Abstract
In this review the dispersability of carbon nanotubes in aqueous solutions containing proteins, or nucleic acids, is discussed. Data reported previously are complemented by unpublished ones. In the mentioned nanotube-based systems several different phases are observed, depending on the type and concentration of biopolymer, as well as the amount of dispersed nanotubes. The phase behavior depends on how much biopolymers are adsorbing, and, naturally, on the molecular details of the adsorbents. Proper modulation of nanotube/biopolymer interactions helps switching between repulsive and attractive regimes. Dispersion or phase separation take place, respectively, and the formation of liquid crystalline phases or gels may prevail with respect to dispersions. We report on systems containing ss-DNA- and lysozyme-stabilized nanotubes, representative of different organization modes. In the former case, ss-DNA rolls around CNTs and ensures complete coverage. Conversely, proteins randomly and non-cooperatively adsorb onto nanotubes. The two functionalization mechanisms are significantly different. A fine-tuning of temperature, added polymer, pH, and/or ionic strength conditions induces the formation of a given supra-molecular organization mode. The biopolymer physico-chemical properties are relevant to induce the formation of different phases made of carbon nanotubes.
Highlights
The combination of their outstanding mechanical, optical, thermal, and electrical conductive properties [1,2] makes nanoparticles useful in the preparation of advanced composites
We report on different aspects and available information on CNT-biopolymer systems
We focused on the possibilities offered by mixing carbon nanotubes and biopolymers
Summary
The combination of their outstanding mechanical, optical, thermal, and electrical conductive properties [1,2] makes nanoparticles useful in the preparation of advanced composites. Functionalization favors the formation of specific groups on CNTs and offers the possibility to anchor binding sites on their surface Such new sites are potentially reactive towards many chemicals. The interactions between CNTs and amino acids or nucleotides functionalize their surface, through anchorage of a given functional group [18] The latter composites, obviously, do not enter into the category of biopolymer-based stabilization. If the effective surface properties are not properly considered, the analysis of the interactions taking place between CNTs and bio-macromolecules may give questionable results [28]. This is because adsorption preferentially takes place onto surface defects, kinks, or at the particles’ edges [29]. Data reported by us or other researchers, indicated in the following, are complemented by unpublished work
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