Physico-chemical properties of poloxamer surfactants related to their adsorption

The properties of poloxamer surfactants were investigated by a number of techniques. The adsorption of P188, P338 and P407, was studied on range of solids. The solids used were hydrophobic and poorly water soluble. An effect of temperature on the adsorption behaviour of the three surfactants was noticed. Poloxamers undergo a transition at a temperature which is dependent on their poly(oxypropylene) content, resulting in the amount of poloxamer adsorbing increasing. The transition can be attributed to a dehydration of the poly(oxypropylene) core of the poloxamer molecule, corresponding to changes in the micellar behaviour of the surfactants. The CMC is highly dependent on temperature. The nature of the adsorbate was found to affect poloxamer adsorption. The surface nature of the solids was investigated using contact angles. The poloxamers were investigated for their surface energy using different methods, and considered as both complete molecules and the sum of their individual components. Poloxamers do not adsorb readily to solids which have higher surface energies or which are more polar, suggesting that knowledge of surface nature could be useful in predicting adsorption behaviour. A model surface was created using chlorotrimethylsilane coated glass. It was possible to produce an artificial surface with known repeatable surface energy. Poloxamers adsorb to the coated slides. Slides with poloxamer adsorbed were shown to have altered surface nature. The hydrophobicity of the plates decreased as poloxamer adsorbed. The effect of temperature on the poly(oxyethylene) component of the poloxamer molecule was investigated by two techniques. Hydrophobic Interaction Chromatography and Photon Correlation Spectroscopy. It was shown that the poly(oxyethylene) reduced in size with increasing temperature. The hydrophobicity does not alter significantly with changes in temperature. These two techniques were also shown to substantiate the effects of temperature on the poly(oxypropylene) shown through adsorption studies.