Gelation of Amphiphilic Lipopolymers at the Air−Water Interface:  2D Analogue to 3D Gelation of Colloidal Systems with Grafted Polymer Chains?

Abstract

Amphiphilic lipopolymers are known to form 2D thermoreversible gels at the air-water interface. Recently, we have reported surface rheology and film balance experiments on poly(ethylene glycol) (PEG) lipopolymers of different molecular weights, which indicated that a sufficient cross-sectional area mismatch between polymer and lipid moieties is necessary to form stable 2D gels (J. Coffman and C. Naumann, Macromolecules 2002, 35, 1835). In the current studies, we have investigated the influence of the hydrophobic anchor on the gelation properties by surface rheology and film balance technique. Experiments on PEG lipopolymers carrying saturated and partially unsaturated alkyl chains and on poly[(2-n-nonyl-2-oxazoline)x-b-(2-methylor 2-ethyl-2-oxazoline)y] (NxMy or NxEy) diblock copolymers of different block length show that the gel formation is not merely the result of the area mismatch between hydrophilic and hydrophobic moieties of the amphiphile (cone shape), but that a sufficient strength of van der Waals interaction within the hydrophobic moiety is necessary for the 2D gel to form, thus verifying earlier predictions that an alkyl chain condensation is a necessary precursor for the gelation process to occur. We also present neutron reflectometry data on PEG lipopolymers above and below the alkyl chain condensation and gelation transitions, which, in agreement to previous neutron and X-ray scattering experiments, reveal that both transitions occur after surface micelles of lipopolymers are formed at the air-water interface. On the basis of these findings, we assume that the gelation process of lipopolymers at the air-water interface is caused by a surface micellization of lipopolymers, which can be seen as the 2D analogue to the 3D gel formation observed for polymeric colloids with grafted polymer chains, such as copolymers and star polymers.

Poly(2‐oxazoline)s based on fatty acids

“…More recently, Langmuir-Blodgett layers of block copolymers consisting of poly(NonOx) and poly(MeOx) or poly(EtOx) were studied as reference experiments to demonstrate that the physical gelation of poly(2-oxazoline) lipopolymers is based on alkyl chain condensation [52].…”

Actin-induced perturbation of PS lipid–cholesterol interaction: A possible mechanism of cytoskeleton-based regulation of membrane organization

“…Interfacial rheology on lipid monolayers at the air-water interface were conducted using a Camtel CIR-100 interfacial rheometer (Camtel, UK) as described previously (Coffman and Naumann, 2002;Foreman et al, 2003). This oscillating stress-strain rheometer is equipped with a Pt/Ir De Noüy ring attached to a virtually frictionless suspension wire.…”

Synergistic Combinations of Multiple Chemotherapeutic Agents in High Capacity Poly(2-oxazoline) Micelles

“…20 Variation of the length of the alkyl side chain in POx allows fine-tuning the hydrophilic-lipophilic balance of each monomer unit, as well as of the entire polymer chain. For example, a short side chain POx, poly(2-methyl-2-oxazoline) (PMeOx) is highly hydrophilic while poly(2-ethyl-2-oxazoline) (PEtOx) shows some amphiphilicity, comparable to PEG 21, 22 and displays a temperature-dependent water solubility (lower critical solution temperature). 23,24 Both, PMeOx and PEtOx exhibit stealth properties and biodistribution similar to PEG when administered alone or grafted onto liposomes.…”