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Using all-atom molecular simulation, a wide range of plasticizers for poly(vinyl chlorid) (PVC), including ortho- and tere-phthalates, trimellitates, citrates, and various aliphatic dicarboxylates, are systematically studied. We focus on the effects of plasticizer molecular structure on its performance, as measured by performance metrics including its thermodynamic compatibility with PVC, effectiveness of reducing the material's Young's modulus, and migration rate in the PVC matrix. The wide variety of plasticizer types covered in the study allows us to investigate the effects of seven molecular design parameters. Experimental findings about the effects of plasticizer molecular design are also compiled from various literature sources and reviewed. Comparison with experiments establishes the reliability of our simulation predictions. The study aims to provide a comprehensive set of guidelines for the selection and design of high-performance plasticizers at the molecular level. Molecular mechanisms for how each design parameter influences plasticizer performance metrics are also discussed. Moreover, we report a nontrivial dependence of plasticizer migration rate on temperature, which reconciles seemingly conflicting experimental reports on the migration tendency of different plasticizers.

Colored poly(vinyl chloride) (PVC) was fabricated by femtosecond laser micromachining without the addition of chemical colorants, eliminating the concern of leaching dyes and pigments. We determined that the changes in surface chemistry and surface topography both contribute to the observed yellow, brown, and black color formation. X-ray photoelectron spectroscopy (XPS) on the machined samples showed that conjugated double bonds are liable for the yellow and brown colors, whereas the presence of oxidized carbon and surface topography contribute to the black color. Fourier transform infrared spectroscopy (FTIR) indicated that laser irradiation altered the material’s properties only near the surface, which left the bulk properties unaltered. Furthermore, chemical resistance tests showed that some of the samples were able to withstand the influence of aggressive chemicals and their color did not fade. Finally, we showed that the fabrication of colored PVC highly depends on its ablation energy threshold which...

Using full-atom molecular simulation, we report the first systematic investigation of common phthalate plasticizers for PVC. A multistep model generation and equilibration protocol are proposed for amorphous polymer–plasticizer mixtures, from which statistically robust prediction of materials properties is achieved. Plasticizer performance is evaluated with our molecular models, which considers both their plasticization efficacy and thermodynamic compatibility with the host polymer. Effects of the alkyl side chain configuration in these phthalates are systematically discussed. The results agree well with all known experimental observations. In addition to the size of the alkyl chains, their branching configuration is another factor affecting the phthalate compatibility with PVC. Relaxation of the alkyl side chains is found to be the limiting step in the diffusion of phthalates in PVC, making it a key design parameter for better migration resistance. With the addition of plasticizers, the dynamics of PVC backbones remain the same in the short-time relaxation process, but an earlier onset of the cooperative motion between molecules allows it to enter the long-time diffusive regime earlier. The main outcomes of this study include (1) a molecular modeling protocol validated with commonly used phthalates, which can be used to predict the performance of alternative plasticizers, and (2) molecular insight that can better inform the molecular design of new plasticizers. As a side outcome, we also report a nontrivial chain-length dependence of the cohesive energy and solubility parameter of long-chain polymers, which is an important consideration in the calculation of these quantities using molecular simulation. (NSERC) Natural Sciences and Engineering Research Council of Canada: RGPIN-4903-2014, EGP-492469-2015, CRDPJ- 514051-17; (CSC) China Scholarship Council:No. 201500090106.

This initial study shows that hydrophobic modification of guar polymers used in eye drops forms weak gels with human serum albumin (HSA), suggesting that modified guar may offer advantages for treatment of dry eye diseases that lead to elevated HSA concentrations in tears. Specifically, hydroxypropyl guar samples were oxidized and derivatized with linear alkyl amines to give a series of modified guar polymers (MGuar) bearing hydroxypropyl, N-alkylamide, and carboxyl moieties. MGuar interactions with lysozyme and HSA were measured by binding and rheological methods as functions of the alkyl chain length and the extent of hydrophobic modification. HSA binds MGuar, giving weak gels, whereas lysozyme shows little tendency to bind MGuar or to interfere with HSA binding. Six mole percent substitution of decyl hydrophobes gave the strongest gels in the presence of HSA.

In this study, effect of curing program on the corrosion performance of un-pigmented polyester and epoxy polyester powder coatings was evaluated, using various test methods. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) studies were carried out to determine suitable time –temperature curing program. Protective behavior of cured powder coatings in optimum situation was investigated, using different test techniques such as electrochemical impedance spectroscopy (EIS), water vapour transmission (WVT), and open circuit potential (OCP) variation as a function of time. EIS studies and OCP evaluation revealed that the polyester/epoxy powder coated samples demonstrated a better performance than polyester powder coated samples, due to higher cross-linked density of epoxy based powder. It is argued that these studies may provide sufficient evidence to show that protective characteristics of coatings is definitely influenced by cross-linking density so that more efficient coatings are ones with higher cross-link density. DMTA revealed that the different curing regimes do not affect the glass temperature of the given powder coatings.

Interactions of three oil-in-water emulsion types with polystyrene-coated quartz crystal microbalance (QCM) sensor surfaces were probed with the QCM cell in both the conventional orientation (i.e., polystyrene surface on the bottom, "looking up") and the inverted orientation (polystyrene on top interior surface of sensor chamber, "looking down"). With the conventionally oriented QCM sensors, the adsorption of soluble and/or dispersed species quickly gave steady-state frequency and dissipation outputs. By contrast, the inverted sensors gave changing responses at long times because of the gravity driven buildup of a viscous consolidation layer next to but not necessarily bound to the sensor surface. Three emulsion types (a simple hexadecane/phosphatidylcholine emulsion, 2% homogenized milk, and a diluted commercial ophthalmic emulsion) displayed a wide range of behaviors. We propose that quiescent QCM measurement made with an inverted sample chamber is a new approach to probing emulsion behaviors near solid surfaces.

The thermal behaviour of an epoxy/polyester hybrid and a polyester clear powder coatings was evaluated by means of Differential Scanning Calorimetry (DSC). The effect of curing temperature on the coating glass transition temperature (Tg) was also studied using a Dynamic Thermo-Mechanical Analyser (DMTA). The DSC method allows the explanation of powder coating systems. The procedures established enable to clearly identify the periods of melting, flow, onset cure and concluding curing, all parameters affecting the visual aspect as well as the durability of a powder coating. Experiments revealed that Tg is dependent on the heating rate in DSC and on the rate of application of stress, the frequency of oscillation and the rate of heating in the dynamic tests. Dynamic mechanical thermal analyses revealed that the different curing regimes do not affect considerably on the Tg of the given powder coating samples. DMTA also showed that the rigidity of the polymer structure does not increase significantly with increasing curing temperature.

The formulation of dilute, transparent ophthalmic emulsions (eye drops) with long shelf lives is a challenge because of the tendency of the emulsion droplets to aggregate, particularly in the presence of the water-soluble polymers typically used in eye drops. While many functions of eye drops, such as lubricity and residence time in the eye, are promoted by high concentrations of high molecular weight water-soluble polymers, emulsified lipids and drugs aggregate in the eye drop bottle if the polymer concentration is above the critical flocculation concentration (CFC). The purpose is to develop a simple approach to predict the CFC for polymers based on information readily available in the literature. High molecular weight guar was hydrolyzed to give a series of guar samples spanning a wide range of average molecular weights. The CFC values and critical viscosity concentrations were measured as functions guar properties, using electrophoresis, dynamic light scattering and rheology measurements. The higher the guar molecular weight, the lower was the CFC, the maximum concentration that can be tolerated in the eye drop formulation. The guar CFC values were approximately equal to the overlap concentrations where guar molecules start to overlap in solution. We propose that the CFC can be estimated for any water-soluble polymer using the polymer molecular weight and the readily available Mark–Houwink parameters, thus providing a design rule for ophthalmic emulsions.