Oxygen Diffusion into Latex Films Annealed at Various Temperatures: A Fluorescence Study O ¨ . Pekcan 1 and S ¸. Ug ˘ur Istanbul Technical University, Department of Physics, 80626, Maslak, Istanbul, Turkey Received February 8, 1999; accepted May 20, 1999 A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into latex films. These latex films were prepared by annealing pyrene (P) labeled polymethyl methac- rylate (PMMA) particles above the glass transition temperature. Transparency of these films were measured by monitoring the trans- mitted photon intensity, I tr , which increased as the annealing tem- perature was increased. Steady state fluorescence was used to mon- itor oxygen diffusion into latex films. Diffusion coefficients, D, of oxygen were determined using fluorescence quenching method and are found to be around 5.6  10 11 cm 2 s 1 . © 1999 Academic Press Key Words: oxygen; diffusion; latex; film; fluorescence. INTRODUCTION Most of the photophysical and chemical reactions taking place in polymers occur as a result of a mass diffusion of reactants. A knowledge of the diffusion coefficient of these reactants into polymeric systems is of prime importance in the development of materials of desired properties. Oxygen is one of the most important reactants to be considered in the diffu- sion phenomenon. The control of the diffusion of oxygen is of particular importance in the design of polymeric membranes for separation processes in the production of films for packing industry and in the developments of biocompactible materials. The usual procedures used to measure the diffusion coeffi- cients of gases through polymeric systems are based upon measurements of the amount of gas which permeates a given area of a polymer in a given time. In addition to this direct method of determination, depending upon the properties of the gases being investigated there are also indirect methods based on the quenching or bleaching action of these gases on the molecular probes imbedded uniformly in the polymer. The diffusion coefficient of oxygen into polymethyl methacrylate (PMMA) was determined by the quenching of phosphores- cence of the phenanthrene added into the polymer (1). Barker had utilized the bleaching action of oxygen on color centers produced by electron beam irradiation of polycarbonate and PMMA by following optically the moving boundary (2). The quenching of fluorescence of naphthalene in PMMA was stud- ied by oxygen in thin films after displacement of nitrogen atmosphere over the sample by oxygen (3). The ESR spectros- copy method was used for measuring the oxygen diffusion coefficient in PMMA spheres (4). Every technique mentioned above carries some inherent advantages and disadvantages. The term “latex film” normally refers to a film formed from soft latex particles (T g below room temperature) where the forces accompanying the evaporation of water are sufficient to compress and deform the particles into transparent, void-free film. However, latex film can also be obtained by compression molding of a film of dried latex powder composed of relatively hard poly- mers such as polystyrene (PS) or PMMA that have T g above room temperature. Aqueous dispersion of soft latex particles are called low-T, while nonaqueous dispersions of hard poly- mer particles are generally referred to as high-T particles. High-T latex particles remain essentially discrete and unde- formed during drying. The mechanical properties of such films can be evolved after all solvent has evaporated, by an anneal- ing process which first leads to the growth of “necks,” molecu- lary contacting interfaces between particles and then equilibra- tion of material properties within those necks take place; namely relaxation of mechanical stresses resulting from defor- mations during neck growth and diffusion of chains across the interface to establish a uniform distribution of entanglements. The process of interparticle polymer interdiffusion has been studied by direct nonradiative energy transfer (DET) using fluorescence decay measurements in conjunction with particles labeled with appropriate donor and acceptor cromophers (5–7). This transient fluorescence technique has been used to examine latex film formation of 1 m diameter high-T (PMMA) parti- cles (6, 7) and of 100 nm diameter low-T polybutyl methac- rylate (PBMA) particles (5). These studies all indicate that in the particular systems examined, annealing the films above T g leads the polymer interdiffusion at the particle–particle junc- tion as the particle interfaces heals. Mazur (8) has written an extensive review on the coalescence of polymer particles, in which he mainly discusses the neck growth mechanism and its several geometrical approximations before the interdiffusion of the polymer chain takes place. DET and the steady state fluorescence (SSF) technique have been used to study interdif- fusion processes at the particle–particle junction during film 1 To whom correspondence should be addressed. Journal of Colloid and Interface Science 217, 154 –159 (1999) Article ID jcis.1999.6337, available online at http://www.idealibrary.com on 154 0021-9797/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.