Fabrication of Block Copolymer Monolayers by Adsorption from Supercritical Fluids: A Versatile Concept for Modification and Functionalization of Polymer Surfaces

Abstract

We describe a generic method for polymer surface modification and functionalization that is applicable for substrates of arbitrary shape. The method involves the deposition of monolayer and submonolayer films of photoactive block copolymers from supercritical fluids. Poly(styrene-b-tert-butyl acrylate), poly(S-b-tBA), block copolymer monolayers form spontaneously on polystyrene substrates by adsorption from scCO2 when hexane is used as a cosolvent. Atomic force microscopy indicates the films are flat and without pores after modification. Ethylene glycol contact angles increase linearly with deposition pressure until a constant value, equal to that of pure P tBA, is attained at pressures of 18 MPa or greater at 40 degrees C. This trend mimics the change in block copolymer solubility with pressure and indicates that the block copolymer self-assembles and orders at the surface, presenting a P tBA layer at the air interface with the PS block orienting toward the PS substrate. The P tBA layer thickness, determined by angle dependent X-ray photoelectron spectroscopy, reaches a saturated monolayer value of ca. 2 nm for pressures of 18 MPa and higher, consistent with the thickness expected for unperturbed PtBA chains comprising a wet brush. This concept for polymer surface modification initially produces a hydrophobic surface due to surface adsorption of the low surface tension PtBA block, but can also be used to prepare hydrophilic, functional surfaces, either modified or patterned with carboxylic acid groups, by photolytic or acid catalyzed deprotection/hydrolysis of the tert-butyl ester groups.

Nanophase separation and structural evolution of block copolymer films: A “green” and “clean” supercritical fluid approach

“…The solubility of a block copolymer generally falls between that of its two homopolymers. 29 As various authors have reported that the solubility of scCO2 of polymers is only significantly influenced by pressure and temperature and almost independent of the molar mass of PS and PEO, 31,[35][36] it seems unlikely that the cause of enhanced phase separation is related to a swelling effect leading to greater free volume and increased chain mobility.…”

“…23,29,31 Figure 7 shows the ratio of swelling for PS:PEO as a function of pressure and temperature, highlighting that the ratio decreases with pressure ( Figure 7a) and increases with temperature ( Figure 7b). These data are attributed to the fact that the rate of increase or decrease of swelling of PEO with pressure and temperature respectively is much faster than that of PS.…”

“…5,[25][26][27][28] Much attention has been paid to ordering and kinetics of BCP thick and thin films by scCO2, examined from both a theoretical and an experimental perspective. 23,25,[29][30] However, to-date surface periodic arrangements of two blocks has only been realized by annealing polymers above their melting points. 25,[30][31] Here, we demonstrate the formation of periodic BCP arrangements via solvo-annealing in compressible scCO2 at low temperatures avoiding crystallization effects.…”

Functionalizing ps microspheres by supercritical deposition of P(S-b-tBA) for diverse interfacial properties exemplified with biocidal ability

“…This phenomenon was known as that block copolymers self-assemble and order at the surface of a homopolymer substrate [11] . One block of this kind of block copolymers is usually identical to the substrate and serves to anchor the block copolymer into the substrate; the second block generally comprises a lower surface tension polymer containing functional groups and forms a surface layer at the airpolymer interface via preferential surface segregation [9,12,13] . The block of lower surface tension therefore delivers its functional groups to the surface of substrate and produces desirable interfacial properties.…”

Surface Modification of PVC Membranes Using Fluorothiophenol Compounds

“…[2,8,13] In the past several practical approaches have been explored for the modification of polymer surfaces, including chemical reactions, [11,[14][15][16][17] blending, [18] plasma treatments, [19] corona discharge treatments, [20] grafting reaction [21] and adsorption of block copolymers. [22] Unfortunately, many of these surface modification methods may come with drawbacks such as added costs, a limited range of chemistries, lack of durability and increased potential for bulk polymer degradation. [23] In fact, to improve the properties of poly(vinyl chloride) (PVC), our group has been devoted to investigate the modification of the pristine material, via nucleophilic substitution of chlorine atoms, in bulk [11,24,25] and at the surface using mixtures of solvents and non-solvents for the polymer.…”