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Small-Angle X-ray Scattering of Concentration Dependent Structures in Block Copolymer Solutions
Choi, Soo-Hyung,Bates, Frank S.,Lodge, Timothy P. American Chemical Society 2014 Macromolecules Vol.47 No.22
<P>The concentration and temperature dependence of the structure of a poly(styrene-<I>b</I>-ethylene-<I>alt</I>-propylene) (PS–PEP) diblock copolymer in squalane, a highly selective solvent for the PEP block, was investigated using small-angle X-ray scattering (SAXS). With decreasing concentration, between 100% and 10% by weight, a nearly monodisperse PS–PEP (block molecular weights of 42 000 g/mol and 62 000 g/mol for PS and PEP, respectively) exhibited lamellae (LAM), hexagonally packed cylinders (HEX), body-centered cubic spheres (BCC) and disordered spherical micelles. The results show that squalane (C<SUB>30</SUB>H<SUB>62</SUB>) is essentially completely segregated into the PEP domains, and thus it behaves like a short PEP homopolymer. With increasing amounts of squalane the conformation of the PS block changes from stretched to nearly fully relaxed at the lowest polymer concentrations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2014/mamobx.2014.47.issue-22/ma5016819/production/images/medium/ma-2014-016819_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma5016819'>ACS Electronic Supporting Info</A></P>
Lone, Saifullah,Ahn, Jeong In,Kim, Mi Ri,Lee, Hyang Moo,Kim, Sung Hoon,Lodge, Timothy P.,Cheong, In Woo American Chemical Society 2014 Langmuir Vol.30 No.31
<P>The photoresponsive phase separation of a poly(<I>N-</I>isopropylacrylamide-<I>co-</I>spironaphthoxazine methacryloyl-<I>co-</I>allyl<I>-</I>2<I>-</I>(2,6<I>-</I>bis((<I>E</I>)<I>-</I>4<I>-</I>(diphenylamino)styryl)<I>-</I>4<I>H-</I>pyran<I>-</I>4<I>-</I>ylidene)<I>-</I>2<I>-</I>cyanoacetate) random copolymer, i.e., poly(NIPAAm-<I>co</I>-SPO-<I>co</I>-fluorophore), in water-in-oil (W/O) droplets is described. The photoresponsive aqueous droplets were generated in the coflow regime of a simple tubular microfluidic device. The phase separation of the copolymer in the W/O droplets was induced by UV light at 365 nm and was affected significantly by the presence of 2,2-diethoxyacetophenone (DEAP) and sorbitan monooleate (Span 80). When the droplets were subjected to UV irradiation for more than 2 min, the phase-separated copolymer was transferred completely from the aqueous droplet to the continuous phase of hexadecane. The phase separation arises from the photoisomerization shifting the spiro to the merocyanine form of the SPO pendant group in the copolymer, which in turn reduces the hydrophilicity of the copolymer via attractive hydrogen-bonding interactions between the merocyanine group and hydrophobic additives, i.e., Span 80, DEAP, and some stable fragments derived from the photocleavage of DEAP under UV irradiation. These interactions cause the copolymer to associate with the additives and then accelerate the phase separation of the copolymer and subsequent phase transfer of copolymer aggregates. The separate effects of DEAP and Span 80 were also investigated by UV spectrophotometric analysis of the rate coefficient of the reverse transformation (merocyanine to spiro) of the photochromic monomer. We propose a mechanism of phase separation of the copolymer in the W/O droplet based on the NMR and GC-MASS analyses of DEAP.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2014/langd5.2014.30.issue-31/la5022005/production/images/medium/la-2014-022005_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la5022005'>ACS Electronic Supporting Info</A></P>
Effect of shear on poly(styrene-b-isoprene)copolymer micelles
방준하,Timothy P. Lodge 한국유변학회 2007 Korea-Australia rheology journal Vol.19 No.4
The use of various shearing apparatuses to study the phase behavior of poly(styrene-b-isoprene) diblockcopolymer micelles is described. A DMTA rheometer was modified so that one can apply oscillatory shearand obtain the scattering pattern along the shear gradient direction. A cone and plate shear cell was designedto access scattering along the shear vorticity direction, and both oscillatory and steady shear can be applied.because a high shear rate can be readily achieved without disturbing the sample by overflow. In this work,oscillatory shear was used to obtain a single crystal-like scattering pattern, and thereby to examine themechanism of the thermotropic transition between face-centered cubic (fcc) and body-centered cubic (bcc)lattices. By applying the steady shear, the response of the fcc lattices to various shear rates is discussed.
Scattering Studies on the Order-order Transitions in Block Copolymer Solutions
박문정,차국헌,( Timothy P. Lodge ) 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.1
The phase behavior of a symmetric styrene-isoprene (SI) diblock copolymer in styrene-selective solvents was investigated by in-situ small angle X-ray scattering on shear-oriented solutions. When marginally good solvent was used, intriguing morphological change among close-packed spheres, body-centered cubic spheres, and hexagonally packed cylinders has been observed by varying temperature presumably due to the reduced repulsive interaction. We have shown that the temperature-induced changes in micellar characteristics, particularly in the mean aggregation number, can be quantified in dilute solution, and that this information provides a good guideline to interpret the observed order-order transitions of block copolymer solutions in high concentration. Two nearly symmetric SI copolymers containing perdeuterated block (PS-dPI and dPS-PI) were synthesized and the scattered intensity for these solutions was measured as a function of temperature on the 30 m NG7 spectrometer at NIST. The experimental results obtained demonstrate that the softening of inter-micelle potential with decrease in aggregation number would be the key feature for the various phase transitions.
On the Selection of FCC and BCC Lattices in Poly(styrene-b-isoprene) Copolymer Micelles
Bang, Joona,Lodge, Timothy P. The Polymer Society of Korea 2008 Macromolecular Research Vol.16 No.1
Spherical micelles of poly(styrene-b-isoprene) (SI) diblock copolymers in selective solvents have been reported to pack onto either face-centered cubic (fcc) or body-centered cubic (bcc) lattices. The selection rule for fcc and bcc lattices has been understood in terms of the intermicellar potentials, and they have been quantified using the ratio of the corona layer thickness to the core radius, $L/R_c$, as suggested by McConnell and Gast. In order to test the validity of the McConnell-Gast criterion, this study compared the $L/R_c$ values from various solutions i.e. nine SI copolymers in several different selective solvents. The McConnell-Gast criterion was not found to be a determining factor, even though it could explain the fcc/bcc selection qualitatively. From the phase diagrams, the transition between fcc and bcc phases was also considered as a function of concentration and temperature, and their physical mechanisms are discussed based on the recent mean-field calculation reported by Grason.
Effect of shear on poly(styrene-b-isoprene) copolymer micelles
Bang, Joon-A,Lodge, Timothy P. The Korean Society of Rheology 2007 Korea-Australia rheology journal Vol.19 No.4
The use of various shearing apparatuses to study the phase behavior of poly(styrene-b-isoprene) diblock copolymer micelles is described. A DMTA rheometer was modified so that one can apply oscillatory shear and obtain the scattering pattern along the shear gradient direction. A cone and plate shear cell was designed to access scattering along the shear vorticity direction, and both oscillatory and steady shear can be applied. The most popular way to employ steady shear on relatively low viscosity fluids is to use a Couette cell, because a high shear rate can be readily achieved without disturbing the sample by overflow. In this work, oscillatory shear was used to obtain a single crystal-like scattering pattern, and thereby to examine the mechanism of the thermotropic transition between face-centered cubic (fcc) and body-centered cubic (bcc) lattices. By applying the steady shear, the response of the fcc lattices to various shear rates is discussed.