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1.
Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: Tg(bulk)-Tg(23 nm) = 10 °\ensuremath T_{{\rm g}}({\rm bulk})-T_{{\rm g}}(23{\,\mbox{nm}})= 10 ^{\circ} C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T g ’s from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T g(bulk) - T g(23 nm) = 15° C via fluorescence. This small difference in the T g confinement effect reflects differences in how fluorescence and ellipsometry report “average T g ” with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution.  相似文献   

2.
The microhardness of coreactive blends of polyethylene terephthalate (PET) and bisphenol A polycarbonate (PC) was investigated over the whole range of compositions. The occurrence of one single glass transition temperature (T g) step in the differential scanning calorimetry (DSC) curves indicated that intensive chemical interactions had taken place during melt blending, resulting in formation of copolycondensates with dominating random sequential order. The parallel decrease of microhardness (H) and of Tg with increasing PET content in the blends has been ascribed to the formation of new copolymer molecules enriched in the component characterized by lower H and T g values. It is emphasized that such noncrystallizable copolymers offer the possibility to evaluate the intrinsic contribution of the repeating units to the H and T g characteristics of copolymers with various compositions and sequential orders.  相似文献   

3.
A recently developed nonequilibrium thermodynamic theory of continuum rheology is combined with a generalized definition of thermomechanical transitions, to produce a single equation for interrelating the basic variables (stress o, strain rate ε, pressure p, temperature T, and structure ?) at a transition. Specialization of ? to represent uncrosslinked polymers leads to incorporation of molecular weight M as a variable. New predictions are thus made for the glass transition [Tg(M), Tg(p), Tg(ε) and others] and compared successfully with data. Particularly remarkable are the results that 1/Tg is a piecewise linear function of In M, and T is piecewise linear with p. Comparable results and confirmation with data arise when applying the theory to the liquid-liquid transition, T ll (M). For random copolymers, application of a single mixing rule to the transition equation leads to a prediction of Tg as a function of composition and the Tgi for the homopolymers (components i). This relationship reduces, in various cases, to several familiar equations in which the parameters were simply empirical, thus providing an interpretation of those parameters and defining restrictions applicable to each case. Finally, an alternative interpretation of ? in terms of free volume allows the theory to be extended to other systems, including those with small molecules.  相似文献   

4.
We present spectroscopic ellipsometry measurements on thin films of polymer nanocomposites consisting of gold nanoparticles embedded in poly(styrene). The temperature dependence of thickness variation is used to estimate the glass transition temperature, T g . In these thin films we find a significant dependence of T g on the nature of dispersion of the embedded nanoparticles. Our work thus highlights the crucial role played by the particle polymer interface morphology in determining the glass transition in particular and thermo-mechanical properties of such nanocomposite films.  相似文献   

5.
We have used transmission ellipsometry to measure the glass transition temperature, Tg, of freely-standing films of atactic and syndiotactic poly(methyl methacrylate) (PMMA). We have prepared films with different molecular weights, MW, (159×103 < M w < 1.3×106) and film thicknesses, h, ( 30nm < h < 200 nm). For the high-MW ( M w > 509×103) atactic PMMA films, we find that Tg decreases linearly with decreasing h, which is qualitatively similar to previous results obtained for high-MW freely-standing polystyrene (PS) films. However, the overall magnitude of the Tg reduction is much less (by roughly a factor of three) for the high-MW freely-standing PMMA films than for freely-standing PS films of comparable MW and h. The observed differences between the freely-standing PMMA and PS film data suggest that differences in chemical structure determine the magnitude of the Tg reduction and we discuss the possible origins of these differences. Our analysis of the MW-dependence of the Tg reductions suggests that the mechanism responsible for the MW-dependent Tg reductions observed in the high-MW freely-standing films is different than that responsible for the MW-independent Tg reductions observed in the low-MW freely-standing and supported films.  相似文献   

6.
We have used ellipsometry to measure the initial stages of interface healing in bilayer polystyrene films. We also used ellipsometry to measure the glass transition temperature Tg of the same or identically prepared samples. The results indicate that as the film thickness is decreased, the time constant for the interface healing process increases, while at the same time the measured glass transition temperature in the same samples decreases as the film thickness is decreased. This qualitative difference in the behavior indicates that it is not always possible to make inferences about one probe of polymer dynamics from measurements of another. We propose a reason for this discrepancy based on a previously discussed origin for reduction in the Tg value of thin films.  相似文献   

7.
The transition metal phosphorus trichalcogenides MnPS3 and the FePS3 are CdCl2 type layered compounds, where the transition metal ions form a hexagonal lattice. While these compounds order anti-ferromagnetically at low temperature, the magnetic structures are different. We have reported that these mixtures Mn0.5Fe0.5PS3 is a spin glass with a glass transition temperature T g=33.7 K. Then, in this work, we report that the results of the temperature variation of the 57Fe Mössbauer spectra of FePS3 and Mn0.5Fe0.5PS3, in detail. In the anti-ferromagnetic state of FePS3, the hyperfine magnetic field H int increases with decreasing temperature and the Isomer shift I. S. increases slightly with decreasing temperature. However in Mn0.5Fe0.5PS3, the two broadened peaks are observed and the two peaks became a single peak with decreasing temperature at about 50.0 K, which is higher than T g=33.7 K. In the spin glass Mn0.5Fe0.5PS3, the Mössbauer spectra suggest that the magnetic interactions exist far above T g.  相似文献   

8.
Dynamic mechanical spectroscopy and differential scanning calorimetry investigations of segmental dynamics are reported for net-poly(methyl methacrylate)-co-poly(n-butyl acrylate) copolymer networks. Three characteristic temperatures, namely, Vogel (T), glass transition (T g ), and crossover (T c ), were used to define cooperativity range and a new reduced temperature parameter (Solidness, S). The results showed that broadness of the α -dispersion (glass transition) and cooperativity length scale at the glass transition temperature decreased with increasing butyl acrylate content and T g -scaled temperature dependence of the relaxation time (fragility). However, the cooperativity range (T c –T), decreased with increasing fragility index. Furthermore, the solidness at T g (S(T g )) was nearly independent of chemical structure of the samples. Finally, a correlation was found between two measures of cooperativity length scale in the glass transition region, namely, average volume of cooperatively rearranging regions, V CRR , and the number of basic units in an act of rearrangement in the glass transition region, Z(T g ), determined from two completely independent experimental techniques.  相似文献   

9.
We have used nulling ellipsometry to measure the glass transition temperature, T g , of thin films of polystyrene in ambient, dry nitrogen, and vacuum environments. For all environments, the measured T g values decrease with decreasing film thickness in a way that is quantitatively similar to previously reported studies in ambient conditions. These results provide strong reinforcement of previous conclusions that such reduced T g values are an intrinsic property of the confined material. Furthermore, the results are in contrast to recent reports which suggest that the T g reductions measured by many researchers are the results of artifacts (i.e. degradation of the polymer due to annealing in ambient conditions, or moisture content).  相似文献   

10.
A series of aromatic polysulfonamides with various monomer ratios of 4,4′-diaminodiphenylsulfone (p-DDS) and 3,3′-diaminodiphenylsulfone (m-DDS) were synthesized to investigate the relationship between copolymer composition and their properties. The copolymer composition was determined from nuclear magnetic resonance (NMR). It was found that the copolymer composition of the polysulfonamides varied little from the monomer ratio; thus, similar reactivity of the two diaminodiphenylsulfones was shown by the results. From the analysis of the thermal properties of the polysulfonamides, high thermal stability of the copolymers was shown both in N2 and air and the decomposition temperature exhibited little dependence on the copolymer composition. However, the glass transition temperatures (Tg ) decreased obviously with increasing m-DDS segments, which is helpful to improve the solubility and spinnability of these polysulfonamides.  相似文献   

11.
《Current Applied Physics》2015,15(4):479-485
Room-temperature spectroscopic ellipsometry data has been analyzed to determine the complex dielectric functions, ɛ(E) = ɛ1(E) + iɛ2(E) of as-deposited Sb-doped ZnO (SZO) thin films grown on n-Si(100) substrates by dual ion beam sputtering deposition system for different growth temperatures (Tg). The dielectric functions have been obtained from ellipsometry data analyses using Cody-Lorentz oscillator in the GenOsc model. A gradual reduction in the value of electron concentration and finally the conversion of doping characteristics from donor type to acceptor type was observed with the rise in Tg. This, in turn, resulted in the decline of broadening of ɛ1 peaks, and hence in the increase of excitonic lifetime. Optical band-gap energy was observed to decrease with increase in Tg from 200 to 300 °C, and then rise continuously with further increase in Tg. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. Hall measurement and X-ray photoelectron spectroscopy analysis confirmed that the change in the electrical conduction from n-to p-type was due to the enhancement in the value of Sb5+/Sb3+ ratio and SbZn–2VZn complex formation in SZO films.  相似文献   

12.
The dielectric characteristics of film samples of P(VDF-TrFE) + TGS composite in the frequency range of 103–107 Hz are studied. The values of the real and imaginary parts of the complex dielectric constant in the temperature range of–40 to 140°C, including the points of the polymer matrix’s transition to the glassy state when Tg ≈–25°C and the ferroelectric phase transition. An analysis of the ferroelectric crystal inclusion effect on the dielectric response of P(VDF-TrFE) copolymer matrix is carried out.  相似文献   

13.
The evolution of autoadhesive strength, σ, with healing temperature, T h, at the symmetric amorphous polystyrene (PS)?PS interfaces of the samples with vitrified bulk has been used to characterize a low-temperature limit of the surface glass transition temperature T g surface(low). The existence of a linear relationship between the square root of σ and T h has been found for both polydisperse and monodisperse polymers. By the extrapolation of straight lines σ 1/2 ? T h to σ 1/2 = 0, the values of T g surface(low) have been determined and compared with those of a high-temperature limit of T g surface, T g surface(high), measured earlier. The differences between T g surface(low) and T g surface(high) have been found to be insignificant, 10–20°C. Using an average value of the shift of T g surface(low) with healing time, t h, the quasi-equilibrium value of the surface glass transition temperature of amorphous PS T surface has been estimated to be 10–15°C.  相似文献   

14.
We report, in this work, Incoherent Inelastic Neutron Scattering (IINS) measurements in amorphous bulk selenium. Taking into account the low frequency Vibrational Density-of-States(VDOS), we study the modification introduced in the Debye-Waller factor by increasing temperature through the glass transition temperature (Tg). The occurrence, in the vibrational density-of-states, of a ω2 dependence in the acoustic region, allowed us to apply the Debye theory from which the variations of the Deybe-Waller factor are calculated in addition. It is shown that the main contribution to it is given by the acoustic region of the vibrational density of states and has a faster increase for temperatures above Tg.  相似文献   

15.
The effect of the structure of copolymers (random, alternate or diblock) on their dynamics has been studied by dielectric spectroscopy. Six copolymers of styrene and methyl methacrylate (three diblocks, one alternate and two random) have been studied. The results show that the sub- T g transitions of the diblock samples can be described by one asymmetric Havriliak-Negami (HN) function, while two are necessary for the rest of the copolymers (β and γ relaxations). The characteristic times of the sub- T g relaxations show an Arrhenius temperature dependence and there is a strong coupling of the α and β relaxations at high temperatures. The deconvolution of the merging relaxations has been made in the framework of the Williams Ansatz set out in terms of Havriliak-Negami distributions. Because the 2D 2H-NMR results excluded any significant contribution from the rotation of the methoxy group of the methacrylate group around the C-OCH3 bond, the γ relaxation may be assigned to the rotation of the methyl methacrylate group in a styrene-rich environment. The Molecular Dynamics simulations of a poly(methyl methacrylate) homopolymer and of the alternate copolymer are in qualitative agreement with the experimental results, although they predict smaller values for the activation energy of the sub- T g relaxations.  相似文献   

16.
57Fe Mössbauer studies of three inorganic glasses through their glass transition temperatures, Tg, show that the Lamb-Mössbauer factor (recoil-free fraction) decreases with temperature, particularly around Tg. An attempt is made to explain the results employing the cluster model which suggests that soft modes may be associated with the glass transition.  相似文献   

17.
The upheaval structure on the surface of polymer induced by the irradiation of a near-infrared (NIR) femto-second laser pulse in polymer bulk was investigated. Copolymers, such as poly(acrylonitrile-styrene) (AS) and poly(acrylonitrilebutadiene-styrene-methyl methacrylate) (ABSM) produced upheaval structures with a flattop just like the crater of a volcano, whereas homopolymers with relatively high glass transition temperature (Tg), such as polycarbonate (PC) and polyether imide (PEI) were more often formed a bell-shaped upheaval structure. A micro-lens effect was observed for the bell-shaped upheaval structure, but that effect was not observed in the case of copolymers with a flattop structure. Replication of the bell-shaped upheaval structure in PC was carried out by electroforming (non-electrolytic plating of Ni and the following electrolytic plating of Ni) and potting approximately 30 wt% THF solution of AS copolymer. A micro-scale bell-shaped upheaval structure in PC induced by a laser pulse was replicated using a Ni mother mold with suitable precision, and the replicated bell-shaped structure also showed a micro-lens effect.  相似文献   

18.
A. P. Khandale  S. S. Bhoga  S. K. Gedam 《Ionics》2013,19(11):1619-1626
Polyvinyl alcohol (PVA) complexes with different compositions of ammonium acetate (AA) are prepared by solution cast technique. Polyvinyl alcohol crystallinity decreased with increasing ammonium acetate salt content. Molecular weight and density of polyvinyl alcohol complex increased with the addition of ammonium acetate salt. The ammonium acetate salt addition resulted in plasticization and hence decreased glass transition temperature (T g) as well as hardness number (HV). 80PVA:20AA presented maximum conductivity (σ?=?1.3?×?10?7S cm?1 at 303 K) with minimum activation energy (E a) 0.151 eV below the T g. The proton transport number determined using EMF method found ≈0.98 for polymer complex with ammonium acetate content >15 mol%. The complex impedance is measured as a function of frequency, temperature, relative humidity, and hydrogen partial pressure. Enhanced bulk conductivity with increased H2 partial pressure and relative humidity suggested H+ mobility within complex polymer electrolyte.  相似文献   

19.
A differential scanning calorimeter (DSC) has been used to monitor the influence of high-energy Co60 gamma-irradiation on physical ageing in Se96Sn4 glass. It is observed that the relaxation process in the studied glass is slow after 1 and 3 years of natural storage, and can be highly accelerated by γ-irradiation. The glass transition temperature Tg and the endothermic peak area, which is directly related to the relaxation enthalpy Δh, were found to exhibit a remarkable change after irradiation and also during an additional natural storage for 6 months and 1 year of the irradiated Se96Sn4 glass. Tg value of γ-irradiated glass increases by 12 K; meanwhile, that of additional 6-months- and 1-year-stored glass Tg increases by 19 and 20 K in comparison to its counterpart of 1-year-aged non-irradiated sample. The same trend is also observed for Δh, which becomes 2.33, 3.61 and 3.65 times that of the 1-year-aged non-irradiated case, respectively, for γ-irradiated, additional 6-months- and 1-year-stored glass. These indications reveal that γ-irradiation activates the relaxation of the glass towards a state thermodynamically close to the equilibrium super-cooled liquid state.  相似文献   

20.
Glassy solid electrolytes were prepared by combining the 50Li2SO4·50Li3BO3 (mol%) ionic glass and the 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMI]BF4) ionic liquid. High-energy ball milling was carried out for the mixture of the inorganic ionic glass and the organic ionic liquid. The ambient temperature conductivity of the glass electrolyte with 10 mol% [EMI]BF4 was 10−4 S cm−1, which was three orders of magnitude higher than that of the 50Li2SO4·50Li3BO3 glass. The addition of [EMI]BF4 to the ionic glass decreased glass transition temperature (Tg) of the glass and the decrease of Tg is closely related to the enhancement of conductivity of the glass. Morphology and local structure of the glass electrolyte was characterized. The dissolution of an ionic liquid in an ionic glass with Li+ ion conductivity is a novel way to developing glass electrolytes for all-solid-state lithium secondary batteries.  相似文献   

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