rheological properties. They may be easily hydrophobically
The dynamic surface tension of aqueous solutions of ethyl (hymodified by grafting small amounts of nonyl phenol groups droxyethyl) cellulose (EHEC) and hydrophobic modified ethyl to the hydrophilic chains. Since this is usually achieved by (hydroxyethyl) cellulose (HM-EHEC) were determined using the a heterogeneous reaction, regional variations in the degree maximum bubble pressure method. Values were monitored over of crystallinity/amorphous of the polymer result. This gives surface lifetimes ranging from 0.15 to 2.5 s (after dead time correcrise to diversifications in the hydrophobic/hydrophilic nature tions). In the low concentration range (รต100 ppm) HM-EHEC of the polymer backbone. One of the major advantages of was shown to be more surface active, and the presence of salt (0.1 these polymers is that the high-molecular-weight versions M) was shown to increase the surface activity of both polymer systems. The results were compared with surface tension measure-are capable of producing high-viscosity aqueous solution ments carried out over longer time scales, determined using the even at low concentration. They are also surface-active du Nouy ring technique. From these results, isotherms were conagents and adsorb strongly at the solid/water, air/water, and structed relating surface tension to surface aging time. Although oil/water interfaces, and this has resulted in their application the results could not be directly correlated to interfacial diffusion as speciality chemicals in mineral processing (flotation demodels, the isotherms were found to be comparable to previous pressants), in ceramic processing (binders and dispersants), data reported for lower-molecular-weight poly(oxyethylene ether) and in polymerization (protective colloids).
surfactants and a higher-molecular-weight EHEC polymer deter-
Recently, the dynamic interfacial characteristics of these mined using the pendant drop technique. Essentially, the isopolymers have been determined on a time scale extending therms could be divided into distinct regions: induction period, from 30 s to about 17 h using the pendant drop technique fast fall region where surface coverage occurs fairly rapidly, and finally the meso-equilibrium region. From the Gibbs equation, the (1, 2). From these studies, it was reported that the polymer number of segments of polymer per unit surface area at saturated molecules slowly diffuse and adsorb at the interface and adsorption levels was calculated over regions of different aging these processes are followed by configuration changes. Also, times, and the results are discussed in terms of configuration it was shown that the surface tension-versus-time isotherms changes of the polymer at the interface. แญง 1997 Academic Press follow a sigmoidal pattern, and from these data it was possi-Key Words: ethyl (hydroxylethyl) cellulose; hydrophobically ble to identify separate consecutive kinetic regions: the inmodified; dynamic interfacial tension measurements; maximum duction period, the surface coverage, and finally a mesophase bubble pressure method.
region. In the mesophase region, slow equilibration occurred which involved a progressive ordering of the polymer segments within the surface layer. In fact, a constant steady-state