Component Of Surface Free Energy Research Articles

Aging of Polylactide Films Exposed to Plasma—Hydrophobic Recovery and Selected Application Properties

In this study, the effect of polylactide (PLA) material on the susceptibility to hydrophobic recovery due to storage was examined, the effectiveness of plasma activation of the film, defined as improving the hydrophilicity of the material, was studied, and the selected film properties that are important from an application point of view were investigated. The study was conducted on three films using oxygen and argon plasma. Contact angles of water, diiodomethane, and ethylene glycol were investigated, and the values of surface free energy (SFE) and its polar and dispersive components were determined immediately after activation, as well as after a specified storage time (after 1, 7, 14, 30, and 60 days). The effects of film activation on its roughness, weight loss, tensile strength, color changes, and gloss were also determined. Based on the results, it was concluded that the type of film influences the course of hydrophobic recovery. At the same time, the trend of changes depends on the type of gas used for activation, while the magnitude of changes depends on the film. Moreover, it was observed that the type of PLA film had a significant effect on the changes in the polar and dispersion components of SFE, as well as on roughness and mass loss due to plasma activation. Furthermore, these parameters also depended on the type of gas used for plasma activation.

Characterisation of the Surface Free Energy of the Recycled Cellulose Layer that Comprises the Middle Component of Corrugated Paperboards

The objective of this study was to determine the polar and dispersive surface free-energy (SFE) components of the central layer of corrugated paperboards, which are made of recycled fibres. The polar and dispersive components of, and the total, SFE (also known as interfacial energy) were calculated from the contact angles of water and diiodomethane liquids on recycled cellulose sheets. The total SFE of the middle component layers of two different grammages which comprised recycled fibres ranged from 47.9 mN/m to 51.05 mN/m. The contribution of the polar component to the total surface free energy of the two types of sheets ranged from 8.6 mN/m to 12.6 mN/m. This polar contribution was significantly lower than that of water. The contact angle method proved to be a consistent way to estimate the surface properties of industrially made recycled paper products.

Estimation of the work of adhesion between ITO and polymer substrates: a surface thermodynamics approach.

Indium tin oxide (ITO) is one of the most widely used semiconductor among transparent conducting oxides (TCOs) due to their electrical conductivity and optical transparency properties. Since the development of low temperature deposition methods, coating of ITO on polymer substrates especially for use in flexible electronics has been a popular topic. The existence of adequate adhesion strength between ITO and polymer is critical in producing a successful film. Nowadays, polycarbonate (PC), poly(methyl methacrylate) (PMMA) and polyethyleneterephtalate (PET) are frequently used as substrates for such coatings. However, there may be other polymeric alternatives that have a potential to be used for this purpose in the future. To evaluate these alternatives, work of adhesion (Wa) knowledge between ITO and polymers is necessary, and it has not been handled systematically previously. In this study, the interphase interaction parameters and Wa values between ITO and various polymers were calculated based on the Dupré, Fowkes and Girifalco-Good equations. PC, PMMA, PET, polystyrene (PS), polyphenylene sulfide (PPS), Nylon 66, polypropylene (PP), polyvinylchloride (PVC), styrene-butadiene rubber (SBR), high density polyethylene (HDPE), low density polyethylene (LDPE), polyvinyl acetate (PVAc), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTrFE) and polyperfluoroalkylethyl acrylate (PPFA) were considered as substrate material. Surface free energy (SFE) components calculated by acid-base, geometric mean and harmonic mean approaches for polymeric substrates were used during the calculations. In the present study, the polymers that can be used as substrates were evaluated in terms of adhesion ability to ITO, the significance of calculation methods on Wa values were also investigated simultaneously. It was determined that the Wa between ITO and polymer substrates was directly related with the total SFE value of the polymers.

Factors to control the alignment of surface-treated titanium dioxide powders to maximize performance of sunscreens.

Titanium dioxide powders are contained in a large class of colour cosmetics and sunscreen formulas. When they are used, the formation of a uniform functional powder layer on the skin is an important factor to show their functionality, such as aesthetic and UV protection. Attempts were made to extract the factors that affect the UV shielding ability of the deposited powder layer. Seven kinds of surface treatments were conducted on nano-sized titanium dioxide powder to modify the surface characteristics. Dispersion samples were prepared by mixing these powders with liquids, such as mixed solutions of cyclopentasiloxane, isododecane, coconuts alkane and dimethicone using a disperser and a bead mill. The dispersions were applied using an applicator on cellulose triacetate film, polycarbonate film and polymethyl pentene film. Laser microscope observation and micro-gloss glossmeter analysis were carried out to assess the flatness of the deposited powder layers, and the UV shielding ability was evaluated using SPF analyser. Factors whose influences on the structure and UV shielding ability of the deposited powder layer being analysed were pseudo-HLB of the powders, liquids for preparing the dispersions and material of the substrates. Higher UV shielding ability was attained when powders having pseudo-HLB at around 6 were employed independent from the kinds of liquids and substrates. Flatness of the deposited layer was found to enhance the UV shielding ability of the UV-B region, while that of the UV-A region was scarcely influenced by the flatness. Employing lower surface tension liquids for preparing the dispersions and materials exhibiting lower polar components of surface free energy as substrates tended to enhance the UV shielding ability. Surface treatments conducted on the powders in this study were found to change UV shielding ability, especially UV-B shielding ability, and the relation between pseudo-HLB and UV shielding ability was scarcely influenced by the kinds of liquids. Both surface tension of liquids and the polar component of surface free energy of substrates affected the UV shielding ability. It was suggested that pseudo-HLB calculated based on chemical structure becomes useful information to choose optimum surface treatment to make uniform powder alignment independent from the surrounding environment.

Effect of warm mix additives and hydrated lime on viscosity and bonding–debonding behaviour of RET and PPA modified asphalt binder with aggregates

Higher energy requirement for asphaltic layer construction with asphalt binder containing reactive elastomeric terpolymer (RET) and poly phosphoric acid (PPA) can be addressed to a greater extent with the addition of warm mix asphalt (WMA) additives. However, moisture damage related problem is one of the concerns with such addition, which further aggravates with an increase in ageing level. The addition of lime may help in addressing moisture damage related problems in such cases. Previous research works show that based on the interaction between asphalt binder and particular WMA additive, the viscosity may undesirably increase also. So far, the influence of different WMA additives (wax, chemical surfactant (CS) and water-based (WB)) on the workability related properties of asphalt binder containing RET and PPA is not understood. It is also not clear if such warm mix additives with/without lime can help in improving long-term bonding with different aggregate types or not. Therefore, this research work aimed at identifying the appropriate WMA additive (with/without lime) which can help in (a) addressing the workability related problem and (b) improving long-term bonding with different aggregate types. To achieve this, different types of WMA additives (with/without lime) were added to RET and PPA modified binder. Viscosity-based measurement and chemical analysis using Fourier transform infrared spectroscopy were performed to understand workability and underlying chemical changes. Results indicated that although wax and CS-based warm mix additives can help in reducing energy demand, the addition of WB warm mix additive will have a negative impact from the workability perspective. Likewise, dynamic contact angle for different binder combinations was measured to evaluate the surface free energy components, which further helped to examine the long-term bonding with different aggregate types. Among different WMA additive types, the use of wax-based WMA additive was found to be most effective in improving compatibility with different aggregate types. Also, irrespective of the binder combination, the addition of lime improved the long-term bonding with considered aggregate types.

Physicochemical Modifications on Thin Films of Poly(Ethylene Terephthalate) and Its Nanocomposite with Expanded Graphite Nanostructured by Ultraviolet and Infrared Femtosecond Laser Irradiation

In this work, the formation of laser-induced periodic surface structures (LIPSS) on the surfaces of thin films of poly(ethylene terephthalate) (PET) and PET reinforced with expanded graphite (EG) was studied. Laser irradiation was carried out by ultraviolet (265 nm) and near-infrared (795 nm) femtosecond laser pulses, and LIPSS were formed in both materials. In all cases, LIPSS had a period close to the irradiation wavelength and were formed parallel to the polarization of the laser beam, although, in the case of UV irradiation, differences in the formation range were observed due to the different thermal properties of the neat polymer in comparison to the composite. To monitor the modification of the physicochemical properties of the surfaces after irradiation as a function of the laser wavelength and of the presence of the filler, different techniques were used. Contact angle measurements were carried out using different reference liquids to measure the wettability and the solid surface free energies. The initially hydrophilic surfaces became more hydrophilic after ultraviolet irradiation, while they evolved to become hydrophobic under near-infrared laser irradiation. The values of the surface free energy components showed changes after nanostructuring, mainly in the polar component. Additionally, for UV-irradiated surfaces, adhesion, determined by the colloidal probe technique, increased, while, for NIR irradiation, adhesion decreased. Finally, nanomechanical properties were measured by the PeakForce Quantitative Nanomechanical Mapping method, obtaining maps of elastic modulus, adhesion, and deformation. The results showed an increase in the elastic modulus in the PET/EG, confirming the reinforcing action of the EG in the polymer matrix. Additionally, an increase in the elastic modulus was observed after LIPSS formation.

Generic prediction of exocytosis rate constants by size-based surface energies of nanoparticles and cells

Nanotechnology brings benefits in fields such as biomedicine but nanoparticles (NPs) may also have adverse health effects. The effects of surface-modified NPs at the cellular level have major implications for both medicine and toxicology. Semi-empirical and mechanism-based models aid to understand the cellular transport of various NPs and its implications for quantitatively biological exposure while avoiding large-scale experiments. We hypothesized relationships between NPs-cellular elimination, surface functionality and elimination pathways by cells. Surface free energy components were used to characterize the transport of NPs onto membranes and with lipid vesicles, covering both influences by size and hydrophobicity of NPs. The model was built based on properties of neutral NPs and cells, defining Van de Waals forces, electrostatic forces and Lewis acid–base (polar) interactions between NPs and vesicles as well as between vesicles and cell membranes. We yielded a generic model for estimating exocytosis rate constants of various neutral NPs by cells based on the vesicle-transported exocytosis pathways. Our results indicate that most models are well fitted (R2 ranging from 0.61 to 0.98) and may provide good predictions of exocytosis rate constants for NPs with differing surface functionalities (prediction errors are within 2 times for macrophages). Exocytosis rates differ between cancerous cells with metastatic potential and non-cancerous cells. Our model provides a reference for cellular elimination of NPs, and intends for medical applications and risk assessment.

In situ plasma cleaning of large-aperture optical components in ICF

The organic contamination damage of large-aperture optical components limits laser energy improvement of inertial confinement fusion (ICF). In situ cleaning of large-aperture optical components via low-pressure plasma is expected to remove organic contaminants from the optical surface. Herein, low-pressure air plasma equipment was proposed and used on surfaces of SiO2 sol–gel antireflection (AR) films in situ by conducting experiments. Its electrical discharge parameters were investigated and optimized during plasma cleaning. Plasma diffusion characteristics and homogeneity in large-aperture windows were analyzed by optical emission spectroscopy. Dramatic degradation in the optical properties of components was observed after organic contamination for 5 h. Transmittance, laser-induced damage threshold and surface morphology observation results demonstrated that low-pressure air plasma removed the organic contaminants from the surface of sol–gel AR films without causing damage and metal contamination. After plasma cleaning, the hydrophilicity of the films increased significantly due to the increase in the polar components of surface free energy. The mechanism of plasma cleaning organic contaminants was confirmed by x-ray photoelectron spectroscopy measurements. These salient results provide a new alternative method for removing organic contaminants in situ from large-aperture optical components and a foundation for improving the energy output of the ICF system.

Effects of Organic Agriculture in Structure and Organic Carbon Adsorption at Colloidal Scale in Marginal Olive Groves, Characterized by the Extended DLVO Model

Relationship between macroscopic and microscopic behavior of soils is a difficult issue, especially when dealing with complex properties such as structure or carbon sequestration, but it is necessary for a suitable understanding of the agricultural soil quality. In this work, we used the extended-DLVO theory to compute total energy of interaction between particles (kT), of three soils over granodiorites. This parameter allows predicting the tendency to aggregate formation at the colloidal scale, being the basis of soil structure. Furthermore, we characterized the mechanism and adsorption capacity of humic molecules on mineral surfaces, and its influence in the interaction energy, by means of the adsorption isotherms. The aim was to compare first the effects of organic farming on conventionally managed soils and, second, to compare these with a non-cultivated forest soil under Mediterranean climate. When total energies are negative (particle attraction), or positive (particle repulsion) but near 0 kT (<100 kT), then particle flocculation occurs and the structure at colloidal scale can be developed. Total energy was less in the forest sample and greater in the soil of conventional groves, with intermediate values in organic farming soil. This indicates a tendency toward particle flocculation and more stability of the structure at colloidal scale in less disturbed soils, agreeing with other soil physical properties such as the total porosity (50, 41 and 37% in forest, organic and conventional plots, respectively) or the aggregate stability index (0.94, 0.73 and 0.66, respectively), which followed the same trend. Of the three components of the total energy of interaction, the acid-base force was a key factor. This component, related with the electron-donor component of surface free energy, γ−, yielded a strong attractive force (−150 kT at 3 nm) when calcium solutions were analyzed for the forest soil. This indicates a clear hydrophobic character of this sample. Because the mineralogical composition of the samples is quite similar, hydrophobicity should be attributed to the organic carbon content of the forest soil, which is much higher than that of the cultivated ones (12.03 vs. 1.44% and 0.88% in organic and conventional farms, respectively), proving to be an essential element for the development of the structure at the colloidal level.

Grafting parameters and surface free energy components of photosensitive poly(methacrylated spiropyran) brushes

Poly(methacrylated spiropyran) (P(MMASP)) brushes on silicon wafers were synthesized using the interface-mediated RAFT polymerization of methacrylated spiropyran (MMASP) monomers to determine their grafting density and surface free energy changes during photoinitiation. The grafting parameters of P(MMASP) layers such as the grafting density (σ), the radius of gyration (Rg ) and average distance between polymer chains (D) were calculated. It is found that 1.25 P(MMASP) chains covered per nm2 area of wafers, and the distance between chains was 1.0 nm which is smaller than doubled Rg , 1.1 nm. Thus, P(MMASP) chains overlapped each other and forced themselves to stretch away from the interface. We evaluated the surface free energy components of P(MMASP) brushes during photo initiation. Van Oss-Good method was used to calculate the surface free energy components of brushes. It is found that spiropyran (SP)-merocyanine (MC) system significantly influenced the surface energy components of P(MMASP) brushes. The electron acceptor and electron donor surface free energies of SP and MC form of P(MMASP) brushes were found as and respectively. It is concluded that MC form of P(MMASP) brushes possess high base character; whereas, SP forms have low base character.

How Interfacial Properties Affect Adhesion: An Analysis from the Interactions between Microalgal Cells and Solid Substrates.

Microalgal biofilm, a stable community of many algal cells attached to a solid substrate, plays a significant role in the efficient accumulation of renewable energy feedstocks, wastewater treatment, and carbon reduction. The adhesion tendency of microalgal cells on solid substrates is the basis for controlling the formation and development of microalgal biofilm. To promote the adhesion of microalgal cells on solid substrates, it is necessary to clarify which surface properties have to be changed in the most critical factors affecting the adhesion. However, there have been few systematic discussions on what surface properties influence the adhesion tendency of algal cells on solid substrates. In this study, the essential principle of microalgal cell adhesion onto solid substrates was explored from the perspective of the interaction energy between microalgal cells and solid substrates. The influence of surface properties between microalgal cells and solid substrates on interaction energies was discussed via extended Derjaguin-Landau-Verwey-Overbeek (eDLVO) theory and a sensitivity analysis. The results showed that surface properties, including surface potential (ξ) and surface free energy components, significantly affect the adhesion tendency of microalgal cells on different solid substrates. When the solid surface possesses positive charges (ξ > 0), reducing ξ or the electron donor components of the solid substrate (γs-) is an effective measure to promote microalgal cell adhesion onto the solid substrate. When the solid surface possesses negative charges (ξ < 0), an increase in either γs- or the absolute value of ξ should be avoided in the process of microalgae adhesion. Overall, this research provides a direction for the selection of solid substrates and a direction for surface modification to facilitate the adhesion tendency of microalgal cells on solid substrates under different scenarios.

Evaluation of the adhesion property and moisture stability of rubber modified asphalt mixture incorporating waste steel slag

The present study was conducted to recycle waste tire rubber and steel slag (SS) in asphalt pavement and investigates the moisture stability of asphalt mixtures incorporating these solid wastes. To this end, two types of aggregates (SS and diabase), three kinds of SS content and multiple freeze–thaw cycles were considered and three kinds of adhesion assessment methods: pull-out test and surface free energy (SFE) method, and freeze–thaw splitting test were performed. Three corresponding adhesion evaluation indicators like adhesion strength, SFE characteristics, and tensile strength ratio were obtained and six energy parameters were introduced to characterize moisture susceptibility of asphalt mixture. To explore the relations between the SFE parameters and the adhesion evaluation indicators, a grey correlation analysis method was adopted. Asphalt mixtures with high consumption of SS obtained a better moisture resistance because SS has a superior adhesion strength and higher SFE components than diabase aggregate. Stripping energy increase was found to be the main failure mode of the asphalt rubber-SS aggregate system. SFE method provides a comprehensive and accurate evaluation of adhesion property of loose asphalt rubber–SS aggregate system and moisture stability of compacted asphalt mixtures.

Influence of Mixing Conditions of Modified Bitumen on Moisture Sensitivity of Asphalt Compounds

Modification of bitumen allows an improving the properties of bitumen, which can be a useful technique to enhance asphalt’s characteristics. Therefore, this research intended to study the effect of mixing time of different percentages of epoxy resin, between 0 to 8%, doped into bitumens on the moisture sensitivity of asphalt compounds containing two types of aggregates, i.e. limestone and siliceous. For this aim, the Sessile Drop Method (SDM) was employed, and moisture resistant parameters associated to surface free energy concept such as surface free energy components, work of cohesion, work of adhesion, work of debonding, adhesion bitumen to aggregate, and wetting bitumen around aggregate surface were assessed. The results revealed that the effect of the mixing time of bitumen and epoxy resin on moisture resistance properties of asphalt compounds significantly depends on the percentage of epoxy resin used in bitumen mixture. For bitumens with 4 and 6% epoxy resin, adhesion and wetting parameters had a similar performance for both mixing times of 10 and 60 minutes. However, asphalt compounds containing 2 and 8% epoxy resin modified bitumens prepared for 10 min mixing time had a better adhesion and wetting performance than those prepared for the longer mixing time, 60 minutes. The effect of mixing time of bitumen modified with epoxy resin on the bitumen and asphalt compound’ performance depend on the percent of additive in the bitumen.

Liquid crystal droplet design by using pseudopeptidic bottlebrush polymer additives.

Liquid crystal (LC) droplets are promising candidates for sensing applications due to their high sensitivity to surface anchoring changes, resulting in readily detectable optical effects. Herein, we have designed and synthesized amino acid-based bottlebrush polymers and investigated their impact on LC director configurations in the droplets. The pseudopeptidic bottlebrush polymers with an aromatic (phenyl) and aliphatic appendages are synthesized using ring-opening metathesis polymerization (ROMP). Polymer dispersed liquid crystal (PDLC) samples are prepared by employing pseudopeptidic bottlebrush polymers and 4-cyano-4'-pentylbiphenyl (5CB) LC via solvent-induced phase separation (SIPS) technique. Due to π-π stacking, the phenyl group favours radial configuration, whereas the repulsion between 5CB and aliphatic groups induces molecular alignment leading to bipolar droplet arrangement. The impact of various pendant groups attached to the polymer on the prepared PDLC sample's surface characteristics and free energy components is illustrated. The sensing capability of 5CB dispersed in pseudopeptidic bottlebrush polymers for various pH solutions is investigated using polarizing optical microscopy (POM). The PDLC samples are moderately permeable to water and sensitive to different pH solutions. The results demonstrate a simplified and straightforward approach for preparing LC-based biosensors and chemical sensors.

Evaluation of polyphenylene sulfide by surface thermodynamics approaches: Comparison with common polymers

AbstractPoly(phenylene sulfide) (PPS) is an advanced thermoplastic and widely used in industrial applications requiring high performance. Research on improving the surface properties of PPS is still ongoing and a detailed surface free energy (SFE) knowledge of this polymer is necessary for its applications related to surface wettability. In this study, wettability characteristics of PPS were evaluated by SFE calculations. For this purpose, the apparent contact angles of nine different test liquids having various surface tensions were measured on the PPS surface by the sessile drop method. After that, the dispersive and polar components of SFE were calculated using geometric (Owens and Wendt's method) and harmonic (Wu's method) mean approaches. The Lifshitz‐van der Waals, acidic and basic components of SFE were calculated using van Oss‐Chaudhury‐Good method. Additionally, the surface tension values of PPS were also determined by equation of state, Zisman's critical surface tension and Fowkes' approaches. In the present study, the effects of calculation methods and selected liquid pairs on SFE parameters were systematically investigated. It was found that selected liquid pairs and calculation methods affected the SFE considerably. The reasons for this were examined and the SFE components of PPS was compared with some common polymers for better evaluation.

Relationship between surface free energy and development process (swelling and dissolution kinetics) of poly(4-hydroxystyrene) film in water and 2.38 wt% tetramethylammonium hydroxide aqueous solution

With the sharpening of optical images, the capability of resist materials has become a serious concern in lithography. The dissolution of a resist polymer is key to the realization of ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the relationships of surface free energy with swelling and dissolution kinetics were investigated using poly(4-hydroxystyrene) (PHS) film with triphenylsulfonium-nonaflate (TPS-nf). Developers were water and 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution. PHS and TPS-nf are a typical backbone polymer (a dissolution agent) and a typical acid generator of chemically amplified resists, respectively. The water intake and dissolution of PHS film with TPS-nf became fast with increasing UV exposure dose. It was found that the increase in the polar components (particularly, the hydrogen bonding component) and the decrease in the dispersion component of surface free energy underlie the fast water intake and dissolution.

Effect of graphene oxide/graphitic nanofiber nanohybrids on interfacial properties and fracture toughness of carbon fibers-reinforced epoxy matrix composites

The fracture toughness of carbon fiber-reinforced epoxy composites (CFRPs) is greatly dependent on the interfacial adhesion between the carbon fibers and the epoxy matrix. Introducing nanofiller reinforcements into the interface is an effective approach to enhancing the interfacial adhesion of CFRP. In the present study, a simple and efficient method is proposed for the deep and stable penetration of graphene oxide/graphitic nanofiber nanohybrids (GO-GNFs) into an epoxy matrix as a CFRPs. To confirm the efficiency of the proposed method, CFRPs are fabricated with various amounts of (i) untreated GNFs, (ii) dry-ozonized GNFs, and (iii) GO-GNFs. For all three types of composites, the optimal nanofiller content is found to be 0.8 wt%. The addition of GO-GNFs is shown to increase the inter-laminar shear strength by 159.5%, and the fracture toughness by 102.8%, compared to those of the pristine CFRPs. The reinforcing mechanisms are explored by analyzing the surface properties of GO-GNFs and the wettability between fiber and nanofillers within the epoxy matrix, are ascribed to the maximal polar component of surface free energy and the minimal contact angles. This approach shows that the GO-GNF composite is a simple and efficient method for the preparation of CFRPs with excellent interfacial adhesion, which has potential applications in the structural composite industry.

Moisture-induced damage potential of asphalt mixes containing polyphosphoric acid and antistripping agent

This study examines the effects of PPA and ASA on interfacial energies and moisture-induced damage potential of mixes using a Surface Free Energy (SFE) method. The SFE components of binder blends containing different amounts of PPA and ASA and aggregates were determined using Dynamic Wilhelmy Plate and Universal Sorption Device-based tests, respectively. Based on the measured SFE components and interfacial energy, it was found that using PPA with or without ASA does not affect cohesive bond of binder. However, depending on aggregate type, PPA may improve adhesive bond. Also, using an amine-based ASA does not improve the resistance to moisture-induced damage of binders or mixes containing PPA. Therefore, using an amine-based ASA with PPA-modified asphalt binder is not recommended. Among different PPA amounts considered, using 1.5% PPA with and without ASA was found to be the most effective concentration in improving the adhesive bond and wettability of binders with aggregates.

Surface thermodynamic properties of sodium carboxymethyl cellulose by inverse gas chromatography

This study constitutes a new development of surface thermodynamic methods to determine the London dispersive surface free energy component γsd, the specific free energy of adsorption and the Lewis acid-base properties of polymers by using inverse gas chromatography (IGC) at infinite dilution. The net retention volumes Vn of n-alkanes and polar solvents adsorbed on a sodium carboxymethyl cellulose (Na-CMC) polymer surface were determined at four temperatures 313.15K, 323.15K, 333.15 and -343.15K by IGC technique The London dispersive surface free energy component of Na-CMC was determined by using Dorris-Gray and Dorris-Gray-Hamieh methods, Van der Waals, Redlich-Kwong, Kiselev, geometric, cylindrical, spherical and Hamieh models. The more accurate value of γsd of Na-CMC was obtained by Hamieh model taking into account the thermal effect on the surface areas of molecules: γsd(T)(mJ/m2)=−0.630T(K)+229.01 showing a maximal temperature TMax = 91°C that can be considered as a new characteristic of the Na-CMC polymer. Above TMax, there is no dispersive component of the surface energy of the polymer surface.The specific interactions of Na-CMC particles were determined by using the various molecular models, and the vapor pressure, the boiling point, the topological index and the deformation polarization IGC methods. The obtained results clearly showed a strong Lewis basicity of Na-CMC (about seven times more basic than acidic polymer surface). It was proved that the IGC methods and models do not give similar results. The thermal model gave the most accurate result of the Lewis acid-base properties of Na-CMC surface.

Comparison of the effects of various reinforcements on the mechanical, morphological, thermal and surface properties of poly(butylene succinate)

Various nanocomposites of poly(butylene succinate) (PBS) with different reinforcements, such as organo-montmorillonite (OMMT), carbon nanofiber (CNF), and nanocrystalline cellulose (NCC) were prepared by the solution blending method. The loading levels were 0.5, 1 and 2 wt% for NCC, while 1 wt% for OMMT and CNF. The effects of different reinforcements on the PBS resin were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), inverse gas chromatography (IGC), water contact angle (WCA) and nanoindentation tests in the aspects of the crystalline structure, thermal stability, the dispersive component of surface free energy, wettability, hardness, and elastic modulus. The morphological characterization of nanocomposites was carried out using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). According to the TGA analysis, the temperature at 5% weight loss of the NCC/PBS nanocomposite increased by 8 °C compared with that of neat PBS. The highest hydrophobicity and the best mechanical properties were achieved with OMMT/PBS nanocomposite. Nanoindentation tests indicated that OMMT incorporation increased modulus (~98%) and hardness (~99%) of PBS.