Effects Of Copolymer Composition And Subphase Conditions On The Aggregation Behavior Of PDMAEMA-b-PLMA

Environmentally responsive polymers have good application prospects in the fields of sensors,gene and drug delivery due to their unique environmental response characteristics.In this paper,Langmuir film balance technique and atomic force microscope were used to study the aggregation behaviors of two environment-responsive diblock polymers poly(2-(dimethylamino)ethyl methacrylate)-block-poly(lauryl methacrylate)(PDMAEMA-b-PLMA,PDMAEMA77%-PLMA and PDMAEMA18%-PLMA)at the air/water interface and their morphologies of Langmuir-Blodgett(LB)films.The effects of copolymer composition and subphase conditions(p H,temperature,ionic strength and ionic specific effect)on the isotherms,hysteresis curves and morphologies of their LB films were systematically studied.In the case of subphase without salt,the isotherms of the two PDMAEMA-bPLMA monolayers gradually shift to larger mean molecular area(mma)with the increase of subphase p H,which is due to the gradually decreased protonation degree of PDMAEMA.Under acidic condition,the fully protonated PDMAEMA chains dissolve into water prior to monolayer compression,and do not return to surface during the expansion process.And thus the compression and expansion isotherms are almost exactly overlapped.Under neutral and alkaline conditions,the unprotonated PDMAEMA chains dissolve into water upon compression but only part of them return to interface upon expansion,showing an obvious hysteresis.The isotherms of PDMAEMA18%-PLMA monolayers are close under acidic and neutral conditions at low temperature,respectively.Except that,the isotherms of the two PDMAEMA-b-PLMA monolayers gradually shift to larger mma with the increase of subphase temperature under different subphase p Hconditions,which is due to the gradually increased flow and expansion degree of copolymer chains.Under acidic conditions with different ionic strengths,the isotherms of the predominantly hydrophilic polymer,PDMAEMA77%-PLMA,monolayers are almost exactly overlapped,while the isotherms of the predominantly hydrophobic copolymer,PDMAEMA18%-PLMA,monolayers successively shift to larger,small,and larger mma with the increase of the ionic strength.Under alkaline conditions,isotherms of the two PDMAEMA-b-PLMA copolymers vary with the increase of salt concentrations due to the ionic specific effects.The LB films of PDMAEMA77%-PLMA exhibit isolated circular micelles under other subphase conditions except for the wormlike aggregates under alkaline condition without at high temperature.Under low temperature and salt-free conditions,the initial LB films of PDMAEMA18%-PLMA monolayers exhibit mixed structures of worm-like aggregates and isolated circular micelles,which the content of the former gradually reduces with the increase of subphase p H.Under unique conditions,the LB films exhibit large PDMAEMA domains due to their low water solubility and local enrichness,while exhibit large aggregates of partially or fully fusion PLMA cores and PDMAEMA shells due to the ionic specific effect.