The document describes a methodology that combines Environmental Scanning Electron Microscopy (ESEM) and a Deben ULTRA Coolstage to study dynamic processes like latex film formation. Polymethylmethacrylate (PMMA) latex specimens were imaged both in wet and freeze-dried conditions using this method. Freeze-drying the specimens resulted in well-defined particle structures being observed at higher resolutions compared to wet specimens. The methodology allows preservation of specimen structure with minimal shrinkage and can be applied to other material systems involving liquid content.

1. A ‘simple’ methodology, combining the use of Environmental Scanning Electron Microscopy
(ESEM) and the Deben ULTRA Coolstage was successfully developed and used to
study dynamic processes, e.g. different stages of latex film formation and
for high resolution imaging of ‘freeze-dried’ structures.
Method
Figure 3 Images of a) wet and b) freeze-dried
PMMA latex specimens
Figure 2 LIMA Carl Zeiss
EVO LS-15 VP-SEM
USING THE DEBEN ULTRA COOLSTAGE FOR IN-SITU (E)SEM
FREEZE-DRYING & HIGH RESOLUTION IMAGING OF POLYMER LATICES
Marzena Tkaczyk1, Kalin I. Dragnevski1, Yekuan Shentu1 & Gary Edwards2
1Laboratory for In-situ Microscopy & Analysis, Department of Engineering Science,
University of Oxford, Parks Road, Oxford, OX1 3PJ, United Kingdom
2Deben UK Ltd., Brickfields Business Park, Woolpit, Bury St. Edmunds, Suffolk IP30 9QS. UK
From the images obtained and shown in Figures 4 & 5 it is clearly
seen that under ‘wet’ (partially dehydrating) conditions, whilst
individual particles can be seen it is difficult to distinguish between
them and any associated boundaries and/or arrangements, whether
cubic or hexagonal 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 (Figure 6).
From the image it is also clearly seen that on this occasion the latex
specimen is in stage II of the film formation process, where partial
evaporation has led to the formation of a concentrated suspension of
particles, some of which are in contact with each other.
Results
Figure 5 ESEM image of in-situ
freeze-dried PMMA latex specimen
Figure 4 ESEM image of hydrated
PMMA latex specimen
Figure 6 High-resolution image of
the same latex specimen, where
individual particles can be well-
defined
The Deben ULTRA Coolstage (Figure 1) offers an extended
temperature range of -60 to +50oC, providing easy conversion of any
(E)SEM chamber (Figure 2) 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. In this study polymethylmetaclylate (PMMA)
latex specimens (Figure 3) were imaged both in wet and freeze-dried
conditions. For the latter, the samples were frozen and dried in-situ at
low vacuum conditions. Once the cycle was completed air pressure of
10Pa and working distance of 10mm were set, which provided optimal
imaging environments, i.e. sufficient resolution and minimal beam
damage. Imaging was carried at an accelerating voltage of 15kV.
Conclusions
In this study we have demonstrated that when combined with an (E)SEM, the Deben ULTRA Coolstage (-60 to +50oC) can not only be used to
study dynamic processes, but also for high resolution imaging of freeze-dried structures; in our case PMMA latex particles. It is strongly believed
that the methodology can be applied to other material systems, including biologicals and pharmaceuticals, where liquid content plays a role.
Furthermore, specimens can also be readily imaged, with or 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.
a) b)
Figure 1 Deben ULTRA
Coolstage
(-60 to +50oC)
Introduction