A ‘simple’ methodology, combining the use of Environmental Scanning Electron Microscopy (ESEM) and the recently introduced DEBEN Enhanced Coolstage was successfully developed and not only used to study dynamic processes, e.g. different stages of latex film formation, but also for high resolution imaging of ‘freeze-dried’ structures. By using the extended temperature capability of the DEBEN Enhanced Coolstage (-50 to +160^oC) it is possible to easily convert any (E)SEM chamber into what essentially can be described as a freeze-drying facility. By using this method it is also possible to preserve the structure and features of the studied system with minimum shrinkage and distortion and in the case of polymer latices at a desired stage of film formation. Moreover, specimens can then be readily imaged, without the need of conductive coatings and at much lower chamber gas pressures, thus minimising the beam skirting effects and allowing higher resolutions to be achieved. In this study this is clearly demonstrated (Figure 1 & 2) using a model poly-methyl methacrylate based latex dispersion; under ‘wet’ (partially dehydrating) conditions, whilst the individual particles can be seen it is difficult to distinguish them and any associated boundaries and/or arrangements, whether cubic or hexagonal; better images, as shown can be obtained from air-dried specimens, but this limits the time-frame of possible observations. However, subsequent freeze drying, as expected, resulted in the observation of a well-defined and more stable (in imaging terms) structure; it was also possible to image individual particles and their interactions at much higher resolutions. It is strongly believed that the methodology can be applied to other material systems, including biologicals and pharmaceuticals. 

Figures:

Figure 1 ESEM images of hydrated, air-dried (insert) polymethyl metaclylate latex

Figure 2 ESEM images of in-situ freeze-dried polymethyl metaclylate latex clearly demonstarting the potential advantages that this methodology offers (insert, high resolution image of the same latex, where individual particles are well-defined)

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EMC Abstracts - https://emc-proceedings.com/abstract/using-the-deben-enhanced-coolstage-for-in-situ-esem-freeze-drying-high-resolution-imaging-of-polymer-latices/