Study of the Molecular Mobility in Polymers with the Thermally Stimulated Recovery Technique—A Review

Thermally stimulated recovery (TSR) is a non‐conventional mechanical spectroscopy technique that allows to analyse in detail the relaxation processes of polymeric systems in the low frequency region. This work reviews the main aspects and potentialities of this technique. The different kinds of TSR experiments that can be performed, global and thermal sampling (TS) experiments, are described and illustrated with several examples. Also, the different methods for the determination of the thermokinetic parameters (activation energy and pre‐exponential factor) of the thermal sampling (TS) procedure are explained and compared. In this context, the compensation phenomenon, which always appears in TSR results when the studies are performed in the glass transition region of a given system, is discussed. Examples of the application of this technique to different polymeric systems during the last 20 years are provided. An emphasis will be made on the analysis of the effect of crystallinity degree and crosslink density on the TSR response. A comparison between the results (characteristic times and activation energies) obtained by different techniques, namely TSR, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC), is made.     

酸催化溶胶-凝胶法制备高强度SiO2增透膜研究进展

高强度增透膜是用于减少表面反射、增加光线透光率的薄膜,具有密度低、折射率可调、耐磨性好的特点.本文综述了高强度增透膜的制备方法与研究进展,介绍了酸催化溶胶-凝胶法制备SiO2溶胶的机理及影响因素,酸催化溶胶-凝胶法及两种辅助酸催化溶胶-凝胶法制备高强度增透膜的方法,对高强增透膜制备的发展方向和应用前景进行了展望.     

Structural Fluctuation of Disilanyl Double‐Pillared Bisheteroarenes

Silacyclophanes possessing two disilanyl pillars were synthesized from tricyclic heteroarenes in one‐pot synthetic procedures. The step‐like anti structures of three congeners bearing two heteroarene units were revealed in single crystals by X‐ray crystallographic analysis. Depending on the structures of aromatic units, torsion angles at the disilanyl pillars altered to maintain the overall step‐like molecular structures. The structure, however, fluctuated between anti and syn conformers in a solution phase despite the presence of eight methyl groups on the ring periphery. The analysis of the coalescence temperature with NMR spectroscopy showed the fundamental energetics of the dynamics. The subtle structural differences affected the dynamic behavior of the silacyclophanes.     

Calculations of dynamic dipole polarizabilities of Li and Na atoms in debye plasma using the model potential technique

The effects of Debye plasma on the frequency‐dependent polarizabilities of Li and Na atoms are investigated using symplectic algorithm within the framework of the pseudostate summation technique. Dynamic dipole polarizabilities of Li (2s ²S) and Na(3s ²S) as functions of scaled number density of the plasma electrons for arbitrary plasma temperature are presented. Screening effects on the resonance frequencies are also presented. In free‐atomic cases, our calculated results are comparable with the reported theoretical and experimental predictions. © 2012 Wiley Periodicals, Inc.     

Equilibrium and Dynamic Surface Tension of Carboxymethylchitosan and Alkyl Trimethylammonium Bromide Mixtures

A water-soluble derivative of chitosan, carboxymethylchitosan (CMCH), was mixed with alkyltrimethylammoniumbromides (C_mTAB) and was studied on the adsorption at air/water interface using equilibrium and dynamic surface tension method. The effects of surfactant and polymer concentrations, surfactant chain length, as well as pH of solution were investigated. Addition of the surfactants remarkably promotes the polymer adsorption. Increasing any one of surfactant concentration, surfactant chain length, and pH will facilitate the adsorption of the mixture whereas little effects of polymer concentration were observed. The results are explained in terms of the interaction between CMCH and C_mTAB under different conditions.     

Dynamic Surface Elasticity of Polyelectrolyte/Surfactant Adsorption Films at the Air/Water Interface: Carboxylmethylchitosan and Cetyltrimethylammonium Bromide

The dynamic surface elasticity of the solution of carboxymethylchitosan (CMCH) and cetyltrimethylammonium bromide (C₁₆TAB) was measured as a function of the surfactant concentration and the surface age by the oscillating drop method. The results showed that the surface layer of the CMCH/C₁₆TAB solution transformed from loose to structured with the increase in the surfactant concentration. The surface elasticity versus the surface pressure curve during the adsorption showed different features at different surfactant concentration ranges, which was connected with the structural transformation of the surface layer. Our results show that the measurement of dynamic surface dilational properties is a powerful tool for studying the surface kinetics, which is helpful for dealing non-equilibrium systems in industry.     

Salinity Controlled Vesicle Formation and Growth in Aqueous Mixture of Aerosol OT/Triton X‐100

Mixed vesicles can be formed spontaneously from aqueous mixture of the double‐tailed anionic surfactant sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) and the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X‐100) under the inducement of salt, the formation mechanism of which should be attributed to the compression of salt on the electric bilayers of the head groups. The stability and the polydispersity of the vesicles are superior to single‐component AOT vesicles, which can be proved by the TEM image and visual observation. The vesicle region was presented in a pseudo‐ternary diagram of AOT/TX‐100/brine. The size of the vesicle was measured using dynamic light scattering. It is found that the vesicle size increases with the salinity but decreases with the content of TX‐100 in the mixture at the same salinity. Especially, the vesicle size is independent of the surfactant concentration at fixed salinity.     

Clouding and Hydrodynamic Behavior of Pluronic-Surfactant Interaction in Aqueous Salt Solutions

Clouding behavior of PEO-PPO-PEO and PPO-PEO-PPO block copolymers were studied in presence of sodium dodecyl sulfate (SDS) and NaCl. Extensive study of Pluronic P84 (EO₁₉PO₄₃EO₁₉) with different salts and ionic surfactants, were carried out using cloud point, viscosity and dynamic light scattering (DLS) measurements. The change in cloud point, as well as the size of P84 micelles in aqueous salt solution obeys the Hofmeister lyotropic series. Results on P84-ionic surfactant mixture indicate stronger interaction in case of SDS compared to those in presence of dodecyl trimethylammonium chloride (DTAC); here interaction seems to diminish in the presence of salts.     

Dispersed Structure of Ethanol‐Gasoline Fuel According to Dynamic Light Scattering Method

The dispersed structures of mixtures of five different gasolines with anhydrous ethanol were investigated by the dynamic light scattering (DLS) method. The aim of the work was to find whether these blends are colloid systems. Influence of different parameters was investigated to verify the results of this research. Ethanol‐gasoline blends were found to be colloid systems with the drop size of 20–150 nm.     

Rheological Properties of Model and Crude Oil Systems when Wax Precipitate under Quiescent and Flowing Conditions

Wax precipitation and deposition is a recurring challenge in transportation of crude oil, and increased knowledge about the behavior of such systems is necessary. Microscopy and differential scanning calorimetry were used to follow the crystallisation of wax for two model systems. The amount of solid was also determined by the latter method as well. The flow and viscoelastic behavior were investigated around the wax precipitation temperature, and the yield stress was determined both after dynamic and static cooling. Interpretation of the results was carried out in view of crystal growth and microstructure of the wax crystals. The variables that were studied were wax composition, amount of wax and thermal and shear history.