Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Nanocomposites

2011 ◽  
Vol 1312 ◽  
Author(s):  
Jesmy Jose ◽  
Abakar Adam Omar ◽  
Guillaume Brotons ◽  
Jean-François Tassin
Keyword(s):  
Molecular Weight ◽  
Preparation Method ◽  
Low Frequency ◽  
Elastic Solid ◽  
Polymer Chains ◽  
Correlation Peak ◽  
Preparation Methods ◽  
Molecular Weights ◽  
Twin Screw ◽  
High Concentrations

ABSTRACTModel polymer nanocomposites based on geometrically well defined and protected Laponite particles dispersed in Poly(ethylene oxide) were investigated in order to improve the understanding of the filler dispersion effects on rheology by varying two experimental factors, namely preparation method and PEO matrix molecular weight. Preparation methods are divided into a solution dispersion and a melt dispersion by twin screw extrusion. The linear viscoelastic properties of the samples prepared by solution method revealed an elastic solid like behaviour at Laponite weight fractions as low as 0.1%, dramatically lower than the percolation threshold so far reported for such kind of systems. The sample preparation by melt dispersion, although leading to dispersed particles, does not achieve the same levels of modulus as compared to solution prepared mixtures. We propose a qualitative interpretation of this phenomenon, based on the mixture between a liquid and a dispersed phase of rather solid character. Further experiments using small angle X-ray scattering techniques (SAXS) show that the modulus level is not necessarily related to the height of the correlation peak characteristic of the Laponite stacks. However, for samples prepared with varying PEO matrix molecular weight the fraction of Laponite stacks decreases with increasing PEO molecular weight. The rheology master curve analyses show that confinements of polymer chains arising from high concentrations of particles and high molecular weight matrix chains do not impact the level of the low frequency modulus. However, a slower polymer dynamics, as observed for higher molecular weights, leads to an increase of the modulus at low particle loadings.

scholarly journals Water vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

2021 ◽  
Author(s):  
Maciej Łojkowski ◽  
Adrian Chlanda ◽  
Emilia Choińska ◽  
Wojciech Swieszkowski
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Self Assembly ◽  
Secondary Phase ◽  
Honeycomb Structure ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Secondary Phase Separation

<p>The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.</p>

Statistical Treatments of Rubber Structure

1960 ◽  
Vol 33 (5) ◽  
pp. 1201-1217 ◽  
Author(s):  
J. Scanlan ◽  
W. F. Watson
Keyword(s):  
Molecular Weight ◽  
Experimental Testing ◽  
Polymer Structure ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Average Value ◽  
Physical Form ◽  
The Subject ◽  
Branched Structures ◽  
Mathematical Analyses

Abstract Chemical reactions are random in nature and can therefore be subjected to mathematical analyses based on probability theory. This is a particularly necessary approach to polymer structure in which the effect of chance inherent in the reactions is preserved in physical form and therefore much attention has been given to deductions from such treatments. It is the purpose of this paper to review the results of those investigations which have particular application to rubbery high polymers. Some emphasis will be given to the authors' view that experimental testing of the derived expressions is still far from being satisfactory and that the subject in spite of the effort expended is still only at its beginning. Consideration of details of polymer structure is not merely an academic exercise. The properties of raw rubbers are highly dependent on polymer chain length and for many important ones such as viscosity, either in solution or in the melt, the dependence is not simply linear. Unless linear dependence on the number of molecules and their size does apply, an average value of molecular weight is insufficient to characterize a rubber sample in respect of the property considered and further knowledge of the distribution of molecular weights among the rubber molecules is required. The properties of rubbers are also markedly influenced by the occurrence of branching in the polymer chains; the insolubility and elasticity conferred by vulcanization are the results of the formation of complex branched structures which have been the subjects for statistical treatments.

scholarly journals The interplay between bi-modal molecular weight distribution in polystyrene and humidity induces self-assembly of biomimetic micropillars/honeycomb morphology in the thin polymer film

2021 ◽  
Author(s):  
Maciej Łojkowski ◽  
Adrian Chlanda ◽  
Emilia Choińska ◽  
Wojciech Swieszkowski
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Self Assembly ◽  
Phase Segregation ◽  
Polymer Chains ◽  
Thin Polymer Film ◽  
Chemical Compositions ◽  
Molecular Weights ◽  
The Right

<p>Segregation of polymer chains of different molecular weights is a well-known process. A traditional experimental approach of studying phase segregation in thin films composed of polymer blends with identical chemical compositions but different molecular weights was focused on functionalisation of chemical group or modification of end-group. In this study, however, a different approach was proposed. Polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. The films were prepared by spin-coating and the segregation between polystyrene phases was investigated by force spectroscopy. The solubility of bimodal polystyrene was explored. At the right molecular weight distribution and soluted in Methyl Ethyl Ketone, the phase segregation occurred. Introduction of moist airflow induced the separation of the lower molecular weight into micropillars and the heavier fraction self-organized into a honeycomb. As a result, an easy, fast, and effective method of obtaining micropillar/honeycomb morphologies was demonstrated. The mechanism of formation of such structures was explained. </p>

The colloidal behaviour of dyes

1952 ◽  
Vol 212 (1109) ◽  
pp. 274-290 ◽  
Keyword(s):  
Molecular Weight ◽  
Orange Ii ◽  
Condensation Polymerization ◽  
Aggregation Process ◽  
Acid Dyes ◽  
Molecular Weights ◽  
Addition Polymerization ◽  
Diffusion Controlled ◽  
Low Concentrations ◽  
High Concentrations

The colloidal behaviour of four acid dyes has been studied by light-scattering. It was shown that none of these dyes was aggregated in the absence of electrolyte and that Orange II does not form stable micelles, even in high concentrations, but the process of flocculation in the absence of dust nuclei can be followed and is similar to addition polymerization. Benzopurpurin forms stable micelles, and the aggregation process is similar to a diffusion-controlled condensation polymerization. In low concentrations of electrolyte, micelles with molecular weights between 10000 and 50000 are formed between 20 and 40° C. In higher concentrations of salt large asymmetric micelles with molecular weights about 10 6 are formed. At 60° C no aggregates were detected in similar electrolyte concentrations. In general, the behaviour of Coomassie Milling Scarlet resembled that of Benzopurpurin except that it was more salt sensitive and did not form giant micelles. Polar Yellow formed a very stable micelle the molecular weight of which, 1·1 x 10 5 , was unchanged over the electrolyte range 0·05 to 0·2 M - NaCl at temperatures between 20 and 60° C, although the micelle dissociates above this temperature. The addition of urea and phenol was found to be effective in preventing the aggregation of Benzopurpurin and Coomassie Milling Scarlet, but not of Polar Yellow. The factors involved in the formation and stability of the colloidal micelles of dyes are discussed.

THE BUTYLLITHIUM-INITIATED POLYMERIZATION OF METHYL METHACRYLATE: PART II. MOLECULAR WEIGHT DISTRIBUTIONS

1963 ◽  
Vol 41 (8) ◽  
pp. 1905-1910 ◽  
Author(s):  
B. J. Cottam ◽  
D. M. Wiles ◽  
S. Bywater
Keyword(s):  
Molecular Weight ◽  
Methyl Methacrylate ◽  
Proton Magnetic Resonance ◽  
Polymer Chains ◽  
Double Peak ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Before And After ◽  
Made In

Samples of poly (methyl methacrylate) have been made in toluene solution at −30° C with n-butyllithium initiator. Different monomer and initiator concentrations were used to obtain products of different overall molecular weights; polymerization times were varied to achieve partial as well as complete polymerization. The polymer samples were divided into fractions which were examined as to molecular weight and microstructure. It was found that the whole polymers have unusually wide molecular weight distributions which can be attributed to a combination of two narrower distributions, one of which occurs at a low and the other at a higher molecular weight region. This "double peak" phenomenon was observed for polymers at lower conversions as well as for polymers representing complete conversion of monomer. Proton magnetic resonance measurements showed that the degree of isotacticity of various fractions of a whole polymer is not the same at all molecular weights.In one case a second portion of monomer was polymerized after the complete polymerization of a first portion. Comparison of the molecular weight distribution before and after the second addition of methyl methacrylate indicated that polymer chains in all molecular weight regions, above a very low minimum value, are capable of further addition of monomer.

Dynamic Mechanical Properties of Cross-Linked Rubbers. II. Effects of Crosslink Spacing and Initial Molecular Weight in Polybutadiene

1966 ◽  
Vol 39 (4) ◽  
pp. 905-914
Author(s):  
Etsuji Maekawa ◽  
Ralph G. Mancke ◽  
John D. Ferry
Keyword(s):  
Molecular Weight ◽  
Crosslink Density ◽  
Low Frequency ◽  
Dynamic Mechanical Properties ◽  
Cross Linking ◽  
Loss Mechanism ◽  
Low Frequencies ◽  
Molecular Weights ◽  
Monomeric Friction Coefficient ◽  
Lower Frequencies

Abstract The complex shear compliances of eight samples of polybutadiene crosslinked by cumyl peroxide and four samples crosslinked by sulfur have been measured over a frequency range from 0.2 to 2 cps at temperatures from − 6 to 45° C by a torsion pendulum. On four of the samples, measurements were extended by the Fitzgerald transducer from 45 to 600 cps at temperatures from − 71 to 55°. The vulcanizates had been prepared from polymers of two different molecular weights (180,000 and 510,000) with sharp molecular weight distribution; the physical crosslink density ranged from 0.57 to 2.68×10−4 mole/cm3, and the chemical crosslink density calculated following Kraus ranged from 0.22 to 1.49×10−4 mole/cm3. The mechanical data were all reduced to T0=298° K by shift factors calculated from the equation log aT=−3.64(T−T0)/(186.5+T−T0). In the transition zone of frequencies, the viscoelastic functions of the cumyl peroxide vulcanizates were closely similar, except for a shift toward lower frequencies with increasing crosslinking, corresponding to a small but unexpected increase in the monomeric friction coefficient. Cross-linking by sulfur caused a somewhat larger shift toward lower frequencies at a comparable crosslink density. In the rubbery zone, the sample with least cross-linking exhibited a substantial secondary loss mechanism at very low frequencies. The low-frequency losses are evident in all the samples, but their magnitude falls rapidly with increasing crosslink density as previously found for natural rubber. It also falls somewhat with increasing initial molecular weight, indicating a contribution from network strands with loose ends. The possible relation of the low-frequency losses to trapped entanglements is discussed.

scholarly journals The cellulolytic enzymes of Botryodiplodia theobromae Pat. Separation and characterization of cellulases and β-glucosidases

1979 ◽  
Vol 177 (1) ◽  
pp. 9-19 ◽  
Author(s):  
Gabriel M. Umezurike
Keyword(s):  
Molecular Weight ◽  
Polyacrylamide Gel Electrophoresis ◽  
Gel Filtration ◽  
Exchange Chromatography ◽  
Cellulolytic Enzymes ◽  
Botryodiplodia Theobromae ◽  
Molecular Weights ◽  
Low Concentrations ◽  
High Concentrations

1. Filtrates from cultures of different ages of Botryodiplodia theobromae Pat. were fractionated by gel filtration, ion-exchange chromatography and polyacrylamide-gel electrophoresis. 2. Five cellulases (C1, C2, C3, C4 and C5) were found, and their molecular weights, estimated by gel filtration, were 46000–48000 (C1), 30000–35000 (C2), 15000–18000 (C3), 10000–11000 (C4) and 4800–5500 (C5). 3. Cellulase C5 was absent from old culture filtrates. 4. Cellulase C1 had little or no activity on CM-cellulose (viscometric assay), but degraded cotton flock and Whatman cellulose powder to give cellobiose only. 5. The other components (C2–C5) produced cellobiose and smaller amounts of glucose and cellotriose from cellulosic substrates and were more active in lowering the viscosity of CM-cellulose. 6. The ratio of activities assayed by viscometry and by the release of reducing sugars from CM-cellulose increased with decrease in the molecular weights of cellulases C2–C5. 7. Cellobiose inhibited the activities of the cellulases, but glucose stimulated at low concentrations although it inhibited at high concentrations. 8. A high-molecular-weight β-glucosidase (component B1, mol.wt. 350000–380000) predominated in filtrates from young cultures, but a low-molecular-weight enzyme (B4, mol.wt. 45000–47000) predominated in older filtrates. 9. Intermediate molecular species of β-glucosidase (B2, mol.wt. 170000–180000; B3, mol.wt. 83000–87000) were also found. 10. Cellulases C2–C5 acted in synergism with C1, particularly in the presence of β-glucosidase.

Influence of Thermal Treatment on the Molecular Weights of Polyhydroxyalkanoate Containing 3-Hydroxyhexanoate

2013 ◽  
Vol 812 ◽  
pp. 250-253 ◽  
Author(s):  
Yoga Sugama Salim ◽  
Chin Han Chan ◽  
Kumar Sudesh ◽  
Seng Neon Gan
Keyword(s):  
Molecular Weight ◽  
Thermal Treatment ◽  
Gel Permeation Chromatography ◽  
Polymer Processing ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Gel Permeation ◽  
Ftir Spectrometer ◽  
Major Reduction ◽  
End Group

With blooming interests in the research of biodegradable polyesters produced from microorganisms as well as polymer processing and technology, this study is intended to reveal the influence of thermal treatment on the molecular weight of poly (3-hydroxybutyrate-co-3 mol% 3-hydroxyhexanoate)/P(3HB-co-3 mol% 3HHx), a copolymer of polyhydroxyalkanoates (PHA). P(3HB-co-3 mol% 3HHx) was thermally treated using Differential Scanning Calorimeter and analyzed using Gel Permeation Chromatography and Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. Results from gel permeation chromatography suggest a major reduction of molecular weight up to 50 % when P(3HB-co-3 mol% 3HHx) is exposed to 180 °C for 30 mins. The half-time degradation of P(3HB-co-3 mol% 3HHx) treated at 170 °C and 180 °C is 14.1 and 9.9 mins, respectively. FTIR spectroscopy shows an increase absorbance intensity of P(3HB-co-3 mol% 3HHx) after thermal treatment, indicating a formation of more alkenyl and carboxylic end-group in polymer chains due to random chain scissions.

scholarly journals Exploiting the Interplay Between Bi-Modal Molecular Weight Distribution in Polystyrene and Humidity to Induce Self-Assembly of Biomimetic Micropillars/honeycomb Morphology in Thin Polymer Film

2021 ◽  
Author(s):  
Maciej Łojkowski ◽  
Adrian Chlanda ◽  
Emilia Choińska ◽  
Wojciech Swieszkowski
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Self Assembly ◽  
Spin Coating ◽  
Phase Segregation ◽  
Polymer Chains ◽  
Thin Polymer Film ◽  
Chemical Compositions ◽  
Molecular Weights

<p>Segregation of polymer chains of different molecular weights is a well-known process. For many years, it was assumed that this process occurs over long-time intervals. On the contrary, solvent evaporation during spin-coating is very fast. A traditional experimental approach of studying phase segregation of thin films composed of polymer blends with identical chemical compositions but different molecular weights, was focused on functionalization of chemical group or modification of end-group. In this study however, a different approach was proposed, in which polystyrene with a bimodal molecular weight distribution but no additional chemical modification was implemented in order to examine and analyze its phase segregation. By doing this, we have presented an easy, fast, effective and fully controlled method of obtaining biomimetic micropillar/honeycomb morphologies. In addition, the evaporation rate during spin-coating and the viscosity of a solution with a bimodal molecular weight distribution was described.</p>

scholarly journals Synthesis, structure and thermogravimetric analysis of α,ω-telechelic polydimethylsiloxanes of low molecular weight

2017 ◽  
Vol 82 (12) ◽  
pp. 1395-1416 ◽  
Author(s):  
Aleksandra Tasic ◽  
Marija Pergal ◽  
Malisa Antic ◽  
Vesna Antic
Keyword(s):  
Molecular Weight ◽  
Thermogravimetric Analysis ◽  
Degradation Mechanism ◽  
Gel Permeation Chromatography ◽  
Polymer Chains ◽  
Low Molecular Weight ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Dilute Solution Viscometry

A series of ?,?-telechelic polydimethylsiloxanes (PDMS), with predetermined molecular weights of about 2500 g mol-1, was synthesized by siloxane equilibration reaction. Syntheses were performed using octamethylcyclotetrasiloxane (D4) and various disiloxanes: hexamethyldisiloxane (HMDS), 1,1,3,3-tetramethyldisiloxane (TMDS), 1,3-divinyltetramethyldisiloxane (DVTMDS), 1,3-bis(3-carboxypropyl)tetramethyldisiloxane (DCPTMDS) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (DAPTMDS). The role of the disiloxane was to introduce terminal functional groups at the end of the polymer chains and to control the molecular weight of the polymers. Polymers with trimethyl, hydrido, vinyl, carboxypropyl and aminopropyl end-groups were obtained in this way. The structure of the ?,?-telechelic PDMSs was confirmed by NMR and IR spectroscopy. The molecular weights of the polymers were determined by 1H-NMR, gel permeation chromatography (GPC) and dilute solution viscometry. Thermogravimetric analysis (TGA) under nitrogen and air showed that the type of the terminal groups significantly influenced the thermal and thermo-oxidative stability, as well as the degradation mechanism of the ?,?-telechelic PDMSs.

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