Aggregation Behavior Of Temperature-sensitive Double Hydrophilic Block Copolymer PNIPAM-b-POEGA At The Air/Water Interface

Amphiphilic block copolymer can formed typical surface micelles,which contains hydrophobic block of core and hydrophilic block of petals.However,the double hydrophilic block copolymer?DHBC?lack of hydrophobic blocks,and the surface micelle structure need to be explored.In this work,the aggregation behavior of DHBC of poly?N-isopropyl acrylamide?-block-poly[oligo?ethylene glycol?acrylate]?PNIPAM-b-POEGA?at the air/water interface and the morphologies of its Langmuir-Blodgett?LB?films were characterized with the Langmuir film balance technique and atomic force microscopy,respectively.we investigated the effects of subphase pH,temperature,ionic strength,ionic kind and concentrantions on the surface pressure-mean molecular area??-A?isotherms and hysteresis curves of the PNIPAM-b-POEGA monolayers and the morphologies of its LB films,and revealed the interfacial aggregation behavior of DHBC under different subphase conditions.With the increase of subphase pH,the isotherm moves to the large mean molecular area?mma?probably due to the gradually increased stretching degree of POEGA chains at the air/water interface.At each subphase pH,the isotherms move to the large mma below the LCST of PNIPAM-b-POEGA,and the isotherms move to the small mma above the LCST.We consider that PNIPAM-b-POEGA form core-shell-petal structure composed of PNIPAM backbone core,amide group shell,and POEGA petal,which is proposed in DHBC for the first time.At different temperatures,with the increase of compression-expansion cycles,the hysteresis degree decreased gradually.The maximum compression moduli of the monolayers are very low,indicating that the DHBC monolayers possess excellent compressibility.Under different subphase conditions,all initial LB films show tiny circular micelles.Upon compression,the diameters slightly increase due to coalescence of adjoining micelle cores.The LB films prepared from alkaline condition show sparser micelles than those from acidic and neutral conditions due to the increased stretching degree of POEGA chains.The micelle core diameters increase slightly with the elevation of temperature because of the improved chain mobility and the coalescence of adjoining cores.Under acidic condition,with the increase of ionic strength of NaCl and Na₂SO₄,the isotherms of PNIPAM-b-POEGA shift positively.Under neutral condition,with the increase of each salt concentration,the isotherms move positively.This means that the presence of NaCl and Na₂SO₄can lead to salting out of PNIPAM-b-POEGA,and reduce the solubility of the POEGA chains.The presence of NaNO₃and NaSCN can lead to salting in of copolymer,and increase the solubility of the POEGA chains and make it more stretched at the air/water interface.All LB films show tiny circular micelles,and the micelle core diameters increase upon compression.Under same salt comcentration,the LB films show more sparser micelles in the case of NaSCN solution.