Stereocomplexation and monolayer morphologies of a stereoregular poly(methylmethacrylate) mixture formed at the air/water surface

The stereocomplexation of stereoregular PMMA at the air/water interface was proved by structure determination using reflection-absorption IR and grazing incidence X-ray diffraction. Morphological studies on LB films of i- and s-PMMA blends with different ratios help to disclose the stereocomplexation process of stereoregular PMMA at the air/water interface. It was found that the stereocomplexes exist in particle aggregates randomly dispersed at the air/water interface. In the systems with the i:s ratio deviated from 1:2, the molecules, either i-PMMA or s-PMMA, that do not participate in the stereocomplexation build separate layer surrounding the stereocomplexes. This layer is much thinner than the particle aggregates of the stereocomplexes. If the i-PMMA molecules are rich in this thinner layer, crystallization of i-PMMA takes place, which generates lamellar structure besides the stereocomplexes.

Monolayer behavior of a pyridyl head-group-containing amphiphile and its miscibility with poly(D,L-lactide-co-glycolide) on different pH subphase

In this paper, we investigated the Langmuir film and Langmuir–Blodgett (LB) monolayer film of a nonionic amphiphilic molecule, 4-(6-p-pyridyloxyl)hexyloxyl-4′-dodecyloxylazobenzene (C12AzoC6Py) and its mixture with poly(d,l-lactide-co-glycolide) (PLG) at different subphase pH values (2.0, 2.6, 3.3, 4.4, and 6.5, respectively) by surface pressure–area (π–A) isotherms, in situ interface Brewster angle microscopy (BAM), and ex situ atomic force microscopy (AFM). For pure C12AzoC6Py, its π–A isotherms display a plateau when the subphase pH value is lower than 3.0. The pressure of the plateau increases with the decrease of pH until 2.0. Over the plateau, the π–A isotherms become almost identical to the one under neutral conditions. The appearance of such a plateau can be explained as the coexistence of protonation and unprotonation of pyridyl head groups of the employed amphiphile. In contrast to the homogeneous surface morphology of pure C12AzoC6Py near the plateau by BAM observation, the surface in the case of its mixing with PLG exhibits a dendritic crystalline state under low surface pressure at subphase pH lower than 3.0. The crystalline state becomes soft and gradually melts into homogeneous aggregates with surface pressure increasing to a higher value than that of the plateau. Meanwhile, the hydrolysis of PLG in the mixture system at the interface has been affirmed to be restrained to a very large extent. And the PLG was believed to be compelled to the up layer of the LB film due to the phase separation, which is examined by AFM. Based on the experimental results, the corresponding discussion was also performed.