pH-responsive Surfaces Research Articles

PH-responsive P(AA-b-SBMA)-grafted magnetic GO high-performance ultrafiltration membrane with improved antifouling tendency and cleaning efficiency

Nanocomposite ultrafiltration polysulfone membrane with pH-responsive surface was designed and synthesized using poly (AA-b-SBMA)-grafted magnetic graphene oxide (MGP) nanofiller. The obtained membranes revealed advanced antifouling, high cleaning-efficiency, and high rejection when compared to pristine PSf membranes. The novel MGP nanofiller was synthesized by copolymerization of acrylic acid and sulfobetaine monomers on the grafted magnetic graphene oxide surface by RAFT polymerization. The non-solvent-induced phase separation was used to prepare polysulfone nanocomposite ultrafiltration membranes with pH-responsive surfaces optimized by the MGP content of 0.05 to 0.3 wt% in the dope solution. The MGP content embedded within the polysulfone matrix greatly influences the water flux. The optimal 144 LMH flux of water, achieved by 0.1 wt% MGP, was almost 80 % higher compared with the pure polysulfone. The optimal MGP-modified nanocomposite membrane showed high antifouling tendency and 72 % flux recovery value. Also, when pH changed from 3 to 8, the pH-responsive membrane revealed the best water flux recovery for bovine serum albumin adsorption-desorption. Comprehensive characterization of MGP nanofiller, the modified polysulfone, and pristine membranes confirmed that the surface hydrophilicity, cross-section morphology, surface roughness, and compositions of the modified ultrafiltration membranes could be modified considerably by the incorporation of MGP nanofiller.

PH-responsive SERS substrates based on AgNP-polyMETAC composites on patterned self-assembled monolayers

Patterned silver nanoparticle (NP)-poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (AgNP-polyMETAC) composites were prepared by electrochemical lithography, surface-initiated atom-transfer radical polymerization (SI-ATRP) and NP growth inside the polymer brushes. For this purpose, polymer brushes of poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (polyMETAC) were utilized as strong electrolyte brush system. These were introduced in form of patterned polymer brushes to create pH-responsive surface enhanced Raman scattering SERS substrates. It is well-known that the charges of strong polyelectrolyte chains are usually insensitive to pH changes, hence, rarely strong polyelectrolyte brushes have been utilized so far to study pH-responsive properties of such films. Here pH-insensitive polyMETAC brushes exhibit pH-sensitive properties and can be used as pH-responsive surfaces for SERS applications due to the embedding of AgNPs into the polymer brushes. When increasing the pH, the assembly of the AgNPs transfers from quasi two-dimensional (2D) aggregates, attaching mainly to the polymer surface, into a three-dimensional (3D) assembly, where the particles are penetrating into the brushes. These changes result in significant alterations of the SERS efficiency of the polymer brush composite. At pH 5, the enhancement of the Raman scattering approaches its maximum. The fabricated SERS substrates show a high sensitivity as well as good experimental reliability at different pH values. Moreover, electrochemical lithography was utilized to fabricate patterned SERS substrate, which allows an easy combination of multiple other functionalities in hierarchical structuring steps. In addition, the microstructure is in our studies beneficial because of a simplified and reliable characterization of the polymer brushes at defined sample areas. The introduction of the microstructured brush system is regarded moreover attractive for the development of high-throughput platforms for rapid, automated screening and analysis applications.

Temperature- and/or pH-Responsive Surfaces with Controllable Wettability: From Parahydrophobicity to Superhydrophilicity.

Multifunctional surfaces with reversible wetting characteristics are fabricated utilizing end-anchored polymer chains on hierarchically roughened surfaces. Temperature- and/or pH-responsive surfaces are developed that exhibit reversible and controllable wettability, from the "parahydrophobic" behavior of natural plant leaves all the way to superhydrophilic properties in response to the external stimuli. For this purpose, dual scale micro/nanoroughened surfaces were prepared by laser irradiation of inorganic surfaces (Si wafers) utilizing ultrafast (femtosecond) laser pulses under a reactive gas atmosphere. End-functionalized polymer chains were anchored onto those surfaces utilizing the "grafting to" method; poly(N-isopropylacrylamide), PNIPAM, and poly(2-vinylpyridine), P2VP, were used for the formation of monofunctional as well as mixed brushes. The surfaces exhibit "parahydrophobic" behavior in the hydrophobic state (high temperature and/or high pH), with high static contact angles (∼120°) and high water adhesion (∼30° contact angle hysteresis), whereas they show superhydrophilic behavior in the hydrophilic state (low temperature and/or low pH). The surfaces were tested for their wettability under repetitive cycles and found to be stable and reproducible.

Switching fluid slippage on pH-responsive superhydrophobic surfaces.

Two stimuli-responsive polymer brushes, poly(dimethylaminoethyl methacrylate) and poly(methacrylic acid), were grafted from initiator-modified anodized alumina substrates to prepare two pH-responsive surfaces. By regulating the swelling states of the two polymers, water droplets can roll off or adhere onto the textured surface because of different adhesion forces. These forces also strongly affect boundary slippage. To determine the different slippage effects of fluid on our pH-responsive surfaces, a series of rheological experiments are carried out on two kinds of surfaces. A large slip length is obtained and reversibly regulated by changing the fluid pH. These responsive superhydrophobic surfaces with considerable slip length and pH-responsive properties have extensive potential applications in intelligent micro- and nanofluidic devices or biodevices, which can solve fluid flow problems.

Photo-induced water–oil separation based on switchable superhydrophobicity–superhydrophilicity and underwater superoleophobicity of the aligned ZnO nanorod array-coated mesh films

Stimulus-responsive surface wettability, especially photoresponsive surface wettability, has been intensively studied. Meanwhile, multifunctional surfaces, especially for the treatment of oil contaminated water, have aroused worldwide attention. Recently, pH-responsive surfaces with controllable oil–water separation have also been reported. However, photoresponsive water–oil separation is still a challenge. Here we report photo-induced water–oil separation based on the switchable superhydrophobicity–superhydrophilicity and underwater superoleophobicity of aligned ZnO nanorod array-coated mesh films, which shows excellent controllability and high separation efficiency of different types of water–oil mixtures in an oil–water–solid three-phase system. The underwater superoleophobicity of the aligned ZnO nanorod array-coated stainless steel mesh film can effectively prevent the mesh film from being polluted by oils. This work is promising in photo-induced water–oil mixture treatments such as water-removal from a micro-reaction system and controllable filtration, and may also provide interesting insight into the design of novel functional devices based on controllable surface wettability.

PH responsive surfaces with nanoscale topography

AbstractWe report the preparation of nanostructured adaptive polymer surfaces by diffusion of an amphihilic block copolymer toward the interface. The surface segregation of a diblock copolymer, polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA), occurred when blended with high molecular weight polystyrene employed as a matrix. On annealing, the polymer surfaces changed both the chemical composition and the hydrophilicity depending on the environment and pH, respectively. By exposure to either water vapor or air, the surface wettability varied between hydrophilic and hydrophobic. In addition, surface enrichment on diblock copolymer by water vapor annealing led to self‐assembly occurring at the interface. Hence, nanostructured domains can be observed by AFM in liquid media. Moreover, the PAA segments placed at the interface respond to pH and can switch from an extended hydrophilic state at basic pH values to a collapsed hydrophobic state in acidic media. Accordingly, the surface morphology changed from swelled micelles to nanometer size holes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2982–2990, 2010

From superhydrophobicity and water repellency to superhydrophilicity: smart polymer-functionalized surfaces

pH-responsive surfaces, reversibly switching between superhydrophilicity and superhydrophobicity/water repellency, are developed by "grafting from" a pH-sensitive polymer onto a hierarchically micro/nano-structured substrate. We quantify the water repellency by investigating the restitution coefficient of water droplets bouncing off the surfaces. The water repellent state requires appropriate hydrophobicity of the functionalizing polymer as well as very low values of contact angle hysteresis.

“Clicking” Polymer Brushes with Thiol-yne Chemistry: Indoors and Out

Thiol-yne click chemistry is demonstrated as a modular platform for rapid and practical fabrication of highly functional, multicomponent surfaces under ambient conditions. The principle is illustrated using a postmodification strategy in which poly(propargyl methacrylate) brushes were generated via surface-initiated photopolymerization and sequentially functionalized using the radical-mediated thiol-yne reaction. Brush surfaces expressing a three-dimensional configuration of "yne" functionalities were modified with high efficiency and short reaction times using a library of commercially available thiols, including functional thiols that demonstrate applicability for pH responsive surfaces and for bioconjugation. Sequential thiol-yne reactions in conjunction with simple UV photolithography were also applied to afford micropatterned, multicomponent surfaces. The practicality of the platform was further demonstrated by carrying out thiol-yne surface reactions in sunlight, suggesting the possibility of large scale modifications using renewable energy resources. Considering the mild reaction conditions, rapid throughput, and compatibility with orthogonal chemistries, we expect this platform to find widespread use among the materials science community.

Tunable Resistive m-dPEG Acid Patterns on Polyelectrolyte Multilayers at Physiological Conditions: Template for Directed Deposition of Biomacromolecules

This paper describes a new class of salt-responsive poly(ethylene glycol) (PEG) self-assembled monolayers (SAMs) on top of polyelectrolyte multilayer (PEMs) films. PEM surfaces with poly(diallyldimethylammonium chloride) as the topmost layer are chemically patterned by microcontact printing (muCP) oligomeric PEG molecules with an activated carboxylic acid terminal group (m-dPEG acid). The resistive m-d-poly(ethylene glycol) (m-dPEG) acid molecules on the PEMs films were subsequently removed from the PEM surface with salt treatment, thus converting the nonadhesive surfaces into adhesive surfaces. The resistive PEG patterns facilitate the directed deposition of various macromolecules such as polymers, dyes, colloidal particles, proteins, liposomes, and nucleic acids. Further, these PEG patterns act as a universal resist for different types of cells (e.g., primary cells, cell lines), thus permitting more flexibility in attaching a wide variety of cells to material surfaces. The patterned films were characterized by optical microscopy and atomic force microscopy (AFM). The PEG patterns were removed from the PEM surface at certain salt conditions without affecting the PEM films underneath the SAMs. Removal of the PEG SAMs and the stability of the PEM films underneath it were characterized with ellipsometry and optical microscopy. Such salt- and pH-responsive surfaces could lead to significant advances in the fields of tissue engineering, targeted drug delivery, materials science, and biology.

Surface modification of microfluidic channels by UV-mediated graft polymerization of non-fouling and ‘smart’ polymers

Microfluidic channels prepared from polydimethylsiloxane (PDMS) have been modified by UV-mediated graft polymerization of temperature-responsive polymers (poly[ N-isopropyl acrylamide] or pNIPAAm), temperature- and pH-responsive copolymers (P[NIPAAm-co-acrylic acid (AAc)]), and a non-fouling hydrogel (polyethyleneglycol diacrylate, or PEGDA). This was done by presorbing a photosensitizer (PS) within the PDMS channel surface regions, contacting the different monomer solutions with the PS-containing surface under nitrogen, and irradiating with UV. The pNIPAAm-grafted surface was hydrophilic below its lower critical solution temperature (LCST), resisting non-specific adsorption, while it was hydrophobic above its LCST, now binding pNIPAAm-coated nanoparticles. Combined temperature- and pH-responsive surfaces were also prepared by UV radiation grafting a monomer mixture of pNIPAAm with AAc. The surfaces have been characterized by advancing water contact angle measurements. These smart microfluidic channels should be useful for many applications such as affinity separations and diagnostic assays.

Self-Assembled Monolayers of Dendron Thiols for Electrodeposition of Gold Nanostructures: Toward Fabrication of Superhydrophobic/Superhydrophilic Surfaces and pH-Responsive Surfaces

This paper describes the fabrication of surfaces with different wettability, superhydrophobic/superhydrophilic, and pH-responsive properties. We used a self-assembled monolayer (SAM) of a dendron thiol as the underlying surface for electrodeposition of gold nanostructures. After this modification with a SAM of n-dodecanethiol or 11-mercaptoundecanol, the surface shows remarkable superhydrophobic properties with a contact angle of about 155 degrees and a tilt angle of less than 2 degrees or superhydrophilic properties with a contact angle of about 0 degrees , respectively. Moreover, a large-scale pH-responsive surface was obtained by modification with 2-(11-mercaptoundecanamido)benzoic acid (7) (MUABA). The pH-responsive behavior was amplified by using rough surfaces.