Dynamic Surface Tension of Aqueous Solutions of Ionic Surfactants: Role of Electrostatics

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy.Comment: 13 pages, 5 figure

Equilibrium and dynamic surface properties of trisiloxane aqueous solutions. Part 1. Experimental results

Tensiometry, ellipsometry and Brewster angle microscopy were used to measure equilibrium and dynamic surface tension, as well as surface adsorption, of aqueous solutions of trisiloxane surfactants. Complex adsorption curves, including inflection points, have been found for the surfactants with long etoxylated chains. Surface aggregates at the liquid–air interfaces have been detected for the trisiloxanes that show superspreading behaviour onto moderately hydrophobic surfaces, while no aggregates were detected for the shorter trisiloxanes. The latter suggests that those surface aggregates may act as reservoirs of surfactant molecules to maintain the required surface tension in the course of spreading

Polarity studies of single polyelectrolyte layers in polyelectrolyte multilayers probed by steady state and life time doxorubicin fluorescence

Hypothesis: Polarity in polyelectrolyte multilayers (PEMs) may vary from the inner to the top layers of the film as the charge compensation of the layers is more effective inside the PEMs than in outer layers. Doxorubicin hydrochloride (DX) is used here to sense polarity at the single polyelectrolyte level inside PEMS. Experimental: DX is complexed electrostatically to a polyanion, either polystyrene sulfonate (PSS) or polyacrylic acid (PAA) and assembled at selected positions in a multilayer of the polyanion and polyally lamine hydrochloride (PAH) as polycation. Local polarity in the layer domain is evaluated through changes in the intensity ratio of the first to second band of spectra of DX (I1/I2 ratio) by steady state flu orescence, and by Lifetime fluorescence. Findings: PAH/PSS multilayers, show a polarity similar to water with DX/PSS as top layer, decreasing to I1/ I2 ratios similar to organic solvents as the number of polyelectrolyte layers assembled on top increases. For PAH/PAA multilayers, polarity values reflect a more polar environment than water when DX/PAA is the top layer, remaining unaltered by the assembly of polyelectrolyte layers on top. Results show that different polar environments may be present in a PEM when considering polarity at the single layer level.Fil: Martinelli, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Centro de Investigación Cooperativa en Biomateriales; EspañaFil: Tasca, Elisamaria. Centro de Investigación Cooperativa en Biomateriales; España. Università degli Studi di Roma "La Sapienza"; ItaliaFil: Andreozzi, Patrizia. Università degli Studi di Firenze; Dipartimento di Chimica “Ugo Schiff”; Italia. Centro de Investigación Cooperativa en Biomateriales; EspañaFil: Libertone, Sara. Centro de Investigación Cooperativa en Biomateriales; EspañaFil: Ritacco, Hernán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Giustini, Mauro. Università degli Studi di Roma "La Sapienza"; Italia. Università degli Studi di Firenze; Dipartimento di Chimica “Ugo Schiff” ; ItaliaFil: Moya, Sergio Enrique. Centro de Investigación Cooperativa en Biomateriales; España. Università degli Studi di Roma "La Sapienza"; Itali

A pH-responsive foam formulated with PAA/gemini hernán martinelli 12-2-12 complexes

In the search for responsive complexes with potential applications in the formulation of smart dispersed systems such as foams, we hypothesized that a pH-responsive system could be formulated with polyacrylic acid (PAA) mixed with a cationic surfactant, Gemini 12-2-12 (G12). We studied PAA-G12 complexes at liquid–air interfaces by equilibrium and dynamic surface tension, surface rheology, and X-ray reflectometry (XRR). We found that complexes adsorb at the interfaces synergistically, lowering the equilibrium surface tension at surfactant concentrations well below the critical micelle concentration (cmc) of the surfactant. We studied the stability of foams formulated with the complexes as a function of pH. The foams respond reversibly to pH changes: at pH 3.5, they are very stable; at pH > 6, the complexes do not form foams at all. The data presented here demonstrate that foam formation and its pH responsiveness are due to interfacial dynamic.Fil: Martinelli, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Dominguez, Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Fernández Leyes, Marcos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Moya, Sergio Enrique. Centro de Investigación Cooperativa en Biomateriales; EspañaFil: Ritacco, Hernán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Polyphosphate Poly(amine) Nanoparticles: Self-Assembly, Thermodynamics, and Stability Studies

The interaction of polyamine poly(allylamine hydrochloride) with Na3PO4, Na4P2O7, Na5P3O10, Na6P6O18, and (NaPO3)26 salts and the formation of polyamine phosphate nanoparticles (PANs) are studied here. Dynamic light scattering, isothermal titration calorimetry (ITC), electrophoretical mobility measurements, atomic force microscopy, and transmission electron microscopy are used to explore the formation, stability, and pH sensitivity of PANs. An optimal concentration for PAN formation is found for each phosphate salt in terms of the most stable size and lowest polydispersity index of the nanoparticles. The minimal concentration of phosphate ions for PAN formation decreases with the increasing number of phosphate groups per phosphate salt. ITC measurements show that all polyphosphates display a characteristic endothermic peak, which is not present when monophosphates are used for PAN formation. pH stability of PANs depends on the type of phosphate salt. PANs formed with small phosphates show a small window of stability with pH from 8 to 9, while those formed with long phosphates are stable in more acidic pH environments. Our findings open multiple possibilities for fine-tuning the pH sensitivity of PANs by varying phosphate salts for potential applications in drug delivery.Fil: Cuenca, Victor Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Martinelli, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Ramirez, Maria de Los Angeles. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ritacco, Hernán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Andreozzi, Patrizia. Cic Biomagune; EspañaFil: Moya, Sergio Enrique. Cic Biomagune; Españ

Assembly and recognition mechanisms of glycosylated PEGylated polyallylamine phosphate nanoparticles: A fluorescence correlation spectroscopy and small angle X-ray scattering study

Hypothesis: Modification of polyallylamine hydrochloride (PAH) with heterobifunctional low molecular weight polyethylene glycol (PEG) (600 and 1395 Da), and subsequent attachment of mannose, glucose, or lactose sugars to PEG, can lead to formation of polyamine phosphate nanoparticles (PANs) with lectin binding affinity and narrow size distribution.Experiments: Size, polydispersity, and internal structure of glycosylated PEGylated PANs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). Fluorescence correlation spectroscopy (FCS) was used to study the association of labelled glycol-PEGylated PANs. The number of polymer chains forming the nanoparticles was determined from the changes in amplitude of the cross-correlation function of the polymers after formation of the nanoparticles. SAXS and fluorescence cross -correlation spectroscopy were used to investigate the interaction of PANs with lectins: concanavalin A with mannose modified PANs, and jacalin with lactose modified ones. Findings: Glyco-PEGylated PANs are highly monodispersed, with diameters of a few tens of nanometers and low charge, and a structure corresponding to spheres with Gaussian chains. FCS shows that the PANs are single chain nanoparticles or formed by two polymer chains. Concanavalin A and jacalin show specific interactions for the glyco-PEGylated PANs with higher affinity than bovine serum albumin