Solvent Quality Effects in Sol-Gel Processing

1992 ◽  
Vol 271 ◽  
Author(s):  
Joseph K. Bailey
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Solubility Parameter ◽  
Sol Gel ◽  
Parameter Range ◽  
Molecular Weights ◽  
Solvent Quality ◽  
Silicon Alkoxides ◽  
Gel Processing

ABSTRACTTo understand how solvent quality can be used to tailor structure in sol-gel processing of silicon alkoxides, polymerized tetramethoxysilane polymers were synthesized and fractionated to give relatively stable, narrow molecular weight dispersion samples. These polymers had molecular weights ranging from 8000 to 45,000. The solubility parameter range for these polymers is 8.9–14.5 (cal/cm3)1/2. Light scattering confirmed that this range could be used to predict solvent quality. Bulk gels prepared using good versus poor solvents demonstrated that solvent quality can be used to tailor properties of the gels, presumably by modifying the extent of interpenetration of the growing polymers.

Evaluation of polydispersity index Mw/Mn by quasielastic light scattering

1987 ◽  
Vol 52 (5) ◽  
pp. 1235-1245 ◽  
Author(s):  
Petr Štěpánek ◽  
Zdeněk Tuzar ◽  
Čestmír Koňák
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Decay Time ◽  
Sampling Time ◽  
Polydispersity Index ◽  
New Method ◽  
Molecular Weights ◽  
Quasielastic Light Scattering ◽  
Good Agreement

The response of quasielastic light scattering to the polydispersity of scattering objects has been investigated. A new method of the polydispersity index determination has been suggested, suitable for the range 1.02 ⪬ Mw/Mn ⪬ 2.0 and consisting in the measurement of the dependence of the apparent decay time on the correlator sampling time. The polydispersity index can be determined by comparing these dependences with the theoretical ones obtained using correlation curves simulated for various values of the polydispersity index, assuming lognormal and Schulz-Zimm distributions of molecular weights. The test measurements on polystyrene standards having molecular weights in the range 9 103 – 20.6 106 give polydispersity index values Mw/Mn that are in a good agreement with those given by the manufacturer. The polydispersity index for polystyrene having the molecular weight Mw = 20.6 106 thus determined was Mw/Mn = 1.35.

Growth of PLZT Thick Films by Polymer Modified Sol-Gel Processing for Optical Shutting

2008 ◽  
Vol 136 ◽  
pp. 67-74 ◽  
Author(s):  
Z.H. Du ◽  
T.S. Zhang ◽  
H.M. Shang ◽  
X.L. Chen ◽  
Jan Ma
Keyword(s):  
Molecular Weight ◽  
Critical Thickness ◽  
Thick Films ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Liquid Phase Sintering ◽  
Optical And Electrical Properties ◽  
Densification Behavior ◽  
Free Films ◽  
Gel Processing

PLZT9/65/35 thick films were prepared from the solution containing PVP360 (polyvinylpyrrolidone, with average molecular weight of 360000). With the solutions, the critical thickness of a single PLZT layer could increase to ~624nm compared with 77nm-thick films prepared without PVP360. Furthermore, by adding 20~35% excess of Pb to the precursor solutions, the nano-porous rosette-like structures and a small amount of pyrochlore remnant, which were found very common in the PVP-modified films, could be eliminated. 35% Pb excess was also found to initiate liquid-phase sintering, leading to dense and crack-free films. The effect of Pb excess on the rosette removal and densification behavior of the films was discussed. Moreover, the optical and electrical properties of the PLZT films with 35% Pb excess were also studied.

Effects of poly(ethylene glycol) additive molecular weight on the microstructure and properties of sol-gel-derived lead zirconate titanate thin films

2003 ◽  
Vol 18 (3) ◽  
pp. 737-741 ◽  
Author(s):  
Shuhui Yu ◽  
Kui Yao ◽  
Santiranjan Shannigrahi ◽  
Francis Tay Eng Hock
Keyword(s):  
Thin Films ◽  
Molecular Weight ◽  
Ethylene Glycol ◽  
Lead Zirconate Titanate ◽  
Sol Gel ◽  
Lead Zirconate ◽  
Poly Ethylene Glycol ◽  
Molecular Weights ◽  
Zirconate Titanate ◽  
Poly Ethylene

Poly(ethylene glycol) (PEG) additives with different molecular weights were used to modify sol-gel precursor solutions for preparing lead zirconate titanate (PZT) thin films. The morphology, crystalline structure, and mechanical and electrical properties of the films were characterized. The relationship between the characteristics of the films and the molecular weight of PEG was investigated. It was observed that the PEG eliminated cracking of the films during multiple pyrolysis treatments. However, with the increase of the PEG molecular weight, the films became less dense, which led to decreased Young's modulus and dielectric constant and increased coercive field. Our experiments showed that films prepared from sols modified by PEG with a molecular weight of 200 exhibited a dense morphology and excellent mechanical and electric properties without cracking.

Solution Properties of Polybutadiene and trans-Polyisoprene Fractions

1963 ◽  
Vol 36 (2) ◽  
pp. 488-501
Author(s):  
W. Cooper ◽  
D. E. Eaves ◽  
G. Vaughan
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Benzene Solution ◽  
Second Virial Coefficient ◽  
Virial Coefficients ◽  
Γ Radiation ◽  
Branched Polymer ◽  
Butyl Lithium ◽  
Second Virial Coefficients ◽  
Molecular Weights

Abstract Linear polybutadienes, prepared with butyl lithium as catalyst, and polybutadienes branched by exposure to γ-radiation have been fractionated and the fractions examined by osmometry and light scattering. Turbidimetric second virial coefficients (A2τ) of mixed polymer fractions are virtually the same as those of the higher molecular weight components of the mixtures for most compositions. This is true both for mixtures of linear with linear and linear with branched polymer. The higher the molecular weight of the fraction, the greater the effect; the addition of 1 per cent microgel to a linear polymer reduced A2τ by a factor of three. The presence of microgel or high molecular weight branched polymer has been shown to be responsible for the very high molecular weights previously reported for polybutadienes from light scattering measurements. It is conveniently removed by shaking the solutions with calcium sulfate. Second virial coefficients obtained either by light scattering or osmometry are, within the limits of experimental error, uninfluenced by branching in the polymer. In general those factors which lead to increased branching also result in increased polydispersity, and it is the latter which results in the decrease in A2τ. The fall of the osmotic second virial coefficient (A2τ) with molecular weight is much smaller than would be calculated theoretically, and the fall in A2τ is greater than would be expected, notwithstanding the fact that for some of the fractions Mw/Mn<1.1. This indicates that A2τ is sensitive to the low molecular weight species present in the fractions, whereas the reverse must apply to A2τ. Natural or synthetic trans-polyisoprene showed analogous behavior to polybutadiene, although, owing to experimental difficulties, sharp branched fractions could not be obtained. The following viscosity-molecular weight relationships were obtained in benzene solution: [η]=1.45×10−4M0.76 for butyl lithium-catalyzed polybutadienes, and [η]=4.37×10−4M0.65 for natural and synthetic trans-polyisoprenes.

Development of Polymeric Micro/Nanostructures For Gene Delivery

2007 ◽  
Vol 1019 ◽  
Author(s):  
Dania Alyounes ◽  
Christopher Yengo ◽  
Tim Doran ◽  
Qi Lu ◽  
Kenneth Gonsalves
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Light Scattering ◽  
Binding Affinity ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Fluorescence Studies ◽  
Molecular Weights ◽  
Fluorescence Techniques ◽  
Exponential Increase

AbstractPluronic® polymers were screened for binding affinity to oligoribonucleotides (ORN) using fluorescence techniques. F127 (Mw 12600 g/mole) proved to have the strongest binding affinity. Urethane linkages were introduced into F127 and two other Pluronics, F38 (Mw 4700 g/mole) and F77 (Mw 6600 g/mole) to prepare polymers that were multiples of their respective initial molecular weights. A series of these polyurethane Pluronics were screened for binding affinity. Fluorescence studies showed a relationship between the molecular weight of the PO units and the binding affinity in the structures of the newly synthesized polyPluronics, especially in the case of F77. Light scattering confirmed the binding affinity between the ORN and F77 polymers. Particle size analysis showed an exponential increase until the critical micelle concentration. Other analogs of these polymers also studied for their binding affinity were poly(ester amines) and PINC.

Determination of Copolymer Molecular Weight

1968 ◽  
Vol 41 (1) ◽  
pp. 245-253 ◽  
Author(s):  
Paul Rempp ◽  
Henri Benoit
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Density Gradient ◽  
Compositional Heterogeneity ◽  
Precise Information ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Binary Copolymers

Abstract From this brief review it appears that determinations of molecular weight averages, of molecular weight distributions, and of compositional inhomogeneity of binary copolymers, require care in the choice of techniques and methods. Some of the most commonly used techniques for molecular weight determinations on homopolymers of various kinds are inadequate for the same determinations on copolymers. Others are more sensitive to fluctuations in composition than in molecular weights. Osmotic methods are the only one which are really insensitive to inhomogeneity, and which yield molecular weights. Ultracentrifugation in a density gradient yields precise information only on fluctuations in composition. Viscosity determinations require calibration, but even so, they may lead to erroneous values of the molecular weight in the case of copolymers. GPC is less sensitive to compositional heterogeneity, but cannot be applied for nonlinear copolymers. Finally, light scattering is a very powerful tool for studies on copolymers, since it leads to molecular weight averages and its helps characterize polydispersity and fluctuations in composition.

LIGHT-SCATTERING STUDIES OF SODIUM THYMONUCLEATE

1950 ◽  
Vol 28b (3) ◽  
pp. 96-104 ◽  
Author(s):  
D. B. Smith ◽  
H. Sheffer
Keyword(s):  
Hydrogen Peroxide ◽  
Molecular Weight ◽  
Light Scattering ◽  
Sodium Chloride ◽  
Aqueous Solutions ◽  
Salt Solution ◽  
Molecular Weights ◽  
Three Samples ◽  
Two Samples ◽  
Viscous Solution

The scattering of light by aqueous solutions of three different samples of sodium thymonucleate has been investigated. It was found that one sample in water consisted of randomly coiled molecules of molecular weight greater than 24 × 106. A second sample gave a less viscous solution in water and was only partially coiled, the coiling of the molecules being increased by the addition of a small amount of sodium chloride. In dilute salt solution the molecular weights of all three samples were greater than 3.7 × 106. Two samples of nucleate were degraded in solution by irradiation with ultraviolet light in the presence of hydrogen peroxide. In both cases the nucleate was converted into material consisting of rodlike molecules, 2400 Å in length and having a molecular weight of 750,000.

Comparison of the molecular weights of deoxyribonucleic acids as determined from light scattering and from sedimentation and viscosity

1959 ◽  
Vol 250 (1260) ◽  
pp. 1-21 ◽  
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Large Change ◽  
Scattering Method ◽  
X Rays ◽  
Single Chain ◽  
Molecular Weights ◽  
Upper Limit ◽  
Rough Approximation ◽  
Main Effect

Measurements have been made of (1) light scattering, (2) sedimentation characteristics, and (3) viscosities of identical, well-clarified solutions of a considerable number of preparations of DNA from various sources and under conditions which permit extrapolation of the relevant molecular quantities to zero concentration. In order to increase the range of sizes examined, similar observations have been made with specimens which had been irradiated with 15 MeV electrons or X-rays. It is found that, to a rough approximation, the relation S 0 α [ η ] ⅓ holds for all samples (except those which were heated). There does not appear to be any correlation between M L , the molecular weight determined by light scattering and either [ η ] or S 0 . Values of M η, s from viscosity and sedimentation data have been calculated using the equation of Mandelkern, Flory, Krigbaum & Scheraga (1952) and it was found that with the unirradiated samples these values did not agree with M L , although reasonable agreement was obtained with the irradiated samples. The validity of the calculation of M η, s is discussed. Analysis of the angular variation of the light scattering shows no significant change in the flexibility of the coils upon irradiation, in contrast with the effect of heating where a large change of flexibility occurs. This is in agreement with the hydrodynamic relations given above. Consequently, the differences between irradiated and unirradiated DNA cannot be ascribed to changes of flexibility and the need to use a different model on that account. Since S 0 and [ η ] are both decreased by small doses of radiation, it is difficult to avoid the conclusion that real changes of molecular weight occur, which have not been discovered by the light-scattering method as employed here. It is shown that both for rods and coils there is an upper limit, at finite angles, to the light scattered by a given concentration of polymer, as the size is increased. For a molecule intermediate between a rod and a coil, the limiting curve may appear to have a finite intercept owing to a concealed high curvature at very small angles of scattering. This may set an upper limit to the observed molecular weight for a given degree of flexibility. If the main effect of irradiation is a decrease of molecular weight without marked changes of flexibility, it is difficult to avoid the conclusion either that single chain breaks do not influence the flexibility of the particle or that a high proportion of double breaks occurs.

Hafnium Metallo-Organic Films and Gels Produced by Sol-Gel Processing

1989 ◽  
Vol 155 ◽  
Author(s):  
Charles D. Gagliardi ◽  
Kris A. Berglund
Keyword(s):  
Light Scattering ◽  
Sol Gel ◽  
Organic Films ◽  
Spin Casting ◽  
Synthesis Technique ◽  
Refractory Oxides ◽  
Sol Gel Process ◽  
Optically Transparent ◽  
Acid Catalyzed ◽  
Gel Processing

ABSTRACTMetallo-organic materials are often used as precursors for highly refractory oxides and hightemperature composites. The feasibility of producing hafnium metallo-organic films and gels by sol-gel techniques is demonstrated in the present study. Since hafnium alkoxides are not commercially available, their preparation is an obstacle in the development of their sol-gel processing applications. A common synthesis technique was used to produce hafnium isopropoxide, which was subsequently hydrolyzed under acid catalyzed conditions to produce films and gels. The films were prepared by spin casting and remained optically transparent. Initially, the gels were also optically transparent, but became translucent upon drying. Raman, IR, and light scattering spectroscopies were used to characterize this sol-gel process, and it is compared with the analogous processing of titanium and zirconium alkoxides.

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