Change in chirality of semiconducting single-walled carbon nanotubes can overcome anionic surfactant stabilisation: a systematic study of aggregation kinetics

Abstract

Single-walled carbon nanotubes’ (SWNT) effectiveness in applications is enhanced by debundling or stabilization. Anionic surfactants are known to effectively stabilize SWNTs. However, the role of specific chirality on surfactant-stabilized SWNT aggregation has not been studied to date. The aggregation behavior of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalized with three anionic surfactants—sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium deoxycholate (SDOCO)—was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and di-valent (CaCl2) electrolytes as well as a 2.5 mg TOC/L Suwannee River humic acid (SRHA) were used as background chemistry. Overall, SDBS showed the most effectiveness in SWNT stability, followed by SDOCO and SDS. However, the relatively larger diameter (7,6) chiral tubes compromised the surfactant stability, compared to (6,5) chiral enrichment, due to enhanced van der Waals interaction. The presence of di-valent electrolytes overshadowed the chirality effects and resulted in similar aggregation behavior for both the SWNT samples. Molecular modeling results enumerated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of SRHA under 10 mM monovalent and mixed electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilization of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure.

Aggregation Behavior of Multiwalled Carbon Nanotube-Titanium Dioxide Nanohybrids: Probing the Part-Whole Question

“…1,37,40,41,45 The MWNTs show the highest EPM values among all the materials (−3.15 ±0.09 × 10 −8 to −1.87 ± 0.07 × 10 −8 m 2 V −1 S 1− at 1 to 100 mM NaCl, respectively), and the values are within the range of previous literature reports (−3.5 × 10 −8 to −2.4 × 10 −8 m 2 V −1 S 1− with high and low oxygen content, respectively at low ionic strength). 25 The highly negative EPM values of the MWNTs likely originate from the ionizable oxygen, attributable to functional groups etched onto MWNT exterior and at the open tube ends during the acid-treatment process.…”

“…The experimental details of the aggregation kinetics experiments and data analysis have been described elsewhere 24,37,40,41,45 and in the SI. The critical coagulation concentration (CCC) parameters are estimated from the intersection of the best-fit lines, fitting the reaction limited aggregation (RLCA) and diffusion limited aggregation (DLCA) regimes.…”

Importance and challenges of environmental ligand binding and exchange: Introducing single molecule imaging as a model characterization technique

“…Several studies have highlighted the importance of NOM and complexity in NOM chemistry on aggregation, transport, and toxicological behavior of NMs [79][80][81][82][83][84][85][86][87][88][89] . However, most of these studies use standardized humic and fulvic acids (e.g., Suwanee River humic acid and NOM) as representative NOMsnano-EHS studies [79][80][81][82][83][84][85] and analyze the role NOM adsorption on nano-EHS. Though the complexity in NOM chemistry is appreciated in literature, little attention has been given to deconvolute the real-life complexity of NOMs.…”

“…Complexity of NM interaction in natural environment further increases from the presence of pre-existing surface coatings on engineered NMs, which are intentionally introduced to particle surfaces for achievinghigher colloidal stability 90 . Small charged molecules (e.g., citrate) and larger synthetic macromolecules, polymeric surfactants, polyelectrolytes (e.g., poly acrylic acid), or nonionic polymers (e.g., polyvinylpyrrolidone) are the most commonly used capping agents for engineered NMs 91 .Surfactants and polymers can be anionic, cationic, zwitterionic, and nonionic 92 , and can either be chemically bound via covalent bonding 93,94 , physisorbed by electrostatic or short ranged hydrophobic interactions 95,96 , or grafted 97 ontoor from the NM surfaces. Different biomolecules are also introduced on NM surfaces as stabilizers, primarily in biomedical and therapeutic applications 98 .…”

Foreword to the Research Front on ‘Nano 2014'

“…The issue continues [3] with methodological development and data for metal NP concentrations in earthworms, allowing bioaccumulation to be quantified. Khan et al [4] further present a study of the critical effects on aggregation of carbon nanotube (CNT) chirality, an important physical property of CNTs. The paper illustrates the significance of NP physico-chemistry on environmental fate and toxicology.…”