Surface Energy Of Polymers Research Articles

Nanocomposites of Hydrophobized Cellulose Nanocrystals and Polypropylene

Cellulose nanocrystals (CNCs) are high-strength sustainable nanomaterials, the incorporation of which to a host polymer matrix can potentially lead to nanocomposites with superior mechanical properties. However, the mismatch in surface energy of CNCs and common structural polymers is a challenge that needs to be overcome to prevent the aggregation of CNCs and ensure the robust integration of CNCs into a polymer matrix. Herein, we report an approach involving the functionalization of CNCs with maleated-anhydride polypropylene (MAPP) through diethylenetriamine (DETA) linkers to significantly enhance the compatibility between CNCs and polypropylene. Polypropylene/modified CNC nanocomposites displayed 74% and 76% increase in elastic modulus in comparison to neat polypropylene and polypropylene/untreated CNC nanocomposites, respectively. The tensile strength was also higher for nanocomposites withmodified CNC than neat polypropylene, as well as nanocomposites with untreated CNCs. The tensile strength at 5.5% strain of polypropylene/modified CNCnanocomposites was 32% and 28% larger that of polypropylene and polypropylene/untreated CNC nanocomposites, respectively. Finally, such CNC-based nanocomposites have a lower density than many competitive systems resulting in opportunities to propagate this environmentally-responsible technology to nanocomposites used in additive manufacturing, automotive applications, construction materials and consumer products.

Strong shear-driven large scale formation of hybrid shish-kebab in carbon nanofiber reinforced polyethylene composites during the melt second flow.

The formation of a hybrid shish-kebab (HSK) structure with different degrees of lamellar orientations was first observed in the solution crystallization of polyethylene (PE) in the presence of carbon nanofibers (CNFs). In this study, PE crystal lamellae were periodically decorated on the surface of CNFs and were aligned approximately perpendicular to the long axes of the CNFs, forming aligned hybrid shish-kebab nanostructures. More importantly, the fascinating structure was directly formed in all regions of the injection molded bars of HDPE/CNF composites, via a gas-assisted injection molding (GAIM), instead of the shell-core structure. In the GAIM process, an intense shear was imposed onto the melt during the melt second flow and drove PE chains to orient along the axes of the CNFs. Then the entropy penalty for PE chains deposited on the CNF surface was drastically decreased. Although the attractive van der Waals interactions were weak, the oriented PE chains could successfully adsorb on the CNF surface due to the decrease of the entropy penalty, therewith the underlayer coating was formed along the axis based on a two-dimensional mode for early nucleation on the CNF surface. Subsequently, subglobules appeared on the ordered structure, which could be regarded as the crystal nucleus. Finally, the oriented PE chains began to epitaxially grow from the subglobules with a folded-chain shape to decrease the polymer surface energy and grew perpendicular to the CNFs long axis, abiding by the "soft epitaxy" crystallization mechanism regardless of strict lattice matching.

Roll bonding of AA5052 and polypropylene sheets: Bonding mechanisms, microstructure and mechanical properties

ABSTRACTStructural, microstructural and mechanical properties in roll bonding of AA5052 and polypropylene sheets have been evaluated in this study. The surface roughness of the AA5052 sheets, rolling temperature and the surface energy of polymer were selected as the bonding variables. The findings indicated that an increase in the surface energy of polypropylene by grafting maleic anhydride would result in higher bonding strength due to chemical interaction between the AA5052 and the maleic anhydride grafted polypropylene (PP-g-MAH). In fact, this reaction caused the formation of an interphase layer at the polymer side of the interface and the diffusion of aluminum into the PP-g-MAH layer. It was also observed that an increase in the rolling temperature increases bonding strength because the polymer penetrates the AA5052 surface irregularities more easily, the PP-g-MAH molecules move more smoothly toward the AA5052 surface, and finally there are more chemical interactions among the layers. An Increase in the bonding strength through increasing the AA5052 surface roughness was attributed to an increase of the van der Waals force and more interaction surface among the layers along with higher mechanical interlocking in the shear tension test.

Control of Conducting Polymer Nanostructures for Parahydrophobic Properties

Controlling the water adhesion is fundamental for various applications such as in water harvesting or liquid transportation. In nature, superhydrophobic properties (high apparent contact angles (Θ) and low water adhesion) as well as parahydrophobic properties (high Θ and high water adhesion) are present in flora and fauna. Here, in order to reproduce parahydrophobic properties, nanostructured conducting polymers are elaborated by electropolymerization of 3,4-propylenedioxythiophene (ProDOT) bearing phenyl groups. The use of phenyl groups allows to reduce the polymer surface energy in comparison to long fluorocarbon of hydrocarbon chains. We show that various fibrous morphologies as well as parahydrophobic properties can be controlled with the used electrolyte. This work is also important with the aim to replace long perfluorocarbon chains due to their bioaccumulative potential. This work also opens new doors to patent these kinds of materials and to envisage their commercialization. Keywords: Conducting polymers, electrochemistry, nanostructures, parahydrophobic, sticky, superhydrophobic, wettability.

Collagen immobilization on ultraviolet light-treated poly(ethylene terephthalate)

The present article is focused on the studies regarding the effects of ultraviolet (UV) light on poly(ethylene terephthalate) (PET) films surfaces using scanning electron microscopy (SEM), Fourier transform infrared, X-ray photoelectron spectrometry (XPS), and atomic force microscopy (AFM) measurements, subsequent to collagen immobilization. UV treatment influences the surface energy of polymers as the result of the polymer chain breaking, followed by insertion of oxygen-containing functional groups. Accordingly, after UV light treatment, collagen was adsorbed on the PET surfaces in different proportions. Significant changes in the surface topography appeared after collagen immobilization on UV-treated PET films, and they were put in evidence by SEM and tapping-mode AFM experiments. XPS measurements demonstrated the adsorption of collagen on PET UV light-altered surfaces by increasing of nitrogen content. The cytocompatibility tests using stem cells have shown good results for all treated polymers.

Fine Tuning Surface Energy of Poly(3-hexylthiophene) by Heteroatom Modification of the Alkyl Side Chains.

Recent work has pointed to polymer miscibility and surface energy as key figures of merit in the formation of organic alloys and synergistic behavior between components in ternary blend solar cells. Here, we present a simple model system and first report of poly(3-hexylthiophene)-based random copolymers featuring either a semifluoroalkyl (P3HT-co-FHT) or oligoether (P3HT-co-MET) side chain, prepared via Stille polycondensation. Water drop contact angle measurements demonstrated that P3HT-co-FHT polymers reached a minimum surface energy of 14.2 mN/m at 50% composition of comonomers, while in contrast, P3HT-co-MET polymers increased as high as 27.0 mN/m at 50% composition, compared to P3HT at 19.9 mN/m. Importantly, the surface energy of the copolymers was found to vary regularly with comonomer composition and exhibited fine-tuning. Optical and electronic properties of the polymers are found to be composition independent as determined by UV-vis and CV measurements; HOMO energy levels ranged from 5.25 to 5.30 eV; and optical band gaps all measured 1.9 eV. Following this model, surface energy modification of state-of-the-art polymers, without altering desirable electronic and optical properties, is proposed as a useful tool in identifying and exploiting more alloying polymer pairs for ternary blend solar cells.

Plasma Solutions for Life Sciences and Medical Device Manufacturing

The medical device industry is highly regulated which demands reliable and reproducible components and manufacturing processing to satisfy said regulators. Regulated devices range from a simple bandage to the most complex implantable heart defibrillator. Developing these devices requires rigorous testing and validation of the materials and processes used to manufacture them. Challenges abound due to issues with bio-compatibility, material mismatch, implant duration, ability to withstand sterilization, wettability, lubricity, and so on. Plasma processes address many of these challenges while enabling more reliable and robust devices. Plasma has been shown to enhance surface wettability, remove surface contamination, improve bondability and maintain the bulk properties of the material treated. Medical diagnostics are highly dependent on reliable chemical analytic techniques where fluids are contacted with reagents in polymer containers such as microtiter plates or plated used in gene sequencing systems or chemiluminescence detection tools. The reliability of such techniques are dependent upon the repeatable wetting of the containers by the fluids and/or reagents. Plasma processing is an excellent choice for increasing the surface energy of polymers enabling more wettable surfaces.Because plasma treatment will enhance the surface energy of samples treated it is chosen prior to adhesive bonding, lubricious coating application, polymer coating application, device printing, etc. Plasma is also useful for depositing polymer films via plasma assisted polymerization. Plasma polymer films can be used to enhance adhesion of subsequent bonding steps and in certain cases forms an excellent tack reduction film when deposited on rubber compounds. Plasma is also utilized to remove surface contaminants that can interfere with subsequent bonding steps.Specific application examples will be presented showing the many uses and benefits of plasma processing for medical devices.

Composition tuning of a mixture of thienothiophene-based polymer (PTB7) and PC70BM using a novel additive, tetrabromothiophene (Br-ADD)

A novel additive, tetrabromothiophene (Br-ADD), is shown to improve the properties of bulk heterojunction consisting of poly(3-hexylthiophene: [6,6]-phenyl-C60 (P3HT:PC60BM) and a thienothiophene-based polymer: C70-butyric acid methyl ester (PTB7:PC70BM). The hydrophobic Br-ADD selectively interacts with the fused heteroaromatic rings on the polymers to increase the polymer surface energy, which improves the bulk heterojunction and photovoltaic performances of the resulting polymer solar cells (23.5% for P3HT and 12.3% for PTB7). The selective interactions between Br-ADD and the polymer and the properties of the bulk heterojunctions are characterized using UV–vis spectroscopy, photoluminescence (PL), atomic force microscopy (AFM), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and J–V measurements.

A method for estimating interfacial tension of liquid crystal embedded in polymer matrix forming PDLC

ABSTRACTA simple and convenient method based on sessile drop technique for measuring surface tensions of polymer and nematic liquid crystal (LC) is described. Contact angles formed by drops of probe liquids and a nematic LC on a photocurable polymer were measured. The surface energies were evaluated using the Fowkes method, Neumann's equation, and new equations developed based on Neumann's approach. The values of surface tensions were used to evaluate the interfacial interaction in term of work of adhesion between the LC and polymer. Further, the effect of dichroic dye on the extent of interaction and work of adhesion was examined by measuring contact angle in consequence of dye addition. A difference in work of adhesion between the lower and higher dye‐doped LC droplets gave an indication of affinity relationship between polymer and LC molecules. A change in work of adhesion resulted in variability of nematic director configurations inside phase separated LC droplets embedded in polymer matrix; when viewed under polarizing optical microscope. Thus, our approach of estimating surface energy of polymer and LC has found to be useful in determining interaction at polymer–LC interface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41137.

Electrical, mechanical, and crystallization properties of ethylene‐tetrafluoroethylene copolymer/multiwalled carbon nanotube composites

ABSTRACTMultiwalled carbon nanotubes (MWCNTs) were melt‐mixed in a conical twin‐screw extruder with a random copolymer of ethylene and tetrafluoroethylene. Surprisingly, the electrical percolation threshold of the resultant composites was quite low; ∼0.9 wt %. In fact, this value is as low or lower than the value for most MWCNT/semicrystalline polymer composites made with roughly equivalent aspect ratio tubes mixed in a similar manner, for example, melt mixing. This low percolation threshold, suggestive of good dispersion, occurred even though the polymer surface energy is quite low which should make tubes more difficult to disperse. Dynamic mechanical measurements confirmed the rather low percolation threshold. The effect of nanotubes on crystallization kinetics was quite small; suggesting perhaps that a lack of nucleation which in turn reduces/eliminates an insulating crystalline polymer layer around the nanotubes might explain the low percolation threshold. Finally, the modulus increased with the addition of nanotubes and the strain at break decreased. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41052.

Surface Activation of Plane and Curved Automotive Polymer Surfaces by Using a Fittable Multi-Pin DBD Plasma Source

In this work, surface activation of automotive polymers using atmospheric pressure plasmas was investigated. The aim was to increase the polar fraction of the surface energy of both plane and convex polymer devices with a radius in the range of 30 mm. For this purpose, a fittable low temperature atmospheric pressure plasma source based on capacitively coupled multi-pin electrodes was set up and applied. Each single electrode generates a treatment spot of approximately 2 cm2 with a tunable power density of up to 1.4 W/cm2. The surface energy was evaluated by contact angle measurements. After treatment at a low energy density of 1.01 J/cm2, the polar fraction of the surface energy of the investigated polymers was increased by a factor of 3.3 to 132, depending on the polymer materials. It was shown that by applying the presented fittable plasma source, this effect is independent of the surface radius of the polymer sample.

English

Plasma and ion beams are considered tools that can improve existing materials or create new materials. Their technology is widely used to alter the surface properties of polymers without affecting their bulk properties. The treated polymers have found various applications in microelectronics, biomedical and chemical industries. In this work, the use of Argon plasma and Argon ions produced from cold cathode ion source as a method for the morphology and wettability of Semi crystalline polyethylene terephtalate (PET) foils are investigated. A cold cathode ion source was used as a preparation tool of the surface of polyethylene terephthalate PET polymer substrate to be ready for various applications as coating or thin film deposition. Argon ions of 1.5 keV are produced from the cold cathode ion source with an operating gas pressure of 2 × 10-4 mbar. The induced effects in the structure, surface morphology, and surface wettability were investigated by means of the Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and by the contact angle methods, respectively. The change in the contact angle on PET as a function of Argon plasma time and ion beam fluence was also studied. Changes in surface free energy of polymer surface after Argon plasma irradiation were observed.   Key words: Cold cathode ion source, Argon plasma and ion beams, polyethylene terephthalate (PET) foils.

Enhancing hydrophilicity of polyethylene terephthalate surface through melt blending

In many industrial sectors, the surface properties of polymers are of particular importance. This applies, for instance, to painting, printing, and any coating on surface of polymeric objects. Hydrophilicity and wettability characteristics are known to be determined by the chemical makeup of the polymer surface. Blending with an additive or a polymer containing high-energy functional groups is widely recognized as a potential technique to overcome disadvantages of low surface energy of polymers due to its convenient processing. Surface migration of polyethylene glycol (PEG) in Polyethylene Terephthalate (PET) host was investigated using a low-molecular-weight PEG (8 kDa) because of its good hydrophilicity, low toxicity, biocompatibility, and chain mobility. A twin-screw extruder was used to blend the materials and prepare the polymer blend films. The results of surface characterizations showed that PEG renders the PET surface more hydrophilic, but not high enough for many applications. In a second approach, the addition of a third component, polystyrene (PS), to the blend in a small amount resulted in a remarkable surface enrichment of PEG at the polymer/air interface for the ternary polymer blend (PET-PEG-PS). Surface analysis revealed that the surface concentration of PEG in the ternary polymer blend film was significantly larger than that of the binary one. POLYM. ENG. SCI., 55:349–358, 2015. © 2014 Society of Plastics Engineers

Cold plasma effect on short glass fibre reinforced composites adhesion properties

The low surface energy and poor wetting properties of polymers make it necessary to modify prior to achieve adhesive bonding. This work is focused on the creation of wettable glass fibre reinforced epoxy and polyester composites, thus improving their adhesion performance. The key to evaluate this parameter as a function of the treatment with an atmospheric pressure plasma torch (APPT) device is the surface energy value. The chemical and morphological effects of APPT on the substrates are characterised by infrared and X-ray photoelectron spectroscopy, while etching of APPT is studied by scanning electron and atomic force microscopy. Benefits of APPT on the composites adhesive behaviour are evaluated through mechanical pull-off tests. Experimental results show an improvement in polarity and Lewis base behaviour of the surfaces as well as the creation of a rougher topography, which would be greatly helpful in the bonding process.

Forced air plasma treatment for enhanced adhesion of polypropylene and polyethylene

This paper describes our investigation of the effects of forced air plasma treatment on polypropylene and polyethylene. The morphology of the treated surfaces has been carefully examined using a variety of tools including optical profiling. The complex surface morphology was observed to change with increasing treatment and varying intensity of the treatment over the surface. Optimum treatment conditions have been deduced using surface energy determinations and can be compared with the morphological changes. Determinations of surface energy, both the polar and non-polar components, have been made after exposure to varying moisture conditions for varying times. Different results are obtained for different environments and from different materials. These results demonstrate that forced air plasma treatment is a highly effective means of increasing the surface energy of polymers, which can be long-lasting, provided the treated surfaces are kept in dry conditions.

Surface energy control of soluble polyimide gate insulators by copolymerization method for high performance pentacene thin-film transistors

We have synthesized a series of surface energy controlled soluble polyimide (PI) gate insulators (KSPI-C1, KSPI-C3, and KSPI-C5) by one-step copolymerization method of the monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4,4-diaminodiphenylmethane, and 1-(3,5-diaminophenyl)-3-octadecylpyrrolidine-2,5-dione (DA-18-IM). The long alkyl chain containing DA-18-IM monomer was used to control the surface energy of PI polymers. Fully imidized PI polymers were found to be completely soluble in organic solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, etc. Thermal gravimetric analysis exhibited that all polymers are stable up to more than 432°C with only 5wt.% weight loss. The glass transition temperatures of polymers are found to be between 208°C and 242°C by differential scanning calorimetry measurement. Thin films of all polymers could be fabricated at only 150°C and a pentacene thin-film transistor (TFT) with KSPI-C3 as a gate dielectric was found to exhibit the highest field effect mobility of 0.53cm2/Vs. Surface energy controlled PI polymers are promising candidates for gate dielectrics for organic TFTs.

Production of microcellular foam based on PP/EPDM: The effects of processing parameters and nanoclay using response surface methodology

AbstractMicrocellular foam is a new class of material with superior properties due to smaller cell size and higher cell density compared to ordinary foams. In this work, microcellular foam of PP/EPDM/Organoclay with supercritical nitrogen as physical blowing agent was prepared via batch process. Experimental design was carried out according to Box-Behnken method and the effects of saturation pressure and foaming times as well as organoclay content on nucleation and final foam morphology were studied using response surface methodology (RSM). Three levels of saturation pressure, nanoclay content, and foaming time were chosen. The mathematical model and response surface graphs have been used to illustrate the relationship between considered parameters and foam properties. The results revealed that cell density and average cell diameter were affected by nanoclay content and pressure. Cell density was in the range of 109-1010 cell/cm3. Larger average cell sizes were observed as a result of increasing foaming time. Classic nucleation theory was used to study the nucleation mechanism. Nanoparticles acted as nucleating agents and changed nucleation mechanism from homogenous to heterogeneous by decreasing nucleating free energy. In order to find out nucleating energy reduction, gas-polymer-nanoparticle contact angle (Ө), was calculated by measuring surface and interfacial free energies of neat polymers and nanoparticle. In addition, nucleation efficiency of organoclay was estimated and the results showed that despite low nucleating efficiency, nucleation is dominated by presence of nanoclay.

Synthesis and characterization of poly(silyl urethane)s derived from glycol‐modified silanes

AbstractHybrid composites are a class of material that have gained substantial recognition due to their highly sought‐after properties of both organics and inorganics. A novel method for incorporating inorganic content into urethane materials is through the use of organically modified silicate cross‐linkers. Glycol‐modified silanes, in particular, allow for the facile preparation of highly cross‐linked urethane materials with a wide range of bulk and surface characteristics including glass transition temperature (−40.4–85.6°C), storage modulus (0.7–1.62 GPa), and surface energy (19.0–62.4 dynes cm−1). Importantly, control of the overall polymer properties remains achievable via the structural control of macrodiols and isocyanates. Additionally, incorporation of silicate cross‐linkers into urethane systems provides these materials with a hydrolyzable character, which may be controlled by altering the bulk polymer composition, cross‐link density, and surface energy. The unique nature of these systems also allows for the preparation of highly cross‐linked urethanes in the absence of any heavy metal catalysts and depending on the composition, with the use of little to no solvent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Attractive and Repulsive Interactions Originating from Lateral Nanometer Variations in Surface Charge/Energy of Hyaluronic Acid and Chondroitin Sulfate Doped Polypyrrole Observed Using Atomic Force Microscopy

Phase imaging in atomic force microscopy (AFM) is a useful technique for determining dissipative tip-sample interactions related to changes in the material surface properties such as local stiffness or adhesion. In this work, we applied both phase imaging and phase spectroscopy measurements to conducting polymer (polypyrrole) doped with either hyaluronic acid or chondroitin sulfate. As observed in previous studies, phase-separated regions correlating with the characteristic nodular topography of polypyrrole and attributed to crystalline (doped) and amorphous (undoped) regions were observed. However, through additional phase spectroscopy measurements, we show that the phase-separated regions can arise due to variation in attractive and repulsive tip-sample interactions across the polymer surface. We show that these attractive and repulsive interactions are dependent on the redox state and degree of doping and suggest that they are related to phase separation of the polymer surface charge and/or energy. The latter may have implications for these materials when under investigation in a fluid, or biological, environment. For example, such surface variations will play a role in electrostatic forces, which in turn can influence protein and cellular interactions.

Formation of SiO2/polytetrafluoroethylene hybrid superhydrophobic coating

Superhydrophobic coating has been fabricated on the glass substrates with modified SiO2 sol and polytetrafluoroethylene emulsion through a sol–gel process. SiO2 sol was modified with γ-glycidoxypropyl trimethoxysilane. The coatings were characterized by water contact angle measurement, Scanning electron microscope, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy and thermal synthetic analysis. The experimental results show that coatings exhibited superhydrophobic and heat-resistant property with a water average contact angle of 156° and sliding angle of 6°, coating has a rough surface with both micro- and nanoscale structures, γ-glycidoxypropyl trimethoxysilane enhanced the hydrophobicity of the coatings. Low surface energy of polymer and special structure of the coatings were responsible for the hydrophobic of the surfaces.