Mi­cro­scope for 3-D imag­ing of sur­face chem­istry of con­fined sys­tems

Chemical Industry Digest - - Science Pages -


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.

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