Abstract
HypothesisBlock copolymers (BCP) consisting of a polar block and a surface active apolar block are widely used for surface functionalization of polymer films. The characteristics of the copolymer blocks determine whether surface segregation and/or phase separation occurs, for a given bulk mixture. This data can be used to find the optimal BCP composition where high surface enrichment is obtained without accumulation of phase separated BCP in the bulk. MethodsThe distribution of poly(ethylene oxide)-polydimethylsiloxane (PEO-PDMS) BCP in a polymer formulation relevant for coating applications is systematically investigated. The surface segregation is studied in liquid formulations with surface tension measurements and dried films with X-ray photoelectron spectroscopy (XPS), whereas phase separation is quantified using turbidity measurements. The results are compared with Scheutjens-Fleer self-consistent field (SF-SCF) computations, which are also applied to determine the effect of film drying on BCP phase stability and surface segregation. FindingsLonger PDMS blocks result in lower interfacial tension of the liquid polymer mixture, whereas for the cured films, the largest PDMS concentration at the interface was obtained for intermediate PDMS block lengths. This is explained by the observation that phase separation already occurs at very low BCP concentrations for long PDMS blocks. The SCF predictions qualitatively agree with the experimental results and reveal that the BCP distribution changes significantly during film drying.
Highlights
Polymer surfaces can be readily functionalized by blending with a low amount of amphiphilic block copolymers, as the surface segregation of the copolymers can impart significant changes in the surface properties [1,2,3]
The results for the surface segregation and phase stability of the poly(ethylene oxide) (PEO)-PDMS block copolymers in coating formulations obtained from the experiments and the Scheutjens-Fleer self-consistent field (SF-self-consistent field (SCF)) model are discussed
For long PDMS chains the incompatibility of the block copolymers with the polymer film results in bulk phase separation, which decreases the amount of block copolymer that segregates towards the surface
Summary
Polymer surfaces can be readily functionalized by blending with a low amount of amphiphilic block copolymers, as the surface segregation of the copolymers can impart significant changes in the surface properties [1,2,3]. The molecular copolymer structure strongly influences the surface affinity of the block copolymers and the compatibility with the polymer material. Block copolymers containing polydimethylsiloxane (PDMS) are commonly used to introduce low surface energy properties on polymeric coatings [8]. Such block copolymers are highly tuned for the specific coating system and application in mind [9,10]. For their role in coating formulations as leveling agents or to impart surface hydrophobicity, the amphiphilic copolymers should be preferentially located at the film-air interface
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