The Interaction Between Surfactants and 2-Hydroxy-3-(N,N-dimethyl-N-dodecylammonium)-propyloxy Starches

Surfactant Structure-Dependent Interactions with Modified Starch Nanoparticles Probed by Fluorescence Spectroscopy

The interactions between the surfactants sodium dodecyl sulfate (SDS) and sodium dioctyl sulfosuccinate (AOT) and starch nanoparticles (SNPs) hydrophobically modified with the hydrophobic dye pyrene (Py-SNPs) were investigated in water by steady-state and time-resolved fluorescence. The Py-SNPs formed interparticulate aggregates in water, which were disrupted by adding SDS to the Py-SNP aqueous dispersions. SDS was found to interact with Py-SNPs at SDS concentrations that were close to 2 orders of magnitude lower than its critical micelle concentration (CMC). These interactions led to the breakup of the Py-SNP aggregates, which was confirmed by conducting fluorescence resonance energy transfer experiments between naphthalene-labeled SNPs (Np-SNPs) and Py-SNPs. By the time the SDS concentration reached the CMC of SDS, the Py-SNPs were separated from each other and excimer was generated from isolated Py-SNPs in the aqueous dispersions. Whereas SDS interacted with the Py-SNPs at SDS concentrations lower than CMC, SDS did not seem to target the hydrophobic pyrene aggregates. Only above the CMC did SDS appear to interact with the pyrene aggregates, as evidenced from diffusive pyrene excimer formation between excited and ground-state pyrenes. Most surprisingly, no interaction was observed between sodium dioctyl sulfosuccinate (AOT) and Py-SNP at AOT concentrations where SDS interacted with the Py-SNPs. This observation led to the conclusion that SDS below its CMC interacted not with hydrophobic pyrene aggregates but rather through the formation of inclusion complexes, which led to the electrostatic stabilization of individual Py-SNPs and enabled the breakup of Py-SNP aggregates. The formation of inclusion complexes with linear surfactants like SDS might thus provide a new means of stabilizing hydrophobically modified starch nanoparticles in water, which bears the promise of finding future applications.

Improving the performance of starch-based wood adhesive by using sodium dodecyl sulfate

Sodium dodecyl sulfate (SDS) was used to improve the performance of starch-based wood adhesive. The effects of SDS on shear strength, viscosity and storage stability were investigated. It was shown that, although the addition of 1.5-2% (dry starch basis) SDS resulted in a slight decrease in shear strength, the mobility and storage stability of adhesive were significantly enhanced. Possible mechanisms regarding specific action of SDS were discussed. It was proved, using blue value or differential scanning calorimetry (DSC) analysis, that the amylose-SDS complexes were formed in the adhesive. The complex formation or simple adsorption of SDS with starch molecules might hinder the aggregation of latex particles, as shown by scanning electron microscopy images, and inhibit starch retrogradation, as observed by DSC analysis. As a result, in the presence of SDS, the adhesive had higher mobility and storage stability, indicating that SDS could be used to prepare starch-based wood adhesives with high performance.