Sentence:  Physicochemical investigations of anionic surfactants , including the soaps , have shown that there is little polymerization or agglomeration of the chain anions below a certain region of concentration called the critical <WSD>micelle</WSD> concentration . 
Meaning of the word marked with <WSD> tags:  an electrically charged particle built up from polymeric molecules or ions and occurring in certain colloidal electrolytic solutions like soaps and detergents