Sentence:  Whereas the usual organic surface-active agent is strongly sorbed at oil-water interfaces , the highly charged ions are most strongly sorbed at interfaces between water and insoluble materials exhibiting an ionic <WSD>structure</WSD> ( see Table 26 - 2 on p. 1678 ) . 
Meaning of the word marked with <WSD> tags:  the manner of construction of something and the arrangement of its parts