  If confocal microscopy is an ubiquitous tool in life science, its
applications in chemistry and materials science are still, in comparison, very
limited. Of particular interest in these domains is the use of confocal
microscopy to investigate temperature-dependent phenomena such as
self-assembly, diffusio- or thermophoresis, or crystal growth. Several hurdles
must be solved to develop a temperature-controlled stage for laser scanning
confocal microscopy, in particular regarding the influence of an elevated
temperature gradient close to the microscope objective, which most people try
very hard to avoid. Here we report the design of a temperature-controlled stage
able to generate stable temperature gradients in both positive and negative
temperature range and does not require use of liquid nitrogen. Our setup
provides an excellent control of the temperature gradient, which can be coupled
with a controlled displacement of the sample, making it useful in particular
for a variety of solidification, chemistry, and interfacial problems. We
illustrate the benefits of our setup with several case studies of interest in
chemistry and materials science: the 3D real-time imaging of ice growth, the
segregation of hard particles by growing crystals, the freezing behaviour of
single emulsions, the self-shaping of oil droplets upon cooling, and the
self-assembly of amphiphile molecules into helical structures. These results
show how confocal microscopy coupled with a temperature-controlled stage is a
welcome addition to the toolkit of chemists and materials scientists.
