Magnetic Microrheology of Block Copolymer Solutions

Abstract

The viscosity of poly(styrene)-b-poly(lactide) [PS-b-PLA] solutions in a neutral solvent was characterized by magnetic microrheology. The effect of polymer concentration on the viscosity of the block polymer solutions was compared with that of the PS and PLA homopolymers in the same solvent. The viscosity of PS-b-PLA solution, unlike the homopolymer solutions, showed a steep increase over a narrow concentration range. The steep rise was concomitant with microphase separation into an ordered cylindrical microstructure as determined by small-angle X-ray scattering. Hence microrheology proved effective as a means of characterizing the order-disorder transition concentration. During an in situ drying experiment, changes in local viscosity through the depth of a block copolymer solution were characterized as a function of drying time. Early in the drying process, the viscosity rose steadily and was uniform through the depth, a result consistent with steadily increasing and uniform polymer concentration. However, later in the drying process as the overall polymer concentration approached that required for microphase separation, the viscosity of the polymer solution near the free surface became an order of magnitude higher than that near the bottom of the container. The zone of high viscosity moved downward as drying proceeded, consistent with a microphase separation front.

Optimization of Long-Range Order in Solvent Vapor Annealed Poly(styrene)-block-poly(lactide) Thin Films for Nanolithography

“…As described previously (see ref 46), SAXS samples were prepared in aluminum DSC pans (Tzero hermetic). A controlled amount of polymer was loaded into a pan, and then solvent was added using a micropipette.…”

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

“…Characterization of thin coating films during composite manufacturing remains challenging. Different experimental methods have been proposed and developed for in situ characterization of rheological properties of thin films and coatings . It appears that unique features of rotation of ferromagnetic nanorods can be used for characterization of very thin films when other methods fall short.…”

Size‐Controlled Hollow Spheres of C/α‐Fe2O3 Prepared through the Quasiemulsion‐Templated Method and Their Electrochemical Properties for Lithium‐Ion Storage

“…This peak is caused by structural rearrangement in the subsequent cycles of the a-Fe 2 O 3 . [15] For both (a) and (b), small changes were observed in the cycles, implying good reversible characteristics during the oxidationreduction reactions with the a-Fe 2 O 3 hollow sphere materials. Figure 6 shows the first discharge-charge voltage profiles of the (a) FHS and (b) C/FHS electrodes at a low current density of 100 m g À1 in the potential range from 0.01 to 3.0 V. The small plateau between 1.6 V and 0.8 V corresponds to the lithium insertion process into the a-Fe 2 O 3 along with the conversion of 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Fe 3 + to Fe 2 + species.…”

“…[29] Three possible factors can contribute to this phenomenon: 1) the electrochemical milling effect, which could create more contact area between the active sites and electrolytes as the size of electroactive materials is decreased; [30] 2) extra Li ion storage via the interfacial lithium storage mechanism at the two-phase boundary of metal/Li 2 O; [31] or 3) dissolution and reversible formation of a gel-like film of the SEI layer. [15] However, these features remain unclear for the cases with some transition metal oxides such as Fe 3 O 4, [32] CoO, [33] ZnMn 2 O 4, [15] and ZnFe 2 O 4. [8] For the C-coated samples in this work, the capacity profiles show monotonic increases with cycles, which could be attributed to the presence of the thin carbon layer of a-Fe 2 O 3 , reducing the agglomeration of the active materials during the repeated charge/discharge cycling.…”

“…[8] 2) Preparation of the electrode materials in nanoscale sizes could increase the surface to volume ratio, which can provide a short diffusion path for both e À and Li + . [15] 3) Constructing nanostructures of the electrode materials could offer empty spaces for reducing the volume changes during the cycles. [16] In this paper, we report the electrochemical properties of hollow structures made of a-Fe 2 O 3 , via a facile quasiemulsion-templated method, in which the size of a-Fe 2 O 3 hollow spheres can be easily controlled with respect to the amount of glycerol during the synthesis process.…”