Phase transition in polyamides

Summary A series of poly(3,3′, 5,5′-tetraethyldiphenylmethane-1,m-alkanedi-carboxamide(poly(TEDPM-ADA(m=8–18)))) were synthesized from 1,m-alkane-dicarboxylic acids(ADA(m=8–18)) and 4,4′-diamino-3,3′,5,5′-tetraethyl-diphenylmethane by use of direct polycondensation in the presence of triphenylphosphite. The enantiotropic nematic liquid crystals were observed in the m=12–18 and monotropic liquid crystals were observed in the m=8–11 in poly(TEDPM-ADA). Mesogenicity of the polyamides increases with an increase in the number of methylene spacers, m.     

Phase transition of 2,3-O-methylcellulose

Summary In this work, a series of 2,3-O-methylcellulose (MC) with different DS value were prepared. Its phase transition behavior in aqueous solution was studied in terms of DS value, concentration and molecular weight. The the following conclusions were obtained. (1) All the 2,3-O-MC samples show no sol-gel transition in aqueous solution despite the molecular weight. (2) No phase separation was observed for the 2,3-O-MCs with a DS value lower than 1.0, even when the temperature was raised to 95°C. (3) The precipitation temperature is surprisingly different between 2,3-O-MCs. and other MCs possessing comparable total DS value. (4) The precipitation temperature of 2,3-O-MCs depends on the molecular weight rather than on the concentration. Received: 3 February 1998/Revised version: 30 March 1998/Accepted: 11 April 1998     

Lipid class composition of the protozoan Perkinsus marinus, an oyster parasite, and its metabolism of a fluorescent phosphatidylcholine analog

Perkinsus marinus is one of two important protozoan parasites of the eastern oyster, Crassostrea virginica. The other is Haplosporidium nelsoni. Lipids extracted from 7-d-old in vitro cultured P. marinus meronts, incubated with fluorescent-labeled phosphatidylcholine (FL PC) and nonincubated P. marinus meronts, were analyzed by a high-performance liquid chromatography (HPLC) system equipped with a diol phase column, in combination with thin-layer chromatography coupled with a flameionization detector (TLC/FID), and high-performance thin-layer chromatography (HPTLC). Various polar and neutral lipid classes were separated by HPLC using a two-gradient solvent system. Five polar lipid classes—phosphatidylcholine (PC), phosphatidylethanolamine (PE), cardiolipin (CL), sphingomyelin (SM), and phosphatidylserine (PS)—were identified from P. marinus extracts. Four neutral lipid classes—triacylglycerol (TAG), steryl ester (SE), cholesterol (CHO), and fatty alcohol—were distinguished. TLC/FID analysis of meront lipids showed that the weight percentages of PC, PE, CL, SM, PS/PI, TAG, SE, and CHO were 21, 10.7, 4, 2.3, 4.3, 48.7, 7.8, and 1.2%, respectively. HPLC and HPTLC analyses revealed the presence of two SM and PS isomers in P. marinus extracts. Perkinsus marinus effectively incorporated FL PC acquired from the medium and metabolized it to various components (i.e., free fatty acid, monoacylglycerol, diacylglycerol, TAG, PE, and CL). Uptake and interconversion of FL PC in P. marinus meronts increased with time. After 48 h the total uptake of fluorescence (FL) was 28.9% of the FL PC added to the medium, and 43% of the incorporated FL resided in TAG.     

Lipid class composition of the protozoan Perkinsus marinus, an oyster parasite, and its metabolism of a fluorescent phosphatidylcholine analog

Perkinsus marinus is one of two important protozoan parasites of the eastern oyster, Crassostrea virginica. The other is Haplosporidium nelsoni. Lipids extracted from 7-d-old in vitro cultured P. marinus meronts, incubated with fluorescent-labeled phosphatidylcholine (FL PC) and nonincubated P. marinus meronts, were analyzed by a high-performance liquid chromatography (HPLC) system equipped with a diol phase column, in combination with thin-layer chromatography coupled with a flame-ionization detector (TLC/FID), and high-performance thin-layer chromatography (HPTLC). Various polar and neutral lipid classes were separated by HPLC using a two-gradient solvent system. Five polar lipid classes--phosphatidylcholine (PC), phosphatidylethanolamine (PE), cardiolipin (CL), sphingomyelin (SM), and phosphatidylserine (PS)--were identified from P. marinus extracts. Four neutral lipid classes--triacylglycerol (TAG), steryl ester (SE), cholesterol (CHO), and fatty alcohol--were distinguished. TLC/FID analysis of meront lipids showed that the weight percentages of PC, PE, CL, SM, PS/PI, TAG, SE, and CHO were 21, 10.7, 4, 2.3, 4.3, 48.7, 7.8, and 1.2%, respectively. HPLC and HPTLC analyses revealed the presence of two SM and PS isomers in P. marinus extracts. Perkinsus marinus effectively incorporated FL PC acquired from the medium and metabolized it to various components (i.e., free fatty acid, monoacylglycerol, diacylglycerol, TAG, PE, and CL). Uptake and interconversion of FL PC in P. marinus meronts increased with time. After 48 h the total uptake of fluorescence (FL) was 28.9% of the FL PC added to the medium, and 43% of the incorporated FL resided in TAG.     

Phase transition in swollen gels

Summary The swelling and mechanical behaviour of networks of copolymers of acrylamide, methylenebisacrylamide and of the quaternary salt-N,N,N-trimethyl-N-methacrylamido-2-ethylammonium chloride (mole fraction of salt x _s =0-0.17) in water-acetone mixtures was investigated. In the range x _s >0.01 the phase transition was observed; with increasing concentration x _s both the extent of transition and the critical concentration of acetone in the mixture, at which the collapse takes place, increase. It was found that, compared with the ester group, the attachment of the positive charge to the main chain through the amide bond increases the extent of transition and decreases the critical acetone concentration. The jumpwise change in the gel volume accompanying the collapse is accompanied by a similar change in the shear modulus of the gel.Dedicated to Dr. Karel Duek on the occasion of his 60th birthday for his important contribution to polymer science     

Phase transition in swollen gels

Summary The swelling and mechanical behaviour of networks of copolymers of acrylamide, methylenebisacrylamide and sodium 2-(2-carboxybenzoyloxy)ethylmethacrylate (mole fraction of salt x _s =0–0.2) in water-acetone mixtures was investigated. In the range x _s 0.01 phase transition (collapse) was observed, with both the extent of the collapse and the critical acetone concentration in the mixture at collapse, a _c , increasing with increasing concentration of the salt. A comparison between these results and those obtained for networks with a quaternary ammonium salt led to a conclusion that an exchange of the positive charge of the ammonium salt (NCl) for the negative charge of the sodium salt (COONa) in the side chain decreases the critical content of salt necessary for the collapse, X _s ^c , from 0.03 to 0.01, and the collapse takes place at lower concentrations of acetone. The collapse may also take place in a mixed solvent waterethanol; the dependence of network swelling on the concentration of ethanol is roughly the same as that on the concentration of acetone.     

Phase transition in swollen gels

Summary The DC conductivity of two networks — a poly(N,N-diethylacrylamide) network (N1) and a network prepared by the copolymerization of N,N-diethylacrylamide with 3 mol.% of sodium methacrylate (N2) — in deionized water in the temperature range 10–55°C was measured. While in the low-temperature range (expanded gel state) the volt-ampere (V-A) behaviour of both networks shows a semiconductive character (conductivity increases with increasing temperature), in the high-temperature range (collapsed gel state) the conductivity of the network N1 rapidly decreases with increasing temperature (metallic character). The presence of charges on the chain raises the conductivity and shifts the temperature of the change in conductivity to higher values. In the collapse region of the ionized network N2 anomalies were observed on the V-A characteristics.     

Phase transition in swollen gels

Summary The temperature dependence of the swelling and mechanical behaviour of two poly(N,N-diethylacrylamide) networks has been investigated in aqueous solutions at pH 7.5. While one network was prepared by the copolymerization of N,N-diethylacrylamide with N,N -methyl-enebisacrylamide in the presence of 92 vol 1.% water, 3 mol.% sodium methacrylate was added to the mixture used in the preparation of the second network. In the network without charges on the chain, both the swelling ratio and modulus were found to be continuously dependent on temperature. On the other hand, the ionized network containing sodium methacrylate showed a pronounced phase transition at the temperature T 51 °C connected with a jumpwise change in both the volume and modulus of the network.     

Phase transition in swollen gels

Summary The dynamic mechanical behaviour of 4% aqueous solutions and networks of poly (N, N-diethylacrylamide) and copolymers of diethylacrylamide with sodium methacrylate (MNa) (molar ratio x_MNA=0–0.05) swollen in water was measured in the temperature range 20–80 °C. With increasing temperature, at T_c polymer chains collapse from random coil to more compact globular conformations. While in the region of coil conformations (T > T_c) the mechanical behaviour of solutions has a liquid-like character (the loss modulus G″ is higher than the storage modulus G′ for a constant frequency ω=1 Hz), in the region of globular conformations (T > T_c) a heterogeneous physical network is built in solutions, and the mechanical behaviour has a solid-like character (G′ > G″). In networks the collapse is reflected in an increase of storage modulus G′; the magnitude of this increase decreases with ionization. The dependence of the loss modulus G″ on the temperature of solutions and networks allows us to conclude that the magnitude of losses in the collapsed state is affected rather by x_MNa (the modulus G″ increases with increasing ionization) than by the heterogeneous structure of the samples.     

Phase transition in swollen gels

Summary The photoelastic behaviour of two networks — polyacrylamide (PAAm) and of a network prepared by the copolymerization of acrylamide with 5 mol.% sodium methacrylate — was investigated in water-acetone mixtures. For the PAAm network the dependence of all photoelastic characteristics on the composition of the mixture is continuous. At 54 vol.% acetone in the mixture, the ionized network undergoes a transition which gives rise to jumpwise changes in the shear modulus, deformational-optical coefficient, C, and in the refractive index of the gel, n_g. While in the collapsed state the optical anisotropy of the statistical segment is negative, –3×10^–24 cm³ (indicating an interaction between the side chains), in the expanded state it is positive, 0.5 × 10^–24 cm³. The dependence of all optical characteristics on the composition of the mixtures suggests that: (a) in both networks we have a transition between two conformational states of the chain; while for the ionized network the transition is a discrete one, for the nonionized network it takes place in the range between 30 and 45 vol.% acetone in the mixture; (b) in both networks the gels are optically homogeneous throughout the whole range of compositions of the mixtures (and thus also in the close vicinity of the collapse of the ionized network).     

Phase transition in swollen gels

Summary The swelling and mechanical behaviour of ionized networks of copolymers of acryl amide (AAm) with N,N,N,N-trimethyl-2-methacryloyloxyethyl ammonium chloride (MOAC) (mole fraction ^xMOAC = 0–0.165) in water-acetone mixtures was investigated. In the range ^xmoac 0.029, phase transition was observed with increasing acetone content; both the extent of the transition, , and the critical acetone concentration at which the collapse takes place increased with increasing ^xmoac. The effect of concentration of the positive charge at the end of side chains of MOAC on the formation and extent of the collapse is roughly five times smaller than that of the negative charge in networks of the copolymer of AAm with sodium methacrylate. The jumpwise change in the gel volume is accompanied by a similar change in the value of the equilibrium modulus.     

Phase transition in swollen gels

Summary The temperature dependences of the small-angle neutron scattering (SANS) from solutions and networks of poly (N,N-diethylacrylamide) (PDEAAm), or from the copolymer of DEAAm and 5 mol.% sodium methacrylate (MNa) in deuterated water were measured. In the low-temperature range (T<30°C, expanded state) the SANS curves have features typical of scattering from polymer coils. At elevated temperatures (T>60°C, collapsed state) the character of SANS curves changes, indicating that in both networks and solutions compact globular structures are formed. The presence of MNa (i.e. of charges on the chains) shifts the temperature of the transition range from the expanded to the collapsed state towards higher temperature by 10–15°C.On leave from the Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences     

Phase diagram of borate-PVA system: Sol-gel transition and demixtion

Summary We study the formation of reversible gels induced by addition of borax in aqueous poly(vinylalcohol). Under suitable conditions, sol, gel or demixed phase is observed. We present a qualitative interpretation of the the number of inter-polymer complexes which is governed by the complexation equilibrium.     

Quantitative Determination of phosphatidylcholine by an HPLC-RI system

The following describes the quantitative determining method for phosphatidylcholine (PC) using the HPLC-RI system which we have developed. It uses Lichromsorb, Si 60 (10 μm), 4.6 mm × 250 mm as the column and a mobile phase consisting of n-hexane/isopropanol/water =1:4:1. In this report, we compared data from selected high-purity (60–100 wt%) samples using the HPLC-RI, HPLC-UV and conventional TLC-P methods. Under the conditions we described, the HPLC-UV method was somewhat affected by fatty acid compositions. As a result, there were some inconsistencies in the measured values. However, the HPLC-RI method we propose was applicable to PC from both egg yolk and soybeans. In addition, the HPLC-RI method produced data which correlated well with data from the TLC-P method, and this data was highly accurate and exhibited satisfac-tory reproductibility.     

Phase transition in the anisotropic cubic model

The critical behaviour of ferroelectrics or ferromagnets with a Hamiltonian of cubic symmetry is studied by the approximate renormalization group techniques, proposed previously in the frames of collective variables method.     

Phase transition in Sol-Gel processed barium titanate ceramics

Ferroelectric barium titanate (BaTiO₃) ceramics have been prepared from barium acetate [Ba(CH₃COO)₂] and titanium isopropoxide [Ti(CH₃)₂CHO)₄] precursors by sol-gel technique The as-grown powder was found to be amorphous which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The ceramics showed well saturated polarization-field (P-E) hysteresis loops at room temperature. The values of spontaneous polarization(P_s), remanent polarization (P_r) and coercive field (E_c) of the ceramics were found to be19.0, 12.66μC-cm^-2 and 30KVcm^-1 respectively. The room temperature dielectric constant (ε) and loss tangent (tanδ) of the ceramics were found to be 1135 and 0.012 respectively. The dielectric constant and tanδ showed anomaly peaks at 125°C showing ferroelectric to paraelectric phase transition. The polarization parameters also vanish at 125°C confirming the phase transition.