorial and post-acrosonal domains (r = -0.77 and -0.85, respectively). This experiment confirmed that cryopreservation methods may severely affect semen quality of pigs and that genotype may further influence these same indices. More research is needed for improving methods of preservation of pig semen quality, from the point of view of perinuclear theca and domain characteristics of spermatozoa.  相似文献   

10.
We have prepared the blends of poly(pentamethylene 2,6-naphthalate) (PPN) with poly(heptamethylene 2,6-naphthalate) (PHepN) by solution blending method and investigated their glass transition behaviour, melting behaviour, and tensile properties. It was observed that the blends of PPN/PHepN(9/1) and PPN/PHepN(1/9) have a single glass transition, reflecting a homogeneous phase, whereas those of PPN/PHepN(7/3), PPN/PHepN(5/5), and PPN/PHepN(3/7) exhibit double glass transitions, representing the existence of two phases. The PPN homopolymer annealed below 90 °C shows triple melting peaks (T m1, T m2, and T m3). It was proved that T m1 is attributed to melting of thin lamellar formed during secondary crystallization process, T m2 to melting of thick lamellar created during primary crystallization, and T m3 to melting of crystals recrystallized after melting the primary crystals at T m2. For the annealed PHepN homopolymer, double melting endotherms (T m1 and T m2) were observed, caused by dual lamellar population with different thickness, i.e. T m1 corresponding to the melting of secondary crystal and T m2 to primary one. The Hoffman-Weeks plots, applied to the melting of primary crystals (T m2s), indicate that the equilibrium melting temperatures of PPN homopolymer, PPN/PHepN(9/1), and PPN/PHepN(7/3) blends are same to be 147 °C, and those of PHepN homopolymer, PPN/PHepN(1/9), and PPN/PHepN(3/7) blends to be 145 °C. Both the glass transition and melting behaviours demonstrate that the PPN/PHepN blend system is partially miscible. In addition, both the modulus and strength for the blends almost follow additive rule against blend composition, indicating that the PPN/PHepN blends are mechanically compatible over all blend compositions.  相似文献   

11.
Poly(ethylene terephthalate) (PET) copolymers containing fluorenylidene bis(2-phenoxyethanol) (FBPE) were prepared. The glass transition temperature of copolymers increased continuously with the composition of FBPE. The glass transition temperature of PET/FBPE copolymer at loading of 15 mol% FBPE was 107 °C, which was 35 °C higher than that of PET. The melting temperature of PET/FBPE copolymers was decreased with the composition of FBPE, and it disappeared above 6 mol% of FBPE. The heat deflection temperature of copolymers increased from 60.7 °C for PET to 89.9 °C for the copolymer containing 15 mol% of FBPE. The values of optical transmittance of copolymers were 89-90 % at 550 nm, and no significant change was observed with the FBPE composition. The impact strength value of copolymer at loading of 10 mol% FBPE was 26 J/m, which was 20 J/m higher than that of PET.  相似文献   

12.
斑茅ACO基因(aco)的克隆及其在水分胁迫下的表达   总被引：2，自引：0，他引：2  
利用RT-PCR技术,首次克隆了斑茅1-氨基环丙烷-1-羧酸氧化酶基因序列.该片段长度为1123bp的片段,包括1个编码322个氨基酸的完整开放读码框,包括具有与异青霉素合成酶功能区类似的氧化功能PcbC区,和1个Fe2 和CO2活性中心。应用实时荧光PCR技术分析了1-氨基环丙烷-1-羧酸氧化酶基因在聚乙二醇胁迫下4个时段的表达。结果表明,聚乙二醇胁迫2h时,该基因在叶片明显上调表达,4h后的表达趋向平缓。本研究为1-氨基环丙烷-1-羧酸氧化酶基因进一步用于基因工程研究奠定基础,同时也初步揭示1-氨基环丙烷-1-羧酸氧化酶基因的表达与水分胁迫相互关系,为探讨乙烯对水分胁迫响应的分子机制提供了初步依据。  相似文献   

13.
The dynamic rheological behaviours of mixtures of glutenin fractions extracted from wheat cultivar Hereward were investigated as a function of the relative concentration of high to low molecular weight glutenin concatenations. Time-temperature superposition could be applied to both the mixtures and to the total gluten, as long as heat-treated samples were distinguished from unheated samples. The ratio of high to low molecular weight concatenations was found to be very important for the rheological behaviour of the network. High molecular weight fractions promoted the network properties of the mixture, as could be seen from the presence of a plateau in the rheological spectrum. Low molecular weight fractions gave rise to a plasticizing effect as indicated by their narrowing effect on the width of the plateau region in the rheological spectrum. Upon heating, the modulus increased over the full range of frequencies, as for single fractions. This increase indicated that a thermal association occurred in the concatenations at temperatures around 40 °C. As a result of heating, the transition zone became apparent in the spectrum at high frequencies. The slopes of the loss modulus G” in the transition zone were found to be higher for mixtures rich in low molecular weight concatenations. The effect of the relative abundance of each fraction on the rheological characteristics of the mixtures was summarized in a number of simple rheological blending rules for the small-deformation rheological properties of glutenin.  相似文献   

14.
The formation and distribution of ice upon the freezing of fresh breadcrumb were investigated using differential scanning calorimetry. Three types of wheat bread containing different amounts of sugar and dietary fiber were measured. Various frozen states were produced through freezing with different cooling rates (0.5, 1, 2, 5, 10, 20 and 30 °C/min) to −30 °C; they were then analyzed and compared by thawing with the same heating rate (10 °C/min) to 20 °C. All DSC heating traces exhibited dual endotherms in the temperature range for the melting of ice: The major transition was attributed to the ice formed in the large crumb pores (gas cells) and the minor event, which preceded the major endotherm, was assigned primarily to the ice formed in the nanometer-sized pores within the gluten-starch matrix. The size of ice crystals in the two classes of pores was estimated using the modified Gibbs–Thompson relation. The distributions of ice in these pores depended on the bread compositions. It is concluded that the complex crumb porosity plays an essential role in shaping the activities of water and ice in the breadcrumb.  相似文献   

15.
The copolymers of vinylidene fluoride and trifluoroethylene (P(VDF/TrFE)) with VDF content of 50–80 mole % can be applied to the field of nonvolatile ferroelectric polymeric random access memory (FePoRAM) devices, since they exhibit stable ferroelectricβ-phase at room temperature with spontaneous polarization of the C-F dipoles towards an external electric field greater than the coercive field. Many researchers have already reported the molecular structures and dynamics of the ferroelectric (F) crystalline phase and the unique change in chain conformation between polarF phase and non-polar paraelectric (P) phase near their Curie transition temperature (T c) which is dependent on factors such as VDF content and annealing treatment conditions. The effect of external electric field strength on theF⇔P crystalline phase transition in P(VDF/TrFE)(72/28) random copolymer samples of nanometer thickness was investigated. Capacitance of 250 nm thick sample measured as a function of heating-cooling under varying external electric field strength exhibited increasingT c’s during heating (T c ↑ ) and cooling (T c ↓ ) under an applied electric field of more than 0.03 MV/cm. Applying cyclic bias electric field (+1 to −1 MV/cm) for samples kept isothermally at just above theirT c(T c ↓ ) during cooling, we were able to observe the field-inducedP→F phase transition. With increasing cycles of the applied electric field for sample maintained just above (T c ↓ ), the bistableC-E hysteresis was observed and the phase change fromP→F is irreversible even after the electric field is removed. However, for samples kept well above (T c ↓ ) and nearT m (100 °C and 120°C respectively) during cooling, theF-phase initially formed through the field-induced phase transition is reversibly transformed to theP-phase when the applied electric field is removed. Drastic changes were observed in both coercive field (E c) and remanent polarization (P r) values during heating and cooling near theT c range due to theF⇔P phase transition and the results are reported in detail here.  相似文献   

16.
A comparison was made of the effect of season and maturity on the in situ ruminal breakdown and intestinal protein digestion in dairy cows between intensively N-fertilized grass (whole sward) and moderately N-fertilized ryegrass and clover from a mixed sward. From May to September 1990, eight consecutive cuts were made, representing alternate harvests of late and early swards. Limited effects of fertilizer-N on chemical and ruminal degradation characteristics and intestinal digestion of grasses were observed. Clover had higher ash, crude protein (CP) and lignin and lower hemicellulose, cellulose and sugar contents than grass. Moreover, soluble fractions of organic matter (OM) and CP were higher, and rumen-undegradable OM and CP fractions were lower. Soluble fractions of grasses and clover decreased and undegradable fractions increased during the season. More mature swards showed increased undegradable fractions. Degradation rates of OM and CP in clover were, respectively, higher than or similar to those of grass. Seasonal effects on degradation rates differed between grass and clover. Effectively rumendegradable (g kg−1 DM) carbohydrates and CP, escaped protein and intestinal digestion of escaped protein were higher in clover than in grasses. Inclusion of clover in swards may result in higher post-rumen protein supply. Supplementation of clover-based diets is suggested to compensate for an increased loss of N in the rumen.  相似文献   

17.
Polyurethane-based side-chain cholesteric liquid crystalline polymers (ChLCPs) with variable clearing temperatures were synthesized in a two-step reaction. The chemical structures of ChLCPs were confirmed by FT-IR and 1H-NMR spectroscopy. The mesogenic properties and phase transition behavior were investigated by means of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction measurements. The DSC studies show that the melting temperature and isotropic transition temperature of the ChLCPs increased with the weight percentage of cholesterol in the polymer. POM shows that the ChLCPs had a distinct spherulite structure that melted at about 140 °C, and these results are consistent with those of the DSC studies. The thermogravimetric studies show that the ChLCPs were stable up to 200 °C, though there was a reduction in the thermal stability as the weight proportion of cholesterol and glycerol in the polymer increased.  相似文献   

18.
The present work emphasizes the effect of alkali (NaOH) solution on macromolecular parameters of sisal fiber. The macromolecular parameters of alkali treated sisal fiber were computed along with air-dried sisal fiber by treating fiber as a non-ideal two-phase system characterized by continuous variation of electron density at the phase boundary. Small angle Xray scattering (SAXS) technique was employed to evaluate the macromolecular parameters, using correlation functions, applying the theories of Vonk, Ruland and Misra et al. The finite value of width of transition layer suggests to treat the fiber to be a non-ideal two-phased system. The evaluated macromolecular parameters are: transversal periodicity, specific inner surface, volume fractions of matter and void phases, transversal lengths in both phases, range of inhomogeneity, volume fraction of transition layer and length of coherence.  相似文献   

19.
Dynamic oscillatory rheology of two wheat protein isolate (Prolite 100 and Prolite 200) doughs (≈48% moisture content, wet basis) were studied over a frequency range of 0.1–10 Hz during temperature sweep from 20 to 90 °C at a heating rate of 2 °C/min. Both doughs behaved similarly during heating; showed a threshold value and increased sharply, thereafter. Prolite 200 dough had a higher elastic modulus (G′) and lower phase angle (δ) whereas Prolite 100 showed a distinct gel point at 52.2 °C followed by significant increase up to 90 °C. Rheological data of doughs after isothermal heating at 90 °C for 15 min followed by cooling to 20 °C resulted in strong mechanical strength. However, Prolite 100 dough showed more viscoelastic characteristics with significant transformation from liquid-like to solid-like behavior after heating than Prolite 200. Thermal analysis of isolates indicated distinct endothermic peaks in wider temperature range (50–130 °C) at various moisture levels. Lower temperatures could be associated with denaturation of various fractions of proteins whereas higher temperature linked to glass transition temperature of isolates. SDS–PAGE did not show any clear distinction among protein subunits between two isolates. Dielectric measurements of isolates at frequencies from 500 to 3000 MHz and temperature range between 30 and 80 °C indicated Prolite 200 had higher dielectric constant (ε′) and loss factor (ε″) than Prolite 100. Isolates showed significant changes in dielectric properties above 50 °C indicating protein denaturation and supported rheological and calorimetric data.  相似文献   

20.
In this article, the thermo-mechanical characterization of poly(butylene terephthalate)/poly(tetramethylene oxide) (PBT/PTMO) is studied by thermal analysis, dynamic mechanical analysis, and uniaxial tensile tests. The results of poly(ether esters) show that the melting temperature is equal to T m =193 °C, which is 31 °C, lower than that of the melting temperature of poly(butylene terephthalate) (PBT). Its glass transition temperature, T g is equal to -61 °C, determined by DMA. The melting and cooling temperatures (T m , T c ) after aging at T0+48 h and T0+week are virtually unchanged. Moreover, the results of the tensile tests show that the effect of the low deformation rate reduces the friction resulting from the sliding mechanisms between the amorphous and crystalline parts.  相似文献   

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