Morphology Modulation in Self-Assembly of Chiral 2-Hydroxy-2-Phenylacetic Acids in Polymeric Diluents

This study focused on the chirality effects that control the lamellar bending sense in self-assembled crystals of chiral 2-hydroxy-2-phenylacetic acids. 2-Hydroxy-2-phenylacetic acid or mandelic acid (MA) was crystallized in the presence of poly(4-vinyl phenol) (PVPh), and its crystalline structures and morphologies were assessed using polarized optical microscopy (POM) and scanning electron microscopy (SEM). MA of two opposite chiral forms (S- and R-) was crystallized with PVPh as the morphology modulator; with adjustment of the PVPh content, the morphology of MA crystals transforms from ring-banded spherulites to highly dendritic spherulites. For MA/PVPh (50/50 wt./wt.) blend and neat MA at same Tc, the dendritic spherulites are packed with single crystals where the lamellae bend at a specific direction varying with Tc and chirality. Contrary to conventional thought, the bending senses of the MA lamellae in the dendritic spherulites are not solely governed by the MA molecular chirality (S or R), but also by Tc. Only at high Tc (>65 °C) is the lamellar bending direction in dendritic spherulites of (S)-MA or (R)-MA blended with PVPh dictated by the chirality, i.e., displaying counterclockwise and clockwise bending direction for (S)-MA/PVPh and (R)-MA/PVPh, respectively. Nevertheless, at low Tc (45 °C), the bending sense of dendritic spherulites displays an opposite direction from those at the higher Tc, which is to say that the chirality alone does not control the lamellar bending direction.

In situ observation of the melting behaviour of PEO single crystals on a PVPh substrate by AFM

PVPh sublayer thickness dependent melting of PEO single crystals.

Effect of PEO molecular weight on the miscibility and dynamics in epoxy/PEO blends

In this work, the effect of poly(ethylene oxide) (PEO) molecular weight in blends of epoxy (ER) and PEO on the miscibility, inter-chain weak interactions and local dynamics were systematically investigated by multi-frequency temperature modulation DSC and solid-state NMR techniques. We found that the molecular weight (M(w)) of PEO was a crucial factor in controlling the miscibility, chain dynamics and hydrogen bonding interactions between PEO and ER. A critical PEO molecular weight (M(crit)) around 4.5k was found. PEO was well miscible with ER when the molecular weight was below M(crit), where the chain motion of PEO was restricted due to strong inter-chain hydrogen bonding interactions. However, for the blends with high molecular weight PEO (M(w) > M(crit)), the miscibility between PEO and ER was poor, and most of PEO chains were considerably mobile. Finally, polarization inversion spin exchange at magic angle (PISEMA) solid-state NMR experiment further revealed the different mobility of the PEO in ER/PEO blends with different molecular weight of PEO at molecular level. Based on the DSC and NMR results, a tentative model was proposed to illustrate the miscibility in ER/PEO blends.

Optimization of a quasi-solid-state dye-sensitized solar cell employing a nanocrystal-polymer composite electrolyte modified with water and ethanol

A quasi-solid-state dye-sensitized solar cell employing a poly(ethylene oxide)-poly(vinylidene fluoride) (PEO-PVDF)/TiO2 gel electrolyte modified by various concentrations of water and ethanol is described. It is shown that the introduction of water and ethanol prevents the crystallization of the polymer matrix, and enhances the free I(-)/I(3)(-) concentration and the networks for ion transportation in the electrolyte, thus leading to an improvement in conductivity. A high energy conversion efficiency of about 5.8% is achieved by controlling the additive concentration in the electrolyte. Optimization of the additive-modified electrolyte performance has been obtained by studying the cross-linking behavior of water and ethanol with Fourier transform infrared (FTIR), differential scanning calorimetry (DSC) and viscosity measurements, and the electrical conduction behavior of the electrolyte with impedance spectra measurements.