Effect Of Subphase Conditions On The Interfacial Aggregation Behavior Of Triblock Copolymer PDMAEMA-b-PLMA-b-POEGMA

Amphiphilic block polyelectrolytes have attracted a lot of attention because of their charged properties and can be applied to electrochemical sensors and drug release applications.Although the properties of amphiphilic diblock polyelectrolytes in aqueous solutions have been studied more,less research has been done on amphiphilic triblock polyelectrolytes,and their aggregation behavior at the interface is even less studied.In this work,the interfacial aggregation behavior and the morphology of Langmuir Blodgett(LB)films of two amphiphilic triblock terpolymers of poly[2-(dimethylamino)ethyl methacrylate]-block-poly(lauryl methacrylate)-block-poly[oligo(ethylene glycol)methacrylate](PDMAEMA-b-PLMA-b-POEGMA)was studied by the Langmuir film balance technique and atomic force microscopy.The conformational changes of interfacial micelles of terpolymer under different subphase pH,temperature,ionic strength,ion specificity and salt concentration were studied.(1)The effects of pH value and temperature of subphase on the monolayers of PDMAEMA-b-PLMA-b-POEGMA were studied under the absence of salt conditions.The terpolymers tend to form isolated circular micelles composed of PLMA cores and mixed PDMAEMA/POEGMA coronas at the air/water interface.The results show that with the increase of the pH value of the subphase,the the POEGMA blocks are more extended at the interface,and the surface pressure-molecular area(π-A)isotherms of the terpolymer monolayers move to large mean molecular area(MMA).Under acidic conditions,the PDMAEMA blocks were dissolved in the subphase due to complete protonation and had no effect on the interface extension of the POEGMA blocks.Under neutral and alkaline conditions,the segments of PDMAEMA blocks adsorption at the interface increases and provide steric hindrance for the extension of POEGMA blocks(crowding effect).As temperature increases,the isotherms first move to large MMA due to the increased repulsion between the PDMAEMA and POEGMA blocks.With the increase of temperature to 40℃,the hydrophilic POEGMA blocks becomes weakly hydrophilic,and the isotherms move to the opposite direction.(2)Under acidic and alkaline conditions,the effect of ionic strength,different kinds of ion types and their salt concentrations on PDMAEMA-bPLM A-b-P OE GM A monolayers was studied,respectively.Under acidic conditions with low ionic strength,anions will produce electrostatic screening effect on positively charged PDMAEMA blocks,and makes their conformation shrink.At high ionic strength,the PDMAEMA blocks immersed in the subphase are adsorbed at the interface due to the salting-out effect.Under alkaline conditions,with the increase of salt concentrations,the isotherms move to large MMA,because the presence of salts makes the PDMAEMA and POEGMA blocks more extended.The degree of influence of different ion types on hydrophilic blocks varies with different concentrations,and their order are inconsistent with the Hofmeister series.This may be due to the conformation constrains of two hydrophilic blocks in the mixed coronas.(3)The effects of various subphase conditions on the LB film morphologies of PDMAEMA-b-PLMA-b-POEGMA were studied.The LB films of both terpolymer show isolated circular micelles.Due to the stretching conformation of the longer POEGMA blocks in the mixed micelle coronas,the micelles of the terpolymer under different subphase conditions with salts show small micellar cores,and the size of the micellar cores does not change significantly with the change of subphase conditions.