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Electrospinning Block Copolymer

[b]Confined Assembly in Coaxially [color=Magenta]Electrospun Block-Copolymer [/color]Fibers[/b]C _xx B

kV[H+a By Vibha Kalra, Sergio Mendez, Jung Hun Lee, Huy Nguyen, Manuel Marquez, and Yong Lak Joo*
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[i]Adv. Mater. 2006, 18, 3299–3303[/i]({Y3p6Fb x;Vh

G(_[4SxA0d'Q Electrospinning has received a lot of attention in recent
:`'mk(E@%T'P9R*u years as a simple process to produce sub-micrometer-scale fibers.
X Sajey The process involves continuous stretching of polymer's,sIzW)z/OQ|za
solution or melt in the presence of a strong electric field, u*Xh\8q-bH
which forms ultrathin fibers. A large amount of research is
.}$D|,Z/NF'U
J being carried out to achieve control of the diameter, morphology,T'x E:VBJ(t1~7p |p
and spatial alignment of electrospun nanofibers. Unlike
$@'vKzYt)e other 1D nanostructures, such as nanowires and nanotubes, `.v/@
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nanofibers exhibit a wide range of unique properties,
[~ySp
Pm's&m making them far more attractive for many applications, such`!i9K0J0M%K
as filtration, catalysis, sensing, protective clothing, and tissueengineering
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BCP self-assembly has attracted increasing interest in recent6B6~0{}#~x%T
years for applications in nanotechnology. Precise control
+SM` i X} over the size, shape, and periodicity of these nanoscale
n{^`7d0X*RG microdomains is the key factor needed to realize nanoscalee"E,Q/j.e)}l
systems. Various methods, including shear and elongational
}a w|*f{-d@ deformation, compressional deformation, electric fields, and6WY5K/R]7^*td.s
temperature gradients, have been utilized to induce orientation
7f-E-a;xT Ce0W of the microdomains.
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We believe that fabrication of continuous coaxial fibers via/~{n1q(r4iw3|
electrospinning of self-assembling BCP and thermally stable6}9B%wcy}%@D|-E
SiO2 as the core and the shell, respectively, together withCc[NuU`!t
annealing can provide a useful means to develop optical materials)eL7i
CY
such as waveguiding structures. By introducing nanoparticles
$C3Tl.b
@|$ZzR into one of the blocks, and eventually removing the
'dK9_1s9r"S'x;k SiO2 via NaOH treatment, we can easily manipulate the
.Xk X5M;E nanoparticles’ spatial distribution for use in gas sensing and
2o2M:d3zve;E catalytic applications with an enhanced efficiency.
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Experimental[/i][/b]2O?;r&]EI

#gKB1R3px`i For the core material, PS-b-PI copolymers were dissolved in THF._u|w)rH{+G%s
We typically used a polymer concentration of 25 wt% for the highmolecular-CN#vPL
weight IS53-143K copolymer and a concentration of
I
o;g? YneC 40 wt% for the low-molecular-weight IS62-27K copolymer. The solution^0_ z])S r!Z;s
used for the sheath material in the present study was preparedH2^HG)g(_
P*b [
using sol–gel synthesis. SiO2 sol–gel was prepared by combining a SiO2;O]pa zu
precursor such as tetraethylorthosilicate (TEOS) with ethanol. Water
Id5SU%p#kp*i#x containing a small amount of catalyst, such as HCl, was added drop by
XH1qtY D9Ug.[ drop, under vigorous mixing, to the TEOS/ethanol solution to controlV6z0aHu!^2~n$S#o_3p
the hydrolysis and condensation reactions. C*A:l:[
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[attach]2373[/attach]
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[b][color=Magenta]Electrospinning[/color] pH-Responsive [color=Magenta]Block Copolym[/color]er Nanofibers[/b]

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By Linge Wang, Paul D. Topham, Oleksandr O. Mykhaylyk, Jonathan R. Howse, Wim Bras,
Z^X9`l/z.]!W-{u Richard A. L. Jones, and Anthony J. Ryan*WT3LK| K
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[i]Adv. Mater. 2007, 19, 3544–3548[/i]
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Herein we discuss the use of a polybase material; a monodisperse
:WX.un*?'?XG triblock copolymer comsisting of poly(methyl methacrylate)-
$Yin2e\ block-poly[2-(diethylamino)ethyl methacrylate]-2v2P+z%\
X5Vj2u
block-poly(methyl methacrylate) (PMMA273-b-PDEA688-b-
a E$K2j1C*r:a ? PMMA273), which has been synthesized via group transfer
o.i ^m%@ I$V)`| @ polymerization (GTP).[11] A schematic diagram of the molecular
Iv:[
I%gv6G#\U'{e structure of the polymer is available as Supporting Information.N^"X*bsCC;]
The gel of the triblock copolymer has been previously
9Uc)z~4?S-{(ylD shown to exhibit inverted pH-responsive behavior (in all three
3n,h hq2X{"pZ(`"M!z+X dimensions) compared with that of the polyacid; where the7d5w[MC,zV0O`%L
polybase was charge-neutral above pH5 (collapsed) and positively
$}#S1p w6pE*sh charged below pH5 (expanded).[12] In an attempt to
-MJ8}9Ze X\UC reduce the response time observed for the gel, we have electrospun,m.f z#D5})X
the same material into fibers with controlled surface8e8G'o@0VVsUg3I
morphology. The morphology of electrospun fibers is primarily
%d%[:}3IiA@W1f3K#V*N influenced by the processing parameters[13–15] (e.g., applied
4k @py,E voltage, flow rate, distance between needle and collector) and6eA,Y*W5K9Z4Q A$\
the solution properties[14,15] (e.g., concentration, viscosity, surfaceVHz&u5b,Q6m
tension, conductivity), so the influence of the co-solvent9LdJ[B+i'n`B$L
system of tetrahydrofuran (THF) and dimethylformamide
/\){ w/dQ [0aV (DMF) on surface morphology and diameter of the electrospun;y1]*b,ra
PMMA-b-PDEA-b-PMMA fiber was initially studied in9om
u9\Q1|yF
an attempt to control the fiber diameter. The results showed$hgvC Wv)WkG
that for the PMMA-b-PDEA-b-PMMA triblock copolymer in0?:VX[R,Zf!_ _
a THF/DMF mixed solvent system, the concentration rangessg;x{
`+R I2xT8W
suitable for electrospinning was between 20 and 40 wt %. A
L{6j!a4w significant change was observed in the fiber diameter when altering
)K"[6p*bd5Zx9O the solvent composition, as shown in Figure 1.
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[attach]2375[/attach]

[b]Self-Assembled Structures in[color=Magenta] Electrospun Poly(styrene-block-isoprene)[/color] Fibers[/b]
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ucN/j vL*uM-TZ Vibha Kalra,† Prashant A. Kakad,‡ Sergio Mendez,† Timur Ivannikov,† Marleen Kamperman,§ and Yong Lak Joo*,†'t[K$H#}8cU,Hj1UX
(Fy"y2T!O0_f
School of Chemical and Biomolecular Engineering, Cornell UniVersity, Ithaca, New York 14853;
$SKI6D){qI2G Department of Textiles and Apparel, Cornell UniVersity, Ithaca, New York 14853; and
rJ/gb,JG`6{ Department of Materials Science and Engineering, Cornell UniVersity, Ithaca, New York 14853
FA&K|1X&n.{D E9g/DP8uER
[i]Macromolecules 2006, 39, 5453-5457[/i]
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ABSTRACT: Formation of various domain shapes in submicron scale fibers of poly(styrene-block-isoprene)
7GanN/x4s@ (PS-b-PI) has been investigated via electrospinning. Monodisperse PS-b-PI block copolymers with 29 and 53 volZRwh|Gi
% of PI were synthesized using two-step anionic polymerization and were dissolved in tetrahydrofuran (THF).
L H#wJnU Solutions of block copolymer with varying concentrations in THF were electrospun, and fibers with average
J)A;v.pR.]._T diameters from 200 nm to 5 ím were obtained. Small-angle X-ray scattering (SAXS) and transmission electron]5mm5B&a{6jJ
microscopy (TEM) studies revealed that cylindrical and lamellar morphology can be formed in electrospun fibersMb H0qx$_6p9O@
of 29% and 53% PI copolymers, respectively. We note that these domain structures in fibers are not as well
*?Ibv)q*]Y developed as those in films possibly due to the short residence time and strong elongational deformation involved
C
h lHz0`"V(dn in the electrospinning process. For both systems we find that the d spacing in electrospun fibers is smaller than
#FS3J,w*X|
] that in the cast film. This could also be attributed to the elongational deformation and fast solvent evaporation~@(Ry+\2tT-gZ
during electrospinning. The domain structures of electrospun fibers from the symmetric (53% PI) copolymer
?n Y9Ft\:T^ exhibit the influence of fiber morphology such as confinement and curvature due to its high molecular weight.6[jcx2GI
More uniform domain structures in the fibers and increase in d spacing are observed after the annealing process.
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[b][color=Magenta]Electrospun Poly(Styrene-block-dimethylsiloxane) Block Copolymer [/color]Fibers Exhibiting Superhydrophobicity[/b]`
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Minglin Ma,† Randal M. Hill,‡ Joseph L. Lowery,† Sergey V. Fridrikh,† and Gregory C. Rutledge*,†{Q3|}jqw%h
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Department of Chemical Engineering, Massachusetts Institute of Technology,
n#wYlk&Jfy+z:J 77 Massachusetts Avenue, Cambridge, Massachusetts 01239, and
2p7K%l*H2gpz Dow Corning Corporation, Midland, Michigan 48686
O7cNZ.iu [i]
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Langmuir 2005, 21, 5549-5554[/i].BysOu"kcX8q9@
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Block copolymer poly(styrene-b-dimethylsiloxane) fibers with submicrometer diameters in the range5T%pQ%O8h
150-400 nm were produced by electrospinning from solution in tetrahydrofuran and dimethylformamide.'Z(p!px}
Contact angle measurements indicate that the nonwoven fibrous mats are superhydrophobic, with a contact
i)nzQ1i{8N%z#s angle of 163° and contact angle hysteresis of 15°. The superhydrophobicity is attributed to the combined
^ls;UgE0Iu effects of surface enrichment in siloxane as revealed by X-ray photoelectron spectroscopy and surfacer)I)_A3~ {'N5Lj
roughness of the electrospun mat itself. Additionally, the fibers are shown by transmission electron
zO`:yU
?Z^ microscopy to exhibit microphase-separated internal structures. Calorimetric studies confirm the strong
zkMj9e6K_ segregation between the polystyrene and poly(dimethylsiloxane) blocks.^;Oa.N&]3W
p_0Iq{/{ll
[attach]2378[/attach]

[b][color=Magenta]Electrospun[/color] Polymer Nanofibers with Internal Periodic Structure Obtained by Microphase Separation of Cylindrically Confined [color=Magenta]Block Copolymers[/color][/b] b{%[)r4O"tm5^
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Minglin Ma,† Vahik Krikorian,‡ Jian H. Yu,† Edwin L. Thomas,‡ and Gregory C. Rutledge*,†
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Department of Chemical Engineering and Department of Material Science and
:v"qV,BZ5sR-\f9T Engineering, Massachusetts Institute of Technology, 77 Massachusetts AVenue,5H4r1~9NAgZp
Cambridge, Massachusetts 02139:S R|Q,l~$I"P y
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[i]NANO LETTERS 2006 Vol. 6, No. 12 2969-2972[/i]C3{0us*c6U
v)g | Uh'W
Continuous fibers are described having concentric layer or aligned sphere microphase-separated, styrene-isoprene block copolymer:TED#?w-D
morphologies. The fibers are obtained by a two-fluid coaxial electrospinning technique in which the desired block copolymer is encapsulated as the core component within a polymer shell having a high glass transition temperature (Tg). The fibers range in diameter from 300 to 800 nm, and the block copolymer core ranges from 50 to 500 nm. Subsequent annealing of the fibers above the upper Tg of the block copolymer but below the Tg of the shell polymer results in microphase separation of the block copolymer under cylindrical confinement. The resulting fibers exhibit improved long-range order. This two-step strategy creates the opportunity to fabricate continuous nanofibers with periodic internal structure.R"^7Y,@0i:gS

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支持楼上的观点
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