Surface-active Block Copolymers Research Articles

Segregation versus Interdigitation in Highly Dynamic Polymer/Surfactant Layers.

Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C12TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface.

Visualization of the distribution of surface-active block copolymers in PDMS-based coatings

Poly(dimethylsiloxane) (PDMS) has been widely employed in the area of fouling-release coatings and other fields due to its unique combination of properties including low elastic modulus and low glass transition temperature. The drawback of PDMS in some applications is its hydrophobic surface, which results in non-specific protein adsorption and wettability issues. Poly(ethylene glycol)-based surface-active block copolymers and surfactants have been added to PDMS coatings and films to impart biofouling resistance and hydrophilicity to the PDMS surface with successful results. Information regarding the distribution and release of these block copolymers from PDMS-based coatings has been previously reported. However, the distribution and behaviour of these compounds in the bulk of the PDMS coating are not fully understood.A novel fluorescent-labelled triblock PEG-b-PDMS-b-PEG copolymer was synthesized and added to a PDMS coating for visualization purposes. The surface-activity and biofouling resistance of the synthesized copolymer was confirmed by water contact angle measurements and seawater immersion experiments. Confocal laser scanning microscopy (CLSM) images showed that the triblock copolymer aggregates in spherical domains within the PDMS coating film. The size of these domains vary between 1 and 7 μm, with larger domains being present on the bulk of the film and smaller closer to the surface. The diffusion of the copolymer could be observed over time, with copolymer molecules diffusing from the bulk to the surfaces of the PDMS film. Finally, an overview of the possibilities provided by the presented methodology in the field of fouling-release coatings is discussed.

Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films

Block copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer–air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite.

Synthesis, properties, and application of surface-active block copolymers based on poly(ethylene oxide) and polyorganosiloxanes in the heterogeneous polymerization of styrene

A number of linear and comb-shaped organosilicon surfactants containing poly(ethylene oxide) blocks were synthesized and studied. The structures of the copolymers were varied systematically, and the obtained copolymers were characterized via elemental analysis, GPC, and 1H NMR. A comparative study of the surface activities of amphiphilic organosilicon block copolymers was performed. Their structures were shown to considerably affect the surface activities as well as the styrene polymerization rates and the sizes of microparticles obtained with the use of the studied copolymers as surfactants.

Fabrication of Bioactive Surfaces by Functionalization of Electroactive and Surface-Active Block Copolymers.

Biofunctional block copolymers are becoming increasingly attractive materials as active components in biosensors and other nanoscale electronic devices. We have described two different classes of block copolymers with biofuctional properties. Biofunctionality for block copolymers is achieved through functionalization with appropriate biospecific ligands. We have synthesized block copolymers of electroactive poly(3-decylthiophene) and 2-hydroxyethyl methacrylate by atom transfer radical polymerization. The block copolymers were functionalized with the dinitrophenyl (DNP) groups, which are capable of binding to Immunoglobulin E (IgE) on cell surfaces. The block copolymers were shown to be redox active. Additionally, the triblock copolymer of α, ω-bi-biotin (poly(ethylene oxide)-b-poly (styrene)-b-poly(ethylene oxide)) was also synthesized to study their capacity to bind fluorescently tagged avidin. The surface-active property of the poly(ethylene oxide) block improved the availability of the biotin functional groups on the polymer surfaces. Fluorescence microscopy observations confirm the specific binding of biotin with avidin.

Reconstruction of Surfaces from Mixed Hydrocarbon and PEG Components in Water: Responsive Surfaces Aid Fouling Release

Coatings derived from surface active block copolymers (SABCs) having a combination of hydrophobic aliphatic (linear hydrocarbon or propylene oxide-derived groups) and hydrophilic poly(ethlyene glycol) (PEG) side chains have been developed. The coatings demonstrate superior performance against protein adsorption as well as resistance to biofouling, providing an alternative to coatings containing fluorinated side chains as the hydrophobe, thus reducing the potential environmental impact. The surfaces were examined using dynamic water contact angle, captive air-bubble contact angle, atomic force microscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure analysis. The PS(8K)-b-P(E/B)(25K)-b-PI(10K) triblock copolymer precursor (K3) initially dominated the dry surface. In contrast to previous studies with mixed fluorinated/PEG surfaces, these new materials displayed significant surface changes after exposure to water that allowed fouling resistant behavior. PEG groups buried several nanometers below the surface in the dry state were able to occupy the coating surface after placement in water. The resulting surface exhibits a very low contact angle and good antifouling properties that are very different from those of K3. The surfaces are strongly resistant to protein adsorption using bovine serum albumin as a standard protein challenge. Biofouling assays with sporelings of the green alga Ulva and cells of the diatom Navicula showed the level of adhesion was significantly reduced relative to that of a PDMS standard and that of the triblock copolymer precursor of the SABCs.

Triblock Copolymers with Grafted Fluorine-Free, Amphiphilic, Non-Ionic Side Chains for Antifouling and Fouling-Release Applications

Fluorine-free, amphiphilic, nonionic surface active block copolymers (SABCs) were synthesized through chemical modification of a polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene triblock copolymer precursor with selected amphiphilic nonionic Brij and other surfactants. Amphiphilicity was imparted by a hydrophobic aliphatic group combined with a hydrophilic poly(ethylene glycol) (PEG) group-containing moiety. The surfaces were characterized by dynamic water contact angle, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) analysis. In biofouling assays, settlement (attachment) of both spores of the green alga Ulva and cells of the diatom Navicula on SABCs modified with Brij nonionic side chains was significantly reduced relative to a PDMS standard, with a nonionic surfactant combining a PEG group and an aliphatic moiety demonstrating the best performance. Additionally, a fouling-release assay using sporelings (young plants) of Ulva and Navicula suggested that the SABC derived from nonionic Brij side chains also out-performed PDMS as a fouling-release material. Good antifouling and fouling-release properties were not demonstrated for the other two amphiphilic surfaces derived from silicone and aromatic group containing nonionic surfactants included in this study. The results suggest that small differences in chemical surface functionality impart more significant changes with respect to the antifouling settlement and fouling-release performance of materials than overall wettability behavior.

High-Concentration Aqueous Dispersions of Graphene Using Nonionic, Biocompatible Block Copolymers

Methods of using a surface active block copolymer to disperse graphene in aqueous medium, such dispersions which can be subsequently separated and processed for a range of end-use applications, including biomedical applications.

Surface Structures of an Amphiphilic Tri-Block Copolymer in Air and in Water Probed Using Sum Frequency Generation Vibrational Spectroscopy

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate surface structures of an amphiphilic surface-active block copolymer (SABC) film deposited on a CaF(2) substrate, in air and in water in situ. Developed as a surface-active component of an antifouling coating for marine applications, this amphiphilic triblock copolymer contains both hydrophobic fluorinated alkyl groups as well as hydrophilic ethoxy groups. It was found that surface structures of the copolymer film in air and in water cannot be probed directly using the SFG experimental geometry we adopted because SFG signals can be contributed from the polymer/air (or polymer/water) interface as well as the buried polymer/CaF(2) substrate interface. Using polymer films with varied thicknesses, structural information about the polymer surfaces in air and in water can be deduced from the detected SFG signals. With SFG, surface restructuring of this polymer has been observed in water, especially the methyl and methylene groups change orientations upon contact with water. However, the hydrophobic fluoroalkyl group was present on the surface in both air and water, and we believe that it was held near the surface in water by its neighboring ethoxy groups.

Amphiphilic Surface Active Triblock Copolymers with Mixed Hydrophobic and Hydrophilic Side Chains for Tuned Marine Fouling-Release Properties

Two series of amphiphilic triblock surface active block copolymers (SABCs) were prepared through chemical modification of two polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene ABC triblock copolymer precursors. The methyl ether of poly(ethylene glycol) [M(n) approximately 550 g/mol (PEG550)] and a semifluorinated alcohol (CF(3)(CF(2))(9)(CH(2))(10)OH) [F10H10] were attached at different molar ratios to impart both hydrophobic and hydrophilic groups to the isoprene segment. Coatings on glass slides consisting of a thin layer of the amphiphilic SABC deposited on a thicker layer of an ABA polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene thermoplastic elastomer were prepared for biofouling assays with algae. Dynamic water contact angle analysis, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) measurements were utilized to characterize the surfaces. Clear differences in surface structure were realized as the composition of attached side chains was varied. In biofouling assays, the settlement (attachment) of zoospores of the green alga Ulva was higher for surfaces incorporating a large proportion of the hydrophobic F10H10 side chains, while surfaces with a large proportion of the PEG550 side chains inhibited settlement. The trend in attachment strength of sporelings (young plants) of Ulva did not show such an obvious pattern. However, amphiphilic SABCs incorporating a mixture of PEG550 and F10H10 side chains performed the best. The number of cells of the diatom Navicula attached after exposure to flow decreased as the content of PEG550 to F10H10 side chains increased.

Protein adsorption resistance of anti-biofouling block copolymers containing amphiphilic side chains

Surface active block copolymers (SABCs) with amphiphilic side chains containing ethoxylated fluoroalkyl groups have previously demonstrated advantageous properties with regard to marine fouling resistance and release. While it was previously postulated that the ability of the block copolymer surface to undergo an environment-dependent transformation in surface structure aided this behaviour, protein adsorption characteristics of the surface were never explored. This study aims to expand our knowledge of protein interaction with the amphiphilic surface active block copolymer in an aqueous environment through experiments with bovine serum albumin (BSA), a widely utilized test protein. Fluorescence microscopy analysis using BSA labelled with fluorescein isothiocyanate (BSA–FITC) was performed on a SABC test surface to establish the polymer's protein adsorption resistance. Additionally, atomic force microscopy (AFM) based chemical force microscopy (CFM) was utilized to examine the force of adhesion of an AFM tip functionalized with strands of BSA protein with the SABC. No measurable force of adhesion was detected for 58% of the measurements of adhesion force taken for a BSA coated AFM tip interacting with the surface of the amphiphilic SABC in a PBS buffer. Furthermore, no measurements of force of adhesion were made in excess of 0.15 nN. This was in contrast to the non-zero mean adhesion force seen for several control surfaces in PBS buffer.

ABC Triblock Surface Active Block Copolymer with Grafted Ethoxylated Fluoroalkyl Amphiphilic Side Chains for Marine Antifouling/Fouling-Release Applications

An amphiphilic triblock surface-active block copolymer (SABC) possessing ethoxylated fluoroalkyl side chains was synthesized through the chemical modification of a polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene polymer precursor. Bilayer coatings on glass slides consisting of a thin layer of the amphiphilic SABC spray coated on a thick layer of a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) thermoplastic elastomer were prepared for biofouling assays with the green alga Ulva and the diatom Navicula. Dynamic water contact angle analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the surfaces. Additionally, the effect of the Young's modulus of the coating on the release properties of sporelings (young plants) of the green alga Ulva was examined through the use of two different SEBS thermoplastic elastomers possessing modulus values of an order of magnitude in difference. The amphiphilic SABC was found to reduce the settlement density of zoospores of Ulva as well as the strength of attachment of sporelings. The attachment strength of the sporelings was further reduced for the amphiphilic SABC on the "low"-modulus SEBS base layer. The weaker adhesion of diatoms, relative to a PDMS standard, further highlights the antifouling potential of this amphiphilic triblock hybrid copolymer.

Physicochemical Characterisation of a Novel Thermogelling Formulation for Percutaneous Penetration of 5-Aminolevulinic Acid

The present contribution was dedicated to the development and characterisation of a semisolid formulation of 5-aminolevulinic acid (5-ALA), appropriate for the diagnosis and treatment of actinic keratosis in photodynamic therapy. To achieve sufficiently high concentrations of the polar substance within the living epithelium after topical application, the semisolid base was enriched with penetration enhancers. A semisolid liquid crystalline system for drug delivering was the formulation of choice. It was composed of isopropyl alcohol, dimethyl isosorbide, medium chain triglycerides, water, and Pluronic F 127 as a polyoxyethylene–polyoxypropylene surface-active block copolymer. Rheometrical investigations were performed in the oscillatory mode and showed a thermo reversible gelification behaviour of the formulation, which therefore was denoted Thermogel. Permeation studies through human stratum corneum revealed higher permeation coefficients for 5-ALA from the Thermogel than from different German Pharmacopoeia creams. For example a 7.5-fold increase in comparison with Basiscreme DAC, and a 19.5-fold increase compared to water containing hydrophilic ointment. With respect to Dolgit® Mikrogel, the permeation coefficient from the Thermogel was 6.4-fold higher. These results were in accordance with those of differential scanning calorimetry measurements. Thermogel disclosed the strongest interactions with stratum corneum lipids.

P277: Direct observations of the interactions of P188 with damaged cell membranes with AFM

The realization that surface-active block copolymers (Poloxamers) can be used to restore the structural integrity of permeabilized cell membranes [1] has established new methods for repairing damaged cell membranes [1-4]. The main goal of the present work is to understand the nature of the interactions between copolymer surfactants and membranes that lead to the restoration of structurally compromised membranes. We characterize structural changes in fibroblast cell membranes associated with the observed permeability increases due to a chemical injury by saponin and successive Poloxamer 188 (P188) mediated membrane sealing by using atomic force microscopy (AFM).

Photochemical Modification and Patterning of Polymer Surfaces by Surface Adsorption of Photoactive Block Copolymers

We report a simple photolithographic approach for the creation and micropatterning of chemical functionality on polymer surfaces by use of surface-active block copolymers that contain protected photoactive functional groups. The block copolymers self-assemble at the substrate-air interface to generate a surface that is initially hydrophobic with low surface tension but that can be rendered hydrophilic and functional by photodeprotection with UV radiation. The block copolymer employed, poly(styrene-b-tert butyl acrylate), segregates preferentially to the surface of a polystyrene substrate because of the low surface tension of the polyacrylate blocks. The strong adsorption of block copolymers causes a bilayer structure to form presenting a photoactive polyacrylate layer at the surface. In the example described, the tert-butyl ester groups on the polyacrylate blocks are deprotected by exposure to UV radiation in the presence of added photoacid generators to form surface carboxylic acid groups. Surface micropatterns of carboxylic acid groups are generated by UV exposure through a contact mask. The success of surface chemical modification and pattern formation is demonstrated by X-ray photoelectron spectroscopy and contact angle measurements along with imaging by optical and fluorescence microscopy methods. The resultant chemically patterned surfaces are then used to template patterns of various biomolecules by means of selective adsorption, covalent bonding and molecular recognition mechanisms. The surface modification/patterning concept can be applied to virtually any polymeric substrate because protected functional groups have intrinsically low surface tensions, rendering properly designed block copolymers surface active in almost all polymeric substrates.

Managing polymer surface structure using surface active block copolymers in block copolymer mixtures

AbstractSurface coatings were prepared from semifluorinated monodendron surface‐active block copolymers (SABC) and a thermoplastic elastomer (TPE) [poly(styrene‐b‐ethylene butylene‐b‐styrene)] by either spin‐casting a bilayer structure or by blending. The surface of these coatings was characterized by contact angle measurements, scanning force microscopy (SFM) and near‐edge X‐ray absorption fine structure (NEXAFS) methods. Both bilayers and blends resulted in very low energy surfaces under the right processing conditions and the liquid crystallinity of the semifluorinated monodendrons gave rise to temporally stable, non‐reconstructing surfaces in water. However for small thicknesses of the SABC top layer or for low SABC content blends, SFM shows islands of the fluorinated block of the SABC and incomplete surface coverage of the TPE, an observation confirmed by NEXAFS analysis. Very high water contact angles were produced by even modest amounts of SABC in either case but to achieve low contact angle hysteresis, it was necessary to produce uniform surface coverage by the SABC. Such uniform coverage can be accomplished by spin casting a top layer of SABC as thin as 60 nm in the bilayer case but at least 10 wt% SABC in TPE combined with drop casting of a hot solutions is needed for the blends to achieve equivalent surface structure and properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 411–420, 2004

Coatings Based on Side-chain Ether-linked Poly(ethylene glycol) and Fluorocarbon Polymers for the Control of Marine Biofouling

The preparation of side group modified polystyrene-based surface-active block copolymers (SABC) for use as marine fouling resistance/release applications is described. Modifying moieties such as poly(ethylene glycol) (PEG) and semifluorinated segments were used. A novel bilayer methodology has been employed that provides both suitable mechanical properties through the use of an elastomeric primer layer of styrene-ethylene/butylene-styrene (SEBS) and control of surface-chemistry through use of the SABCs. This approach has potential as a cost-effective technology for environmentally benign coatings that resist and release marine biofouling. Initial testing of these materials included determination of captive bubble contact angles and protein adsorption. Testing against marine fouling organisms was performed using settlement and adhesion bioassays with zoospores of the green alga Enteromorpha . The results showed that all surfaces had markedly reduced levels of zoospore settlement compared with glass controls and that adhesion strength was strongly affected by the semifluorinated SABC. The results are discussed in terms of surface properties.

Polyoxyethylene-polyoxypropylene block copolymer gels as sustained release vehicles for subcutaneous drug administration

Polyoxyethylene-polyoxypropylene surface-active block copolymers (Pluronic®) were evaluated as a vehicle for subcutaneous administration of drugs using a phenolsulfophthalein (PR) as a tracer. The type of Pluronic® copolymer (F108 or F127), and their concentrations, and the effect of solutes (NaOH, NaCl or PR) on gelation properties were studied. Sodium hydroxide and sodium chloride decreased the gel-sol transition temperature, whereas the opposite effect was observed with PR. The ‘in vitro’ release rates obtained for PR were inversely proportional to the concentration of Pluronic used and a zero-order release rate was observed in all preparations assayed. Pluronic® F127/PR preparations were administered subcutaneously (SC) to Wistar rats and PR plasma levels were compared with those reached after SC or intravenous (i.v.) administration of a PR aqueous solution. The gel formulation produced a sustained plateau level within 15 min that lasted 8–9 h. In vivo data analysis was performed with the JANA and PCNONLIN computer programs. The best fittings for experimental data from Pluronic gels were obtained using a zero-order input and first-order output two-compartment model. The results obtained suggest that PF127 aqueous gels may be of practical use as a vehicle for SC administration of drugs.

Chemical Structure and Surface Activity

In a reaction of bis(2-hydroxyethyl)disulphide with methyl- or ethyloxirane (proylene or α-butylene oxide) carried out in the presence of ternary amine as catalyst, hydrophobic oligomers were obtained. By reacting them with oxirane (ethylene oxide), surface active block copolymers were obtained. The all-block copolymers were characterized and their efficiency of adsorption as well as foaming and wetting properties were measured

Pluronic F-127 gels as a vehicle for topical administration of anticancer agents.

Pluronic F-127 (a polyoxyethylene-polyoxypropylene surface-active block copolymer) was evaluated as a vehicle substance for topical administration of anticancer agents. 5-Fluorouracil and adriamycin were used in this evaluation. The effects of the concentration of Pluronic F-127, temperature, and the drug concentration on the release were studied by means of an in vitro release method using a cellulose membrane. With increasing concentration of Pluronic F-127 in the vehicle a corresponding decrease in the apparent release rate of the anticancer agents occurred. The apparent release rate increased with increasing temperature from 30 to 44°C. Increase in drug concentration increased the drug release rate. The Pluronic F-127 gels appeared to have good potential for use in topical drug delivery systems since they exhibit reverse thermal gelation behavior and have good drug release characteristics and low toxicity.