Studies On Organized Assemblies And Functional Properties Of Sodium Alginate And Its Derivates

Alginate has been extensively used in the fields of pharmacy, food and cosmetics due to its natural, non-toxic, safty, biocompatibility, degradability and absorbability. Based on the self-assembly behaviors of sodium alginate (NaAlg) in aqueous solution, the effects of pH and hydrophobic modification on the properties and structures of NaAlg aggregates have been investigated. The possible mechanisms of the interactions between NaAlg and traditional surfactants have been proposed. Subsquently, gold and silver nanoparticles with particular size and morphology have been fabricated using NaAlg (and NaAlg/surfactants aggregates) as soft templates.Main results and conclusions are as follows,1. In the dilute NaAlg solution containing inorganic salt, the pH effect on the aggregate structures was investigated. Because plenty of hydrophilic–COO- groups in the NaAlg polymer chain switched to–COOH groups, which can induce the NaAlg molecular chains aggregating into micelles untile the random group-like precipitate is generated. At pH 3.0-4.0, spherical micelles can be clearly observed by TEM and AFM, which was in the coindence with the proofs of fluorescence spectroscopy, electrical properties, laser light scattering and other experimental results. When pH value of the system decreases to about 2.0, electrostatic repulsion among the micelles obviously weakens, resulting in approach and aggregation among micelles. As the pH value further decreases, alginate acid heavily aggregates, and the precipitation finally appears.2. Interactions between cationic surfactant cetyltrimethylammonium bromide (CTAB) and NaAlg are studied with isothermal titration calorimetry, surface tension, conductivity, Zeta potential, viscosity and fluorescence spectrum, etc. In the NaAlg / CTAB system, the c1 of CTAB decreases and c2 increases as the concentration of NaAlg increases. As the surfactant concentration is less than c1, CTAB monomers mainly manifest oriented adsorption on the solution surface, and surface tension of the solution apparently decreases. When the surfactant concentration is over c1, electrostatic interactions between the cationic polar heads on CTAB monomers and -COO- groups along alginate chains take place, and hydrophobic microdomain forms. When the CTAB concentration further increases and excesses cζ=0, hydrophobic interactions happen between hydrophobic chains of CTAB monomers and hydrophobic microdomain of CTAB/alginate complexes. When the CTAB concentration further increases till more than c2, the degree of combination of CTAB molecules with alginate macromolecule chain is saturated, then CTAB monomers begin to form free micelles that coexist with mixed CTAB/alginate micelles. Moreover, with the decrease of the pH of the solution, this makes larger networking aggregate and the viscosity of solution sharply increase.3. The complex micelle can be formed between NaAlg and the anionic surfactant sodium dodecyl sulfate (SDS) as well as the non-ionic surfactant octylphenol polyethoxylates (Tritonx-100), which depends upon the pH value and salt concentration of the solution. In the experimental conditions, when the pH value of the solution decreases from 7.0 to 5.0, SDS can not combine with alginate because of electrostatic repulsion. As the pH value of solution decreases from 5.0 to 3.0, NaAlg combines with SDS to form complex micelle by hydrophobic interaction. At the same time, TritonX-100 and NaAlg form complex micelle by hydrophobic interaction in the acidic solution.4. NaAlg reacts with fatty amine in the presence of the coupling agent, 1-ethyl- (3-dimethylamino-propyl) carbodiimide (EDC) to obtain hydrophobically modified alginate derivative. The products are characterized by FT-IR, 1H-NMR, DSC and TG, etc, and the substituting degree of amide is confirmed by elementary analysis. The self-assembled behaviors of the hydrophobically modified alginate derivatives (HMA-R) and the interactions between alginate derivatives and surfactants in aqueous solution are investigated by isothermal titration calorimetry, fluorescence spectrum, surface tension and conductivity, etc. In the dilute solution, surface tension of the derivatives solutions decreases as the concentration increases. At the same concentration, the surface tension and conductivity decreases as the substituting degree increases. At the same substituting degree and concentration, surface tension decreases as the number of carbon in the hydrophobic pendants increases. Fluorescence spectroscopy shows hydrophobic microdomain can be formed in the lower concentration and the polarity of microdomain decreases as substituting degree increases. Interactions between SDS and hydrophobically modified alginate derivatives mainly manifest the hydrophobic combination, and the surface tension of mixed system is much lower compared to that of indivadule system. In the mixed system the c1 of SDS will decrease and the c2 of SDS increase with substitution degree increasing.5. The gold and silver nano-micnon particles are fabricated by a seeding growth approach in NaAlg solution. The formation mechanisms of noble metal nano-micnon particles are explored in NaAlg solution with or without different surfactants by means of UV-vis spectrum, FT-IR, X-ray diffraction and transmission electron microscope (TEM), etc, and then the variation laws of microstructures, sizes and morphologies of the noble metal materials are revealed. The results show that NaAlg reduces HAuCl to Au in NaAlg/HAuCl4 reaction system, and the nucleation process can be strengthened by the microwave radiation. Once crystal nucleus forms, Au ion on crystal nucleus can be easily reduced to elementary substance and then grow. From X-ray diffraction analysis, the crystal face (111) of prepared gold nanoparticles show a great diffraction intensity, which demonstrates that gold nanoparticles can easily grow along the face. We also find that surfactants have unique influence on preparing gold nanoparticles. At ambient condition, sodium alginate slowly reduces Ag(I) to Ag(0) on the surfaces of Ag seeds, and then form branch structure. Ag particles aggregate into the branch structures with different morphologies under various concentration of NaAlg aqueous solution.