A liquid crystal polymer based single layer chemo-responsive actuator

Kamal, Tahseen,Park, Soo-Young The Royal Society of Chemistry 2014 Chemical communications Vol.50 No.16

<P>A single layer, mono-component, fast, stable, and controllable curling motion actuator is prepared from a mixture of di-acrylate mesogenic monomer and 5CB using a photo-polymerization induced phase separation method. This actuator is capable of sensing water in acetone.</P> <P>Graphic Abstract</P><P>A single layer, mono-component, fast, stable, and controllable curling motion actuator is prepared from a mixture of di-acrylate mesogenic monomer and 5CB using a photo-polymerization induced phase separation method. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc48409b'> </P>

Synthesis, characterization, and physical properties of a poly(acrylamide-<i>co</i>-4-cyanobiphenyl-4′-oxyundecylacrylate)

Kamal, Tahseen,Park, Soo-young The Royal Society of Chemistry 2015 New Journal of Chemistry Vol.39 No.1

<P>A series of copolymers containing 4-cyanobiphenyl-4′-oxyundecylacrylate (LC11) as the hydrophobic liquid crystal (LC) unit and acrylamide (AAm) as the hydrophilic unit were synthesized by free radical polymerization. <SUP>1</SUP>H NMR spectra of the copolymers confirmed the successful copolymerization. The PAAm-<I>co</I>-PLC11 (75/25), (80/20), and (85/15) copolymers showed swelling behavior in water and formed hydrogels because of the hydrophilic AAm units in the copolymer chains while the LC11 units formed cross-linking junctions by organizing into microstructures. The organization of the LC11 units into microstructures was revealed by a polarized optical microscopy (POM) study of the copolymer hydrogels. The copolymers with LC11 ratios higher than 25 mol% were too hydrophobic to swell in water to form hydrogels. This might be because of the molecular weight of the LC11 units, which is several fold higher than AAm. The copolymers with less than 15 mol% LC11 were so hydrophilic that water dissolved them. The POM and wide angle X-ray scattering (WAXS) studies of the copolymer fiber revealed that the LC11 units were aligned with the mesogens' direction, which is perpendicular to the fiber axis.</P> <P>Graphic Abstract</P><P>The synthesis and characterization of a copolymer containing an LC unit and a hydrophilic unit are reported. The copolymer forms hydrogel in water with the LC component serving as the physical crosslink. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4nj01685h'> </P>

Uniaxial Tensile Deformation of Poly(ε-caprolactone) Studied with SAXS and WAXS Techniques Using Synchrotron Radiation

Kamal, Tahseen,Shin, Tae Joo,Park, Soo-Young American Chemical Society 2012 Macromolecules Vol.45 No.21

<P>The structural evolution of poly(ε-caprolactone) (PCL) during uniaxial tensile deformation at 25 °C was examined using small- and wide-angle X-ray scatterings (SAXS and WAXS) techniques with simultaneous stress and strain (S–S) curves. A high-energy X-ray beam at the recently upgraded Pohang synchrotron radiation source revealed the complete lamellar deformation behavior of PCL. Slope-based division of the S–S curves indicated three distinct regions of elastic (region I), yielding (region II) and plastic deformations (region III). In region I, which showed elastic deformation, the WAXS patterns were isotropic, whereas the SAXS patterns became oblate due to elongation of the amorphous chains along the draw direction. In region II, which showed yielding deformation, the WAXS patterns showed a slight orientation, whereas the SAXS patterns exhibited a change from oblate to four-point and to six-point patterns due to the simultaneous fragmentation and melting of the chain-folded lamellae (leading to the four-point pattern) and the subsequent formation of chain-extended lamellae (adding another two maxima along the meridian). In region III, the WAXS patterns revealed the development of the orientation of PCL crystals, whereas SAXS patterns exhibited a two-point pattern. The newly formed chain-extended lamellae in regions II and III might produce network junctions that can transfer an applied force to the PCL crystals for increased orientation. The six-point pattern in region II for PCL was not observed or reported in the past during the uniaxial tensile deformation experiment. This might be due to fast acquisition of the X-ray patterns during mechanical drawing using synchrotron radiation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2012/mamobx.2012.45.issue-21/ma301714f/production/images/medium/ma-2012-01714f_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma301714f'>ACS Electronic Supporting Info</A></P>

Structural Evolution of Poly(ether-b-amide12) Elastomers During the Uniaxial Stretching: An In situ Wide-Angle X-Ray Scattering Study

Tahseen Kamal,박수영,박정현,장영욱 한국고분자학회 2012 Macromolecular Research Vol.20 No.7

The structural evolution of poly(ether-b-amide12) (PEBAX®) elastomers was studied by using wide angle X-ray scattering (WAXS) at a synchrotron radiation source during the uniaxial stretching. The changes in the crystal structure of the nylon 12 were tracked during the stretching of the P6333 and P2533 compressed films, which represent a hard rubber and a soft elastomer, respectively. The nylon 12 chains of both samples favored the γ-phase in the unstrained state but their responses to the external drawing force were different. For the P6333 film containing small amounts of the soft segments, the applied force dilated the 001 crystalline lattice plane of nylon 12 which is perpendicular to its main chain and the γ form was transformed into the α" form when the applied force was high enough. However, for the P2533 containing large amounts of the soft segments, the lattice dimensions of the nylon 12 crystals did not change with the external drawing force and the transient α" form was not observed. These results might suggest that the transfer of the external force to the crystal was difficult for P2533 due to the chain relaxation of the soft segments.

Structural Evolution of Poly(ether-b-amide12) Elastomers During the Uniaxial Stretching: An In situ Wide-Angle X-Ray Scattering Study

Kamal, Tahseen,Park, Soo-Young,Park, Jung-Hyun,Chang, Young-Wook 한국고분자학회 2012 Macromolecular Research Vol.20 No.7

The structural evolution of poly(ether-b-amide12) (PEBAX$^{(R)}$) elastomers was studied by using wide angle X-ray scattering (WAXS) at a synchrotron radiation source during the uniaxial stretching. The changes in the crystal structure of the nylon 12 were tracked during the stretching of the P6333 and P2533 compressed films, which represent a hard rubber and a soft elastomer, respectively. The nylon 12 chains of both samples favored the ${\gamma}$-phase in the unstrained state but their responses to the external drawing force were different. For the P6333 film containing small amounts of the soft segments, the applied force dilated the 001 crystalline lattice plane of nylon 12 which is perpendicular to its main chain and the ${\gamma}$ form was transformed into the ${\alpha}$" form when the applied force was high enough. However, for the P2533 containing large amounts of the soft segments, the lattice dimensions of the nylon 12 crystals did not change with the external drawing force and the transient ${\alpha}$" form was not observed. These results might suggest that the transfer of the external force to the crystal was difficult for P2533 due to the chain relaxation of the soft segments.

Shape-Responsive Actuator from a Single Layer of a Liquid-Crystal Polymer

Kamal, Tahseen,Park, Soo-young American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.20

<P>Actuation of various shape changes, including bending, helical twisting, and reversible hinging, has been achieved from a single-layer sheet of poly(1,4-di(4-(3-acryloyloxypropyloxy)benzoyloxy)-2-methylbenzene) [poly(RM257)]. This actuator was developed through photopolymerization of a reactive liquid-crystal (LC) monomer (RM257) mixed with 4-pentyl-4′-cyanobiphenyl (5CB, nematic LC at room temperature) in a planar polyimide-coated LC cell. The UV beam perpendicular to one side of the LC cell produced an asymmetric phase separation between the poly(RM257) network and 5CB that resulted in an asymmetric porous structure along the thickness direction when the 5CB was extracted, in which the UV-exposed surface was pore-free and compact while the opposite surface was highly porous. As a result of this structure, the dry and curled poly(RM257) film exhibits actuation behavior when placed in acetone because of a difference in swelling between the two morphologically different sides, the film UV-exposed and nonexposed sides. The actuation of a three-dimensional tetrahedron (pyramidal) structure is also demonstrated for the first time by using a simple photopatterning technique to selectively control its asymmetric morphology at specific locations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-20/am504910h/production/images/medium/am-2014-04910h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am504910h'>ACS Electronic Supporting Info</A></P>

Preparation, Chemical, and Thermal Characterization of Nylon 4/6 Copolymers by Anionic Ring Opening Polymerization of 2-Pyrrolidone and ${\varepsilon}$-Caprolactam

Kim, Nam Cheol,Kamal, Tahseen,Park, Soo-Young,Cho, Chang-Gi,Kim, Ji-Heung,Yoo, Young-Tai,Nam, Sung Woo,Jeon, Boong Soo,Kim, Young Jun THE KOREAN FIBER SOCIETY 2014 FIBERS AND POLYMERS Vol.15 No.5

Nylon 4/6 copolymers based on 2-pyrrolidone (C4) and ${\varepsilon}$-caprolactam (C6) were synthesized and characterized as part of ongoing efforts to develop thermally stable, melt-processable 2-pyrrolidone (C4) based Nylons. Copolymers of various compositions were synthesized at between 50 and $100^{\circ}C$ via the anionic ring opening polymerization of C4 and C6 using a potassium tert-butoxide catalyst and a benzoyl chloride initiator. The polymers were characterized by NMR spectroscopy, DSC, TGA, GPC, intrinsic viscosity measurements, and X-ray scattering (SAXS and WAXS). Their chemical compositions and sequence distributions were obtained by $^1H-$ and $^{13}C-NMR$ spectroscopies, respectively. X-ray scattering was used to investigate the lamellar morphologies and the crystal structures of solvent cast films of the copolymers. WAXS revealed the presence of ${\alpha}$-phase crystals in the copolymers. TGA data coupled with molecular weight and sequence distribution information indicated that the polymers' thermal stability depended on both their chemical composition and their sequence distribution.

Preparation and Structure of Nylon 4/6 Random-Copolymer Nanofibers

Muhammad Omer,박수영,Tahseen Kamal,조현혹,김동국 한국고분자학회 2012 Macromolecular Research Vol.20 No.8

Nylon 4/6 copolymers were synthesized by a melt-condensation method using ε-caprolactam and 2-pyrrolidone as monomers and 6-aminocaproic acid as a catalyst. Their structures and morphologies were studied using wide and small angle X-ray scatterings, differential scanning calorimetry, and scanning electron microscopy. The nylon 4 units were included into the nylon 6 chain up to 25 mol%. Random introduction of the small amount of the nylon 4 units to the nylon 6 decreased the crystallinities. The synthesized copolymers were successfully electrospun into nanofiber mats with diameter ranges of 90-130 nm, and their structures were compared to those of the films. The copolymers adopted the crystal structure of the pure nylon 6 with mixed nylon 4 and 6 units in the amorphous region, although the crystal structures of the nanofiber mats and the films were the γ and α forms of nylon 6, respectively. The crystallinity of the nanofiber mats decreased compared to those of the films. The water absorption of the nylon 4/6 copolymers increased as the mol% of nylon 4 increased in the copolymers.

Self-assembly of a liquid crystal ABA triblock copolymer in a nematic liquid crystal solvent

Islam, Mohammad Tariqul,Kamal, Tahseen,Shin, Taegyu,Seong, Baekseok,Park, Soo-Young Elsevier 2014 Polymer Vol.55 No.16

<P><B>Abstract</B></P> <P>An ABA type triblock copolymer, consisting of liquid crystalline polymer (LCP, poly(4-cyanobiphenyl-4-oxyundecylacrylate)) ‘A’ end blocks and a deuterated polystyrene (dPS) ‘B’ mid block (LCP–dPS–LCP) was successfully synthesized by atom transfer radical polymerization (ATRP). The number average molecular weight (<I>M</I> <SUB>n</SUB>) of LCP–dPS–LCP was LCP (7.1 K)–dPS (19.4 K)–LCP (7.1 K) with a polydispersity index (PDI) of 1.41. LCP–dPS–LCP was self-assembled in a nematic liquid crystal solvent of 4-pentyl-4′-cyanobiphenyl (5CB) into spherical micelles with a LCP corona and a dPS core, in which dPS was folded to produce a V-shape structure. Micellar structures of LCP–dPS–LCP in 5CB were examined by small angle neutron scattering at various block copolymer concentrations and temperatures using a curve fitting method. The critical micelle concentration was 0.25 wt% and the self-assembled micelles dissociated into unimers at 33 °C, which is lower than the nematic to isotropic transition temperature (<I>T</I> <SUB>ni</SUB>) of 5CB (36 °C). The entropic penalty imposed on dPS by the ordered nematic state of the 5CB solvent caused phase separation of the flexible dPS block to form micelles, which vanished above the <I>T</I> <SUB>ni</SUB> of the 5CB solvent. Magnetic field-induced global orientation of 5CB revealed the structure of the dPS core of the micelle to be prolate (an elongated sphere) oriented with its long axis along the direction of the applied magnetic field.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of Chemical Modification of Graphene on Mechanical, Electrical, and Thermal Properties of Polyimide/Graphene Nanocomposites

Ha, Hun Wook,Choudhury, Arup,Kamal, Tahseen,Kim, Dong-Hun,Park, Soo-Young American Chemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.9

<P>Chemically modified graphene sheets were dispersed in a high-performance polyimide (PI) matrix using polyamic acid (PAA)/graphene nanocomposite as a precursor. PI nanocomposite films with different loadings of graphene sheets were prepared by thermal imidization of the as-prepared PAA/graphene nanocomposites. Graphene oxide (GO) synthesized by Hummer’s method was chemically reduced with various reducing agents to produce reduced GOs (rGOs). The incorporation of only 5 wt % GO resulted in an ∼12-fold and ∼18-fold increase in the tensile strength and tensile modulus of PI, respectively, while the PI/rGO nanocomposites were found to have relatively inferior tensile properties. The superior mechanical properties of the PI/GO nanocomposites were attributed to the good dispersion and effective stress transfer between the polymer and GO sheets, as evidenced by the results from X-ray diffraction (XRD) and morphological studies. Furthermore, the PI/GO nanocomposites exhibited higher loading capacity than PI/rGO. The thermo-oxidative stability of PI was also remarkably improved with the addition of both GO and rGOs, but rGOs had a more pronounced effect. The electrical conductivity of PI/rGO nanocomposites was higher than that of PI/GO, suggesting restoration of the graphene basal plane upon the reduction of GO. The highest electrical conductivity was achieved for the <SMALL>l</SMALL>-ascorbic acid reduced GO-reinforced PI nanocomposites.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-9/am300999g/production/images/medium/am-2012-00999g_0013.gif'></P>