Low Surface Energy Polymeric Films from Solventless Liquid Oligoesters and Partially Fluorinated Isocyanates

Spatial and Bidirectional Work Function Modulation of Monolayer Graphene with Patterned Polymer "Fluorozwitterists"

Understanding the electronic properties resulting from soft-hard material interfacial contact has elevated the utility of functional polymers in advanced materials and nanoscale structures, such as in work function engineering of two-dimensional (2D) materials to produce new types of high-performance devices. In this paper, we describe the electronic impact of functional polymers, containing both zwitterionic and fluorocarbon components in their side chains, on the work function of monolayer graphene through the preparation of negative-tone photoresists, which we term "fluorozwitterists." The zwitterionic and fluorinated groups each represent dipole-containing moieties capable of producing distinct surface energies as thin films. Kelvin probe force microscopy revealed these polymers to have a p-doping effect on graphene, which contrasts the work function decrease typically associated with polymer-to-graphene contact. Copolymerization of fluorinated zwitterionic monomers with methyl methacrylate and a benzophenone-substituted methacrylate produced copolymers that were amenable to photolithographic fabrication of fluorozwitterist structures. Consequently, spatial alteration of zwitterion coverage across graphene yielded stripes that resemble a lateral p-i-n diode configuration, with local increase or decrease of work function. Overall, this polymeric fluorozwitterist design is suitable for enabling simple, solution-based surface patterning and is anticipated to be useful for spatial work function modulation of 2D materials integrated into electronic devices.

Non-isocyanate Polyurethane Coating with High Hardness, Superior Flexibility, and Strong Substrate Adhesion

Flexible hard coatings with strong adhesion are critical requirements for several foldable devices and marine applications; however, only a few such coatings have been reported. Herein, we report a non-isocyanate polyurethane (NIPU) coating prepared by the epoxy-oligosiloxane nanocluster-amine curing reaction and cyclic carbonate-amine polyaddition, where the former provides the coating with ceramic-like hardness and polymer-like flexibility while the latter polymerization results in NIPU with strong substrate adhesion. The coating is transparent (>92% transmittance), hard (5-7 H), and flexible (2 mm bending diameter). It has strong adhesion to various substrates including aluminum alloy, titanium, steel, glass, ceramic, epoxy, and polyethylene terephthalate (2-8 MPa), which can be attributed to the high density of polar groups in NIPU. Moreover, we can facilely endow the coating with anti-icing, self-cleaning, and anti-smudge capabilities by incorporating amine-terminated low-surface-tension polydimethylsiloxane (PDMS) to replace a part of the amine curing agent. Particularly, the mechanical properties of NIPU coatings are only slightly affected by the introduction of low-content PDMS since it intends to enrich on the surface. The novel coating has promising future for use in fields of foldable devices and marine applications.

A novel dual-layer approach towards omniphobic polyurethane coatings

Omniphobic surfaces have a plethora of applications ranging from household paints to sensors. The predominant practice of fabricating those materials/surfaces is to use fluorinated materials which are environmentally harmful, and thus have limited practical applications. In this study, we report a novel dual-layer approach of fabrication towards omniphobic surfaces using polyurethane (PU) as a matrix and polydimethylsiloxane (PDMS) as a self-cleaning ingredient. This approach was also used to produce omniphobic PU nanocomposites, where nanofillers (e.g., nanoclay, cellulose nanocrystals (CNCs) and graphene oxide (GO)) were incorporated. The resultant coatings were investigated for their performance, such as optical clarity, durability, and self-cleaning properties. In addition, scanning electron microscopy (SEM) was used for microstructural analysis of the obtained coatings. The facile nature of fabrication and the use of PDMS, an environmentally benign material relative to fluorinated chemicals, thus offer an eco-friendly sustainable scheme for practical applications aimed at omniphobic purposes.

Omniphobic surfaces have a plethora of applications ranging from household paints to sensors.

Effect of Varying Chain Length and Content of Poly(dimethylsiloxane) on Dynamic Dewetting Performance of NP-GLIDE Polyurethane Coatings

Polyurethane coatings containing nanopools of a grafted lubricating liquid ingredient for dewetting enablement (NP-GLIDE) are prepared by curing a commercial polyol P0, a hexamethylene diisocyanate trimer, and P1- g-PDMS, which is a graft copolymer consisting of a polyol backbone P1 bearing poly(dimethylsiloxane) (PDMS) side chains. These materials are known as NP-GLIDE because most test liquids have no problem to cleanly glide off them and because segregated nanopools of the grafted lubricating ingredient (PDMS) for dewetting enablement are dispersed throughout the coating matrix. To optimize the dewetting performance of the NP-GLIDE coatings, the molecular weights of the PDMS side chains in the P1- g-PDMS samples were increased from 1.0 kDa (1k) to 5.0 kDa (5k) and 10.0 kDa (10k). A comparative study of the coatings containing three different P1- g-PDMS samples at a constant PDMS mass fraction of either 6.0 or 2.00% (m/m) showed that P1- g-PDMS_5k-based coatings exhibited the best dewetting properties. These properties included the lowest sliding angles for test liquids that were incompatible with PDMS and the fastest and most effective contraction of marker ink traces and a paint. Coatings containing 0.50 and 1.00% (m/m) of PDMS_5k were also prepared from P1- g-PDMS_5k and compared with those containing 2.00 and 6.0% (m/m) of PDMS_5k. The coatings were shown to retain their dewetting properties with the PDMS contents as low as 1.00% (m/m). Although the results of this study provided valuable insight into the design of future practical NP-GLIDE coatings, a model has also been proposed for the surface structure of the coatings to justify our observations.

Controlling Surface Segregation of a Polymer To Display Carboxy Groups on an Outermost Surface Using Perfluoroacyl Groups

Controlling the surface properties of solid polymers is important for practical applications. We here succeeded in controlling the surface segregation of polymers to display carboxy groups on an outermost surface, which allowed the covalent immobilization of functional molecules via the carboxy groups on a substrate surface. Random methacrylate-based copolymers containing carboxy groups, which were protected with perfluoroacyl (R_f) groups, were dip-coated on acrylic substrate surfaces. X-ray photoelectron spectroscopy and contact-angle measurements revealed that the R_f groups were segregated to the outermost surface of the dip-coated substrates. The R_f groups were removed by hydrolysis of the R_f esters in the copolymers, resulting in the display of carboxy groups on the surface. The quantification of carboxy groups on a surface revealed that the carboxy groups were reactive to a water-soluble solute in an aqueous solution. The surface segregation was affected by the molecular structure of the copolymer used for dip-coating.

Fluorine-Free Anti-Smudge Polyurethane Coatings

Conventionally, low-surface-tension fluorinated reagents are incorporated into anti-smudge (oil- and water-repellent) coatings for oil repellency. However, fluorinated compounds are expensive and an environmental concern because of their high stability and bioaccumulation. These factors limit their widespread application. We report herein the development of fluorine-free anti-smudge polyurethane coatings that are clear at thicknesses up to tens of micrometers and are able to sustain extensive surface damage. We demonstrate that these coatings can be applied readily onto a diverse range of substrates.

Effect of surface compositional heterogeneities and microphase segregation of fluorinated amphiphilic copolymers on antifouling performance

In this paper, a series of fluorinated amphiphilic copolymers composed of 2-perfluorooctylethyl methacrylate (FMA) and 2-hydroxyethyl methacrylate (HEMA) monomers were prepared, and their surface properties and antifouling performance were investigated. Bovine serum albumin (BSA) and human plasma fibrinogen (HFg) were used as model proteins to study protein adsorption onto the fluorinated amphiphilic surfaces. All the fluorinated amphiphilic surfaces exhibit excellent resistant performance of protein adsorption measured by X-ray photoelectron spectroscopy (XPS). The surface compositional heterogeneities on the molecular scale play an important role in the antifouling properties. It was found that the copolymers exhibited better antifouling properties than the corresponding homopolymers did, when the percentage of hydrophilic hydroxyl groups is from 4% to 7% and the percentage of hydrophobic fluorinated moieties is from 4% to 14% on the surface. In addition, the protein molecular size scale and the pattern of microphase segregation domains on the surface strongly affect the protein adsorption behaviors. These results demonstrate the desirable protein-resistant performance from the fluorinated amphiphilic copolymers and provide deeper insight of the effect of surface compositional heterogeneity and microphase segregation on the protein adsorption behaviors.

Self-replenishing surfaces

Damaged surfaces self-replenish their chemical composition by the spontaneous re-orientation of functional groups chemically bonded to the polymer network. The repair of the surface chemistry leads to the recovery of surface functionality. This self-replenishing approach is suitable to recover many surface-related properties and constitutes a major breakthrough in extending the service life-time of functional materials.

Ion-implanted polytetrafluoroethylene enhances Saccharomyces cerevisiae biofilm formation for improved immobilization

The surface of polytetrafluoroethylene (PTFE) was modified using plasma immersion ion implantation (PIII) with the aim of improving its ability to immobilize yeast. The density of immobilized cells on PIII-treated and -untreated PTFE was compared as a function of incubation time over 24 h. Rehydrated yeast cells attached to the PIII-treated PTFE surface more rapidly, with higher density, and greater attachment strength than on the untreated surface. The immobilized yeast cells were removed mechanically or chemically with sodium hydroxide and the residues left on the surfaces were analysed with Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). The results revealed that the mechanism of cell attachment on both surfaces differs and a model is presented for each. Rapid attachment on the PIII-treated surface occurs through covalent bonds of cell wall proteins and the radicals on the treated surface. In contrast, on the untreated surface, only physisorbed molecules were found in the residue and lipids were more highly concentrated than proteins. The presence of lipids in the residue was found to be a consequence of damage to the plasma membrane during the rehydration process and the increased cell stress was also apparent by the amount of Hsp12 in the protein residue. The immobilized yeast cells on PIII-treated PTFE were found to be as active as yeast cells in suspension.

Surface depletion of the fluorine content of electrospun fibers of fluorinated polyurethane

For materials containing fluorine, it has been generally accepted that fluorinated segments or end groups tend to aggregate in the outer surface because of the low surface energy, which endows the fluorinated materials with special surface properties such as self-cleaning, superhydrophobicity, and so forth. However, for the electrospun fibrous membranes of polyurethane elastomers containing perfluoropolyether segments (FPU), abnormal fluorine aggregations in the core of the electrospun fibers were observed. The XPS analysis indicated a rather low fluorine content at the surface of the electrospun FPU fibers. Further study with dynamic light scattering and fluorescence showed that FPU chains can form aggregates in the concentrated solution. Therefore, it can be deduced that the rapid evaporation of solvent and fast formation of fibers during the electrospinning process could result in the freeze-in of the aggregated chain conformation and the depletion of fluorine units on the surface of the electrospun FPU fibers.

Biomimetic superhydrophobic and highly oleophobic cotton textiles

We report a biomimetic procedure to prepare superhydrophobic cotton textiles. By in situ introducing silica particles to cotton fibers to generate a dual-size surface roughness, followed by hydrophobization with polydimethylsiloxane (PDMS), normally hydrophilic cotton has been easily turned superhydrophobic, which exhibits a static water contact angle of 155 degrees for a 10 microL droplet. The roll-off angle of water droplets depends on the droplet volume, ranging from 7 degrees for a droplet of 50 microL to 20 degrees for a 7 microL droplet. When a perfluoroalkyl chain is introduced to the silica particle surface, the superhydrophobic textile also becomes highly oleophobic, as demonstrated by a static contact angle of 140 degrees and a roll-off angle of 24 degrees for a 15 microL sunflower oil droplet.