Influence of sodium dodecyl sulfate on the phase transition of thermoresponsive hyperbranched polymer in water

Abstract

The influence of sodium dodecyl sulfate (SDS) on the cloud point temperature (Tcp) of the aqueous solution of thermoresponsive hyperbranched polyethylenimine derivative HPEI-IBAm was studied systematically. When pH was below 8.5, HPEI-IBAm was positively-charged. Initially, the Tcp of HPEI-IBAm decreased significantly, followed by an obvious increase with the increase of SDS concentration. The lower the pH was, the higher the SDS concentration was required to achieve the minimum Tcp. When pH was above 8.5, HPEI-IBAm was neutral and raising the SDS concentration led to the gradual increase of Tcp. Compared to linear poly(N-isopropyl acrylamide) (PNIPAm), the Tcp of the current hyperbranched HPEI-IBAm was more sensitive to SDS. The thermoresponsive HPEI-IBAm/SDS complex was used as host to accommodate the non-polar pyrene in water. The lowest SDS concentration for effectively enhancing the solubility of pyrene in water was around 6.4 mmol·L-1. When HPEI-IBAm was present, the SDS concentration threshhold was decreased to about 0.31 mmol·L-1. Fluorescence technique with pyrene as the hydrophobic probe demonstrated that the SDS concentration of 7.2 mmol·L-1 was required to form the hydrophobic domain to accommodate pyrene guests without HPEI-IBAm, while only 0.2 mmol·L-1 of SDS was required in the presence of HPEI-IBAm.