The dilational modulus (E) of polymer films has been commonly measured using the oscillating ring/bubble/drop methods with an external force, and often without specifying the state of the adsorbed film. This study explores an approach where E was determined from the relaxations of surface tension (ST) and surface area (SA) of natural perturbations, in which ST and SA were monitored using a pendant bubble tensiometer. The E of the adsorbed film of PAA (polyacrylic acid) was evaluated for aqueous solutions at C = 5 × 10 g/cm, [MW = 5, 25, and 250 (kDa)]. The E (=dγ/dlnA) was estimated from the surface dilational rate (dlnA/dt) and the rate of ST change (dγ/dt) of the bubble surface from the natural perturbation caused by minute variations in ambient temperature. The data revealed that (i) a considerable time is required to reach the equilibrium-ST (γ) and to attain the saturated dilational modulus (E) of the adsorbed PAA film, (ii) both γ and E of PAA solutions increase with MW of PAA, (iii) a lower MW solution requires a longer time to reach its γ and E, and (iv) this approach is workable for evaluating the E of adsorbed polymer films.
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| http://dx.doi.org/10.3390/polym16101359 | DOI Listing |
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