16 results on '"Macosko, Christopher W."'
Search Results
2. Localizing graphene at the interface of cocontinuous polymer blends: Morphology, rheology, and conductivity of cocontinuous conductive polymer composites.
- Author
-
Lian Bai, Siyao He, Fruehwirth, John W., Stein, Andreas, Macosko, Christopher W., and Xiang Cheng
- Subjects
GRAPHENE ,POLYMER blends ,RHEOLOGY ,POLYMERS ,CONDUCTING polymer composites ,POLYLACTIC acid ,POLYSTYRENE ,GRAPHENE oxide - Abstract
Interfacial localization of graphene in cocontinuous polymer blends is shown to be effective in stabilizing the cocontinuous morphology and increasing conductivity with a low electrical percolation threshold. We created polylactic acid (PLA) and polystyrene (PS) cocontinuous blends filled with thermally reduced graphene oxide (r-GO) localized at the interface. The resulting conductive composites show dramatically improved conductivity at low filler loadings and an ultralow percolation threshold of 0.028 vol. %. We systematically studied the changes of conductivity and rheology of the PLA-PS composites during annealing. We found that r-GO transfers from the PLA phase to the interface during melt compounding and annealing and forms a spanning 3D network, which effectively suppresses the coarsening of the cocontinuous structure. Our study demonstrated that the 3D r-GO network significantly increases the conductivity and the storage modulus of the melt blends. Finally, we constructed a simple model, which quantitatively explains the correlations between structural, electrical, and rheological properties of conductive polymer composites. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
3. Rheology of compatibilized immiscible blends with droplet-matrix and cocontinuous morphologies during coarsening.
- Author
-
López-Barrón, Carlos R. and Macosko, Christopher W.
- Subjects
- *
OSTWALD ripening , *BLOCK copolymers , *POLYMER blends , *MICROSTRUCTURE , *INTERFACIAL tension , *POLYSTYRENE - Abstract
It is well known that addition of block copolymers to immiscible polymer blends may result in finer and more stable microstructures by reducing the driving force for coarsening, namely, the interfacial tension. This compatibilization is also reflected in the rheological behavior of the blends. We present an experimental study on the morphology and rheology of model blends composed of fluorescently labeled polystyrene and styrene-ran-acrylonitrile copolymer compatibilized with a polystyrene-b-polymethyl methacrylate diblock copolymer (BC). Three different weight ratios (wt/ wt) are studied: 20/80, 35/65, and 50/50, with the following morphologies: Droplet/matrix, metastable cocontinuous, and abiding cocontinuous, respectively. It is found that regardless the type of initial morphology, the addition of BC reduces the characteristic size and increases the elastic modulus in the terminal regime, where the relaxation of the interface is probed. The relaxation spectra in the terminal zone are greatly affected by the presence of BC, which reflects the strong dependence of the viscoelastic behavior on the local microstructure (shape and area) of the interface. Furthermore, the addition of BC reduces the rate of coarsening, which is characterized by the time evolution of both the elastic modulus and the specific interfacial area. These effects are more pronounced when the molecular weight or concentration of the BC is higher. Finally, two regimes of coarsening in the symmetric (50/50) blends were identified and characterized by two different power laws. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
4. Measurement of geometrical parameters in cocontinuous polymer blends: 3D versus 2D image analysis.
- Author
-
LÓPEZ-BARRÓN, CARLOS R. and MACOSKO, CHRISTOPHER W.
- Subjects
- *
POLYMERS , *STEREOLOGY , *GEOMETRIC modeling , *MICROGRAPHICS , *CONFOCAL microscopy , *POLYSTYRENE , *ACRYLONITRILE , *COPOLYMERS - Abstract
Formulae of stereology are used to estimate 3D geometrical parameters of cocontinuous structures measured from 2D micrographs of polymer blends. 3D images of symmetric and nonsymmetric polymer blends made of fluorescently labelled polystyrene and styrene-ran-acrylonitrile copolymer were obtained with laser scanning confocal microscopy. Geometrical parameters of the blend interface, specifically volume fraction, surface area per unit volume () and average of local mean curvature were measured directly from the 3D images and compared to the values estimated from analysis of a number of 2D slices combined with stereological relations. When the total length of phase boundary considered in the analysis of the 2D slices () was at least 6000 times bigger than the characteristic length of the microstructure (), the standard deviation for all the parameters measured became negligible. However, considerable discrepancies between the average values computed from 3D and 2D images were observed for any value of . The mean curvature distribution was also measured from both the 3D images and the 2D slices. The distribution was estimated from the 2D slices but with a width about 2.4 times that of the true value obtained from the 3D images. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
5. Direct Correlation Between Adhesion Promotion and Coupling Reaction at Immiscible Polymer-Polymer Interfaces.
- Author
-
Jianbin Zhang, Cole, Phillip J., Nagpal, Umang, Macosko, Christopher W., and Lodge, Timothy P.
- Subjects
ADHESION ,POLYMERS ,POLYPROPYLENE ,MALEIC anhydride ,POLYSTYRENE ,FLUORESCENCE - Abstract
Hugh Brown has shown that interfacial entanglements govern adhesion between two polymers. We demonstrate this for three systems by adding interfacial chains via chemical coupling. The adhesion between polypropylene (PP)/amorphous polyamide (aPA) was reinforced by the coupling reaction of maleic anhydride grafted PP (PP- g -MA) and the primary amine groups on aPA; huge increases in adhesion were observed. A good correlation between critical fracture toughness, G c , and PP- g -MA concentration squared follows Brown's crazing mechanism. For a polystyrene (PS)/aPA interface reinforced by the coupling reaction of poly(styrene- r -maleic anhydride) (PS- r -MA)/aPA only modest adhesion increases in G c were observed through the whole PS- r -MA concentration range. This different behavior of G c vs . functional polymer concentration is believed to be caused by segregation of the formed graft copolymers at the interface. The relationship between G c and the extent of coupling was studied quantitatively with a model PS/PMMA system. The interface was reinforced by the coupling reaction of 0–10% PS-NH 2 /PMMA-anh. G c was measured with the asymmetric dual cantilever beam test (ADCB) and the amount of copolymer formed at the interface was determined by a fluorescence labeling technique. G c is low and is linear in block copolymer interfacial coverage (Σ), indicating a chain scission mechanism. Reasonable agreement was achieved between experiment and theoretical prediction based on the energy to break C–C bonds. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
6. Comparison of Methods for the Detection of Cocontinuity in Poly(ethylene oxide)/Polystyrene Blends.
- Author
-
Galloway, Jeffrey A. and Macosko, Christopher W.
- Subjects
POLYETHYLENE oxide ,POLYSTYRENE ,SCANNING electron microscopy ,IMAGE analysis ,ELECTRIC conductivity ,POLYMERS - Abstract
Compares methods, such as scanning electron microscopy with image analysis, solvent extraction, electrical conductivity measurements and rheological measurements, for detecting continuity in a poly(ethylene oxide)/polystyrene system. Key issues of interest; Analysis of pertinent topics and relevant issues; Implications on polymer engineering and science.
- Published
- 2004
- Full Text
- View/download PDF
7. Visualization of block copolymer distribution on a sheared drop
- Author
-
Jeon, Hyun K. and Macosko, Christopher W.
- Subjects
- *
POLYMETHYLMETHACRYLATE , *POLYMERS , *COPOLYMERS , *MICROSCOPY , *STYRENE , *POLYSTYRENE - Abstract
We have visualized a fluorescently-labeled poly(styrene-b-methylmethacrylate) (NBD-PS-b-PMMA) block copolymer on the surface of a polymethylmethacrylate (PMMA) drop in a polystyrene (PS) matrix. Confocal microscopy revealed that the block copolymer distributed uniformly on the drop surface before deformation. However, in shear flow the copolymer concentration was higher at the tips and edges of the drop. Visualization of drop deformation using a counter-rotating apparatus showed enhanced drop deformation for a drop with block copolymer resulting in larger area generation. Drops with block copolymer showed widening even for shear strains exceeding 10, in contrast to bare drops, which first widened and then shrank. These results agree qualitatively with the observed distribution of fluorescent block copolymer. Copolymer concentration is highest in the regions of high curvature, where lowering interfacial tension should be most effective in retarding drop retraction. Block copolymer on these highly curved surfaces is found to be very effective since the exact theory for zero interfacial tension by Cristini fits our drop widening results well. [Copyright &y& Elsevier]
- Published
- 2003
- Full Text
- View/download PDF
8. Morphology and Rheology of Cocontinuous Blends.
- Author
-
Barron, Carlos R. Lopez and Macosko, Christopher W.
- Subjects
- *
ANNEALING of metals , *RHEOLOGY , *MORPHOLOGY , *POLYSTYRENE , *MONOTONIC functions - Abstract
The time evolution of the elastic modulus and the geometrical parameters of interfaces in a 50/50 PS/SAN cocontinuous blend are analyzed during annealing. The interfaces were tracked via LSCM (laser scanning confocal microscopy) coupled with 3D-image analysis. The evolution of G′ and the geometrical variables can be described with power laws. Experiments reveal that interfaces relax faster (dQ/dt∝Q2.4) than predicted by the Doi-Ohta theory (dQ/dt∝Q2) [1]. Rheological behavior is a result of interfacial relaxation which includes interface expansion and curvature relaxation. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
9. Reactive compatibilization of poly(lactic acid)/polystyrene blends and its application to preparation of hierarchically porous poly(lactic acid).
- Author
-
Gu, Liangliang, Nessim, Elizabeth E., and Macosko, Christopher W.
- Subjects
- *
POLYLACTIC acid , *POLYSTYRENE , *POROUS materials , *OXAZOLINE , *CARBOXYLIC acids - Abstract
In this work hierarchically porous poly(lactic acid) (PLA) with bimodal pore size distribution was derived from reactively compatibilized ternary immiscible polymer blends. We first demonstrated the generation of submicron pores from cocontinuous PLA/oxazoline functional polystyrene (PS-OX) blends. The oxazoline groups in PS-OX reacted with the carboxylic acid end groups of PLA and formed graft copolymer at the interface, which significantly reduced the domain size. Hierarchically structured “tri-continuous” morphology was further obtained in a ternary PLA/PS-OX/linear low density polyethylene (LLDPE) blend. Porous PLA was made by selectively removing the PS-OX and LLDPE phases. Static annealing was used to control the pore size. The pores formed by PS-OX (∼0.5–2 μm) were one order of magnitude smaller than the pores formed by LLDPE (∼5–20 μm). The underlying thermodynamic mechanism for formation of hierarchical morphology in PLA/PS-OX/LLDPE blend was studied, and it was found that PLA/PS/PE ternary blends demonstrated complete wetting behavior with PS located at PLA/PE interface. Our results show that compatibilization with graft/block copolymer is a versatile way to achieve hierarchical microstructures in multiphase polymer blends. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
10. Premade vs. reactively formed compatibilizers for PMMA/PS melt blends
- Author
-
Jeon, Hyun K., Zhang, Jianbin, and Macosko, Christopher W.
- Subjects
- *
GRAFT copolymers , *COPOLYMERS , *POLYSTYRENE , *METHYL methacrylate , *ACRYLATES - Abstract
Abstract: The efficiency of two compatibilization methods, adding premade copolymers versus in situ formation of copolymers, were compared by evaluating the minor phase size and size distribution. Premade diblock copolymers were formed by coupling amine terminal polystyrene (PS-NH2) with anhydride terminal poly(methyl methacrylate) (PMMA-An) in solution. Mid-functional PMMA was coupled with the PS-NH2 to form graft copolymers. The same block and graft copolymers were formed in situ during melt blending. After mixing, the particle size and distribution were analyzed by transmission electron microscope (TEM). While both methods compatibilized blends, in situ formation reduced the minor phase size further. For the reactive case, graft copolymers are slight better than the block ones. This is attributed to a greater capacity for reducing interfacial tension. For the premade case, block copolymers compatibilize better at low copolymer concentration while graft copolymers work better at high concentration. As the amount of block copolymers added into the blends increases, the number of micelles increases significantly. This is believed to be the reason why premade copolymers are less capable of compatibilizing blends than the reactively formed ones. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
- View/download PDF
11. Image analysis for interfacial area and cocontinuity detection in polymer blends
- Author
-
Galloway, Jeffrey A., Montminy, Matthew D., and Macosko, Christopher W.
- Subjects
- *
IMAGE processing , *EXTRACTION (Chemistry) , *POLYMERS , *ELECTRON microscopy , *POLYSTYRENE - Abstract
A novel image processing method was developed to extract interfacial area concentration measurements from 2D micrographs of immiscible polymer blends. Although this method can be used for analyzing different types of 2D micrographs such as optical or transmission electron microscopy images, it was designed for analyzing scanning electron microscopy (SEM) images. The method operates by detecting edges within the images and using standard image processing operations to selectively eliminate false edges. SEM images of polyethylene oxide/polystyrene (PEO/PS) blends were analyzed using this image processing method to measure the amount of interfacial area in the samples. Interfacial area per unit volume exhibits maxima for blend compositions at the boundary between droplet and cocontinuous morphologies. In addition to the detection of cocontinuity, the interfacial area measurements facilitated by this method may be used in future investigations of blend dynamics, including coalescence, drop deformation, and blend rheology studies. These measurements may also be used to quantify the effects of compatibilizers on blend morphology. [Copyright &y& Elsevier]
- Published
- 2002
- Full Text
- View/download PDF
12. Meltblown fibers: Influence of viscosity and elasticity on diameter distribution
- Author
-
Tan, Dawud H., Zhou, Chunfeng, Ellison, Christopher J., Kumar, Satish, Macosko, Christopher W., and Bates, Frank S.
- Subjects
- *
FIBERS , *VISCOSITY , *ELASTICITY , *RELAXATION phenomena , *POLYSTYRENE , *MOLECULAR weights , *JETS (Fluid dynamics) , *MAXWELL equations , *MELTBLOWN textile manufacturing - Abstract
Abstract: Both melt viscosity (η o) and elasticity (correlated here with the longest melt relaxation time λ 1) were found to control the diameter distribution of meltblown fibers. Fibers were formed by melt blowing binary polystyrene (PS) blends containing widely differing component molecular weights using a custom-built laboratory apparatus. Varying the concentration and molecular weight of a high molecular weight PS provided independent control over η o and λ 1. These rheological parameters influence the average diameter (d av) and the distribution of diameters (coefficient of variation, CV) of meltblown fibers in different ways. Increasing η o leads to an increase in d av but has little impact on CV. On the other hand, increasing λ 1 beyond a threshold value reduces CV while simultaneously increasing d av. A one-dimensional slender-jet theoretical model with both upper convected Maxwell and Phan–Thien and Tanner constitutive equations was developed to investigate the influence of viscoelasticity and processing parameters on the properties of meltblown fibers. This model predicts a strong dependence of fiber diameter on the air shear stress and variations in fiber diameter with viscoelasticity that are in qualitative agreement with the experimental results. We believe these results suggest that carefully controlling the viscoelastic profile of polymers used in melt blowing is a viable approach for producing nanofibers with narrow fiber diameter distributions using current commercial equipment. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
13. Melt blown nanofibers: Fiber diameter distributions and onset of fiber breakup
- Author
-
Ellison, Christopher J., Phatak, Alhad, Giles, David W., Macosko, Christopher W., and Bates, Frank S.
- Subjects
- *
POLYPROPYLENE , *POLYSTYRENE , *ATTENUATION (Physics) , *SURFACE tension , *FIBROUS composites - Abstract
Abstract: Poly(butylene terephthalate), polypropylene, and polystyrene nanofibers with average diameters less than 500nm have been produced by a single orifice melt blowing apparatus using commercially viable processing conditions. This result is a major step towards closing the gap between melt blowing technology and electrospinning in terms of the ability to produce nano-scale fibers. Furthermore, analysis of fiber diameter distributions reveals they are well described by a log-normal distribution function regardless of average fiber diameter, indicating that the underlying fiber attenuation mechanisms are retained even when producing nanofibers. However, a comparison of the breadth of the distributions between mats with differing average fiber diameters indicates that the dependence of the breadth with average fiber diameter is not universal (i.e., it is material dependent). Finally, under certain processing conditions, we observe fiber breakup that we believe is driven by surface tension and these instabilities may represent the onset of an underlying fundamental limit to the process. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
14. Block copolymer compatibilization of cocontinuous polymer blends
- Author
-
Galloway, Jeffrey A., Jeon, Hyun K., Bell, Joel R., and Macosko, Christopher W.
- Subjects
- *
BLOCK copolymers , *POLYMERS , *POLYSTYRENE , *THERMOPLASTICS , *HIGH density polyethylene - Abstract
Abstract: The effect of block copolymers on the cocontinuous morphology of 50/50 (w/w) polystyrene (PS)/high density polyethylene (HDPE) blends was investigated using symmetric polystyrene–polyethylene block copolymers (PS–PE) with molecular weights varying from 6 to 200kg/mol. The coarsening rate during annealing was compared to the Doi–Ohta theory. An intermediate molecular weight PS–PE, 40kg/mol, showed remarkable results in reducing the phase size and stabilizing the blend morphology during annealing. Mixing small amounts of 6, 100 or 200kg/mol PS–PE in the blend did not reduce the phase size significantly, but did decrease the coarsening rate during annealing. In stabilizing the morphology, 6kg/mol PS–PE was inferior to 100 and 200kg/mol. The existence of an optimal molecular weight block copolymer is due to a balance between the ability of the block copolymer to reach the interface and its relative stabilization effect at the interface. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
- View/download PDF
15. Effect of sample size on solvent extraction for detecting cocontinuity in polymer blends
- Author
-
Galloway, Jeffrey A., Koester, Kurt J., Paasch, Benjamin J., and Macosko, Christopher W.
- Subjects
- *
SOLVENTS , *EXTRACTION (Chemistry) , *POLYMERS , *POLYSTYRENE , *ELECTRIC conductivity - Abstract
The effect of sample size on the results of solvent extraction measurements for detecting cocontinuity in polymer blends was investigated. Poly(ethylene oxide)/polystyrene (PEO/PS) blend samples of several thicknesses were analyzed by removing the PEO phase using water extraction. The experimental degree of continuity was shown to have a linear dependence on the reciprocal of sample thickness. A model is proposed to explain this dependence and to allow the bulk or true degree of continuity to be determined. Measurement of the bulk degree of continuity is useful for understanding properties of cocontinuous polymer blends such as electrical conductivity, impact strength, or tensile strength. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
16. Reactively formed block and graft copolymers as compatibilizers for polyamide 66/PS blends
- Author
-
Jeon, Hyun K., Feist, Benjamin J., Koh, Sok Boon, Chang, Kwanho, Macosko, Christopher W., and Dion, Robert P.
- Subjects
- *
POLYSTYRENE , *COPOLYMERS , *MOLECULAR weights , *GEL permeation chromatography , *ANTHRACENE - Abstract
Phthalic anhydride terminated polystyrene (PS-An) and styrene-maleic anhydride copolymer (SMA) were compared as a compatibilizer at low loadings (<10 wt%) in 70/30 polyamide 66 (PA66)/polystyrene (PS) blends. Compatibilization efficiency was judged by morphology of the blends and the extent of interfacial coupling to copolymer. Fluorescent labels of functional PS''s (anthracene and pyrene for PS-An and SMA, respectively) allowed the detection of small amounts of reactively formed block (PA66-b-PS) or graft copolymer (SMA-g-PA66) in the blends via gel permeation chromatography with a fluorescence detector. Extremely fast reactions giving >60% conversion in 0.5 min mixing were observed regardless of the molecular weight, the structure, and the amount of the functional PS''s. Interfacial stability of the reactively formed copolymers was estimated by micelle formation in the bulk phases and the interfacial coverage,
Σ. PS-An with higher molecular weight (37 kg/mol) was most effective as a compatibilizer at the interface, showing less tendency to form microemulsions by suppressing interfacial roughening. However, a large portion of PA66-b-PS from low molecular weight PS-An (10 kg/mol) and SMA-g-PA66 from random functional SMA (16 kg/mol) migrated to the bulk phase to form micelles even at <2 wt% loadings. Blends of PA66 with syndiotactic PS compatibilized with PS-An gave very similar morphology to the PA66/PS blends indicating that these conclusions apply also to PA66/sPS blends. [Copyright &y& Elsevier]- Published
- 2004
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.