Interdiffusion in carboxylated styrene/butyl acrylate latex films studied by topographic and thermal analysis

Atomic force microscopy, AFM, was used to study polymer interdiffusion in styrene/butyl acrylate latex films in the presence and absence of a methacrylic acid copolymer. The interdiffusion monitored as the disappearance of particle contours was found to be dependent on annealing time and temperature and was strongly influenced by the type of neutralizing agent. In the presence of NaOH, AFM images suggested the formation of a salt shell around the particles, which retarded the interdiffusion. The concentration of surface acid groups determined from titration in combination with measured particle dimensions resulted in a calculated shell thickness of about 10 nm. This polyelectrolyte layer is claimed to have a higher glass transition temperature, T_g, than the measured bulk T_g of the copolymer, thus explaining the retarded particle–particle interdiffusion. Less severe retardation was found when using ammonia for neutralization, presumably due to evaporation of the volatile base. Appropriate diffusion coefficients calculated using literature data on similar polymers confirmed the experimental observations with a decrease by about one order of magnitude in the presence of a methacrylic acid shell and a further decrease when sodium hydroxide was used for neutralization.     

Film formation from surfactant-free,slightly crosslinked,fluorescein-labeled polystyrene particles

A steady state-fluorescence (SSF) technique for studying film formation from surfactant-free, slightly crosslinked polystyrene (PS) latex particles is reported. The powder films were prepared from fluorescein (F)-labeled PS particles at room temperature. The mechanically strong films were obtained by annealing these films at elevated temperatures in 5, 10, 20, and 30 min time intervals above the glass transition (T_g) temperature of polystyrene. Scattered light (I_s) and fluorescence (I_F) intensities from F were monitored after each annealing step to investigate the three different film formation stages called void closure, healing, and interdiffusion. The evolution of transparency of the latex films was monitored by using a photon transmission technique. Scanning electron microscopy (SEM) was employed to detect the variation in physical structure of the annealed latex films. Onset temperature for void closure, T_m’, and healing temperatures, T_h, were determined and corresponding activation energies were measured. Void closure and interdiffusion stages were also modeled and the related activation energies were also determined. It was observed that lower energy is needed for the void closure process than interdiffusion of chains across the particle-particle boundaries.     

Effects of surface functional groups on film formation and tensile strength development in reactive latex systems

The effect of surface functional groups on chain interdiffusion at the interfacial zone of reactive latexes was investigated. A series of latexes with different surface functionalities was prepared by batch or shot-growth emulsion polymerizations. The particle surface properties were varied by changing the number density of functional groups. The rate of tensile strength development decreases with the increasing number density of surface functional groups, which indicated that inter-particle crosslinking restricted the interdiffusion of polymer chains during film formation and annealing. The average diffusion coefficient D of polymer chains across particle interfaces was obtained from dynamic mechanical analysis and compared well with the results from the rate of tensile strength development. The magnitude of D of the reactive latex film was lower than that of the homopolymer film. The lower chain mobility of reactive latexes prevented mechanical strength development.     

The effect of solid content on latex coalescence and film formation: Steady-state energy transfer study with fluorescence labeled polymers

The steady-state fluorescence technique was used to examine the healing and interdiffusion of polymer molecules as a function of solid content during annealing of latex films above the glass transition (T_g). Films were prepared from a mixture of naphthalene (N)- and pyrene (P)-labeled poly(methy methacrylate) (PMMA) latex particles. Above T_g, interdiffusion of polymer chains was observed by detecting the steady-state energy transfer from excited naphthalene to pyrene molecules. Various latex films with different latex content were used to measure the critical occupation percent for the reliable steady-state fluorescence measurements. Diffusion activation energies in these latex films were measured and found to be around 30 kcal/mol, which was attributed to the backbone motion of PMMA chains. © 1996 John Wiley & Sons, Inc.     

Formation of nanostructured composites with environmentally-dependent electrical properties based on poly(vinylidene fluoride)-polyaniline core-shell latex system

Submicron poly(vinylidene fluoride) (PVDF)/polyaniline (PANI) core-shell latex particles are synthesized and examined as an active component in a simple conductometric chemical sensor. The structure and physical properties of these particles and nanostructured composite PVDF-PANI polymer films built of them are characterized with transmission electron, atomic force, and helium ion microscopy techniques, differential scanning calorimetry, and conductivity measurements. The nanostructured composite films with conductivity of about 4 × 10⁻⁴ S/cm suitable for sensor applications are prepared by casting from the core-shell particles dispersions on glass substrates patterned with silver electrodes followed by annealing at 180 °C, i.e. above T_m of the PVDF component. Sensor properties of these films are tested by measuring current-voltage (I-V) characteristics in response to varying concentration of NH₃ or HCl vapors. The developed thin film sensor heterostructures with electrically conductive percolation network of PANI as an active component and employing the conductometric detection scheme show high sensitivity to both analytes. However, the polymer material is especially efficient for application to NH₃ sensing with the detection limit as low as 100 ppb, and good reproducible recovery behavior upon repeated exposure to NH₃ at ambient conditions.     

Interfacial structure in vulcanized EPDM filled with mercaptosilane-treated Al(OH)3 and its influence on the mechanical properties

The reactivity of the alkoxy group in a silane coupling agent toward inorganic surfaces was investigated, and the structure of a silane-treated layer on the particle surface was analyzed. For this purpose, the various inorganic filler particles, SiO₂, Al(OH)₃, Mg(OH)₂, Al₂O₃, and CaCO₃ were treated with γ-mercaptopropyltrimethoxysilane. A strong interaction between the particle surface and the silane due to the hydrogen bonding and ionic interaction was confirmed except for CaCO₃ by electron spectroscopy for chemical analysis (ESCA). The structure of the silane layer on the particle surface was affected significantly by both the amount of added silane and the treatment conditions. Different silane structures, such as monolayer- or network-like, were formed on the particle surface. Their influences on the mechanical properties of filled vulcanized rubber were also investigated. The silane-treated filler particles, except CaCO₃, showed ability as a semi-reinforcing filler for vulcanized rubber. However, the structure of the silane-layer on the particle surface hardly affected the mechanical properties.     

Film formation and mechanical properties of the alkoxysilane-functionalized poly (styrene-co-butyl acrylate) latex prepared by miniemulsion copolymerization

Alkoxysilane-functionalized poly (styrene-co-butyl acrylate) latex was prepared via miniemulsion copolymerization of γ-methacryloxypropyltrimethoxysilane (MPS), styrene and butyl acrylate using AIBN at neutral condition. The effects of initiator types, pH values, and MPS contents on the premature cross-linking of the latex particles and the mechanical properties of the films were investigated by the swelling experiments and dynamic mechanical analysis. It was found that the storage modulus of the latex films and the glass transition temperature (T_g) increased with increasing MPS content. The acidification of latex prior to film formation and annealing the latex films could improve the mechanical properties of the films.     

Initial surface film on magnesium metal: A characterization by X-ray photoelectron spectroscopy (XPS) and photocurrent spectroscopy (PCS)

A detailed investigation of the initial film grown on mechanically polished Mg electrodes has been carried out by ex situ X-ray Photoelectron Spectroscopy (XPS) and in situ Photocurrent Spectroscopy (PCS), allowing to reach a detailed picture of the passive layer structure. The XPS data show that the films formed soon after mechanical treatment and immersion in aqueous electrolyte have a bilayer structure, consisting of an ultra-thin MgO inner layer (∼2.5 nm) and a Mg(OH)₂ external layer. The thickness of the Mg(OH)₂ layer is a function of immersion time and solution temperature. After mechanical treatment and immersion in aqueous solution at room temperature, the MgO/Mg(OH)₂ layer in some area of electrodes is so thin to allow an electron photoemission process from the Mg Fermi level to the electrolyte conduction band. Only internal photoemission processes are evidenced for Mg electrodes aged in NaOH at 80 °C, due the formation of a thicker Mg(OH)₂ layer. From anodic photocurrent spectra an optical band gap of ∼4.25 eV has been estimated for Mg(OH)₂, lower with respect to the optical gap of the corresponding anhydrous counterpart.     

Preparation of chitosan films mixed with superabsorbent polymer and evaluation of its haemostatic and antibacterial activities

In this study, polycaprolactone/C₆₀ (PCL/C₆₀) hybrids were prepared via a melt‐blending method. To enhance the compatibility between PCL and C₆₀, the acrylic acid‐grafted polycaprolactone (PCL‐g‐AA) was first transformed to PCL? NH₂ by mixing with 1,6‐diaminohexane, while C₆₀ was oxidized using a mixture of H₂SO₄/HNO₃ and NaOH to derive C₆₀ fullerol (C₆₀? OH). Thereafter, C₆₀? OH and PCL? NH₂ were used to replace PCL and C₆₀, respectively. The resulting products were characterized using FTIR, solid‐state ¹³C‐ and ¹H‐ NMR, TGA, DMA, SEM, TEM, and Instron mechanical testing. Because of the formation of ? NHCO groups through the reaction between amino groups of PCL? NH₂ and hydroxyl groups of C₆₀? OH, thermal and mechanical properties of the PCL? NH₂/C₆₀? OH composite were significantly superior to those of PCL/C₆₀. The optimal blend was the 5 wt % C₆₀? OH with PCL? NH₂, producing an 84°C increase in initial decomposition temperature (IDT). C₆₀? OH in excess of 5 wt % aggregated and caused separation of the organic and inorganic phases, lowering their compatibility.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of NH4F and NH4OH on the structure and physical properties of thin SnO2 films synthesized by the sol-gel method

Undoped films and films with the addition of NH₄F and NH₄OH have been prepared by layer precipitation of solutions on glass substrates by sol-gel technology with the use of centrifugation. It has been shown via X-ray diffraction that all films under study are composed of SnO₂ nanocrystals. Measurements of surface resistance confirmed the presence of fluorine atoms in the films that were prepared from the solutions with NH₄F. Scanning electron microscopy has demonstrated the formation of a dendrite structure and an increase in film porosity with the addition of NH₄F and NH₄OH to the film-forming solution. Addition of NH₄F and NH₄OH to the solution has resulted in the increase of the gas sensitivity of the films; however, it has been accompanied by a decrease in film transparency and the disappearance of interference peaks in the transmittance spectra.     

Film formation of latices with crosslinked particles

Summary The mechanical strength of latex films is caused by the diffusion of chain segments across particle boundaries and the formation of entanglements. This process should be hindered when the film is formed from crosslinked particles with an average network chain length M_c smaller than the entanglement length M_e. This assumption is verified by tensile tests of of crosslinking. In films of too highly crosslinked particles no mechanical strength is developed by annealing above the glass transition temperature.     

Effect of acrylic acid on the physical properties of UV-cured poly(urethane acrylate-co-acrylic acid) films for metal coating

UV-cured poly(urethane acrylate-co-acrylic acid) (PU-co-AA) films with five different compositions were prepared by reacting isophorone diisocyanate (IPDI), polycaprolactone triol (PCLT), 2-hydroxyethyl acrylate (HEA), and different weight ratios of trimethylolpropane triacrylate (TMPTA) and acrylic acid (AA) as diluents. Their synthesis and physical properties including gel content, adhesion properties, morphological structure, thermal properties, and mechanical hardness were investigated as a function of the AA content. It was found that the physical properties of the PU-co-AA films are strongly dependent upon the AA content. Crosscut tests showed that PU-co-AA films with lower AA content showed 0% adhesion (0B), and the adhesion of films increased dramatically as the AA content increased to 40–50%. The pull-off measurements showed that the adhesion force of the PU-co-AA films to stainless steel substrates varied from 6 to 31 kg_f/cm² and increased linearly with increasing AA content. PU-co-AA films with higher AA content can be good candidates for UV-curable coating of metal substrates such as stainless steel. However, the thermal stabilities and mechanical hardness decreased with increasing AA content, which results from the relatively linear and flexible structure of AA.     

Dynamic mechanical and thermal properties of the composites of thermoplastic starch and lanthanum hydroxide nanoparticles

Nanostructured lanthanum (III)‐oxide (La₂O₃) particles were prepared by a polymer complex solution method and further used for the preparation of lanthanum hydroxide (La(OH)₃) nanoparticles. The La(OH)₃ nanopowder was mixed with glycerol‐plasticized maize starch and the effect of the filler on the thermal, mechanical, and viscoelastic properties of the matrix was investigated. It was expected that this nanofiller, which shows an affinity toward OH groups, would strongly affect the physical properties of thermoplastic starch (TPS). The pure TPS and the TPS‐La(OH)₃ nanocomposite films (with 1, 2, and 3 wt % filler) were conditioned at various relative humidities (RHs) (35, 57, 75, and 99% RH). After conditioning at 99% RH, the pure TPS films exhibited higher affinity toward water than the nanocomposites. Differential scanning calorimetric measurements showed that, due to retrogradation effects, the melting enthalpies of the films increased with increasing RH. Dynamic mechanical analysis revealed that the mechanical properties in the linear range strongly depend on both the humidity conditions and the concentration of the filler. The results also show that La(OH)₃ nanoparticles are good reinforcement for TPS films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication of sintered porous polymeric materials: effect of chain interdiffusion time on mechanical properties

In this study, sintered porous polymeric materials made of high density polyethylene (HDPE) were fabricated through controlling the chain interdiffusion time at the transition temperature of semicrystalline and melt states. At this intermediate state, where both crystalline and amorphous phases coexist, the interfacial welding of HDPE particles is facilitated thanks to interdiffusion caused by chain relaxation phenomena. Then, by assuming a spherical shape and a cubic packing configuration of particles, a geometrical model was developed to predict porosity variations as sintering progresses. Moreover, the HDPE used, as a broad molecular weight distributed polymer, has different family chains with different specific molecular weight ranges. Accordingly, the melt coalescence rate of the particles was tracked using an optical microscope equipped with a hot stage, in order to determine the diffusion characteristic times for each family. During the characterization stage, SEM images proved the presence of porous structures in the sintered samples. In addition, mechanical properties were assessed through the shear punch test. It was shown that the mechanical properties are governed by the interdiffusion of long chains which occurs at relatively long sintering times. The results also demonstrated the role of reptation motion of long chains in the interfacial welding of polymeric particles. They revealed the compatibility of macroscopic properties of the samples and chain motions at microscopic levels. © 2017 Society of Chemical Industry     

Single particle MS,SNMS, SIMS,XPS, and FTIR spectroscopic analysis of soot particles during the AIDA campaign

Within the framework of the AIDA soot aerosol campaign diesel soot particles, spark generated soot particles, and aerosol mixtures were characterized with respect to their chemical state using different surface sensitive analysis methods. A comparison between diesel soot and graphite spark generated soot revealed a significant difference in the chemical composition of the particle surfaces. No distinct change from external to internal mixing could be detected by single particle mass spectrometry for mixtures of diesel soot and (NH₄)₂SO₄ aerosol since the spectra of diesel soot and (NH₄)₂SO₄ aerosol were surprisingly similar due to sulfate on the surface of diesel soot particles and traces of carbon impurities on ammonium sulfate particles. In addition to the expected formation of new particles a considerable change of the soot particle surface was detected while exposing diesel soot or spark generated soot to α-pinene and ozone, indicating a surface layer formed by oxidation products of α-pinene. However, the oxygen-containing hydrocarbon fragments detected by single particle mass spectrometry were distinctly different for the two soot types, which can be explained by either the different product adsorption or ionization behavior. Depositions of α-pinene reaction products on the surface could be confirmed by QMS-SIMS and XPS for particles of both types of soot. Due to the high mass resolution of TOF-SIMS acidic derivatives were identified as reaction products of α-pinene and ozone. The analytical methods applied in this work elucidated the different properties of spark generated soot compared to diesel soot. Therefore, spark generated soot should only be used with care as a general diesel soot surrogate.     

Influence of Alkaline Additives and Buffers on Mineral Trapping of CO2 under Mild Conditions

Carbon dioxide (CO₂) gas is the main contributor to climate change. CO₂ storage in underground brines and oil‐field brines by mineral trapping has been considered as a promising alternative in order to reduce CO₂ emissions. However, permanent storage of CO₂ in stable carbonate minerals is greatly dependent on brine pH, being favored over an alkaline pH. The effect of alkaline additives (NaOH, KOH, CaO) and buffer solutions (NaHCO₃/NaOH, Na₂HPO₄/NaOH, NH₄Cl/NH₄OH) on the mineral trapping of CO₂ under mild conditions using a synthetic brine is investigated. The results indicate that both NaOH+NH₄Cl/NH₄OH and KOH+NH₄Cl/NH₄OH mixtures promote precipitation mainly of calcium carbonate (CaCO₃).     

Production of natural graphite particles with high electrical conductivity by grinding in alcoholic vapors

Natural graphite particles with a high crystallinity, which were sieved to obtain particles less than 63 μm, were ground with a ball mill under a dry atmosphere and various alcoholic vapors such as i-C₃H₈OH, n-C₃H₈OH, C₂H₅OH, and CH₃OH. The size and flakiness of the ground products and the electrical conductivity of the films made from the ground products were experimentally examined. Grinding the particles under alcoholic vapors slowly reduced the particle size and was similar to grinding in dry air, but grinding in alcoholic vapors produced flakier products. The graphite films, which were composed of flakier particles and were ground in alcoholic vapor, displayed higher electrical conductivities than the feed graphite particles. The products ground in C₂H₅OH, i-C₃H₇O and n-C₃H₇OH vapors had 50% or less of the specific resistance of the feed particles.     

Creating layers of concentrated inorganic particles by interdiffusion of polyethylenes in microlayers

Interdiffusion of a polymer pair in microlayers was exploited to increase the concentration of inorganic particles in one of the components. When microlayers of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) were taken into the melt, greater mobility of linear LLDPE chains compared to branched LDPE chains caused the layer boundary to move in the direction of the more slowly diffusing chains in a manner similar to the Kirkendall effect in metals. This resulted in substantial shrinkage of the LLDPE layers and corresponding thickening of the LDPE layers. Adding a particulate in the LLDPE did not impede the process of interdiffusion in the melt, and the resultant shrinkage served to increase the particle concentration. For example, resistivity of initially nonconductive LLDPE layers containing nickel platelets decreased by 6 orders of magnitude into the semiconductor range after shrinkage concentrated the particles. The concentrating effect was also demonstrated with TiO₂ particles and talc platelets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2877–2885, 1999     

Formation of double-surface-silvered polyimide films via a direct ion-exchange self-metallization technique: The case of BPADA/ODA and [Ag(NH3)2]+

Double-surface-silvered polyimide (PI) films have been successfully fabricated via a direct ion-exchange self-metallization method using silver ammonia complex cation ([Ag(NH₃)₂]⁺) as silver resource and bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride/4,4′-oxydianiline (BPADA/ODA)-based poly(amic acid) (PAA) as the PI precursor. The alkaline characteristic of the silver precursor dramatically improves the efficiency of the ion exchange and film metallization process. By using an aqueous [Ag(NH₃)₂]⁺ solution with a concentration of only 0.01M and an ion-exchange time of only 5 min, metallized films with desirable performance could be easily obtained by simply heating the silver(I)-doped PAA films to 300°C. The strong hydrolysis effect of the basic [Ag(NH₃)₂]⁺ cations on the flexible and acidic BPADA/ODA PAA chains was observed during the ion exchange process by the quantitative evaluation of the mass loss of PAA matrix. Nevertheless, under the present experimental conditions, the final metallized film essentially retained the basic structural, thermal, and mechanical properties of the pristine PI, which make it a truly applicable material. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical properties of Mg(OH)2/polypropylene composites modified by functionalized polypropylene

Modified Mg(OH)₂/polypropylene (PP) composites were prepared by the addition of functionalized polypropylene (FPP); and acrylic acid (AA) and by the formation of in situ FPP. The effects of the addition of FPP and AA and the formation of in situ FPP on the mechanical properties of Mg(OH)₂/PP composites were investigated. Experimental results indicated that the addition of Mg(OH)₂ markedly reduced the mechanical properties of PP. The extent of reduction in notch impact strength of PP was higher than that in flexural strength and tensile strength. However, tensile modulus and flexural modulus increased with increased Mg(OH)₂ content. The addition of FPP facilitated the improvement in the flexural strength and tensile strength of Mg(OH)₂/PP composites. The higher the Mg(OH)₂ content was, the more significant the effect of FPP was. The incorporation of AA resulted in further increased mechanical properties, in particular the flexural strength, tensile strength, and notch impact strength of Mg(OH)₂/PP composites containing high levels of Mg(OH)₂. It not only improved mechanical properties but also increased the flame retardance of Mg(OH)₂/PP composites. Although the mechanical properties of composites modified by the formation of in situ FPP were lower than those of composites modified by only the addition of AA in the absence of diamylperoxide, the mechanical properties did not decline with increased Mg(OH)₂ content. Moreover, the mechanical properties increased with increasing AA content. The addition of an oxidation resistant did not influence the mechanical properties of the modified Mg(OH)₂/PP composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2139–2147, 2003