Dynamic Surface Properties of Solutions of Poly(ethylene oxide) and Polyethylene Glycols

Abstract

The damping coefficient and the length of transversal (at the frequencies from 100 to 300 Hz) and longitudinal (at the frequencies from 0.1 to 3 Hz) surface waves have been measured as a function of the concentration of solutions of poly(ethylene glycol)s (PEG) and poly(ethylene oxide) (PEO), and the molecular weight of the polymer. A local maximum of the damping coefficient of transversal waves has been discovered for dilute solutions of PEG 400. This maximum disappears and the damping coefficient decreases monotonically with the concentration of polymers of higher molecular weight in the region of dilute solutions. A fast increase of the damping with concentration has been discovered for semidilute solutions. These experimental data are used for the calculation of the real and imaginary components of the dynamic surface elasticity as a function of concentration and frequency. The obtained dependencies can be explained with the help of a dynamic model of the surface layer of polymer solutions where the main relaxation processes are connected with the monomer exchange between different regions of the surface layer. In the investigated concentration range, the corresponding relaxation time determined from the experimental data changes by more than 2 orders of magnitude.

Dynamic Properties of Poly(styrene)–Poly(ethylene oxide) Diblock Copolymer Films at the Air–Water Interface

“…If the number of loops and tails decreases, the relaxation time increases and can be determined by the experimental methods used in this work. This is probably the case of poly(ethylene glycol)-adsorbed surface films where the number of loops and tails can be determined by more or less fortuitous details of the adsorption process and where the relaxation times in the range from 0.001 to 0.1 s have been discovered recently (36,37). It follows also from the obtained results that the dissolution of PEO segments as loops and tails starts not at the beginning of the pseudoplateau, as usually considered (8,45), but in the region of the maximum of the surface elasticity where the dynamic surface elasticity begins to deviate from the static values.…”

“…The experimental setups for measurements of the surface wave characteristics and surface tension oscillations in a Langmuir trough together with the corresponding experimental procedures were described in detail elsewhere (37)(38)(39)(40)(41)(42). Here, only the basic principles of the employed techniques are given.…”

“…The longitudinal waves were created by harmonic oscillations of a platinum wire (of 0.1 mm diameter) immersed in the liquid and moving parallel to the surface (37,40). Transverse capillary waves of higher frequency (180 Hz) propagating perpendicular to the longitudinal waves were used to detect the longitudinal oscillations of the liquid surface.…”

“…Only Naumann et al have investigated recently the surface shear viscoelasticity of grafted polymers in a narrow frequency range close to 1 Hz (26). Meantime recent studies of adsorbed films of PEO and poly(ethylene glycol) at the water-air interface have discovered relaxation processes with characteristic times from 0.001 to 0.1 s, thus indicating the importance of frequencies in the range between 0.01 Hz and 10 kHz for copolymers containing PEO blocks (36,37).…”

Dynamic Surface Properties of Poly(vinylpyrrolidone) Solutions

“…The deviation of the transverse surface viscosity from zero in contradiction to the theory is another problem of this method (11). Moreover, the SQELS method can be applied only at high frequencies (≥10 Hz) while the main relaxation processes for polymer films usually correspond to the lower range of the spectrum (12,16,17) where other methods of mechanical relaxation spectrometry of surface layers must be used.…”