Compression-expansion curves of poly(DL-lactic acid-co-glycolic acid) monolayers

Abstract

The copolymer poly(DL-lactic acid-co-glycolic acid), used in the design of nanoparticles as drug delivery systems, forms stable monolayers at the air/water interface when spread from solutions of chloroform or 4:1 (v:v) chloroform-ethanol mixtures. The -A curves obtained show a plateau at a surface pressure of about 9 mN-m'1, corresponding to a change from high to low compressibility monolayer states. Since the surface pressure in the plateau region was hardly altered by increasing temperature from 10 to 35 °C, the plateau is interpreted as reflecting compression-induced reorientation of the polar groups of the polymer. There was marked hysteresis when the film was compressed to the collapse surface pressure (60 mN-m"1) and then expanded to its initial area: the first compression-expansion cycle did not return the monolayer to its original state, probably due to irreversible loss of molecules during collapse. Below the collapse surface pressure, however, the film showed reversible behavior.

Anomalous spreading behaviour of polyethyleneglycoldistearate monolayers at air/water interface

“…The larger areas with increase in temperature is indicative of an energy barrier that the molecules must overcome in order to leave the water surface and form a multilayer. This observed temperature dependence is consistent with decreased solubility seen for polyethyleneglycol with increase in temperature 34,35 .…”

Axisymmetric Drop Shape Analysis as a Film Balance: Rate Dependence of the Collapse Pressure and Molecular Area at Close Packing of 1-Octadecanol Monolayers

“…In general, the collapse mechanism seems to be complicated. It has long been thought to depend on the nature of the substance, temperature, pH, pressure, and the rate of molecular area compression. ,,,− Recent electron micrographs and atomic force microscopy (AFM) images obtained by Kato et al . showed platelet-like layers on the order of a micrometer in size and small granular structures with a height of several nanometers. , …”

Mixed Calcitonin−Poly[(d,l-lactic acid)-co-(glycolic acid)] Monolayers

“…Our previous studies have proved that both calcitonin 19 and PLA/GA 20 form stable monolayers when spread on a subphase of pH 7 at 20 °C. Figure 1 shows the π-A isotherms of the pure and mixed films under these conditions.…”

“…The short pseudoplateau at a surface pressure of about 20 mN/m in the isotherm of the pure calcitonin monolayer (curve 1) was attributed 19 to progressive submersion of the amino acids with the most polar and highly solvated groups in the subphase, where they formed a “transition layer” just below the interface; however, in the postplateau region, compression of the closely packed, vertically oriented apolar groups left at the interface gave rise to a sharp increase in surface pressure. The pure PLA/GA monolayer was more expanded than the calcitonin monolayer at low surface pressure, and the pseudoplateau at a surface pressure of about 10 mN/m in its isotherm (Curve 6 in Figure ) was attributed to the reorientation of polar groups rather than to the collapse, which occurred at around 60 mN/m 1 π− A isotherms of monolayers of calcitonin and/or PLA/GA compressed on a subphase of pH 7 at 20 °C.…”

“…The pure PLA/GA monolayer was more expanded than the calcitonin monolayer at low surface pressure, and the pseudoplateau at a surface pressure of about 10 mN/m in its isotherm (Curve 6 in Figure 1) was attributed to the reorientation of polar groups rather than to the collapse, which occurred at around 60 mN/m. 20 With the increase in the mole fraction of PLA/GA in the mixed monolayers, there is also an increase in their average area/residue at low surface pressure; a pseudoplateau appeared in the π-A isotherm at 10 mN/m which grew in length; however, the pseudoplateau that appeared at around 20 mN/m was shortened until it was hardly detectable for the mixed film with the mole fraction of polymer being 0.8 (curves 2-5 in Figure 1).…”