PubMed · 15430652
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
L G LONGSWORTH. 1950. Tests of flowing junction diffusion cells with interference methods.. https://doi.org/10.1063/1.1745641
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Effective image analysis of dynamic processes, such as diffusion and dissolution, requires precise reporting of component locations in space and time. An improved method for analyzing FTIR images is described which employs hypothesis testing in the spatial and temporal domains. Changes in the observed absorbance (over space and time) are revealed by comparison to a reference statistic, which can be tailored by choosing the size of a region of interest. This improved analysis method was used to compare the rates of diffusion of nicotine into poly(ethylene-co-vinyl acetate) film from aqueous solutions containing anionic and nonionic surfactants. Compared to a solution without surfactant, sodium dodecyl sulfate inhibited the uptake of nicotine from aqueous solution whereas Tween 40 enhanced the uptake. The nicotine diffusion rate also showed a dependence on the length of the hydrophobic segment of nonionic surfactants. These results demonstrate the roles of solubilization, wetting, and viscosity on diffusion-controlled drug release.
Concentration dependence of photoluminescence quantum yield of FMN aqueous solutions (66mM potassium phosphate buffer, pH 7.0) is investigated over the concentration range from 6.31x10(-5) M to 1.8x10(-2) M at temperatures 298.2 and 323.9K. Experimental data are compared with those obtained theoretically based on two different models of excitation energy transfer and migration in the system of FMN monomers and dimers. The first model does not take the material diffusion into account [Acta Phys. Acad. Sci. Hung. 30 (1971) 145] and the second model is based on the second-order transfer rates which are diffusion dependent [Chem. Phys. Lett. 41 (1976) 139; J. Lumin. 27 (1982) 441]. The comparison shows that the process of material diffusion cannot be neglected in the solutions studied as the relative contribution of the diffusion accelerated nonradiative energy transfer to the total drop of the quantum yield can be even higher then 70%. It is also shown, that in order to obtain a good agreement of the experimental and theoretical data it is necessary to introduce into the theory an additional channel of deactivation for the excitation energy. It is proposed that this additional channel can be partial degradation of excitation energy during its migration between the monomers.
Dynamic light scattering (DLS) has been used to measure the diffusion coefficients of 108+/-7 (+/-S.D.) and 495+/-23 nm positively charged amino latex nanospheres (ALNs) and negatively charged carboxyl latex nanospheres (CLNs) (48+/-7, 91+/-9.8 and 483+/-10 nm) in three different media, water, glycerol aqueous solutions and hydroxypropyl methylcellulose (HPMC) gels. The translational diffusion coefficients (D) of these latex spheres in water were found to be 13.00 (+/-0.12), 5.11 (+/-0.06), 0.89 (+/-0.01) microm2/s for 48, 91 and 483 nm CLN, and 3.26 (+/-0.01) and 0.88 (+/-0.03) microm2/s for 108 and 495 nm ALN, respectively. In Newtonian glycerol aqueous solutions as anticipated the diffusion could be predicted by the Stokes-Einstein relationship over a range of system viscosities. In HPMC gels the results show the deviation of the diffusion coefficient from the Stokes-Einstein equation when the viscosity of the medium is increased. In addition, there was an increase in the polydispersity index (PI) from 0.217 to 0.928 with 108 nm ALN on increasing HPMC concentrations from 0.2% to 0.8% (w/v), which implied an interaction between the positively charged nanospheres and the gel. From the D values, the "effective" or "microscopic" viscosities of the HPMC medium were calculated, and ranged from 0.899 to 0.925 mPa s.