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Langmuir : the ACS journal of surfaces and colloids 2010 Aug;
Cross-Linked Network Development in Compatibilized AlkydAcrylic Hybrid Latex Films for the Creation of Hard Coatings.
Hybrids made from an alkyd resin and an acrylic copolymer can potentially combine the desired properties of each component. Alkyd/acrylic hybrid latex particles were synthesized via miniemulsion polymerization and used to create films at room tempera... expand abstractture. Comparisons of the alkyd auto-oxidative cross-linking rates and the associated network development are made between two alkyd resins (with differing levels of hydrophilicity as measured by their acid numbers). The effects of increasing the compatibilization between the alkyd and the acrylic phase via functionalization with glycidyl methacrylate (GMA) are investigated. Magnetic resonance profiling and microindentation measurements reveal that film hardening occurs much faster in a GMA-functionalized alkyd hybrid than in the standard hybrid. The film's hardness increases by a factor of 4 over a 5-day period. The rate of cross-linking is significantly slower in nonfunctionalized alkyd hybrid films and when the more hydrophilic alkyd resin is used. Tensile deformation of the hybrid latex films reveals the effects of GMA functionalization and drier concentration in creating a denser cross-linked network. Modeling of the tensile deformation behavior of the hybrid films used a combination of the upper convected Maxwell model (to describe the viscoelastic component) and the Gent model (to describe the elastic component). The modeling provides a correlation between the cross-linked network formation and the resulting mechanical properties. collapse abstract
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ACS applied materials & interfaces 2010 May; 2(6)
Achieving a stable time response in polymeric radiation sensors under charge injection by X-rays.
Existing inorganic materials for radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, lack of tissue-equivalence, toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triaryl... expand abstractamine) (PTAA) diodes have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. A single layer of PTAA is deposited on indium tin oxide (ITO) substrates, with top electrodes selected from Al, Au, Ni, and Pd. The choice of metal electrode has a pronounced effect on the performance of the device; there is a direct correlation between the diode rectification factor and the metal-PTAA barrier height. A diode with an Al contact shows the highest quality of rectifying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo Kalpha X-radiation over long time scales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. Diodes with a low band gap, 'Ohmic' contact, such as ITO/PTAA/Au, show a slow transient response. This result can be explained by the build-up of space charge at the metal-PTAA interface, caused by a high level of charge injection due to X-ray-induced carriers. These data provide new insights into the optimum selection of metals for Schottky contacts on organic materials, with wider applications in light sensors and photovoltaic devices. collapse abstract
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Biofouling 2010 Apr; 26(4)
Adhesion of microorganisms to bovine submaxillary mucin coatings: effect of coating deposition conditions.
The adhesion of Staphylococcus epidermidis, Escherichia coli, and Candida albicans on mucin coatings was evaluated to explore the feasibility of using the coating to increase the infection resistance of biomaterials. Coatings of bovine submaxillary m... expand abstractucin (BSM) were deposited on a base layer consisting of a poly(acrylic acid-b-methyl methacrylate) (PAA-b-PMMA) diblock copolymer. This bi-layer system exploits the mucoadhesive interactions of the PAA block to aid the adhesion of mucin to the substratum, whereas the PMMA block prevents dissolution of the coating in aqueous environments. The thickness of the mucin coating was adjusted by varying the pH of the solution from which it was deposited. Thin mucin coatings decreased the numbers of bacteria but increased the numbers of C. albicans adhering to the copolymer and control surfaces. Increasing the mucin film thickness resulted in a further lowering of the density of adhering S. epidermidis cells, but it did not affect the density of E. coli. In contrast, the density of C. albicans increased with an increase in mucin thickness. collapse abstract
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Macromolecular Rapid Communications 2010 Apr; 31(7)
ColloidAssisted SelfAssembly of Robust, ThreeDimensional Networks of Carbon Nanotubes over Large Areas
Natural materials, such as bone and spider silk, possess remarkable properties as a result of sophisticated nanoscale structuring. They have inspired the design of synthetic materials whose structure at the nanoscale is carefully engineered or where ... expand abstractnanoparticles, such as rods or wires, are self-assembled. Although much work has been done in recent years to create ordered structures using diblock copolymers and template-assisted assembly, no reports describe highly ordered, three-dimensional nanotube arrays within a polymeric material. There are only reports of two-dimensional network structures and structures on micrometer-size scales. Here, we describe an approach that uses plasticized colloidal particles as a template for the self-assembly of carbon nanotubes (CNTs) into ordered, three-dimensional networks. The nanocomposites can be strained by over 200% and still retain high conductivity when relaxed. The method is potentially general and so may find applications in areas such as sensing, photonics, and functional composites. collapse abstract
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ACS applied materials & interfaces 2010 Jan; 2(2)
Waterborne, semicrystalline, pressure-sensitive adhesives with temperature-responsiveness and optimum properties.
The synthesis and resulting temperature-responsive properties of semicrystalline waterborne pressure-sensitive adhesives (PSAs) were investigated. A crystalline polymer fraction was produced in situ within waterborne particles by miniemulsion polymer... expand abstractization of non-branched long chain acrylates. The degree of crystallinity was controlled by copolymerization with a short chain acrylate. The polymerization strategy determined the polymer architecture and film structure, which then influenced the adhesion properties. The high sensitivity of the adhesion strength of these PSAs to temperature, in the range around the crystal melting point, opens up the possibility of designing temperature-responsive adhesives. With the right distribution and concentration of crystalline polymers, a simultaneous increase in both the peel strength and the shear resistance was obtained, which is a combination that is often not found when optimizing adhesive properties. collapse abstract
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Langmuir 2009 Sep; 25(18)
A Comparison of Tackified, Miniemulsion Core−Shell Acrylic Latex Films with Corresponding Particle-Blend Films: Structure−Property Relationships
Tackifying resins (TRs) are often added to pressure-sensitive adhesive films to increase their peel strength and adhesion energy. In waterborne adhesives, the TR is dispersed in water using surfactants and then blended with colloidal polymers in wate... expand abstractr (i.e., latex). In such waterborne systems, there are problems with the colloidal stability and difficulty in applying coatings of the particle blends; the films are often hydrophilic and subject to water uptake. Here, an alternative method of making waterborne, tackified adhesives is demonstrated. The TR is incorporated within the core of colloidal polymer particles via miniemulsion polymerization. Atomic force microscopy (AFM) combined with force spectroscopy analysis reveals there is heterogeneity in the distribution of the TR in films made from particle blends and also in films made from miniemulsion polymers. Two populations, corresponding to TR-rich and acrylic-rich components, were identified through analysis of the AFM force-displacement curves. The n... collapse abstract
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Langmuir : the ACS journal of surfaces and colloids 2009 Sep; 25(18)
A comparison of tackified, miniemulsion core-shell acrylic latex films with corresponding particle-blend films: structure-property relationships.
Tackifying resins (TRs) are often added to pressure-sensitive adhesive films to increase their peel strength and adhesion energy. In waterborne adhesives, the TR is dispersed in water using surfactants and then blended with colloidal polymers in wate... expand abstractr (i.e., latex). In such waterborne systems, there are problems with the colloidal stability and difficulty in applying coatings of the particle blends; the films are often hydrophilic and subject to water uptake. Here, an alternative method of making waterborne, tackified adhesives is demonstrated. The TR is incorporated within the core of colloidal polymer particles via miniemulsion polymerization. Atomic force microscopy (AFM) combined with force spectroscopy analysis reveals there is heterogeneity in the distribution of the TR in films made from particle blends and also in films made from miniemulsion polymers. Two populations, corresponding to TR-rich and acrylic-rich components, were identified through analysis of the AFM force-displacement curves. The nanoscale maximum adhesion force and adhesion energy were found to be higher in a miniemulsion film containing 12 wt % tackifying resin in comparison to an equivalent blended film. The macroscale tack and viscoelasticity are interpreted by consideration of the nanoscale structure and properties. The incorporation of tackifying resin through a miniemulsion polymerization process not only offers clear benefits in the processing of the adhesive, but it also leads to enhanced adhesion properties. collapse abstract
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Langmuir : the ACS journal of surfaces and colloids 2009 Aug; 25(17)
The uptake and release of cationic surfactant from polyampholyte microgel particles in dispersion and as an adsorbed monolayer.
The use of novel polyampholyte microgel particles for the controlled absorption and release of a cationic surfactant has been investigated. The addition of cetylpyridinium chloride (CPC) to aqueous dispersions of poly(2-diethylamino)ethyl methacrylat... expand abstracte-co-methacrylic acid (DEAEM-co-MAAc) microgel particles has been studied with respect to CPC concentration and solution pH. CPC was found to absorb into the polyampholyte microgel particles, resulting in reduced hydrodynamic diameter and electrophoretic mobility, when added to microgel dispersion at pH 11. Strong desorption could be induced by switching the pH from 11 to 3, with most of the desorption occurring in the region of the isoelectric pH of the particles. The properties of surface-adsorbed monolayers of polyampholyte microgel particles were also investigated, both in the presence and absence of CPC. The substrate surface charge was found to influence the swelling profile of the adsorbed microgel monolayers. The interaction of CPC surfactant with monolayers of adsorbed microgel particles shows strong correlations with the interaction of CPC surfactant with microgel particles in dispersion. collapse abstract
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Applied spectroscopy 2009 Jul; 63(8)
Spectroscopic ellipsometry of mucin layers on an amphiphilic diblock copolymer surface.
Both visible and infrared (IR) spectroscopic ellipsometry have been employed to study the structure of thin layers of bovine submaxillary mucin (BSM) adsorbed on poly(acrylic acid-block-methyl methacrylate) (PAA-b-PMMA) copolymer and poly(methyl meth... expand abstractacrylate) (PMMA) surfaces at three pH values (3, 7, and 10). The adsorbed mucin layer on the copolymer surface had the greatest thickness (17 nm) when adsorbed from a mucin solution at a pH of 3. For the first time, IR ellipsometry was used to identify adhesive interactions and conformational changes in mucin/polymer double layers. After applying the regularized method of deconvolution in the analysis, the formation of hydrogen bonds between the carboxyl groups of the BSM and PAA-b-PMMA copolymer in double layers has been found. The IR ellipsometry data, in agreement with the visible ellipsometry analysis, indicate the pH dependence of adhesion of mucin to the copolymer surface. There is an increase in the amount of hydrogen-bonded carboxyl groups in mucin deposited at a pH of 3. There is no evidence that the amide groups of the mucin participate in this bonding. At the lower pH, the IR ellipsometry spectra after deconvolution reveal an increase in the proportion of beta-sheets in the BSM upon adsorption on the copolymer surface, indicating a more unfolded, aggregated structure. The IR ellipsometry data also indicated some changes in the conformational states of the side groups in the copolymer induced by entanglements and bonding interactions with the mucin macromolecules. Deconvolution provides an unprecedented level of information from the IR ellipsometry spectra and yields important insights. collapse abstract
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Langmuir : the ACS journal of surfaces and colloids 2009 Apr; 25(8)
Protein nanopatterning on self-organized poly(styrene-b-isoprene) thin film templates.
Templated surfaces can be used to create patterns of proteins for applications in cell biology, biosensors, and tissue engineering. A diblock copolymer template, which contains a pair of hydrophobic blocks, has been developed. The template is created... expand abstract from well-ordered, nonequilibrium surface structures of poly(styrene-b-isoprene) (PS-b-PI) diblock copolymers, which are achieved in ultrathin films having a thickness of less than one domain period. Adsorption and nanopatterning of bovine serum albumin (BSA) on these thin films were studied. After incubation of the copolymer templates in BSA solutions (500 microg/mL) for a period of 1 h, BSA molecules formed either a striped or a dense, ringlike structure, closely resembling the underlying polymer templates. In this "hard-soft" PS-b-PI system, BSA molecules were preferentially adsorbed on the hard PS domains, rather than on the soft PI domains. Secondary ion mass spectroscopy (SIMS) and contact angle analysis revealed that, with more PI localized at the free surface, fewer BSA molecules were adsorbed. SIMS analysis confirmed that BSA molecules were adsorbed selectively on the PS blocks. This is the first example of two hydrophobic blocks of a diblock copolymer being used as a protein patterning template. Previously reported diblock copolymer templates used hydrophilic and hydrophobic pairs. A potentially useful characteristic of this template is that it is effective at high protein solution concentrations (up to 1 mg/mL) and for long incubation times (up to 2 h), which broadens its range of applicability in various uses. collapse abstract
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ACS applied materials & interfaces 2009 Feb; 1(3)
pH dependence of the properties of waterborne pressure-sensitive adhesives containing acrylic acid.
Polymer colloids are often copolymerized with acrylic acid monomers in order to impart colloidal stability. Here, the effects of the pH on the nanoscale and macroscopic adhesive properties of waterborne poly(butyl acrylate-co-acrylic acid) films are ... expand abstractreported. In films cast from acidic colloidal dispersions, hydrogen bonding between carboxylic acid groups dominates the particle-particle interactions, whereas ionic dipolar interactions are dominant in films cast from basic dispersions. Force spectroscopy using an atomic force microscope and macroscale mechanical measurements show that latex films with hydrogen-bonding interactions have lower elastic moduli and are more deformable. They yield higher adhesion energies. On the other hand, in basic latex, ionic dipolar interactions increase the moduli of the dried films. These materials are stiffer and less deformable and, consequently, exhibit lower adhesion energies. The rate of water loss from acidic latex is slower, perhaps because of hydrogen bonding with the water. Therefore, although acid latex offers greater adhesion, there is a limitation in the film formation. collapse abstract
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The European Physical Journal - Special Topics 2009 Feb; 166(1)
An experimental test of the scaling prediction for the spatial distribution of water during the drying of colloidal films
A Peclet number, Pe, for the drying of colloidal films can be used as a predictor of the uniformity of water concentration in the direction normal to the film. Uniform drying is predicted to occur when Pe < 1, whereas with , a layer of packed par... expand abstractticles is expected to develop above a more dilute layer. Routh and Zimmerman have more recently proposed that the particle concentration gradient between the packed and dilute layers, , will scale as . Here, this scaling relation is tested experimentally with magnetic resonance profiling data obtained from waterborne colloidal films dried under conditions to yield a range of Pe. It is found that increases with Pe but scales as . This disagreement with the prediction can be attributed to an underestimate of Pe when there are greater non-uniformities of drying, because of an unquantified slowing down of the evaporation rate. collapse abstract
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AIChE Journal 2008 Nov; 54(12)
Lateral surface nonuniformities in drying latex films
The length scales of film thickness nonuniformities, commonly observed in polymer colloid (i.e., latex) films, are predicted. This prediction is achieved by investigating the stability behavior of drying latex films. A linear stability analysis is pe... expand abstractrformed on a base solution representing a uniformly drying latex film containing a surfactant. The analysis identifies film thickness nonuniformities over two length scales: long (millimeter) range (from lubrication theory) and short (micrometer) range (from nonlubrication theory). Evaporation and surfactant desorption into the bulk film are identified as the primary destabilizing mechanisms during drying. Experimental evidence through direct visualization and atomic force microscopy confirm the existence of nonuniformities over both length scales, which are shown to be functions of parameters such as initial particle volume fraction, surfactant amount, and desorption strength, while being independent of drying rate. © 2008 American Institute of Chemical Engineers AIChE J, 2008 collapse abstract
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Macromolecules 2008 Nov; 41(22)
Correlation of Silicone Incorporation into Hybrid Acrylic Coatings with the Resulting Hydrophobic and Thermal Properties
A series of high-solids hybrid silicone−acrylic latexes, with varying silicone concentrations and reactivities, was prepared via miniemulsion polymerization. The properties of the resulting coatings have been correlated with their structure and... expand abstract the extent of silicone grafting. The highest silicone incorporation was obtained with silicones containing two reactive vinyl groups polymerized by a semicontinuous method with a delayed addition of neat monomer. It was found that the amount of silicone grafted to the acrylic chains, not the overall total amount in the formulation, was the main factor affecting film properties. Hydrophobicity, water resistance, and thermal stability all increased with the amount of grafted silicone. Coatings that contained high levels of nongrafted silicone displayed separate submicrometer silicone phases and exhibited inferior properties. When silicone was incorporated into the acrylic particles, the total drying time of the coating was shorter, and the water distributionas deter... collapse abstract
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Macromolecules 2008 Oct; 41(20)
Importance of Molecular Friction in a Soft Polymer−Nanotube Nanocomposite
The effects of physisorbed polymer molecules on carbon nanotubes dispersed in a soft polymer matrix on the resulting mechanical strength of the nanocomposite are reported. From measurements of the large-strain deformation of the nanocomposites, the s... expand abstracthear strength, τ, of the nanotube/matrix interface was determined as a function of the interfacial polymer chain length and the chain density, Σ. The results show that the value of τ (per chain) increases with increasing chain length. τ likewise increases with Σ but then levels off above a critical value. These results are explained by the molecular friction of the adsorbed polymer chains sliding along the rubbery polymer matrix. The results can be used to guide the interfacial design of polymer nanocomposites to obtain ultimate macroscopic mechanical control. In particular, the monomeric friction coefficient, ξ1, could be used to adjust the macroscopic properties of this type of nanocomposite. collapse abstract
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Advances in colloid and interface science 147-148
Design and fabrication of colloidal polymer nanocomposites.
It is well established that colloidal polymer particles can be used to create organised structures by methods of horizontal deposition, vertical deposition, spin-casting, and surface pattern-assisted deposition. Each particle acts as a building block... expand abstract in the structure. This paper reviews how two-phase (or hybrid) polymer colloids can offer an attractive method to create nanocomposites. Structure in the composite can be controlled at the nanoscale by using such particles. Methods to create armored particles, such as via methods of hetero-flocculation and Pickering polymerization, are of particular interest here. Polymer colloids can also be blended with other types of nanoparticles, e.g. nanotubes and clay platelets, to create nanocomposites. Structure can be controlled over length scales approaching the macroscopic through the assembly of hybrid particles or particle blends via any of the various deposition methods. Colloidal nanocomposites can offer unprecedented long-range 2D or 3D order that provides a periodic modulation of physical properties. They can also be employed as porous templates for further nanomaterial fabrication. Challenges in the design and control of the macroscopic properties, especially mechanical, are considered. The importance of the internal interfacial structure (e.g. between inorganic and polymer particles) is highlighted. collapse abstract
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Langmuir : the ACS journal of surfaces and colloids 2008 Jul; 24(14)
Heterogeneous drying of colloidal polymer films: dependence on added salt.
Using magnetic resonance profiling coupled with dynamic light scattering, we have investigated the mechanisms leading to the formation of a partly coalesced surface layer, or "open skin", during film formation from waterborne polymer dispersions. We ... expand abstractpresent the first use of the skewness of the distribution of free water as a model-free indicator of the spatial nonuniformity of drying. The skewness reaches a maximum at the same time at which a strong, static component, presumably originating from a skin at the film/air interface, appears in the light scattering data. Addition of salt to the dispersion increases both the skewness of the distribution of free water and the propensity for skin formation. Surprisingly, the drying is influenced not only by the concentration and valency of the ions in the salt but also by the particular ion. At intermediate particle densities, added salt strongly lowers the cooperative diffusion coefficient, Dcoop. When the particles reach close packing, Dcoop sharply increases. If the particles readily coalesce, the effects of the increased diffusivity will be counteracted, thereby inducing the formation of a skin. A modified Peclet number, Pe, using Dcoop, is proposed, so that the presence of salt is explicitly considered. This modified Pe is able to predict the nonuniformity in drying that leads to skin formation. collapse abstract
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Journal of Coatings Technology and Research 2008 Apr; 5(3)
The diacetone acrylamide crosslinking reaction and its influence on the film formation of an acrylic latex
Waterborne colloidal polymers (i.e. latex) represent a promising alternative to organic solvent-based systems in coatings applications. The development of mechanical strength and hardness is often enhanced by chemical crosslinking that creates a thre... expand abstracte-dimensional network. If extensive crosslinking occurs within the particles prior to their coalescence, however, interdiffusion will be prevented. A weaker product will result. We have explored the inter-relationship between coalescence, crosslinking, and surfactant exudation in an acrylic latex containing diacetone acrylamide exploiting the “keto-hydrazide” crosslinking reaction. The complementary use of spectroscopic techniques on a model system determined that the crosslinking reaction yields an imine, not an enamine as has been proposed in some literature. Gel fraction measurements were used to probe the rate and amount of crosslinking and identified a slower rate in larger particles, suggesting that the transport of crosslinking agent is rate-limiting. The keto-hydrazide reaction was found to be acid catalyzed and favored at lower water concentration. Measurement of the latex pH relative to the polymer mass fraction during film formation clarified the expected point of onset for crosslinking in relation to particle packing. Atomic force microscopy was used to follow surface leveling relative to the competing influence of crosslinking. The rate and total amount of surfactant exudation were found to be influenced by crosslinking, particle deformability (as determined by the temperature relative to the polymer glass transition temperature), and the evaporation rate (as controlled by the relative humidity). There is evidence that surfactant exudation can be triggered by the particle deformation that occurs at film formation temperatures well above the glass transition temperature. Keywords Crosslinking - Diacetone acrylamide - Film formation - Keto-hydrazide - Surfactant 2007 Roon Awards winner, presented at 2007 FutureCoat! Conference, sponsored by Federation of Societies for Coatings Technology, October 3–5, 2007, in Toronto, Ontario, Canada. collapse abstract
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Advanced Materials 2008 Jan; 20(1)
A Molecular Mechanism for Toughening and Strengthening Waterborne Nanocomposites
A high molecular-weight polymer – not a small molecule or surfactant – is superior for dispersing carbon nanotubes in water when processing a waterborne, polymeric nanocomposite. A polymeric dispersant above its entanglement molecular wei... expand abstractght creates a brush structure on the nanotube that increases molecular friction on entangles with the matrix, yielding increased adhesion energy, as shown, along with greater toughness and energy dissipation during deformation. A dispersant can thereby be used to tune a nanocomposite's mechanical properties. collapse abstract
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Journal of Coatings Technology 2007 Nov; 73(912)
Nano-mechanical properties and topography of thermosetting acrylic powder coatings
Both nano-scratching and nano-indentation techniques have been used to evaluate the mechanical properties of the surface of acrylic coatings, with and without added pigment. The coatings were formed from thermosetting, acrylic powders. Both types of ... expand abstractcoatings—clear and pigmented—do not exhibit any significant differences in their hardness with an increase in baking time from 7 to 15 min. According to the scratching profiles, the deformation induced at the surface is virtually elastic. Introducing the pigment causes a slight increase in the elastic modulus but no significant variation in hardness. In all coatings, the computed hardness and the elastic modulus values are higher near the surface (perhaps as a result of tip geometry effects), but these readily reach plateau values that are consistent with other work available in the literature. A long-range surface profiler, which provided two-dimensional and three-dimensional topographical maps of the coating surfaces, reveals undulations in the surface with a wavelength on the order of 2–4 mm. Moreover, the topography of the pigmented coating is significantly smoother than that of the clear coating in which shallow pits (about 100 µm in diameter) are randomly distributed at the surface. The nano-mechanical properties within these pits are similar to the bulk of the coating. School of Physics and Chemistry, Guildford, Surrey, GU2 7XH, UK. collapse abstract
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Journal of Coatings Technology 2007 Nov; 74(933)
Influence of drier combination on through-drying in waterborne alkyd emulsion coatings observed with magnetic resonance profiling
Achieving fast and uniform crosslinking in alkyd coatings poses a challenge to formulators that demands a fundamental understanding of drier efficiency. In recognition of this, we have examined the physical changes that accompany autooxidative crossl... expand abstractinking in alkyd films (cast from waterborne emulsions) in the presence of various combinations of metal carboxylate driers. A newly developed type of magnetic resonance (MR) profiling was used in conjunction with conventional techniques: Beck-Koller drying tests, pendulum hardness, and mass uptake. MR profiling noninvasively probes the molecular mobility of the alkyd as a function of depth (with a pixel resolution of about 9 µm), over drying times ranging from minutes to weeks. It thereby indicates drier efficiency via its sensitivity to viscosity build-up during drying and to subsequent film hardening. We show unequivocally that more uniform crosslinking is achieved using a combination of a primary (Co) and a secondary (Ca) drier, in support of conventional belief. Furthermore, these results yield new insight into the chemical mechanisms induced by the driers and are thus of clear benefit to coatings researchers and formulators. Notably, the secondary driers improve the efficiency of the hydroperoxide decomposition reactions, but they are only active during an initial period, after which crosslinking nonuniformity develops. Presented at the 79th Annual Meeting of the Federation of Societies for Coatings Technology, Nov. 3–5, 2001, in Atlanta, GA. collapse abstract
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Journal of Applied Polymer Science 2007 Oct; 106(1)
An alternative approach to the modification of talc for the fabrication of polypropylenetalc composites
We report an alternative method to modify talc for use in the fabrication of composites of polypropylene (PP) and talc. Grinding pulverization is employed to prepare talc fillers (referred to hereafter as p-talc). The properties of composites made wi... expand abstractth p-talc compare favorably with composites made with pulverized talc that has been further treated with a silane coupling agent (referred to as s-talc). The morphology of PP/p-talc composites illustrates particle orientation and a uniform dispersion of pulverized talc in the PP matrix. Modulated DSC analysis shows the ability of p-talc and s-talc to nucleate PP crystallization. The mechanical properties (i.e., the dynamic modulus, tensile strength, and impact resistance) of the PP/p-talc composites are very similar to PP/s-talc composites. The modification of talc by grinding is thus a highly effective alternative method to prepare PP/talc composites that does not require chemical treatment of the talc. The pulverization method is simpler and less expensive in comparison to silane treatment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 collapse abstract
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Langmuir : the ACS journal of surfaces and colloids 2007 Sep; 23(19)
Absorption of cetylpyridinium chloride into poly(N-isopropylacrylamide)-based microgel particles, in dispersion and as surface-deposited monolayers.
The addition of cetylpyridinium chloride (CPC) to aqueous dispersions of poly(N-isopropylacrylamide) [poly(NIPAM)] and poly(N-isopropylacrylamide-co-acrylic acid) [poly(NIPAM-co-AAc)] microgel particles leads to absorption of the CPC into the particl... expand abstractes and to corresponding changes in their hydrodynamic diameter. With the latter set of particles there is a strong pH dependence. The dependence of both hydrodynamic diameter and electrophoretic mobility of the microgel particles on the added CPC concentration show a strong correlation with CPC uptake, as obtained from direct CPC absorption measurements. Various mechanisms for CPC absorption into the microgel particles are postulated, including electrostatic, polar, and hydrophobic interactions. A comparison has also been made between the effect of added CPC on the hydrodynamic diameter of free microgel particles in dispersion, determined by dynamic light scattering, and the thickness of adsorbed monolayers of the same microgel particles deposited on cationically modified, oxidized silicon surfaces, as determined from ellipsometry measurements. The trends observed in both cases are broadly similar. This work opens the way for development of microgel layers for controlled uptake and release applications. collapse abstract
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Journal of materials science. Materials in medicine 2007 Dec; 19(1)
Protein adsorption on materials for recording sites on implantable microelectrodes.
Implantable microelectrodes have the potential to become part of neural prostheses to restore lost nerve function after nerve damage. The initial adsorption of proteins to materials for implantable microelectrodes is an important factor in determinin... expand abstractg the longevity and stability of the implant. Once an implant is in the body, protein adsorption takes place almost instantly before the cells reach the surface of an implant. The aim of this study was to identify an optimum material for electrode recording sites on implantable microelectrodes. Common materials for electrode sites are gold, platinum, iridium, and indium tin oxide. These, along with a reference material (titanium), were investigated. The thickness and the structure of adsorbed proteins on these materials were measured using a combination of atomic force microscopy and ellipsometry. The adsorbed protein layers on gold (after 7 and 28 days of exposure to serum) were the smoothest and the thinnest compared to all the other substrate materials, indicating that gold is the material of choice for electrode recording sites on implantable microelectrodes. However, the results also show that indium tin oxide might also be a good choice for these applications. collapse abstract
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Journal of colloid and interface science 2007 Feb; 307(1)
Probing particle structure in waterborne pressure-sensitive adhesives with atomic force microscopy.
There is a need to know the nanostructure of pressure-sensitive adhesive (PSA) films obtained from waterborne polymer colloids so that it can be correlated with properties. Intermittent-contact atomic force microscopy (AFM) of an acrylic waterborne P... expand abstractSA film identifies two components, which can be attributed to the polymer and the solids in the serum (mainly surfactant). It is found that when the average AFM tapping force, F(av), is relatively low, the polymer particles appear to be concave. But when F(av) is higher, the particles appear to have a convex shape. This observation is explained by a height artefact caused by differences in the indentation depths into the two components that vary with the tapping amplitude and F(av). To achieve the maximum contrast between the polymer and serum components, F(av) should be set such that the indentation depths are as different as possible. Unlike what is found for the height images, the phase contrast images of the PSA do not show a reversal in contrast over the range of tapping conditions applied. The phase images are thus reliable in distinguishing the two components of the PSA according to their viscoelastic properties. At the surface of films dried at room temperature, the serum component is found in localized regions within permanent depression into the film. collapse abstract
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