Michael Arlen - Academia.edu (original) (raw)

Papers by Michael Arlen

APS March Meeting Abstracts, Mar 1, 2002

Aps Meeting Abstracts, Mar 1, 2000

Aps Meeting Abstracts, Mar 1, 2002

Electrical transport studies of multi-walled carbon nanotube (c-MWNT)/polymer nanocomposites have... more Electrical transport studies of multi-walled carbon nanotube (c-MWNT)/polymer nanocomposites have shown metallic behavior with conductivity sigma=sigma0( phi-phic )^t above the percolation threshold. The conductivity depends on three aspects of the conducting network (CN): the conductivity of the constituent c-MWNT, the number of c-MWNT making up the CN, and the detailed interconnectivity of the CN. Using conducting-tip atomic force microscopy (C-AFM), we have studied the density and conductivity of the c-MWNT CN as a function of c-MWNT loading between 0.5 - 5.0 wt % in a polyimide matrix. Using the Principle of Delesse, the volume fraction of the c-MWNT CN can be calculated from the conducting areal density measured in the C-AFM scans. The results of the C-AFM tests have shown localized areas of electrical transport associated with c-MWNT as well a clear dependence of conducting areal density and conductivity on the c-MWNT loading. This work was performed in part at the US Departme...

Adaptive materials undergo large-scale shape or property change in response to an external stimul... more Adaptive materials undergo large-scale shape or property change in response to an external stimulus such as stress, temp., light, or pH. Technol. uses range from durable, shape recovery eye-glass frames, to temp. sensitive switches, to the generation of stress to induced mech. motion. Here in, we demonstrate that the uniform dispersion of 1-5vol% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1-5vol%) and improve shape fixity by enhancing strain-induced crystn. Non-radiative decay of IR photons absorbed by the nanotubes raises the internal temp., melting the polymer crystallites (which act as phys. cross-links that secure the deformed shape) and remotely triggering the release of the stored strain energy. Comparable effects occur for elec.-induced actuation asso...

Journal of Polymer Science Part B: Polymer Physics, 2004

A protocol for using neutron reflectivity to monitor the dynamic properties of a copolymer in a h... more A protocol for using neutron reflectivity to monitor the dynamic properties of a copolymer in a homopolymer matrix is described. This technique may be used to monitor a broad range of systems, as long as the copolymer and homopolymer form a miscible blend at low copolymer concentrations. Moreover, with knowledge of the Flory–Huggins interaction parameter between the copolymer and homopolymer, the molecular dynamic parameters of the copolymer, such as the tracer diffusion coefficient, segmental friction factor, and longest relaxation time, can be quantitatively determined. This technique is demonstrated by the determination of these parameters for a series of styrene/methyl methacrylate alternating copolymers dispersed in a matrix of deuterated poly(methyl methacrylate). Interestingly, the segmental friction factor of these alternating copolymers is significantly different from that of similar diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3235–3247, 2004

The Journal of Chemical Physics, 2006

The effect of copolymer composition on the dynamics of random copolymers in a homopolymer matrix ... more The effect of copolymer composition on the dynamics of random copolymers in a homopolymer matrix is studied using computer simulations within the framework of the bond-fluctuation model on blends containing low concentrations (10%) of A-B copolymers, where A and B are two different types of monomers, dispersed in a homopolymer matrix of chains with only A-type monomers. Four copolymer compositions were studied, ϕA=0.33, ϕA=0.5, ϕA=0.66, and ϕA=0.82, while maintaining a statistically random sequence distribution. For this study, we have only included intermolecular interactions between A and B monomers. Our results indicate, in agreement with experimental data, that copolymer composition has an impact on system dynamics. Analysis of the structure reveals that copolymers with majority A content are expanded in the homopolymer matrix, have fewer interchain copolymer-copolymer contacts, and are well dispersed in the homopolymer matrix. On the other hand, copolymers with lower A content ...

Journal of Applied Physics, 2008

Using conducting-tip atomic force microscopy (C-AFM), we study the spatial distribution of curren... more Using conducting-tip atomic force microscopy (C-AFM), we study the spatial distribution of current paths and local electrical properties in carbon nanofiber/polymer nanocomposites. Previous studies of similar systems were hindered by a polymer-rich skin layer that exists at the nanocomposite surfaces. We present an experimental technique using oxygen plasma etching to controllably remove this polymer skin layer. After this treatment, we can directly probe the microscopic transport characteristics of the nanocomposite using C-AFM. The C-AFM results show that the electrical transport is solely carried by the carbon nanofiber (CNF) networks in the nanocomposites. In addition, high-resolution C-AFM maps show nonuniform distribution of current along the length of some CNFs, suggesting the presence of a heterogeneously distributed adsorbed polymer layer around nanofibers. Finally, two probe conductivity measurements in which one electrode (the C-AFM tip) is contacting a single constituent...

Polymer, 2003

Asymmetric double cantilever beam studies are presented that document the ability of alternating ... more Asymmetric double cantilever beam studies are presented that document the ability of alternating copolymers to strengthen a polymer/polymer interface. For polystyrene/poly(methyl methacrylate) interfaces, these results show that the alternating copolymer is the least effective sequence distribution of a linear copolymer at strengthening the polystyrene/poly(methyl methacrylate) interface, where the copolymers that are compared all have similar molecular weight and composition. The results also demonstrate that the effect of copolymer molecular weight on the ability of the copolymer to strengthen an interface is controlled by the balance between the increased entanglements and decreased miscibility of the copolymer with the homopolymers with increasing molecular weight.

Second International Conference on Smart Materials and Nanotechnology in Engineering, Jul 25, 2009

ABSTRACT

Polymer, Jun 1, 2010

High-performance aerospace-grade polyimides such as CP2 fulfill many important roles in a wide ra... more High-performance aerospace-grade polyimides such as CP2 fulfill many important roles in a wide range of applications. A thorough understanding of the polymer matrix's physiochemical properties is an important consideration when developing polymer nanocomposite materials. In this work, we report the dielectric properties of polyimide CP2 including the primary and two secondary dipole relaxations, and their thermal characteristics by way of temperature variable impedance spectroscopy (10 À2 to 10 6 Hz, À40 to 225 C). Special emphasis has been placed on detailing the characteristic phenomena near CP2 0 s glass transition (199 C). The consequences of residual DMAc solvent on CP2 0 s overall loss and relaxation characteristics are also discussed.

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Sep 1, 2008

Bulletin of the American Physical Society, Mar 13, 2006

Philosophical Magazine Letters, Sep 1, 2010

... Enis Tuncer a * , Richard A. Vaia b &amp;amp; Michael Arlen b pages 663-675. ... Othe... more ... Enis Tuncer a * , Richard A. Vaia b &amp;amp; Michael Arlen b pages 663-675. ... Other expressions to determine the percolation transition can also be found in the literature 2424. Coleman, JN, Curran, S, Dalton, AB, Davey, AP, McCarthy, B, Blau, W and Barklie, RC. 1998. Phys. Rev. ...

Macromolecules, Jul 26, 2007

Vapor-grown carbon nanofibers (VGCNF) were functionalized with amine-containing pendants via a Fr... more Vapor-grown carbon nanofibers (VGCNF) were functionalized with amine-containing pendants via a Friedel-Crafts acylation reaction with 4-(3-aminophenoxy)benzoic acid. The resulting H 2 N-VGCNF with relatively high degree of functionalization was in attendance during the synthesis of a polyimide (previously designated as CP2) from 2,2-bis(phthalic anhydride)-1,1,1,3,3,3-hexafluoroisopropane (6FDA) and 1,3-bis(3aminophenoxy)benzene (APB) in N,N-dimethylacetamide (DMAc). Thus, a series of CP2-based nanocomposite films, which contained 0.18-9.19 wt % of H 2 N-VGCNF (corresponding to 0.10-5.0 wt % of basic VGCNF) were obtained using the conventional poly(amic acid) precursor method. For comparison purposes, the pristine VGCNF (0.10-5.0 wt %) was also used in the in situ polymerization of 6FDA and ABP. These two series of nanocomposite films were cast from the respective poly(amic acid)/VGCNF/DMAc solutions, followed by thermal imidization at curing temperatures up to 250°C. The benefit and limitation of functionalized VGCNF on the length scale and the extent of CNF dispersion in a polyimide matrix were clear: (a) 0.18 wt % H 2 N-VGCNFg-CP2 film was visually transparent whereas a similarly prepared (0.10 wt %) VGCNF/CP2 film showed the presence of large CNF aggregates throughout; (b) at 0.55 wt % H 2 N-VGCNF (equivalent to 0.30 wt % VGCNF) content, the nanocomposite film had become translucent, and at 9.19 wt % (equivalent to 5.0 wt % VGCNF), it was opaque. Since CP2 is very soluble in THF, the CP2-grafted VGCNF were simply separated from the free CP2 by solvent extraction. The molecular weights of the extracted CP2 were measured using gel-permeation chromatography (GPC). The effects of VGCNF on molecular weight (MW) and glass-transition (T g) were discussed in terms of GPC and thermal analysis results, respectively. The dispersion of VGCNF in CP2 was evaluated using scanning electron microscopy (SEM). The tensile properties of these nanocomposite films were determined, showing up to 45% increase in modulus.

This report is published in the interest of scientific and technical information exchange, and it... more This report is published in the interest of scientific and technical information exchange, and its publication does not constitute the Government's approval or disapproval of its ideas or findings.

Polymer, 2010