The behavior of alternating poly(styrene−maleic anhydride) (SMA) in aqueous solution and at the air−water interface was studied by static and dynamic light scattering, by surface tension measurements, and by transmission electron microscopy (TEM). The variables of interest were the polymer concentration, the molecular weight, and the degree of ionization varied with pH. SMA polymers can associate in aqueous solution. The critical size of SMA in solution ranges from the predicted Gaussian radius of gyration (r g) up to 150 nm. The size of the associates increases with decreasing molecular weight. A maximum in associate size was measured at pH = 6.5, which corresponds to the polymer salt under its monosodium form. A mechanism by which SMA molecules zip together forming a macrocoil made of two molecules in cross section was proposed. SMA molecules also adsorb at the air−water interface, very likely as 2D-coils. An equilibrium links the concentration of SMA in solution and at the air−water interface.
The corona compositions and morphologies in aggregates of mixtures of amphiphilic polystyrene-block-poly(acrylic acid) (PS-b-PAA) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers are influenced by controllable assembly parameters such as the hydrophilic block length and solution pH. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. When mineral acids or bases are present during aggregate formation, they can exert a strong influence on the corona composition. Morphology changes were also seen with changing pH, as well as changes in corona composition, specifically for vesicles. Because of complications introduced by the presence of ions, the general hypothesis that the external corona of the vesicles is composed of the longer chains, while the shorter chains form the inner corona, which is valid only in mixtures containing only nonionic chains without any additives (no acids or bases) or within a well-defined narrow pH range. In addition to the numerical block lengths and the pH, the solubility of the hydrophilic blocks can also influence the morphology and as well as the interfacial composition of vesicles; as the numerically longer chains become less soluble, they can contract and move to the interior, while the numerically shorter but more soluble chains go to the external corona. A remarkable morphological feature of the pH continuum is that for some compositions vesicles are observed in four distinct pH regions, separated by pH ranges in which other morphologies dominate. The effect of pH and microion content on coil dimensions of the PVP and PAA chains in the block copolymers is most likely responsible for the observed behavior.
The morphologies and corona compositions in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers are influenced by controllable assembly parameters such as water content, block copolymer molar ratios, and solvent effects as well as the hydrophilic block lengths and block length ratios. All these factors can affect the morphology of the aggregates as well as their corona composition, the latter especially in vesicles, where two interfaces are involved. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. They depend, to a large extent, on the solubility of P4VP and PAA in the given organic solvent (e.g., DMF, THF, or dioxane), which influences the coil dimensions of the hydrophilic chains. The water content affects both the size and the shape of the block copolymer aggregates as well as the corona composition. Water acts as a precipitant for the hydrophobic block in the common solvent and, therefore, its progressive addition to the solution changes the interaction parameter with the hydrophobic block. The block copolymer molar ratio has an effect on both the morphology and the corona composition of the aggregates. With increasing PS-b-P4VP content in the mixture, the morphology transforms gradually from large compound micelles (LCMs), through coexistence of LCMs and small spherical micelles (SSMs), and eventually to vesicles. As expected, the corona composition of the aggregates is also affected by the block copolymer molar ratio, and changes progressively from pure PAA to a mixture of PAA and P4VP and to pure P4VP with increasing PS-b-P4VP content. It is clear that the use of mixtures of the soluble chains offers the opportunity of fine-tuning the corona composition in block copolymer aggregates under assembly conditions.
The kinetics of loading of polystyrene197-block-poly(acrylic acid)47 (PS197-b-PAA47) micelles, suspended in water, with thiocyanomethylthiobenzothiazole biocide and its subsequent release were investigated. Loading of the micelles was found to be a two-step process. First, the surface of the PS core of the micelles is saturated with biocide, with a rate determined by the transfer of solid biocide to micelles during transient micelle-biocide contacts. Next, the biocide penetrates as a front into the micelles, lowering the Tg in the process (non-Fickian case II diffusion). The slow rate of release is governed by the height of the energy barrier that a biocide molecule must overcome to pass from PS into water, resulting in a uniform biocide concentration within the micelle, until Tg is increased to the point that diffusion inside the micelles becomes very slow. Maximum loading of biocide into micelles is approximately 30% (w/w) and is achieved in 1 h. From partition experiments, it can be concluded that the biocide has a similar preference for polystyrene as for ethylbenzene over water, implying that the maximum loading is governed by thermodynamics.
An extremely efficient bactericidal filter paper is developed that is capable of removing 99.99999% of Escherichia coli bacteria in a simple filtration process. The novel approach utilizes two active bactericidal components: a bactericidal agent, triclosan, which acts synergistically with a cationic polyelectrolyte binder with antibacterial properties. The biocide is incorporated into the block copolymer micelles attached to the cellulose fibers via the cationic polyelectrolyte. As the water containing the bacteria is passed by gravity through the filter paper, the bactericidal agents are transferred to the bacteria through collisions with the micelles or coated fibers. A synergy between the biocide and the polyelectrolyte is responsible for the extremely high efficiency in deactivating the bacteria. The filtered water is free of biocide other than that transported by the dead bacteria. This technology represents a very simple approach to provide potable water under a wide range of primitive conditions.
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