Bending‐beam study of water sorption by thin poly(methyl methacrylate) films

Abstract

SynopsisA bending-beam technique has been employed to study the effects of film thickness (7-55 pm) and rate of cooling during film preparation ( -6"C/h to a dry ice quench) on sorption characteristics of water by poly(methy1 methacrylate) films coated on thin fused quartz beams ( -84 pm thick). In each experiment, the curvature of a polymer coated beam exposed to liquid water was monitored as a function of time by a low power laser pointer. With the use of a transport model which considers the sorption process as the linear superposition of contributions from Fickian diffusion and a first-order polymer molecular relaxation process, the beam curvature data were analyzed to determine the governing transport kinetics and associated transport parameters such as water diffusion coefficient and relaxation rate constant. From curvature analysis for thin films (7-13 pm in thickness), it was found that water diffusion proceeds at early times in a Fickian-like manner with a diffusion constant of 2-4 X cm2/s. At later times, significant relaxation contributions lead to non-Fickian diffusion behavior, an effect that is more pronounced as the film thickness or sample cooling rate decreases. In addition, sorption of water was found to reduce the film stress (initially tensile a t -10* dyn/cm2) a t a rate that increases with sample cooling rate.The high initial film stress not present in free-standing films may account for the relatively higher diffusion coefficient ( -2 X lo-' cm2/s) found here for very thick (55 pm) PMMA coatings.Because the bending-beam technique uses coated samples, it is especially well suited for studying penetrant transport into polymer coatings.

“Tunable” diffusion of D2O in CO2‐swollen poly(methyl methacrylate) films

“…Since the expression describing anomalous diffusion is independent of the concentration gradient and linear with time in the limit as time goes to zero, it is consistent with Case I1 diffusion (Tong and Saenger, 1989) at short times. F{D) is the full series solution of the diffusion into a finite plane sheet (Crank, 1979, where D is the diffusion coefficient and 1 is the film thickness.…”

“…where MI and M, are the mass of penetrant absorbed at time t and at equilibrium, respectively; (1a ) is the fraction of M, due to Fickian diffusion (Tong and Saenger, 1989).…”

“…Water is also known to decrease the Tg of PMMA due to hydrogen bonding (Smith and Schmitz, 1988). Since the transport of water in PMMA is crucial to the production of advanced materials, the diffusion of water in PMMA is well documented (Barrie, 1968;Tong and Saenger, 1989;Turner, 1987;Turner and Abell, 1987).…”

Water‐sorption behaviors of poly(3,4′‐oxydiphenylene pyromellitimide) films depending on the thickness variation

“…5 Until now, water-sorption behaviors of PMDA-4,4ЈODA films have been extensively studied using various methods in either thermally imidized films from the polyamic acid precursor or Kapton films, which were chemically imidized and then given thermal treatment. 9 -12 The water sorption causes the potential reliability problems in microelectronic devices, [13][14][15][16] such as displacement, package crack, delamination, loss of adhesion, potential corrosion, and mechanical failures in thin films.…”

New Techniques for Diffusion Studies of Thin Polymer Films

“…The bendingbeam technique for studies of moisture transport in polymers was pioneered by Berry and Pritchet [3], and is illustrated by the recent work of Tong and Saenger [6] who studied room-temperature moisture diffusion into both quenched and annealed films of poly(methyl methacrylate) (PMMA) immersed in water. The laser interferometric technique, used previously [5] for monitoring solvent removal from solution cast films of polyamic acid in n-methyl-2-pyrrolidone (NMP), has been applied to study the swelling of fully cured polyimide in liquid NMP at different temperatures [7].…”