In situ hot-stage transmission electron microscopy of Pb(Zr0.52Ti0.48)O3

The domain structure of Pb(Zr_0.52Ti_0.48)O₃ before and after hot-stage experiment has been studied. The influence of maximum temperature, heating and cooling rate on the domain configuration of Pb(Zr_{1? x} , Ti _x )O₃ with x = 0.40, 0.45, 0.48 and 0.55 was analysed. A reliable basis for further hot-stage experiments of Pb(Zr_1?x, Ti_x)O₃ has been established. The investigations revealed a temperature dependent appearance and disappearance of nano- and microdomains. The appearance of microdomains in the nano scale range during cooling, denoted as domain miniaturisation, and the time dependent recovering of the former domain structure, revealed that under specific experimental conditions the domain configuration is reversible.     

Nanodomains in a hydrophilic-hydrophobic IPN based on poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate)

The morphology of a series of hydrogels based on the interpenetration of poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate) has been studied through transmission electron microscopy, TEM, atomic force microscopy, AFM, and dynamic-mechanical spectroscopy, DMA. For the TEM analysis phosphotungstic acid, PTA, was used as alternative selective staining agent to those commonly used. The good agreement between TEM and AFM images allowed us to confirm that the PTA technique is a very powerful tool for TEM analysis of these hydrogel systems. All the results show that the IPNs presented phase-separation with two kinds of microdomains: those preferentially with a hydrophilic nature and those with preferentially a hydrophobic one, of sizes that range from 30 nm to 100 nm. Each one of these domains is composed by smaller nanodomains of alternating hydrophobic and hydrophilic component ranging between 6 and 10 nm sizes, those preferentially with a hydrophilic nature having a larger proportion of hydrophilic nanodomains. The AFM images of the IPN with the highest PHEA mass fraction, x_PHEA = 0.75, suggest that the hydrophilic phase is co-continuous in the material. A disperse hydrophilic phase is found when the PHEA mass fraction is reduced up to x_PHEA = 0.38. This phase-separation is explained in terms of some characteristic parameters of the networks such as the mesh size and the number of units between cross-links. The morphology found makes the systems very attractive for cell adhesion substrates and for matrices of scaffolds in soft tissue engineering.