Alignment of nanoparticles in polymer matrices

This paper briefly summarizes the state of the art in the field of designing composites containing semiconductor nanoparticles distributed in a polymer matrix. Special attention is focused on (i) nanocomposites based on block copolymers and (ii) LC polymer matrices capable of controlling the localization and alignment of nanoparticles.     

Imaging fingerprinting of excitation emission matrices

The spectral fingerprinting of the excitation emission matrix (EEM) of fluorescent substances is demonstrated using polychromatic light sources and tri-chromatic image detectors. A model of the measured fingerprints explaining their features and classification performance, based on the polychromatic excitation of the indicators is proposed.Substantial amount of spectral information is retained in the fingerprints as corroborated by multivariate analysis and experimental conditions that favor such situation are identified.In average, for five different substances, the model shows a fitting goodness measured by the Pearson's r coefficient and the root mean square deviation of 0.8541 and 0.0247 respectively, while principal component classification patterns satisfactorily compare with the EEM spectroscopy classification and respectively explain 96% and 93% of the information in the fist two principal components.The measurements can be performed using regular computer screens as illumination and web cameras as detectors, which constitute ubiquitous and affordable platforms compatible with distributed evaluations, in contrast to regular instrumentation for EEM measurements.     

Elastification of heat-resistant epoxy polymer matrices

The behavior of fracture toughness parameters in comparison with other physicomechanical parameters of failure was examined with the aim to evaluate the efficiency of modification (elastification) of heat-resistant binders, with four epoxy-amine compounds taken as examples.     

Amplified emission of phthalocyanine isolated in cryogenic matrices

Laser induced fluorescence spectroscopy of free-base (H(2)Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices reveals a quite unexpected phenomenon with a moderate increase in the laser intensity. In all matrices except Xe, a huge increase occurs in the intensity of an emission band near 755 nm when pumping the S(1) <-- S(0) transition. The band involves a vibrational mode of the ground state, located at 1550 and 1525 cm(-1) for H(2)Pc and ZnPc, respectively. Many of the characteristics of amplified emission (AE) are exhibited by this vibronic transition. Excitation scans recorded for the AE band yield greatly enhanced site selectivity compared to what is obtained in normal fluorescence excitation scans.     

Photochromism of diarylethene single molecules in polymer matrices

Robust fluorescent photoswitching molecules, having perylene bisimide as the fluorescent unit and diarylethene as the switching unit, were prepared, and their photochromic reactions were measured at the single-molecule level in various polymer matrices. The histograms of the fluorescent on and off times were found to deviate from normal exponential distribution and showed a peak when the molecules are embedded in rigid polymer matrices, such as Zeonex or poly(methyl methacrylate) (PMMA). In soft polymer matrices, such as poly(n-buthyl methacrylate) (PnBMA), exponential distribution was observed for the on and off times. The abnormal distribution suggests that the quantum yields of the photoreactions are not constant and the molecules undergo the reactions after absorbing a certain number of photons. A multilocal minima model was proposed to explain the environmental effect.     

Internal rotation in molecules dispersed in polymer matrices

Studies of certain polar or photochromic molecules dispersed in polymer matrices show that internal motion may be profoundly affected by the matrix. Thus, in polystyrene, dielectric studies of relatively small molecules show that the inversion motion of the central ring of xanthene becomes possible at temperatures below the recognized β and glass transition temperatures of the polymer. On the other hand, movement of the central oxazole ring in 2,5-diphenyl oxazole becomes marked at temperatures corresponding to the onset of polymer β motion, but dipole reorientation of diphenyl ether is not appreciable below the main glass transition.Considering a slightly larger molecule, the bleaching rate of the coloured isomer of 6′-nitro-1,3,3, trimethylindolinobenzopyrylospiran also depends on the nature of the polymer matrix. The observations are best explained in terms of a matrix-controlled internal rotation in which the photochromic molecules exist in a distribution of environments in the glassy matrix.     

Kinetic features of photolysis of phenols in polymer matrices

The low quantum yields of photoconversion of phenols and the low probability of formation of phenoxy radicals in solid polymers indicate significant cage effects. An increase in the degree of shielding of the hydroxyl group results in an increase, while incorporation of electron-acceptor substituants in the p position results in a decrease in the reactivity of the phenols in the polymers. The increase in the quantum yields of photoconversion and the decrease in the quantum yields of the fluorescence of phenols with a decrease in the wavelength are due to the occurrence of a reaction and induced radiationless deactivation with the participation of higher excited states.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 18–23, January, 1990.We would like to thank G. A. Nikiforov for providing phenols (I)–(V).     

Electrochromism of indolinobenzospirans dissolved in rigid amorphous polymer matrices

The effect of a static electric field on the position of absorption bands of colored stereoisomers of two photochromic compounds of the indolinobenzospiropiran group dissolved in matrices of poly(methyl methacrylate), poly(n-butyl methacrylate), polystyrene, and polycarbonate at room temperature was studied. In the case of matrices with the polymethacrylates the effects observed show that applied electric field produces a shift of thermal equilibrium towards stablization of stereoisomers of larger dipole moment. On the basis of kinetic measurements of attainment of thermal equilibrium on switching the electric field off, the rate constants of their interconversion have been determined. In the case of matrices with polystyrene and polycarbonate, a small red shift only was observed.     

Solid-state NMR studies of pharmaceutical solids in polymer matrices

Biodegradable drug-delivery systems can be formulated to release drug for hours to years and have been used for the controlled release of medications in animals and humans. An important consideration in developing a drug-delivery matrix is knowledge of the long-term stability of the form of the drug and matrix after formulation and any changes that might occur to the drug throughout the delivery process. Solid-state NMR spectroscopy is an effective technique for studying the state of both the drug and the matrix. Two systems that have been studied using solid-state NMR spectroscopy are presented. The first system studied involved bupivacaine, a local anesthetic compound, which was incorporated into microspheres composed of tristearin and encapsulated using a solid protein matrix. Solid-state ¹³C NMR spectroscopy was used to investigate the solid forms of bupivacaine in their bulk form or as incorporated into the tristearin/protein matrix. Bupivacaine free base and bupivacaine-HCl have very different solid-state NMR spectra, indicating that the molecules of these compounds pack in different crystal forms. In the tristearin matrix, the drug form could be determined at levels as low as 1:100 (w/w), and the form of bupivacaine was identified upon loading into the tristearin/protein matrix. In the second case, the possibility of using solid-state ¹³C NMR spectroscopy to characterize biomolecules lyophilized within polymer matrices is evaluated by studying uniformly ¹³C-labeled asparagine (Asn) in 1:250 (w/w) formulations with poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA). This work shows the capability of solid-state NMR spectroscopy to study interactions between the amino acid and the polymer matrix for synthetic peptides and peptidomimetics containing selective ¹³C labeling at the Asn residue.     

Room temperature phosphorescence as a liquid chromatographic detection method for polychlorinated naphthalenes and biphenyls in complex matrices

Quenched and sensitized room temperature phosphorescence techniques have been used for the detection of PCNs and PCBs after liquid chromatographic separation. The usefulness of these techniques to fingerprinting of commercial Aroclor and Halowax mixtures in complex matrices has been shown. The complementary nature of these detection modes yield valuable information in addition to UV detection. a signal inverter is proposed for linearization of the quenched RTPL signals. In this way linear calibration plots over more than two orders can be obtained. Detection limits are generally in the low nanogram or subnanogram concentration region. The application of RTPL detection techniques to the analysis of commercial PCN and PCB mixtures in surface water and urine is demonstrated. Pre-columns can be used to advantage for pre-concentration and clean-up of this type of samples.     

Small molecule self‐assembly in polymer matrices

Using small molecules in polymer matrices is common in applications such as (i) plasticizing polymers to modify the glass transition and mechanical properties and (ii) dispersion of photoactive or electroactive small molecules in polymer matrices in organic‐electronic devices Aggregation of these small molecules and phase separation leading to crystallization often cannot be morphologically controlled. If these are designed with self‐assembling codes such as hydrogen bonding or aromatic interactions, their phase separation behavior would be distinctly different. This review summarizes the studies on morphologies in such situations, such as (i) sub‐surface assembly in polymer matrices, (ii) controlled polymerization‐induced phase separation to create polymer blends, (iii) using the polymer to direct the assembly of small molecules in liquid crystalline devices, (iv) functionalizing a polymer with self‐assembling small molecules to cause organo‐gelation which the polymer itself would not by itself, and (v) using such systems as templates to create porous polymer structures. Organic–inorganic hybrids using polymers as templates for nanostructures and imprinted porous membranes is an emerging area. Since self‐assembly is one of the dominating area of research with respect to both small molecules, polymers as well as the combination of the two, this review summarizes the studies on the aforementioned topics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 451–478     

Singlet oxygen-triplet organic molecule annihilation fluorescence in polymer matrices

This communication reports the discovery of a molecular oxygen induced fluorescence of aromatic hydrocarbons in polymer matrices which conclusively establishes the central idea of the singlet oxygen feedback mechanism postulated by Bolton, Kenner and Khan. Admission of air to a phosphorescing sample gives rise to a burst of light with the same emission spectrum as the normal fluorescence of the organic molecule. This identifies the phenomenon as singlet oxygen-triplet organic molecule annihilation fluorescence.     

Acoustic emission of a crazing polymer

The acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment is described. Acoustic emission appears as a series of bursts which most likely correspond to the initiation and growth of crazes. The emission intensity is characterised by acoustic activity (pulse rate) measured by the ring-down technique. The average activity increases with strain. During repeated loading the acoustic activity shows a measurable intensity and significant rise only beyond the maximum strain of the former runs. This is equivalent to Kaiser's effect in metals. Acoustic emission during the creep experiment occurs in three characteristic periods. They are characterized as the relaxation, fatigue, and breakdown periods. Visual observations indicate that the relaxation period corresponds to the initiation, and the fatigue period to the growth of crazes. In the breakdown period a macroscopic crack develops and the sample fails.     

Ferromagnetic resonance spectra of nanosized metal particles in polymer matrices

Specific ways of using the radiospectroscopic technique to determine parameters of nanoparticles of metals and their oxides—such as size, mass-distribution type, polydomain character, and coercive force- and relaxation characteristics of particles in the superparamagnetic state are considered.     

Luminescence of Ln3+ lanthanide complexes in polymer matrices

The photoluminescence properties of Tb³⁺ and Eu³⁺ complexes with polymer ligands containing various kinds of complexing groups??namely, carboxyl (5?C20 mol %), pyridylquinoline (5 mol %), or pyridylnaphthyl (5 and 10 mol %) groups??in solution and block are considered. The chemical structure of a neutral comonomer (methyl methacrylate; styrene; isopropyl-, phenyl-, or benzylmethacrylamide; and N-vinylamides) in polymer ligands is varied. The intensity of photoluminescence is dependent not only on the chemical nature of a complexing group but also the chemical nature of a neutral comonomer and a spacer. Variation in the nature of a comonomer and a ligand makes it possible to prepare complexes in which a high luminescence of a low-molecular-mass complex is preserved and advantages inherent in a polymer complex are acquired. The effect of the nature of the polymer matrix (photoactive and photoinert) on the efficiency of electronic-excitation energy transfer is ascertained. The data on the photoluminescence of metal-polymer complexes that are based on polymer ligands containing vinylcarbozole units and that possess hole conductivity make it possible to regard them as materials for electroluminescence. The intensity of photoluminescence of these complexes is related to the competition of oppositely directed photophysical processes in a macromolecule: formation of excimers and migration of electronic excitation energy. An analysis of the published data and of the results of the authors shows that detailed studies of these polymer systems in solution and in matrices are needed to gain insight into the relationship between photo- and electroluminescence properties of metal-polymer complexes, because the matrix plays different roles in photoluminescence and electroluminescence (inner filter or conduction); as a consequence, the emission spectra may differ appreciably. It is shown that the efficiency of electroluminescence may be improved if the transfer of energy from the lanthanide ligand in a complex to the conducting matrix is decreased.