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However , the presence of free PEI chains in the solution mixture produces a long - ranged ( > 60 nm ) attractive force between two PEI - coated surfaces with the range and magnitude tunable by pH value , PEI and salt concentrations .
 Chemical: PEI; Chemical: PEI; Chemical: PEI
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: PEI; Chemical: PEI; Chemical: PEI