Significance of Surface Resistance in Absorption by Polymers

Abstract

Solvent absorption has been followed in injection-molded samples for 13 solvents in cyclic olefinic copolymer (COC), 4 solvents in two different grades of polycarbonate (PC), and 2 solvents in the terpolymer acrylonitrile/butadiene/styrene (ABS). It was discovered that a surface resistance to absorption was significant in 19 of these 23 cases. Approximate surface mass transfer coefficients and approximate diffusion coefficients were determined where possible. There is no surface resistance to absorption where the absorbing molecules are smaller and linear. When the molecules of the test chemicals are too large or bulky, no absorption occurs. The molecules can simply not get through the surface layer, and its resistance is therefore effectively infinitely large. Between these extremes are situations where surface resistance clearly affects the absorption process. Surface resistance becomes significant when molecules can be transported away from the surface into the bulk of the polymer faster than they can be adsorbed/absorbed just at/in the surface.

Oil migration in chocolate: A case of non-Fickian diffusion

“…2) show an initial time lag period where no important weight gain is observed. The same type of ''S"-shape curves has been observed in systems where the surface resistance becomes important (Nielsen and Hansenm, 2005). k was estimated experimentally from the uptake curves as the point where a back extrapolation line, from the middle points of the curve, crosses the x-axis and q s0 was zero for all the simulations.…”

A detailed micrometer scale investigation of the solvent bonding process for microfluidic chip fabrication

“…The solvent activation process by exposure of polymers to solvent vapour involves the adsorption/absorption of solvent molecules onto the polymer surface, passage through the surface, and nally distribution in the bulk. 25 Due to Brownian motion, solvent molecules randomly hit the polymer surface.…”

“…A process of solvent vapour infusion, however, has been reported to show non-reproducible bonding behaviour 15,20,23 possibly due to the effect of a surface resistance. 25 Wallow et al 20 also mention when "some of the plastic components are not fully exposed to the permeanta surface layer or "skin" develops -[which] interferes with the bonding process [making it] necessary for all the plastic components to be bonded to receive at least a brief exposure to the permeant in order to break through this surface layer". Nevertheless, the infusion process has been shown to be successful for PMMA and COP/COC chip production even aer exposure of just one component and only for a few minutes of activation.…”

Lamination‐based rapid prototyping of microfluidic devices using flexible thermoplastic substrates

“…), but it dissolves in various nonpolar solvents (various alkanes, toluene, etc.). A recent study [41] discusses the surface adsorption of solvents on COC and various other polymers. Dissolution tests indicated that solvents like toluene and heptane completely dissolved COC in a short time.…”