Fluorescence studies of the volume phase transition of poly(acrylamide) gels with a dansyl group

Abstract

The changes in microenvironments during a pH-induced volume transition of poly(acry1amide) (PAAm) gels with a dansyl group as a fluorescent probe in an acetone/water (9111) mixed solvent have been studied by the fluorescence spectrum, anisotropy, and lifetime measurements. Irrespective of the presence or absence of fluorescence probe groups labeled on the network of PAAm gels, the gels are in the collapsed state at pH = 1.0-5.0. They show a discontinuous volume phase transition (DVPT) at pH = 5.1 and remain swollen up to pH = 9.6. The fluorescence anisotropy ratio, r, also changes at pH = 5.1 for the dansyl group, but the peak shift of the fluorescence spectra of the dansyl group takes place at pH = 3.8, i.e., before the DVPT. The fluorescence decay measurements demonstrated two emitting states for the excited dansyl group depending on pH values. The microscopic changes in hydrophobicity and mobility around polymer segments are demonstrated at pH = 3.8 by the fluorescent dansyl probe, although the macroscopic DVPT occurs at pH = 5.1.

Interfacial characterization of epoxy/silica nanocomposites measured by fluorescence

“…Decay lifetimes are shown in Table 3 at 480 nm emission wavelength along with the normalized amplitude A i and relative intensity f i (i.e., the normalized contribution of each lifetime to the total intensity in the stationary spectrum), calculated according to the following equations [37]: the f values (very close to 1), the main contribution to the stationary spectra comes from the long lifetime, which ranges between 12 and 14 ns, in good agreement with data reported for dansyl in other polar and viscous media [50,73], and its contribution increases with emission wavelength that will be presented in the following sections. The short lifetime is only important at lower wavelengths and has a constant value at around 1.7 ns.Long lifetime, s 1 ,is plotted as a function of emission wavelength for all studied systems in Fig.…”

“…If the energy of both states is similar, the emission would come from both. In fact, DNS has been extensively used for solvent polarity studies, gelation and swelling or solvation dynamics in micellar environments [49][50][51][52][53]. Dansyl has been also employed to monitor microheterogeneity in surfaces [54] and polymer networks [55], curing behavior of thermosets [56,57], and thermal transitions and conformational changes in polymers, hybrid materials and composites [58,59].…”

Deuterium isotope effects on swelling-shrinking states of polymer gels in aqueous solutions:Fluorescence study

“…Dansyl group, which is used in the present work, has been widely used as a fluorescence probe to study the microenvironment of the transitions of polymer systems, [6,[9][10][11][12][13][14][15][16][17][18][19][20][21] because dansyl group is very sensitive to the polarity of the medium. [22] It is very interesting to compare the deuterium isotope effects of the bulk state and the microenvironment on the state of the hydrogels.…”

Free-volume change in volume phase transition of polyacrylamide gel as studied by positron annihilation: Salt dependence

“…Recent investigations using such microprobes as quasielastic light-scattering, 3 small-or wideangle X-ray, 4 or neutron [5][6][7] scatterings, nuclear magnetic resonance, 8 -10 and fluorescence, 11,12 have unveiled novel images of the microscopic environments for the polymer gels. Positron an-nihilation lifetime technique, [13][14][15] which provides information in relation to the free-space holes at a molecular level, has been used for the determination of the free-volume characteristics.…”