Subphase pH Effect on Surface Micelle of Polystyrene-b-poly(2-vinylpyridine) Diblock Copolymers at the Air−Water Interface

Abstract

The subphase pH effect on the surface micelles of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers was investigated by the π−A isotherm and the morphology of the Langmuir−Blodgett (LB) film. Ionization of P2VP block significantly affects the π−A isotherm of the surface micelles at the air−water interface. At high pH, where the degree of ionization is low, the π−A isotherm shows a more expanded form and high transition surface pressure reflecting the strong tendency of P2VP blocks spreading on the subphase surface. As the subphase pH is lowered, the transition surface pressure decreases while the transition region is more extended, indicating the facile equilibrium between the flotation and submergence of the P2VP blocks upon surface pressure change. At pH 1.8 at which the 2VP units are completely ionized, the ionized P2VP blocks submerge into the subphase even at low surface pressure, and the transition behavior is not observed. The π−A isotherm behavior can be understood considering the balance of the solubility and the electrostatic repulsion of the ionized P2VP chains. Atomic force microscopy images of the LB films of the PS-b-P2VP surface micelles show isolated circular micelles at high pH. As the subphase pH decreases, the intermicellar distance becomes shorter and the micelles eventually contact each other to form a laced network of circular micelles. The association behavior of surface micelles and the π−A isotherms at low pH are strongly dependent on the ionic strength of the subphase. The linear association of the surface micelles at low pH appears to result from the balance of the hydrophobic attraction among the floated PS cores and the electrostatic repulsion among the submerged P2VP chains. On the other hand, the average aggregation number of each surface micelle is independent of subphase pH, which indicates that the aggregation of the block copolymers to form surface micelles is likely to take place before the P2VP blocks are ionized.

Cationic Gemini surfactant at the air/water interface

“…The variation of morphology of 18-Ar-18,2Br −1 with increasing surface pressure at the air/water interface resembles that of the diblock copolymers [51][52][53]. Prior to A L being reached, a complete absence of surface pressure suggests that the alkyl chains are in horizontal configuration.…”

Creation of dense polymer brush layers by the controlled deposition of an amphiphilic responsive comb polymer

“…In fact, the size of features in the SFM images matches exactly with the calculated area/molecule deposited with the LB trough further supporting an average molecular weight of the comb molecules as being around 130 kDa. Some research into creating dense layers via amphiphilic copolymer LB assembly has been performed in the past [26][27][28][29][30][31][32][33][34][35], but we have shown that multi-molecular micellation (creating structures > 100 nm) has been largely prevented through controlling polymer chain architecture. Such films could potentially be used as ultrathin size-selective nanofiltration films for sensor applications, templates for nanolithography, or an environmentally acceptable way to tune the physical and chemical properties of a flat surface.…”

In situ investigation of annealing effect on lamellar stacking structure of polyethylene thin films by synchrotron grazing-incidence small-angle and wide-angle X-ray scattering

“…The q y of these peaks relates to the long period, the average distance between stacked crystalline lamellae. The Yoneda peak arises in the in-plane direction owing to the interference effect of the incident and scattered wave (Chung et al, 2006). By stepwise annealing, these scattering peaks slightly shifted to the lower q y range in the in-plane direction and increased in relative intensity with an increase in T a .…”

“…GISAXS analysis based on distorted-wave Born approximation (DWBA) theory was applied for various multi-layer systems consisting of these films and substrates (Mü ller-Buschbaum et al, 2004;Xu et al, 2004;Tang et al, 2005;Park et al, 2005;Chung et al, 2006). In this study, we have tried to detect grazingincidence small-angle and wide-angle X-ray scattering (GISWAXS) from crystalline polymer thin films.…”