Study of the interaction between a diblock polyelectrolyte PDMA-b-PAA and a gemini surfactant 12-6-12 in basic media

Cationic gemini surfactant as a dual linker for a cholic acid-modified polysaccharide in aqueous solution: thermodynamics of interaction and phase behavior

Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-α,ω-bis(dodecyldimethylammonium bromide) (C₁₂C₆C₁₂Br₂) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (ΔH_obs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.

Interactional behavior of the polyelectrolyte poly sodium 4-styrene sulphonate (NaPSS) with imidazolium based surface active ionic liquids in an aqueous medium

The present study aims to develop an understanding of the interactions between an anionic polyelectrolyte, poly sodium 4-styrene sulphonate (NaPSS), and cationic surface active imidazolium based ionic liquids (SAILs), [Cnmim][Cl] (n = 10, 12, 14) using a multi-technique approach. Various physicochemical and electrochemical techniques such as surface tension, conductivity, fluorescence, isothermal titration calorimetry (ITC), dynamic light scattering (DLS), turbidity, potentiometry, cyclic voltammetry (CV), and differential pulse voltammetry (DPV) are employed to obtain comprehensive information about NaPSS-SAIL interactions. Different stages of interaction, corresponding to the critical aggregation concentration (cac), critical saturation concentration (Cs) and critical micelle concentration (cmc) have been observed owing to the strong electrostatic and hydrophobic interactions, and the results obtained from different techniques complement each other very well. The results extracted from DLS and turbidity measurements clearly indicated that the size of the micelle like aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using potentiometry show a concentration dependence and the highly co-operative nature of the interactions which is attributed to aggregation of the polyelectrolyte-SAIL complexes. The diffusion coefficients (Dm) of the electroactive probe in the pure and NaPSS-SAIL mixed systems were obtained, which were further used to obtain the values of the micellar self-diffusion coefficients (D) and inter-micellar interaction parameters (kd).

Solution properties of gemini surfactant of decanediyl-1-10-bis (dimethyltetradecylammonium bromide) in aqueous medium

The solution properties of a typical gemini surfactant of decanediyl-1-10-bis (dimethyltetradecylammonium bromide) (abbrev. 14-10-14,2Br(-)) were examined in an aqueous medium at temperatures of 288.2, 298.2, and 308.2 K. The characterization was performed by employing surface tension measurements, electrical conductivity measurements, steady-state fluorescence quenching (SSFQ), and dynamic light scattering (DLS). The surface tension was measured with the drop volume method, in which an improved tensiometer was used and the experimental operation was modified. The resultant data were well reproducible and the equilibrium adsorption time after producing the droplet onto the tip of the capillary was on the order of minutes. In addition, the critical micelle concentration obtained from the surface tension data is in good agreement with that obtained from the conductivity data. Using the conductivity variation as a function of surfactant concentration, the thermodynamic parameters of micellization were calculated. Furthermore, the SSFQ method suggests a small and constant aggregation number, irrespective of temperature. The formation of small-size micelles was also confirmed by DLS measurements.

Dual-stimuli responsive behaviors of diblock polyampholyte PDMAEMA-b-PAA in aqueous solution

Two poly(2-(dimethylamino)ethyl methacrylate)-b-poly(acrylic acid) diblock copolymers, PDMAEMA(84)-b-PAA(18) and PDMAEMA(50)-b-PAA(18), were synthesized by the atom transfer radical polymerization (ATRP) and their dual-stimuli responsive behaviors to the changes in temperature and pH in aqueous solutions were investigated by UV-vis spectroscopy, dynamic light scattering (DLS), (1)H NMR spectroscopy and surface tension measurement. Different from PDMAEMA(84)-b-PAA(18) solutions where no aggregation is observed between pH 7.0 and 9.5, the PDMAEMA(50)-b-PAA(18) aggregates can exist in this broad pH range due to the hydrophobic interactions among the charge-balanced polyampholyte chains. At high pH, e.g., 11.0, the DMAEMA segments collapse to form the core of micelles due to the hydrophobic property of the de-protonized DMAEMA stabilized with the highly ionized AA segments on the surface of the micelles upon heating. At pH around the IEP, e.g., 9.5, large micelles can be formed in PDMAEMA(84)-b-PAA(18) solution upon heating, just like that at pH 11.0, while PDMAEMA(50)-b-PAA(18) first formed the micelles due to the electrostatic attraction between ionized AA segments and protonated DMAEMA segments, but the aggregation of the micelles was hardly happened upon heating due to the smaller DMAEMA segment. Moreover, LCST can be exactly estimated by surface tension experiment.