In situ real-time monitoring of epoxy/amine kinetics by remote near infrared spectroscopy

An experimental set-up for in situ real-time monitoring of chemical reactions by remote fiber optic near-infrared spectroscopy was assembled in our laboratory and is described in this communication. A series of epoxy/amine formulations, nonpolymer-forming, and polymerforming alike, were prepared and their reaction kinetics investigated. Accurate and reproducible spectra were generated, the characteristic near-infrared peaks assigned, and the reaction kinetics evaluated by monitoring the rates of disappearance and/or appearance of the characteristic peaks. The effect of the chemical structure and functionality of the components were pointed out and a method suggested to correlate the spectral information with the chemophysical changes in multifunctional formulations.     

Generating equations approach for quadratic matrix equations

We show how Van Loan's method for annulling the (2,1) block of skew‐Hamiltonian matrices by symplectic‐orthogonal similarity transformation generalizes to general matrices and provides a numerical algorithm for solving the general quadratic matrix equation: For skew‐Hamiltonian matrices we find their canonical form under a similarity transformation and find the class of all symplectic‐orthogonal similarity transformations for annulling the (2,1) block and simultaneously bringing the (1,1) block to Hessenberg form. We present a structure‐preserving algorithm for the solution of continuous‐time algebraic Riccati equation. Unlike other methods in the literature, the final transformed Hamiltonian matrix is not in Hamiltonian–Schur form. Three applications are presented: (a) for a special system of partial differential equations of second order for a single unknown function, we obtain the matrix of partial derivatives of second order of the unknown function by only algebraic operations and differentiation of functions; (b) for a similar transformation of a complex matrix into a symmetric (and three‐diagonal) one by applying only finite algebraic transformations; and (c) for finite‐step reduction of the eigenvalues–eigenvectors problem of a Hermitian matrix to the eigenvalues– eigenvectors problem of a real symmetric matrix of the same dimension. Copyright © 1999 John Wiley & Sons, Ltd.     

Impedance spectroscopy of reactive polymers. 4. An improved experimental procedure for measurement of effective resistivity

Impedance spectroscopy of reactive systems, polymer-forming and non-polymer-forming alike, has been under active investigation in our laboratory for several years. In this article we describe an improved experimental procedure for the determination of fundamental dielectric properties during reaction. A series of experimental steps was established and is recommended in order to generate reproducible and reliable results. © 1996 John Wiley & Sons, Inc.     

The thermal susceptibility of poly(chloroethyl methacrylates)

The non-oxidative thermal degradation kinetics and mechanism of poly(2-monochloro, 2, 2-dichloro and 2, 2, 2, -trichloroethyl methacrylates) were studied. The influence of the antioxidant IRGA-NOX 1010 on the thermal degradation of the monochloroethyl derivative was also investigated. Initial hydrolysis data on the major degradation products, the corresponding monomers, were obtained.     

Reformulating the permselectivity-conductivity tradeoff relation in ion-exchange membranes

Polymer membranes used in separation applications exhibit a tradeoff between permeability and selectivity. That is, membranes that are highly permeable tend to have low selectivity and vice versa. For ion-exchange membranes used in applications such as electrodialysis and reverse electrodialysis, this tradeoff is expressed in terms of membrane permselectivity (i.e., ability to selectively permeate counter-ions over co-ions) and ionic conductivity (i.e., ability to transport ions in the presence of an electric field). The use of membrane permselectivity and ionic conductivity to illustrate a tradeoff between counter-ion throughput and counter-ion/co-ion selectivity in ion-exchange membranes complicates the analysis since permselectivity depends on the properties of the external solution and ionic conductivity depends on the transport of all mobile ions within a membrane. Furthermore, the use of these parameters restricts the analysis to ion-exchange membranes used in applications in which counter-ion/co-ion selectivity is required. In this study, the permselectivity-conductivity tradeoff relation for ion-exchange membranes is reformulated in terms of ion concentrations and diffusion coefficients in the membrane. The reformulated framework enables a direct comparison between counter-ion throughput and counter-ion/co-ion selectivity and is general. The generalizability of the reformulated tradeoff relation is demonstrated for cation-exchange membranes used in vanadium redox flow batteries.     

Two compartmental fractional derivative model with fractional derivatives of different order

This study presents a new two compartmental model that contains fractional derivatives of different order. The model is so formulated that the mass balance is preserved. In this way we give an answer on a claim that such a model is not possible. The generalization that includes nonlinear terms and fractional order dynamics between compartments is also discussed. We derived a physically correct two compartmental system (i.e., the one preserving the mass balance) by the use of the Taylor expansion formula. Moreover, we derived in the Appendix such a system preserving the mass balance without the use of the Taylor formula but by the use of mass balance for systems with equal order fractional derivatives.     

Dimensions of prevalent continuous functions

Let K be a compact subset of ${\mathbb{R}^{d}}$ and write C(K) for the family of continuous functions on K. In this paper we study different fractal and multifractal dimensions of functions in C(K) that are generic in the sense of prevalence. We first prove a number of general results, namely, for arbitrary ??dimension?? functions ${\Delta:C(K) \to \mathbb{R}}$ satisfying various natural scaling conditions, we obtain formulas for the ??dimension?? ??(f) of a prevalent function f in C(K); this is the contents of Theorems 1.1?C1.3. By applying Theorems 1.1?C1.3 to appropriate choices of ?? we obtain the following results: we compute the (lower and upper) local dimension of a prevalent function f in C(K); we compute the (lower or upper) H?lder exponent at a point x of a prevalent function f in C(K); finally, we compute the (lower or upper) Renyi dimensions of a prevalent function f in C(K). Perhaps surprisingly, in many cases our results are very different from the corresponding results for continuous functions that are generic in the sense of Baire category.     

Studies of magnetic resonance phenomena in polymers. I. The effects of free volume and segmental mobility on the motion of nitroxide spin probes and labels in poly(methyl methacrylate)

Thin films of spin-probed and spin-labeled poly(methyl methacrylate) (PMMA) have been examined by electron spin resonance (ESR) at X-band frequency (9.2 GH_z) and at various temperatures. Direct spectral evidence is presented to indicate that the composite ESR spectra observed in a certain temperature range originate from two states of distinctly different mobility, one with slow motions corresponding to a glassy state and the other with fast motions corresponding to a liquidlike state. The coexistence of these two states at temperatures considerably below the glass transition temperature can be explained as a result of the effect of free volume in a solid polymeric glass.     

Quenching of semiconductor quantum dot photoluminescence by a pi-conjugated polymer

In this communication we discuss the possibility of hole transfer between a photoexcited semiconductor quantum dot and a pi-conjugated polymer. This charge-transfer event will be investigated (exploited) on the basis of its implication toward a solar energy conversion scheme. Experimentally, we show that the steady-state photoluminescence (PL) of a solution of InP quantum dots is quenched by the introduction of solvated poly(3-hexylthiophene). Time-resolved PL experiments on these solutions are also presented. It was observed that the PL transients did not significantly change upon the addition of the conductive polymer. These new results indicate that said PL quenching is static in nature. This suggests that in solution, the quantum dot and the polymer exhibit a strong intermolecular interaction. As the two species encounter each other through diffusion, the polymer quenches the quantum dot photoluminescence without altering the population's PL lifetime. This new evidence suggests that the polymer and the quantum dot form a relatively stable complex.