Iwona Iwaszkiewicz-Kostka

Molecular dynamics of poly(ethylene glycol)s studied by optical Kerr effect and Brillouin spectroscopy

The optical Kerr effect and Brillouin scattering study of a series of poly(ethylene glycol)s (PEGs) in the function of temperature and molecular weight (MW) have been performed. The obtained results enabled us to determine some macroscopic and microscopic parameters (such as molecular Kerr constant, hypersonic velocity, adiabatic compressibility), of the compounds investigated. The values of these parameters were found to depend strongly on both temperature and PEGs MW. Analysis of the results indicates on the presence of molecular interactions leading to formation of molecular aggregates. The increase in the MW leads to folding of PEG chains and to formation of statistical coils.

Optically induced birefringence in a series of analogous diols

Optically induced birefringence has been analysed in a series of analogous diols containing heteroatoms, such as O, N or S. The presence of a heteroatom in a diol molecule can change the arrangement of hydrogen bonding and, consequently, the arrangement of molecules. This hypothesis was confirmed by the results of our study. The measurements were performed at temperatures from 280 to 350 K. The values of the absolute and molar Kerr constants were calculated. The character and magnitude of the temperature changes of molar Kerr constant depend on the type of the heteroatom. According to the theory of the optical Kerr effect such a temperature behaviour indicates the presence of molecular interactions leading to formation of molecular aggregates. The sign of the calculated values of angular correlation factor indicates the predominant parallel arrangement of molecules in such molecular ensembles.

Optical Kerr effect study in viscous media. The series of homologous polyoxyethylenediols

Systematic measurements of optically induced birefringence in the series of homologous polyoxyethylenediols have been carried out. Macroscopic and microscopic parameters of the molecular liquids studied, such as viscosity, molecular Kerr constant and effective optical anisotropy, have been calculated. The majority of the monomers studied have been found to show an untypical increase in the Kerr constant with increasing temperature. The possible explanation of this effect has been proposed.

Rayleigh scattering study of selected polymers

The Rayleight scattering spectra of polyethyleneglycols with different average molecular weight are presented. In the study we used the compounds with average molecular weight 1500 and 2000. The temperature and concentration dependencies of the Rayleigh scattering spectra have given the possibility to determine Rayleigh parameters, also isotropy and anisotropy scattering molecular factors.

Raman scattering study of selected polymers

The Raman scattering spectra of polyethyleneglycols with different mean molecular weight have been obtained vs. concentration and temperature. The measurements were performed for compounds of mean molecular weight 1500 and 2000. On the basis of the characteristic frequency data of atomic group vibration in organic compounds, the bands observed in Raman spectra have been assigned. The temperature ranges of the phase transition and the change in the order parameters have been estimated from the temperature dependence of the phonon band parameters of the polymers studied. Moreover, the shape of the O - H band vs. polymer concentration has been examined.

Investigation of the local structure of selected dimethacrylates by Brillouin light scattering

Temperature dependence of Brillouin light scattering in selected dimethacrylates has been studied. For the compounds studied, being multifunctional monomers, the values of hypersound speed have been determined. It has been established that with increasing temperature the hypersound speed decreases for all substances studied.

Intermolecular interactions in n,n-dimethylnitramine solutions in benzene

Temperature dependence of the optical Kerr effect was studied in solutions of 1.4, 2.6, and 4.5% n,n- dimethylnitramine in benzene. The optical Kerr constant was observed to decrease with increasing temperature (from 290 to 360K). For solutions of higher concentrations, the temperature dependencies of the OKE signal indicate an increasing role of intermolecular interactions.

Influence of thermal effect on the optical Kerr effect in pulse measurements

Influence of the thermal effect on nonlinear optical phenomenon of Kerr effect was studied for two laser beams. This effect is important for subnanosecond or picosecond laser working at a high repetition ratio. Its neglect leads to an even 50% underestimation of the values measured.