Electroactive shape memory effect of radiation cross-linked SBS/LLDPE composites filled with carbon black

The poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer and linear low-density polyethylene (LLDPE) were blended and irradiated by γ rays to prepare shape memory polymer (SMP). Different weight fractions of conductive carbon black (CB) were filled into SMP to form a novel electroactive shape memory CB/SBS/LLDPE composite. The CB reinforced radiation cross-linked SBS/LLDPE blends for the improvement of the mechanical weakness and conductivity of SBS/LLDPE bulk and for wide practical engineering uses. The electroactive shape memory CB/SBS/LLDPE composites were investigated by electrical properties, mechanical, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electroactive shape memory effects. It is found that the tensile strength, storage modulus, and resistance against mechanical and thermal mechanical cycle loading in the developed composites increased due to the role of reinforcement of CB. The melting temperatures and volume resistance of the composites decreased with the increment of CB for excellent electrical conductivity of CB. The electroactive shape memory effects of developed CB/SBS/LLDPE composites were affected by CB weight fractions and applied voltage, while good shape recovery could be obtained in the shape recovery test. When the CB fraction is more than 5 wt%, full recovery can be observed after tens of seconds and shape recovery speed increased with CB fractions and voltage increasing. However, the shape recovery rate decreases slightly with increment of cycle times.     

A strategy to find minimal energy nanocluster structures

An unbiased strategy to search for the global and local minimal energy structures of free standing nanoclusters is presented. Our objectives are twofold: to find a diverse set of low lying local minima, as well as the global minimum. To do so, we use massively the fast inertial relaxation engine algorithm as an efficient local minimizer. This procedure turns out to be quite efficient to reach the global minimum, and also most of the local minima. We test the method with the Lennard–Jones (LJ) potential, for which an abundant literature does exist, and obtain novel results, which include a new local minimum for LJ₁₃, 10 new local minima for LJ₁₄, and thousands of new local minima for . Insights on how to choose the initial configurations, analyzing the effectiveness of the method in reaching low‐energy structures, including the global minimum, are developed as a function of the number of atoms of the cluster. Also, a novel characterization of the potential energy surface, analyzing properties of the local minima basins, is provided. The procedure constitutes a promising tool to generate a diverse set of cluster conformations, both two‐ and three‐dimensional, that can be used as an input for refinement by means of ab initio methods. © 2013 Wiley Periodicals, Inc.     

Potential energy and free energy landscapes

Familiar concepts for small molecules may require reinterpretation for larger systems. For example, rearrangements between geometrical isomers are usually considered in terms of transitions between the corresponding local minima on the underlying potential energy surface, V. However, transitions between bulk phases such as solid and liquid, or between the denatured and native states of a protein, are normally addressed in terms of free energy minima. To reestablish a connection with the potential energy surface we must think in terms of representative samples of local minima of V, from which a free energy surface is projected by averaging over most of the coordinates. The present contribution outlines how this connection can be developed into a tool for quantitative calculations. In particular, stepping between the local minima of V provides powerful methods for locating the global potential energy minimum, and for calculating global thermodynamic properties. When the transition states that link local minima are also sampled we can exploit statistical rate theory to obtain insight into global dynamics and rare events. Visualizing the potential energy landscape helps to explain how the network of local minima and transition states determines properties such as heat capacity features, which signify transitions between free energy minima. The organization of the landscape also reveals how certain systems can reliably locate particular structures on the experimental time scale from among an exponentially large number of local minima. Such directed searches not only enable proteins to overcome Levinthal's paradox but may also underlie the formation of "magic numbers" in molecular beams, the self-assembly of macromolecular structures, and crystallization.     

Microscopic solvation: spectroscopic results vs. Monte Carlo simulations

Van-der-Waals clusters of carbazole (representing the ‘solute’) with up to 40 nitrogen or methane solvent molecules were characterized using two-color resonant two-photon ionization spectroscopy. Features in these spectra (redshift, homogeneous and heterogeneous broadening, etc.) are interpreted as being caused by various static and dynamic effects of the solvent shell surrounding the aromatic substrate. For a better understanding of such effects, Monte Carlo simulations of the clusters were performed: Statics: Using a Monte Carlo simulated annealing minimization procedure, minimum energy structures (local, probably global) were found for the various cluster species. Using a simple empirical additivity rule, spectral shifts are rationalized from these structures.Dynamics: Starting from these minimum configurations, canonical ensemble simulations were carried out in a temperature range from 0 to 35 K. Severalorder-disorder transitions were identified including:

1. orientational isomerization or ‘melting’
2. surface isomerization or decoupling
3. rigid → fluxional transitions
4. full cluster ‘melting’

We present some of our experimental results on the systems carbazole · (N₂) _n and carbazole · (CH₄) _n together with the corresponding simulation data.     

Synthesis and properties of metal clusters in polymeric matrices

A one-step plasma deposition process is described which allows the uniform dispersion of small metal clusters throughout a thin film polymer matrix. Plasma parameters and plasma gas phase diagnostics relevant to the control of film composition and structure are discussed. Chemical and structural analytical techniques such as I.R. absorption spectroscopy, E.S.C.A., Auger electron spectroscopy, X-ray fluorescence, X-ray and electron diffraction and microscopy are used to characterize the cluster containing films. Changes in cluster size and shape as a function of volume fraction and as a result of post deposition annealing are described. Optical and electrical properties are presented below and above the onset of percolation and are evaluated in terms of contemporary effective medium theories.     

Adsorption — desorption kinetics on epitaxially oriented palladium clusters

Palladium clusters with a low size dispersion and a single crystallographic shape have been obtained by epitaxial growth on (100) MgO. The isothermal adsorption — desorption kinetics of CO is obtained by a molecular beam method allowing the direct determination of the global adsorption probability and of the mean life time of CO molecules on the clusters. Three main results are deduced from these measurements: — an increase of the adsorption rate of CO on the clusters by the capture of CO molecules physisorbed on the substrate, — a faster desorption rate from (100) than from (111) facets at high coverage, — an increase of the adsorption energy for clusters smaller than 3 nm.     

Structure of maltodextrin gels — a small angle X-ray scattering study

The structure of maltodextrin gels was investigated by small angle X-ray scattering. The inhomogeneities in the maltodextrin gels are molecular aggregates with maximum dimensions of almost 300 nm. Their shape can be approximated by oblate ellipsoids of revolution with an axial ratio of 0.1. The radius of gyration of the aggregates amounts to about 90 nm. For this reason in the nomenclature of Papkov the gels are polymer gels of the 2^nd type. The melting of these aggregates is measured by SAXS with a position sensitive detector in the range near 56 °C.     

Calorimetry and thermal analysis studies on the binding of 13-phenylalkyl and 13-diphenylalkyl berberine analogs to tRNAphe

The interaction of 13- monophenylalkyl and diphenylalkyl berberine analogs with tRNA^phe has been investigated using various thermochemical techniques like thermal melting, isothermal titration calorimetry, and differential scanning calorimetry experiments. Thermal melting studies revealed that all the analogs stabilized the tRNA^phe better than berberine. The binding affinity for the analogs was of the order of 10⁵ M^?1. Calorimetry results suggested that the binding of these analogs was predominantly entropy driven with small negative enthalpy contribution to the standard molar Gibbs energy. The temperature dependence of the standard molar enthalpy changes yielded negative values of standard molar heat capacity changes for the complexation revealing substantial hydrophobic contribution in the RNA binding of these analogs. An enthalpy–entropy compensation behavior was also seen in all the systems. The diphenylalkyl analogs were found to be more effective tRNA^phe binders compared to the monophenylalkyl analogs. The utility of the present work lies in understanding the structural and energetic aspects of the interaction of these berberine analogs with tRNA, which may be useful in the development of RNA-targeted drugs.     

Melting of non-spherical ultrafine particles

The behaviour of lead particles, with size up to 100 nm, embedded in a SiO matrix have been investigated versus temperature by dark field electron microscopy. When the particle is not spherical, it is shown that the melting process initiates on the surface regions of the particle where curvature is maximum. The process is continuous and reversible as far as a solid core exists. When the temperature increases, the volume of the solid core decreases and its shape evolves towards a sphere. Final melting of the core occurs as a first order transition (with size effect). These direct observations are in good agreement with previous results deduced from a high-sensitive reflectance experiment which gives an information averaged on the size and the state of the particles. Emphasis is laid on the dimension of the particle perpendicular to the substrate which is not generally obtained through electron microscopy measurements and appears here as an important parameter.     

Hydration of cement with superabsorbent polymers

Hydration of cement is a complex thermodynamic system where a number of heterogeneous compounds interact with each other to form cement hydrates. Superabsorbent polymers (SAP) can be added to cement systems with many different reasons, so it is relevant that the basic knowledge of this new compound on the development of hydration is well understood. This paper reports basic research on thermal analysis of cement pastes with SAP—a suspension-polymerized poly acrylic acid–acrylamide copolymer. Several parameters were analysed: the concentration of SAP, the effect of particle size distribution and their influence on the hydration process with focus on ordinary Portland cement. The methodology included thermogravimetric analysis and differential scanning calorimetry. Combined water method was employed at different thermodynamic conditions, so the energy of activation in the different systems can be accessed. The introduction of SAP in cement-based materials significantly affects the chemical balance of ordinary Portland cement. The effect is not only in terms of the amount of hydrates, but also the type of hydrates being generated, thermodynamically favourable to precipitation of calcium hydroxide. This paper provides information relevant to hydration modelling and comprehension of cementitious materials when internal curing is active.     

The evolution of properties of recycled poly(ethylene terephthalate) as function of chain extenders,the extrusion cycle and heat treatment

Poly(ethylene terephthalate) (PET) is the most widely used plastic in beverages packaging. It is also the most recycled plastic in the world. It is estimated that 6 million tons of PET are recycled (rPET) each year worldwide. Recycling of this material by melt processing has been the subject of many studies, in order to limit the degradation processes that lead to a significant decrease in the molecular weight (viscosity). Two key points are highlighted: The former is the presence of impurities like adhesive, glue and Poly Vinyl Chloride etc. The latter is the presence of water. These were therefore the main factors of the degradation of rPET. The impurities can be eliminated by a selective recovery and the moisture by a suitable drying combined with the addition of chain extenders namely Caprolactam (CAP) and/or Trimellitic anhydride (TMA). This combination has proved to be very promising since extruded mixtures (rPET/TMA or CAP) have quite acceptable rheological properties especially in terms of intrinsic viscosity, dynamic viscosity and melt flow index (MFI) at low concentration of chain extender. Rheological and FTIR analysis showed that the degradation of rPET becomes more significant from the second extrusion cycle. Finally, DSC analysis showed that T _g were not affected by extrusion cycle number; However, cold crystallization temperature T _cc2 were significantly affected by heat treatment. The DSC analysis showed also that from the 2nd extrusion cycle, a conversion of heating crystallization temperature (T _c) which appeared during the first heating (1st scan) to a melting temperature (T _m1) that appeared during the second heating (3rd scan) occurred due to the change of the decomposition mechanism environment (from oxygen environment to that of nitrogen).     

Solute-solvent interactions in acid-base dissociation: nine protonated nitrogen bases in water-DMSO solvents

A titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction has been used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO). The mole fraction of DMSO in the mixed solvents was 0.2, 0.4, 0.6, and 0.8. The cell was calibrated with HCl (molality=0.01 mole-kg^?1) in the mixed solvents, and the ionic strength and chloride molality remained substantially unchanged during the titration with added base. This method minimizes the errors resulting from the formation of AgCl ₂ ^? in the media rich in DMSO. The pK _a of all the protonated bases passes through a minimum at a solvent composition close to that at which H₂O-DMSO mixtures display a maximum solvent structure. The results are discussed in terms of the preferential solvation of ions by the two types of solvent molecules. They are consistent with the hypothesis that increased solvent structure is accompanied by increased desolvation of the cation acids.     

Protein structure prediction using a combination of sequence homology and global energy minimization I. Global energy minimization of surface loops

A procedure has been developed for global energy minimization of surface loops of proteins in the presence of a fixed core. The ECEPP potential function has been modified to allow more accurate representations of hydrogen bond interactions and intrinsic torsional energies. A computationally efficient representation of hydration free energy has been introduced. A local minimization procedure has been developed that uses a cutoff distance, minimization with respect to subsets of degrees of freedom, analytical second derivatives, and distance constraints between rigid segments to achieve efficiency in applications to surface loops. Efficient procedures have been developed for deforming segments of the initial backbone structure and for removing overlaps. Global energy minimization of a surface loop is accomplished by generating a sequence (or a trajectory) of local minima, the component steps of which are generated by searching collections of local minima obtained by deforming seven-residue segments of the surface loop. The search at each component step consists of the following calculations: (1) A large collection of backbone structures is generated by deforming a seven-residue segment of the initial backbone structure. (2) A collection of low-energy backbone structures is generated by applying local energy minimization to the resulting collection of backbone structures (interactions involving side chains that will be searched in this component step are not included in the energy). (3) One low-energy side-chain structure is generated for each of the resulting low-energy backbone structures. (4) A collection of low-energy local minima is generated by applying local energy minimization to the resulting collection of structures. (5) The local minimum with the lowest energy is retained as the next point of the trajectory. Applications of our global search procedure to surface segments of bovine pancreatic trypsin inhibitor (BPTI) and bovine trypsin suggest that component-step searches are reasonably complete. The computational efficiency of component-step searches is such that trajectories consisting of about 10 component steps are feasible using an FPS-5200 array processor. Our procedure for global energy minimization of surface loops is being used to identify and correct problems with the potential function and to calculate protein structure using a combination of sequence homology and global energy minimization.     

Searching and optimizing structure ensembles for complex flexible sugars

NMR restrictions are suitable to specify the geometry of a molecule when a single well-defined global free energy minimum exists that is significantly lower than other local minima. Carbohydrates are quite flexible, and therefore, NMR observables do not always correlate with a single conformer but instead with an ensemble of low free energy conformers that can be accessed by thermal fluctuations. In this communication, we describe a novel procedure to identify and weight the contribution to the ensemble of local minima conformers based on comparison to residual dipolar couplings (RDCs) or other NMR observables, such as scalar couplings. A genetic algorithm is implemented to globally minimize the R factor comparing calculated RDCs to experiment. This is done by optimizing the weights of different conformers derived from the exhaustive local minima conformational search program, fast sugar structure prediction software (FSPS). We apply this framework to six human milk sugars, LND-1, LNF-1, LNF-2, LNF-3, LNnT, and LNT, and are able to determine corresponding population weights for the ensemble of conformers. Interestingly, our results indicate that in all cases the RDCs can be well represented by only a few most important conformers. This confirms that several, but not all of the glycosidic linkages in histo-blood group "epitopes" are quite rigid.     

Preparation,thermal property,and thermal stability of microencapsulated n-octadecane with poly(stearyl methacrylate) as shell

This study focused on preparation and thermal properties of poly(stearyl methacrylate) shell (PSMA) microcapsules containing n-octadecane as a phase change material (PCM). Pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) were employed as crosslinking agents. The surface morphologies, particle sizes, and distributions of the microencapsulated phase change material (microPCM) were studied by scanning electron microscopy. The thermal properties, thermal reliabilities, and thermal stabilities of the microPCMs were investigated by differential scanning calorimetry and thermal gravimetric analysis. The microPCM with DVB exhibits higher phase change enthalpies of melting (87.9 J g^?1) and crystallization (94.8 J g^?1) and a greater thermal stability in comparison with the microPCM with PETA. The phase change temperatures and enthalpies of the microPCMs varied little after thermal cycles. Thermal images showed that the gypsum board with PSMA/n-octadecane microPCM possessed temperature-regulated property. Therefore, microencapsulated n-octadecane with PSMA as shell has good thermal energy storage and thermal regulation potential.     

Thermodynamic properties of aqueous solutions of ammonium Nitrate salts

We present Differential Scanning Calorimetry (DSC) results on Hydroxyl Ammonium Nitrate (HAN) solutions and Triethanol Ammonium Nitrate (TEAN) solutions with varying concentrations. These results are used to generate phase diagrams of these solutions. The results of the melting points of these liquids are compared with the theoretical calculations of the depression of melting points. The melting temperatures of the HAN solutions at some specified concentration range are predicted rather well using the two electrolyte assumption. The phase diagram of the TEAN solutions explains an instability with respect to phase separation of this liquid.     

TG-FTIR kinetic study of the thermal cleaning of wood laminated flooring waste

The enhancement of wood waste is a promising solution for the production of energy from renewable resources. Nevertheless, wood waste often needs a preliminary treatment step to remove pollutants present in the material. The thermal cleaning of wood laminated flooring (WLF) waste is studied through thermogravimetric and FTIR analyses. As a first step, it has been shown, through non iso-thermal tests, that degradation temperature ranges for wood and additives (aminoplast resins) are different, making it possible to proceed to a thermal cleaning through a low temperature pyrolysis. It has also been highlighted that chemical linkages between the different components of WLF waste influence their own thermal behaviour making it difficult to predict the thermal behaviour of the whole material. Fourier transform infra-red spectrometry analyses reveal that NH₃ and HNCO are the main nitrogen-containing gases produced during pyrolysis, which highlights the pyrolysis efficiency in terms of nitrogen (i.e., resin) removing. Lastly, thermal degradation of wood and WLF has been modelled to provide information for reactor designing.     

Degradation of nitric acid-trbeated bulk polyethylene

LDPE samples with differing branching content were treated with fuming nitric acid for times up to 180 h at 60°C. The samples were examined by differential scanning calorimetry and small angle X-ray diffraction. While the crystal thickness derived from the X-ray long period remains practically constant throughout treatment timet, a conspicuous sharpening and shifting of the melting curves to higher temperatures witht is observed. It is suggested that the shift in melting peak is caused by the contribution of the dicarboxylic groups attached to the crystal surface after treatment. It is further shown that the shift depends inversely on the crystal thickness. The comparison of melting points for long time nitric acid treated PE samples with data from dicarboxylic acids has permitted the derivation of an expression for the melting temperature of longer molecular diacids.     

Differential scanning calorimetric analysis of irradiated polytetrafluoroethylene films

Crystalline content of polytetrafluoroethylene (PTFE) can be substantially increased by electron beam irradiation. These changes as a function of radiation dose were examined in PTFE films by differential scanning calorimetry (DSC). Surprisingly small radiation doses (<0.002 Mrad) were found to cause a, fairly substantial increase (25%) in their heat of fusion. Variations in the heat of fusion and the peak melting temperature of PTFE films with radiation dose, in the range of 0.0017 to 16 Mrad, are examined.     

Modelling of catalytic hydrocracking and fractionation of refinery vacuum residue

The main objective of this work was to create a kinetic model of refinery vacuum residue hydrocracking and to monitor the impact of the operating conditions on the product yields. Data and yield measurements were gathered from a residual hydrocracking unit (RHC). Reaction temperature ranged from 401°C to 412°C at the pressure of 18–20 MPa. A simplified kinetic yield model was applied; where the feed and each product fraction are represented by one lump (reactant or product of cracking) represented by the number of pseudo-components. The product fractions were determined by fractional distillation of the output mixture from the reactor. The kinetic model includes eight reaction steps and the following six fractions: vacuum residue, vacuum distillate, gas oil, kerosene, naphtha, and gas. In addition, a model for hydrodesulphurisation has been proposed. The average relative deviation between model and experimental yields was 5.36 %, and that for the sulphur conversion model was 1.04 %. An Excel file with the kinetic model was implemented in the Aspen Plus program using a user-defined model of the reactor. This model allows to input/output data between the Aspen Plus and Excel programs. The Excel subroutine calculates the reaction kinetics of cracking from the set temperature and residence time, and distributes the products into 30 pseudo-components created in the Aspen Plus program. The remaining part of the RHC unit was simulated in the Aspen Plus environment. The effects of the reaction conditions such as temperature and residence time on the conversion of the feed and on the distillation curves of the output mixture from the reactor were investigated. The model was verified by comparison of the distillation curves of simulated and real products.