Abstract
The self-assembly of an amphiphilic Y-shaped copolymer consisting of two hydrophilic branches and one hydrophobic branch in a thin film is investigated under different conditions by virtue of mesoscopic computer modelling, accompanied by doping with a single solvent, doping with a binary solvent, and those solvent environments together with the introduction of confinement defined by various acting distances and influencing regions. A cylindrical micellar structure is maintained, as it is in the thin film with the doping of either 10% hydrophobic solvent or 10% hydrophilic solvent, whose structure consists of the hydrophobic core and hydrophilic shell. Attributed to the hydrophobicity/hydrophilia nature of the solvents, different solvents play an obvious role on the self-assembled structure, i.e., the hydrophobic solvent presents as a swelling effect, conversely, the hydrophilic solvent presents as a shrinking effect. Further, the synergistic effect of the binary solvents on the self-assembly produces the lowest values in both the average volumetric size and free energy density when the quantity of hydrophobic solvent and hydrophilic solvent is equivalent. Interestingly, the solvent effect becomes more pronounced under the existent of a confinement. When a lateral-oriented confinement is introduced, a periodically fluctuating change in the cylindrical size occurs in two near-wall regions, but the further addition of either hydrophobic or hydrophilic solvent can effectively eliminate such resulting hierarchical-sized cylinders and generate uniform small-sized cylinders. However, with the introduction of a horizontal-orientated confinement, the copolymers self-assemble into the spherical micellar structure. Moreover, the further addition of hydrophobic solvent leads to a decrease in the average size of micelles via coalescence mechanism, in contrast, the further addition of hydrophilic solvent causes an increase in the average size of micelles via splitting mechanism. These findings enrich our knowledge of the potential for the solvent effect on the self-assembly of amphiphilic copolymer system, and then provide theoretical supports on improving and regulating the mesoscopic structure of nanomaterials.
Highlights
Discussion formed by aand hydrophobic branch guarantees that the short-chained copolymer molecules will encounter less steric hindrance and entanglement during the self-assembly process
XY plane construction with very two monotonous, ends, both consisting ofan hydrophilic branches, and end but being largely flattened along the the constituent content of hydrophilic branches being formed by a hydrophobic branch guarantees that the short-chained copolymer molecules will for each copolymer relatively and high,entanglement so the possibility of “meeting with” the same component is encounter less stericishindrance during the self-assembly process
Higher for the component than for the component, which results in the outer coalescence compared with the broad space in the XY plane, the relatively narrow space along the Z axis makes of EO componentoffacilitating acceleration of the formation of the innerpossessing hydrophobic in the thetheconformations the copolymeric molecules very monotonous, ancore extended self-assembled structure, and a core-shell-structured planethe is formed
Summary
Due to their abundance in thermodynamics and kinetics [1,2], as well as their wide use as an industrial commodity in coatings and lubricants [3,4,5], polymer thin films (thickness less than 100 nm) have become an indispensable part of the developmental needs in modern high-tech applications such as nanolithography, biotechnology, optoelectronics, novel sensors and actuators [6,7,8,9,10,11]. In our previous work [49], the self-assembly of a reformed symmetric H-shaped amphiphilic copolymer consisting of four hydrophilic branches and one hydrophobic stem was systematically investigated. In this study, a further-reformed Y-shaped amphiphilic copolymer is the new research object, whose molecular topology is obtained by tailoring the H-shaped amphiphilic copolymer from the middle of the hydrophobic stem. An intensive investigation of the solvent effect on self-assembly in response to different external conditions (according to the conditions of being in the thin film only and being under confinement, as mentioned above) is exerted. In addition to the comparison of self-assembly between the Y-shaped copolymer system and the H-shaped copolymer system, which can exhibit the features of the Y-shaped copolymer system, different solvent effects on the self-assembly are discussed, which are expected to elucidate the according mechanism, aiming to provide reliable theoretical evidence for preparing well-defined materials via regulation of the external factors
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