For millennia, it has been thought that contact charging of dielectrics results in two materials, one positively charged and the other negatively charged. This misconception was led by the lack of instrumental techniques that were available to correctly measure the charge on dielectrics. Recently, we have shown that surfaces, regardless of the sign of net charge on them, bear both negatively and positively charged domains of charge . Following this observation, mechanism of contact charging, which has been on debate ever since the times of Thales (ca. 2000 years ago), became open to questions once again. Though there are theories on electron and ion transfer of contact charging of dielectrics, the very nature of the contact charging involving "contact" and the following material transfer has not been studied in connection with it. Here, by affecting on material transfer between contact-charged surfaces we were able to get a change -from positive to negative or from negative to positive- of sign of net charge on the same objects. Apart from reviewing the mechanism of contact electrification, this study points out a new way of controlling charge on surfaces which has found an application in industry, i.e. in drug manufacture.
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