A Systematic Infrared Reflection−Absorption Spectroscopy and Film Balance Study of the Phase Behavior of Lipopolymer Monolayers at the Air−Water Interface

Abstract

Lipopolymers are lipids with a polymer chain covalently attached to the lipid. We systematically studied the monolayer behavior of a series of lipopolymers by use of infrared reflection−absorption spectroscopy (IRRAS) and classical Langmuir film balance techniques. The lipopolymers differed in chemical composition both in the lipid chains and in the polymers. However, the lipid chains contained 18 carbon atoms in all cases. We find the lipopolymers to show a very complex phase behavior at the air−water interface, depending on such diverse parameters as polymer hydrophilicity, length of polymer, and saturation of the lipid chains. We were able to measure up to two different plateau regimes in the monolayer isotherms. One is observed for lipopolymers where the polymer part is only slightly water-soluble and is correlated with the desorption of the polymer from the water surface. This desorption transition can be termed a pancake−mushroom transition. The origin of the second plateau regime is more uncertain. Baekmark et al. (Langmuir 1995, 11, 3975) interpreted this plateau as a transition within the polymer (mushroom-to-polymer brush conformation), but in two recent publications, by Gonçalves da Silva et al. (Langmuir 1996, 12, 6547) and Baekmark et al. (Langmuir 1997, 13, 5521) this interpretation has been questioned. In the present work we show that this second transition is native to lipopolymers in the sense that it can only be observed when a lipid and polymer are present in the same molecule. On the same basis of the film balance and the IRRAS data, we are able to show that the lipid alkyl chains must be involved in the molecular processes constituting the “native” transition. To account for the origin of the “native” transition, we suggest that a process of alkyl chain condensation coupled to a strong reduction in the number of gauche isomers within the alkyl chains supply the driving force for the “native” transition.

Nonionic polyoxazoline surfactants based on renewable source: Synthesis, surface and bulk properties

“…The large demand for surfactants urgently calls for sustainable surfactants made from renewable raw materials to reduce the impact on the environment and to save fossil resources [13]. In this sense few nonionic polyoxazoline surfactants based on vegetable biomass have been synthesized from glycerol [14] and lipopolymers [15][16][17][18]. Schubert et al have recently reported the synthesis of amphiphilic poly(2-ethyl-2-oxazoline-block-2-"soyalkyl"-2-oxazoline) copolymers from soybean fatty acid [19,20].…”

Quartz Crystal Microbalance Studies on Conformational Change of Polymer Chains at Interface

“…[31][32][33] As discussed above, PNIPAM chains are not only grafted with their end groups but also adsorbed with their segments on gold surface. At a low grafting density, the chains form a pancake-like structure.…”

Hydrophilic/Hydrophobic Nanostripes in Lipopolymer Monolayers

“…[12] Water is a good solvent for EO N and MOXAN N , whereas it is a marginal solvent for EOXAN N . This condensed phase was not found for shorter lipid tails (< C 14 ) or unsaturated alkyl chains.…”