Comparison Between Volume and Enthalpy Relaxations in Non-crystalline Solids Based on the Fictive Relaxation Rate

The volume and enthalpy relaxation rate of inorganic glasses and organic polymeric materials subjected to temperature jump T has been analyzed. It is shown that the relaxation behavior in isothermal conditions can be compared on the basis of the fictive relaxation rate defined as R_f=(dT_f/dlogt)_i. No significant difference between volume and enthalpy relaxation rate has been found for all materials examined. A simple equation relating the R_f and parameters of Tool-Naraynaswamy-Moynihan (TNM) phenomenological model has been derived. This equation predicts increasing R_f with the magnitude of temperature jump. It seems that correct determination of TNM parameters might be problematic for slowly relaxing polymers as the effect of these parameters becomes comparable with experimental uncertainty.This revised version was published online in November 2005 with corrections to the Cover Date.     

Structural relaxation of amorphous Ge38S62 studied by length dilatometry and calorimetry

The structural relaxation of Ge₃₈S₆₂ glass has been studied by length dilatometry and calorimetry. The Tool-Narayanaswamy-Moynihan model was applied on obtained data of structural relaxation and parameters of this model were determined: Δh*= 483±2 kJ mol^-1, ln(A/s)= -81±1, β= 0.7±0.1 and x=0.6±0.1. Both dilatometric and calorimetric relaxation data were compared on the basis of the fictive relaxation rate. It was found that the relaxation rates are very similar and well correspond to the prediction of phenomenological model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Structural Studies of Porous Organobridged Silicate Amorphous Powder

Novel amorphous organobridged polysilsesquioxane porous powders have been prepared via hydrolytic precipitation from solutions of 1,4-bis(trichlorosilylmethyl)benzene. These new porous materials have been characterized by SEM, nitrogen sorption measurements and solid state 13C and 29Si NMR spectroscopy. The internal structure and porosity of the amorphous materials are correlated to the process conditions.     

EXAFS研究Ni-B和Ni-Ce-B超细非晶态合金的退火晶化

采用同步辐射EXAFS技术定量地研究化学还原法制备的Ni-B和Ni-Ce-B超细非晶态合金中Ni原子的局域环境结构随退火温度升高而产生的变化,结果表明,对于Ni-B和Ni-Ce-B超细非晶态合金初始样品：Ni-Ni最邻近配位壳层的平均键长RNi-Ni、配位数N、热无序σT、结构无序σs分别为0．275nm,11.9.0.0069nm,0.034nm;0.276nm,12.4,0.0067nm,0.035nm,Ni-B最邻近配位壳层的RNi-B,N, σT,σs分别为0．215nm,2.7,0.0055nm,0.0048nm;0.214nm,2.0,0.0058nm,0.0042nm,Ni-Ni配位的σs很大,是其σT的4－5倍,比Ni－B配位的σs大近一个数量级,在300℃退火后,Ni－B样品开始发生晶化生成晶态Ni3B,其RNi-Ni和σs分别为0．254nm和0．011nm,σs降低近2倍;而．3％原子比的Ce掺入后使Ni-Ce-B超细非晶态合金的晶化温度升高100℃左右。在500℃退火后,Ni－B样品的结构参数与Ni箔的相近,但Ni-Ce-B样品中的Ni-Ni配位的σs仍为0．0073nm,Ni-B配位的N为1．2,表明稀土元素Ce（以CeO2)显著增强了Ni与B的相互作用,且同时使退火晶化成的Ni晶结构产生畸变。     

Simultaneous Plasticization and Doping of Polyaniline Studied by Thermal Analysis Methods

The thermal behaviour of polyaniline plasticized by an oligoester of phosphoric acid was investigated by means of thermogravimetry, either alone or coupled with Fourier transform infrared spectroscopy, and differential scanning calorimetry. It was found that additional thermal transitions, resulting from the dopant, occur in the temperature range 200-250°C. The emission of volatile products, as evidenced by the Gram-Schmidt chromatograms, was suppressed by the plasticizer used. This stabilization was probably due to a decreased possibility of diffusion in the three-dimensional honeycomb polymer-plasticizer structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Local Transient Jamming in Stress Relaxation of Bulk Amorphous Polymers

Bulk amorphous polymers become stretched and parallel-aligned under loading stress, and their intermolecular cooperation slows down the subsequent stress relaxation process. By means of dynamic Monte Carlo simulations, we employed the linear viscoelastic Maxwell model for stress relaxation of single polymers and investigated their intermolecular cooperation in the stress relaxation process of stretched and parallel-aligned bulk amorphous polymers. We carried out thermal fluctuation analysis on t...     

Indomethacin: The Interplay between Structural Relaxation,Viscous Flow and Crystal Growth

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (d_aver) and heating rate (q⁺) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited d_aver-independent kinetics, with the q⁺ dependences based on the apparent activation energies of 342 and 106 kJ·mol⁻¹, respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q⁺, the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q⁺ led to the formation of the thermodynamically stable γ polymorph, fast q⁺ produced a significant amount of the metastable α polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger’s decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed.     

Enthalpy,volume and structural relaxation in glass-forming silicate melts

Through structural relaxation, the configuration of a viscous liquid changes to allow the Gibbs free energy to be minimum in response to temperature variations. In this review, the practical importance of relaxation in silicate melts is first illustrated by configurational heat capacity and entropy and their connection with viscosity via Adam-Gibbs theory. Relaxation effects on thermal expansion and compressibility are then examined, and the similarity of the kinetics of structural, enthalpy and volume relaxation is pointed out. Turning to microscopic mechanisms, we finally stress the importance of Si-O bond exchange and its decoupling with the motion of network-modifying elements near the glass transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

La55Al25Ni10Cu10大块金属玻璃结构弛豫过程中的焓变

用铜模吸铸法制备直径为4 mm的La55Al25Ni10Cu10大块金属玻璃非晶棒。采用差示扫描量热仪（DSC）研究了金属玻璃结构弛豫行为,并运用Stretched-Exponential弛豫方程对焓弛豫动力学进行描述。结果表明：La55Al25Ni10Cu10金属玻璃在玻璃转变温度Tg以下不同时间等温退火中会发生焓弛豫,用Stretched-Exponential弛豫方程能很好地描述焓弛豫动力学行为,得到Kohlrausch指数β=0.78,弛豫激活能E=60.8kJ.mol^-1。La55Al25Ni10Cu10金属玻璃形成液体的脆性指数为54,其玻璃形成液体属于强液体。     

Coating Polymer-plasticizer Interaction in Relation to the Enthalpy Relaxation of Polymer

In the course of the formulation of coated dosage forms, the selection of the suitable composition of the coating system is of great importance in respect of the final dosage form. Since the applied coating systems are multicomponent, the possible interactions between the components determine the physico-chemical stability of the formulated dosage form, the drug release process, as well as the formulation parameters. In the present study, the influence of the applied plasticizer, dibutyl sebacate on the enthalpy relaxation of casted Eudragit L 30D films was determined as a function of the plasticizer concentration. The enthalpy relaxation was recorded by DSC during the applied isothermal recovery process of Eudragit films. The obtained results indicate that enthalpy relaxation can be measured by DSC at 20 mass/mass% dibutyl sebacate concentration, which refers to the increased molecular mobility consequently to the effect of the interaction between the polymer and plasticizer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-Field NMR Relaxation Analysis of High-Pressure Ethane Adsorption in Mesoporous Silicas

Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz) ¹H nuclear magnetic resonance (NMR) relaxation measurements to characterise ethane dynamics within mesoporous silica materials exhibiting mean pore diameters between 6 and 50 nm. Our measurements provide NMR-based adsorption isotherms within the range 25–50 bar and at ambient temperature, incorporating the ethane condensation point (40.7 bar at our experimental temperature of 23.6 °C). The quantitative nature of the acquired data is validated via a direct comparison of NMR-derived excess adsorption capacities with ex situ gravimetric ethane adsorption measurements, which are demonstrated to agree to within 0.2 mmol g⁻¹ of the observed ethane capacity. NMR relaxation time distributions are further demonstrated as a means to decouple interparticle and mesopore dominated adsorption phenomena, with unexpectedly rapid relaxation rates associated with interparticle ethane gas confirmed via a direct comparison with NMR self-diffusion analysis.     

Effects of Deformation Rate on the Necking of an Amorphous Copolyester Studied by Modulated DSC

The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly higher glass transition temperature (T_g). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a non-reversing part was considered as appearance of possible microcrystallinity. The T_g range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Short-Range Structural Correlations in Amorphous 2D Polymers

Many 2D covalent polymers synthesized as single layers on surfaces show inherent disorder, expressed for example in their ring-size distribution. Systems which are expected to form the thermodynamically favored hexagonal lattice usually deviate from crystallinity and include high numbers of pentagons, heptagons, and rings of other sizes. The amorphous structure of two different covalent polymers in real space using scanning tunneling microscopy is investigated. Molecular dynamics simulations are employed to extract additional information. We show that short-range correlations exist in the structure of one polymer, i. e. that polygons are not tessellating the surface randomly but that ring neighborhoods have preferential compositions. The correlation is dictated by the energy of formation of the ring neighborhoods.     

Volume and enthalpy relaxation in a-PMMA after temperature up-jumps

the volume and enthalpy relaxation in a-PMMA subjected to temperature jumps in t_g region has been analysed. The measured H and V data were compared with respect to aging time and proportionality between them as a slope of (∂H/∂V)_T dependencies has been found. According to previous works the slope was identified as an apparent bulk modulus, K _a. This method is applied to aging following temperature up-jumps after consolidation periods of varying lengths. the main finding is a marked increase of K _a with consolidation time, approaching a limiting value in an asymptotic fashion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Volume and enthalpy relaxation response after combined temperature history in polycarbonate

Summary Volume and enthalpy relaxation in polycarbonate subjected to double temperature jumps in the T_g region has been analysed. It concerns both initial T_down-jump from equilibrium above T_g to consolidation temperature below T_g and fina1 T_up-jump to relaxation temperature, also below T_g. The measured H and V data after T_up-jump were compared with respect to aging time calculating (dH/dV) ratio denoted as aging bulk modulus, K_a. According this new methodology H and V relaxation response after T_up-jump demonstrates differences in relaxation responses.     

Effect of Molecular Weight on Enthalpy Relaxation in Syndiotactic Poly(Methyl-Methacrylate)

The structural relaxation behaviour of narrow fractions (M_w/M_n < 1.1) of syndiotactic poly(methyl methacrylate) with molecular masses ranging from 2,000 to 200,000 Daltons have been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy (Δh*) of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (T_a = T_g − 10 °C). As expected, the increase of molecular weights gives rise to both a continuous increase of Δh* and a decrease of the apparent isothermal relaxation rate. More interestingly, both Δh* and the apparent isothermal relaxation rate showed abrupt changes around the syndiotactic PMMA entanglement mass (M_e ).     

Electrochemical Synthesis of Amorphous VO2 Colloids and Their Rapid Thermal Transforming to VO2(M) Nanoparticles with Good Thermochromic Performance

Amorphous VO₂ (a‐VO₂) colloids were synthesized by electrochemical anodic oxidation of metallic vanadium. It was found that the a‐VO₂ colloids have a cotton‐like morphology composed of very small clusters, and that the crystallization temperature of the a‐VO₂ colloids can be adjusted either by the electrolyte of the anodic oxidation or/and the dispersion agent of the colloids. VO₂(M) nanoparticles (NPs) (and a NP film) with an average size of about 50 nm can be obtained by a rapid thermal annealing of the a‐VO₂ colloids at 310 °C under air, which is beneficial for practical applications. The VO₂(M) NP film shows an obvious metal–semiconductor transition with a resistance less than 10 Ω in the metallic state. An integral visible transmittance of 40.7 %, a solar transmittance modulation of 9.4 %, and a resistance modulation in the order of 5×10⁴ were realized in the VO₂(M) NP film.