Behavior of Syndiotactic Poly(methyl methacrylate) Monolayers at the Air/Water Interface: Influence of Temperature and Molecular Weight on the Surface Pressure−Area Isotherms and Brewster Angle Microscopy Images

Abstract

On aqueous subphases of pH 6, the behavior of syndiotactic poly(methyl methacrylate) (synd-PMMA) (average molecular weight, M w )120 000 g/mol) monolayers at the air/water interface was investigated in the range of temperatures between 15 and 50 °C. The monolayer characteristics of synd-PMMA stereoisomer were studied and compared in terms of surface pressure-area per residue (π-A) isotherms, surface compressional modulus-surface pressure (C s -1 π) curves, hysteresis phenomena, film thickness, and the phase images observed from Brewster angle microscopy (BAM). The results show that synd-PMMA (120 000) monolayer exhibits a phase transition LE-L′E (from a liquid-expanded to another liquid-expanded state) at surface pressures of ca. 15-17 mN/m when the temperature is raised from 25 to 50 °C, which is attributed to the formation of reversible loops and tails in the monolayer. On the other hand, the study of the effect of the molecular weight on the PMMA monolayer behavior showed that the polymer of M w ) 15 000 g/mol exhibits a limiting area of 19.7 Å 2 per monomer repeating unity at 30 °C, which is close to the value for the trans conformation of PMMA at the air-water interface. Nevertheless, the limiting area of PMMA (120 000) was lower (14.1 Å 2 /monomer), suggesting that not all monomers are located at the interface. The morphology and thickness of monolayers confirm at microscopic level the structural characteristics deduced from the π-A isotherms.

How to obtain a well-spread monolayer of lysozyme at the air/water interfaces

“…On the other hand, under these conditions of collapse, along the pseudoplateau in the p-A curve, amino acid segments of the monolayer are spelled outside the interface, forming loops and tails, which, according to these results, return reversibly to the surface along the film expansion. A similar behavior was observed in some polymer monolayers [28][29][30]. (3) Irreversible collapse was observed when the monolayer was over-compressed above the collapse pressure (at 40 mN/m), where the p-A curves corresponding to the compression-expansion cycle show a considerable hysteresis (Fig.…”

“…Thus, when the monolayer returns to the initial sate, does not take up the original surface area. This behavior could be attributed to an irreversible loss of protein molecules (or amino acid segments) into the subphase [27,29,31] in which case the curve for a new compression (recompression curve) should not coincide with that of the first compression, but should be shifted to lower areas, because in this situation would be less protein molecules at the A/W interface. However, this is not the case: the recompression curve in Fig.…”

Characterization of poly(2-hydroxyethyl methacrylate) (PHEMA) contact lens using the Langmuir monolayer technique

“…In the case of PMMA (M w = 15000), the value obtained by us for this parameter was 19.7 Å 2 /monomer [14], a value that matches that obtained from molecular models when this polymer is in trans conformation (20 Å 2 /monomer) [11,15]. In accordance with this, we can postulate that the 19.9 Å 2 /monomer value obtained in our study seems to be correct and it is in agreement with the existence of a similar configuration to that described for PMMA, which in the case of PHEMA is facilitated by the presence of the hydroxyethyl end group that tends to incorporate itself with greater ease inside the water subphase than does PMMA's oxymethyl group (OCH3) (Scheme 2).…”

Mixed monolayers of pmas with poly(styrene‐b‐methyl methacrylate) at the air/water interface

“…The high inflection pressures (corresponding to the minimum and plateau in Figs. 1–9) are likely because of liquid expanded to liquid condensed transition or liquid expanded to another liquid expanded transition [19]. For PPMA at 40°C and PBMA at 25°C and 40°C, there are three inflection pressures detected because of previous observations of two minimum compressibility values.…”