Living polymers and polymer solutions: a misleading analogy

 Experimental results from colloidal suspensions of worm-like micelles are currently interpreted in terms of close analogies between this kind of systems and polymeric solutions. In particular, it was hypothesized that the viscoelastic properties of dense systems of giant flexible cylindrical micelles can be rationalized in terms of an entangled network of worm-like aggregates, very similar to a neutral random polymeric network. Such an idea is strongly supported by theoretical results that, in a mean-field appro ximation, suggests for an unlimited growth process of the micellar contour length with concentration. The mean-field theory indicates for an exponentially shaped length distribution function, with mean <L> depending on concentration, φ, in agreement with a scaling law <L>∝φ^α (α=0.5 in the simpler approach). A number of experimental results seem to be successfully interpretable within this framework. Aim of this work is to show that the agreement between theory and experiment is just an accident, being the mean-field approach, in principle, inadequate in describing systems dense enough to show a concen tration dependence of the mean micellar size. It will be unambiguously shown that there is no way to describe semi-diluted micellar solutions through a mean-field approximation and that there does not exist any scaling law of the kind <L>∝φ^α. Furthermore, it will be shown that the shape of the size distribution function is markedly different from the exponential one. The basis for a more realistic approach for the growth process of micellar aggregates is also presented and some pre liminary indications are success fully compared with experimental results. Received: 24 February 1997 Accepted: 22 April 1997     

Laser fluorescent microirradiation: Two examples of application to biology. a. Study of the functional state of chromatin; b. Study of hematoporphyrin derivative (HpD) in cells

In this paper two examples are presented of the application of laser fluorescent microirradiationto biology. The experiments, performed using a pulsed-laser microfluorometer with high spatial and temporal resolution, concern: (i) a study of the functional state of chromatin and (ii) a study of the fluorescence properties of Hematoporphyrin-derivative in tissue- and culture-cells. (i) The in situ evaluation of the functional state of chromatin has been done in chromosomes and nuclei “in toto” stained with the fluorescent probe Quinacrine Mustard. It has been found that chromatin fractions with different degree of activity, morphologically recognizable at the microscope, present fluorescence decay times markedly different, with a longer decay time for active chromatin. This result has been attributed to the stainability of DNA, which appears to be lower for active chromatin than for the inactive one. A similar result has been obtained in a preliminary experiment on cultures of human lymphocytes, after activation with Phytohemagglutinin. (ii) The fluorescent properties of Hematoporphyrin-derSvative have been studied in single cells, obtained from both normal and tumor tissues and cultures. In agreement with the results obtained with other techniques in tissues, it has been found that the tumor cells examined present an HpD uptake higher than that of the normal cells of the corresponding tissue, and that, within a cell, HpD becomes localized mainly in the cytoplasm. Preliminary results indicate a difference in the fluorescence decay time between stimulated and unstimulated human lymphocytes treated with HpD. Furthermore, it has been found that the fluorescence decay time is different in cells as compared with HpD solution and that the presence of HpD stabilizes cell autofluorescence.     

Novel ethylene/norbornene copolymers as nonreleasing antioxidants for food‐contact polyolefinic materials

An efficient procedure for the copolymerization of ethylene (E) with a novel norbornenic comonomer (N_ArOH) bearing a stabilizing moiety analogous to commercial antioxidant 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT) is successfully developed. This study is aimed at: i) tuning the concentration of the stabilizing function along the polymer chain, and ii) preparing “nonreleasing” polymeric additives specifically destined to protect commercial low‐density polyethylene (LDPE). Films obtained from blends of the novel E/N_ArOH copolymers with an antioxidant‐free LDPE matrix are characterized by superior thermal, thermo‐oxidative, and photostability when compared not only with neat LDPE films but also with films stabilized by the commercial BHT additive. Specific migration tests conducted in order to investigate the nonreleasing character of the novel macromolecular additives confirm the reduced risk of migration, from the films into food simulants, of unreacted comonomer or degradation products bearing the antioxidant moiety. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 , 51, 1007–1016     

Detection of Copper(II) in Water by Methylene Blue Derivatives

Two novel phenothiazin-5-ium derivatives bearing cyclam moieties ( 3 a⁺ and 3 b⁺ ) were synthesized and investigated as Cu²⁺ sensors. Both ligands show intense spectral changes in the presence of Cu²⁺ in aqueous solutions. The high molar extinction coefficient of the chromophore allows both naked eye detection and spectrophotometric quantitative determination of the cation at a micromolar-concentration scale. 3 a⁺ was found to outperform 3 b⁺ , showing negligible spectral changes in the presence of excesses of other metal cations.     

Renormalized quantum tomography

Quantum tomography allows to expand operators over functions of a continuous set of spectral densities — the so-called quorum of observables. We present new nontrivial operator expansions for the quorum of quadratures of the harmonic oscillator, and introduce a general framework to generate new expansions based on the Kolmogorov construction.     

Design and Synthesis of Olefin Copolymers with Tunable Amounts of Comonomers Bearing Stabilizing Functionalities

The aim of this work is to search for innovative solutions to avoid physical migration of the stabilizers from plastic films. New families of macromolecular additives bearing tuned amounts of a selected functionality were explored, in particular, novel random copolymers of ethylene with 1‐olefin co‐units bearing an efficient antioxidant and/or anti‐UV moiety covalently bonded to a mono‐ or disubstituted olefinic bond. Polyolefin blends containing the novel macromolecular additives showed higher degradation temperatures with respect to the neat matrix and its blends with 2,6‐t‐butyl‐4‐methoxyphenol (BHA). Aging tests showed that the novel antioxidants also constitute a protection against photo‐oxidation.