Effect of selenium-position on the redox responsivity of isomeric selenium-containing anionic surfactants

The effect of Se-position on the redox responsivity of three isomeric selenium-containing surfactants (C_mSeC_nSO₄Na, n = 3, 8, and 11, m + n = 15) was investigated under the conditions of monomer, micelle, and adsorbed layer at the liquid paraffin-water interface. The divalent selenide group in C_mSeC_nSO₄Na (the reduction form, C_mSeC_nSO₄Na-Re) was oxidized to a more hydrophilic tetravalent selenoxide by the oxidation with H₂O₂ to afford C_mSeOC_nSO₄Na (the oxidation form, C_mSeC_nSO₄Na-Ox), and the selenoxide group of C_mSeC_nSO₄Na-Ox could be reduced to selenide by the reduction with Na₂SO₃ to form C_mSeC_nSO₄Na-Re again. In the oxidation process of the monomeric C_mSeC_nSO₄Na in water, no obvious difference in the oxidation responsivity among three Se-position isomers was observed. In contrast, a remarkable effect of the Se-position on the oxidation responsivity was observed in the cases of C_mSeC_nSO₄Na self-assemblies, including micelles and adsorbed layers at the liquid paraffin-water interface. Both the steric hindrance of the well-organized self-assemblies and the hydrophobic microenvironment of the selenide group in the self-assemblies hindered the Se atom from reacting with H₂O₂. The greater n, the harder was the oxidation of Se with H₂O₂. In the reduction process of C_mSeC_nSO₄Na-Ox, the hydrophilic selenoxide group was exposed outright to water, allowing the selenoxide group to readily react with Na₂SO₃ regardless of whether C_mSeC_nSO₄Na-Ox was self-assembled or not.     

Permeation of alkylbenzene isomers of molecular weight 120 through nitrile gloves

Factors determining the permeation of eight alkylbenzene isomers of molecular weight 120.19 (three ethyl toluenes, three trimethylbenzenes, and two propl benzenes) were investigated for a lined nitrile industrial type glove using an ASTM-type cell, liquid collection, and gas chromatography/mass spectrometry. The initial permeation rate P_i correlated inversely with the logarithm of the lag time t_l. The logarithm of the steady-state permeation rate P_s correlated inversely with the logarithm of the breakthrough time t_b. P_s/P_i for a given compound correlated directly with P_s and with t_l/t_b. P_i depended directly on the logarithm of the entropy of fusion divided by the square of the refractive index and divided by the solubility parameter. The t_b was inversely correlated to the logarithm of the water solubility. The logarithm of t_l was most directly correlated to the entropy of vaporization. High P_s for 1,2,4-trimethylbenzene, m-ethyltoluene, and p-ethyl toluene was linked to a common structural similarity to 1,2,4-trimethylbenzene relative to the unhindered geometry of the methyl group in the ethyl side chain. The existence of optimum radii of gyration for enhanced P_s and for long t_b suggested that the protective properties of nitrile followed discontinuous relationships rather than continuous ones and so are not explainable by correlative relationships of continuous functions. © 1996 John Wiley & Sons, Inc.     

Fourier transform infrared spectroscopic study of transitions above Tg in atactic polystyrene

Fourier transform infrared spectroscopy (FT-IR) has been applied to the study of the molecular mechanisms of transitions of atactic polystyrene above T_g. Intensity measurements of vibrational modes as a function of temperature revealed two transitions above T_g, which are designated as T_u and T′_u. T′_u is independent of molecular weight as opposed to the molecular weight dependent T_u whose behavior is similar to T_g. Infrared measurements are more sensitive to T′_u than T_u. Conformationally sensitive bands show that T′_u may be related to disruption of local order where there is a negligible barrier to conformational change.     

Synthesis and properties of polyamide derived from piperazine and lower purity dimer acid as hot melt adhesive

Polyamide hot melt adhesive was synthesized from lower purity dimer acid (composition: ∼23% trimer acid, ∼75% dimer acid and ∼3% monomer acid), sebacic acid, ethylenediamine and piperazine. The effect of piperazine and dimer acid concentration on properties of polyamides such as thermal properties: fusion temperature (T_f), heat of fusion (H_f), crystallization temperature (T_c), heat of crystallization (H_c), softening point (T_s) and glass transition temperature (T_g), mechanical properties: tensile strength and hardness, adhesion properties like lap shear strength (LSS) and T-peel strength (TPS), and rheological properties were investigated. Concentration of piperazine was varied from 12.5 to 37.5 mol% while that of dimer from 37.5 to 42 mol%. Piperazine has one hydrogen atom on each of its two nitrogen atoms in the ring structure. When it undergoes reaction with acids to form polyamide, these hydrogen atoms get consumed, making the amide linkage unable to form hydrogen bonding with the neighboring polyamide polymer chains. This leads to decrease in crystallinity of the polyamide. Thus, as the mole percentage of piperazine in the polyamide increases, it becomes more amorphous, decreasing T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity. Dimer acid and trimer acid are bulky compounds. As their percentages in the polyamide increase, it becomes difficult for the neighboring polyamide chains to come closer. Thus, inter-molecular hydrogen bonding decreases. This leads to decrease in crystallinity of the polyamide, lowering T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity.     

Microwave Dielectric Properties of (Mg1−xNix)2TiO4 (x=0.02–0.1) Ceramics

Low-loss ceramics in the system (Mg_1−xNi_x)₂TiO₄ (x=0.02–0.1) have been prepared using the conventional solid-state ceramic route. The formation of (Mg_1−xNi_x)₂TiO₄ (x=0.02–0.1) solid solutions was confirmed by the EDX analysis and the lattice parameters measured, which linearly varied from Mg₂TiO₄ (a=b=c=8.4410 Å) to (Mg_0.9Ni_0.1)₂TiO₄ (a=b=c=8.4335 Å). The X-ray diffraction analysis also confirmed the coexistence of a cubic-structured (Mg_1−xNi_x)₂TiO₄ and an ilmenite-structured second phase (Mg_1−xNi_x)TiO₃. By increasing x, not only could the Q×f of the (Mg_1−xNi_x)₂TiO₄ solid solution be considerably increased from 150,000 GHz at x=0 to a maximum 238,000 GHz at x=0.05, the highest ɛ_r∼16.43 could also be obtained simultaneously. This was mainly due to the uniform grain morphology and the highest density of the specimen. A good combination of microwave dielectric properties (ɛ_r∼16.43, Q×f∼238,000 GHz at 9.8 GHz, and τ_f∼−55 ppm/°C) can be achieved for a specimen using (Mg_0.95Ni_0.05)₂TiO₄ sintered at 1400°C for 4 h.     

Growth modes for monoclinic yttria‐stabilized zirconia during the martensitic transformation

The tetragonal to monoclinic martensitic transformation of plasma‐sprayed 3 mol% Y₂O₃–ZrO₂ coatings is investigated by electron backscatter diffraction. The original metastable tetragonal phase shows an approximate “basal” texture with {001}_t parallel to the coating surface. Based on the orientation analysis, plenty of monoclinic variants with atypical correspondence which indicates the c_t axis transforms to the a_m axis where (100)_m//(001)_t, (010)_m, and (001)_m//{110}_t are clearly identified in addition to the correspondence where the c_t axis transforms to the c_m axis. Moreover, three growth modes are proposed and discussed according to strain accommodation. The observed sequential growth obeys the correspondence of the c_t axis to the c_m axis. Fourfold growth combines the correspondences of the c_t axis to the c_m and a_m axes. The interleaving growth follows the correspondences of the c_t axis to the c_m axis within three tetragonal domains. These phenomena demonstrate the typical twin‐related and self‐accommodating configuration, which is in agreement with the phenomenological theory. These finding provide fundamental insight into the martensitic transformation mechanism and demonstrate a route for increasing the lifetime by controlling the tetragonal to monoclinic phase transformation.     

Compressional behavior of inked open-cell foams

The mechanical behavior of various classes of inked and non-inked (dry) open-cell foam rollers has been investigated from stress/strain measurements in compression. Hysteresis, creep, and recovery in dynamic loading were used to differentiate the rollers as to their utility in printing applications. Creep, ?_c(t), and recovery, ?_r(t), were determined in a compression mode from force measurements and strain decay, ?(t), i.e., Δ?_c(t) = ?₀ – ?(t) [?₀ = ?(t = 0)] or ?_c(t) = 2?₀ – ?(t). The creep function, Δ?_c(t), represents the plastic strain, ?_pl(t = t_h), and is uniquely defined from the recovery function, Δ?_c(t) = ?_r(t = t_h), where t_h is the hold or contact time. The recovery results for a polyurethane ester (PUE) and acrylonitrile/butadiene (AB) rollers (dry/ink), poly(vinylidene fluoride) film (PVF₂) (air/vapor) and low-density polyethylene film (LDPE) (air/vapor) were found to fit a master curve of the form F_r(θ) = EXP[-K_r(t_h)θ] = [?_r(t) – ?_∞(t_h)]/[?₀(t = O) – ?_∞(t_h)] at a reduced time of K_r(t_h)θ {θ = t/t_h and K_r(t_h) = k′_r(t_h)t_h = C₀/(t_h)^α?1 (where C₀ depends on the material's “dry” or “wet” state, α is a function of the type of material, and ?_∞ is the permanent set). These empirical results are consistent with the observed decreases in print intensity during transfer to a paper substrate and weight changes of the roller, i.e., creep and recovery are important in the printing characteristics of a given roller material. Other factors of importance in the overall transfer and print quality, but of longer-term considerations, are diffusion processes within the polymer and the nature of the polymer (e.g., porosity, chemical constitution, surface and interfacial tensions).     

A relationship between the glass transition temperature (Tg) and fractional conversion for thermosetting systems

An equation, based on thermodynamic considerations to relate the glass transition temperature, T_g, to compositional variation of a polymer system, is adapted in this article for modeling the T_g vs. fractional conversion (x) relationship of reactive thermosetting systems. Agreement between the adapted equation and experimental T_g vs. x data is found for several thermosetting crosslinking systems (i.e., epoxies and cyanate ester/polycyanurate) as well as for reactive thermosetting linear polymer systems (i.e., polyamic acid and esters to polyimides). The equation models the experimentally obtained T_g vs. x behavior of thermosetting systems which include competing reactions. Agreement for widely varying molecular structures demonstrates the generality of the equation. The entire T_g vs. x relationship can be predicted for a thermosetting material by using the T_g vs. x equation and the values of the initial glass transition temperature, T_g0, the fully reacted system glass transition temperature, T_g∞, and the ratio of the change in specific heat from the liquid or rubbery state to the glassy state (Δc_p) at T_g0 and T_g∞, Δc_p∞/Δc_p0. The values of T_g0, T_g∞, and Δc_p∞/Δc_p0 can be measured generally from two differential scanning calorimetric experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 3–14, 1997     

Evolution with heat treatment of crystallinity in carbons

The variation with heat treatment of the dimensions L_a and L_c of the graphite-like crystallites of graphitizable and non-graphitizable carbons is studied. The increases of L_a and L_c with heat treatment temperature (HTT) owing to three processes (crystallite growth in-plane, coalescence of crystallites along the c-axis and coalescence of crystallites along the a-axis) are functionally separated. The evolution with HTT of the number of crystallites (N_cr), the mean volume of the crystallites (v_cr) and the total volume occupied by the crystallites (V_cr) are determined in terms of the changes of L_a, L_c and d₀₀₂. Since among other characteristics the crystallites form the electrical and thermal conducting phase of the carbon, N_cr, v_cr and V_cr are important parameters in many physical properties of these materials. The developed expressions were applied to a non-graphitizable and to a graphitizable carbon.     

The Effect of Adding Ce1–xSmxO2–x/2 with Different Sm Contents on the Electrochemical Performance of GdBaCo2O5+δ Based Composite Cathode

In this paper, the Ce_1–xSm_xO_2–x/2 (x = 0.025, 0.05, 0.1, 0.2) samples were synthesized and then mixed with GdBaCo₂O_5+δ (GBCO) to form GBCO–Ce_1–xSm_xO_2–x/2 composite cathodes. The electrochemical performance of the composite cathodes was investigated by the electrochemical impedance spectroscopy (EIS) as a function of temperature and oxygen partial pressure. The impedance spectra results demonstrated that the introduction of proper Ce_1–xSm_xO_2–x/2 phase remarkably enhanced the electrochemical performance of GBCO cathode and caused a reduction in the total polarization resistance (Rp). Furthermore, as the amount of Ce_1–xSm_xO_2–x/2 in composite cathode was fixed, the variation of Sm content in Ce_1–xSm_xO_2–x/2 also had a significant influence on the electrochemical performance of the GBCO–Ce_1–xSm_xO_2–x/2 cathodes. For example, the Rp of GBCO cathodes containing 10 wt.% Ce_1–xSm_xO_2–x/2 considerably reduced from 0.37 to 0.17 Ω cm² at 600 °C with the decreasing Sm content x from 0.2 to 0.025. The improvement in performance of the GBCO–Ce_1–xSm_xO_2–x/2 cathodes compared to pure GBCO cathode could be mainly attributed to the catalytic activity of Ce_1–xSm_xO_2–x/2 towards the surface diffusion related processes, which was an elementary step in oxygen reduction reaction at cathode.     

Effect of Polyoxyethylene Chain Length on the Physicochemical Properties of N,N‐Dimethyl‐N‐dodecyl Polyoxyethylene Amine Oxide Hybrid Surfactants (C12EOnAO,with n = 1–4)

In order to determine the structure‐performance relationship of nonionic‐zwitterionic hybrid surfactants, N,N‐dimethyl‐N‐dodecyl polyoxyethylene (n) amine oxides (C₁₂EO_nAO) with different polyoxyethylene lengths (EO_n, n = 1–4) were synthesized. For homologous C₁₂EO_nAO, it was observed that the critical micelle concentration (CMC), the maximum surface excess (Γ_m), CMC/C₂₀, and the critical micelle aggregation number (N_m,c) decreased on going from 1 to 4 in EO_n. However, there were concomitant increases in surface tension at the CMC (γ_CMC), minimum molecular cross‐sectional area (A_min), adsorption efficiency (pC₂₀), and the polarity ([I₁/I₃]_m) based on the locus of solubilization for pyrene. The values of log CMC and N_m,c decreased linearly with EO_n lengthening from 1 to 4, although the impact of each EO unit on the CMC of C₁₂EO_nAO (n = 1–4) was much smaller than that typically seen for methylene units in the hydrophobic main chains of traditional surfactants. Compared to the structurally related conventional surfactant N,N‐dimethyl‐N‐dodecyl amine oxide (C₁₂AO), C₁₂EO_nAO (n = 1–4) have smaller CMC, A_min, and CMC/C₂₀, but larger pC₂₀, Γ_m, and N_m,c with a higher [I₁/I₃]_m. This may be attributed to the moderately amphiphilic EO_n (n = 1–4) between the hydrophobic C₁₂ tail and the hydrophilic AO head group.     

Phase transitions and microwave dielectric behaviors of the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4 ceramics

Microwave dielectric ceramics with intrinsic low sintering temperatures are potential candidates for low temperature co-fired ceramics technology. In the present work, the (Li_0.5Y_0.5)MoO₄ ceramic with tetragonal scheelite structures was selected to improve microwave dielectric properties of BiVO₄ ceramics. As proved by X-ray diffraction (XRD) results, scheelite structured solid-solution ceramics were formed with x value ≤0.1 in the (Bi_1−xLi_0.5xY_0.5x)(V_1−xMo_x)O₄. In situ XRD results further confirmed that the addition of (Li_0.5Y_0.5)MoO₄ also lowered transition temperature from distorted monoclinic to tetragonal scheelite structure. When x value increased further, zircon phase was detected by XRD. Room and high-temperature Raman spectra also supported the XRD results. Differences of thermal expansion coefficients of both monoclinic and tetragonal scheelite phases lead to an abnormality at phase transition temperature. Good microwave dielectric properties with permittivity above 70 and Qf (Q = quality factor = 1/dielectric loss and f = frequency) value above 8000 GHz were obtained in the (Bi_1−xLi_0.5xY_0.5x)(V_1−xMo_x)O₄ solid-solution ceramics with x value ≤0.1 sintered below 800°C. However, permittivity peak values at phase transition temperatures lead to large positive or negative temperature coefficient of resonant frequency, and this needs to be modified via composite technologies in the future.     

Creep/recovery behavior of open-cell foams

Static measurements have been used to predict the dynamic response of ldquo;unboundedrdquo; open-cell noninked (dry) and inked foam materials. Creep, e_c(t), and recovery, e_r(t), were determined in compression from static and dynamic modes. Force measurements, f(t), and strain decay, e(t), were used to determine the change in creep, δe_c(t). The change in creep represents the plastic strain, e_p1(t=t_h), and is uniquely defined by the recovery function, e_r(t=t_h), where t_h is the hold time. Creep and recovery results of various classes of foam materials and nonfoam materials were found to fit a master curve of the form F_r(t) =exp[–k′_r(t_h)t] = [e_r(t) - e₀₀( t_h)]/[e₀ (t = 0) - e₀₀(t_h)] at a reduced time of k′_r(t_h) t [k′_r(t_h)] C₀/(t_h)^a (where Co depends on the material's “dry” or “wet” state), a is a function of the type of material, and em is the permanent set]. These empirical results are applicable to printing ink transfer and print quality. Other important factors of concern are diffusion processes within the polymer matrix and the nature of the polymer (e. g., chemical constitution, porosity, molecular weight, and solubility). © 1995 John Wiley & Sons, Inc.     

Phase Structure Evolution and Thermo‐Physical Properties of Nonstoichiometry Nd2−xZr2+xO7+x/2 Pyrochlore Ceramics

Nonstoichiometry pyrochlore composites of Nd_2?xZr_2+xO_7+x/2 (x = 0, 0.1, 0.2) were synthesized by chemical‐coprecipitation and calcination method. The phase structure evolution and thermo‐physical properties of Nd_2?xZr_2+xO_7+x/2 were investigated. Structural analysis by Raman spectroscopy showed that Nd_2?xZr_2+xO_7+x/2 underwent an ordering degree decrease and a lattice distortion increase with increasing x value. Nd_1.9Zr_2.1O_7.05 and Nd_1.8Zr_2.2O_7.1 exhibited lower thermal conductivities than Nd₂Zr₂O₇, which might be related to the lower ordering degree and the enhanced phonon scattering due to lattice distortion. As ZrO₂ content increasing, the thermal expansion coefficients of Nd_2?xZr_2+xO_7+x/2 increased, which possibly arised from the decreased crystal energy due to reduced ordering degree.     

Kinetics of graft copolymerization of methyl methacrylate in wool fibers

The graft copolymerization of methyl methacrylate in wool fibers was investigated in the aqueous LiBr–K₂S₂O₈ system without homopolymer. The rate of grafting and the degree of polymerization of graft polymer were determined on varying the extent of reduction of wool fibers and the concentration of monomer. From the graft copolymerization behavior observed at a given concentration of redox catalysts (LiBr and K₂S₂O₈), the thiol groups in wool fibers were considered to play a role as a sort of catalyst of polymerization, not as the chain transfer agent, and also to give the grafting sites. So, the initiation process of grafting was assumed to be started by d[S·]/dt = k_i[SH]_eff, and the kinetic consideration was found to lead to the following expression in agreement with the experimental results: 1/DP = (k_t/k_p²[M]_fib²)R_p, where d[S·]/dt is the rate of formation of thiol radicals by radicalotropy to ? SH from SO₄^?., OH·, or Br·; k_i, k_p, and k_t are the rate constants of initiation, propagation, and termination, respectively; [SH]_eff and [M]_fib are the concentration of the effective thiol groups and the MMA monomers within the wool fibers, respectively; DP is the average degree of polymerization of graft polymers, and R_p the overall rate of grafting.     

Clouding Behavior of C13EOx (x = 10–19) Micelles in a Wide Range of Salinity and Hardness: Concomitant Effects of Salinity and Degree of Ethoxylation

The effect of salinity and degree of ethoxylation on the cloud point, T_cp, in C₁₃EO_x (x = 10–19) micelles was investigated in distilled water and in the salinity range S = 1.96–196 g L⁻¹. At a fixed x value, the rate dT_cp/dS was given by dT_cp/dS = α _b + β _bS with α _b < 0 and β _b > 0. This trend suggests that dT_cp/dS is the result of two opposing effects, an entirely (negative) surfactant-dependent effect (α _b) and a combined (positive) surfactant-solvent (β _bS)-dependent effect. In addition, the rate dT_cp/dS was found to become increasingly less negative with increasing salinity (dT_cp/dS) < 0), suggesting an overwhelming contribution of the α _b effect as compared to the β _bS effect. On the other hand, at fixed S, the rate was given by dT_cp/dx = α _x + β _xx with α _x > 0 and β _x < 0. This trend also suggests the existence of two opposing effects, a strictly (positive) solvent-dependent effect (α _x) and a concomitant solvent (β _x)-surfactant (x)-dependent effect. Contrary to dT_cp/dS, the rate dT_cp/dx was found to become increasingly less positive with increasing x values (dT_cp/dx > 0), suggesting that α _x is the dominant factor in the surfactants’ susceptibility to be salted in. Both constants α_b and α _x were attributed to a dual temperature-salinity effect on the structure of water molecules not involved in surfactant's hydration. On the other hand, β _b and β _x were associated with the change in the structure of water due to the dehydration of surfactants’ oxyethylene moieties with increasing temperature.     

Polymorphism of mixed triglycerides containing odd fatty acids

Paris of C _n C_(n+1)C _n (i.e., C₁₆C₁₇C₁₆ and C₁₈C₁₉C₁₈) and C _n C_(n-1)C _n triglycerides (C ₁₆ C ₁₅ C ₁₆ and C ₁₈ C ₁₇ C ₁₈ ) triglycerides,n even, were prepared to compare with C _n C_(n+2)C _n and C _n C_(n-2)C _n glycerides, respectively, in polymorphic behavior. It was found that C _n C_(n+1)C _n compounds were β′ tending and C _n C_(n-1)C _n compounds β tending in line with their all-even counterparts. The glyceride C₁₁C₁₃C₁₁ is β′ stable, like C₁₀C₁₂C₁₀ and C₁₆C₁₈C₁₆, and seems closely related to them in physical behavior and diffraction characteristics.     

Reinterpretation of the DSC data for atactic polystyrenes by Stadnicki et al.

Reexamination of published DSC traces for first and second heatings of atactic polystyrenes with M?_n from 2050 to 1.99 × 10₆, M?_w/M?_n ～ 1.1, is discussed in terms of some newly enunciated principles of calorimetry for the liquid state of atactic polymers. These traces were originally stated to reveal only an endothermic peak above T_g, identified with T_ll at M?_n < ca. 10⁵. Three types of behavior are now distinguished: (1) First heating, M?_n < M_c (the entanglement molecular weight), an endothermic slope change attributed to T_u, followed by an exotherm at T_exo ascribed to melt flow and/or wetting of the DSC pan; (2) first heating for M?_n above M_c, only an endothermic slope change; (3) second heating, all molecular weights, only an endothermic slope change for T_ll and, in some cases, T_lp. T_ll thus defined reaches an asymptotic limit when plotted against log M?_n, just as T_g does. Texo begins to level off, and then, starting at M_c, increases without limit. T_ll is an isofree volume state as is T_g; T_exo is an isoviscous state and hence a pure relaxation process. DSC traces on first heating at M?_n < 10⁵ provide the first known experimental evidence for both the transitional and the relaxational aspects of T_ll in the same experiment. The role of zero shear melt viscosity, η₀, in DSC is noted: T_ll depends only on M?_n; T_exo on η₀ and hence on M?_w. The T_ll temperature is independent of physical form of the specimen: powder, pellet, film. DSC studies on bimodal blends of PS show T_ll uniquely dependent on M?_n, while the T_f – (T_exo) exotherm depends on M?_w. Such blends can eliminate interference between the T_ll endotherm and the T_f exotherm. Exotherms using weighted pan lids and exotherms from sintering are also presented. DSC evidence for T_lp > T_ll is indicated.     

Synergism on antioxidant activity between natural compounds optimized by response surface methodology

Despite the increase in the use of natural compounds in place of synthetic derivatives as antioxidants in food products, the extent of this substitution is limited by cost constraints. Thus, the objective of this study was to explore the synergism on the antioxidant activity of natural compounds, for further application in food products. Three hydrosoluble compounds (x₁ = caffeic acid, x₂ = carnosic acid, and x₃ = glutathione) and three liposoluble compounds (x₁ = quercetin, x₂ = rutin, and x₃ = genistein) were mixed according to a “centroid simplex design”. The antioxidant activity of the mixtures was analyzed by the ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) methodologies, and activity was also evaluated in an oxidized mixed micelle prepared with linoleic acid (LAOX). Cubic polynomial models with predictive capacity were obtained when the mixtures were submitted to the LAOX methodology (? = 0.56 x₁ + 0.59 x₂ + 0.04 x₃ + 0.41 x₁x₂ – 0.41 x₁x₃ – 1.12 x₂x₃ – 4.01 x₁x₂x₃) for the hydrosoluble compounds, and to FRAP methodology (? = 3.26 x₁ + 2.39 x₂ + 0.04 x₃ + 1.51 x₁x₂ + 1.03 x₁x₃ + 0.29 x₂x₃ + 3.20 x₁x₂x₃) for the liposoluble compounds. Optimization of the models suggested that a mixture containing 47% caffeic acid + 53% carnosic acid and a mixture containing 67% quercetin + 33% rutin were potential synergistic combinations for further evaluation using a food matrix.     

Effect of dispersity on the Tll (>Tg) transition in polystyrene

The presence of a high temperature (>T_g) relaxation in amorphous polystyrene has been investigated further. In the previous work,¹ the techniques of differential thermal analysis (DTA) and torsional braid analysis (TBA) were employed to study polystyrene as a function of “monodisperse” molecular weight. The occurrence of the T_ll transition appeared to be associated with the attainment of a critical viscosity level with also corresponded with a free volume level. An entanglement network developed at a critical value of molecular weight, M_c, giving a break in the T_ll-versus-M plots. The present work deals with the influence of dispersity on the T_ll transition, below and above M_c. A series of binary blends of “monodisperse” anionically polymerized polystyrenes with systematic changes in M?_n and heterogeneity index (M?_w/M?_n) was tested by TBA. The results show that when both components have molecular weights below M_c, single and average values of T_g and T_ll are observed which are linearly related to M?_n^?1, as predicted by free volume arguments. Although a single T_g is observed when one component has a molecular weight above and the other has a molecular weight below M_c, the components appear to undergo the T_ll relaxation independently. The results indicate that both the glass transition and the T_ll transition are basically governed by the same type of molecular motion but at different length ranges.