High Density Polymer Brush Spontaneously Formed by the Segregation of Amphiphilic Diblock Copolymers to the Polymer/Water Interface

Abstract

A self-repairable high density polymer brush of poly(ethylene glycol) (PEG) is formed at the interface between cross-linked poly(dimethyl siloxane) (PDMS) and water by spontaneous surface segregation of an amphiphilic diblock copolymer consisting of PEG and PDMS. The surface reconstruction by the formation of the brush was observed as the large hysteresis of the contact angle of the water droplet. Neutron reflectivity measurement revealed that the grafting density of the polymer brush is 2.8 chain/ nm 2 , which is comparable to those of polymer brushes by the surfaceinitiated polymerization method. The formation of such a remarkably dense polymer brush by segregation can be well supported by the balance between the mixing enthalpy of PEG and water and the stretching energy of PEG.

Ultralow Friction with Hydrophilic Polymer Brushes in Water as Segregated from Silicone Matrix

“…The osmotic pressure in the PAA(6.1) (Π sum = 25.4 MPa) is ≈9 MPa higher than in the PEG(2.1) brush (Π sum = 16.3 MPa), despite the fact that the modeled grafting density is higher for PEG(2.1) ( σ = 2.52 chains nm −2 ) than for PAA(6.1) ( σ = 1.39 chains nm −2 ). The predicted σ = 2.52 chains nm −2 for PEG(2.1) according to this model was very close to the experimentally determined value σ = 2.8 chains nm −2 by Inutsuka et al [ 22 ] for the same size PEG block segregated into water from PDMS matrix, which supports the validity of the presently proposed model for segregation. See Table 1 for calculated H , φ , σ , and Π at minimum Δ F total at different pH for the block copolymers.…”

“…Interfaces 2016, 3, 1500472 www.advmatinterfaces.de www.MaterialsViews.com The main driving force of the segregation of hydrophilic chains from PDMS matrix is facile solvation of polymer chains in solvent that is interfacing with PDMS surface. Recently, Inutsuka et al [ 22 ] have also shown a spontaneous formation of PEG brushes from PDMS(1.0)-b -PEG(2.1) at the interface between PDMS and water via segregation from PDMS network. We consider that the same mechanism governs the distribution of the PDMS(5.0)-b -PEG(2.1) copolymers within the PDMS matrix in this study.…”

“…This was inspired partly by the expectation of spontaneous segregation of PEG chains of the diblock copolymer at the PDMS/water interface. [ 22 ] For the case of PDMS(5.0)-b -PEG(2.1) diblock copolymer, PEG(2.1) block has smaller R g ≈ 1.2 nm (in poor solvent) and lower polarity than PAA(6.1) block, and thus is expected to diffuse more readily in the PDMS matrix. In fact, lower water contact angles ( Figure 3 ) observed from SC20%-PDMS(5.0)-b -PEG(2.1), but not from SC20%-PDMS(4.7)-b -PEG(5.0), support that PEG brush layers can be formed via spontaneous segregation without initiating tribostress when the R g is suffi ciently small and the overall polarity of the diblock is relatively low (see the Discussion section).…”

“…In this approach, namely, "inverted grafting-to" (Scheme 1 C), [ 22 ] grafting of the polymer chain is achieved with an "internal" source that facilitates continuous (re)generation of brush-like layers. For example, under a harsher environment leading to damage of the fi lms, the brush layer can be readily regenerated without any external sources or means.…”

Self-restoring polymer brushes under tribological stress and the biomedical applications

“…This PDMS thin film incorporating diblock copolymers can be deposited on various materials' surfaces. Upon exposure to water [4], or often after applying initiating tribostress in water, hydrophilic blocks (PAA) of the copolymers are selectively segregated from the PDMS network to form brush-like layers, whereas the hydrophobic blocks (PDMS) remain trapped inside the PDMS network acting as anchors for the hydrophilic polymer brushes. Excellent anchoring stability of hydrophilic brush layer is a distinct novelty of this system, indebted from high reluctance of hydrophobic blocks to get exposed to aqueous solution and/or from facile replenishment of the diblock copolymers in case of film damage.…”