Cylindrical micelles formed by a charged comb-shaped copolymer in aqueous solutions studied by small-angle neutron scattering

Abstract

We present the analysis of a series of small-angle neutron scattering data of a comb-shaped copolymer, poly( 1-octadecene-co-(maleic anhydride)), dissolved a t various concentrations in D20 a t room temperature. The results show a t full ionization the copolymers self-associate to form cylindrical micelles with a radius of 27 A and a length of 99 A. At low concentrations, the number of repeating units of the copolymer per micelle is determined to be 233 A 5 and the hydration number per hydrophilic head group equals 10. The number of repeating units gradually decreases to 98 with concomitant increase in the hydration number to 30 at 20 wt % solution. This indicates that the system tends to lower its free energy by decreasing the aggregation number of micelles at higher concentrations.ABSTRACT Lattice models for the prediction of conformational characteristics and thermodynamic properties at bulk polymer/solid and bulk polymer/gas interfaces are critically examined. Existing models are shown to fall into two broad categories: bond models, in which the probability of a chain conformation is expressed as a product of bond transition probabilities, and site models, in which the probability of a conformation is proportional to a product of probabilities characteristic of the sites occupied by successive chain segments. A general mathematical formulation is developed for bond models, which includes Dill and Flory's model of liquid bilayer membranes and Helfand's model of a pure homopolymer at an interface as special cases.The key assumptions, leading to closure of the bond model equations in each of these two cases, are elucidated.

Direct Measurement of Counterion Distribution around Cylindrical Micelles by Small-Angle X-Ray Scattering

“…10 Since the dimension of the cylindrical micelle had been independently determined by previous small-angle neutron scattering measurements, 13 the computation of SAXS intensity distribution could be made without using any adjustable parameters. We can thus quantitatively test the accuracy of the analytical solutions of the PB equation against the experimental data.…”

Molecular concepts, self-organisation and properties of polysoaps

“…The presence of "regional micelles" would be consistent with the data, too. The combination of viscosimetric and solubilization experiments [78], Potentiometrie titrations [180,181] and neutron scattering studies [190][191] also support the "local micelle" or the "regional micelle" models.…”

“…Small angle neutron scattering experiments yield aggregation numbers of polymeric micelles greater than the degree of polymerization [190][191][192]. This suggests the overlap of intra-and intermolecular aggregation as observed by light scattering investigations of polysoaps [392,394] In contrast to the above discussion, theoretical treatments favour the model of the "molecular micelle" [195,207].…”

“…In particular many types of head groups have been realized, covering non-ionic, cationic, anionic and zwitterionic ones (Fig. 7, Tables 1-5 Considering hydrocarbon tails, it seems that the minimal length to produce polysoap properties is about C 8 [52,191,199,200]. Polysoap behaviour was reported even for some shorter chains, but then additional hydrophobic units in the backbone must be present (see below).…”

“…Whereas polymers with decyl tails behave like polysoaps at any degree of dissociation, polymers with hexyl tails act as polysoaps only when less than 40%, polymers with pentyl tails when less than 30% and polymers with butyl tails when less than 20% of the -COOH groups are deprotonated [54,176,177,181]. As for the latter examples, much hydrophobicity derives from the polymer backbone in the partially dissociated state, and these polymers may be considered as intermediate cases [54,169,170,182,186,190,196]; 34: [191,192]; 35, 37, 38: [168]; 36: [314] between the longitudinal knotting of surfactant units and the lateral knotting found in classical polysoaps (see Figs, le and If). The alternative to "main chain spacers" is the separation of backbone and surfactant fragments by "side chain spacers" (Fig.…”