Fábio H. Florenzano

Characterization of dioctadecyldimethylammonium chloride vesicles prepared by membrane extrusion and dichloromethane injection

Abstract Vesicles of dioctadecyltrimethylammonium chloride were prepared by sonication, membrane extrusion and dichloromethane injection. The diameter of the vesicles were determined using quasi-elastic light scattering and freeze fracture electron microscopy. The incorporation of water soluble probes in the vesicles allowed the determination of a molar volume of 6 to 8 L/mole for the CH2Cl2 injected vesicles and 1.0 L/mole for the membrane extruded vesicles, in very good agreement with the data calculated from the vesicle diameters. The permeability of the injected CH2Cl2 vesicles is dependent on temperature and probe structure. Membrane extruded vesicles are more permeable than injected vesicles, both below and above the phase transition temperature.

Poly(dimethylsiloxane) and Poly(vinyltrimethoxysilane-co-2-(dimethylamino) ethyl methacrylate) Based Cross-Linked Organic-Inorganic Hybrid Adsorbent for Copper(II) Removal from Aqueous Solutions

An organic-inorganic hybrid adsorbent was prepared and its application for the uptake of CuII ions from aqueous solutions was studied. The polymer network was composed of poly(dimethylsiloxane) (PDMS), vinyltrimethoxysilane (VTMS), and 2-(dimethylamino)ethyl methacrylate (DMAEMA), described as PDMS-net-P(VTMS-co-DMAEMA). The chemical groups, thermal stability and morphology of this hybrid adsorbent were characterized using techniques of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). In adsorption studies, saturation of the active sites of the material was observed at pH 5, after 3 days, with each gram of material capable of adsorbing 0.48 mmol of copper(II). The fractionary-order and Sips models provided the best fits to the experimental data in kinetic and equilibrium studies of the adsorption process, respectively. Moreover, an acceptable reusability was found for this cross-linked organic-inorganic hybrid adsorbent after usage-regeneration cycles without significantly losing its original activity.

Real-Time Determination of Ultraviolet Degradation Kinetics of Polymers in Solution

Abstract Real time monitoring of ultraviolet degradation of polystyrene with varying degrees of methylvinyl ketone (MVK) substitutions was carried out. This automated technique is demonstrated to be rapid, accurate and quantitative, yielding the absolute degradation rate constant in terms of number of bonds broken per second per initial g/mol of polymer mass. The MVK substituted heteropolymers yielded degradation rates around two orders of magnitude higher than pure polystyrene, which varied linearly with the percentage of MVK substitution. By the use of an actinometric determination of absorbed flux in the sample, approximate degradation quantum efficiencies of 0.00169, 0.0965, 0.159 and 0.194 were obtained for pure polystyrene and the 5, 10 and 15% MVK substituted copolymers, respectively.

Urea Decreases Specific Ion Effects on the LCST of PMMA-block-PDMAEMA Aggregates

Urea is a well-known additive used as a mild protein denaturant. The effect of urea on proteins, micellar systems and other colloids is still under debate. In particular, urea has shown interesting effects on the ion binding in systems like charged micelles, vesicles or Langmuir-Blodgett films. The urea effect on polymeric aggregates in water is still an open field. For instance, the additive may affect properties such as cmc, LCST, UCST and others. In particular, LCST is a property that can be very convenient for designing smart systems that respond to temperature. Previous studies have indicated that the LCST of positive charged copolymers aggregates based on poly(N-dimethyl(ethylamine methacrylate)), PDMAEMA, can be nicely modulated by anions in aqueous solution and such phenomenon depends on the nature of the anion present. In this work, it has been demonstrated that urea also affects the LCST of PMMA- block-PDMAEMA aggregates in aqueous solution. In addition, in the presence of high concentrations of the additive, the specific behavior of the anions is lost, supporting the general mechanism of urea reducing the differences on ion binding to surfaces in aqueous solutions. To the best of our knowledge, this is the first time those phenomena are shown in polymer micelles.

Perspectivas atuais para a obtenção controlada de polímeros e sua caracterização

The advent of Controlled Radical Polymerization (CRP) techniques has allowed the production of (co)polymers with narrow molar mass distributions and with all kinds of copolymer morphologies, even though using common monomers via the radical mechanism. In particular, three variants of CRP have been widely and successfully applied to obtain tailor-made polymers: Atom Transfer Radical Polymerization (ATRP), Nitroxide Mediated Polymerization (NMP) and Reversible Addition-Fragmentation Chain Transfer (RAFT). All of them are based on decreasing the polymerization termination rates. Polymer characterization is also essential to ensure that the (co)polymer designed has been obtained as desired. An up-to-date overview of CRP and polymer characterization and their roles in the production of tailor-made (co)polymers are presented here.