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Transmission electron microscopy showed structures at two length scales , where the mCNCs and PBD form domains having internal aligned self - assemblies of alternating hard mCNCs and soft PBD with periodicity of ca .
 Chemical: PBD; Chemical: PBD
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: PBD; Chemical: PBD