posted on 2021-02-11, 17:36authored byHongxu Chen, Gangyao Wen, Varvara Chrysostomou, Stergios Pispas, Hongfei Li, Zhaoyan Sun
The ion specificity effect on the
water solubility of poly(N-isopropylacrylamide)-containing
copolymers complies with
the Hofmeister series, which is applicable to other copolymers or
not need to be explored. In this work, effects of ionic strength under
acidic conditions and ion specificity under alkaline conditions on
the air/water interface behavior of two amphiphilic diblock copolymers
poly(dimethylaminoethyl methacrylate)–poly(lauryl methacrylate)
(PDMAEMA-PLMA) were systematically studied. Under acidic conditions,
the surface pressure–area isotherms of a predominantly hydrophilic
copolymer are insensitive to ionic strength. In contrast, the isotherms
of a predominantly hydrophobic copolymer successively shift to the
large, small, and large molecular area with the increase of ionic
strength. Under alkaline conditions, the interfacial stretch degrees
of PDMAEMA chains of two copolymers change with salt species and concentrations,
which do not comply with the Hofmeister series. All of the Langmuir–Blodgett
films of the former copolymer exhibit separate circular micelles.
Nevertheless, those of the latter copolymer obtained under alkaline
conditions exhibit various distinctive morphologies such as separate
circular micelles, large separate PLMA cores within large PDMAEMA
domains, and large PLMA domains/aggregates surrounded by short PDMAEMA
shells. It can be attributed to the high deformability of PLMA chains,
the ion specificity effect on the stretch degree of PDMAEMA blocks,
and their underwater solubility upon compression.