Study of Temperature Sensitive Polymeric Microgels with Light Scattering and Spectrophometry

Hydroxypropylcellulose (HPC) polymer can be cross-linked to form microgel nanoparticles that undergo a temperature dependent volume phase transition. We studied the structure and dynamics of HPC microgels and HPC polymer that microgels were made from using Dynamic (DLS) and Static Light Scattering (SLS) and Spectrophotometry. Our results determined the transition behavior of the microgels and polymer as temperatures were varied from Troom to above the transition temperature TC = 41C. The HPC microgels showed a reversible deswelling by a factor of 4-8 volume as temperature was brought above TC. The deswelling is caused by HPC chains becoming more hydrophobic at the TC and aggregating together to diminish water contact. SLS measurements yielded the relative molecular weight MW of microgels and MW of polymer. We also found the change of microgels\u27 MW and Rg/Rh with increase of solution temperature (T): MW decreased steadily from 20C to 40C (possibly due to microgels losing water) and then increased with T rising to 50C (possibly due to loose polymer chains fusing into microgels). The Rg/Rh ratio ranged from 0.4 to 0.7, consistent with a soft sphere and hard sphere models. The transition in polymer was found to be sharper than in microgels and the MW of the polymer clusters above the transition was found to be 30 times larger then MW of microgels. The light scattering study of microgels was complemented by Atomic Force Microscopy