A mixed amphiphilic system composed of the anionic surfactant Aerosol OT (AOT), in water forming a lamellar phase, to which is added a neutral noninteracting polymer, poly(N,N-dimethylacrylamide), is studied experimentally by SAXS, 2 H NMR, and microscopy, in a range of surfactant and polymer compositions. Addition of the polymer produces a decrease in the lamellar spacing, the decrease by the polymer being almost twice that produced by an equal volume of AOT. Microscopy reveals heterogeneity, but no macroscopic phase separation occurs. 2 H NMR detects that on increasing the polymer concentration some water is in an isotropic environment. It is inferred that the presence of the polymer induces a microscopic phase separation into a polymer-rich isotropic phase and a surfactant-rich lamellar phase, and this is tested theoretically by calculating the osmotic pressures in these two phases. In the lamellar phase, the effect of electrostatic, undulation, van der Waals, and hydration forces on the AOT bilayer is considered; in the isotropic phase, the osmotic contribution of the polymer is considered. These two pressures correlate well, supporting theoretically the hypothesis of the two phases in equilibrium.

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The liquid crystal formed by surfactant AOT/water mixtures in its lamellar mesophase at a spacing between lamellae, d, equal to 8 nm, is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight in the range M h n) 2-20 × 10 3 ; the polymers are synthesized by living radical polymerization. The lowest molecular weights do not affect d significantly, indicating that the polymer coils penetrate inside the lamellar phase and dissolve in the water layers. With higher molecular weights, d decreases with added polymer, this decrease being stronger as the molecular weight of the polymer is higher, and the mixture becomes microheterogeneous. This indicates that the higher-molecular-weight polymers are segregated in a separate microphase that partially deswells the lamellae and that this segregation increases with the molecular weight of the polymer. The law, which governs the deswelling of lamella with added polymer, is deduced assuming that a fraction of each polymer can dissolve in the lamellar phase, while the rest of the polymer is segregated from it. This latter fraction is then obtained for each polymer simply by fitting to this law the experimental d as function of polymer concentration. It is proposed that the reason for this fractionation of polymer is that the lamellar structure acts as a grating which sieves the polymer coils according to their size relative to d, chains with molecular weight above a certain cutoff value, determined by d, being excluded from the interlamellar space. The fraction of chains excluded from the lamellae is calculated comparing the experimental molecular weight distributions (from SEC) of the polymers with the cutoff values determined by d. The results show that the polymer samples synthesized here cover the whole spectrum of behaviors, from almost total penetration to almost total exclusion. Both this method of cutting off the molecular weight distribution according to d and the other method of fitting d to the law for lamellar deswelling give similar results for the fraction of polymer that is segregated from the lamellae.

The determination of single-chain properties for heterogeneous molecules such as a rigid-flexible block copolymer requires the use of solvents capable of reducing selective interactions involving the blocks and the diluent. Molecular dispersion is displayed by a two-block copolymer of benzoyl-terminated poly(p-benzamide) (poly(imin0-1,4-phenylenecarbonyl) and anilino-terminated poly(m-phenyleneisophthalamide) in 96 wt.-% sulfuric acid. For a series of such copolymers, intrinsic viscosities were measured avoiding degradation effects due to H2S04. The intrinsic viscosity ([a]) of the copolymers was found to decrease with increasing length of the flexible block, but [a] remained larger than the value corresponding to an equimolar blend of rigid and flexible homopolymers. These results are explained by theoretical considerations within the framework of the hydrodynamic behavior of single rodlike and single coiled macromolecules. a) part 1 : cf. ref. l). b, Structure-based IUPAC name for poly(p-benzamide) is: poly(imino-1 ,Cphenylenecarbonyl).

N,N-Dimethylacrylamide is polymerized in the lyotropic surfactant system containing Aerosol-OT (AOT) and water. The polymerization is thermally initiated with AIBN, which allows a homogeneous initiation in this very viscous mixture. The starting mixture contains a lamellar liquid crystalline phase and an isotropic phase in equilibrium. After the polymerization, new phases develop which appear to have a lamellar structure, even if originated from the initial isotropic phase. More phases appear after the polymerization, and they are lamellar, since the phase behavior shifts toward the lamellar region when the monomer is consumed. Once the polymer is formed in situ, it segregates from the lamellae and forms an isotropic microphase which does not macroscopically separate. The appearance of this polymer-rich phase modifies the structure of the lamellar mesophase by partially deswelling it. This gives a shorter lamellar spacing. The law that expresses how the AOT−H2O spacing is contracted by the polymer is deduced from the equilibrium between the two (lamellar and isotropic) microphases. All the macroscopic final phases contain polymer, although in different proportions. The molecular weight of the polymer is the same in all phases. The presence of AOT in the medium has no influence on the resulting tacticity, which is the same as that for a polymer obtained in pure water.