Thermoacoustic properties of methyl esters ofn-alkanoic acids

A number of thermoacoustic parameters, including the Sharma constant S₀, the isochoric temperature coefficient of volume expansivity (d Inα/d InT)_V, the isochoric temperature coefficient of internal pressure (d InP _i/d InT)_V, reduced volume V, reduced compressibility β and the Huggins parameter F, are estimated by using only the volume expansivity α from the density temperature data for a number of methyl esters ofn-alkanoic acids. The methyl esters give excellent separation of saturated fatty acid mixtures. The Sharma constant, which relates the molecular constantn and other thermoacoustic parameters, is a constant with a characteristic value of 1.11+0.01 for all these esters.     

Transport parameters and solubility coefficients of polymers at their glass transition temperatures

Many parameters of polymers exhibit breaks when temperature passes through glass transition. It is also often assumed that fractional free volume (FFV) at the glass transition temperature (T_g) has a standard value (the isofree volume concept). As gas diffusion (D) and permeability (P) coefficients depend on FFV, and mechanism of sorption and permeation is different above and below T_g, a question can be asked if D and P parameters of various gases in polymers have standard values at corresponding T_g, and, if not, how the values of D(T_g) and P(T_g) vary with T_g in different polymers. To examine this problem, two approaches were used: (1) extrapolation to T_g of numerous P and D values measured at ambient temperatures; (2) an analysis of direct data obtained in different polymers at their T_g. In both cases, qualitatively similar results were obtained: the D(T_g) and P(T_g) values increase with growing T_g independently of the nature of gas. Permselectivity P_i(T_g)/P_j(T_g) and selectivity of diffusion D_i(T_g)/D_j(T_g) are reduced when T_g increases. The dependence of the solubility coefficients S(T_g) = D(T_g)/P(T_g) is much weaker than those of D(T_g) and P(T_g). This conclusion was confirmed by the results of direct measurements of S in a wide range of temperature including T_g for several gas/polymer systems. An analysis of the results of positron annihilation studies of free volume in polymers led to the conclusion that the observed increases in the D(T_g) and P(T_g) values with T_g are caused mainly by thermal activation of diffusion processes at T_g. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1691–1705, 2000     

The influence of molecular weight distribution on melt viscosity,melt elasticity,processing behavior and properties of polystyrene

The influence of molecular weight and molecular weight distribution on the melt rheological behavior of two polystrenes of approximately the same weight average molecular weight, but of widely different molecular weight distribution, was determined. Then, using a series of capillaries with different length-to-diameter ratios in an Instron Capillary Rheometer, the entrance correction methods of E. B. Bagley and the relationships of W. Philippoff and F. H. Gaskins, the recoverable shear strain (S_R) in the melt at the capillary wall for these mono- and polydisperse polystyrenes was determined. Shear modulus (G) and normal stress (P_N) were calculated using the relationships: G = τ_RC/S_R and P_N = 2τ_RC S_R, where τ_RC is the corrected shear stress at the capillary wall. These are compared to values obtained using a Weissenberg Rheogonimeter. These two polystyrenes were also injection molded into an ASTM specimen mold over a wide range of stock temperature, using a 12 OZ . in-line reciprocating screw injection press, and evaluated for mechanical property values. The effects of the elasticity parameters (S_R G & P_N) and their magnitude on the rheology, processability and mechanical properties of these polystyrenes are discussed.     

Conductometric Probe Analysis of the Effect of Benzyldimethylhexadecylammonium Chloride on the Micellization Behavior of Dodecyltrimethylammonium Bromide in Aqueous/Urea Solution: Investigation of Concentration and Temperature Effect

Surfactant mixtures are used in many different industrial formulations. In this study, the mixed micelle formation behavior of 2 different cationic surfactants, namely dodecyltrimethylammonium bromide (DTAB) and benzyldimethylhexadecylammonium chloride (BDHAC), in the absence and presence of urea at various temperatures (298.15–318.15 K) was studied using the conductometric method. The attractive interaction between DTAB and BDHAC was estimated from the values of critical micelle concentration (CMC) and the CMC for ideal mixing (CMC^id). Urea increases the CMC value as a result of the enrichment in the surface charge of the micelles/mixed micelles. The values of micellar mole fraction (X₁^Rub [Rubingh], X₁^M [Motomura], X₁^Rod [Rodenas]) and ideal micellar (X₁^id) of surfactant BDHAC were obtained by different models and are shown to exhibit the high contribution or effective involvement of BDHAC in mixed micelles and increase with increasing BDHAC mole fraction (α₁). Activity coefficients (f₁ and f₂) were also evaluated from the relevant formula given in the literature. The negative values of the interaction parameters (β) show the attractive interaction among the studied components. Excess Gibbs free energy (?G_ex) of micellization revealed that the stability of mixed micelles is higher in aqueous solution than in urea solution. The thermodynamic parameters, namely the Gibbs free energy change, enthalpy change, and entropy change (?G^o_m, ΔH^o_m, and ?S^o_m, respectively), were also calculated from the conventional standard equations.     

Estimation of sharma constant and thermoacoustic properties of fatty acids

From the volume expansivity α, a number of thermoacoustic parameters, including the Sharma constant,S ₀, are estimated for four fatty acids as a function of temperature. The Sharma constant, which was established to be a constant with the characteristic value 1.11 ± 0.01 over a number of systems investigated by earlier investigators, is also found to be a constant with the same value for all fatty acids under investigation. Further, the Sharma constant,S ₀, is independent of temperature and dependent only on α. All other parameters estimated are discussed and compared with the values reported in the literature by earlier workers for different systems.     

A simple approach to the dielectric relaxation behaviour of a liquid crystalline polymer and its application to the determination of the director order parameter for partially aligned materials

A theory for the dielectric relaxation behaviour of a partially aligned liquid crystalline (LC) material is described. It is shown, quite generally, that the complex dielectric permittivity may be expressed in terms of the parallel (?_‖) and perpendicular (?_?) components for the permittivity of the mesophase and S_d, the director order parameter, where ?_‖ and ?_? may themselves be expressed in terms of molecular quantities, including S the mesophase order parameter. The theory is applied to experimental data for a nematic siloxane LC side-chain polymer. The consistency of the derived values of S_d provides experimental confirmation of our approach. In addition, dielectric isosbestic points are observed in both loss factor and capacitance data as the sample alignment is varied, providing further confirmation of our approach. The variation of S_d with time for a sample being realigned from planar to homeotropic in an electric field is determined from dielectric measurements and the form of S_d(t) is briefly discussed.     

Estimation of solubility parameter components of solutes and polymers using heat of vaporization and heat of sorption of solutes

In a recent study, a two‐dimensional solubility parameter model was used to correlate the heat of solution for solutes ranging from n‐alkanes to alcohols, dissolved in isotatic polypropylene (PP), poly(ethyl ethylene) (PEE), and poly(dimethylsiloxane) (PDMS). When literature data of solubility parameter components of solutes were used, the correlation had some scattering for solutes with low values of cohesive energy density. In this study, the components of solubility parameters of solutes and polymers were estimated from cohesive energy and heat of sorption of solutes. Good correlation was obtained for the specific heat of sorption (ΔU_sorp/V) for solutes ranging from n‐alkanes to alcohols, and PDMS had a polar component as previously estimated. Free volume effect in solution process may be the source of a small systematic deviation from the model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Physicochemical studies of globular proteins—Bovine serum albumin,egg albumin,and lysozyme—In some aqueous iodide salts solutions of IA group and cetyltrimethyl ammonium bromide systems

Densities (ρ, kg m^?3), and viscosities (η, 0.1 kg m^?1 s^?1) of Bovine Serum Albumin (BSA), Egg Albumin, and Lysozyme in aqueous iodide salts of lithium, sodium, and potassium, along with cationic surfactant‐cetyltrimethyl ammonium bromide (CTAB) were measured at a temperature of 303.15 K. The 0.0010–0.0018 g %, w/v of each protein at an interval of 0.0002 mol L^?1 in 0.2, 0.4, and 0.8 millimol L^?1 of salt and CTAB are studied. Data are used for apparent molar volumes (V_?, 10^?6 m³ mol^?1) and intrinsic viscosities ([η], dL kg^?1), respectively. Data are regressed and extrapolated to zero concentrations for ρ⁰, η⁰, and limiting values and S_d, S_η and S_V corresponding slopes for protein–salt structural interactions. With size of cations, the densities decrease as CTAB > LiI > NaI > KI and increase with salts concentrations, with salts the densities are as Lysozyme > BSA > Egg Albumin, viscosities and V_? as BSA > Egg–Albumin > Lysozyme. The ρ and η values with CTAB higher and [η] are lower and converse at around 0.4 mmol L^?1 salt and is effective for greater stability of proteins. The [η] in CTAB are higher than other salts and decreases with size of cations with stronger intermolecular forces. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Conformational analysis of serricornin: Application of molecular mechanics calculations to stereochemical assignment of serricornin,sex pheromone of cigarette beetle (Lasioderma serricorne F.)

Conformational analysis using molecular mechanics (MM) was performed for a determination of the stereochemistry of serricornin, the sex pheromone of the cigarette beetle (Lasioderma serricorne F.). An exhaustive conformational analysis using MM2 calculations with algorithms for covering torsional energy surfaces of flexible molecules furnishes coordinates and steric energies of all local energy minimum conformers of serricornin, both acyclic and the corresponding cyclic forms. These coordinates gave angles required for the calculation of vicinal H/H coupling constants (³ J _HHs) of each energy minima by Altona's modified Karplus equation. The Boltzmann distributions of all local energy minima were calculated from their steric energies to furnish populations of each energy minimum conformer. Populationweighted averaged³ J _HHs of four enantiomeric pairs, (S ^*,S ^*,S ^*)-, (S ^*,S ^*,R ^*)-, (S ^*,R ^*,S ^*)-, and (R ^*,S ^*,S ^*)-serricornins were calculated from the data above. The observed³ J _HHs of the naturally occurring serricornin, both acyclic and cyclic forms, are fitted best to calcd.³ J _HHs of (4S ^*, 6S ^*, 7S ^*)-acyclic and (3S ^*, 5S ^*, 6S ^*)-cyclic serricornin, respectively, among those of four enantiomeric pairs of serricornin.     

Correlation of low density polyethylene rheological measurements,with optical and processing properties

The processing properties of low density polyethylene melts, such as drawdown and neck-in, and the final product properties, such as film haze and gloss, have been successfully correlated with rheological functions and the level of longchain branching. The rheological functions employed are the entrance pressure drop ΔP_o and the swell ratio S_o, determined at a specified shear stress using aft-orifice with a length/ diameter (L/D) ratio of zero. The calculation of shear stress requires additional measurements using adie with a finite L/D e.g. 20. The rheological functions ΔP_o, and S_o are governed by the level of high molecular weight species and/or the level of long-chain branching(LCB). If determined at a constant shear stress, in order to eliminate the effect of viscosity, they are a relative measure of elasticity. Higher ΔP₀ and S_o indicate a higher level of LCB and correlate with poorer optical properties and drawdown in films.     

Theoretical Approaches on the Synergistic Interaction between Double-Headed Anionic Amino Acid-Based Surfactants and Hexadecyltrimethylammonium Bromide

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, −aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X^σ), interaction parameters at the bulk/interface (β^R/β^σ), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (α_AAS), the magnitude of the (β^R/β^σ) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing α_AAS, the micellar mole fraction of HTAB (X₂) decreased insignificantly and X₂ values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS () differed from micellar mole fraction of AAS (X₁), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( ∆G_m ) values are more negative than the free energy of micellization for ideal mixing (), indicating the micellization process is spontaneous. With increasing α_AAS, the enthalpy of micellization (ΔH_m) and entropy of micellization (ΔS_m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.     

Estimation of the sharma constant and thermoacoustic properties of vegetable oils

The density and volume of four Indian edible vegetable oils, sunflower, rice bran, groundnut and coconut, and one Indian nonedible oil, castor oil, have been experimentally determined. The values obtained were used to estimate the volume expansivity α, hence the thermoacoustic parameters, such as the Sharma constantS ₀, the isochoric temperature coefficient of internal pressure , the isochoric temperature coefficient of volume expansion , reduced volume , reduced compressibility and the Huggins parameter F. The results obtained show that the Sharma constantS ₀ has the same characteristic value of 1.11±0.01 for the five oils, thus establishing the constancy of the Sharma parameter. All the other parameters are of the expected order of magnitude; however, in all cases there is a uniform deviation at 293°K, which can be attributed to the behavior of density and volume at this temperature.     

Synthesis,Characterization, and Metabolism Studies of Fluspidine Enantiomers

The enantiomers of the potent σ₁ ligand fluspidine ( 1 ) were prepared by using chiral preparative HPLC. Synthesis of racemic tosylate 2 and subsequent separation of enantiomers yielded (R)‐ 2 and (S)‐ 2 in excellent enantiomeric purities. The fluspidine enantiomers (R)‐ 1 and (S)‐ 1 were synthesized from (R)‐ 2 and (S)‐ 2 by nucleophilic substitution with tetra‐n‐butylammonium fluoride, affording (R)‐ 1 with 99.6 % ee and (S)‐ 1 with 96.4 % ee. Tosylates (R)‐ 2 and (S)‐ 2 can also serve as precursors for the radiosynthesis of enantiomerically pure radiotracers [¹⁸F](R)‐ 1 and [¹⁸F](S)‐ 1 . The absolute configuration of the pure enantiomers was elucidated by comparison of their CD spectra with a calculated CD spectrum of a simplified model compound. In receptor binding studies, both enantiomers displayed very high σ₁ receptor affinity and selectivity against the σ₂ receptor. (R)‐Fluspidine ((R)‐ 1 ) is the eutomer, with a K_i value of 0.57 nM and a eudysmic ratio of 4. Incubation of (R)‐ 1 and (S)‐ 1 with rat liver microsomes led to the identification of seven and eight metabolites, respectively. Although the S‐configured enantiomer formed additional metabolite (S)‐ 1‐3 , it is metabolically more stable than (R)‐ 1 .     

A Study of Sodium–Copper and Sodium–Nickel Polyphosphate Glasses by Differential Scanning Calorimetry1

Sodium polyphosphate and sodium–copper and sodium–nickel copolyphosphate glasses (with the ratio Na : M = 9 : 1 and 8 : 2, where M is Cu or Ni) are studied. The glass transition (T _g) and melting (T _m) temperatures are determined by differential scanning calorimetry (DSC). It is revealed that the T _gand T _mtemperatures depend on the molecular weight M _t(determined from terminal groups) of polymeric glasses, the Na : M ratio, and the glass synthesis conditions. The activation energies are calculated, and the thermodynamic parameters H, S, and C _pare measured.     

Dielectric relaxation and thermodynamic properties of polyvinylpyrrolidone using time domain reflectometry

Temperature‐dependent values of dielectric permittivity ε′ and dielectric loss ε″ of polyvinylpyrrolidone (PVP, commercialized as PVP K‐60) solution of average molecular weight 160 000 g mol^?1 were measured. The measurements were carried out in the frequency range 10 MHz to 20 GHz using time domain reflectometry at temperatures from 25 to 0 °C. The dielectric spectra can be described by the Davidson‐Cole model. Dielectric parameters such as the static dielectric constant ε₀, the high frequency limiting dielectric constant ε_∞, the relaxation time τ₀ and the distribution parameter β and thermodynamic parameters such as the free energy of activation ΔF_τ, the enthalpy of activation ΔH_τ and the entropy of activation ΔS_τ were determined. The average free energy of activation was found to be in the range 12.55–14.65 KJ mol^?1 and the enthalpy of activation was found to be 6.86 KJ mol^?1. Entropies of activation were found to be positive at all the measured temperature values and these large positive values of entropies reveal a less ordered structure of the PVP solution. The Kirkwood correlation factor g and the dipole moment µ were also determined for PVP solution. The results were compared with the results of the PVP‐water system studied previously. Copyright © 2011 Society of Chemical Industry     

Preparation of vinyl polymers bearing photo‐labile diethylthiocarbamoylthiyl (S2CNEt2) groups via ATRP

Direct synthesis of vinyl polymers functionalized with photo‐labile diethylthiocarbamoylthiyl (S₂CNEt₂) groups was reviewed via three living polymerization procedures: normal atom‐transfer radical polymerization (ATRP), reverse ATRP and photo ATRP. The S₂CNEt₂ group was transferred by mediating the dormant–active species equilibrium in the course of polymerization and eventually ω‐terminating the resulting polymer chain. ATRP of methyl methacrylate (MMA) was successfully performed with a p‐toluenesulfonyl chloride/Cu(S₂CNEt₂)/2,2′‐bipyridine(bpy) or benzoyl peroxide (BPO)/Cu(S₂CNEt₂)/bpy initiation system. The oxidized complex, Cu(S₂CNEt₂)Cl/bpy, catalyzed the reverse ATRP of vinyl monomers initiated with BPO or 2,2′‐azobisisobutyronitrile (AIBN), producing tailor‐made polymers with ω‐S₂CNEt₂ groups and a narrow molecular‐weight distribution. Without external ligands, the living polymerization of vinyl monomers was achieved under the thermal initiation of diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS) in conjunction with Fe(S₂CNEt₂)₃ catalyst. Photo ATRP of MMA and styrene was first realized in the presence of 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA)/Fe(S₂CNEt₂)₃ under UV irradiation at ambient temperature. Copyright © 2004 Society of Chemical Industry     

Mark–Houwink equation and GPC calibration for linear short-chain branched polyolefines,including polypropylene and ethylene–propylene copolymers

The reduction in molecular dimensions due to the presence of short side chains in otherwise linear polyolefins can very simply by calculated by assuming that the configuration of the main chain is not influenced by the side chains. This enables us to express the intrinsic viscosity–molar mass relationship as a function of the mass fraction of side chains (S): [η] = (1 ? S)^α+1K_PEM_ν^α and, with use of the universal calibration principle, to convert the GPC calibration for purely linear polymers samples into the calibration for short-chain branched polymers: M^* = (1 ? S)M. Experimental data from literature on short-chain branched poly-ethylenes, and our own data on ethylene–propylene copolymers are used to verify the above assumption. It appears that the experimentally found relations between [η], M_w and M^*_w (GPC) within the usual accuracy justify this approach.     

Molecular dissolution behaviors on porous membrane surface using hierarchical metal–organic framework lamellar membrane

Lamellar membranes, especially assembled by microporous framework nanosheets, have excited interest for fast molecular permeation. However, the underlying molecular dissolution behaviors on membrane surface, especially at pore entrances, remain unclear. Here, hierarchical metal–organic framework (MOF) lamellar membranes with 7 nm-thick surface layer and 553 nm-thick support layer are prepared. Hydrophilic (–NH₂) or hydrophobic (–CH₃) groups are decorated at pore entrances on surface layer to manipulate wettability, while –CH₃ groups on support layer provide comparable, low-resistance paths. We demonstrate that molecular dissolution behaviors are determined by molecule–molecule and molecule–pore interactions, derived from intrinsic parameters of molecule and membrane. Importantly, two dissolution model equations are established: for hydrophobic membrane surface, dissolution activation energy (E_S) obeys E_S = K_mln[(γ_L-γ_C)μd²], while turns to E_S=K_aln[(γ_L-γ_C)δ_eμd²] for hydrophilic one. Particularly, hydrophilic pore entrances exert strong interaction with polar molecules, thus compensating the energy consumed by molecule rearrangement, giving fast permeation (>270 L m⁻² h⁻¹ bar⁻¹).     

Parameters,affecting the sensitivity of poly(methyl methacrylate) as a positive lithographic resist

The contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/S_o = S_R, of the exposed, S, and unexposed, S_o, material. The G-value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with S_R than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n-alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n-alkyl acetates which enhanced the sensitivity of PMMA.