Development of pendant drop mechanical analysis as a technique for determining the stress–relaxation and water‐permeation properties of interfacially polymerized barrier layers

Abstract

Interfacial polymerization (IP) involves the formation of solid polymeric films at the interface between aqueous and immiscible organic solutions via an interfacial polycondensation reaction between complementary monomeric reactants present in the two solutions. IP films are very thin (Ͻ0.25 m) and form effective barrier layers in interfacially polymerized thin-film composite membranes. Considerable difficulties are encountered in applying conventional characterization techniques to such unsupported IP thin films. This article describes the development of a novel technique, pendant drop mechanical analysis (PDMA), which can be used to study the mechanical and transport behavior of unsupported IP films. Experiments were conducted on films formed in a PDMA apparatus via the IP polymerization of m-phenylene diamine and trimesoyl chloride (TMC). Stress-relaxation data obtained via PDMA were fitted with the Williams-Watts equation, and the results indicated a statistically significant dependence of the model parameters on the TMC concentration. Permeation experiments also demonstrated a statistically significant dependence of the membrane constant on the TMC concentration. The results provide unique insights regarding the relationship between structure and performance in unsupported IP films and suggest that network formation is enhanced in a concentration range of 0.1-0.3 wt % TMC. Although refinements are required, PDMA appears to be a promising technique for identifying optimum IP reaction conditions and assessing corresponding mechanical and transport characteristics.

Interfacial polycondensation—Modeling of kinetics and film properties

“…C nr , m = 1 to n max (20) In order to avoid double counting in the second last term of the Eq. (20), the k p4 should be k p4 /2 if (m − n − 1) / = n.…”

“…In the third approach, a film thickness is calculated based on the polymer concentration in the reaction zone, and the diffusion of monomers is modeled as taking place through a gel-like structure. Experimental evidence [3,5,6,11,[18][19][20][21] points to a strong influence of the conditions employed in the preparation on the nature and properties of the film that forms. However, most of the models [7][8][9][10][11][14][15][16][17] focus on the kinetics and the variation of film thickness with time, and do not attempt to predict quantitatively the polymer properties as a function of process parameters.…”

“…However, most of the models [7][8][9][10][11][14][15][16][17] focus on the kinetics and the variation of film thickness with time, and do not attempt to predict quantitatively the polymer properties as a function of process parameters. Properties such as molecular weight, polydispersity and crystallinity affect important characteristics of the polymer [20][21][22] such as mechanical properties, viscosity, ease of processing, permeability. Indeed, in their work on encapsulation, Yadav et al [22] observed an order-of-magnitude variation in the permeability of the capsule wall because of variations in crystallinity.…”

Investigation of the viscoelastic and transport properties of interfacially polymerized barrier layers using pendant drop mechanical analysis

“…Many studies have been conducted on the IP formation process in the FT‐30 as well as other appropriate systems. A recent review of the literature4 indicates that most work has focused on assessing the effects of various chemical parameters, such as the reactant functionality and type, on IP‐TFC performance. In contrast, studies by Arthur5 and Jiang and coworkers6 suggest that membrane transport depends on the extent of free volume and the conformational mobility of the polymer chains.…”

“…In response to these limitations, our research group developed pendant drop mechanical analysis (PDMA), which exploits the capabilities of a specially modified pendant drop tensiometer. By monitoring the pressure and deformation responses of an IP film formed at the surface of a liquid drop, the viscoelastic and transport properties of the unsupported barrier layer can be obtained 4, 7, 8. Whereas a previous study4 focused only on the effect of TMC concentration on film behavior, this article describes the results of a series of systematic PDMA experiments that consider the effect of reactant composition and contact time as well as organic‐phase functionality on unsupported barrier layers formed from the MPD–TMC system by IP.…”