Photooxidation of some metallocenes in a polymer matrix

The changes in the electronic absorption spectra (UV-Vis) of some metallocene-doped poly(methyl methacrylate) (PMMA) thin films containing chloroform molecules as impurities were studied after photoexcitation in the nitrogen atmosphere. Photoexcitations were made by monochromatic radiation (using a Xe-lamp source and a monochromator) at an interval of few nanometers in the spectral range 210-750 nm. The changes in spectra were studied as a function of photoexcitation time (duration), amount of metallocene in the film and the amount of chloroform molecules present in the film. Occurrence of photoinduced charge-transfer between some metallocenes and chloroform molecules confined in the PMMA thin films was observed, which indicated photooxidation of the metallocenes in the polymer matrix. Photoresponse in the case of ferrocene derivatives was observed to decrease with the increase in the value of para- Hammett constant for the substituent attached to the ferrocene unit and also with increasing half-wave potential for the ferrocene derivatives. Photoeffects on the metallocenes having different central metal atom were studied and it was noticed that the photoeffects on the metallocenes with "18 valence electrons", as in ferrocene and ruthenocene, favored the occurrence of photoinduced charge-transfer between the metallocene and chloroform molecules present in a PMMA film. The photooxidation of a metallocene in a PMMA thin film resulted in an enhanced photoconductivity of the polymeric film.     

Charge-transfer spectra of ferrocene in halocarbon solvents under photoexcitation

The changes in the electronic absorption spectra of ferrocene in the halocarbon solvents chloroform and carbontetrachloride have been investigated under photoexcitation in nitrogen atmosphere. Photoexcitations have been made with monochromatic light (using an Xe-source and a monochromator), at intervals of a few nanometers in the spectral range 220–750 nm. Analysing the spectra by a modified method the position of the charge-transfer-to-solvent (CTTS) band has been located for both the solvents. The position of the CTTS band in the case of carbontetrachloride solution located (320 nm) by the present study is different from the previously reported value (307 nm), while from the previous studies the position of the CTTS band in the case of the spectra of ferrocene in chloroform was not clear. From the present investigation, the changes in spectra after photoexcitation studied as a function, the concentration of ferrocene in the solution and the time (duration) of photoexcitations, have been observed to be systematic. Using the position of the new band (320 nm) for the CTTS transition in the case of carbontetrachloride, ionization potential of ferrocene has been estimated and the estimated value has shown excellent agreement with the experimental value indicating the exactness of the newly located CTTS band position.     

Non-Linear Vibration of a Travelling Beam Having an Intermediate Guide

The free and forced responses of a non-linear travelling beam having an intermediate guide have been analysed. The guide is modelled as a purely elastic constraint with no inertia. While a suitably located guide increases the natural frequencies, the friction present in the guide-beam interface tends to destabilize the system. The presence of the guide reduces the vibration level by avoiding resonance conditions. The effect of the non-linear term is very sensitive to the location of the guide if the guide stiffness is small. It is suggested that the guide is placed near the antinode of the predominantly excited mode.     

Generalized thermoviscoelastic interaction due to periodically varying heat source with three-phase-lag effect

The present paper aims at studying the thermo-visco-elastic interaction in a homogeneous, infinite Kelvin-Voigt-type viscoelastic, thermally conducting medium due to the presence of periodically varying heat sources. Three-phase-lag thermoelastic model, GN model II (TEWOED) and GN model III (TEWED) are employed to study the thermomechanical coupling, thermal and mechanical relaxation effects. In the absence of mechanical relaxations (viscous effect), the results for various generalized theories of thermoelasticity may be obtained as particular cases. The governing equations are expressed in Laplace-Fourier double transform domain and are solved in that domain. The inversion of the Fourier transform is carried out by using residual calculus, where poles of the integrand are obtained numerically in complex domain by using Laguerre’s method and the inversion of Laplace transform is done numerically using a method based on Fourier series expansion technique. The numerical estimates of the displacement, temperature and stress are obtained for a hypothetical material. A comparison of the results for different theories (three-phase-lag model, GN model II, GN model III) is presented and the effect of viscosity is also shown. In absence of viscous effect the results corresponding to GN model II and GN model III agree with the results of the existing literature.     

Large deflection of cantilever beams with geometric non-linearity: Analytical and numerical approaches

Non-linear shooting and Adomian decomposition methods have been proposed to determine the large deflection of a cantilever beam under arbitrary loading conditions. Results obtained only due to end loading are validated using elliptic integral solutions. The non-linear shooting method gives accurate numerical results while the Adomian decomposition method yields polynomial expressions for the beam configuration. With high load parameters, occurrence of multiple solutions is discussed with reference to possible buckling of the beam-column. An example of concentrated intermediate loading (cantilever beam subjected to two concentrated self-balanced moments), for which no closed form solution can be obtained, is solved using these two methods. Some of the limitations and recipes to obviate these are included. The methods will be useful toward the design of compliant mechanisms driven by smart actuators.     

Inhibition of matrix metalloproteinase-9 by "multi-prong" surface binding groups

A novel strategy of blocking the active site accessibility of MMP-9 by "multi-prong" surface binding groups is described.