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1.
Isocyanate-treated graphite oxides(i GOs) were well-dispersed into the polystyrene(PS) thin films and formed a novel network structure. With control in fabrication, an i GOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by i GOs. This work demonstrated that the i GOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures(Tg). Via annealing the 50–120 nm thick composite and associated neat PS films at temperatures ranging from 35 °C to 70 °C above Tg, surface morphology evolution of the films was monitored by atomic force microscopy(AFM). The i GOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.  相似文献   

2.
Based on free volume, an equation has been derived enabling calculation of glass transition temperature (Tg) of plasticized polymers, knowing the plasticizer content, the thermal expansion coefficients and values of Tg of the polymer and plasticizer. Determined and calculated Tg are in satisfactory agreement up to the plasticizer concentration which dissolves the polymer.  相似文献   

3.
A series of aromatic diamines were polymerized with two aromatic dianhydrides, pyromellitic dianhydride and 3,3,4,4-biphenyltetracarboxylic dianhydride, and the resulting poly(amic acid)s were thermally cyclodehydrated to aromatic polyimides. The polyimides were characterized by determining the glass transition temperatures (Tg), thermal stability, coefficients of thermal expansion, and wide-angle X-ray diffraction. Structure-property relationships are elucidated and discussed in terms of the structural fragments in the polymer chain. The PMDA-based polyimides generally revealed a higher Tg than the corresponding BPDA-based analogues. Generally, the dilution of the imide content by the insertion of oxyphenylene segments into the diamines significantly reduced the Tg. The introduction of m- or o-phenylene units into the polymer backbone usually resulted in a decrease in Tg. The attachment of pendant groups on the backbone may lead to decreased or increased Tgs, depending on the structure of pendant groups. As evidenced by X-ray diffraction, the polyimides derived from rigid, rod-like diamines or the diamines having two or three p-oxyphenylene showed a higher crystalline tendency. The presence of aliphatic pendant groups slightly reduced the thermal stability of the polyimides. The other structural changes did not show a dramatic influence on the thermal stability. Some polyimides obtained from p- or m-phenylenediamine had low thermal expansion coefficients below 2×10−5°C−1.  相似文献   

4.
Compatible polymer blends have been found to have widespread commercial applications. The simplest criterion for judging polymer—polymer miscibility in the solid state is the glass transition temperature (Tg), which can vary widely according to blend composition for a compatible system.Recently, an equation which predicts the Tg of intimate mixtures of compatible polymers has been derived, based on classical thermodynamics. Only a knowledge of the Tg and heat capacity increment (ΔCp) of each pure component is required to predict the Tg at any composition.In this paper, the validity of this entropy-based relationship is investigated for a variety of commercial compatible polymer blends, including some based on poly(vinyl chloride), polystyrene, and poly(2,6-dimethyl-,4-phenylene oxide). The Tg and ΔCp of each pure component are measured with a Perkin-Elmer DSC-2 differential scanning calorimeter, are predicted glass transition temperatures are compared with those observed experimentally.  相似文献   

5.
Bioactive glasses prepared in SiO2–CaO–Na2O and P2O5 system are used as biomaterials in orthopaedic and maxillofacial surgery. Zn presents high physiological interest. It enhances physiological effects of implanted biomaterials. In this work, the thermal characteristics (T g, T c and T f) of pure bioactive glass elaborated with different amounts of CaO, Na2O in pure glass and with different amounts of introduced Zn in glass (ranging from 0.1 to 10 in mass%), were studied. The excess entropy was calculated for different compounds. Glasses were prepared by the melting process. The thermal behaviour of obtained bioactive glasses was determined using differential thermal analysis. Therefore, the glass transition (T g), the crystallization (T c) and the melting temperatures (T f) were revealed. Moreover, according to Dietzel formula, the thermal stability (TS) of the studied bioactive glasses has been calculated. The first results concerning the impact of different oxides, revealed a decrease of the TS, T g, T c and T f when the SiO2/CaO increases and revealed an increase of these thermal characteristics when the SiO2/Na2O and CaO/Na2O ratios increase. Introducing Zn into the bioactive glasses induces a decrease of T f and an increase of TS. Contrary to crystals, prepared glasses have entropy different to zero at T = 0 K and vary versus T f. The excess entropy of pure glasses and Zn-doped glasses were calculated. The significant variations were registered.  相似文献   

6.
This work presents new results concerning characterization of polymethyl(α-n-pentyl)acrylate polymer by means of thermal analysis. In differential scanning calorimetry investigations, the measured values of T g, T f and ΔC p, i.e. the glass transition temperature, the fictive temperature and the heat capacity step at T g, show that the polymer can be considered as fragile. Thermogravimetric analysis revealed two mass losses, the first, at low temperature, being associated with the evaporation of water molecules, and the second, at high temperature, corresponding degradation of the polymer. This degradation is a two-step phenomenon. Finally, study of the β and the α transitions by elementary and complex TSDC led to the following values: T β=?40°C, T α=36°C, T c=47°C, τc=2.5 s and ΔH=85 to 165 kJ mol?1.  相似文献   

7.
A series of new semi-ladder poly[bis(benzimidazobenzisoquinolinones)], obtained by the polycondensation of dinaphthalene dianhydrides and aromatic tetraamines was investigated by TG, DSC and DMA methods. The influence of polymer structure on the thermal behaviour of the poly[bis(benzimidazobenzisoquinolinones)] was examined. The polymers were found to be thermally stable with Td > 723 K in air and Tg ranging from 585 to 701 K. A good agreement was obtained in Tg values measured by DSC and DMA methods. It was found that some cross-linking processes occurred at temperatures above Tg. Some of the isothermal ageing curves were used to find the activation energies of isothermal cross-linking and decomposition.  相似文献   

8.
《Mendeleev Communications》2023,33(2):259-260
Quasi-liquid composites based on poly(ethylene terephthalate) (PET) films with 9 wt% solution of the C60 (70%) and C70 (∼30%) fullerenes mixture in dichlorobenzene (DCB) have been obtained. It has been shown that PET swelling in the fullerene solution in DCB is accompanied by penetration of fullerene into the polymer structure, and PET films are deformed by the mechanism of intercrystallite crazing. As has been revealed by UV spectroscopy, fullerene incorporated into composite remains monomeric as in solution.  相似文献   

9.
The mechanical characteristics and thermal properties of composite films based on the thermally stable aromatic polyimide (PI) (PMDA‐ODA) and carbon nanocones/discs (CNC) were studied. The introduction of CNC to PMDA‐ODA leads to the substantial increase of film stiffness. The Young's modulus values of the composite films are somewhat higher than those of the previously characterized composite films of this PI filled with nanoclay, carbon nanofibers, and asbestos‐like hydrosilicate nanotubes. The introduction of CNC into PMDA‐ODA (concentrations of CNC were up to 15 vol%) does not cause any marked aggregation of nanoparticles. The presence of CNC in the PI matrix does not affect the glass transition temperature of the polymer but hinders chain mobility at temperatures above Tg. This behavior makes it possible to increase the working temperature range of the composite films containing more than 5 vol% of CNCs, up to the temperature of thermal decomposition. The introduction of CNC into PMDA‐ODA leads to dramatic (~12 orders of magnitude) increase of active electrical conductivity of the material. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Thin films containing photochromatic spiropyran (SP) was prepared from polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), poly(n-butyl methacrylate) (PnBMA), and styrene-butadiene-styrene copolymer (SBS). The thin films were illuminated with the ultraviolet light (365 nm) under various temperatures. The photochromic response was monitored with a multichannel photodetector. The results show that the photocoloring rate of SP was faster in PMMA, while the thermal decoloring rate was faster in SBS. In addition, the decoloring rate was higher in a polymer matrix with lower Tg.  相似文献   

11.
Thermal properties and degree of conversion (DC%) of two composite resins (microhybrid and nanocomposite) and two photo-activation methods (continuous and gradual) displayed by the light-emitting diode (LED) light-curing units (LCUs) were investigated in this study. Differential scanning calorimetry (DSC) thermal analysis technique was used to investigate the glass transition temperature (T g) and degradation temperature. The DC% was determined by Fourier transform infrared spectroscopy (FT-IR). The results showed that the microhybrid composite resin presented the highest T g and degradation temperature values, i.e., the best thermal stability. Gradual photo-activation methods showed higher or similar T g and degradation temperature values when compared to continuous method. The Elipar Freelight 2TM LCU showed the lowest T g values. With respect to the DC%, the photo-activation method did not influence the final conversion of composite resins. However, Elipar Freelight 2TM LCU and microhybrid resin showed the lowest DC% values. Thus, the presented results suggest that gradual method photo-activation with LED LCUs provides adequate degree of conversion without promoting changes in the polymer chain of composite resins. However, the thermal properties and final conversion of composite resins can be influenced by the kind of composite resin and LCU.  相似文献   

12.
We used advanced thermal analysis methods to characterize a new family of A-B di-block copolymers based on the amino acid sequences of Nephila clavipes major ampulate dragline spider silk. Using temperature modulated differential scanning calorimetry with a thermal cycling method and thermogravimetry, we captured the effect of bound water acting as a plasticizer for spider silk-like biopolymer films which had been cast from water solution and then dried. A low glass transition because of bound water removal was observed in the first heating cycle, after which, a shift of glass transition was observed in A-block film due to crystallization and annealing, and in BA film due to annealing. No shift of glass transition after bound water removal was observed in B-block film. The reversing heat capacities, C p, for temperatures below and above the glass transition were measured and compared to the calculated values. The solid state heat capacity was modeled below T g, based on the vibrational motions of the constituent poly(amino acid)s, heat capacities of which are known from the ATHAS Data Bank. Excellent agreement was found between the measured and calculated values of the heat capacity, showing that this model can serve as a standard method to predict the solid state C p for other biologically inspired block-copolymers. We also calculated the liquid state heat capacities of the 100% amorphous biopolymer at T g, and this predicted value can be use to determined the crystallinity of protein-based materials.  相似文献   

13.
The thermal behavior of poly(1,3-phenyl-1,4-phenyl)-4-phenyl-1,2,4-triazole has been investigated using different scanning calorimetry (DSC) and thermogravimetry (TG). Processes are studied for this thermally stable polymer that take place between 200 and 500°C. While the polycondensation reaction product in powder from appeared to be partially crystalline, films prepared by casting from a formic acid solution appeared to be completely amorphous. A thermal treatment between Tg(~ 270°C) and Tm(~ 430°C) can introduce crystallinity in the films because of the polymer's ability to cold crystallize. The cold crystallization temperature Tc seems to be dependent on the preparation history of the solid polymer phase. Thermal annealing of the films just below Tg does not introduce crystallinity but inhibits subsequent cold crystallization at higher temperatures. Crystallization upon cooling from the crystalline melt has not been observed either. At temperatures just above the crystalline melting point the polymer starts to decompose in an exothermic reaction.  相似文献   

14.
The miscibility of blends of isotactic polypropylene and propylene-1-hexene (PH) copolymers with 11 and 21 mol% of 1-hexene (PH11 and PH21, respectively) has been studied theoretically and using DSC, DMA, and AFM techniques. Using experimental PVT data, the solubility parameter approach leads to a critical difference in 1-hexene content for melt miscibility of 17 mass% (~11 mol%) at 200 °C and 0.1 MPa. The theoretical window for miscibility is in close agreement with thermal properties of the blends. The glass transition (T g) of miscible blends (iPP/PH11 and PH11/PH21) decreases proportionally to the content of PH having the lowest T g, while immiscible blends (iPP/PH21) display invariable T g with blend composition. The same trend was extracted from the analysis of the β-relaxation by dynamic mechanical analysis. Room temperature AFM images of blends quenched from 200 °C into liquid nitrogen confirm phase segregation of iPP/PH21 in domains of 1–5 microns, while the AFM images of iPP/PH11 and PH11/PH21 lack any obvious signature of phase separation prior to crystallization.  相似文献   

15.
Multi-walled carbon nanotubes (MWCNT) have been used as fillers to improve thermal properties such as glass transition temperature (T g) of epoxy materials. In this work, nanocomposites based on diglycidyl ether of bisphenol A resin and triethylenetetramine (TETA) were prepared by a three-roll mill process with TETA-functionalized (MWCNT–COTETA) and neat MWCNT. Thermogravimetric analysis of the nanofillers showed that in the case of MWCNT–COTETA, there is a 15 % mass loss that can be attributed to –COTETA and residual oxygen-containing functional groups. The influence of chemical modification on the behavior of the glass T g was evaluated by dynamic scanning calorimetry. The MWCNT–COTETA allowed a ~20 °C reproducible increase of T g in concentrations in the range of 0.5–1.0 mass%. Furthermore, images obtained by scanning electron microscopy were used to investigate the morphology of the polymer matrix and its interfaces. The quality of the dispersion and interaction of the nanotubes in the epoxy matrix was assessed from the images. Both the neat epoxy and the nanocomposite with MWCNT showed low thermal shrinkage upon curing.  相似文献   

16.
In this study, the thermal behavior in terms of glass transition (T g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min?1) during DSC. The results show that the Xtrabase composite displayed the highest T g (120 °C at a 5 °C min?1 heating rate) and E a (157.64 kJ mol?1) values associated with thermal degradation from the main chain of the polymer.  相似文献   

17.
Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.  相似文献   

18.
The effects of confinement on glass transition temperature (Tg) and physical aging are measured in polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-vinyl pyridine) (P2VP) nanocomposites containing 10- to 15-nm-diameter silica nanospheres or 47-nm-diameter alumina nanospheres. Nanocomposites are made by spin coating films from sonicated solutions of polymer, nanofiller, and dye. The Tgs and physical aging rates are measured by fluorescence of trace levels of dye in the films. At 0.1–10 vol % nanofiller, Tg values can be enhanced or depressed relative to neat, bulk Tg (Tg,bulk) or invariant with nanofiller content. For alumina nanocomposites, Tg increases relative to Tg,bulk by as much as 16 K in P2VP, decreases by as much as 5 K in PMMA, and is invariant in PS. By analogy with thin polymer films, these results are explained by wetted P2VP–nanofiller interfaces with attractive interactions, nonwetted PMMA–nanofiller interfaces (free space at the interface), and wetted PS–nanofiller interfaces lacking attractive interactions, respectively. The presence of wetted or nonwetted interfaces is controlled by choice of solvent. For example, 0.1–0.6 vol % silica/PMMA nanocomposites exhibit Tg enhancements as large as 5 K or Tg reductions as large as 17 K relative to Tg,bulk when films are made from methyl ethyl ketone or acetic acid solutions, respectively. A factor of 17 reduction of physical aging rate relative to that of neat, bulk P2VP is demonstrated in a 4 vol % alumina/P2VP nanocomposite. This suggests that a strategy for achieving nonequilibrium, glassy polymeric systems that are stable or nearly stable to physical aging is to incorporate well-dispersed nanoparticles possessing attractive interfacial interactions with the polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2935–2943, 2006  相似文献   

19.
Effect of fullerene C60 was investigated on thermal, mechanical and optical properties of polymethylmethacrylate (PMMA) under ionizing radiation. It was stated that fullerene C60 behaves as an effective antirad with respect to PMMA. Fullerene C60 addition raises temperature of destruction for polymer subjected to electron radiation by 20-25 °C, lowers the rate from 4 to 4.5 times and increases the activation barrier for radiated PMMA destruction reaction. Fullerene C60 addition promotes improvement of strength properties of PMMA: for films containing C60 addition and else subjected to electron radiation treatment a decrease in rupture strength is 10-15%, for samples containing no fullerene it equals ∼25%. Interaction of free radicals with fullerene at radiation treatment influences optical characteristics of PMMA films.  相似文献   

20.
In this study, a series of binary mixtures of N-butyl stearate (nBS) and methyl palmitate (MP) were used to produce a novel composite phase change material (CPCM) for potential application in the eastern China, and their thermal properties were investigated by differential scanning calorimetry (DSC). The results of DSC indicated that the mixture consisting of 10 mass% nBS and 90 mass% MP is optimum as the CPCM in terms of the phase change temperature ranges (T f = 19.74–5.59 °C; T m = 18.34–33.80 °C) and latent heats (ΔH f = 176.8 J g?1; ΔH m = 189.3 J g?1). On the other hand, the thermal reliability and chemical stability of the CPCM after 120, 180, 240, 300, 360 and 500 accelerated thermal cycling tests were studied by DSC and fourier transform infrared (FTIR) analysis. The results demonstrated that the CPCM had good thermal reliability and chemical stability.  相似文献   

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