Molecular Composites of Rodlike/Flexible Polyimides

1989 ◽  
Vol 171 ◽  
Author(s):  
S. R. Rojstaczer ◽  
D.Y. Yoon ◽  
W. Volksen ◽  
B.A. Smith
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Light Scattering ◽  
Film Thickness ◽  
Domain Size ◽  
Amic Acid ◽  
Solution Blending ◽  
Thermal Imidization ◽  
Precursor Polymers ◽  
Molecular Composites

ABSTRACTMixtures of a rodlike and a flexible polyimide were prepared by solution-blending of the respective poly(amic alkyl ester) and poly(amic acid), followed by solvent evaporation and thermal imidization. The size scale of the phase separation, as measured by light scattering, is primarily set during the demixing of the precursor polymers, with no significant coarsening observed due to the imidization performed at 400°C. The observed variation of the domain size with parameters such as composition, molecular weight and film thickness is discussed in terms of the miscibility of the precursor polymers as well as the thermal history to which these were exposed.

Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology

2017 ◽  
Vol 5 (25) ◽  
pp. 13176-13188 ◽  
Author(s):  
Joo-Hyun Kim ◽  
Abay Gadisa ◽  
Charley Schaefer ◽  
Huifeng Yao ◽  
Bhoj R. Gautam ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Mobility ◽  
Bulk Heterojunction ◽  
Morphological Evolution ◽  
Domain Size ◽  
S Phase ◽  
Polymer Molecular Weight ◽  
Solvent Interactions ◽  
Polymer Solvent

The morphological evolution is initiated by L–L or L–S phase separation (left) and further developed by molecular mobility, governed by polymer–solvent interactions which determine the final domain size of the BHJ layer (right).

Molecular Weight Dependence of Domain Structure in Silica-Siloxane Molecular Composites

1992 ◽  
Vol 274 ◽  
Author(s):  
Tamara A. Ulibarri ◽  
Greg Beaucage ◽  
Dale W. Schaefer ◽  
Bernard J. Olivier ◽  
Roger A. Assink
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Composite Materials ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Precursor Polymer ◽  
Molecular Weight Dependence ◽  
Molecular Composites ◽  
Filler Phase

ABSTRACTA detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes' description of phase separation in a crosslinked system (R ∝ M1/2).

Polycarbodiimide and polyimide/cyanate thermoset in situ molecular composites

1998 ◽  
Vol 13 (7) ◽  
pp. 1840-1847 ◽  
Author(s):  
D. R. Wiff ◽  
G. M. Lenke ◽  
P. D. Fleming
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Mechanics ◽  
High Molecular Weight ◽  
Molecular Composites ◽  
Rigid Rod ◽  
Composite Reinforcement

The synthesis of polycarbodiimide and polyimide in a cyanate resin precursor was achieved. A unique procedure for achieving a high molecular weight of the molecular composite reinforcement molecules was demonstrated. In spite of phase separation being present during the processing, the final cured composites were transparent. The enhanced mechanical properties and the presence of a single Tg, which increases with rigid rod content, were indications that a molecular composite was achieved. The agreement between measured mechanical properties and those predicted using molecular mechanics simulations CERIUS2 software was encouraging.

Structure And Properties Of Binary Rodlike/Flexible Polyimide mixtures.

1991 ◽  
Vol 227 ◽  
Author(s):  
S. Rojstaczer ◽  
M. Ree ◽  
D Y. Yoon ◽  
W. Volksen
Keyword(s):  
Photoelectron Spectroscopy ◽  
Surface Segregation ◽  
Amic Acid ◽  
Structure And Properties ◽  
Matrix Component ◽  
X Ray ◽  
Solution Blending ◽  
Thermal Imidization ◽  
Rodlike Polymers ◽  
Strong Surface

Abbstract:Binary mixtures of a rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA) and a flexible 6F-BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2-bis(4-aminophenoxy-p-phenylene) hexafluoropropane were prepared by solution-blending of the meta-PMDA-PDA poly(amic ethyl ester) and 6F-BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. The size scale of the phase separation, as measured by light scattering, is ca. I μm or smaller in most cases. Dynamical mechanical thermal analysis measurements indicate that the glass transition temperature of 6F-BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X-ray photoelectron spectroscopy results show a strong surface segregation of 6F-BDAF in mixtures containing as low as 10% by weight of the 6F-BDAF component in the bulk. The mixtures with PMDA-PDA as the major matrix component therefore maintain excellent bulk properties of rodlike polymers, i.e., high modulus to 500°C, and low coefficients of thermal expansion (< ca. 10 ppm/°C). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F-BDAF, resulting in excellent polymer/polymer self-adhesion (lamination) properties between fully imidized films.

MIXING AND PHASE SEPARATION IN LIQUID CRYSTAL/MATRIX SYSTEMS

1993 ◽  
Vol 07 (25) ◽  
pp. 4187-4213 ◽  
Author(s):  
GEORGE W. SMITH
Keyword(s):  
Molecular Weight ◽  
Liquid Crystal ◽  
Phase Separation ◽  
Light Scattering ◽  
Specific Heat ◽  
Film Formation ◽  
Solution Temperature ◽  
Heat Of Mixing ◽  
The Matrix ◽  
Liquid Crystal Matrix

We review mixing and phase separation (demixing) in mixtures of low molecular weight liquid crystals (LCs) and organic matrices, with emphasis on aspects relevant to the formation of polymer-dispersed liquid crystal films. These films, which contain a myriad of micron-sized LC droplets, are of interest because of their electro-optic properties. Film formation is simple: A liquid crystal and a liquid polymer precursor are initially mixed to form a single phase. Subsequently the polymer is hardened, and LC microdroplets phase-separate from the matrix. Although matrix hardening can be achieved in several ways, this review focuses on curing, during which cross-linking reactions lead to an increased matrix molecular weight. Topics discussed include: phase behavior of the binary system before, during, and after cure and LC/matrix solubilities. The Flory-Huggins model for phase separation (as modified by several workers) has provided a theoretical basis for the studies. Principal experimental tools have been calorimetry and light scattering. Uncured LC/matrix binaries possess phase diagrams with an upper critical solution temperature. Such systems, when heated through the mixing temperature, exhibit a decrease in specific heat, the (negative) excess specific heat of mixing, ∆ C mix . A plot of ∆ C mix vs. LC concentration exhibits a minimum, from which we can estimate LC and uncured-matrix solubilities. Matrix cure plays a major role in the phase separation process: In partially-cured samples, ∆ C mix transitions persist until cure is nearly complete, at which time a fraction of the LC is permanently phase-separated, with the rest remaining dissolved in the matrix. The kinetics of phase separation can be determined by calorimetry or light scattering. Cure rates have been shown to control LC microdroplet size, with fast cures leading to small droplets. Calorimetry of the fully cured system also allows us to determine the solubility of liquid crystal in the polymer matrix, as well as the fraction of phase-separated LC. An approximation based on the lever rule and the Flory-Huggins spinodal curve provides an upper bound for the solubilities and also describes their temperature dependence.

A Time-Resolved Low-Angle Light Scattering Apparatus. Application to Phase Separation Problems in Polymer Systems

2001 ◽  
Vol 66 (6) ◽  
pp. 973-982 ◽  
Author(s):  
Čestmír Koňák ◽  
Jaroslav Holoubek ◽  
Petr Štěpánek
Keyword(s):  
Phase Separation ◽  
Light Scattering ◽  
Signal To Noise Ratio ◽  
Scattered Light ◽  
Ccd Camera ◽  
Time Resolved ◽  
Polymer Systems ◽  
Software Analysis ◽  
Phase Separation Kinetics ◽  
Small Angle Light Scattering

A time-resolved small-angle light scattering apparatus equipped with azimuthal integration by means of a conical lens or software analysis of scattering patterns detected with a CCD camera was developed. Averaging allows a significant reduction of the signal-to-noise ratio of scattered light and makes this technique suitable for investigation of phase separation kinetics. Examples of applications to time evolution of phase separation in concentrated statistical copolymer solutions and dissolution of phase-separated domains in polymer blends are given.

scholarly journals Tunable thermo-reversible bicontinuous nanoparticle gel driven by the binary solvent segregation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yuyin Xi ◽  
Ronald S. Lankone ◽  
Li-Piin Sung ◽  
Yun Liu
Keyword(s):  
Phase Separation ◽  
Domain Size ◽  
Binary Solvent ◽  
Colloidal Systems ◽  
Colloidal Assembly ◽  
Structures And Properties ◽  
Wide Range ◽  
Equilibrium Process ◽  
Equilibrium Structures ◽  
Non Equilibrium

AbstractBicontinuous porous structures through colloidal assembly realized by non-equilibrium process is crucial to various applications, including water treatment, catalysis and energy storage. However, as non-equilibrium structures are process-dependent, it is very challenging to simultaneously achieve reversibility, reproducibility, scalability, and tunability over material structures and properties. Here, a novel solvent segregation driven gel (SeedGel) is proposed and demonstrated to arrest bicontinuous structures with excellent thermal structural reversibility and reproducibility, tunable domain size, adjustable gel transition temperature, and amazing optical properties. It is achieved by trapping nanoparticles into one of the solvent domains upon the phase separation of the binary solvent. Due to the universality of the solvent driven particle phase separation, SeedGel is thus potentially a generic method for a wide range of colloidal systems.

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