Abstract
1/1 dispersions of ss-DNA/CNT complexes in mass ratios were investigated in a mixture with didodecyldimethylammonium bromide, DDAB. Depending on the amounts of the surface-active agent and of the complexes, solutions, precipitates, or re-dissolution occur. DDAB titrates the phosphate groups on the outer surface of the complex and controls the phase sequence in these systems. The combination of different experimental methods determined the phases that occur therein. The results are based on optical absorbance, Dynamic Light Scattering, ionic conductivity, ζ-potential, optical microscopy and AFM. From the above findings a (pseudo)-binary phase diagram is attained. The system has strong similarities with polymer-surfactant mixtures. In fact, its properties conform to cases in which interactions between rigid rod-like polyelectrolytes and oppositely charged species take place. The peculiarities of double-chained DDAB in the process imply significant differences with respect to the behavior of single chain surfactants. In fact, DDAB associates into vesicular entities, when the homologous single chain species forms small micellar aggregates.
Highlights
Colloids exhibit different organization modes, depending on whether they belong to the intrinsic or the association category [1,2,3]
We report on systems made of carbon nanotubes, CNTs, onto which single-strand DNA, ss-DNA, is anchored by non-covalent functionalization
We report on the fundamental aspects of such mixtures, and make evident the similarities and differences met between the present and canonical polymer-surfactant systems
Summary
Colloids exhibit different organization modes, depending on whether they belong to the intrinsic or the association category [1,2,3]. In real applications the above classification loses relevance. Mixing intrinsic and association colloids gives entities that do not univocally fit in any of the above definitions. Hybrid organic/inorganic colloids from sea shells [4] are examples of the above statements. Efforts were made to build up hybrid colloids by mixing those from intrinsic and association categories, in such a way that their properties self-support and self-complement [5]. Well focused experiments allow getting hybrid materials in which inorganic particles anchor bio-macromolecules. Protein-functionalized silica particles are an example [6,7]
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