6978
The hydrodynamic radius of the nanogels , observed to be 26 . 5 +/- 5 . 1 nm at pH 7 . 0 , increased by ~ 135 % upon acidification of the solution to pH 4 . 0 .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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