Pyrene was inserted into a low-density polyethylene matrix. Fluorescence spectra as a function of temperature and the differential scanning calorimetry (DSC) trace were recorded simultaneously. Along with the usual vibronic bands, a low-intensity band at 365 nm appears at higher energies with respect to the 0−0 transition in the pyrene fluorescence spectra. The fluorescence intensity of this small band increased with temperature, and an isoemissive point was observed to occur at 368 nm.This emission was interpreted as arising from pyrene molecules located in the outer rigid interfacial region of polymer crystallites. Its temperature-dependent fluorescence was interpreted in terms of electron−phonon coupling; two phonons which coincide with fundamental vibrations of polyethylene were necessary to fit experimental data. Coupling with a high-energy phonon was possible at low temperature, whereas, above the β relaxation temperature, phonon coupling occurs with a lowerenergy phonon. The α relaxation was detected as a maximum in fluorescence intensity since above its characteristic temperature, nonradiative processes begin to operate. l. IntroductionLuminescent techniques have long been employed in biological systems. 1 However, only recently have these techniques begun to be considered as customary tools in synthetic polymer research. 2 , 3 The main benefits of using molecular fluorescent probes and labels are the multiple interactions that may occur between excited states and their environment. Using an adequate probe selection and insertion procedure, different research topics of current interest can be approached: polymer miscibility, 4 conformational dynamics in solution,S· 7 diffusion in polymers, 8 surface characterization,9 poly mer relaxation processes, 10,11 and monitoring of polym erization reactions. 12 · 13 Another important experimen tal advantage is that fluorescent probes can be incor porated either intrinsically or extrinsically with very low concentration and fluorescence can be detected with very high sensitivity.Secondary relaxation processes of polyethylene (PE}, although extensively studied, are not fully understood because of the morpholo i.\ ical and microstructural com plexity of this polymer. 1 , ts Using anthracene lumines cence, 1 6 one of the authors observed that the change of fluorescence intensity with temperature parallels the three main relaxations reported for polyethylene. Since this molecular probe was not located inside the crystal line region, fluorescent intensity changes were inter preted as due to relaxations in the amorphous bulk polymer and at the crystallite interfaces. In fact, it is currently thought that the interfacial crystalline struc ture is coupled with the motion within the crystallite interior. 14 Location of fluorescence probes at the crys tallite interfaces may prove to be a powerful tool for studying such kind of coupled crystallite and interfacial relaxation processes. In addition, because of the dif ferent time and length scales in which thermal, dynamic mech...
SYNOPSISGlass fibers have been treated with y-aminopropyl-triethoxysilane (APES) through different silanizating procedures, which include APES aqueous solutions and APES vapor adsorption.Transmission Fourier transform I R (FTIR) measurements have been performed on the silanized samples to characterize the silanization reaction. Dansyl-sulfonamide conjugates have then been formed by reaction of dansyl chloride in dimethylformamide solution with the amine functionality's immobilized on the glass fiber surface. Steady-state and timeresolved fluorescence measurements have been performed on dansylated samples. A dependence of the fluorescence intensity and the wavelength of the maximum emission on the silanization procedure has been observed. Good fits of the fluorescence decays of dansyl labels are found when biexponential functions are used for deconvolution, whereas the decay of dansylamides in fluid solution is single exponential. A two-state model for the solid solvent relaxation seems t o apply for this samples. Several surface structural changes produced by the different silanization methods have been proposed. FTIR results support the conclusions drawn from fluorescence measurements. C3 1996 .John Wiley 6; Sons, Inc.
Commercial glass fibers have been subjected to different activation treatments under neutral and acidic conditions to achieve different coating degrees when silanized with -y-aminopropyltriethoxisi-lane (APES). A fluorescent sulfonamide (PSA) was formed between the amine residue and a fluorescent probe, pyrenesulfonyl chloride (PSC). Reflectance UVVis spectra of the pyrene-doped fibres show that pyrene is present in the form of preassociated dimers when the coating degree is low. Emission and excitation fluorescence spectra revea! the existence of a charge transfer ground-state complex with exciplex emission at 460-515 nm and absorption red-shifted with respect to the S0 � SI transition. Lifetime measurements yield three lifetimes, which are assigned to dimer, exciplex, and monomer emission. From the photophysical data it is concluded that the fibers with the highest silane content have an open structure with the highest fraction of isolated fluorescent moieties.
Glass fibers have been silanized with y-aminopropyltriethoxysilane. 1-pyrenesulphonyl chloride (PSC) has been grafted onto the fibers via adduct formation with the amine functionality. Absorption spectra from SPC stock solutions shows aggregation. Emission spectra from the fibers also reveal aggregation of the cromophore at extremely low concentration (10-9 mol/g).
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