RESUMO
A study has been conducted in order to determine presence of free volume gaps in the structure of structure of polymer hydrogel contact lenses made in phosphoryl choline technology and of the degree of defect of its structure. The study was made by means of positron annihilation lifetime spectroscopy. As a result of the conducted measurements, curves were obtained, which described numbers of counts of the acts of annihilation in the time function. The conducted studies revealed existence of three components τ(1), τ(2) and τ(3). The τ(3) component is attributed to the pick-off annihilation of o-Ps orthopositronium trapping by free volume gaps and provides information about geometrical parameters of the volumes. At the same time, the UV-vis-NIR spectrometry examination was conducted on the same samples in the spectral range 200-1,000 nm.
Assuntos
Lentes de Contato , Hidrogel de Polietilenoglicol-Dimetacrilato/química , Polímeros/química , Elétrons , Contaminação de Equipamentos , Humanos , Teste de Materiais , Espectrofotometria Ultravioleta/métodos , Espectroscopia de Luz Próxima ao Infravermelho/métodosRESUMO
For the first time we have discovered drastic photoinduced effects in the transparency for the pyrrole films. Photoinduced investigations of transparency were performed for the polypyrroles with different number of the pyrrole rings. We have established a considerable increase of the transparency from 70-75% up to 82-84% for the wavelengths of the probing lasers operating within the 530-1040 nm spectral range. The photoexcitation was performed by nanosecond pulsed polarized Nd-YAG laser generating at 1.34 microm. The phototransparent changes are completely reversible and disappear after switching off the laser treatment. The typical relaxation time for the photoinduced transparency is equal to about 10-20 micros and the changes of the transparency are strictly related with the values of state dipole moments of the polypyrroles. As a possible mechanism for explanation of the observed dependences one can consider existence of the charged trapping levels intra the forbidden energy gaps which effectively interact with the electric strength of the external polarized optical field and state dipole moments of the particular polymers.
Assuntos
Polímeros/química , Pirróis/química , Espectrofotometria/métodos , Fenômenos Químicos , Química , Desenho de Equipamento , Lasers , Luz , Modelos Químicos , Modelos Moleculares , Conformação Molecular , Neodímio/química , Fotoquímica/métodos , Teoria Quântica , Fatores de TempoRESUMO
UV-vis optical spectra of several polythiophene with number of dimers n=1, 5, 10, 15 for cis- and trans-forms were investigated. The study was done theoretically using semi-empirical AM1 (Austin Model 1) and PM3 (Parametric Method 3) methods with the appropriate molecular geometry optimization. The experimental UV-vis absorption spectra were used for verification of the both semi-empirical theoretical models. With the increasing number of dimers a red shift of the absorption edge was observed. Solvent does not play a crucial role on behavior of the absorption spectrum. A comparison of the both semi-empirical methods with the observed experimental absorption spectra is performed. Role of state dipole moments of the investigated polythiophenes in the behavior of the observed UV-vis spectra is discussed. Particular role of pi-conjugated bonds is demonstrated.