Controlling orientational order in block copolymers using low-intensity magnetic fields
Controlling orientational order in block copolymers using low-intensity magnetic fields
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DOI：
10.1073/pnas.1712631114
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发表时间：
2017-11-07
影响因子：
11.1
通讯作者：
Osuji, Chinedum O.
中科院分区：
文献类型：
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作者：
Gopinadhan, Manesh;Choo, Youngwoo;Osuji, Chinedum O.
在相变过程中，场与凝聚态物质的相互作用产生了丰富多样的物理现象。例如，液晶嵌段共聚物（LC BCP）在磁场存在下的自组装，由于LC BCP的各向异性磁化率，可以产生高度定向的微观结构。我们表明，这种定向中间相可以使用低强度场（< 0.5 T）来产生，而低强度场（< 0.5 T）可以使用永磁体来获得，而不是使用高强度场（bbbb4 T）和超导磁体。低强度的场对准是通过加入与系统的向列和近晶A介相结合的不稳定的介原来实现的。取向饱和场强度和取向动力学与游离介质浓度有明显的关系。在小至0.2 t的磁场下，取向分布系数接近于1的高度排列态得到了。这种显著的场响应源于粘度的降低导致排列动力学的增强，以及在不稳定的介质存在下，晶粒尺寸的增加导致静磁能的增加。这些发展为控制bcp的结构秩序提供了途径，包括通过使用磁性纳米颗粒局部筛选场来产生非平凡纹理和排列模式的可能性。
The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP's anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields (< 0.5 T) that are accessible using permanent magnets, in contrast to the high fields (> 4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system's nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles.