Apparent Molar Volumes and Heat Capacities of Various Adsorbed Additives on Polystyrene Latexes

Abstract

Flow densimetry and flow microcalorimetry have been used to study the effect of electrolytes, surfactants, and alcohols on positively and negatively charged polystyrene latexes. The thermodynamic volumes and heat capacities of transfer of the latex from water to the aqueous solutions and of the additives from water to the latex dispersions were measured as a function of the additive concentration. With some systems, the adsorption isotherms were also determined. These thermodynamic properties are largely insensitive to electrostatic interactions but depend significantly on changes in hydrophobic interactions resulting from adsorption of the additive on the latex. Negligible changes in the quantities of transfer are thus observed for electrolytes, methoxyethanol, and methanol, but ionic and nonionic surfactants are adsorbed on both types of latexes. The adsorption of medium-chain-length alcohols and alkoxyethanols increases with their hydrophobic character. A simple model based on the Langmuir isotherm, the thermodynamic properties of the additives in water, and the properties of the adsorbed additives correctly predicts the general trends of the transfer functions of the additive and of the latex. However, a detailed analysis of the data indicates that the adsorption isotherm is more complex than expected from the Langmuir equation and that the thermodynamic properties of the adsorbed species depend on the extent of coverage. At high concentrations, the volumes and heat capacities of adsorbed surfactants are of the same order of magnitude as the corresponding values of the surfactants in micellar form.

Polystyrene nanoparticles in the presence of (ethylene oxide)13(propylene oxide)30(ethylene oxide)13, N,N-dimethyloctylamine-N-oxide and their mixtures. A calorimetric and dynamic light scattering study

“…The specific conductivity of this suspension is 0.50 mS cm À1 at 25 1C which proves that the nanoparticles are charged. This result agrees with the findings 22 which reported negative values for the Zeta potential for the latex prepared according the same procedure employed here. Such a charge is ascribable to the presence of sulfate groups which were originated from the initiator.…”

“…The DLS technique is very useful in evidencing the adsorption of the surfactant onto the PS nanoparticles but it is not able to provide the energetics and mechanism of the adsorption process. In this area, thermodynamic properties of transfer such as volume, 22,24 enthalpy 13 and heat capacity 22,24 Langmuir type L64 adsorption on polystyrene nanoparticles. The DH L vs. m C trend is reminiscent of the Langmuir type adsorption.…”

“…This method ensures to obtain well-characterized small particles with large surface areas. [20][21][22] The styrene (30 g) was emulsified in 300 g of an aqueous NaDeS micellar solution (ca. 0.15 mol kg À1 ) under stirring and under fluxing nitrogen in the aqueous media for ca.…”

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

“…Flow instruments [24][25][26] may be used to study the adsorption process of solutes onto the solid phase by determining the properties of transfer of either the solute or the solid.…”

“…The enthalpy measurements were carried out by using a flow LKB 2107 microcalorimeter at 298.15 AE 0.01 K. The mixtures were pushed into the instrument through a Gilson peristaltic pump (Minipuls 2). Flow instruments [24][25][26] may be used to study the adsorption process of solutes onto the solid phase by determining the properties of transfer of either the solute or the solid. The experimental enthalpy (DH exp ) was evaluated as the difference between the thermal effect produced by the mixing process of the macromolecule solution and the RD dispersion and that due to the dilution process of the same macromolecule solution with water.…”