The effect of hybrid nanoparticle additives on epoxy‐nanocomposite behavior and morphology

Amine modified polyhedral oligomeric silsesquioxane (POSS‐NH₂) was used to modify sodium montmorillonite (MMT) nanoclays for improved dispersion in epoxy resin. The dispersion of the clay particles was inspected using scanning electron microscopy, energy dispersive spectroscopy (EDS) and X‐Ray diffraction and the thermal properties compared using differential scanning calorimetry (DSC) and thermogravametric analysis. The introduction of the amine‐POSS was found to have a positive effect on the dispersion of the MMT clays and prevented agglomeration. The absence of clay agglomerates lead to an increase in glass transition temperature (T_g) from 44°C in the samples with the untreated clay up to 54°C in the samples with 10% additional POSS‐NH₂. The addition of POSS‐NH₂ initial increase of the weight loss (T_{d 5%}) but slowed down the rate of degradation due to the formation of an inert silica layer and eventually leading to an increased charyield. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The kinetics of solution copolymerization of vinyl chloroacetate with vinyl acetate in a CSTR

The kinetics of isothermal, solution copolymerization of vinyl chloroacetate (VCLAC) with vinyl acetate (VAC) in methyl isobutyl ketone (MIBK) has been investigated using a continuous flow stirred-tank reactor (CSTR). The initiator used was 2,2′-azobis 2,4-dimethyl valeronitrile (ADVN). Polymerizations were carried out to moderately high conversions, necessitating the use of a modified parameter estimation method to determine the reactivity ratios. The copolymer composition conforms to terminal model kinetics. The values obtained for r₁ and r₂ are 1.18 and 0.80, respectively, with VCLAC as M₁ and VAC as M₂. Both values are close to unity indicating random copolymerization. The cross termination factor ? strongly depends on the composition of the comonomer feed ratio, implying that the chain-termination step is possibly diffusion controlled. The variation of ? could also be caused by chain transfer to the solvent retarding the reaction rate. Such a possibility is consistent with the observed reduction in the molecular weight of the copolymer in the presence of the solvent. The approach to steady-state in the reactor was characterized. It was not possible to obtain good agreement between experiment and simulation with a single value of the ? factor.     

Photoinitiated polymerization of 1-vinylimidazole

The polymerization of 1-vinylimidazole differs from that of 1-vinyl-2-methylimidazole in that degradative chain addition to the monomer is an important factor, as previously indicated by Bamford and Schofield. The consequence of this is a dependence of rate on monomer concentration, which starts with the first power but levels off to a constant rate or even decreases slightly as the initial monomer concentration rises to 1–4 mol/L. Thus, the mechanism proposed by Bamford and Schofield appears to be confirmed. Initiator dependence of rate is best correlated by using the light absorbed by the initiator rather than the initiator concentration as the independent variable. The 0.72 power dependence found may be higher than the expected 0.5 power because the rates were measured at a monomer concentration (0.25 mol/L) just beyond the linear region. Low values of activation energy are expected, since photoinitiation rate is independent of temperature. The measured value reflects only the propagation and termination steps. Even then, the value found of 1.5 kcal/mol is low compared to the value of 3.9 kcal/mol for 1-vinyl-2-methylimidazole.     

Nucleation and growth modes deduced from particle density distributions: Nanocrystallization of fcc Al in amorphous Al85Ni8Y5Co2

A general model to simulate the particle density distribution of a product phase upon phase transformation has been developed in a modular way. In particular, the influence of different nucleation and growth mechanisms known from solid-state phase transformations on the shape of the product phase particle density distribution has been investigated. The model has been fitted to experimental particle density distributions of nanoparticles of fcc Al developing in amorphous Al₈₅Ni₈Y₅Co₂ upon annealing for different times (1 minute to 2 hours) at various temperatures (473 to 508 K). Transient nucleation at a limited number of favored nucleation sites in combination with a two-stage growth mechanism (interface-controlled growth in the beginning and volume diffusion-controlled growth in the subsequent growth stage) very well describes the nanocrystallization process of amorphous Al₈₅Ni₈Y₅Co₂.     

The oxidative dehydrodimerization of propylene over BiSn oxide catalysts: III. Reduction and temperature-programmed reoxidation of the catalyst

A bismuth-tin oxide catalyst, which is active for the oxidative dehydrodimerization of propylene, was studied with the objective of characterizing its redox properties. The redox properties were investigated by kinetic methods and temperature-programmed reoxidation. The initial rate of reduction of the catalyst exhibited a first-order dependence on propylene partial pressure and an activation energy of 22 kcal/mol. The results of the temperature-programmed reoxidation investigation suggested a low-temperature reoxidation region and a high-temperature reoxidation region. The activation energy for the low-temperature reoxidation was 23 kcal/mol; the activation energy for the high-temperature reoxidation was 45 kcal/mol. Additional information regarding the physicochemical changes which occur in the catalyst in the two temperature regions was obtained from an examination of the catalyst by Auger and ESCA. The results obtained from these investigations suggested that the tin cations are more resistent to reduction than the bismuth cations. In addition, the low-temperature reoxidation appears to be associated with the transformation of Sn⁰ to Sn⁴⁺ and Bi⁰ to possibly an intermediate oxidation state. The high-temperature reoxidation appears to be associated with the full reoxidation of Bi to Bi³⁺. The redox properties and the physicochemical changes also correlated with the mechanism suggested for the oxidative dehydrodimerization of propylene in the earlier studies.     

An Exploratory Look at Students' Experiences of Problematic Peers in Academic Professional Psychology Programs.

This exploratory survey investigated the issue of problematic students/trainees from the perspective of master's and doctoral students in clinical and counseling psychology programs. Findings suggest that students (a) were aware of problematic trainees in their programs; (b) believed faculty were primarily responsible for handling problematic peers, though students were unclear about procedures for handling this issue; (c) expressed greatest concerns about issues involving peers' interpersonal functioning; and (d) responded by gossiping or consulting with other peers, withdrawing, and, less often, confronting a problem peer. Problematic peers impacted respondents' own functioning, relationships with peers, and perceptions of faculty, and they disrupted the learning environment. Study implications and limitations are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Small punch creep in Fe28Al3Cr0.02Ce alloy

Small punch testing of Fe₃Al-based intermetallic alloy with Cr, Mn and Ce additions was performed in temperature range 773–873 K. It is shown that the testing procedure enables to study the creep properties of the alloy. The time dependence of the central deflection resembles creep curves observed in conventional uniaxial creep testing and the minimum deflection rate can be determined. Similarly as in conventional creep tests, the deflection process is then analyzed in terms of the activation energy and force exponent. In accordance with the phase structure of the alloy, two distinct areas can be observed. In the B2 range, the activation energy equals 181 kJ/mol; the force exponent is about 4.6. In the DO₃ range, the activation energy equals 82 kJ/mol and the stress exponent is about 44. The transformation temperature DO₃B2 is close to 812 K. The technique can be used for an estimation of creep resistance.