Can Water Float on Oil?

The tensile strength of interfaces between air/liquid and immiscible liquid/liquid systems has been the driving force in nature and industrial processes such as wetting/dewetting and coating. Despite its small magnitude, interfacial tension can be the dominant force in capillary tubes, microgravity conditions, and nanofluids. In addition to capillary rise, the surface tension can work against gravity and support a solid body floating in water surface, which has been noticed as early as 350 BC by Aristotle. In nature, insects such as water striders rely on surface tension to walk on water. Experimentally, small spherical particles, few millimeters in diameter, have been reported as floating on the air/water interface. In contrast to rigid bodies, a fluid droplet at surface of another fluid has three deformable interfaces and variable contact angles. The equilibrium of three interface tensions at the contact line, if it exists, results in an unique combination of three contact angles, which form a Neumann’s triangle.The interfacial interaction between three fluids has been investigated for an oil droplet spreading on water surface by Langmuir and for a fluid droplet at the interface between two fluids by Princen.
More recently, numerical methods were applied to identify the shape of such droplets. In these instances, the liquid droplet is less dense than the supporting liquid, and gravity always plays a stabilizing role on the system.

In this work a numerical model was developed from the Young−Laplace equation on three interfaces (water/oil, water/air, and oil/air) to predict the theoretical equilibration conditions. The model was verified successfully with an oil/water system. The stability of the floating droplet depends on the combination of three interface tensions, oil density, and water droplet volume. For practical purposes, however, the equilibrium contact angle has to be greater than 5° so the water droplet can effectively float. This result has significant applications for biodegrading oil wastes.



Can Water Float on Oil?
Chi M. Phan,* Benjamin Allen, Luke B. Peters, Thu N. Le, and Moses O. Tade
Department of Chemical Engineering, Curtin University, GPO Box U1987, Perth WA 6845, Australia


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Micropatterning of Bioactive Glass Nanoparticles on Chitosan Membranes for Spatial Controlled Biomineralization

In recent years, the biomaterials field has witnessed the rise of a third generation of materials able to stimulate specific cellular responses.Exposed to the right surface chemistry and topography, cells can adhere, proliferate, and differentiate.Microcontact printing (μCP) of biologically relevant ligands using a soft poly(dimethylsiloxane) PDMS stamp is the most common technique to generate specific patterns with different and well-defined chemistries. Patterns of proteins, molecules, polymers, nanoparticles, self-assembled monolayers, colloids, and metals have been reported.

Different methods can be applied to engineer culture substrates for guiding cellular responses with spatial control. Bioactive glass has been demonstrated to have a beneficial effect in bone regeneration, skin, articular regeneration, and angiogenesis applications as it binds to both bone and soft tissue.

Bioactive glass has been mainly applied in orthopedic and dental areas, since it promotes deposition of apatite under physiological conditions. A few works have reported the fabrication of substrates with spatial control of biomineralization. 

This team has been developed bioactive glass nanoparticles (BG-NPs) capable of inducing apatite precipitation upon immersion in simulated body fluid (SBF) were patterned on free-standing chitosan membranes by microcontact printing using a poly(dimethylsiloxane) (PDMS) stamp inked in a BG-NPs pad. Formation of the patterns was characterized by scanning electron microscopy (SEM). Mineralization of the bioactive glass patterns was induced in vitro by soaking the samples in SBF over different time points up to 7 days. The confined apatite deposition in the patterned regions with diameters of 50 μm was confirmed by Fouriertransformed infrared spectroscopy (FTIR), energy-dispersive X-ray (EDX) analysis, and SEM. In vitro tests confirmed the preferential attachment and proliferation of L929 cells to the areas printed with BG-NPs of the membranes. This approach permits one to spatially control the properties of biomaterials at the microlevel and could be potentially used in guided tissue regeneration for skin, vascular, articular, and bone tissue engineering and in cellular cocultures or to develop substrates able to confine cells in regions with controlled geometry at the cell’s length scale.

Micropatterning of Bioactive Glass Nanoparticles on Chitosan Membranes for Spatial Controlled Biomineralization

Gisela M. Luz, Luciano Boesel, Aranzazu del Campo, ́and Joao F. Mano 

3B’s Research Group-Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, 4806-909 Caldas das Taipas, Portugal

ICVS/3B’s-PT Government Associated Laboratory, Braga/Guimaraes, Portugal 

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

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Direct Observation of Nanoparticle Cancer Cell Nucleus Interactions

The nucleus is the most important organelle in the growth, proliferation, and apoptosis of a cell. Controlling the processes governed by the nucleus has been a primary goal for nuclear-targeted cancer therapy. Conventionally, viral vectors are used to deliver drugs to cell nuclei, but a drawback is the resulting immunogenic response.

Recently, nuclear targeting by peptide-modified gold NPs has seen some success and shown improved anticancer efficacy; however, the mechanism responsible for the increased cell death is unknown because no nanoscale direct visualization of how the NPs affected the nucleus was shown.

Nucleolin is the most abundant nucleolar phosphoprotein in the nucleus of normal cells but in metastatic and rapidly dividing cells is overexpressed in the cytoplasm and translocated to the cell membrane. The trafficking ability of nucleolin has been implicated in transporting anticancer ligands from the cell surface to the nucleus.

                              

This report includes the direct visualization of interactions between drug-loaded nanoparticles and the cancer cell nucleus. Nanoconstructs composed of nucleolin-specific aptamers and gold nanostars were actively transported to the nucleus and induced major changes to the nuclear phenotype via nuclear envelope invaginations near the site of the construct. The number of local deformations could be increased by ultrafast, light-triggered release of the aptamers from the surface of the gold nanostars. Cancer cells with more nuclear envelope folding showed increased caspase 3 and 7 activity (apoptosis) as well as decreased cell viability. This

newly revealed correlation between drug-induced changes in nuclear phenotype and increased therapeutic efficacy could provide new insight for nuclear-targeted cancer therapy.

Duncan Hieu M. Dam, Jung Heon Lee, Patrick N. Sisco, Dick T. Co, Ming Zhang, Michael R. Wasielewski, and Teri W. Odom 


Department of Chemistry and Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States, Department of Molecular Pharmacology and Biological Chemistry, Northwestern University, Chicago, Illinois 60611, United States, and School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon, South Korea 


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Polysaccharide-Coated Thermosets For Orthopaedic Applications: From Material Characterization To In Vivo Tests

The development of tissue engineering and regenerative medicine techniques has introduced the new concept of “bioactive” biomaterial, able to induce specific biological responses by engaging interactions with the surrounding living tissue at  the molecular level.In particular, for applications in orthopaedics and dentistry the ideal biomaterial surface should be able to induce osteogenesis and ensure a stable biological/chemical bond between implant and bone.

Various materials are clinically used for orthopaedic implants, in particular titanium, CoCrMo and  stainless steel alloys. In spite of their good biocompatibility, such metallic materials have some drawbacks, mostly related to high stiffness, possible wear of surface oxide and lack of bioactivity.  Alternative materials are being sought to overcome such limitations.

The long term stability and success of orthopaedic implants depend on the osseointegration process  which is strongly influenced by the biomaterial surface. A promising approach to enhance implant  integration involves the modification of the surface of the implant by means of polymers which mimic the natural components of the extracellular matrix,  e.g. polysaccharides. In this study methacrylate thermosets (bisphenol A glycidylmethacrylate/triethyleneglycol dimethacrylate), a widely used composition for orthopaedic and dental applications, have been coated by electrostatic deposition of a bioactive chitosan-derivative. This polysaccharide was shown to induce osteoblasts aggregation in vitro, to stimulate cell proliferation and to enhance alkaline phosphatase activity. 
The coating deposition was studied by analyzing the effect of pH and ionic strength on the grafting of the polysaccharide. Contact angle studies show that the functionalized material displays a higher hydrophilic character owing to the increase of surface polar groups. The mechanical properties of the coating were evaluated by nanoindentation studies which point to higher values of indentation 
hardness and modulus (E) of the polysaccharide surface layer, while the influence of cyclic stress on the construct was assessed by fatigue tests. Finally, in vivo tests in minipigs showed that the polysaccharide-based implant showed a good biocompatibility and an ability for osseointegration at least similar to that of the titanium Ti6Al4V alloy with roughened surface.  



Polysaccharide-Coated Thermosets for Orthopaedic Applications: from Material 
Characterization to In Vivo Tests 
Andrea Travan*, Eleonora Marsich*, Ivan Donati*, Marie-Pierre Foulc, Niko Moritz,
Hannu T. Aro, Sergio Paoletti* 
*Department of Life Sciences, University of Trieste, Via Giorgieri 1, Trieste I-34127, Italy 
Rescoll, Société de Recherche, 8 Allée Geoffroy Saint-Hilaire, 33615 Pessac, France 
Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology,               
University of Turku, Kiinamyllynkatu 10, 20520, Turku, Finland


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Effect of the Novel Low Molecular Weight Hydrolyzed Chicken Sternal Cartilage Extract, BioCell Collagen, on Improving Osteoarthritis-Related Symptoms: A Randomized, Double-Blind, Placebo-Controlled Trial

Osteoarthritis (OA) is a degenerative disease of the joints, which involves progressive deterioration of the articular cartilage.The etiology of OA is unknown. However, obesity, aging, trauma, repetitive strenuous joint activity, and genetics are risk factors associated with the development of the disease. The progression of OA results in disability due to joint pain, stiffness, and swelling in the knees, hips, hands, and spine. The molecular pathogenesis of OA appears to involve complex interactions among multiple pathways leading to the loss of structural components, including collagen type II and glycosaminoglycans (GAGs) such as chondroitin sulfate and hyaluronic acid (HA), and to inflammation and senescence of chondrocytes. Because there is no cure, treatment of OA aims to control progression of disease, to control pain, to improve or maintain range of movement, and ultimately to improve or maintainunction. Pharmaceutical regimens involve analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) to alleviate pain. However, these interventions provide only partial symptomatic relief and are not believed to affect underlying disease progression. NSAID therapy is also associated with gastrointestinal and cardiovascular complications. Intraarticular injection of HA is practiced by clinicians, but considered costly, its clinical effects often being temporal and its benefits controversial.In an effort to discover active compounds that are safe, efficacious, and cost-effective in managing OA symptoms, some dietary supplements including glucosamine, chondroitin, vitamin D, and polyunsaturated fatty acids have been evaluated in clinical trials. Many of these trials have demonstrated that these supplements might help reduce joint pain and in some cases favorably affect structural changes.

The aim of this randomized, double-blind, placebo-controlled trial was to investigate the tolerability and efficacy of BioCell Collagen (BCC), a low molecular weight dietary supplement consisting of hydrolyzed chicken sternal cartilage extract, in the treatment of OA symptoms. Patients (n = 80) in the study had physician-verified evidence of progressive OA in their hip and/or knee joint. Joint pain had been present for 3 months or longer at enrollment, and pain levels were 4 or higher at baseline as assessed by Physician Global Assessment scores. Subjects were divided into two groups and administered either 2 g of BCC or placebo for 70 days.Intent-to-treat analysis showed that the treatment group, as compared to placebo, had a significant reduction of VAS pain on day 70. The BCC group experienced a significant improvement in physical activities compared to the placebo group on days 35 (p = 0.007) and 70 (p < 0.001). BCC was well tolerated and found to be effective in managing OA-associated symptoms over the study period, thereby improving patient’s activities of daily living. BCC can be considered a potential complement to current OA therapies.

Effect of the Novel Low Molecular Weight Hydrolyzed Chicken Sternal Cartilage Extract, BioCell Collagen, on Improving Osteoarthritis-Related Symptoms: A Randomized, Double-Blind, Placebo-Controlled 
Trial Alexander G. Schauss, Jerome Stenehjem, Joosang Park, John R. Endres, and Amy Clewell
AIBMR Life Sciences, Inc., 4117 South Meridian, Puyallup, Washington 98373, United States
Division of Trauma, Surgical Critical Care & Burns, School of Medicine, University of California at San Diego, 2999 Health Center Drive, San Diego, California 92123, United States


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Flexible and micro-porous chitosan hydrogel/nano ZnO composite bandages for wound dressing: In vitro & in vivo evaluation

Wound infection is the major difficulty in the field of wound care management because such infections can cause exudate formation, delay the wound healing, facilitate improper collagen deposition etc. Microbes are the major reason for infection and the prevalence of the same is high in around us. The major infection causing bacteria were Staphylococcus aureus (S.aureus) and Escherichia coli (E. coli). Once entered to the body, these microbes grow immediately and start to form colonies. The microbes can easily be entered to the body through the wounds and can reach to deeper portions of the tissue and further can lead to internal infection.

The remedy for above mentioned harms would be the use of wound dressing with

antibacterial activity.Hydrogel based wound dressings would be helpful to provide cooling sensation, moisture environment and act as barrier to microbes. To overcome these hassles, they have developed flexible and micro-porous chitosan hydrogel/nano zinc oxide composite bandage (CZB) by the incorporation zinc oxide nanoparticles (nZnO) into chitosan hydrogel.

Swelling, degradation, blood clotting, antibacterial, cytocompatibility, cell attachment on the material and cell infiltration into the composite bandages were evaluated. The nanocomposite bandage showed enhanced swelling, blood clotting and antibacterial activity. Cytocompatibility of the composite bandage has been analyzed in normal human dermal fibroblast cells. Cell attachment and infiltration studies showed that the cells were found attached on to the nanocomposite bandages and penetrated into the interior. Further, the in vivo evaluations in sprague-dawley rats revealed that, these nanocomposite bandages enhanced the wound healing and helped for faster reepithelialization and collagen deposition. The obtained data strongly encourage the use of these composite bandages for burn wound, chronic wound and diabetic foot ulcers.

Flexible and micro-porous chitosan hydrogel/nano ZnO composite bandages for wound dressing: In vitro & in vivo evaluation

P.T. Sudheesh Kumar, Vinoth Kumar Lakshmanan, T.V. Anilkumar, C. Ramya,

P. Reshmi, A.G. Unnikrishnan, Shantikumar V. Nair, and Jayakumar Rangasamy

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Co-electrospun Nanofibrous Membranes of Collagen and Zein for Wound Healing

In recent years, electrospun polymeric nanofibers have been shown great potential as dressing materials for wound healing.Up to now, various biopolymers and their derivatives have been used widely for this purpose because of their biological origin, nontoxicity, hydrophilicity,

biocompatibility, biodegradability, and low cost.

However, single-component biopolymer solution is often insufficient for good electrospinnability or could not result in good fiber properties. In this work, this team attempt to develop biocompatible electrospun nanofibers for wound healing by coelectrospinning of collagen and zein in aqueous acetic acid solution. Collagen is one of the main proteins in the connective tissues and has been shown to have many advantageous features including biodegradability, weak antigenecity, and superior biocompatibility in medical applications.

It was found that the combination of zein could improve the electrospinnability of collagen. For the resultant electrospun membrane, its fiber diameter, surface wettability, mechanical, and in vitro degradable properties as well as cell adhesive ability could be modulated by the change of

collagen/zein blending ratio. Moreover, berberine drug could be incorporated in situ into the electrospun nanofibrous membrane for its controlled release and antibacterial activity. The addition of berberine showed little effects on the fiber morphology and cell viability. In addition, the wound healing performance of the as-obtained nanofibrous membranes was examined in vivo by using female Sprague−Dawley rats and histological observation.

Co-electrospun Nanofibrous Membranes of Collagen and Zein for Wound Healing

Jiantao Lin, Caihong Li, Yi Zhao, Jianchan Hu, and Li-Ming Zhang

DSAPM Lab and PCFM Lab, Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-sen University,

Guangzhou 510275, China

Guangdong Medical College, Dongguan 523808, China

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Cell Therapy for Skin Wound Using Fibroblast Encapsulated Poly(ethylene glycol)-poly(L-alanine) Thermogel

Thermogels that undergo sol-to-gel transition with increasing temperature have been extensively investigated, focusing on the new materials development, transition mechanisms, and new biomedical applications. Polyesters, chitosan, polyphosphazenes, polycarbonates, polycyanoacrylates, polyorthoesters, and polypeptides have been developed as a thermogel.

A simple procedure for encapsulating pharmaceuticals agents including drugs and cells makes the thermogel a promising material for drug delivery and tissue engineering and postsurgical adhesion prevention.

In particular, a thermogel has the advantages of filling irregular-shaped defects and providing a three-dimensional cell growth matrix. Therefore, thermogels have been suggested as a promising platform for an injectable tissue engineering scaffold.The wound healing process in skin includes inflammation, proliferation, and remodeling of the skin tissue. All three phases can overlap during the healing process.

As a new application of a thermogel, a poly-(ethylene glycol)-b-poly(L-alanine) (PEG-L-PA) gel encapsulating fibroblasts was investigated for wound healing. The fibroblasts were encapsulated by the temperature sensitive sol-to-gel transition of the polymer aqueous solution. Under the in vitro three-dimensional (3D) cell culture condition, the PEG-L-PA thermogel was comparable with Matrigel for cell proliferation and was significantly better than Matrigel for collagen types I and III formation. After confirming the excellent 3D microenvironment of the PEG-L-PA thermogel for fibroblasts, in vivo wound healing was investigated by injecting the cell-suspended polymer, aqueous solution on incisions of rat skin, where the cell-encapsulated gel was formed in situ. Compared with the phosphate buffered saline treated system and the cell-free PEG-L-PA thermogel, the cell-encapsulated PEG-L-PA thermogel not only accelerated the wound closure but also improved epithelialization and the formation of skin appendages such as keratinocyte layer (epidermis), hair follicles, and sebaceous glands. The results demonstrate the potential of thermogels for cell therapy as an injectable tissue-engineering scaffold.

Cell Therapy for Skin Wound Using Fibroblast Encapsulated Poly(ethylene glycol)-poly(L-alanine) Thermogel

Eun Jung Yun, Bora Yon, Min Kyung Joo, and Byeongmoon Jeong

Department of Bioinspired Science and Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750,

Korea.

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Clay−Chitosan Nanobrick Walls: Completely Renewable Gas Barrier and Flame-Retardant Nanocoatings

Polysaccharides are naturally occurring polymers that are widely available in nature. Of the many types of polysaccharides, chitin is the second most abundant after cellulose. Chitin is extracted from the shells of crustaceans (e.g., lobsters and shrimp) and the exoskeletons of arthropods (e.g., insects). Despite its abundance, unmodified chitin’s usefulness is very limited, because of its poor solubility in most solvents. Chitosan, which is an amino polysaccharide obtained via the alkaline deacetylation of chitin is soluble in acidic aqueous solutions, because of the protonation of its amino groups at pH <6.2.In addition to its solubility, chitosan is biodegradable, biocompatible, and benign. These traits have led to the significant study of chitosan’s use in biomedical applications, such as drug delivery, wound-dressing materials, artificial skin, and blood anticoagulants.

In an effort to create fully renewable and multifunctional assemblies, thin films of chitosan and MMT clay were deposited on polyurethane (PU) foam and polylactic acid (PLA) film. P Thin films prepared via a layer-by-layer (LbL) assembly of renewable materials exhibit exceptional oxygen barrier and flame-retardant properties. Positively charged chitosan (CH), at two different pH levels (pH 3 and pH 6), was paired with anionic montmorillonite (MMT) clay nanoplatelets. Thin-film assemblies prepared with CH at high pH are thicker, because if the low polymer charge density. A 30- bilayer (CH pH 6-MMT) nanocoating (∼100 nm thick) reduces the oxygen permeability of a 0.5-mm-thick polylactic acid film by four orders of magnitude. This same coating system completely stops the melting of a flexible polyurethane foam, when exposed to direct flame from a butane torch, with just 10 bilayers (∼30 nm thick). Cone calorimetry confirms that this coated foam exhibited a reduced peak heatrelease rate, by as much as 52%, relative to the uncoated control. These environmentally benign nanocoatings could prove beneficial for new types of food packaging or a replacement for environmentally persistent antiflammable compounds.

The goal of this work was to develop a truly “green” film with flame-retardant and oxygen-barrier characteristics. Films assembled with high-pH or low-pH chitosan (CH) and clay (montmorillonite, MMT) showed linear growth as a function of the number of bilayers deposited. Higher chitosan pH resulted in much thicker assemblies with higher clay loading. An oxygen permeability of <0.03 × 10−16cm3cm/(cm2s Pa) was achieved with 30 bilayers (30 BL) of CH pH 6-MMT(< 100 nm thick). The combination of all of these features it is generally recognized as a safe material, it has high oxygen barriers, and the transparency exhibited by this film makes it an ideal candidate for food and other types of high-performance packaging.

Clay−Chitosan Nanobrick Walls: Completely Renewable Gas Barrier and Flame-Retardant Nanocoatings

Galina Laufer, Christopher Kirkland, Amanda A. Cain, and Jaime C. Grunlan*

Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, United State

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Transparent, Superhydrophobic Surfaces from One-Step Spin Coating of Hydrophobic Nanoparticles

Superhydrophobic surface with a water contact angle of 150° or higher and very little flow resistance are of interest for numerous applications, including self-cleaning coatings, impermeable textiles, microfluidics, lab-on-a-chip devices, and biotechnology. To create superhydrophobic surface, a combination of low surface energy chemistry and dual-scaled (micro and nano) surface roughness is needed. There has been significant progress both theoretically and experimentally in creating topographically rough surfaces with extremely high water-repellency.

In this Study they present the nonwettability and transparency from the assembly of fluorosilane modified silica nanoparticles (F-SiO2 NPs) via onestep spin-coating and dip-coating without any surface postpassivation steps. When spin-coating the hydrophobic NPs (100 nm in diameter) at a concentration ≥0.8 wt % in a fluorinated solvent, the surface exhibited superhydrophobicity with an advancing water contact angle greater than 150° and a water droplet (5 μL) roll-off angle less than 5°. In comparison, superhydrophobicity was not achieved by dip-coating the same hydrophobic NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images revealed that NPs formed a nearly close-packed assembly in the superhydrophobic films, which effectively minimized the exposure of the underlying substrate while offering sufficiently trapped air pockets. In the dipcoated films, however, the surface coverage was rather random and incomplete. Therefore, the underlying substrate was exposed and water was able to impregnate between the NPs, leading to smaller water contact angle and larger water contact angle hysteresis. The spincoated superhydrophobic film was also highly transparent with greater than 95% transmittance in the visible region. Further, we demonstrated that the one-step coating strategy could be extended to different polymeric substrates, including poly(methyl methacrylate) and polyester fabrics, to achieve superhydrophobicity.

To sum up they reported a simple procedure to create a superhydrophobic surface by spin-coating fluorosilane-functionalized silica NPs without any post-treatment of the substrate with a low-surface-energy coating. The method is simple and versatile; superhydrophobicity is achieved on Si wafer, glass substrate, PMMA, and polyester fabric, however it needs to be improved.

Transparent, Superhydrophobic Surfaces from One-Step Spin Coating of Hydrophobic Nanoparticles

Lebo Xu, Raghuraman G. Karunakaran, Jia Guo, and Shu Yang*

Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104, United States

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Sun-Believable Solar Paint. A Transformative One-Step Approach for Designing Nanocrystalline Solar Cell

In recent years semiconductor nanocrystal or quantum-dot-based solar cells have drawn significant attention as viable candidates for boosting the energy conversion efficiency beyond the traditional Shockley and Queisser limit of 32% for Si-based solar cells.

Because of the extremely small size of semiconductor quantum dots and high absorption cross section, it is possible to capture nearly all of the incident solar light in the visible region with an extremely thin layer of semiconductor materials. These heterojunction semiconductor solar cells, often referred as ETA (extremely thin absorber) cells, offer new opportunities to develop relatively inexpensive solar cells.

A transformative approach is required to meet the demand of economically viable solar cell technology. By making use of recent advances in semiconductor nanocrystal research, scientifics of Notre Dame University have now developed a one-coat solar paint for designing quantum dot solar cells. A binder-free paste consisting of CdS, CdSe, and TiO2 semiconductor nanoparticles was prepared, they adopted two synthetic strategies: (1) physical mixing of commercially available TiO2 (Degussa P25) and bulk CdS (Aldrich) in a mixed solvent (water and t-butanol); (2) a pseudoSILAR (sequential ionic layer adsorption and reaction) method of depositing CdS (or CdSe) on suspended TiO2 nanoparticles by the addition of Cd2+ and S2-(or Se2) in a stepwise fashion; and the resulting thick, yellow paste of TiO2 and CdS could then be applied directly on conducting glass electrodes at 473 K. The photoconversion behavior of these semiconductor film electrodes was evaluated in a photoelectrochemical cell consisting of grapheneCu2S counter electrode and sulfide/polysulfide redox couple. Open-circuit voltage as high as 600 mV and short circuit current of 3.1 mA/cm2 were obtained with CdS/TiO2CdSe/TiO2 electrodes. A power conversion efficiency exceeding 1% has been obtained for solar cells constructed using the simple conventional paint brush approach under ambient conditions.

Whereas further improvements are necessary to develop strategies for large area, all solid state devices, this initial effort to prepare solar paint offers the advantages of simple design and economically viable next generation solar cells.

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Matthew P. Genovese, Ian V. Lightcap, and Prashant V. Kamat

ACS Nano 2012 6 (1), 865-872