Apiradee Honglawan

Pillar-Assisted Epitaxial Assembly of Toric Focal Conic Domains of Smectic-A Liquid Crystals

SU-8 pillar-assisted epitaxial assembly of toric focal conic domains (TFCDs) arrays of smectic-A liquid crystals is studied. The 3D nature of the pillar array is crucial to confine and direct the formation of TFCDs on the top of each pillar and between neighboring pillars, leading to highly ordered square and hexagonal array TFCDs. Excellent agreement between the experimentally obtained critical pillar diameter and elasticity calculation is found.

Topographically induced hierarchical assembly and geometrical transformation of focal conic domain arrays in smectic liquid crystals.

Controlling topological defects in 3D liquid crystal phases is a crucial element in the development of novel devices, from blue-phase displays to passive biochemical sensors. However, it remains challenging to realize the 3D topological conditions necessary to robustly and arbitrarily direct the formation of defects. Here, using a series of short pillar arrays as topological templates, we demonstrate the hierarchical assembly of focal conic domains (FCDs) in smectic-A liquid crystals that break the underlying symmetry of the pillar lattice, exhibit tunable eccentricity, and together develop a nontrivial yet organized array of defects. The key to our approach lies in the selection of the appropriate ratio of the size of focal domain to the dimension of pillars such that the system favors the “pinning” of FCD centers near pillar edges while avoiding the opposing effect of confinement. Our study unequivocally shows that the arrangement of FCDs is strongly influenced by the height and shape of the pillars, a feature that promotes both a variety of nontrivial self-assembled lattice types and the attraction of FCD centers to pillar edges, especially at regions of high curvature. Finally, we propose a geometric model to reconstruct the smectic layer structure in the gaps between neighboring FCDs to estimate the energetic effects of nonzero eccentricity and assess their thermodynamic stability.

Fabrication of periodic nanoparticle clusters using a soft lithographic template

A novel fabrication method has been developed for the preparation of a periodic array of nanoparticle clusters (NPCs) using a sublimable liquid crystal (LC) material. The defect structures of the LC film provide the specific topographical confinement to trap nanoparticles (NPs) and assemble the NPs to generate NPCs during thermal annealing. This system shows a simple regulation of the size of NPCs by varying the concentration of the NP-suspension. Additionally, an illumination system using quantum dots (QDs) is fabricated using the manipulation method reported here.

Synthesis of random copolymer based pH-responsive nanoparticles as drug carriers for cancer therapeutics†

We report the design and synthesis of pH-responsive vesicular nanoparticles (NPs) based on amphiphilic random copolymers as novel drug carriers for chemotherapy. The random copolymers were photopolymerized from acryloyl chloride, followed by assembly in acetone. The resulting vesicular PAC NPs with an acrylate-functionalized shell were hydrolyzed in aqueous solution to form NPs with a carboxylated shell, which were further modified with branched poly(ethyleneimine) (PEI) to obtain positively charged PEI NPs. The resulting NPs maintained their structures and were pH-sensitive. The effects of molecular weight and concentration of PEI on the grafting efficiency, surface charge, and pH-sensitivity of PEI NPs were investigated by Fourier transform infrared (FT-IR) spectroscopy, electron microscopy, dynamic light scattering and zeta-potential measurements, respectively. We examined two packaging strategies to load the anticancer drug molecule, doxorubicin hydrochloride (Dox), into the NPs by encapsulating Dox inside the cavity of NPs during the assembly of the PAC NPs and by coupling Dox to the shell of PEI modified NPs. The first showed ∼30 wt% Dox loading efficiency, which was 15 times more than the latter, likely due to the larger loading capacity of both within the cavity and on the NP shell. We then tested in vitro delivery of Dox using cavity and surface loaded PEI NPs to HEK 293T cells. At the optimal concentration of NPs (9 μg mL−1), approximately 10 times more Dox were delivered compared to the naked Dox with a low level of cytotoxicity (over 90% relative cell viability).

Evaporative assembly of ordered microporous films and their hierarchical structures from amphiphilic random copolymers

Ordered microporous films were obtained via evaporative assembly from amphiphilic random copolymers of poly(acryloyl chloride) with self-crosslinked components. The quality and morphology of the porous structures were found to be highly dependent on the ratio of good solvent for the polymer (e.g. acetone) and nonsolvent (e.g. toluene), choice of nonsolvent, and surface chemistry of the supporting substrate. When increasing the polymer concentration in acetone–toluene solution, a morphological evolution from vesicles to microporous films with decreased pore size was observed. Using SU-8 micropillar arrays with spatially controlled surface chemistry to direct the evaporative assembly, we constructed hierarchical microporous structures with tunable pore size and symmetry (e.g. square arrays vs. hexagonal arrays). Finally, we selectively assembled TOPO-stabilized CdSe nanocrystals into the hydrophobic core of the random copolymers dispersed in acetone–toluene, and created fluorescent microporous structures after solvent evaporation.

Arrangement and SERS Applications of Nanoparticle Clusters Using Liquid Crystalline Template

Manipulation of nanomaterials such as nanoparticles (NPs) and nanorods (NRs) to make clusters is of significant interest in material science and nanotechnology due to the unusual collective opto-electric properties in such structures that cannot be found in the individual NPs. This work demonstrates an effective way to arrange NP clusters (NPCs) to make the desired arrays based on removable and NP-guidable liquid crystalline template using sublimation and reconstruction phenomenon. The position of the NPCs is precisely controlled by the defect structure of the liquid crystal (LC), namely toric focal conic domains (TFCDs), during thermal annealing to construct the LC and corresponding NPC structures. As a proof of concept, the surface-enhanced Raman scattering (SERS) activity of a fabricated array of gold nanorod (GNR) clusters is measured and shown to have highly sensitive detection characteristics essential for potential sensing applications.

Focal Conic Flower Textures at Curved Interfaces

Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA(Received 23 October 2013; published 10 December 2013)Focal conic domains (FCDs) in smectic-A liquid crystals have drawn much attention, both for theirexquisitely structured internal form and for their ability to direct the assembly of micromaterials andnanomaterials in a variety of patterns. A key to directing FCD assembly is control over the eccentricity ofthe domain. Here, we demonstrate a new paradigm for creating spatially varying FCD eccentricity byconfining a hybrid-aligned smectic with curved interfaces. In particular, we manipulate interface behaviorwith colloidal particles in order to experimentally produce two examples of what has recently beendubbed the flower texture [C. Meyer et al., Focal Conic Stacking in Smectic A Liquid Crystals: SmecticFlower and Apollonius Tiling, Materials 2, 499, 2009], where the focal hyperbolae diverge radiallyoutward from the center of the texture, rather than inward as in the canonical e´ventail or fan texture. Weexplain how this unconventional assembly can arise from appropriately curved interfaces. Finally, wepresent a model for this system that applies the law of corresponding cones, showing how FCDs may beembedded smoothly within a ‘‘background texture’’ of large FCDs and concentric spherical layers, in amannerconsistentwiththequalitativefeaturesofthesmecticflower.Suchunderstandingcouldpotentiallylead to disruptive liquid-crystal technologies beyond displays, including patterning, smart surfaces,microlens arrays, sensors, and nanomanufacturing.

Directing 3D Topological Defects in Smectic Liquid Crystals and Their Applications as an Emerging Class of Building Blocks

Controlling topological defects in three-dimensional (3D) liquid crystals (LCs) with complex geometries is not only a scientific curiosity but also crucial to the development of advanced technologies, including displays, sensors and self-assembly of nanostructures. It was not until recently that the smectic phase of LCs, characterized by arrangement of anisotropic molecules into layers with the long molecular axis parallel to the layer normal, has drawn significant interests because in thin film geometry topological defects known as focal conic domains (FCDs) can self-organize into a variety of highly regular micro- and nanostructures over a large area. Depending on surface anchoring at interfaces and elastic properties of smectic LCs, FCDs of different size and symmetry can be obtained by tailoring surface chemistry and physical confinement from chemically or topographically patterned substrates. This chapter will review the recent advances in design of geometric confinement of smectic LCs with uniform and mixed surface anchoring to control FCD formation, its size, size distribution and packing symmetries. We then discuss the applications of these highly ordered structures to various technologies, including patterning, smart surfaces, microlen arrays and directed self-assembly of functional materials (e.g. nanoparticles). The review concludes with perspectives on future directions and potential technological impacts.