Influence of high pressure on higher-order structures of poly(oxyethylene) in its blend with poly(d,l-lactide)

Abstract

The effect of high pressure on the higher-order structures of poly (oxyethylene) (PEG) crystallites in poly(d,l-lactide)/poly(oxyethylene) (PDLLA/PEG) blends during melting and recrystallization was investigated by in situ small-angle X-ray scattering (SAXS) measurements. It was found that melting temperature (T m ) increases at 50 MPa in accordance with the prediction by the Clausius-Clapeyron equation. However, T m at slightly pressurized state (5 MPa) surprisingly decreased, suggesting that the effect of pressure is not so straightforward. It may be due to an increase of the miscibility under higher pressure, causing the melting point depression. Meanwhile, an advantage of analyses of SAXS data enabled us to determine directly discrete distribution of lamellar thickness as a function of temperature under pressure. As a result, lamellar thickening was observed at 5 and 50 MPa as temperature approaches closer to the melting point, but the tendency of thickening was lesser as compared to that observed at ambient pressure.& Nguyen-Dung Tien

Recent developments in polymer applications of synchrotron small‐angle X‐ray scattering

“…That study is the first showing quantitative evidence of the well‐known concept of ‘lamellar thickening’ when a crystalline polymer is thermally annealed just below its melting temperature. Tien et al have also conducted the same evaluation under higher pressure (5 and 50 MPa) …”

“…Note here that torque was simultaneously measured during the SAXS experiments. In situ SAXS measurements have also been conducted for polymer melts under high pressure (5 and 50 MPa) …”

“…In block copolymer microdomain systems, a Gaussian distribution of the particle size has been assumed and no effort for the determination of the discrete size distribution had been made. Only recently, direct determination of the discrete size distribution has been available by fitting the theoretical scattering function to the experimentally obtained SAXS profile (plot of the scattering intensity as a function of q ) where the abundance of particles having a given size was treated as a floating parameter with a step of one nanometer (the step can be more precise) …”

SAXS Evaluation of Size Distribution for Nanoparticles

“…That study is the first showing quantitative evidence of the well-known concept of 'lamellar thickening' when a crystalline polymer is thermally annealed just below its melting temperature. Tien et al have also conducted the same evaluation under higher pressure (5 and 50 MPa) [26]. The SAXS measurements were conducted in the heating process.…”