Ionic amphiphilic diblock copolymers, such as polystyreneb-poly(styrenesulfonate), show non-surface activity when some requirements are satisfied. The main origin of this unique property has been thought to be an image charge repulsion at the air/water interface. In this study, surface activity/non-activity was examined for random copolymers in addition to homopolymers. Random copolymers of styrene and styrenesulfonate were found to be surface active, while the poly(styrenesulfonate) homopolymer was slightly surface active. This observation cannot be interpreted by image charge repulsion alone since these are all polyanions and the block copolymer is mostly hydrophobic. Stable polymer micelle formation in the block copolymer system is also an essential origin of non-surface activity.Ionic amphiphilic diblock copolymers, which consist of hydrophobic and ionic blocks, show non-surface activity under suitable conditions.19 Their aqueous solutions show no or little reduction of surface tension and foam formation, while a multimolecular micelle is formed in the bulk solution. This phenomenon is, in a sense, out of common sense of surface and interface science since the micelle has been believed to be formed by the "surfactant (surface active agent)" above the critical micelle concentration (cmc). We have systematically investigated this unique property for strongly 1,2,4,5 and weakly 3 anionic amphiphilic block copolymers and also cationic 6,7 block copolymers. As a result, we have proposed an image charge effect 1014 at the air/water interface as the first essential origin of this phenomenon. Since the hydrophilic segment is a polyelectrolyte, which has many charges, the block copolymer adsorbed at the air/water interface by a hydrophobic effect is destabilized by strong image charge repulsion from the water surface. When salt was added into the solution, the polymers changed to be surface active; the surface tension of the solution decreased and showed foam formation activity. From this result, it is obvious that the electrostatic effect plays an important role in the origin of non-surface activity.4 Also, when the hydrophobic block becomes long enough compared to the length of the hydrophilic, ionic block, the polymer shows surface activity. The hydrophobic adsorption effect might be stronger than the image charge repulsion. Also, the total length (molecular weight) should be long enough to be surface active. Chen et al. reported that the polymer with a block length of m:n = 30:30 was non-surface active while m:n = 15:15 polymer showed surface activity.9 In this sense, non-surface activity is some kind of polymer effect. Furthermore, non-surface activity was also observed and has been reported by other researchers for different systems. 1523On the other hand, most polyelectrolyte homopolymers are slightly surface active. 24,25 Sen et al. reported the reduction of surface tension of aqueous poly(styrenesulfonate) (PSS) solutions, 24 and Yim et al. detected the adsorbed poly(syrenesulfonate) potassium salt molecule...

Amphiphilic random copolymers of poly(γ-glutamic acid)-graf t-L-phenylalanine (γ-PGA-Phe), with various lengths of γ-PGA main chains (molecular weight of 70, 140, and 220 kDa) plus hydrophobic moieties of Phe groups (grafting degree 12−60%), self-assembled in aqueous media to form nanoparticles (NPs). The aggregation number (N agg ) could be adjusted according to their molecular structures as well as the preparative methods/conditions. The γ-PGA-Phe NPs were further characterized by means of dynamic and static light scattering, small-angle neutron scattering, as well as steady-state fluorescence measurements/quenching techniques. The single chain state had hydrophobic domains, and formed spherical structures, herein called unimer NPs, and were obtained using molecular weights of γ-PGA higher than 140 kDa conjugated with Phe at 27−42% due to the balance of hydrophobicity/hydrophilicity along the single polymer chain. The number of hydrophobic domains in one NP (N domain ), estimated by means of fluorescence quenching techniques and the rigidity of the inner particles detected by dipyrene fluorescence demonstrated that the N domain and the rigidity were affected by the particle size and preparative methods. In addition, the effect of pH on the stability of the unimer NPs indicated a reduction of the N domain upon the pH, supporting a loose packing due to hydrophobic association under alkaline conditions.

Surface tension and micellization behavior of an ionic amphiphilic diblock copolymer, poly(n-butyl acrylate)-b-poly(styrenesulfonate) sodium salt, which shows non-surface active nature in pure water, were investigated in seawater. The block copolymer became surface active in seawater, but the relationship between polymer concentration and surface tension showed a second bending point at a higher concentration in addition to that at the critical micelle concentration (CMC). Polymer micelles were also found in seawater, although the hydrodynamic size was very small. However, larger aggregation numbers of micelles were found in solutions above the second bending point. Experiments using solutions with one, two, or three salt species revealed that cmc was governed by sodium chloride, which is the most abundant salt in seawater, but the micelle structure was sensitive to divalent ions such as Ca2+ and Mg2+, although their amount is very small compared to that of NaCl.