Pressure Effect on the Chain Shrinkage of Poly(vinylpyrrolidone) Induced by Complexation with a Hydrophobic Compound in Aqueous Solution

Microscopic evidence of "necklace and bead"-like morphology of polymer-surfactant complexes: a comparative study on poly(vinylpyrrolidone)-sodium dodecyl sulfate and poly(diallyldimethylammonium chloride)-sodium dodecyl sulfate systems

Here, we report the microscopic evidence of "necklace and bead"-like morphology, which has long been the most widely accepted model for polymer-surfactant complexes. The lack of microscopic evidence of the initial complexation between surfactant and polymer has resulted in many contradictory reports in the literature. In this paper, we visualized these initial complexes formed between negatively charged surfactant sodium dodecyl sulfate (SDS) with neutral poly(vinylpyrrolidone) (PVP) and cationic poly(diallyldimethylammonium chloride) (PDADMAC) polymer through photoluminescence (PL) microscopy and atomic force microscopy (AFM) using silicon quantum dot (Si QD) as an external PL marker. It is observed that, for the PVP-SDS system, SDS molecules bind at the hydrophobic sites on the random-coiled PVP chain through their hydrocarbon tails, while for the PDADMAC-SDS system, SDS head groups are associated with the positively charged nitrogen centers of the polymer, where the polymer chain wraps around the surfactant head groups.

Surfactant induced drug delivery based on the use of thermosensitive polymers

A novel approach of controlled drug delivery using thermosensitive polymers is developed in this paper. The drug release occurs at physiological temperature, at which the polymer is normally not soluble, and no medium temperature changes are required to bring about the delivery. For this purpose benefit is taken from the specific binding properties of some anionic surfactants and poly(N-isopropylacrylamide) (PNIPAAm) in order to modify the dissolution properties of PNIPAAm and of a copolymer with N-vinyl-acetamide (NVA), and so to induce the release of a drug contained in compression coated tablets. The influence of surfactant type and amount on the drug release rates and lag times from tablets coated with PNIPAAm or with the copolymer are discussed. It was found that the lag time is influenced by the surfactant species and amount. When use is made of a copolymer as coating agent, it is possible to bring about the release of the drug by incorporating only a very small amount (as low as 2%) of sodium dodecyl sulfate (SDS) in the coating.

Effect of some physiological and non-physiological compounds on the phase transition temperature of thermoresponsive polymers intended for oral controlled-drug delivery

Poly-N-isopropylacrylamide (PNIPAAm) thermosensibility makes this polymer a very attractive candidate for controlled drug delivery systems. The polymer possesses a lower critical solution temperature (LCST) which was found to be around 32 degrees C in pure water, but which can be affected by the medium composition, i.e. presence of salts or surfactants. The knowledge of the effects of such substances on the LCST is very important while using PNIPAAm as a controlled drug delivery agent. The influence of a number of physiological and non-physiological salts and surfactants has been studied. The results obtained show that the addition of salts provokes an important decrease of the LCST of the polymer (salting out effect). A strong influence of the valence and of the size of the anions of the halide group was found. As to the surfactants, according to their type and concentration, a decrease or an increase of the LCST or even no effect at all were found. The effect of the GI secretions on the PNIPAAm phase separation temperature is also discussed.