Christian Bindschaedler

Aqueous nanodispersions prepared by a salting-out process

Cellulose acetate phthalate nanodispersions were prepared in the form of a redispersible powder by a new preparation technique based on the salting-out process between two miscible solvents. This method involved the selection of salts producing the salting-out of acetone from water. Poly(vinyl alcohol) was used as protective colloid during the particle formation step and in the finished product. For a pharmaceutical use, the advantage of this new technique is that the process does not require any surfactant or increase in temperature and thus may be useful for biopolymers or heat-sensitive substances. These nanodispersions may also be dried by lyophilization and the particles subsequently redispersed in an aqueous medium before use.

Osmotically controlled drug delivery systems produced from organic solutions and aqueous dispersions of cellulose acetate

Abstract The use of aqueous colloidal dispersions of cellulose acetate instead of organic solutions is proposed as an alternative way to obtain osmotic tablets. At the same plasticizer level, the semipermeable membranes produced from latices were more permeable to water and swelled to a greater extent than those prepared from organic solutions. Consequently, the release rate of the model drug potassium chloride from coated tablets produced from aqueous dispersions was higher and the time delay before constant release was shorter. Generally, the permeability and the solute release rate varied over a wide range, depending on the physico-chemical properties and concentration of plasticizer and on the coating conditions (coating temperature, rate of coating and drying duration). Plasticizers with low vapor pressure gave more permeable films. The mechanical properties of the membranes were also examined and strong films could also be produced from aqueous dispersions, despite the mechanism involved in the formation of such films.

Concept and development of ophthalmic pseudo-latexes triggered by pH

Abstract The apparent p K a , acid value and maximum buffer capacity have been calculated for various polyacids generally utilized for enteric coating, in order to select a polymeric model compound for the preparation of pseudo-latexes triggered by pH for ophthalmic application. The solubility of the selected polymer (cellulose acetate phthalate) was estimated from a ternary plot of its solvents vs fractional solubility parameters. Pseudo-latexes were prepared by emulsification of various organic polymer solutions and removal of the solvents by vacuum distillation. The viscosity behaviour of 30% by weight pseudo-latexes was simulated in vitro to show the sharp and high increase of their viscosity vs pH.

Mechanically strong films produced from cellulose acetate latexes

Mechanically strong films, comparable with those obtained from organic solutions, can be produced from cellulose acetate latexes, a new type of dispersion, both by casting and spraying. The prerequisite conditions for high strength, which include choice of water‐soluble plasticizers possessing some degree of volatility, are discussed.

Thermodynamics of swelling of polymer latex particles by a water-soluble solvent: I. Theoretical considerations

Abstract Thermodynamic and equilibrium swelling characteristics of three-component emulsions of polymer particles are important in producing latex systems. J. Ugelstad and P. C. Mork ( Adv. Colloid Interface Sci. 13 , 101, 1980) examined the thermodynamic properties of ternary systems consisting of an organic solvent, a polymer, and water. We have developed a new theoretical model which can be used to predict the equilibrium content of organic solvent in the polymer particles, when this solvent is also partially soluble in the external aqueous phase. In Part II (C. Bindschaedler, R. Gurny, E. Doelker, and N. A. Peppas, J. Colloid Interface Sci. 108 , 83, 1985), this model is used to interpret the equilibrium properties of cellulose acetate emulsions.

Detachment of small axisymmetric particles from fluid-liquid interfaces

Abstract Free-energy and force analyses neglecting gravitational effects were developed to predict the equilibrium position of smooth particles of any axisymmetric shape undergoing compressive or tensile forces at fluid-liquid interfaces. The force required to pull a particle from a liquid interface defined by a perforated plate was shown to be a function of the interfacial tensions, the shape of the particle and the particle/plate gap. Predictions are also given of the force at the point of particle detachment and the distance at which this process takes place. Implicit analytical expressions are provided for a conical punch or for spherical and spheroidal particles, and force-displacement diagrams are discussed. The free-energy and the force analyses are numerically equivalent, provided Youngs equation is valid. The new framework provides a method to measure the contact angle properties of small particles, and the interfacial tension of the fluid-liquid interface in contact with the particle. This technique is potentially interesting in the field of bioadhesion, since it furnishes a direct method to test the adhesion of a particle to a biological substrate.

Thermodynamics of swelling of polymer latex particles by a water-soluble solvent: II. Experimental results on cellulose acetate latices

Abstract The predictive capabilities of the theoretical model of particle swelling developed in Part I (C. Bindschaedler, R. Gurny, E. Doelker, and N.A. Peppas, J. Colloid Interface Sci. 108, 75, 1985) are discussed by comparison with experimental values of solvent partitioning in cellulose acetate latices. Satisfactory agreement is obtained when considering the water contained in the particles.