A study of chain dynamics in water‐swollen gels of poly(ethylene oxide) dialkyl ethers using NMR and differential scanning calorimetry

Abstract

Water swollen gels of (unbranched) dialkyl ethers (n = 16, 17, 18, 20 and 21) of poly(ethy1ene oxide) (a,, = 10OO0, 20000 and 30000) have been investigated using NMR spectroscopy and differential scanning calorimetry (DSC). Aggregates of the alkyl segments were found to undergo a 'solid/liquid' transition at a temperature approximating the melting point of an unbranched hydrocarbon about three to four carbon atoms shorter than the alkyl chain. Below the transition temperature, the alkyl component gave a broad NMR line whose second moment was approximately one-quarter that of a crystalline alkane of similar length. The enthalpy of the transition was approximately one-third that of the corresponding unbranched alkane. These results indicate a partially crystalline structure for the 'solid' aggregates.

Spherical Micelles with Nonspherical Cores: Effect of Chain Packing on the Micellar Shape

“…By comparing the melting enthalpy obtained from DSC with the melting enthalpy of the corresponding bulk n -alkanes, we could estimate a degree of crystallinity around 30–50%. 19 , 28 Furthermore, our observed transition temperatures are quite close to the bulk melting temperatures of corresponding n -alkanes, 32 and the difference can be excellently described by a simple Gibbs–Thomson behavior. 23 , 29 Nonetheless, one cannot describe the state of the n -alkane blocks within the core as crystalline in a classical sense because the maximum domain size is very small as it is constrained by the micellar core radius R c .…”

Surfactant or block copolymer micelles? Structural properties of a series of well-defined n-alkyl–PEO micelles in water studied by SANS

“…Thus, the conformation of the alkyl chains can be considered as more exible which coincides with the assumption that the spherical core has a homogeneous density prole. It should be mentioned that long alkyl chains might crystallize 60,61 partly resulting in a non-spherical core domain. Crystalline micellar cores together with the high interfacial tension and a temperature insensitive aggregation number would support micelles in the super-strong segregation limit (SSSL) where the micellar coronas are still spherical.…”

“…Calculation of volume fractions was done assuming additivity of volumes. To ensure complete dissolution and micellar equilibration the samples were heated up to 60 C for approximately 3 hours. We should note that this procedure lead to equilibrium structures as we know from kinetic studies on these materials.…”

Association Properties of a Diblock Copolymer of Ethylene Oxide and Styrene Oxide in Aqueous Solution Studied by Light Scattering and Rheometry

“…[6,50] A number of factors combine to produce the effect: the micelle-molecule equilibrium, the negative temperature coefficient of solubility of the molecules, and modification of the hydrogen-bonded structure of water in concentrated poly(oxyethylene) solution. The effect is disrupted by any factor which stabilises micelles at low temperature, whether thermodynamic (e. g. crystallisation of blocks in the micelle core) [51] or kinetic (glass formation in the core). [14,19,52] In the present case of E/S copolymers neither of these proven explanations obviously applies: the S block is atactic [24] so crystallisation is not a factor, while the glass transition temperature of high-molar-mass poly(styrene oxide) is only 40 8C [33] and will be lower for the short block lengths under consideration.…”