Hervé Marand | Virginia Tech (original) (raw)
Papers by Hervé Marand
Macromolecules, 1989
ABSTRACT Molecular energy calculations are used to assess the lattice strain energy density ε and... more ABSTRACT Molecular energy calculations are used to assess the lattice strain energy density ε and the corresponding interfacial surface free energy σs in melt-crystallized polyethylene crystals. The quantity ε, which is defined as the difference in lattice energy density between an unstrained crystal and a strained crystal, is calculated with the use of published lattice expansion data. A strain-induced interfacial surface free energy σs of about 0.9 erg·cm-2 (mJ·m-2) was derived from the strain energy density for a lamellar thickness of around 14 nm. This result compares favorably with the value obtained in the recent extension of nucleation theory by J.D. Hoffman and R.L. Miller describing the geometry and the growth kinetic of curved-edge polyethylene crystals.
Journal of thermal analysis, 1997
ABSTRACT We report the results of an investigation by differential scanning calorimetry (DSC) of ... more ABSTRACT We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (T g) and secondary crystallization aboveT g. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer — the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained from small strain creep studies of “physical aging” of semicrystalline PEEK below and aboveT g.
We have established that a number of inconsistencies exist when one attempts to correlate the cha... more We have established that a number of inconsistencies exist when one attempts to correlate the change in the degree of crystallinity during secondary crystallization through various techniques. Some of these discrepancies can be conceptually explained in terms of the crystallization time and temperature dependence of the crystal and amorphous densities or the average specific heat capacity of the amorphous fraction.
Isothermal spherulitic growth rates were measured for a series of narrow molecular weight distrib... more Isothermal spherulitic growth rates were measured for a series of narrow molecular weight distribution isotactic poly(styrene) samples (250,000 - 1,600,000 g/mol) between 120.5C and 223.5C. Curve fitting analyses of the spherulitic growth rate data using a modified version of the Lauritzen-Hoffman theory allowed us to derive the equilibrium melting temperature, the secondary nucleation constant, and the Vogel parameters (B and T(infinity)) describing the temperature dependence of segmental relaxation in the liquid state. The Vogel parameters derived from the crystal growth rate analysis are in quantitative agreement with those derived from our study of the temperature dependence of the stress relaxation modulus. The equilibrium melting temperature derived from our analysis is significantly higher than that estimated in the literature using the Hoffman-Weeks method. The spherulitic growth rates are independent of chain length in the molecular weight range investigated. S! caling laws...
The temperature dependence of the spherulitic growth rate, G(Tx), for isotactic polypropylene has... more The temperature dependence of the spherulitic growth rate, G(Tx), for isotactic polypropylene has been analyzed by a number of authors in the context of the Lauritzen-Hoffman secondary nucleation theory. In all cases, the existence of a regime II to regime III transition has been reported. We carried out similar studies using a number of metallocene based isotactic polypropylene fractions and failed to see any such transition when plotting ln G vs. Tx. On the other hand, plots of lnG vs 1/Tx(Tm-Tx), where Tm is the equilibrium melting temperature, do exhibit a change in slope at temperatures in the vicinity of the reported II-III regime transition. Studies of the melting behavior and birefringence of it-PP fractions crystallized isothermally in a temperature range encompassing this so called transition revealed a change in the slope of observed melting temperature vs crystallization temperature and a change in the sign of spherulite birefringence in the near vicinity of the II-III r...
The time dependence of morphological characteristics of poly(ethylene terephtalate) was studied d... more The time dependence of morphological characteristics of poly(ethylene terephtalate) was studied during the secondary stage of the cold crystallization process by time-resolved small angle X-ray scattering, and wide angle X-ray diffraction, dilatometry, and calorimetry. The evolution of segmental relaxation processes in the amorphous phase of PET during secondary cold crystallization was investigated by dynamic mechanical spectroscopy. Our experimental results clearly show inconsistencies when comparing the rates of change of crystallinity estimated by different techniques in the context of the classical two phase model of semicrystalline polymers. Dynamic mechanical and creep studies of PET provide further confirmation of the inapplicability of the two phase model for semicrystalline polymers and emphasize the need to investigate the changes in the nature and the rate of the segmental relaxation of the amorphous phase with extent of crystallization. Results of these spec! ific studi...
The crystallization and melting behavior of statistical copolymers of ethylene and styrene (0 - 1... more The crystallization and melting behavior of statistical copolymers of ethylene and styrene (0 - 11 molwere studied using classical and temperature-modulated (TM) differential scanning calorimetry. The evolution of the reversible part of the excess heat capacity was measured during the slowest stage of primary crystallization and during secondary crystallization using TM-DSC in the quasi-isothermal mode. Evolution of the degree of crystallinity and the melting temperature(s) during primary and secondary crystallization was recorded with classical DSC. We will discuss the effect of crystallization temperature and copolymer composition on the primary and secondary crystallization behaviors and show correlations between the evolution of the excess heat capacity, the degree of crystallinity and the melting temperature(s). We will also show that TM-DSC experiments carried under quasi-isothermal conditions enable us to obtain information on the establishment of constraints during secondary...
It has been accepted for nearly four decades that the limited thickness of folded chain polymer c... more It has been accepted for nearly four decades that the limited thickness of folded chain polymer crystals results from secondary nucleation barriers. In recent years, however, simulations of polymer crystallization indicate that the observed crystal thickness is a consequence of free energy minimization, not kinetic pathways. An analysis in terms of classical (homogeneous) nucleation theory indeed gives a column-like equilibrium crystal shape (thickness/width > 1) that results from anisotropic surface energies. All dimensions increase commensurately as the crystal grows, with the equilibrium thickness approaching the extended chain length when an unlimited number of chains are available to crystallize. Beyond a certain point in the growth process, however, one expects nucleation barriers to favor less thick crystals that have non-equilibrium, plate-like shapes. For simulations done with a limited number of chains the equilibrium crystal thickness is observed because the crystal is...
The morphology and crystal growth kinetics in thin films of PEO/PMMA blends were studied optical ... more The morphology and crystal growth kinetics in thin films of PEO/PMMA blends were studied optical microscopy in the reflection mode. Samples (ca. 100 nm thick) were prepared by spin-casting a dilute dichloroethane solution onto a cleaned silicon wafer and subsequent drying under vacuum. Crystal growth rates were measured as a function of blend composition, crystallization temperature and film thickness. This presentation will specifically focus on studies of dendritic growth in 30/70 PEO/PMMA blends. Studies of the temperature dependence of the crystal growth rate and the morphology indicate that both are a complex function of the thermal history.
The applicability of the classical Lauritzen-Hoffman (LH) crystal growth theory to the isothermal... more The applicability of the classical Lauritzen-Hoffman (LH) crystal growth theory to the isothermal crystallization of polymers is discussed in the case of linear and cyclic poly(dimethylsiloxane) fractions and poly([epsilon]-caprolactone), with special emphasis on the effect of chain flexibility, chain architecture and molecular weight on the magnitude of the crystal growth rate and on its temperature dependence. Use of the Gibbs-Thomson-Tammann
Polymer, 1993
ABSTRACT A relatively new method for graphite composite formation, aqueous dispersion prepregging... more ABSTRACT A relatively new method for graphite composite formation, aqueous dispersion prepregging, could potentially circumvent many of the environmental and processing problems of the current methods. However, aqueous dispersion prepregging requires that the high-performance polymer be in the form of a stable colloidal dispersion, preferably of small uniform particles. This research will examine the formation of submicrometre particles from the high-performance thermoplastic polymer, poly(ether ether ketone)(PEEK), for use in aqueous dispersion prepregging. The procedure will involve first the synthesis of the monomer 4,4′-difluoro(N-benzohydroxylidene aniline) and the polymerization of this monomer and hydroquinone to form the amorphous PEEK derivative poly(ether ether ketimine). 4,4′-Difluoro(N-benzohydroxylidene aniline) can also be copolymerized with 4,4′-difluorobenzophenone to form a semicrystalline, soluble PEEK derivative. The subsequent hydrolysis of these derivatives to semicrystalline PEEK results in the formation of submicrometre particles.
Polymer, 1993
ABSTRACT The formation of submicrometre particles of high temperature polyimides by precipitation... more ABSTRACT The formation of submicrometre particles of high temperature polyimides by precipitation from a homogeneous solution in a mixed solvent of water and N-methyl pyrrolidone (H2O/NMP) was investigated. The two polyimides consisted of those based on benzophenone tetracarboxylic dianhydride/2,2′-bis(4-aminophenyl)propane (BTDA-Bis A) and pyromellitic dianhydride/1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (PMDA-3F diamine). Phase diagrams of the BTDA-Bis A polyimide/NMP/H2O ternary system were obtained for two solvent compositions through cloud point measurements. The observed mixed solvent composition dependence of the cloud point behaviour suggests that the water weight fraction plays a fundamental role in the solubility characteristics of polyimides. Preliminary precipitation studies indicate that the size distribution of the polyimide particles is governed by the cooling rate below the cloud point curve. At an average cooling rate of 23°C min−1, narrow size distribution particles of 0.2 and 0.5 μm average diameter were obtained for the PMDA-3F diamine and the BDTA-Bis A polyimides, respectively. For slower cooling rates of 10 or 2°C min−1, the particle size distributions were notably broader, probably as a result of nucleation and growth over a larger temperature range.
Makromolekulare Chemie. Macromolecular Symposia, 1992
ABSTRACT This paper reports the synthesis and characterization of hydroxyl functionalized poly(bu... more ABSTRACT This paper reports the synthesis and characterization of hydroxyl functionalized poly(butyl vinyl ether) oligomers, and block copolymers comprised of poly(butyl vinyl ether) and poly(ϵ-caprolactone). Using the HI/ZnI2 initiating system in toluene at −20°C, monofunctional poly(butyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde or primary hydroxyl endgroups have been prepared. Furthermore, the primary hydroxyl end functionality has been utilized to initiate ring opening polymerization of ϵ-caprolactone in the presence of stannous octanoate as the catalyst. This ring opening reaction provides an entry into new poly[(butyl vinyl ether)-block-poly(ϵ-caprolactone)] copolymers.
Polymer, 1993
Poly(ether ether ketone) (PEEK) composites were made by impregnation of continuous carbon fibres ... more Poly(ether ether ketone) (PEEK) composites were made by impregnation of continuous carbon fibres with aqueous suspensions of PEEK particles made by a novel precipitation process. These particles were suspended in aqueous solutions of ammonium salts of polyamic acids which performed two essential roles: as a polymeric dispersant and as a binder at the fibre-matrix interface. The resulting composite panels had properties that were comparable in some cases to those of commercially available PEEK composites. Fracture surface analysis from unidirectional panels suggests that the miscibility of the matrix and binder affects the failure mode at the fibre-matrix interface.
The Journal of Physical Chemistry, 1989
Growth rates of the crystalline objects formed from the subcooled melt in poly (pivalolactone), P... more Growth rates of the crystalline objects formed from the subcooled melt in poly (pivalolactone), PPVL, were measured optically at various temperatures T, between 180 and 218 OC. Spherulites were formed over most of this range, but axialite-like objects were ...
Macromolecules, 1989
ABSTRACT Molecular energy calculations are used to assess the lattice strain energy density ε and... more ABSTRACT Molecular energy calculations are used to assess the lattice strain energy density ε and the corresponding interfacial surface free energy σs in melt-crystallized polyethylene crystals. The quantity ε, which is defined as the difference in lattice energy density between an unstrained crystal and a strained crystal, is calculated with the use of published lattice expansion data. A strain-induced interfacial surface free energy σs of about 0.9 erg·cm-2 (mJ·m-2) was derived from the strain energy density for a lamellar thickness of around 14 nm. This result compares favorably with the value obtained in the recent extension of nucleation theory by J.D. Hoffman and R.L. Miller describing the geometry and the growth kinetic of curved-edge polyethylene crystals.
Journal of thermal analysis, 1997
ABSTRACT We report the results of an investigation by differential scanning calorimetry (DSC) of ... more ABSTRACT We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (T g) and secondary crystallization aboveT g. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer — the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained from small strain creep studies of “physical aging” of semicrystalline PEEK below and aboveT g.
We have established that a number of inconsistencies exist when one attempts to correlate the cha... more We have established that a number of inconsistencies exist when one attempts to correlate the change in the degree of crystallinity during secondary crystallization through various techniques. Some of these discrepancies can be conceptually explained in terms of the crystallization time and temperature dependence of the crystal and amorphous densities or the average specific heat capacity of the amorphous fraction.
Isothermal spherulitic growth rates were measured for a series of narrow molecular weight distrib... more Isothermal spherulitic growth rates were measured for a series of narrow molecular weight distribution isotactic poly(styrene) samples (250,000 - 1,600,000 g/mol) between 120.5C and 223.5C. Curve fitting analyses of the spherulitic growth rate data using a modified version of the Lauritzen-Hoffman theory allowed us to derive the equilibrium melting temperature, the secondary nucleation constant, and the Vogel parameters (B and T(infinity)) describing the temperature dependence of segmental relaxation in the liquid state. The Vogel parameters derived from the crystal growth rate analysis are in quantitative agreement with those derived from our study of the temperature dependence of the stress relaxation modulus. The equilibrium melting temperature derived from our analysis is significantly higher than that estimated in the literature using the Hoffman-Weeks method. The spherulitic growth rates are independent of chain length in the molecular weight range investigated. S! caling laws...
The temperature dependence of the spherulitic growth rate, G(Tx), for isotactic polypropylene has... more The temperature dependence of the spherulitic growth rate, G(Tx), for isotactic polypropylene has been analyzed by a number of authors in the context of the Lauritzen-Hoffman secondary nucleation theory. In all cases, the existence of a regime II to regime III transition has been reported. We carried out similar studies using a number of metallocene based isotactic polypropylene fractions and failed to see any such transition when plotting ln G vs. Tx. On the other hand, plots of lnG vs 1/Tx(Tm-Tx), where Tm is the equilibrium melting temperature, do exhibit a change in slope at temperatures in the vicinity of the reported II-III regime transition. Studies of the melting behavior and birefringence of it-PP fractions crystallized isothermally in a temperature range encompassing this so called transition revealed a change in the slope of observed melting temperature vs crystallization temperature and a change in the sign of spherulite birefringence in the near vicinity of the II-III r...
The time dependence of morphological characteristics of poly(ethylene terephtalate) was studied d... more The time dependence of morphological characteristics of poly(ethylene terephtalate) was studied during the secondary stage of the cold crystallization process by time-resolved small angle X-ray scattering, and wide angle X-ray diffraction, dilatometry, and calorimetry. The evolution of segmental relaxation processes in the amorphous phase of PET during secondary cold crystallization was investigated by dynamic mechanical spectroscopy. Our experimental results clearly show inconsistencies when comparing the rates of change of crystallinity estimated by different techniques in the context of the classical two phase model of semicrystalline polymers. Dynamic mechanical and creep studies of PET provide further confirmation of the inapplicability of the two phase model for semicrystalline polymers and emphasize the need to investigate the changes in the nature and the rate of the segmental relaxation of the amorphous phase with extent of crystallization. Results of these spec! ific studi...
The crystallization and melting behavior of statistical copolymers of ethylene and styrene (0 - 1... more The crystallization and melting behavior of statistical copolymers of ethylene and styrene (0 - 11 molwere studied using classical and temperature-modulated (TM) differential scanning calorimetry. The evolution of the reversible part of the excess heat capacity was measured during the slowest stage of primary crystallization and during secondary crystallization using TM-DSC in the quasi-isothermal mode. Evolution of the degree of crystallinity and the melting temperature(s) during primary and secondary crystallization was recorded with classical DSC. We will discuss the effect of crystallization temperature and copolymer composition on the primary and secondary crystallization behaviors and show correlations between the evolution of the excess heat capacity, the degree of crystallinity and the melting temperature(s). We will also show that TM-DSC experiments carried under quasi-isothermal conditions enable us to obtain information on the establishment of constraints during secondary...
It has been accepted for nearly four decades that the limited thickness of folded chain polymer c... more It has been accepted for nearly four decades that the limited thickness of folded chain polymer crystals results from secondary nucleation barriers. In recent years, however, simulations of polymer crystallization indicate that the observed crystal thickness is a consequence of free energy minimization, not kinetic pathways. An analysis in terms of classical (homogeneous) nucleation theory indeed gives a column-like equilibrium crystal shape (thickness/width > 1) that results from anisotropic surface energies. All dimensions increase commensurately as the crystal grows, with the equilibrium thickness approaching the extended chain length when an unlimited number of chains are available to crystallize. Beyond a certain point in the growth process, however, one expects nucleation barriers to favor less thick crystals that have non-equilibrium, plate-like shapes. For simulations done with a limited number of chains the equilibrium crystal thickness is observed because the crystal is...
The morphology and crystal growth kinetics in thin films of PEO/PMMA blends were studied optical ... more The morphology and crystal growth kinetics in thin films of PEO/PMMA blends were studied optical microscopy in the reflection mode. Samples (ca. 100 nm thick) were prepared by spin-casting a dilute dichloroethane solution onto a cleaned silicon wafer and subsequent drying under vacuum. Crystal growth rates were measured as a function of blend composition, crystallization temperature and film thickness. This presentation will specifically focus on studies of dendritic growth in 30/70 PEO/PMMA blends. Studies of the temperature dependence of the crystal growth rate and the morphology indicate that both are a complex function of the thermal history.
The applicability of the classical Lauritzen-Hoffman (LH) crystal growth theory to the isothermal... more The applicability of the classical Lauritzen-Hoffman (LH) crystal growth theory to the isothermal crystallization of polymers is discussed in the case of linear and cyclic poly(dimethylsiloxane) fractions and poly([epsilon]-caprolactone), with special emphasis on the effect of chain flexibility, chain architecture and molecular weight on the magnitude of the crystal growth rate and on its temperature dependence. Use of the Gibbs-Thomson-Tammann
Polymer, 1993
ABSTRACT A relatively new method for graphite composite formation, aqueous dispersion prepregging... more ABSTRACT A relatively new method for graphite composite formation, aqueous dispersion prepregging, could potentially circumvent many of the environmental and processing problems of the current methods. However, aqueous dispersion prepregging requires that the high-performance polymer be in the form of a stable colloidal dispersion, preferably of small uniform particles. This research will examine the formation of submicrometre particles from the high-performance thermoplastic polymer, poly(ether ether ketone)(PEEK), for use in aqueous dispersion prepregging. The procedure will involve first the synthesis of the monomer 4,4′-difluoro(N-benzohydroxylidene aniline) and the polymerization of this monomer and hydroquinone to form the amorphous PEEK derivative poly(ether ether ketimine). 4,4′-Difluoro(N-benzohydroxylidene aniline) can also be copolymerized with 4,4′-difluorobenzophenone to form a semicrystalline, soluble PEEK derivative. The subsequent hydrolysis of these derivatives to semicrystalline PEEK results in the formation of submicrometre particles.
Polymer, 1993
ABSTRACT The formation of submicrometre particles of high temperature polyimides by precipitation... more ABSTRACT The formation of submicrometre particles of high temperature polyimides by precipitation from a homogeneous solution in a mixed solvent of water and N-methyl pyrrolidone (H2O/NMP) was investigated. The two polyimides consisted of those based on benzophenone tetracarboxylic dianhydride/2,2′-bis(4-aminophenyl)propane (BTDA-Bis A) and pyromellitic dianhydride/1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (PMDA-3F diamine). Phase diagrams of the BTDA-Bis A polyimide/NMP/H2O ternary system were obtained for two solvent compositions through cloud point measurements. The observed mixed solvent composition dependence of the cloud point behaviour suggests that the water weight fraction plays a fundamental role in the solubility characteristics of polyimides. Preliminary precipitation studies indicate that the size distribution of the polyimide particles is governed by the cooling rate below the cloud point curve. At an average cooling rate of 23°C min−1, narrow size distribution particles of 0.2 and 0.5 μm average diameter were obtained for the PMDA-3F diamine and the BDTA-Bis A polyimides, respectively. For slower cooling rates of 10 or 2°C min−1, the particle size distributions were notably broader, probably as a result of nucleation and growth over a larger temperature range.
Makromolekulare Chemie. Macromolecular Symposia, 1992
ABSTRACT This paper reports the synthesis and characterization of hydroxyl functionalized poly(bu... more ABSTRACT This paper reports the synthesis and characterization of hydroxyl functionalized poly(butyl vinyl ether) oligomers, and block copolymers comprised of poly(butyl vinyl ether) and poly(ϵ-caprolactone). Using the HI/ZnI2 initiating system in toluene at −20°C, monofunctional poly(butyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde or primary hydroxyl endgroups have been prepared. Furthermore, the primary hydroxyl end functionality has been utilized to initiate ring opening polymerization of ϵ-caprolactone in the presence of stannous octanoate as the catalyst. This ring opening reaction provides an entry into new poly[(butyl vinyl ether)-block-poly(ϵ-caprolactone)] copolymers.
Polymer, 1993
Poly(ether ether ketone) (PEEK) composites were made by impregnation of continuous carbon fibres ... more Poly(ether ether ketone) (PEEK) composites were made by impregnation of continuous carbon fibres with aqueous suspensions of PEEK particles made by a novel precipitation process. These particles were suspended in aqueous solutions of ammonium salts of polyamic acids which performed two essential roles: as a polymeric dispersant and as a binder at the fibre-matrix interface. The resulting composite panels had properties that were comparable in some cases to those of commercially available PEEK composites. Fracture surface analysis from unidirectional panels suggests that the miscibility of the matrix and binder affects the failure mode at the fibre-matrix interface.
The Journal of Physical Chemistry, 1989
Growth rates of the crystalline objects formed from the subcooled melt in poly (pivalolactone), P... more Growth rates of the crystalline objects formed from the subcooled melt in poly (pivalolactone), PPVL, were measured optically at various temperatures T, between 180 and 218 OC. Spherulites were formed over most of this range, but axialite-like objects were ...