Study on polymer micelles of hydrophobically modified ethyl hydroxyethyl cellulose using single-molecule force spectroscopy

Individual hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC) molecules under different conditions were elongated using a new atomic forc e microscope (AFM) based technique-single-molecule force spectroscopy (SMFS ). The critical concentration of HM-EHEC for micelle-like clusters at a sol id/liquid interface was around 0.8 wt %, which is lower than that in soluti on. The different mechanical properties of HM-EHEC below and above the crit ical concentration were displayed on force-extension curves. Through a comp arison with unmodified hydroxyethyl cellulose, substituent-induced effects on nanomechanical features of HM-EHEC were investigated. Because of hydroph obic interactions and cooperative binding with the polymer, surfactants suc h as sodium dodecyl sulfate (SDS) dramatically influence the elastic proper ties of HM-EHEC below the critical concentration, and further addition of S DS reduces the interactions between the hydrophobic groups and the surfacta nt.