Relationships on the effect of water on glass transition temperature and young's modulus of nylon 6

The glass transition temperature T_g of nylon 6 decreases monotonically toward a finite value T_gl upon increase of the moisture content. The mechanism of this decrease entails the reversible replacement of intercaternary hydrogen bonds in the accessible regions of the polyamide. The limiting glass transition temperature T_gl is approached when the moisture content approaches W_l, which corresponds to the amount of water required for complete interaction with all accessible amide groups. Denoting with T_g0 the glass transition temperature of the dry polymer, the effect of water on T_g is represented by the equation, T_g = (ΔT_g)₀ exp{?[ln(ΔT_g)₀]W/_τW_l} + T_gl, where (ΔT_g)₀ = T_g0 ?T_gl, and τ = W(T_gl+1)/W_l. This equation appears to be generally applicable to hydrophilic polymers, since correspondingly calculated data are also in very good agreement with experimental data for polymers such as nylon 66, poly(vinyl alcohol), and polyN-vinylpyrrolidone. The effect of water of Young's modulus E of nylon 6 is represented by an analogous relationship, and the quantity In[(E?E_l)/(T_g?T_gl)] is a linear function of the moisture content.     

Isomer effects on transport properties of polyesters based on bisphenol-A

Pure gas sorption and transport properties of polyesters based on bisphenol-A and both pure isophthalic and pure terephthalic acid chloride were obtained for He, N₂, O₂, CH₄, and CO₂ at 35°C. The polymers were synthesized in our laboratory and amorphous films were prepared with a specialized solvent casting procedure. The polymer containing m-phenylene groups shows higher permselectivity for most of the gas pairs. The ideal selectivity of O₂/N₂ was increased by 33% when p-phenylene units were replaced by m-phenylene ones. On the other hand, the polyester containing only p-phenylene groups, shows higher permeability to all the gases studied. The polymer based on pure terephthalic acid chloride has a 75% higher oxygen permeability and a 1.1-fold higher carbon dioxide permeability than the isophthalic acid derivative. The polyester containing meta-phenylene units has lower T_g, higher permselectivity, lower permeability, lower fractional free volume (FFV), and lower d-spacing. The values of FFV, and lower d-spacing. The values of FFV and d-spacing were only slightly different between the two isomers. Moreover, for the sub-T_gγ transition the maximum in tan δ occured at essentially the same temperature (?55°C). The polymer with a higher concentration of p-phenylene units shows somewhat larger area under the γ-peak, indicating slightly more sub-T_g motion. The Distribution of FFV is considered to be the determining factor for the differences in transport properties observed. © 1993 John Wiley & Sons, Inc.     

The effect of plasticization on craze microstructure

The structure of crazes in plasticized polystyrene has been studied by means of small-angle x-ray scattering and optical interference microscopy. Addition of plasticizer causes a rapid increase in the mean fibril diameter D and a slow decrease in the craze fibril volume fraction v_f. The crazing stress σ_c was also measured and it was found that the product D σ_c is independent of plasticizer concentration. These results are shown to be consistent with the entanglement model for controlling v_f and the meniscus instability model of craze thickness growth.     

Solvent effect on radical polymerization of butyl acrylate

The propagation and termination rate constants k_p and k_t for the radical polymerization of butyl acrylate initiated by biacetyl have been measured by using the rotating-sector method, in various solvents at 30°C. The value of k_p and initiation rate R_i varied with solvents, while the value of k_t did not change with solvents except for benzonitrile. The variation of k_p with aromatic solvents has a trend against Hammett σ_p of the solvent substituents similar to that for methyl methacrylate or phenyl methacrylate except for the value in benzonitrile, when it is larger than the variation for methyl methacrylate or phenyl methacrylate. The larger variation of k_p for butyl acrylate is compatible with the view that the origin of the solvent effect lies in complex formation between the propagating radical and aromatic solvent molecules. The exceptional decrease in k_p and k_t in benzonitrile is explained by a contraction of the poly(butyl acrylate) chain in the poor solvent.     

Effect of radical scavenger on initiation efficiency

In order to analyze the effect of the scavenger on initiator efficiency f or ratio of combination between two radicals (1 ? f), an equation was derived by solving the modified Smoluchowski equation under the boundary condition based on the law of conservation of mass. At time t approaching infinity in a stationary state, this equation becomes: f = {D + a(Dk[S])^1/2}/{ak₀ + D + a(Dk[S])^1/2}, where D is the sum of the diffusion constants of two radicals, a is the diameter of the radical particle, k₀ is a specific rate of recombination in the cage between two radicals, k is the rate constant of reaction between the radical and the scavenger as a pair, and [S] is the scavenger concentration. When ak₀ ? D and k[S] is small, this equation approximates the previously derived Wijsman's equation. An equation of the same type as Noyes' equation is also derived from this equation, when [S] = 0. By using the equations derived in this paper, the effect of α,α′-diphenyl-β-picrylhydrazyl on the ratio of recombination of the (CH₃)-(CN)C^* radical and the effect of monomer on the initiation efficiency are satisfactorily explained.     

Analysis of critical points on the potential energy surface

A simple classification scheme is proposed for critical points, based only on rankr and signatures of the (n,n)-matrixG of harmonic force constants. The determination ofr ands, e.g. by the well-known factorizationG=L ^T gL (L: triangular matrix,g: diagonal matrix), has several theoretical as well as practical (computational) advantages over the inspection of eigenvalues ofG, so far used in quantum chemistry. The eigenvalues are sufficient butnot necessary for a classification whereas rank and signature are the only necessary and sufficient prerequisites for solving the task. For the purpose of presenting a working example, by calculating only a 2×2 torque constant matrix, it is shown that the coplanar ethylbenzene is unstable in the CNDO/2 picture.     

Effect of bubble size on foam fractionation of ovalbumin

The bubble size distribution and void fraction (ɛ _g ) (at two bulk liquid pool positions below the bulk liquid-foam interface and one lower foam phase position) in a continuous foam fractionation column containing ovalbumin were obtained using a photoelectric capillary probe. The bubble size and ɛ _g data were gathered for different operating conditions (including the changes in the superficial gas velocity and feed flow rate) at a feed solution of pH 6.5 and used to calculate the specific area, a, of the bubbles. Thus, local enrichment (ER _l ), values of ovalbumin could be estimated and compared with directly obtained experimental results. The ER _l results were also correlated with the bubble size and ɛ _g to understand better the concentration mechanisms of foam fractionation. The high ER _l in the lower foam phase was largely attributable to the abrupt increase in ɛ _g (from 0.25 to 0.75), or the a (from about 12 to 25 cm²/cm³) from the bulk liquid to the foam phase. These changes correspond with enhanced gravity drainage. With an increase in the superficial gas velocity, the bubble size increased and the a decreased in both the bulk liquid and lower foam phases, resulting in a decrease in the local experimentally determined enrichments at high superficial gas velocities. At intermediate feed flow rates, the bubble size reached the maximum. The ɛ _g and a, on the other hand, were the largest for the largest feed flow rate. The ER _l in the lower foam phase was maximized at the lowest feed flow rate. It follows, therefore, that a alone is not sufficient to determine the magnitude of the ER _l in the foam phase.     

Impact of high pyruvate concentration on kinetics of rabbit muscle lactate dehydrogenase

In order to evaluate the effectiveness of l-lactate dehydrogenase (LDH) from rabbit muscle as a regenerative catalyst of the biologically important cofactor nicotinamide adenine dinucleotide (NAD), the kinetics over broad concentrations were studied to develop a suitable kinetic rate expression. Despite robust literature describing the intricate complexations, the mammalian rabbit muscle LDH lacks a quantitative kinetic rate expression accounting for simultaneous inhibition parameters, specifically at high pyruvate concentrations. Product inhibition by l-lactate was observed to reduce activity at concentrations greater than 25 mM, while expected substrate inhibition by pyruvate was significant above 4.3 mM concentration. The combined effect of ternary and binary complexes of pyruvate and the coenzymes led to experimental rates as little as a third of expected activity. The convenience of the statistical software package JMP allowed for effective determination of experimental kinetic constants and simplification to a suitable rate expression:

Effect of microroughness on rubber friction

Friction was measured and analyzed for rubber belts sliding against paper and polymer film surfaces of different roughness. As expected, increased paper smoothness created an increase in the friction coefficient. However, it was found that continuous rubber usage during testing also created an increase in friction coefficient for constant surface roughness of both paper and film. This was analyzed as due to an increase in N and C values for the load-dependent friction coefficient, μ = CW^?N where W is normal load and N_max ≈ 0.33 (papers) or N_max ≈ 0.6 (polymer films). Using adhesion friction theory, it was shown that friction data can be fitted with a unified equation: C = μ₀c^?N, where μ₀ = μ N = 0 and c is a constant for the rubber and belt configuration tested.     

Notes on polymer hydrodynamics

The sedimentation of an unperturbed polymer chain in dilute solution is reformulated by using Burgers' method, in which the no-slip boundary condition on the surface of each chain element is taken into account approximately. It is shown that the forcevelocity proportionality relation employed so far as the basis of theoretical developments in polymer hydrodynamics can be justified as a first approximation to the no-slip condition. The derived expression for the translational friction coefficient f_t is a complex function of n and a/b, where n is the number of chain elements in a single molecule and a/b is the ratio of the Stokes radius of a chain element to the effective bond length. Three special cases corresponding mathematically to b = ∞ (no hydrodynamic interaction), a ? b (Kirkwood-Riseman theory), and b = 2a (touching-sphere model) are examined in detail. Finally, it is shown that when a/b = 0.2360, our f_t varies linearly with n^1/2 over the entire range of n.     

Estimation of molecular weight distribution based on chain length dependence of termination rate

When a chain length dependence of polymer-polymer termination is given by k_t,ns = const. (n^?2a + s^?2a) where n and s are the chain lengths for the polymer radicals and a is parameter, an instantaneous weight fraction of the non-reacting polymers is derived as: where h and k? are the kinetic parameters, p is a parameter depending on a, and p_n is instantaneous number-average chain length. Such a weight fraction corresponds to the experimental one over a wide range of conversion in the polymerization of styrene. On the scope of this correspondence, the polymer-polymer termination rate is estimated as: k?_t = 8πR₀D₁/100 ( = 4πR_sD_s) where R₀ is reaction radius between monomer radicals and D₁ is the diffusion coefficient of the monomer; R_s is reaction radius between segment radicals with n ? 100 and D_s is the diffusion coefficient of the segment. The Fujita-Doolittle theory applies to such a rate. Further, the rate also yields 1.5 × 10⁷1./mole-sec, which is the observable extent at conversions less than 0.2.     

Effect of length and number of interlinking molecules on the strength of adhesion

The fracture energy G of an adhesive bond appears to be a product of two terms: G = G_O [1 + f(R, T)], where G_O is the intrinsic (chemical) strength of the interface and f(R, T), usually much larger than unity, reflects energy dissipated within the adherends at a crack speed R and temperature T. Values of G_O have been determined for interlinked sheets of an SBR elastomer by measuring the peel strength at low rates and high temperatures, and in the swollen state, to minimize internal losses. Both the density ΔN and molecular length L of interlinking molecules were varied. G_O was found to increase in proportion to (ΔN)L^3/2, in accord with the molecular theory of Lake and Thomas. As the peel rate was raised and the test temperature lowered, G was considerably increased by internal dissipative processes, becoming as much as 1000 × G_O near the glass transition. The loss function f(R, T) was found to depend somewhat upon the strand length L, being about twice as large at intermediate peel rates when L was increased by 40%. It also depended on the density ΔN of interlinking molecules, being about twice as large at high peel rates when the density of interlinks was reduced by a factor of six. Thus, the loss function f(R, T) is greater when the interlinking molecules are few and long, and it is lower when they are many and short. However, it is mainly governed by two parameters: peel rate R and temperature difference (T − T_g), in accord with a viscoelastic loss mechanism. © 1996 John Wiley & Sons, Inc.     

维生素C溶液有氧降解动力学

建立了一种恒温高压氧药物稳定性加速试验方法, 用这种方法可在较短的时间内求得药物氧化反应的动力学参数. 以10%维生素C溶液为例, 维生素C在有氧和无氧条件下均可降解, 总的降解速率常数k_t由两部分构成: k_t＝k_an＋k_ae, k_an为无氧降解速率常数, 可表达为k_an＝A_an•exp(－E_a,an /RT); k_ae为有氧降解速率常数, 可表达为k_ae＝A_ae•exp(－E_a,ae/ RT)• .     

The effect of different arms on the properties of chiral branched-arm liquid crystals based on isosorbide as the chiral core

A new series of two-arm ( MA₁ , MA₂ ), four-arm ( MA₃ ) and six-arm ( MA₄ ) chiral liquid crystalline compounds containing isosorbide as the chiral core were synthesised. Four precursors of branched-arm A₁–A₄ were first obtained, and then were esterised separately with isosorbide to obtain four chiral branched-arm liquid crystals ( MA₁–MA₄ ). The structure and properties have been characterised. The results show that MA₁ was smectic–cholesteric phase with a fan-like and oily streak texture; MA₂–MA₄ showed a cholesteric phase with oily streak texture, or lined texture and finger print texture. Isosorbide successfully induced a cholesteric phase. The melting point and clearing point values for MA₁–MA₄ first increased and then decreased. The branched-arm and chiral core quantity affected the liquid crystalline properties. At the same time, the difference in side-arms resulted in different directions of rotation. MA₁–MA₂ showed right-handed rotation and had selective reflection; MA₃–MA₄ demonstrated left-handed rotation and did not have selective reflection.     

Influence of Modified Terminal Segments on Dynamic Modulus and Viscosity of Dendrimer

Theoretical studies of the influence of modified terminal segments (TSs) on the relaxation spectrum of a dendrimer and dendrimer mechanical properties such as dynamic viscosity, η(ω), the elastic, G′(ω), and loss, G″(ω), moduli have been carried out by the Rouse model. Two major types of modified TS have been studied: (i) TS with an attached rigid massive group (i.e., TSs with additional friction) and (ii) TSs with a length different from the length of an inner segment. In the low‐frequency region, G′(ω), G″(ω), and η(ω) increase with the rise of friction of TS. In the high‐frequency region, dynamic moduli and viscosity depend on the length of TS. In the intermediate region, the moduli and viscosity are determined by a combined parameter: the characteristic time of TS, τ_end, which depends on the friction and length of TS. For both types of TSs, the position of the G″(ω) maximum, ω_max, depends on τ_end. In most of the considered cases, the linear dependence of ω_max on τ_end has been found. The method, which takes into account a deceleration of TS mobility with the rise in the number of generations, n, has been proposed. It was supposed that the effect of the deceleration corresponds to the forming of a dense surface shell with the rise of n, but similar behavior can also be caused by other reasons. In this case, ω_max shifts to the low‐frequency region with an increase in the number of generations. The conclusions of the theory developed in this paper are in agreement with results of the experiment, in which G′(ω) and G″(ω) were obtained for polyamidoamine dendrimers.

     

Some remarks on the dynamics of polymer melts

Considering one long chain (N monomeric units) in a homodisperse melt of chemically identical, but shorter, “solvent” chains (P monomers per chain), we propose some tentative scaling laws for the self-diffusion constant D(N) and the relaxation time T(N) of the solute chain. We also discuss the viscosity increment δ_η due to a small volume fraction Φ of the long chains. We find three regimes of behavior, depending on N and P, and on the distance between entanglement points (assumed smaller than N and P): (A) reptation of the N chain; (B) Stokes–Einstein regime; the solute moves like a usual polymer coil in a viscous fluid of P chains; (C) mixed regime, where D(N) is controlled by reptation, while δ_η is of type B. Contrary to our earlier belief, we find no significant regime where the process of “tube renewal” could be dominant.     

Effect of polycondensation methods on molecular weight distribution of nylon 610

Polycondensation methods greatly influence the molecular weight distribution of poly(hexamethylene sebacamide) (nylon 610) as determined by gel permeation chromatography (GPC). The ratio of weight average molecular weight to number average molecular weight (M_w/M_n) was used as a measure for estimating the molecular weight distribution. The M_w/M_n ratios of nylon 610 obtained from melt, solid phase, and high temperature polycondensation methods were 2 to 3.5, which were expected values for the most probable distribution. However, those for polymers obtained from the direct polycondensation in the presence of triphenylphosphine, interfacial polycondensation and low temperature polycondensation using an acid chloride varied over a wide range from 3.5 to 8.5. The effect of the kind of organic solvents in the interfacial method on the M_w/M_n ratios was especially large, and the molecular weight distribution could be controlled to some extent by selecting an appropriate solvent.     

Effect of copper and manganese ions on activities of laccase and peroxidases in three Pleurotus species grown on agricultural wastes

Copper (Cu²⁺) and manganese (Mn²⁺) ions influenced laccase (Lac) and peroxidase production in Pleurotus eryngii, Pleurotus ostreatus, and Pleurotus pulmonarius. In P. eryngii, the optimum Cu²⁺ concentration for Lac production was 1 mM and for peroxidases 10mM, and Mn²⁺ concentration of 5mM led to peaks of Lac and peroxidase activity. In P. ostreatus HAI 493, the highest level of Lac activity was at Cu²⁺ concentrations of 1 and 10 mM and Mn²⁺ concentration of 1mM, respectively. The absence of Cu²⁺ and Mn²⁺ caused the highest levels of peroxidase production. In P. ostreatus HAI 494, the highest level of Lac activity was at a Cu²⁺ concentration of 5 mM and at Mn²⁺ concentration of 1 mM, respectively. High levels of peroxidase activity were found in the medium without and with 1mM Cu²⁺, and at 1 and 5 mM Mn²⁺, respectively. In P. pulmonarius, the highest Lac activity was found in the presence of 5 mM Cu²⁺ and 5 mM Mn²⁺, respectively. The absence of Cu²⁺ and Mn²⁺ as well as their presence at a concentration of 1 mM led to the peaks of peroxidase activities.     

Corrigendum on ‘investigation on molecular interaction studies of binary mixture of Dehpa and Petrofin at 298.15 K’

Expressions of Redlich–Kister (RK) excess function using polynomials on difference of molar composition are used. Calculated values of excess properties from experimental values are well presented in some curves as a function of mole fraction (x₂) of the second pure component of the studied binary liquid mixture. Nevertheless, the authors presented values of adjustable parameters, not for the polynomial of the popular RK equation (i.e. vs. x₂–x₁), but for globally the excess property Y^E as an overall three degree polynomial on (x₂) including implicitly the molar fraction product (x₁·x₂) in their nonlinear regression, which can then induces some readers to probable confusion.     

Kinetics of fluid spreading on viscoelastic substrates

The spontaneous spreading of non‐film‐forming fluids on the surfaces of aqueous solutions of poly(2‐acrylamido‐2‐methyl‐propanesulfonic acid) and its chemically crosslinked gels was studied. The experiments were performed in the same concentration range for the solutions and gels, far above the overlap concentration of the polymer solutions. The leading edge (R) of the spreading liquid showed a power‐law behavior with time t: R = K(t + c)^α, where α is the spreading exponent and K is the spreading prefactor. α and K were significantly different for the polymer solutions and gels. Here c was a constant that depended on the initial conditions of the spreading liquids. Depending on the polymer concentration, α of the polymer solutions varied between the upper (3/4) and lower (1/10) theoretical limits for viscose liquids and solids, respectively. This indicates that no universal scaling law exists for the spreading process on viscoelastic surfaces. On the polymer gels, which were elastic substrates, universal values of α could be observed and could be expressed as R ∝ (t + c)^0.45 and R ∝ (t + c)^0.3 for miscible and nonmiscible spreading liquids, respectively; they showed no dependence on the polymer concentration or network mesh size. This shows that on an elastic gel surface, spreading is more or less similar to that on a solid surface. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 562–572, 2005