N. Muratore

Aqueous laponite clay dispersions in the presence of poly(ethylene oxide) or poly(propylene oxide) oligomers and their triblock copolymers.

The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low M w whereas the opposite occurs for larger Mw. This behavior is explained on the basis that an effective R G is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of noninteracting polydisperse core+shell disks, where the thickness of the polymer layer increases with the Mw. The adsorbed polymer is in a more compact conformation compared to a random coil distribution while the fraction of the polymer in the shell formed around the laponite RD particles is nearly independent of Mw. For increasing laponite RD amounts, at a given polymer composition, the thickness of the polymer slightly changes. In some cases, where also gelation is sped up, a structure factor with attractive interaction was employed which allowed to evaluate the attractive forces between the laponite RD particles. The gelation time was determined for mixtures at fixed copolymer and laponite RD concentrations. Surprisingly, it is observed that gels are formed despite the fact that the binding sites of the laponite RD particles are almost covered but the polymer size is too small to prevent aggregation. The gelation rate is correlated to structure and thermodynamics of these systems. Namely, when the balance between the steric forces and the depletion attractive forces undergoes an abrupt change the gelation time also undergoes a sharp variation. For lower and comparable Mw, PPO speeds up the gelation more efficiently than PEO while for higher Mw the gelation kinetics is slowed down again. Interestingly, copolymers of PEO and PPO blocks do not induce gelation in the time-window where the homopolymers do.

Pb(II) adsorption by a novel activated carbon alginate composite material. A kinetic and equilibrium study

The adsorption capacity of an activated carbon - calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ion from aqueous solution. The study was carried out at pH=5, in NaCl medium and in the ionic strength range 0.1-0.75molL-1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared. Calcium alginate (AA-Ca) improves the adsorption capacity (qm) of active carbon (AC) in the ACAA-Ca adsorbent material (e.g., qm=15.7 and 10.5mgg-1 at I=0.25molL-1, for ACAA-Ca and AC, respectively). SEM-EDX and thermogravimetric (TGA) measurements were carried out in order to characterize the composite material. The results of the speciation study on the Pb(II) solution and of the characterization of the ACAA-Ca and of the pristine AA-Ca and AC were evaluated in order to explain the specific contribution of AC and AA-Ca to the adsorption of the metal ion.

Volumes and heat capacities of the aqueous sodium dodecanoate/sodium perfluorooctanoate mixtures in the presence of β-cyclodextrin

Apparent molar volumes (VΦ) and heat capacities (CΦ) of the sodium dodecanoate (NaL)/sodium perfluorooctanoate (NaPFO) mixtures in the water/β-cyclodextrin (β-CD) solvent as functions of the surfactant total molality (mt) were determined at 25°C. For a given surfactant mixture, VΦ decreases with mt to ca. 0.05 mol kg−1 thereafter it increases tending to a constant value. CΦ displays a behaviour opposite to VΦ. The mt values where the apparent molar properties exhibit extrema are nearly coincident with the critical micellar concentrations determined by conductivity. An equation correlating VΦ to mt was derived by assuming that the equilibria for the 1∶1 surfactant/cyclodextrin complex formation and the micellization were simultaneously present. A mass action model described the aggregation process of each pure surfactant. The VΦ quantitative analysis of the NaL/β-CD and NaPFO/β-CD mixtures provided the volume changes for the complex formation. It was impossible to extend an analogous treatment to VΦ of the NaL/NaPFO mixtures. Therefore, simulations were done based on the following points: (1) the pseudo-phase transition model for micellization was employed; (2) the composition of the mixed micelles was set equal to the stoichiometric NaL/NaPFO ratio and (3) the properties of the β-CD/NaL and β-CD/NaPFO complex formation in water were used. As concerns the heat capacity, the equation correlating CΦ to mt contained also the terms due to the presence of the contributions for the shift of the equilibria of micellization and the surfactant/cyclodextrin inclusion complex formation with temperature. The heat capacity changes for the β-CD/NaL and β-CD/NaPFO complex formation were evaluated from data of pure surfactants. Then, according to the approach used for the volume, CΦ of the NaL/NaPFO mixtures were computed. As a general result, the simulations of both the volume and the heat capacity were rather satisfactory. The relevance of this study is due to the ability in predicting the thermodynamic properties of the surfactant–surfactant–cyclodextrin–water quaternary systems based on the acquaintance of the thermodynamics of micellization of the surfactant mixtures in water and the complex formation between each surfactant and cyclodextrin in water.

Adsorption of triblock copolymers and their homopolymers at laponite clay/solution interface. Role played by the copolymer nature.

The adsorption thermodynamics of copolymers, based on ethylene oxide (EO) and propylene oxide (PO) units, at the laponite (RD) clay/liquid interface was determined at 298 K. The copolymer nature was tuned at molecular level by changing the hydrophilicity, the architecture and the molecular weight (Mw) keeping constant the EO/PO ratio. Polyethylene (PEGs) and polypropylene (PPGs) glycols with varying Mw and their mixture were also investigated to discriminate the role of the EO and the PO segments in the adsorption process. Enthalpies of transfer of RD, at fixed concentration, from water to the aqueous macromolecule solutions as functions of the macromolecule molality were determined. They were treated quantitatively by means of a model based on two equilibria: (1) one-to-one binding between the macromolecule and the site on the solid and (2) two-to-one binding following which one macromolecule interacts with another one adsorbed onto the solid. The good agreement between the equilibrium constants obtained from calorimetry and those determined from kinetic experiments confirmed the reliability of the experimental and theoretical approaches. Almost all of the systems investigated are highlighted by the one-to-one binding; the L35 and 10R5 systems present both equilibria. The insights provided by the thermodynamics of adsorption of their homopolymers onto RD were fruitful in obtaining detailed information on the nature of the forces involved between RD and the copolymers. The data obtained in the present work clearly evidenced that for comparable polymer Mw, PPG is more suitable in building up a steric barrier around the RD particles and, indeed, exhibits several advantages and no drawbacks. Moreover, the parent copolymers may properly functionalize the RD surface by exploiting both their high affinity to the solid surface and the ability to self-assemble onto it as L35 and 10R5 clearly showed.

Experimental and robust modeling approach for lead(II) uptake by alginate gel beads: influence of the ionic strength and medium composition.

Systematic kinetic and equilibrium studies on the lead ions removal ability by Ca-alginate gel beads have been performed by varying several internal parameters, namely, number of gel beads, nature and composition of the ionic medium and pH, which allowed us to model a wastewater in order to closely reproduce the composition of a real sample. Moreover, the effects brought about the different ionic species present in the reacting medium have been evaluated. Differential Pulse Anodic Stripping Voltammetry (DP-ASV), has been systematically used to perform kinetic and equilibrium measurements over continuous time in a wide range of concentration. Kinetic and equilibrium data have been quantitatively analyzed by means of robust approach both for the non-linear regression and the subsequent residuals analysis in order to significantly improve the results in terms of precision and accuracy. Alginate gel beads have been characterized by SEM and an investigation on their swelling behavior has also been made. Removal efficiency of the calcium-alginate gel beads has been calculated and results obtained have showed a relevant dependence on ionic strength, composition of ionic media, pH of solution and number of gel beads. The number of gel beads takes part as key crucial components, i.e., the higher the number of beads the greater the amount of Pb(II) species removed from the sample, the lower the time needed to reach the maximum removal efficiency of 90%.

Thermodynamics of surfactants, block copolymers and their mixtures in water: the role of the isothermal calorimetry.

The thermodynamics of conventional surfactants, block copolymers and their mixtures in water was described to the light of the enthalpy function. The two methodologies, i.e. the van’t Hoff approach and the isothermal calorimetry, used to determine the enthalpy of micellization of pure surfactants and block copolymers were described. The van’t Hoff method was critically discussed. The aqueous copolymer+surfactant mixtures were analyzed by means of the isothermal titration calorimetry and the enthalpy of transfer of the copolymer from the water to the aqueous surfactant solutions. Thermodynamic models were presented to show the procedure to extract straightforward molecular insights from the bulk properties.

Solubilization of an organic solute in aqueous solutions of unimeric block copolymers and their mixtures with monomeric surfactant: volume, surface tension, differential scanning calorimetry, viscosity, and fluorescence spectroscopy studies.

The ability of aqueous systems, formed by unimeric copolymers and their mixtures with a monomeric surfactant, in solubilizing large quantities of 1-nitropropane (PrNO2) was explored. The copolymers are F68 and L64, which differ for the hydrophilicity, and the surfactant is sodium dodecanoate. For a better understanding of the mechanism of solubilization, thermodynamic (volume and differential scanning calorimetry), spectroscopy (steady-state fluorescence), viscosity, and interfacial investigations were carried out. PrNO2 causes the micellization of the unimeric copolymer, and the required amount of PrNO2 depends on the composition, the copolymer nature, and the temperature. Large quantities of PrNO2 form mixed micelles where PrNO2 experiences an environment similar to its pure liquid state. The presence of the additive allows a decrease of the critical micellar temperature, evidence of which is quantitatively explained through a novel thermodynamic approach. A synergistic effect in solubilizing PrNO2 was observed when surfactant monomers were added to the unimeric copolymer solutions. The increased amount of PrNO2 leads to the complete self-assembling of both the copolymer and the surfactant; a process favored by temperature increase. For all of the investigated systems, the presence of PrNO2 generates a viscosity increase.

Issues Related to the Restoration of Mirrors of the Wooden paliotto della chiesa del Santissimo Crocifisso all’Albergheria, Sicily (Italy)

ABSTRACT In this work, the decision-making process involved in the restoration of the eighteenth century paliotto ligneo (wooden altar frontal) della chiesa del Santissimo Crocifisso all’Albergheria of Palermo is presented. Earlier research concerning mirror restoration was based on only a few case studies and the proposed techniques were not suitable for the artwork here. As a consequence, it was necessary to re-examine theories and protocols of modern restoration to plan an appropriate intervention of the altar frontal. Since in this artwork the role of mirrors is not to give back images, as usual, but rather to create special light effects and play of lights, this work aims to find an approach to the restoration of the altar frontal and its decorations that allows a homogeneous overview of the piece. Thus, the mirrors were not substituted or re-created. Only a visual integration of the damaged ancient mirrors was proposed, with the use of metallic-polymeric films, permitting a completely reversible restoration.