Long-wavelength dynamics of spread films of poly(methyl methacrylate) and poly(ethylene oxide) at the air/water interface

Abstract

Surface quasi-elastic Jight scattering data for poly(methy1 methacrylate) (PMMA) and poly(ethy1ene oxide) (PEO) films spread at the air/water interface have been interpreted using simple phenomenological models. PMMA behaves as a Voigt solid, whereas PEO can be described as a Maxwell fluid. However, the surface waves for the spread PEO film exhibit mode mixing at a surface concentration of ca. 0.6 mg m-* which is where the polymer penetrates the subphase. Although negative dilational viscosities are observed and the dependence of the normalised damping coefficient of the capillary waves on surface wave number is commensurate with such dilational viscosities being the source of mode mixing, large positive values of the transverse viscosity are also evident. Such large transverse viscosities were originally cited as the cause of mode mixing. However, the dispersion curves of the normalised damping coefficient do not reproduce the experimental observations for the spread PEO films. It is speculated that the negative dilational viscosities may be the result of the current absence of appropriate theory which would lead to a more accurate dispersion equation.

Interfacial behaviour of poly(lactic acid) and Pluronic6400 mixed monolayers at the air–water interface

“…Several investigations concerning the interfacial properties of spread PEO [20][21][22][23] and also PEO-containing diblock copolymer layers [24][25][26][27][28][29] were interpreted based on the scaling theory. The various regions of the isotherm can be assigned to different conformations or conformational transitions of the polymer chains.…”

Relaxation Processes in Surface Excess Layers of Aqueous Solutions of Poly(ethylene oxide)

“…In Figure we do see a reduction in the magnitudes of the dilational viscosities of the three polymer solutions with increasing frequency; however, the sign of all of the measured viscosities is negative. This apparently unphysical result has been observed independently in other PEO-containing systems and low molecular weight surfactant solutions. ,,,

5 SQELS-determined values of dilational modulus for the 15 K (○), 106 K(▵), and 828 K (+) polymer solutions.

6 SQELS-determined values of dilational viscosity for the 15 K (○), 106 K (▵), and 828 K (+) polymer solutions.

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“…The measurement of negative dilational viscosities is not unique to this system or this laboratory; ,,, generally, they are observed in systems characterized by the surface active materials being soluble. The exception to this are recent experiments in this laboratory on some insoluble spread films (spread PEO, PMMA- graft -PEO 9,11 ) which have also shown negative dilational viscosities, but only when the subphase becomes appreciably penetrated by one or more components of the polymer.…”

“…The Voigt model predicts a frequency-independent γ ο (ε ο ) and γ‘ (ε‘), whereas the Maxwell model predicts a relaxation region where γ ο (ε ο ) increases and γ‘ (ε‘) decreases. Although these models have been successfully applied to surface films, ,,, they are only phenomenological: the notional “spring” and “dashpot” cannot easily be related to real physical parameters.…”

“…SQELS has previously been applied to various polymer film systems, − including some studies on PEO-containing copolymers and PEO homopolymer films, although different workers have studied different aspects of the systems. Sauer and Yu 17 investigated spread and adsorbed films of PEO using a similar molecular weight range to that used here but at much lower bulk polymer concentrations (10 -4 to 10 -3 %w/w) and found no difference in the adsorbed and spread film behavior.…”