Adsorption of Hydrophobically Modified Poly(acrylic acid) Sodium Salt at the Air/Water Interface by Combined Surface Tension and X-ray Reflectivity Measurements

Abstract

The adsorption at the air/water interface of hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) with various degrees of grafting and lengths of graft has been investigated using both tensiometry and X-ray reflectivity techniques. Tensiometry has provided the Gibbs adsorption isotherms and has revealed that HMPAANa associating copolymers behave like low molecular weight surfactants with surface tensions leveling off at the critical aggregate concentrations (cac) determined from viscosity measurements. However, very long times (up to 2 days) were required to achieve equilibrium. X-ray reflectivity measurements have permitted us to detect a monomer units-rich zone at the air/water interface, corresponding to the proximal zone of the adsorbed polymer layer. This zone thickens with increasing either the bulk polymer concentration or the salt concentration but remains unchanged with varying the polymer backbone molecular weight. The polymer concentration within the zone is 40% in volume fraction with a bulk concentration equal to cac. By coupling both techniques, we show that the Gibbs adsorption theory is valid for HMPAANa copolymers and that the longest polymer loops and tails extending into the sublayer do not contribute to the surface activity. As a matter of fact, a good agreement between the values of the excess surface concentration Γ is obtained using both techniques.

Adsorption kinetics of hydrophobic polysoaps at the methylene chloride–water interface

“…The similar behavior, i.e. the existence of the lag-time and the long relaxation time (sometimes ∼10 6 s) for the surface and interfacial tension, was reported for hydrophobically modified polymers and proteins, which unfold at the interface and may adsorb irreversibly by "anchoring" their multiple hydrophobic functional groups into the non-polar phase [6][7][8][9][10][11][12]. The decrease of the interfacial tension during so long time signifies that this decrease is controlled not only by the diffusion of macromolecules from the bulk to the interface and their adsorption but mainly by the diffusion of surface active segments of the already adsorbed macromolecules via their reconformation inside the adsorption layer.…”

“…The decrease of the interfacial tension during so long time signifies that this decrease is controlled not only by the diffusion of macromolecules from the bulk to the interface and their adsorption but mainly by the diffusion of surface active segments of the already adsorbed macromolecules via their reconformation inside the adsorption layer. The phase transition phenomena (collapse, aggregation, gellation) inside the adsorption layers may oc- cur as well in the course of the ageing of the adsorption layers and under compression [9,10]. Unlike the water-soluble polymers and proteins, which adsorb at the oil-water interface by their hydrophobic moieties (Fig.…”

Surface Activity and Emulsification Properties of Hydrophobically Modified Dextrans

“…However, at increasing polymer concentrations, a singular increase in σ values was clearly observed, particularly with the DexP 15 and DexP 22 derivatives. Similar behaviors were obtained with hydroxypropyl methylcellulose (6) or short polyoxyethylene dodecyl ether (19). This could be explained by a change in the polymer conformation at the interface but further investigations are necessary to clarify this point.…”

“…Since these values are much lower than those found for C * , the question was then "is the polymer aggregation in the aqueous phase really related to the CC values?" Differences between C * and CC values can be explained as follows: at CC, a dense and viscoelastic DexP layer is formed at the air-water interface, with no possible diffusive exchange with the bulk phase since the polymer, having much more than one phenoxy anchoring group per chain, is quite irreversibly adsorbed at the interface (19)(20)(21). Thus, further increases in the bulk concentration do not cause any more adsorption and the surface tension remains constant, even in the absence of large polymeric aggregates in the solution.…”

Preparation and Properties of Moisture-absorbing Film Impregnated with Polyacrylic Acid Partial Sodium Salt Material

“…수분을 흡착하는 역할을 한다 [12]. 이 PASS은 무독성 물질로 수분과 직접 접촉으로 빠르게 수분을 흡수하여 위생용품, 의료용, 그리고 산 업용 실링재 등 상용화 소재로 사용되고 있다 [13].…”