Aggregation behavior of hydrophobically modified polyacrylate in aqueous solution

Self-assembly of poly(ethylene oxide)-block-poly(acrylic acid) induced by CaCl2: mechanistic study

The interaction between CaCl 2 and double hydrophilic block copolymer, poly(ethylene oxide) 45- block-poly(acrylic acid) 70, PEO 45- b-PAA 70, was investigated. At a stoichiometric ratio of Ca2+:COO (-) = 0.5, Ca2+ ions were bound to COO (-) groups on PAA segments via electrostatic interaction. Small particles of 4-8 nm in diameter were observed, suggesting the formation of coil-like polymeric globule induced by charge neutralization. At Ca2+:COO (-) >or= 2.5, monodispersed aggregates of average hydrodynamic diameter of 52.0 +/- 7.4 nm were produced. The ISE, ITC, surface tension and fluorescence spectroscopic data confirmed that the formation of these aggregates is not the result of interaction between excess Ca2+ ions and the polymer, but rather it is due to changes in the water activity that triggers the structural rearrangement of Ca2+/PEO 45- b-PAA 70 complex.

Thickening properties and emulsification mechanisms of new derivatives of polysaccharide in aqueous solution

The thickening properties and association behavior of aqueous solutions of HHM-HEC (hydrophobically-hydrophilically modified hydroxyethyl cellulose) with various hydrophobic and hydrophilic substitution degrees were investigated. The HHM-HEC was used as an oil-in-water emulsifier and stable compositional regions were investigated as a function of polymer concentration and substitution degree. The viscosity of aqueous solutions of HHM-HEC increased drastically at lower concentration for HHM-HEC with a higher hydrophobic/hydrophilic substitution ratio. The intensity ratio of the first and third vibrational bands of pyrene (I(1)/I(3)) decreased with the increase of HHM-HEC concentration and the I(1)/I(3) reached a lower plateau at a lower concentration for HHM-HEC with a higher hydrophobic/hydrophilic substitution ratio. The concentration ranges of HHM-HEC solutions which stabilize O/W emulsions differ by the hydrophobic/hydrophilic substitution ratio. However the viscosity ranges of these HHM-HEC solutions were almost the same regardless of the hydrophobic/hydrophilic substitution ratio. At the suitable concentration range for emulsification, HHM-HEC networks have two properties: (1) oil particle retention capacity and (2) laxation which can trap emulsified particles.

Fluorescence enhancement of yttrium(III)-rutin by nucleic acids in the presence of cetyltrimethylammonium bromide

It is found that nucleic acids can enhance the fluorescence intensity of yttrium(III) (Y(3+))-rutin in presence of cetyltrimethylammonium bromide (CTMAB) system. In hexamethylenetetramine (HMTA)-HCl buffer, the maximum enhanced fluorescence is produced, with maximum excitation and emission wavelengths at 452 and 520 nm, respectively. Based on this, a new fluorimetric method of determination of nucleic acids is proposed. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 1.0 x 10(-7) to 1.0 x 10(-5)g/ml for fish sperm DNA (fsDNA), 1.0 x 10(-7) to 4.6 x 10(-6)g/ml for yeast RNA (yRNA), their detection limits (S/N=3) are 7.5 x 10(-8), 8.0 x 10(-8)g/ml, respectively. The interaction mechanism is also studied.