Abstract
We have synthesized a range of zwitterionic amphiphilic diblock copolymers with the same hydrophilic block (carboxybetaine) but with different hydrophobic blocks (n-butylmethacrylate (n-BMA) or 2-ethylhexylacrylate (EHA)) by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. Herein, we systematically examined the role of hydrophobicity and salt concentration dependency of surface activity and micellization behaviour of block copolymer. Transition from surface active to non-surface active occurred with increasing hydrophobicity of the hydrophobic block of block copolymer (i.e., replacing P(n-BMA) by PEHA). Foam formation of block copolymer slightly decreased with the similar variation of the hydrophobic block of block copolymer. Block copolymer with higher hydrophobicity preferred micelle formation rather than adsorption at the air–water interface. Dynamic light scattering studies showed that block copolymer having P(n-BMA) produced near-monodisperse micelles, whereas block copolymer composed of PEHA produced polydisperse micelles. Zimm plot results revealed that the value of the second virial coefficient (A2) changed from positive to negative when the hydrophobic block of block copolymer was changed from P(n-BMA) to PEHA. This indicates that the solubility of block copolymer having P(n-BMA) in water may be higher than that of block copolymer having PEHA in water. Unlike ionic amphiphilic block copolymer micelles, the micellar shape of zwitterionic amphiphilic block copolymer micelles is not affected by addition of salt, with a value of packing parameters of block copolymer micelles of less than 0.3.
Highlights
Over the past few decades, amphiphilic block copolymers are gaining attention because of their wide range of applications in our daily life, in either solid or solution form [1,2,3]
We found that the surface activity and micellization behaviour of zwitterionic amphiphilic block copolymers (ZABCs) were opposite those of ionic amphiphilic block copolymer (IABC) both in the presence and absence of salt
We investigated the influence of salt on the surface activity and micellization behaviour of ZABC containing n-BA and carboxybetaine [22]
Summary
Over the past few decades, amphiphilic block copolymers are gaining attention because of their wide range of applications in our daily life, in either solid or solution form [1,2,3]. Polymers 2017, 9, 412 systems, several factors such as molecular weight of both hydrophobic and hydrophilic blocks of block copolymers, salt, pH, type of ionizing groups (strong or weak), glass transition temperature of hydrophobic block affect their properties namely, surface activity, foam formation and micellization behaviour [7,8,9,10,11,12,13,14,15]. Hydrophobic adsorption force, which depends on the relative molecular weight of hydrophobic and hydrophilic blocks, played a vital role in deciding the surface activity of IABC. We studied the effect of hydrophobicity, salt, block length and glass transition temperature on the surface activity and micellization behaviour of ZABC. Static light scattering (SLS) and dynamic light scattering (DLS) measurements were applied to carefully and systematically investigate the interfacial properties of ZABC at air–water interface as well as their hydrodynamic properties in aqueous media
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