20860
Using in - situ X - ray photoelectron spectroscopy at the vapor - water interface , the affinity of nanometer - sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density .
 Chemical: silica
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: silica