Chlorophyll a(naturally occurring Mg porphyrene)has been entrapped in nano/porous silica gel using sol-gel method at room temperature,producing a stable composite.HR TEM observationreveals regular nanoscale[around 15-...Chlorophyll a(naturally occurring Mg porphyrene)has been entrapped in nano/porous silica gel using sol-gel method at room temperature,producing a stable composite.HR TEM observationreveals regular nanoscale[around 15-20 nm diameter]distribution of aggregated polycrystalinechlorophylla within porous silica matrix.UV-vis study also corroborates the presence of variousaggregated chlorophyll a species within the system.Low field measurement shows almost 400times enhancement of dielectric constant(1700)with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz.The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml.Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties ofthe composite can be attributed to the long-range electron delocalization[nomadic polarization]in chlorophyl a aggregates.The electric modulus(M*)formalism used in this study enabled us todistinguish and separate various relaxation processes.It is found that with increasing chlorophyll concentration D.C.relaxation time decreases exponentially at room temperature.It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due toheterogeneous distribution of chlorophyll aggregates.The low values of room temperature acti-vation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.展开更多
文摘Chlorophyll a(naturally occurring Mg porphyrene)has been entrapped in nano/porous silica gel using sol-gel method at room temperature,producing a stable composite.HR TEM observationreveals regular nanoscale[around 15-20 nm diameter]distribution of aggregated polycrystalinechlorophylla within porous silica matrix.UV-vis study also corroborates the presence of variousaggregated chlorophyll a species within the system.Low field measurement shows almost 400times enhancement of dielectric constant(1700)with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz.The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml.Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties ofthe composite can be attributed to the long-range electron delocalization[nomadic polarization]in chlorophyl a aggregates.The electric modulus(M*)formalism used in this study enabled us todistinguish and separate various relaxation processes.It is found that with increasing chlorophyll concentration D.C.relaxation time decreases exponentially at room temperature.It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due toheterogeneous distribution of chlorophyll aggregates.The low values of room temperature acti-vation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.
