Microscope for 3-D imaging of surface chemistry of confined systems
polytechnique fédérale de Lausanne (EPFL) researchers have developed an optical imaging tool to visualize surface chemistry in real time. They imaged the interfacial chemistry in the microscop- ically confined geometry of a simple glass micro-capillary. The glass is covered with hydroxyl (-OH) groups that can lose a proton. A 100-micron long capillary displayed a remarkable spread in surface OH bond dissociation constant of a factor of a billion.
The researchers have designed a microscope that can track, in real time, three-dimensional spatial changes in the molecular structure and chemistry of confined systems, such as curved surfaces and pores. The microscope was used to image the surface chemical structure of the inside of a glass microcapillary. Surface potential maps were constructed from the millisecond images, and the chemical reaction constant of each 188nm-wide pixel was determined. Surprisingly, this very simple system - which is used in many devices - displayed a remarkable spread in surface heterogeneity. The researchers’ findings were published in Science. Their method will be a boon for understanding fundamental electrochemical, geological and catalytic processes and for building new devices.
The researchers then imaged the deprotonation reaction of the in-
ner silica capillary/water interface in real time. The data shows why there is a remarkable spread in surface reactivity, even on a very small portion of a capillary. It will help in the development of theoretical models that are more effective at capturing this surprising complexity. In addition, the imaging method can be used for a wide variety of processes, such as for analyzing the real-time functioning of a fuel cell, or for seeing which structural facet of a mineral is most chemically active. More insights can be gained into nanochannels and both artificial and natural pores.