Amphiphilic Polymer Conetworks Studied by SANS: Effect of the Type of Solubilizate and Molecular Architecture on the Swollen Gel Structure

Amphiphilic polymer conetworks (APCNs) are hydrogels with hydrophobic regions synthesized by cross-linking well-defined copolymers. Due to their amphiphilicity, they have oil solubilization ability. In this paper, we present a small-angle neutron scattering (SANS) study of the oil solubilization at the mesoscopic level in APCNs swollen in D2O, where for better contrast conditions, the hydrophobic monomer (M) was deuterated. The study was carried out on a series of APCNs where we systematically varied the mol fraction of the hydrophobic methyl methacrylate (M) monomer repeating units (from 0.1 to 0.9) with respect to the hydrophilic 2-(dimethylamino)-ethyl methacrylate (D) monomer repeating units as well as the general block copolymer architecture (MDM vs DMD). First, the structure of the D2O-swollen APCNs was characterized by means of SANS, which showed a well-defined structure with a repeat spacing of the domains, d, that scales directly with the architecture of the building blocks of the APCNs. In the second step, the solubilization of oils of different polarities (octane, toluene, eugenol, and 1-hexanol) was probed, and a clear correlation of oil solubilization with the oil polarity was observed. The most unpolar oil, octane, did not solubilize at all, while the much more polar toluene and 1-hexanol were incorporated very well but in a markedly different fashion. Toluene completely swelled the M part, while 1-hexanol appeared to be much more associated with the amphiphilic interface. This demonstrates that the studied APCNs are very selective with respect to their solubilization properties and efficient for distinguishing different types of oils.